Effects of Paclobutrazol Application on Plants as a Chilling Stress Ameliorator

Paclobutrazol ((2RS, 3RS)-1-4(-chlorophenyl)-4,4-dimethyl-2-1,2,4-triazol-1-yl-penten-3-ol) is a member of the triazole family, that protects plants against various stresses. Probably paclobutrazol affects the morphology and biochemical and physiological reactions of plant by regulating the level of endogenous hormones (inhibition of gibberellin biosynthesis, increase of abscisic acid, decrease of ethylene, change of cytokinin content and modulation of their transporter genes). Morphological effects of paclobutrazol are include reduction of stem length and lower internode length, increase in stem physical strength, thicker stems, increase in leaf thickness, thicker epicuticular wax layer on leaf, reduction of leaf area, larger chloroplasts, and increase in root growth. Biochemical effects of paclobutrazol include the increase of proline, chlorophyll and carotenoids, polyamines, protein, and soluble carbohydrates and the detoxification of reactive oxygen species through the increase of antioxidant activities. These changes increase the tolerance of plants to environmental stress. One of the environmental stresses that disrupts the natural activity of plants, and the use of paclobutrazol helps to moderate its negative effects, is chilling stress. Chilling stress, especially in tropical and sub-tropical species, through changes in biochemical and physiological processes, causes negative effects on plants. Paclobutrazol protects plants against chilling stress and ameliorates chilling damage by strengthening the antioxidant defense system, regulating hormone levels, and improving photosynthesis system. In this article, the role of paclobutrazol to alleviate the adverse effects of cold stress in plants is examined. Moreover, various morphological, biochemical and physiological processes leading to improved crop production under the effect of paclobutrazol are discoursed in detail.