Influencing the activity of plant growth regulators

Details Influencing the activity of plant growth regulators Influencing the activity of plant growth regulators

1998-03-13

2001-06-05

Clardy, S. Mark (Department: 1616)

Plant protecting and regulating compositions

Plant growth regulating compositions

C504S189000, C504S302000, C504S359000

Reexamination Certificate

active

06242381

ABSTRACT:

The present invention relates to a method for increasing and/or prolonging the activity of plant growth regulators (PGRs) after in vivo or in vitro application.
Plant growth regulators are natural or synthetic compounds which play a part in a large number of growth, development and metabolic processes in the plant. The best known plant growth regulator are auxins, gibberellins, cytokinins, ethylene, abscisic acid and jasmonic acid.
By administering such PGRs it is possible to intervene in different physiological processes, such as root formation in tissue culture, in cuttings and embryos, the maturing of fruit or vegetables, senescence (ageing) of flowers and yellowing of leaves and the like, germination of seed, induction of flowers, fruits, buds and the like.
In addition to influencing these natural processes, effects which do not occur naturally can also be achieved, for instance the development of seedless fruit, larger fruits, regulating of the harvest by preventing the fall of fruits, thinning out of fruits in fruit trees, a regulated growth retarding of trees and branches or shoots and young plants, regulated branch formation, induction of shoot formation for instance in barley in order to produce malt, an increase in the sensitivity to herbicides, inhibiting the coarsening of the skin of fruits such as apples, bananas, production of somatic embryos and the like.
Different PGRs can play a part in influencing these and other processes in plants or parts thereof. Although it would seem evident that such influencing could be realized by increasing the concentration of a PGR or by applying a number of PGRs, this is found in practice not to be the case.
Most PGRs are degraded without achieving their final purpose after being taken up into the plant. In addition, high concentrations of PGR in particular have an effect on any random cell, which can be disadvantageous if a very localized activity is sought after.
In addition, problems also occur with particular PGRs in the administering thereof. PGRs are generally added to water which is supplied to the plant by watering, sprinkling and the like. The insolubility of some PGRs in water results in poor absorption into the plant.
It is the object of the present invention to increase and/or prolong and/or time the activity of PGRs in vivo or in vitro in order to enable a specific influencing of physiological and other processes at the right moment and place.
This is achieved by the invention by locally increasing the concentration of active plant growth regulators in a plant and/or plant part(s) and/or increasing the sensitivity of the plant and/or plant part(s) to the activity of the plant growth regulators. The combination of these can be used to time the availability and/or action of the plant growth regulators as will be explained hereinbelow.
The increase in the concentration of active plant growth regulators in the plant and/or plant part(s) is for instance achieved by administering the PGRs in encapsulated form to the plant and/or plant part(s). Such a capsule can be a liposome or micelle-like structure. Although liposomes are known per se, the use thereof to administer substances to plants is new.
It has been found according to the invention that by administering the PGRs in a liposome or micelle a pool of (potentially active) PGRs is formed in the plant tissue. Through differences in lipophilicity and by varying the size of the micelles and liposomes the transport in the plant can be regulated. In addition, the liposomes and micelles can optionally be sent to a specific tissue or organ by including in the membrane so-called “targeting” molecules. The localization of the activity is hereby enhanced.
The stability of the liposomes, which consist of a double layer of phospholipids, can be regulated since this greatly depends on the composition of the lipid membrane. Substances can thus be included in the membrane which are degraded in the plant. In this way the liposome will begin to leak and releases its contents. The stability can also be influenced by enzymes, such as esterases, lipases and phospholipases, which are present in the plant. Conversely, the stability can be increased by addition of sterols or through the use of saturated phospholipids. Further, addition of surface active agents (detergents) can trigger the release of the contents. In such a case the liposomes or micelles are first administered to the plant and later a detergent, whereby the liposomes or micelles dissolve and release their contents.
Micelles consist of molecules with a polar water-soluble and a non-polar fat-soluble side and are very suitable for dissolving non-polar PGRs in a polar medium such as water. When non-polar PGRs are mixed with the micelle-forming molecules, the non-polar ends will encapsulate the PGR, whereafter the polar ends will dissolve the whole in the surrounding medium. It is likewise possible to first dissolve the PGR in oil and then to introduce the small oil droplets into micelles. The mixture of micelles and oil with PGRs can be mixed with water. The thus obtained solution can be carried into the plant by sprinkling or by administering to the roots or the severed surface of the stem.
In another embodiment the PGRs can be chemically modified by linking one or more carrier molecules thereto in covalent manner. Such carrier molecules can have different functions.
There are therefore carrier molecules which have a transporting function. It is known that particular transport systems are present inside a plant. Carbohydrate molecules are for instance transported to young developing tissue, flowers or roots. By linking a PGR to such a carrier molecule, transport to a desired tissue can be effected.
The transportable compounds can be chosen for instance from the group which consists of carbohydrates, such as sucrose, glucose, sorbitol, sterols, terpenes, phosphorylated hydrocarbons and the like.
Another type of carrier molecule has polarity-influencing properties. This is important for the absorption of the PGRS. When a PGR has to be absorbed through the leaf, it must first pass through the wax layer on the leaf. This is facilitated when the PGR is linked to a non-polar, fat-soluble substance. Conversely, absorption via the severed stem proceeds better when the PGR is polar, water-soluble and preferably negatively charged. The negative charge is advantageous because positively charged compounds bind easily to the vascular tissue of the stem.
PGRs are nearly all acidic compounds and therefore polar. By linking a PGR to a carrier, a spacer or a second PGR molecule (optionally of the same type) the polarity disappears because the charged group is used for linking. Such linking can proceed via ester or peptide bonds. In the case of an alkaline PGR an acidic carrier or spacer can be used. If it is wished however to make the PGR polar, this can for instance take place by linking to a sugar via an ester bond or by making a sulphonate of the PGR. Such compounds have more charge than the PGR itself and therefore make it even more polar.
The activity of PGRs is often brought to an end in the plant by degrading processes. Because the carrier molecule with the group which the (degradation) metabolism affects is bound to the PGR, a PGR compound is created which is protected against degradation and the lifespan of the PGR in the plant can be prolonged. It is however important here that the protective group either does not deactivate the PGR or that the binding of the protective group is reversible, so that the PGR which is deactivated by binding of the group regains its activity after splicing from the group. Such a protective compound is preferably linked to the site in the PGR which is involved in metabolic reactions.
The carrier molecules can be linked directly or with interposing of one or more spacers to the PGRS, for instance by means of a covalent ester, ether or amide bond. The choice of the spacer and the ambient conditions determine the release speed of free PGR from the carrier molecule.
Another way of protecting a PGR against degr

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