Avaliação de genótipos de milho quanto a tolerância à alta temperatura durante a germinação de sementes e desenvolvimento inicial de plântulas

Abstract

The germination process of corn seeds is influenced by temperature. Under adverse temperatures the establishment of the plant population can be compromised, as well as the grain yield. With the advancement of corn growth in warmer regions, it is important to understand the physiological, biochemical and molecular mechanisms related to the tolerance to high temperatures during germination, aiming to help breeding programs in the selection stages to develop hybrids adapted to the regions where temperatures are high during seed germination. Thus, the objective was to evaluate the physiological and molecular aspects involved in high temperature tolerance during the process of seed germination and seedling emergence of different corn genotypes. Seeds of four corn inbred were used, two classified as tolerant (91 and 54) to high temperature during seed germination and two intolerant (44 and 64), hybrid seeds of the reciprocals were also used, which were produced from of the lines classified as tolerant and intolerant and the F2 population. Seeds of 20 maize genotypes were subjected to temperatures of 25 and 35 ºC during the germination process. Germination was evaluated at six days, and vigor by the first germination count (4 days), germination speed index, primary root and shoot length and number of seminal roots. After analyzing the results, two lines, the more discrepant ones, were selected in terms of tolerance to high temperature, 35 ºC, L91 (tolerant) and L44 (intolerant) and their respective hybrids and reciprocals, whose seeds were subjected to imbibition for the construction of the imbibition curve. The seeds submitted to the imbibition process were used to analyze the expression of the enzymes pyruvate decarboxylase, alcohol dehydrogenase, malate dehydrogenase, esterase, glutamate oxaloacetate transaminase, alpha-amylase, superoxide dismutase (SOD), catalase (CAT), peroxidase and proteins resistant to heat using, through the gel electrophoresis technique. The quantification of hydrogen peroxide, lipid peroxidation and the activity of SOD, CAT and ascorbate peroxidase enzymes, and total protein, were performed using the microplate spectrophotometry technique. There is effect of the genotype on high temperature tolerance during the process of seed germination and initial development of corn seedlings. There is a higher imbibition speed in seeds of genotypes classified as tolerant to high temperature during seed germination. There are variations in the expression of enzymes associated with respiration and the antioxidant system in dry and soaked seeds at 25 and 35 °C, from genotypes classified as high temperature tolerance during the process of seed germination and initial development of seedlings. The enzymes from respiration: pyruvate decarboxylase and alcohol dehydrogenase and the antioxidant system superoxide dismutase, catalase, peroxidase and ascorbate peroxidase were identified as good markers to evaluate high temperature tolerant corn genotypes during seed germination and early seedling development. There is greater expression of α-amylase and esterase enzymes in genotypes tolerant to high temperature.