Insects and plants. The substances developed by plants for scaring away of insects

you are: Insects and plants

Involving a number of insects-opylitelej, plants at the same time suffer that many insects, especially on larva stages, or caterpillars, on them are fed, eating generally their leaves. Fortunately, it does not concern bees almost; they only collect nectar and pollen from plants and only sometimes destroy wood. for protection against insects of a plant have a wide set ' secondary metabolitov ' which do them for insects unpleasant. Under secondary metabolitami understand the various substances of a phytogenesis which are not playing any role in primary metabolic processes, such, as breath or synthesis of separate cellular components. We do this conclusion about absence at them any role in primary metabolic processes on the basis of that any of such specific substances is not peculiar to all plants or at least the majority of kinds. Often given secondary metabolit meets only at any one family, and sometimes even at one kind or a version. there are thousand secondary metabolitov; their number is so great that for the present not all they to us are known, and many chemists-organic chemistry spend all time for identification ' new ' connections of this group. Biologists for many years built guesses about a role of these substances. Now, apparently, it is possible to tell with confidence that secondary metabolity form the protective system used by plants against insects and patogenov, and sometimes and against other plants.

How there could be such protective system? Most likely a casual way. We will imagine that the given plant had a mutation which has mentioned this or that metabolic way therefore in a plant formation of any new connection has begun. if this connection has appeared poisonous or unpleasant for wreckers chances of a survival at such plant, naturally, have raised in comparison with it ' more tasty ' relatives; will eat first of all, of course, them. Chances that the gene supervising synthesis of this connection, will be transferred following generation of plants have accordingly increased also. If such change has occurred at all plants insects would have become nothing to be fed. However insects too possess extremely strong variability. The casual mutation can make an insect tolerant to poison, and it will have an opportunity to eat that for others is unsuitable; Therefore it will survive and will succeed in conditions, adverse for other individuals of the same kind. As a result the mutant insect will transfer the gene of stability bolshemu to number of individuals in following generation. Parallel evolution in which are involved as already it was marked above, not separate individuals, and the whole populations of plants and the insects, changing in common will be a consequence of it.

The Substances serving to plants for protection against insects, are very various. Among them are available poisonous, capable to kill any animal who will take in head to try such plant; therefore the animals deprived of corresponding antidote, usually feel danger and avoid poisonous plants, do not eat them. Other group of substances impacts to plants unpleasant relish that also frightens off rastitelnojadnyh animals so sometimes they even do not touch to similar ' tasteless ' to plants. Possibly, this role play at plants numerous izoprenoidnye connections, in particular terpeny and essence (fig. 15.3). For any animal, apparently, are toxic present at plants alkaloidy, tsianogennye glikozidy and some ' unusual ' amino acids. Tsianogennye glikozidy decay at damage of a fabric with allocation of cyanic hydrogen that does by their very powerful repellents. The toxic amino acids which are present at seeds of tropical representatives of family bean, cause lethal effect, it is obvious, because they join in fibers synthesised by an organism instead of normal amino acids. Insects who can without harm for itself are fed on the plants containing any poisonous connection, possess ability or to destroy this connection, or to connect it chemically and such way to translate in the inactive form. One more way to avoid danger of a poisoning is found out at zernovki (this. Bruchidae), steady against toxic amino acid kanavaninu. This insect eats seeds Dio-dea megacarpa in which 8% kanavanina contain, and meanwhile, as it is known, even 0,25% kanavanina are enough for lethal action. The reason of such stability consists in this case that available for an insect arginil-tRnK-sintetaza possesses ability to distinguish arginin from kanavanina and to choose '.правильную ' amino acid.

On this way it is possible to consider as Following step such situation when the substance, toxic for all other insects, is not simply neutralised in an organism of a kind adapting for it, but becomes for this kind attraktantom; individuals of such kind are found out usually only on the plant containing given substance, and do not meet more anywhere (fig. 15.2). So caterpillars of Rapilioajax are fed only on leaves of some umbellate, containing certain essence, mainly metilhavikol and terpen karvon (fig. 15.3 see). Only in the presence of these substances of a caterpillar start feeding; they eat even the filtering paper moistened pure karvonom.

Naturally, there is a question: whether win something in turn those poisonous plants for which the insect adapts? It appears, in other cases win. Insects who are fed on them without harm for itself, accumulate vegetative poison in the organism and get as a result of it the strong smell which is frightening off not only enemies of these insects, but also others rastitelnojadnyh animals. This circumstance generates good enough symbiosis between such plants and insects.

As it is known, plants eat not only insects. There is a great number rastitelnojadnyh mammals and if they ate poisonous plants hardly they would have many chances to survive. They avoid such plants, perceiving a corresponding flavouring signal; differently, poisonous plants seem them tasteless and consequently are rejected. Certainly, we distinguish only that is tasteless for us, and we can not be assured that same it will seem, for example, to a cow. However it is noticed that plants which seem us bitter, and the plants rejected by animals (including livestock), well enough coincide. The bitterness, apparently, frightens off all. The important factor defining a choice of food at wild animals, it is possible to consider also tartness, or the knitting taste caused by presence tanninov (fig. 15.3 see): animals prefer usually the plants which absolutely not are not containing tanninov or with their very small maintenance. The majority of bitter or tart substances are really toxic, though separate kinds of animals and can have the mechanisms providing their neutralisation. Some kinds of plants enter into a diet of a gorilla only, and there are data that all these plants - bitter. Gorillas, however, have got used to them and prefer them just as we, for example, get used to weak bitterness of tea, beer, various greens or our culinary seasonings. At the same time sweet taste or a sweet smell opposite usually involve animals. Substances with such properties, possibly, play a part in any interactions between plants and animals, for example in distribution of seeds by the animals eating juicy fruits.