1 00:00:08,080 --> 00:00:11,740 For a long time, we have known that plants can move. 2 00:00:14,100 --> 00:00:18,220 But recent studies have found that they can also smell, touch 3 00:00:18,220 --> 00:00:21,740 and taste, respond to sound, 4 00:00:21,740 --> 00:00:24,980 perceive shapes and hold memories. 5 00:00:28,260 --> 00:00:32,780 We knew plants were sensitive to temperature, sunshine and humidity, 6 00:00:32,780 --> 00:00:38,580 but new research proves plants also have other surprising senses, 7 00:00:38,580 --> 00:00:40,860 offering us new insights. 8 00:00:53,140 --> 00:00:57,020 When seen up close, and even very, very close, 9 00:00:57,020 --> 00:01:00,300 nature takes on a whole other dimension. 10 00:01:01,660 --> 00:01:05,700 Our eye perceives plants as a branch with leaves, a flower, 11 00:01:05,700 --> 00:01:07,540 the silhouettes of trees. 12 00:01:09,420 --> 00:01:13,340 But when closely examined, the intimate details of plant life 13 00:01:13,340 --> 00:01:16,300 are both curious and stunning in their complexity. 14 00:01:18,220 --> 00:01:22,820 These strange-looking antennae are in fact the epidermis of an ordinary 15 00:01:22,820 --> 00:01:28,180 leaf, enlarged hundreds of times through digital 3D microscopes. 16 00:01:33,140 --> 00:01:38,140 Scientific imagery enables us to see the world of plants in ever greater 17 00:01:38,140 --> 00:01:43,180 detail, whilst revealing that plants still hold many mysteries for us. 18 00:01:49,540 --> 00:01:53,540 Like humans, plants have a vascular system similar 19 00:01:53,540 --> 00:01:55,420 to our veins and arteries. 20 00:01:57,780 --> 00:02:02,620 An electric network like our nerves, hormones and other similarities. 21 00:02:15,660 --> 00:02:19,100 But with no heart or brain - essential for us - 22 00:02:19,100 --> 00:02:22,060 plants have developed other solutions for survival 23 00:02:22,060 --> 00:02:23,980 throughout their evolution. 24 00:02:23,980 --> 00:02:25,980 Solutions we could learn from. 25 00:02:32,660 --> 00:02:36,460 Stefano Mancuso, a professor at the University of Florence 26 00:02:36,460 --> 00:02:39,860 in Italy, founded the first international laboratory 27 00:02:39,860 --> 00:02:43,380 of vegetal neurobiology over ten years ago. 28 00:02:43,380 --> 00:02:46,500 The lab studies the interaction between plants 29 00:02:46,500 --> 00:02:48,100 and their environment. 30 00:02:52,300 --> 00:02:57,340 - Plants are able to sense the environment in an exquisite way. 31 00:02:57,340 --> 00:02:59,700 They are much more sensitive than animals, 32 00:02:59,700 --> 00:03:03,140 and they need to be more sensitive because 33 00:03:03,140 --> 00:03:06,060 they cannot run away from the danger. 34 00:03:08,300 --> 00:03:12,260 - Rooted to the ground, plants have evolved fine-tuned 35 00:03:12,260 --> 00:03:15,540 and highly efficient sensory capabilities. 36 00:03:16,980 --> 00:03:21,260 - Sensitivity is not something that is linked to a brain. 37 00:03:21,260 --> 00:03:26,420 The brain in itself is a stupid organ. 38 00:03:26,420 --> 00:03:30,500 It's just an amount of cells that we have here, 39 00:03:30,500 --> 00:03:32,180 and every animals have. 40 00:03:34,180 --> 00:03:38,180 There is nothing mysterious or supernatural 41 00:03:38,180 --> 00:03:41,020 about the cells of our brains. 42 00:03:41,020 --> 00:03:46,660 They are just a kind, a specific kind of cells called neurons. 43 00:03:46,660 --> 00:03:49,820 But you don't need neurons to make this stuff. 44 00:03:49,820 --> 00:03:53,980 You can have other kind of cells having the same function, 45 00:03:53,980 --> 00:03:58,300 so it means transmitting signals from one cell to the other. 46 00:04:01,180 --> 00:04:03,940 - Humans react instantly to their environment, 47 00:04:03,940 --> 00:04:06,860 especially when confronted with danger. 48 00:04:06,860 --> 00:04:10,220 Nerve impulses transmit through our nervous system at a speed 49 00:04:10,220 --> 00:04:12,820 of 100 metres a second. 50 00:04:12,820 --> 00:04:15,540 But do plants have a similar response? 51 00:04:21,340 --> 00:04:24,860 To calculate the speed of electric signals in a plant, 52 00:04:24,860 --> 00:04:28,860 Bruno Moulia and his team from the French National Research 53 00:04:28,860 --> 00:04:33,460 Institute for Agriculture, Food and the Environment place electrodes 54 00:04:33,460 --> 00:04:35,140 on the stem of a shrub. 55 00:05:07,940 --> 00:05:11,740 The electric impulse, seen in this sped-up footage, 56 00:05:11,740 --> 00:05:14,620 is only six to eight centimetres per minute. 57 00:05:16,900 --> 00:05:20,860 The slower speed is logical given the plant's sedentary nature. 58 00:05:28,540 --> 00:05:31,780 To create the organic matter required for growth, 59 00:05:31,780 --> 00:05:34,740 a plant needs light provided by the sun, 60 00:05:34,740 --> 00:05:38,980 carbon dioxide present in the atmosphere, and water. 61 00:05:41,780 --> 00:05:44,220 Light is absorbed through chlorophyll, 62 00:05:44,220 --> 00:05:47,660 the tiny round globes contained in plant cells. 63 00:05:47,660 --> 00:05:49,460 Thanks to chlorophyll, 64 00:05:49,460 --> 00:05:53,500 light, water and carbon dioxide are transformed into sugars, 65 00:05:53,500 --> 00:05:55,340 which the plant feeds on. 66 00:05:58,100 --> 00:06:02,180 This process, known as photosynthesis, releases oxygen 67 00:06:02,180 --> 00:06:06,180 into the Earth's atmosphere and provides all the organic matter 68 00:06:06,180 --> 00:06:09,300 and the energy necessary for life on Earth. 