Stress abiotici e bilancio ormonale nelle piante coltivate

Abiotic stresses cause extensive losses to agricultural production worldwide. The most important abiotic stresses, i.e. those causing main losses of productivity, are induced by water deficiency, high salinity, high or low temperatures and nutient deficiency. From a strictly agronomic point of view, however, we must consider as relevant also other stresses, such as hypoxia due to waterlogging , excessive concentrations of nutrients or the presence of heavy metals in the soil, mechanical perturbation due to intense meteoric events (rain, wind and hail) or to the manipulation to which plants are subjected during cultivation, post production handling and storage. Particular stress conditions are those due to the reduced substrate volume (root restriction), and the elevate plant density, which causes the so-called “shade avoidance syndrome”. These last two stresses are particularly important in nursery and in pot plant production. Plants are able to perceive environmental stimuli and to adapt to different environments, however, the degree of tolerance and adaptability to abiotic stresses varies among species and varieties. Plant hormones are involved in the response to environmental stresses, in many cases acting as chemical messengers and triggering metabolic pathways leading to the acquisition of stress tolerance. It is now widely accepted that abscisic acid (ABA) plays a major role in the physiological changes induced by environmental stresses and endogenous ABA levels significantly increase in response to many environmental stimuli. Also other hormones, however, play an important role in many stress situations, such as ethylene, whose biosynthesis can be considered as a physiological marker of plant health status, or cytokinins which mediate many responses of the plant to abiotic stresses, often interacting with abscisic acid, auxins and ethylene. The present paper is aimed to analyze the role of endogenous plant hormones in the plant response to different environmental stresses. For each hormone, after a brief description, which also deals with the basic biochemical aspects, we focused our attention on particular stress situations pointing out the possible interactions with other hormones and presenting simple physiological models.of the mechanism of stress tolerance acquisition.