Características fotossintéticas e modulação do sistema antioxidante de defesa celular em resposta ao estresse de curta duração por alta luminosidade em plantas de três genótipos de Arabidopsis

Abstract

Plants are sessile organisms that constantly need to adapt to environmental changes. Among the different abiotic factors that can affect plant growth and development, there are daily variations in luminosity. Stress from excess luminosity can affect the photosynthetic process and generate harmful effects on its machinery. To avoid this, plants have developed photoprotection mechanisms to prevent damage. Thus, the objective of this paper was to evaluate the effect of different levels of short-term light stress on photosynthesis, as well as its relationship with carotenoid metabolism. For the development of this study, plants of Arabidopsis thaliana of the ecotype Columbia-O (wild - Wt), and of the mutants deficient in the formation of zeaxanthin in high light (npq1 lack of the enzyme violaxanthin de-epoxidase) and lutein (lut2 lack of -lycopene cyclase enzyme) were conducted under natural conditions of light, approximately 100 ± 20 μmol photons m-2 s-1 and temperature of 20 ± 3 ºC. When the plants were between 6- 8 weeks old, tests of photosynthetic characterization of the three genotypes were carried out concerning the gas exchange and transient chlorophyll fluorescence. In additional tests, detached leaves, different light intensities (100, 800, and 1200 μmol photons m-2 s-1) were applied for 30 minutes, then, for the recovery treatments, the leaves were kept for 15 minutes in the dark. The photosynthetic characterization showed similar behavior for the three evaluated genotypes. However, a slight favoring of lut2 plants was observed. When subjected to high light intensities, npq1, and lut2 mutant plants showed failures in the functionality of photoprotection mechanisms, without affecting antioxidant enzymatic metabolism. Therefore, it is concluded that xanthophylls are extremely important in the dissipation of short-term excess light, protecting the photosynthetic machinery.