Expressão de genes responsivos ao déficit hídrico na fase inicial de crescimento do algodoeiro

Abstract

The cotton has high adaptability to adverse conditions, however, one of the main factors for losses in production is the water deficit. The use of molecular tools in conjunction with biochemical and physiological data has elucidated some questions regarding the complexity of plant responses to water stress. In view of the above, the identification of genes that make up this complex chain is of great importance. The objective of this study was to determine the effects of water stress on GUSP1 and MYB60 gene expression and on physiological, biochemical and growth variables in the vegetative (V1) phase of cotton plants. Gossypium hirsutum genotypes from Embrapa Cotton BAG were used. The seeds were planted in tubes. The experimental design was completely randomized, in a factorial scheme 4 (genotypes) x 2 (irrigated and non-irrigated), with 10 replications. The gas exchanges (g, ci, E and A) were performed with an apparatus containing IRGA (Infra Red Gas Analylser). Plant height (ALT), stem diameter (DH), number of leaves (NF), root phytomass (FITOR) and shoot phytomass (FITOA) were measured at 25 DEH. The activities of superoxide dismutase (SOD), catalase (CAT) and gene expression via RT-qPCR were analyzed in leaves. In relation to the first study all variables were significantly affected (p <0.05) by water treatments. Mocó 1 and CNPA Precoce 1 showed significant reductions in the variables NF, DC, FITOA and FITOR. SOD and CAT presented similar behavior in all genotypes, but CNPA Precoce 1 presented the highest level of activity with 80-90% of stomatal closure (phase 2), indicating that this genotype was the most affected by the stress imposed. GUSP1 gradually increased expression in all genotypes, especially Moc 2 in phase 2, while MYB 60 showed a peak expression with 50% of the stomatal closure (phase 1), decreasing with the severity of the stress. In the second study, the variables related to gas exchange were not significantly affected (p <0.05), since they were performed in phase 1. The genotypes adapted to the northeastern semi-arid region presented the smallest reductions in physiological variables, indicating a higher tolerance to water stress. For the study of gene expression, GUSP1 presented the highest levels in these same genotypes, the opposite was observed for the MYB60 gene, where the relatively more sensitive genotypes showed the highest levels of expression, data that corroborate with studies involving the genes studied. According to the results, the genes can contribute to the selection of materials more tolerant to water stress, since they were able to identify the most tolerant genotypes at the beginning of the growth phase V1, making this strategy more practical due to the earlier identification.