69 00:06:12,420 --> 00:06:15,860 The procedure seems simple, but in everyday life, 70 00:06:15,860 --> 00:06:19,300 plants are regularly confronted with vital problems. 71 00:06:20,900 --> 00:06:25,860 Water is capricious and plants don't want too much or too little, 72 00:06:25,860 --> 00:06:28,380 and it must fall at the right time. 73 00:06:32,700 --> 00:06:36,580 Roots capture water in the soil through a network of hairs. 74 00:06:37,580 --> 00:06:41,180 When water is scarce, the roots perceive the threat, 75 00:06:41,180 --> 00:06:43,100 causing the stomata to close. 76 00:06:50,740 --> 00:06:55,220 Stomata are mouth-like pores found on the epidermis of leaves... 77 00:06:57,300 --> 00:07:00,540 ..enabling gas exchange and the release of water vapour 78 00:07:00,540 --> 00:07:02,500 produced by photosynthesis. 79 00:07:06,780 --> 00:07:11,820 When roots signal a lack of water, the stomata pores shrink. 80 00:07:11,820 --> 00:07:16,140 The plant captures less carbon dioxide and growth slows. 81 00:07:21,580 --> 00:07:26,460 Daniel Chamovitz, a botanical genetic scientist, discovered a gene 82 00:07:26,460 --> 00:07:29,660 in the hairs of plants that is similar to those responsible 83 00:07:29,660 --> 00:07:32,940 for the vibrating hairs in the inner ear of humans. 84 00:07:34,460 --> 00:07:35,980 - From a genetic point of view, 85 00:07:35,980 --> 00:07:39,100 plants have the same genes that are needed for hearing 86 00:07:39,100 --> 00:07:43,340 that animals have. This gene in animals is a gene which enables 87 00:07:43,340 --> 00:07:46,660 the hairs of our inner ears to be formed, and these are the hairs 88 00:07:46,660 --> 00:07:48,340 that vibrate in sound waves. 89 00:07:48,340 --> 00:07:50,860 These are genes that are needed for us to hear. 90 00:07:52,660 --> 00:07:56,900 Plants have essentially the same genes, which might lead us to think 91 00:07:56,900 --> 00:07:59,020 that plants hear the same way. 92 00:08:00,020 --> 00:08:02,580 But when we look more in depth at what these genes do, 93 00:08:02,580 --> 00:08:06,860 they are necessary for forming of hairs at the tips of roots. 94 00:08:06,860 --> 00:08:10,780 But these hairs apparently are not listening, but they're necessary 95 00:08:10,780 --> 00:08:13,180 for the roots to absorb water. 96 00:08:13,180 --> 00:08:18,740 So while the genes cause the same structures to be formed - hairs - 97 00:08:18,740 --> 00:08:21,020 in humans, it's needed for hearing, 98 00:08:21,020 --> 00:08:23,620 and in plants, it's needed for drinking. 99 00:08:33,380 --> 00:08:39,540 - This unexpected proximity fascinates and drives Stefano Mancuso. 100 00:08:39,540 --> 00:08:45,820 - We are quite sure that plants are able to use the information 101 00:08:45,820 --> 00:08:50,380 coming from the sounds in the soil, for example, to detect the quality 102 00:08:50,380 --> 00:08:54,300 of the soils, the amount of water in the soils, the presence 103 00:08:54,300 --> 00:08:57,060 of obstacles in the soil. 104 00:08:57,060 --> 00:09:03,740 So they are, in some way, using information coming from 105 00:09:03,740 --> 00:09:07,740 sounds for... To have an idea of the space around them. 106 00:09:12,020 --> 00:09:16,100 So just put a loudspeaker close to these roots, and you will see 107 00:09:16,100 --> 00:09:19,700 that if the frequencies are in the range between 108 00:09:19,700 --> 00:09:25,060 100 to 1,000 hertz, the roots will turn toward the source of frequency. 109 00:09:25,060 --> 00:09:30,780 If the frequencies are higher than 5,000, the roots will grow 110 00:09:30,780 --> 00:09:33,620 against the source of the sound. 111 00:09:40,860 --> 00:09:47,740 - The plant Desmodium gyrans was once thought to dance to music, 112 00:09:47,740 --> 00:09:52,220 but in fact, it moves its leaves towards the best light source. 113 00:09:56,540 --> 00:10:00,420 Some may say that plants do better and grow faster 114 00:10:00,420 --> 00:10:01,980 when music is played. 115 00:10:04,060 --> 00:10:08,460 - What is important for plants is not the music, but the frequencies. 116 00:10:08,460 --> 00:10:13,300 We found that there are a range of frequencies 117 00:10:13,300 --> 00:10:18,260 in the low part of the spectrum, between 100 and 1,000 hertz. 118 00:10:18,260 --> 00:10:22,500 There are many frequencies that we could say plants like. 119 00:10:22,500 --> 00:10:25,500 They are completely insensitive 120 00:10:25,500 --> 00:10:30,340 to the quality - if it's classical rock, blues and so on - 121 00:10:30,340 --> 00:10:35,460 of the music, but they are able to detect specific frequencies 122 00:10:35,460 --> 00:10:38,980 and to react to these frequencies accordingly. 123 00:10:44,420 --> 00:10:47,820 - If there is one sound which humans find disturbing, 124 00:10:47,820 --> 00:10:50,860 it's the whining of a mosquito in the dark. 125 00:10:52,540 --> 00:10:55,420 Are plants aware of buzzing insects? 126 00:11:03,100 --> 00:11:06,620 In Israel and in the global scientific community, 127 00:11:06,620 --> 00:11:09,900 the work of Lilach Hadany is creating a buzz. 128 00:11:10,940 --> 00:11:14,140 Her research shows that plants can identify the sounds 129 00:11:14,140 --> 00:11:15,620 made by pollinators. 130 00:11:18,260 --> 00:11:21,420 Flowers produce nectar to attract the pollinators that feed 131 00:11:21,420 --> 00:11:23,220 on the sugar it contains. 132 00:11:25,140 --> 00:11:28,780 When harvesting the nectar, pollinators fertilise the flower 133 00:11:28,780 --> 00:11:31,100 with pollen brought from other flowers. 134 00:11:36,580 --> 00:11:39,340 A researcher at the University of Tel Aviv, 135 00:11:39,340 --> 00:11:42,940 she has recorded bees as they sip nectar. 