Role of Phytohormones in Plants

At present, the involvement of plant hormones and their effects on plant has become a subject of interest in plant water relations. The effect of water stress on plant hormones (GAs, IAA and ABA) level in the leaves and flower-bud formation of the Satsuma mandarin (Citrus unshiu Marc.) trees was studied to determine the relationship between flower-bud induction and the level of endogenous plant hormones as a result of water stress. The quantity of GA was significantly higher in the leaves of the trees under severe water stress than in the leaves of the trees enduring the moderate water stress. The quantity of IAAin the leaves of the trees under moderate water stress was higher. These findings indicate that the levels of GA are increased by severe water stress, higher in the leaves from the branches that produce fewer flowers during flower-bud induction periods. The levels of IAA were higher in the leaves from the branches that produced more flowers during the season when flower-buds form. Plant water stress and some other stresses enhance senescence. They also bring about decrease in the levels of endogenous Cytokinins. 

Exogenous Cytokinins retard leaf senescence and may stimulate stomatal opening. Later on, studies in the subject gained momentum from the various observations of the role of abscisicacid in stomatal opening. Abscisic acid brings about rapid stomatal closure and its endogenous levels in leaves increase rapidly when plants are subjected to water stress or several other stresses. Hypotheses and data relevant to the possible role of hormones in plants subjected to environmental stresses are presented and studied. The role of plant hormones is complicated biologically and biochemically. In most cases it is which will signal a hormonal response. When applied, the  hormones will regulate the organization of the internal chemistry of the plant cell, and the interaction among cells, but the degree of interaction will still depend upon the plant species, the stage of plant development and the external environment.