Phytohormone interaction

A classification related to the "phytohormonal interaction principle" is also appropriate in a systematic overview of various groups of exogenous PBRs. 

Table I. Overview of Exogenous Plant Bioregulators Classified according to Their Phytohormonal Interaction (Abstract)...

Phytohormones such as ethylene, salicylic acid (SA), JA, and abscisic acid (ABA) regulate responses of plants to stresses via action referred as signaling crosstalk. Moreover, reactive oxygen species (ROS), the toxic byproducts of aerobic metabolism, play the important role of signaling molecules. Usually, the defensive responses of plants depend on the interaction (positive or negative) between phytohormone signaling pathways rather than on the independent contribution of each of them. " ... 

Krauss, A. (1985). Interaction of nitrogen nutrition, phytohormones, and tuberization. In P. Li (Ed.), Potato Physiology. Academic Press, Orlando, US. 

After these detailed remarks about anti-gibberellins and their mode of action, it should be emphasized that the action of not all bioregulatory active substances can be assigned so precisely to an interaction with a specific phytohormone. This partially applies to daminozide (succinic acid 2,2-dimethylhydrazide), which is frequently classified as a retardant (7). 

The biological activity of fusicoccin A appears to be associated with its effect on the plasma membrane, where it binds to a protein and interacts with the H" -ATPase. The binding to the protein leads to an opening of the stomata, a consequent high loss of water and the wilting of the leaves. The interaction of the fusicoccins and coylenins with the plasma H" -ATPase can also lead to some phytohormone-like effects. 

Brassinosteroids are reported to stimulate overall plant growth and development, especially under stress conditions, to enhance auxin-induced growth as well as auxin-induced ethylene production (5, 6). Brassinosteroids interact with most of the phytohormones, such as cytokinins and gibberellins, and in particular with auxin. 

These results confirm that expression of IAA-genes alone is sufficient to initiate the development of knots on oleander, while cytokinins are necessary for the full expression of the disease symptoms (determining knot size). This finding also indicates that plant tissues (stems and leaves) react differently to various strains of the bacterium, and suggests that, besides phytohormones, other pathogenic factors could be involved in this host-pathogen interaction. The necrotic reaction of oleander leaves heavily inoculated with olive strains was interpreted as a possible form of hypersensitivity reaction [42]. 

Beside the functional analysis, specific selection techniques have been developed in yeast to identify transcription factors that bind to hormone responsive elements in plant promoters or interacting partners of known components in phytohormone signalling. These techniques are based on the fact that transcription factors consist of two separate domains, a DNA binding domain (DNA-BD) and a transcription activation domain (AD). 

Once components in phytohormone signalling have been identified and characterized, these can be used to screen for upstream or downstream interacting factors in the yeast two-hybrid system. 

HATCHER, P.E., MOORE, J., TAYLOR, J.E., TINNEY, G.W., PAUL, N.D., Phytohormones and plant-herbivore-pathogen interactions Integrating the molecular with the ecological. Ecology, 2004, 85, 59-69. ... 

In regulatory systems, a substantial role is attributed to phytohormones. Apart from pfcgrtohormones with promotive effects a plant also contains their antagonists - endogenous grovrth inhibitors. The coordinated interaction of these two groups of compounds (in the cytoplasm) determines the normal growth process. 

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