136 00:11:42,940 --> 00:11:46,300 She plays the recorded buzz through a loudspeaker held above 137 00:11:46,300 --> 00:11:48,220 a flowerbed of primroses. 138 00:11:55,540 --> 00:11:59,140 Lilach and one of her colleagues then harvest the nectar secreted 139 00:11:59,140 --> 00:12:02,780 by the flowers and measure its sugar levels with an analyser. 140 00:12:11,420 --> 00:12:13,140 - Much sweeter nectar this time. 141 00:12:15,780 --> 00:12:17,260 - INSECT BUZZES 142 00:12:28,660 --> 00:12:33,820 - It's estimated up to 30% of the energy of the plant 143 00:12:33,820 --> 00:12:37,580 is wasted on nectar. So, to keep nectar high in all times 144 00:12:37,580 --> 00:12:39,620 is a very expensive process 145 00:12:39,620 --> 00:12:45,980 and also that attracts all sorts of robbers - bacteria, fungi, birds. 146 00:12:45,980 --> 00:12:50,180 If you can have nectar low when pollinators are not around 147 00:12:50,180 --> 00:12:54,380 and increasing sugar concentration only in times where pollinators 148 00:12:54,380 --> 00:12:58,220 are around, that could save the plant a lot of energy. 149 00:13:06,420 --> 00:13:10,340 - While the forms and shapes of flowers are very diverse, 150 00:13:10,340 --> 00:13:13,740 many are concave - shaped like a bowl or a bell. 151 00:13:17,660 --> 00:13:21,220 - If we look at this flower, 152 00:13:21,220 --> 00:13:25,380 it has this, uh, bowl shape, 153 00:13:25,380 --> 00:13:28,860 a bit like a small satellite dish. 154 00:13:28,860 --> 00:13:34,460 So, we suggest that the flower is the external ear of the plant. 155 00:13:35,460 --> 00:13:40,260 An ear that has evolved to respond specifically to the sounds 156 00:13:40,260 --> 00:13:43,180 of the pollinators of this very plant. 157 00:13:43,180 --> 00:13:45,780 Bees or moths. 158 00:13:45,780 --> 00:13:50,060 This flower vibrates in response to the sound of bees. 159 00:13:50,060 --> 00:13:53,100 But if we remove some of the petals... 160 00:13:58,060 --> 00:14:00,860 ..this remaining petal would not be able 161 00:14:00,860 --> 00:14:03,140 to respond so much to the sounds. 162 00:14:12,660 --> 00:14:16,780 - Lilach picks a few primroses to take back to her lab. 163 00:14:16,780 --> 00:14:20,260 She wants to see if the petals can detect the sound of bee flight. 164 00:14:31,300 --> 00:14:36,300 She observes them under a high-resolution optical microscope. 165 00:14:36,300 --> 00:14:39,100 When she plays the recordings of buzzing bees and other 166 00:14:39,100 --> 00:14:42,740 pollinators, a laser beam measures the petal vibrations 167 00:14:42,740 --> 00:14:45,740 to establish a scale of the flower's reactions. 168 00:14:52,620 --> 00:14:56,500 - With the laser vibrometer, we were able to detect tiny 169 00:14:56,500 --> 00:15:00,140 vibrations in response to sound, 170 00:15:00,140 --> 00:15:04,940 and we saw that indeed the flower vibrates in response 171 00:15:04,940 --> 00:15:09,100 to bee sound, but not in response to much higher 172 00:15:09,100 --> 00:15:11,500 sounds like bat sounds. 173 00:15:14,700 --> 00:15:17,900 - The flower does not react to sounds made by other animals. 174 00:15:20,220 --> 00:15:22,700 But a buzzing bee results in the flower 175 00:15:22,700 --> 00:15:24,620 producing a sweeter nectar. 176 00:15:27,820 --> 00:15:32,220 - If plants hear, if plants sense sound waves, 177 00:15:32,220 --> 00:15:34,860 they do it in a completely different way. 178 00:15:34,860 --> 00:15:37,860 It didn't say, "Oh, what should we listen to today?" 179 00:15:37,860 --> 00:15:42,340 But it did develop the ability to respond to the sound 180 00:15:42,340 --> 00:15:45,700 of a pollinator, and then to differentiate between a pollinator 181 00:15:45,700 --> 00:15:46,940 and a non-pollinator. 182 00:15:46,940 --> 00:15:50,260 And that makes sense, also, because if you're responding to every 183 00:15:50,260 --> 00:15:55,500 wavelength, then you're just wasting energy in making 184 00:15:55,500 --> 00:15:57,700 nectar for someone who will never drink it. 185 00:16:08,300 --> 00:16:12,580 - We are still thinking of the possibility of plant 186 00:16:12,580 --> 00:16:16,860 communication after hearing the bee sound. For example, 187 00:16:16,860 --> 00:16:20,340 within the same bush of the evening primrose, 188 00:16:20,340 --> 00:16:24,820 there is one flower exposed directly to the bee. 189 00:16:24,820 --> 00:16:30,020 But is the signal transmitted to other flowers on the same plant? 190 00:16:30,020 --> 00:16:31,900 This is something we intend to study. 191 00:16:31,900 --> 00:16:35,220 - MUSIC: Flight Of The Bumblebee 192 00:16:44,060 --> 00:16:48,260 Could the Flight Of The Bumblebee by Nikolai Rimsky-Korsakov 193 00:16:48,260 --> 00:16:50,980 have been composed for the wellbeing of his plants? 194 00:16:53,700 --> 00:16:57,580 If plants can sense specific sounds for their own benefit, 195 00:16:57,580 --> 00:16:58,980 can they emit sounds? 196 00:17:01,100 --> 00:17:04,820 RUSTLING 197 00:17:10,540 --> 00:17:13,620 Over the years, scientists have wondered how the clicking sounds 198 00:17:13,620 --> 00:17:15,700 in plant stems were produced. 199 00:17:21,420 --> 00:17:24,380 Many believed that the clicks were air bubbles bursting 200 00:17:24,380 --> 00:17:26,860 within the stem's vascular system. 201 00:17:39,660 --> 00:17:41,900 At Tel Aviv University, 202 00:17:41,900 --> 00:17:44,900 Lilach and her team have shown that the plant clicks 203 00:17:44,900 --> 00:17:47,540 are very high frequency sounds, 204 00:17:47,540 --> 00:17:49,140 like bursting popcorn. 