ESTRESSES ABI[OTICOS EM MICROTOMATEIROS: ALTERAÇÕES FISIOLÓGICAS, BIOQUÍMICAS E ANATÔMICAS

Abstract

This paper aimed to evaluate isolated and combined abiotic stresses on micro tomato plants and their physiological, biochemical, and anatomical changes. Two experiments were carried out independently; the first one was in randomized blocks, 2 x 2 factorial scheme, with two tomato genotypes [wt (wild and mutant); hp1 (high pigment 1)] under two conditions [Control (100% CC + 450 μmol m-2 s-1) and stress (40% CC + 1800 μmol m-2 s-1)]. In the second experiment, four genotypes were used [one wild (wt) and three mutants (aurea, hp1, and hp2)], under four conditions: (a) Control (CONT), 450 μmol m-2 s-1 and 25 °C/20 °C; (b) High irradiance (HI), 1500 µmol m-2 s-1 and 25 °C/20 °C; c) High temperature (HT), 450 μmol m-2 s-1 and 40 °C/20 ºC; and (d) Combined stress (HI+HT), 1500 μmol m-2 s-1 and 40 °C/20 ºC. Water and osmotic potentials, gas exchange, chlorophyll fluorescence, proline concentration, antioxidant enzyme activity, chloroplast pigments, leaf anatomy, electron transport rate, protein, and leaf malonaldehyde MDA were analyzed. In Chapter I, the combinations of high irradiance and water deficit caused changes in the wt and hp1 genotypes. It was found that the photosynthetic performance was not significant with a decrease in gas exchange under the combined stresses, even with hp1 genotype having a higher content of chloroplast pigments in relation to wt genotype. The hp1 defense mechanisms were not activated in a precise way, not being able to minimize the effect of the combined stress. There were anatomical adjustments to the combined stresses, that is, wt stood out over hp1 for the spongy parenchyma and mesophyll. Most of the variables in this study did not differ among the micro tomato plant genotypes under the conditions imposed. The wt caused a greater number of defense mechanisms in response to stress, and the hp1 mutant was more susceptible to the imposed stress conditions. In Chapter II, gas exchange and chlorophyll a fluorescence showed no interaction between genotypes and conditions; there was significant difference only for the isolated factor conditions. The stomatal index and the adaxial stomatal density showed significant differences for the genotype isolated factor. There was an interaction between genotypes and conditions for the micromorphometry of the epidermis, chloroplast pigments, proteins, MDA, and in the enzyme activity of the enzymatic antioxidant system. Results obtained showed that the conditions used in these genotypes promoted greater plant acclimatization under the control condition (450 μmol m-2 s-1) than under the combined condition of high irradiance (1500 μmol m-2 s-1) and temperature (40 °C). This temperature caused damage to metabolism, but the high irradiance favored reversing such damage, when these conditions were imposed in combination; when they were exposed in isolation, they developed different acclimatization and/or defense strategies, seeking to overcome the imposed stress condition.