The Plant Kingdom's Most Unusual Talents
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The Plant Kingdom's Most Unusual Talents Plants do not just laze about, soaking up rays. They shift around, hunt, eat, attack--and defend themselves Wikim Plants seem so passive. Tree branches bow to the wind, losing their leaves. Lettuce just sits there as snails help themselves to a free salad bar. And grass lets everyone walk all over it. But all that apparent listlessness is deceptive. In truth, plants are incredibly active members of their communities. Plants move on their own all the time—creeping, digging, reaching, blooming. However, most of the action happens too slowly for our eyes to see unaided. In his 1995 documentary series The Private Life of Plants, David Attenborough and his crew created beautiful time-lapse videos to showcase plants' hidden mobility. Climbing jungle vines race one another up tree trunks, stretching towards the sunlight. The thorny bramble whips from side to side, shoving competing plants out of the way to expand its territory. A spindly orange vine known as dodder is a particularly striking example of dynamic plant life. Dodder is a parasite—it lives off of other plants. Instead of waiting around for a suitable host, the vine hunts one down.Conseulo De Moraes of Penn State University planted a young dodder near a tomato plant and continuously filmed the pair for several days. Her time-lapse video reveals a growing dodder flailing around, tasting the air like a snake, until it finally brushes the tomato's stem and begins to encircle its victim. Eventually it would sink tiny nozzles into the tomato plant to suck out vital juices. De Moraes discovered something surprising about the dodder: it can smell. The vine sniffs out its hosts, growing toward telltale chemicals released by its neighbors. And it is picky. Dodder prefers juicy tomato plants to slender wheat and healthy plants to sick plants. Tel Aviv University biologist Daniel Chamovitz discusses dodder and many other fascinating plants in his upcoming book, What A Plant Knows, an excerpt from which appears in the May issue of Scientific American. Dodder is hardly the only plant whose mobility and abilities would surprise most people. The plant kingdom is full of unusual talents that are more common than biologists first realized. The Venus flytrap is only one of several different kinds of carnivorous plants that have developed astonighing ways to catch and digest insects and other small animals. Almost all plants have evolved chemical defenses against herbivores and many plants recognize when their neighbors are under attack, preparing for battle themselves. Alpine buttercups track the sun's arc over the course of a day to keep their blossoms warm and appealing to heat-seeking pollinators. The telegraph plant swivels its leaves to maximize exposure to sunlight, adjusting so quickly that you can see the leaves moves in real time. Some plants may even distinguish between family and strangers, sharing resources only with the former. Like most organisms, plants sense and respond to their environments. To appreciate just how sensible plants are, we have to look at the world—or even smell the world—from their perspective. The spindly orange vine as knows as Dodder (Cuscuta pentagona) is a parasite plant. Time-lapse video reveals that a dodder seedling twirls through the air, sniffing volatile chemicals released by neighboring plants in search for a suitable host. When it finds one, dodder entwines its victim and inserts nozzles into the host’s stem, siphoning vital nutrients. The workings of the trap mechanism in Dionaea are complex and depend on changes in the osmotic potential of the cells in the hinge. The traps close when one or other of the trigger hairs is touched more than once in quick succession; if nothing is caught, traps reopen after about a day. Once an insect is trapped, flaps close tighter to squash it, and enzymes are secreted to digest the prey. Mucilage is secreted to seal the margins of the trap. Some days later, after the insect is digested, the trap reopens. The traps are unusual in that they spring shut. Similar traps are found in the aquatic genus Aldovandra (also in the family Droseraceae), but these only catch minute aquatic animals. Most species of Drosera (sundews) also catch insects, but by using sticky hairs that cover the leaf, after which the leaf slowly coils over the insect before digesting it. Codariocalyx motorius known as the telegraph plant is a tropical Asian shrub, one of a few plants capable of rapid movement. This plant is famous for its movement of small, lateral leaflets at speeds rapid enough to be perceivable with the naked eye. This is possibly a strategy to maximise light by tracking the sun. Each leaf is equipped with a hinge that permits it to be moved to receive more sunlight, but the weight of these leaves means the plant must