205 00:17:51,820 --> 00:17:55,140 To avoid interference from any background noise, 206 00:17:55,140 --> 00:17:59,020 the team installed ultra-sensitive microphones ten centimetres 207 00:17:59,020 --> 00:18:00,380 from the test plants. 208 00:18:01,700 --> 00:18:03,100 - It actually worked. 209 00:18:03,100 --> 00:18:07,820 Within a few hours, we discovered that plants indeed emit sounds - 210 00:18:07,820 --> 00:18:11,940 brief ultrasonic clicks high above human hearing ability. 211 00:18:11,940 --> 00:18:14,340 - CLICKING 212 00:18:14,340 --> 00:18:18,700 - Moreover, these sounds contained information 213 00:18:18,700 --> 00:18:21,180 about the stress of the plant. 214 00:18:30,140 --> 00:18:33,620 - The frequency of sounds emitted by tomato plants and vines 215 00:18:33,620 --> 00:18:38,380 in distress was between 20 and 100 kilohertz. 216 00:18:38,380 --> 00:18:42,420 This is beyond human hearing, which is limited to 16 kilohertz. 217 00:18:51,780 --> 00:18:54,860 The experiment continued in the acoustic chambers 218 00:18:54,860 --> 00:18:57,620 of the university's soundproof bunker. 219 00:19:06,500 --> 00:19:09,700 Scientists stress the plants by cutting them, 220 00:19:09,700 --> 00:19:12,780 pinching them, or depriving them of water. 221 00:19:30,020 --> 00:19:33,700 CLICKING 222 00:19:44,180 --> 00:19:48,020 - You see, this is a strong sound, this drying plant is actually 223 00:19:48,020 --> 00:19:52,060 emitting a lot of sounds and is in significant stress. 224 00:19:53,780 --> 00:19:57,660 In our experiments, they peaked about the fifth day without water, 225 00:19:57,660 --> 00:20:02,940 and then, the sounds start declining until a very dry plant does not 226 00:20:02,940 --> 00:20:04,420 emit much sound. 227 00:20:08,220 --> 00:20:13,900 We cannot say yet if plants speak, in the sense of emit sounds 228 00:20:13,900 --> 00:20:16,460 for communication purposes 229 00:20:16,460 --> 00:20:21,380 that are identified by someone else in a constructive way. 230 00:20:23,380 --> 00:20:26,940 - CLICKING 231 00:20:26,940 --> 00:20:29,780 Plant sounds increase in number and intensity 232 00:20:29,780 --> 00:20:31,940 as stress levels increase, 233 00:20:31,940 --> 00:20:34,660 but long before they are visually dehydrated. 234 00:20:38,740 --> 00:20:41,660 Lilach and her team are pursuing this research. 235 00:20:41,660 --> 00:20:45,140 If plants emit sound signals that have a meaning, especially 236 00:20:45,140 --> 00:20:48,900 at the start of a drought, this information could help farmers. 237 00:20:55,340 --> 00:20:59,020 In humans, some body odours attract mosquitoes, 238 00:20:59,020 --> 00:21:00,620 while other body odours do not. 239 00:21:05,860 --> 00:21:08,580 Are there any similarities in the green kingdom? 240 00:21:24,140 --> 00:21:28,060 Each plant species has its own olfactory signature, 241 00:21:28,060 --> 00:21:31,060 which comes from the complex structure of the fragrant 242 00:21:31,060 --> 00:21:32,700 compounds it releases. 243 00:21:39,700 --> 00:21:43,660 Odiferous capsules and bulbs are very common on the leaves 244 00:21:43,660 --> 00:21:45,940 of tomatoes or cannabis. 245 00:21:47,140 --> 00:21:51,700 These capsules release a strong scent which is easily identifiable. 246 00:21:53,580 --> 00:21:57,100 The strong smell of lavender is produced by large pockets 247 00:21:57,100 --> 00:21:59,100 that burst upon contact. 248 00:22:13,060 --> 00:22:15,220 Professor Consuelo De Moraes, 249 00:22:15,220 --> 00:22:18,700 from the Swiss Federal Institute of Technology in Zurich, 250 00:22:18,700 --> 00:22:21,780 has spent many years studying plant odours 251 00:22:21,780 --> 00:22:23,500 and how plants detect odours. 252 00:22:25,900 --> 00:22:29,020 Odours are measured under these glass domes, 253 00:22:29,020 --> 00:22:33,460 where tomato plants are infested by a strange vampire plant. 254 00:22:37,700 --> 00:22:42,460 - Cuscuta is a parasitic plant, so it needs a host to survive. 255 00:22:42,460 --> 00:22:44,460 So, it's a true parasite. 256 00:22:44,460 --> 00:22:46,420 It doesn't have roots. 257 00:22:46,420 --> 00:22:48,100 It doesn't do photosynthesis. 258 00:22:48,100 --> 00:22:50,900 So, in order to survive, it has to attach to a host. 259 00:22:50,900 --> 00:22:52,660 It has to find that host. 260 00:22:52,660 --> 00:22:56,100 And the question is - how do they find the host plant? 261 00:22:56,100 --> 00:23:00,180 And what we discovered was that they actually smell 262 00:23:00,180 --> 00:23:01,380 the host plant. 263 00:23:06,020 --> 00:23:10,260 - The cuscuta seed does not have long to find a host once it sprouts. 264 00:23:15,740 --> 00:23:19,500 One might think it latches on to the first plant within reach, 265 00:23:19,500 --> 00:23:20,900 but that's not the case. 266 00:23:20,900 --> 00:23:22,300 It makes a choice. 267 00:23:26,860 --> 00:23:30,820 This high-speed footage shows the cuscuta hunting for a host. 268 00:23:33,660 --> 00:23:37,460 - I think they're smelling the tomato plants as, 269 00:23:37,460 --> 00:23:40,740 "This is something that I can survive on." 270 00:23:40,740 --> 00:23:42,260 They really can sniff. 271 00:23:47,380 --> 00:23:50,140 - How do the cuscuta find the tomato plants? 272 00:23:51,740 --> 00:23:54,340 - Cuscuta, like, germinates, it comes out of the ground. 273 00:23:54,340 --> 00:23:56,460 And then they, like, you know, start growing 274 00:23:56,460 --> 00:23:58,740 towards the tomato plant. 275 00:23:58,740 --> 00:24:03,820 And our hypothesis is that the perception of the smell 276 00:24:03,820 --> 00:24:06,620 is at the tip of the vine. 277 00:24:31,020 --> 00:24:35,820 We now know that plants can perceive smells, but we don't know yet 278 00:24:35,820 --> 00:24:37,220 how they do that. 279 00:24:37,220 --> 00:24:40,740 What are the mechanisms of this nose perception? 280 00:24:48,540 --> 00:24:52,780 - The differing odours allow the cuscuta to select a plant 281 00:24:52,780 --> 00:24:55,100 which smells strong enough to support it. 282 00:25:01,860 --> 00:25:04,540 - One thing that we were amazed to see is that the cuscuta 283 00:25:04,540 --> 00:25:07,900 have this ability also to perceive, you know, 284 00:25:07,900 --> 00:25:10,300 a healthy plant versus a sick plant. 285 00:25:12,260 --> 00:25:16,140 They have - I mean, in my view - an incredible sense. 286 00:25:19,220 --> 00:25:21,060 - This plant is unhealthy, 287 00:25:21,060 --> 00:25:22,780 so the cuscuta rejects it. 288 00:25:28,180 --> 00:25:32,100 Once a host has been selected, the cuscuta wraps around it 289 00:25:32,100 --> 00:25:36,340 and sucks its sap, leaving just enough to keep the host alive. 290 00:25:41,420 --> 00:25:45,780 When the cuscuta have flowered and produced their seeds, 291 00:25:45,780 --> 00:25:48,420 they exhaust their host and die with it. 292 00:25:52,020 --> 00:25:54,460 If plants can smell each other, 293 00:25:54,460 --> 00:25:57,940 some can also smell pest insects. 294 00:25:57,940 --> 00:26:02,820 - One of our recent discoveries is that actually plants can also 295 00:26:02,820 --> 00:26:05,540 perceive insect pheromones. 296 00:26:05,540 --> 00:26:10,340 So, we showed that eurosta flies produce pheromones that attract 297 00:26:10,340 --> 00:26:13,380 the females, and the plants, 298 00:26:13,380 --> 00:26:15,900 these plants that they have co-evolved with, 299 00:26:15,900 --> 00:26:19,860 these goldenrod plants can perceive these pheromones 300 00:26:19,860 --> 00:26:24,380 by smelling the specific compound that the flies are producing. 301 00:26:24,380 --> 00:26:28,780 This pheromone indicates an upcoming threat for the plants. 302 00:26:30,260 --> 00:26:34,020 - When it detects the eurosta parasite fly pheromones, 303 00:26:34,020 --> 00:26:36,380 the plant defends itself. 304 00:26:36,380 --> 00:26:38,980 For instance, it flowers at a different time. 305 00:26:41,220 --> 00:26:45,140 Discovering that plants can perceive the smell of some insects opens 306 00:26:45,140 --> 00:26:47,420 a wide field of research, 307 00:26:47,420 --> 00:26:50,100 including applications for ecological farming. 308 00:27:03,060 --> 00:27:08,100 If water is vital for plants, light is just as important. 309 00:27:08,100 --> 00:27:10,380 - What is light for a plant? 310 00:27:10,380 --> 00:27:14,380 But it's its energy to make food through photosynthesis. 311 00:27:14,380 --> 00:27:17,460 A plant has to know where the sunlight is, so that it could do 312 00:27:17,460 --> 00:27:19,980 photosynthesis, in order to make its sugars, 313 00:27:19,980 --> 00:27:21,580 in order to have energy. 314 00:27:23,380 --> 00:27:26,140 And so, therefore, it has to be exquisitely sensitive 315 00:27:26,140 --> 00:27:27,620 to where the sun is. 316 00:27:31,260 --> 00:27:35,660 - Plants do not sense light with an organ like the eye, 317 00:27:35,660 --> 00:27:37,380 but with each and every cell. 318 00:27:44,460 --> 00:27:48,060 Translating light signals into action - 319 00:27:48,060 --> 00:27:51,140 germination, growth, flowering. 320 00:27:53,980 --> 00:27:58,020 - Compared to plants, humans are visually impaired. 321 00:27:58,020 --> 00:28:00,380 While we can see the colours of a rainbow, 322 00:28:00,380 --> 00:28:02,620 that's the whole spectrum we see from blue all the way 323 00:28:02,620 --> 00:28:03,980 through to red, 324 00:28:03,980 --> 00:28:08,140 plants see, respond to all of the visual light that we see, 325 00:28:08,140 --> 00:28:12,020 but they also perceive, sense and respond to light waves 326 00:28:12,020 --> 00:28:15,860 that we're blind to, such as UV light or far-red light. 327 00:28:19,700 --> 00:28:21,980 - Hydroponic farms light their plantations 328 00:28:21,980 --> 00:28:26,340 with ultraviolet and infrared light, which favour photosynthesis. 329 00:28:29,500 --> 00:28:33,020 This ensures maximum continuous plant productivity. 330 00:28:43,060 --> 00:28:45,260 At France's Institute for Agriculture, 331 00:28:45,260 --> 00:28:49,340 Food and the Environment, Elzbieta Frak is studying 332 00:28:49,340 --> 00:28:51,860 how plants communicate through light signals. 333 00:28:54,340 --> 00:28:58,900 Exposure to coloured filters reveals that plants absorb blue, 334 00:28:58,900 --> 00:29:03,020 use red for photosynthesis, reflect green, 335 00:29:03,020 --> 00:29:04,900 and communicate in infrared. 336 00:29:17,700 --> 00:29:22,340 To demonstrate the infrared communication, Elzbieta tracks 337 00:29:22,340 --> 00:29:25,020 a control plant as it moves along a rail. 338 00:29:26,340 --> 00:29:30,980 A light source and an optical sensor are placed behind the plant. 339 00:29:30,980 --> 00:29:32,780 Measured in nanometres, 340 00:29:32,780 --> 00:29:36,500 the optical sensor detects the movement of the control plant 341 00:29:36,500 --> 00:29:40,420 by the variations in the infrared light signal being reflected 342 00:29:40,420 --> 00:29:42,140 as it moves along the rail... 343 00:29:43,820 --> 00:29:46,300 ..similar to the way an infrared camera starts 344 00:29:46,300 --> 00:29:48,660 recording when an animal passes in front of it. 345 00:30:59,540 --> 00:31:03,740 Elzbieta has installed masts equipped with high-precision 346 00:31:03,740 --> 00:31:05,220 optical sensors. 