expend a lot of energy in moving it. To optimise its movement, each large leaf has two small leaflets at its base. These move constantly along an elliptical path, sampling the intensity of sunlight, and directing the large leaf to the area of most intensity. Another hypothesis has been offered that the rapid movements are intended to deter potential predators. The flowers of the alpine snow buttercup Ranunculus adoneus track the sun's movement from early morning until mid-afternoon. Individual blooms last up to a week: younger female stage flowers show greater solar tracking fidelity than older hermaphrodite or dehisced flowers. Flowers aligned parallel to the sun's rays reach mean internal temperatures several degrees Celsius above ambient air temperature. As a flower's angle of deviation from the sun increases beyond 45 degrees, internal flower temperature is significantly reduced. Fly pollinators are seen disproportionately often on flowers aligned with the sun; this is due, in part, to their greater residence time on tracking flowers. Fly visitation is important to fecundity. When flies were excluded from flowers, some selfed seeds were matured, but total seed production was much less than in either handoutcrossed or open-pollinated flowers. Flowers that were tethered at random angles to prevent solar tracking set fewer, smaller seeds than unmanipulated control flowers. Reductions in seed weight were statistically consistent at different times in the season, but tethering influenced seed number per flower most strongly in the early season. Effects of tethering on maternal reproduction could be due to either pollinator diserimination, post-pollination developmental processes, or both. In a second series of experiments using fluorescent dye particles as pollen analogs, tethered donor flowers dispersed dye to as many recipients as paired control flowers, suggesting that solar tracking fidelity may have little effect upon this component of male reproduction. The sensitive plant is popular in cultivation around the world, and is enjoyed by many as a curiosity due to its highly touch-sensitive leaves. Robert Hooke (English scientist famous for his microscopy work, 1635-1703) was one of the first people to investigate the movements of Mimosa pudica, and at that time it had been suggested that plants had nerves and tissues similar to those in animals. It was later discovered that the leaves fold as a result of the internal movement of water, and the mechanics of the process are now well-documented. A stimulus, such as touch or air movement, triggers certain areas of the stem to release chemicals, which cause water to move out of cell vacuoles and leads to cell collapse. This rapid plant movement is thought to act as a defence against herbivores, which may be deterred by the dramatic response, or if they are small, may be dislodged as the leaves collapse. CLINGY CREEPER: The wild cucumber's (Sicyos angulatus) spidering tendrils, which grab onto fences and other plants for support, are super-sensers. Most people cannot feel the weight of a string weighing less than 2 grams. But the tendrils of the wild cucumber respond to the touch of a string weighing only 0.25 grams and immediately start twirling around the tiny thread. ZERO GRAVITY: Like most plants, morning glories (Ipomea nil) usually grow up towards the sun. But this strain of morning glory, called Shidare asagao, has lost its balance – it has lost its ability to sense gravity. It doesn’t know where ―up‖ is. Hence the vines of this morning glory fall down, making for a beautiful ornamental plant. FAMILY VALUES: In lab experiments, researchers have shown that a weedy beach plant known as sea rocket (Cakile) recognizes its siblings and restrains its root growth in their presence. The idea is that siblings benefit from sharing nutrients and helping each other pass on genes they have in common. When planted near strangers, however, sea rocket grows as many roots as possible, since there is no benefit to helping out an unrelated plant. Sea rocket probably identifies family based on chemicals that roots secrete into the soil. MOLECULAR MEMORY: Common bread wheat (Triticum aestivum), also known as ―winter wheat," only flowers and makes grain following a cold winter. If winter snows do not blanket the sprouts, they never flower. But if prior to planting, farmers keep the seeds in the freezer for a while, then the sprouts will flower even in the absence of snow. In other words, the plants remember their exposure to the cold. How do they encode this memory? The cold induces characteristic changes in the pattern of molecules hitched to DNA, a process known as epigenetics that in turn modifies gene expression. RISE AND SHINE: Irises bloom in the spring and early summer. They know that the time for flowering has arrived because they can sense that the days are getting longer and the nights are getting shorter.