347 00:31:05,220 --> 00:31:09,060 Each sensor is placed in the middle of a ring of evenly spaced 348 00:31:09,060 --> 00:31:14,140 identical young plants, and pivots through 360 degrees. 349 00:31:16,540 --> 00:31:20,060 The sensor measures the signals exchanged by the plants 350 00:31:20,060 --> 00:31:22,060 in the near-infrared, 351 00:31:22,060 --> 00:31:25,300 the specific wavelengths that neighbouring plants reflect. 352 00:31:29,980 --> 00:31:33,820 The signals reveal that each plant locates its neighbours 353 00:31:33,820 --> 00:31:37,540 and adapts its growth so that it does not waste energy. 354 00:31:59,100 --> 00:32:02,740 Elzbieta Frak is at the forefront of research revolutionising our 355 00:32:02,740 --> 00:32:04,620 knowledge of plants. 356 00:32:04,620 --> 00:32:08,540 In the near future, farmers could use mathematical models 357 00:32:08,540 --> 00:32:11,500 to predict the interaction between plants of the same 358 00:32:11,500 --> 00:32:13,340 and different species, 359 00:32:13,340 --> 00:32:15,500 or with natural elements such as wind. 360 00:32:20,780 --> 00:32:24,420 We are often sheltered from wind in our daily lives, 361 00:32:24,420 --> 00:32:27,340 but wind is part of the natural environment of plants. 362 00:32:31,620 --> 00:32:35,620 In Clermont-Ferrand, Bruno Moulia and his team are studying plant 363 00:32:35,620 --> 00:32:37,820 reactions to all kinds of wind... 364 00:32:40,340 --> 00:32:42,420 ..from a caressing breeze 365 00:32:42,420 --> 00:32:44,980 to the violent shocks caused by storms. 366 00:33:32,060 --> 00:33:35,260 The experiment is repeated under natural conditions. 367 00:33:46,260 --> 00:33:49,380 Several trees are restrained with straps and cables. 368 00:33:52,540 --> 00:33:56,260 Monitors are installed that measure the degree a tree bends 369 00:33:56,260 --> 00:33:57,860 according to wind strength. 370 00:34:05,340 --> 00:34:08,580 Bruno attaches the same type of monitor to other trees, 371 00:34:08,580 --> 00:34:11,060 which are not restrained and can move freely. 372 00:34:37,380 --> 00:34:40,420 Distinguishing unusual, dangerous winds 373 00:34:40,420 --> 00:34:42,980 from ordinary, inoffensive winds 374 00:34:42,980 --> 00:34:46,820 supposes that trees have an active memory over long periods 375 00:34:46,820 --> 00:34:50,380 of time, perhaps even throughout their entire lifespan. 376 00:35:13,900 --> 00:35:16,540 The sharp angle at the base of the tree is damaged 377 00:35:16,540 --> 00:35:19,260 from an exceptional gust of wind. 378 00:35:19,260 --> 00:35:21,580 The tree was bent but survived. 379 00:35:23,580 --> 00:35:26,540 The cells of the wood fibres that make up the trunk of the tree 380 00:35:26,540 --> 00:35:30,980 stretch and retract permanently, like hydraulic cylinders, 381 00:35:30,980 --> 00:35:33,340 depending on the strength of the wind. 382 00:35:33,340 --> 00:35:37,020 This elasticity allows it to bend without breaking, 383 00:35:37,020 --> 00:35:39,540 and, once the gust of wind has passed, 384 00:35:39,540 --> 00:35:41,420 to recover a vertical position. 385 00:36:05,020 --> 00:36:10,460 The forest of Krzywy in Poland is known as the Crooked Forest, 386 00:36:10,460 --> 00:36:12,580 marked by a wind that almost destroyed it. 387 00:36:15,500 --> 00:36:18,740 Events sculpt the silhouettes of trees telling us 388 00:36:18,740 --> 00:36:20,060 about their lives. 389 00:36:24,980 --> 00:36:28,220 If knocked over, why do trees straighten up again? 390 00:36:30,540 --> 00:36:33,900 This irrepressible tendency has fascinated scientists. 391 00:36:37,300 --> 00:36:42,020 In the 1900s, the botanist Wilhelm Pfeiffer was one of the first 392 00:36:42,020 --> 00:36:44,540 to create moving pictures of this phenomena. 393 00:36:48,380 --> 00:36:51,060 Do plants only straighten up to capture 394 00:36:51,060 --> 00:36:52,980 sunlight more efficiently? 395 00:37:04,940 --> 00:37:08,740 Bruno Moulia has designed an experimental lighting chamber 396 00:37:08,740 --> 00:37:13,300 with over 90 fluorescent light bulbs shining from all directions. 397 00:37:44,780 --> 00:37:47,700 Under uniform lighting conditions, 398 00:37:47,700 --> 00:37:51,020 the plant still straightens up vertically in a single day. 399 00:37:52,540 --> 00:37:56,220 The conclusion? It is not light perception that guides the plant 400 00:37:56,220 --> 00:37:58,100 upwards, but another sense. 401 00:38:01,260 --> 00:38:03,980 Could plants be sensitive to gravity? 402 00:38:06,580 --> 00:38:10,860 To answer this, we need to examine how the plant cells react 403 00:38:10,860 --> 00:38:12,460 to a change of direction. 404 00:38:50,020 --> 00:38:53,580 The French team pursued its investigation. 405 00:38:53,580 --> 00:38:58,460 They wanted to know if the plant could locate itself in space. 406 00:38:58,460 --> 00:39:03,060 So, in the absence of gravity, could it still find its stem, 407 00:39:03,060 --> 00:39:06,140 branches and leaves in relation to each other? 408 00:39:09,820 --> 00:39:14,740 Bruno Moulia's team cancelled the effect of gravity by rotating 409 00:39:14,740 --> 00:39:17,860 young plants in a device called a gravitron. 410 00:39:26,780 --> 00:39:30,060 The plants were photographed over several days. 411 00:39:32,020 --> 00:39:34,780 The experiment showed that plants can perceive 412 00:39:34,780 --> 00:39:36,380 their location in space. 413 00:39:38,820 --> 00:39:40,700 Like humans and animals, 414 00:39:40,700 --> 00:39:43,740 they also have a sixth sense called proprioception. 415 00:39:50,820 --> 00:39:53,580 To perceive the position of your own body in the space 416 00:39:53,580 --> 00:39:56,620 around you is vital for organisms that grow 417 00:39:56,620 --> 00:39:58,700 in an ever-changing environment. 418 00:40:00,860 --> 00:40:04,860 But unlike humans, plants simultaneously inhabit 419 00:40:04,860 --> 00:40:09,820 two environments. One above ground and another below, 420 00:40:09,820 --> 00:40:13,180 with their roots also facing ever-changing conditions. 421 00:40:19,540 --> 00:40:22,780 Roots endlessly explore underground, 422 00:40:22,780 --> 00:40:26,020 each one searching for vital water and nutriments. 423 00:40:29,620 --> 00:40:34,820 The neurobiologists Frantisek Baluska and Stefano Mancuso 424 00:40:34,820 --> 00:40:38,500 are interested in the tips of the roots called the apex. 425 00:40:38,500 --> 00:40:41,580 - All the root apices, they are coordinated in their activities 426 00:40:41,580 --> 00:40:45,020 and growth, and they resemble some swarms, 427 00:40:45,020 --> 00:40:48,180 for example insect swarms or birds. 428 00:40:48,180 --> 00:40:50,220 Somehow there is some communication. 429 00:40:50,220 --> 00:40:52,700 We still don't understand how it is going on, 430 00:40:52,700 --> 00:40:55,620 but they are coordinating and behave as one swarm. 431 00:41:04,700 --> 00:41:07,220 - Each plant root is like one unit, 432 00:41:07,220 --> 00:41:11,100 like a swallow, an ant or a termite within its community. 433 00:41:15,580 --> 00:41:19,940 Information collected by each apex is transmitted to every cell 434 00:41:19,940 --> 00:41:22,580 in the root and body of the plant, 435 00:41:22,580 --> 00:41:24,900 creating a collective intelligence 436 00:41:24,900 --> 00:41:28,700 that determines future tasks and coordinates action. 437 00:41:31,700 --> 00:41:33,940 - There is no central organiser, 438 00:41:33,940 --> 00:41:36,060 and that's why these networks are not 439 00:41:36,060 --> 00:41:39,420 vulnerable to some stress situations. 440 00:41:39,420 --> 00:41:43,140 These networks can self-organise very effectively 441 00:41:43,140 --> 00:41:47,260 and they can survive any bad stress situation. 442 00:41:47,260 --> 00:41:50,380 The network resembles very closely the internet network, 443 00:41:50,380 --> 00:41:53,660 so one could call it a root-wide web. 444 00:41:55,220 --> 00:41:59,900 - The networks are all connected, and depending on the information 445 00:41:59,900 --> 00:42:02,100 collected by the multiple apex, 446 00:42:02,100 --> 00:42:04,460 the root filaments change direction, 447 00:42:04,460 --> 00:42:08,140 accelerate, slow down or branch out. 448 00:42:08,140 --> 00:42:12,500 However, if a root apex is cut off, the root does not change direction. 449 00:42:14,020 --> 00:42:17,660 The upper root with no apex grows straight, 450 00:42:17,660 --> 00:42:20,540 while the lower root, with an intact apex, 451 00:42:20,540 --> 00:42:23,580 moves around, constantly seeking information. 452 00:42:27,140 --> 00:42:31,060 Strong electrical activity can be detected in the apex, 453 00:42:31,060 --> 00:42:35,300 and it is the part of the plant that uses the most oxygen. 454 00:42:35,300 --> 00:42:39,580 - This is the same kind of signal we can record in the animal brain. - Yes. 455 00:42:46,940 --> 00:42:50,540 Really, these networks are also used to exchange information, 456 00:42:50,540 --> 00:42:53,740 not just to provide water or nutrition. 457 00:42:53,740 --> 00:42:57,940 We have still no idea how complex the communication there is. 458 00:43:07,420 --> 00:43:09,340 - In every plant habitat, 459 00:43:09,340 --> 00:43:12,020 roots are weaving infinite networks. 460 00:43:16,100 --> 00:43:19,940 These root networks are further enhanced by uniting with another 461 00:43:19,940 --> 00:43:23,780 complex underground network - filaments of fungi. 462 00:43:36,300 --> 00:43:40,700 Roots and filaments grow in symbiosis to form the mycorrhiza. 463 00:43:44,300 --> 00:43:47,940 In a forest, this network links the trees, 464 00:43:47,940 --> 00:43:49,780 increasing the reach and capacity 465 00:43:49,780 --> 00:43:53,660 of both root and filament networks 10,000-fold. 466 00:44:01,420 --> 00:44:05,020 The mycorrhiza is a network of intense interaction. 467 00:44:10,020 --> 00:44:13,980 Exchanging information, rare mineral elements 468 00:44:13,980 --> 00:44:16,180 and sugars produced by the trees. 469 00:44:27,900 --> 00:44:30,260 In this forest near Jerusalem, 470 00:44:30,260 --> 00:44:35,060 pine, oaks, cypress, carob and pistachio trees 471 00:44:35,060 --> 00:44:36,620 all grow together. 472 00:44:47,340 --> 00:44:50,620 The Weizmann Institute is at the forefront of research 473 00:44:50,620 --> 00:44:52,460 into mycorrhiza networks. 474 00:45:09,420 --> 00:45:12,300 - On the root of this big pine tree behind us, 475 00:45:12,300 --> 00:45:15,060 we see the mycorrhiza growing all over the root, 476 00:45:15,060 --> 00:45:17,860 transporting materials from the root 477 00:45:17,860 --> 00:45:20,620 of this tree to the next tree, and on and on. 478 00:45:25,580 --> 00:45:29,460 - With a specialist underground camera, researchers map 479 00:45:29,460 --> 00:45:31,220 the mycorrhiza networks. 480 00:45:33,220 --> 00:45:35,100 - Wow. Look at these roots. 481 00:45:35,100 --> 00:45:37,260 And it seems like they are full of mycorrhiza. 482 00:45:37,260 --> 00:45:38,820 - Wow. It's amazing. 483 00:45:38,820 --> 00:45:42,420 Maybe it's connected to the younger pine. 484 00:45:42,420 --> 00:45:46,580 - The underground maps charted by the Weizmann Institute team show 485 00:45:46,580 --> 00:45:50,180 that the trees share carbon, and therefore sugar, 486 00:45:50,180 --> 00:45:54,740 with neighbours of the same species, but also with other species of tree. 487 00:45:54,740 --> 00:45:58,820 - We showed that up to 40% of the biomass in the fine root 488 00:45:58,820 --> 00:46:03,540 of this pine tree can actually come from carbon 489 00:46:03,540 --> 00:46:05,820 exported from an oak tree nearby 490 00:46:05,820 --> 00:46:09,220 through this mycorrhizal connection. We know that both 491 00:46:09,220 --> 00:46:11,380 control the association. 492 00:46:11,380 --> 00:46:16,860 For example, a tree can stop giving carbon to a fungi that is not 493 00:46:16,860 --> 00:46:19,420 providing water or nutrients. 494 00:46:19,420 --> 00:46:23,700 And the fungi themselves, they are very flexible and agile. 495 00:46:23,700 --> 00:46:29,260 They can leave a tree and reconnect to another side of a tree 496 00:46:29,260 --> 00:46:31,420 where they get the carbon from. 497 00:46:41,740 --> 00:46:45,220 - The scientists measure the level of carbon in the tree roots 498 00:46:45,220 --> 00:46:47,620 and in the mycorrhizal fungal networks. 499 00:47:05,260 --> 00:47:08,780 They also measure the level of carbon in leaves with a device 500 00:47:08,780 --> 00:47:11,660 that captures their photosynthesis data. 501 00:47:41,020 --> 00:47:44,980 Back in the laboratory, a new generation of sequencing 502 00:47:44,980 --> 00:47:48,420 techniques quantifies the carbon in the samples. 503 00:47:58,220 --> 00:48:00,260 - Using the carbon measurement, 504 00:48:00,260 --> 00:48:04,940 we discovered that the carbon can move from leaves to roots 505 00:48:04,940 --> 00:48:08,020 in a tree within three days, 506 00:48:08,020 --> 00:48:11,500 and it takes another six days to move 507 00:48:11,500 --> 00:48:13,820 from the roots of one tree 508 00:48:13,820 --> 00:48:17,220 over five metres to the roots of another tree 509 00:48:17,220 --> 00:48:19,500 through the mycorrhizal hyphae. 510 00:48:35,900 --> 00:48:38,820 - Are the mycorrhiza capable of feeding the trees 511 00:48:38,820 --> 00:48:41,980 in extreme climatic conditions? 512 00:48:41,980 --> 00:48:45,900 To find out, pine trees have been covered by opaque bags 513 00:48:45,900 --> 00:48:48,700 to prevent them from photosynthesising. 514 00:48:53,420 --> 00:48:54,660 - Wow! 515 00:48:54,660 --> 00:48:56,660 Look at this poor plant. 516 00:48:56,660 --> 00:48:58,940 It died because it was not connected. 517 00:48:58,940 --> 00:49:02,380 It was separated from the middle plant here. 518 00:49:02,380 --> 00:49:05,260 But this one survived the shading 519 00:49:05,260 --> 00:49:08,340 because it was connected and got 520 00:49:08,340 --> 00:49:11,340 carbon from the middle pine to this pine. 521 00:49:20,380 --> 00:49:23,460 - The Israelis are concerned about the possible impacts of climate 522 00:49:23,460 --> 00:49:25,020 change on their forests. 523 00:49:25,020 --> 00:49:27,780 They have set up an experiment that restricts the amount 524 00:49:27,780 --> 00:49:29,860 of rainwater in the soil. 525 00:49:29,860 --> 00:49:33,060 It will take five years to understand how the drier 526 00:49:33,060 --> 00:49:36,020 conditions impact the mycorrhiza network. 527 00:49:37,820 --> 00:49:41,340 - In agriculture, you can breed specific mycorrhiza and apply 528 00:49:41,340 --> 00:49:43,260 it to your fields in big scale, 529 00:49:43,260 --> 00:49:45,580 but in forests, it is actually impossible. 530 00:49:45,580 --> 00:49:48,620 We have to learn what the nature does. 531 00:49:48,620 --> 00:49:50,780 We have to think about the diversity. 532 00:49:50,780 --> 00:49:52,900 The more tree species that we plant, 533 00:49:52,900 --> 00:49:54,620 the more mycorrhizal species 534 00:49:54,620 --> 00:49:56,780 that will be there below ground, 535 00:49:56,780 --> 00:50:00,380 and will make more intricate, more complex networks 536 00:50:00,380 --> 00:50:03,580 that will make the forest more resilient and more sustainable. 537 00:50:05,660 --> 00:50:09,460 - Science is still far from having made an exhaustive inventory 538 00:50:09,460 --> 00:50:12,780 of the senses of plants and their resources. 539 00:50:12,780 --> 00:50:17,380 Future discoveries will no doubt bring many new surprises. 540 00:50:17,380 --> 00:50:21,260 The more we learn about plants, the more they amaze us. 541 00:50:24,420 --> 00:50:29,740 The Swiss Federal Ethics Committee on Non-Human Biotechnology considers 542 00:50:29,740 --> 00:50:33,900 that plants, like animals, have dignity and a moral value. 543 00:50:37,700 --> 00:50:41,860 - If tomorrow, the humans would disappear from the planet, 544 00:50:41,860 --> 00:50:45,620 in a few centuries, plants would take control of everything, 545 00:50:45,620 --> 00:50:48,780 and every single trace of the human civilisation 546 00:50:48,780 --> 00:50:50,700 would be hidden by plants. 547 00:50:50,700 --> 00:50:54,340 But if tomorrow, the plants would start to disappear 548 00:50:54,340 --> 00:50:57,820 from the planet, in a few weeks, probably, at least 549 00:50:57,820 --> 00:51:00,180 all the terrestrial life would disappear, 550 00:51:00,180 --> 00:51:02,540 transforming the planet in a desert. 551 00:51:04,660 --> 00:51:08,500 - The latest discoveries teach us that the frontiers between 552 00:51:08,500 --> 00:51:12,900 the human world, the animal world and the plant world 553 00:51:12,900 --> 00:51:16,660 are not as distinct as we once thought. 554 00:51:16,660 --> 00:51:20,900 Revolutionary thinking is bringing an immense change to how we see 555 00:51:20,900 --> 00:51:22,140 the living world.