Estudo das alterações anatômicas, bioquímicas e fisiológicas em plântulas de milho híbrido e crioulo submetidas a diferentes temperaturas

Abstract

The objective of this study was to evaluate the anatomical, physiological and biochemical changes in the germination and vigor of hybrid and creole corn seeds submitted to different temperatures. The study was carried out at the Growth and Plant Physiology Laboratories of the Universidade Federal da Fronteira Sul (UFFS), campus Laranjeiras do Sul campus, Paraná. Seeds of Creole and hybrid corn were used. Creole corn seeds (MPA1 and Catarina varieties) came from the MPA – Movimento dos pequenos agricultores, from the city of Porto Barreiro, Paraná. Hybrid corn seeds (Herculex® and Conventional cultivars) were acquired from Pioneer. The experiments were divided into three trials. In the first experiment, the germination temperature was 25 ºC, recommended for the species. In the second, the germination temperature was 35 ºC and in the third, the temperature was 15 ºC. In order to evaluate the physiological quality of the seeds, the following tests were performed: germination, and index of germination velocity, and time for 50% for germination (T50%). For the anatomical characterization of the plants were observed the number of stomata and equatorial and polar diameter of the stomata. For the biochemical evaluation, the concentrations of chlorophyll, total soluble sugars, reducing sugars and starch, proteins, the activity of the enzymes Superoxide dismutase - SOD and Ascorbate peroxidase - APX and the damage caused by lipid peroxidation (LPO) in leaf tissue were quantified. The physiological quality of the hybrid seeds was superior, although the creole variety Catarina presented similar results to the Conventional variety. The temperature of 15 °C reduced the speed of the germination of corn seeds, of general way, but did not affect the process itself. The temperature of 35 ºC affected drastically the germination process of all the varieties. The parameter polar diameter of stomata is sensitive to the temperature of 35 ° C, being influenced by the stress caused by the temperature. The corn chlorophyll a and b content were altered as a function of temperature. The temperature influenced the accumulation of sugars, as the starch concentration was higher under stress conditions. Hybrid varieties are more influenced by temperature in the protein accumulation and lipid peroxidation. The MPA1 creole variety showed the highestprotein concentration and lower damage by lipid peroxidation in the different temperatures. Conventional and Catarina varieties showed greater adaptation to high and low temperatures since they presented greater of the APX activity. The high temperature affected the SOD activity differently in the hybrids and creoles varieties, reducing activity in the creole and increasing in the hybrids. Although the physiological quality of the creole seeds is inferior to that of the hybrid seeds, due to the less efficient production and storage care, It was observed that the creole varieties present biochemical quality similar to the hybrids, and can perform well in the field when subjected to temperature stress, due to being adapted to the climate where they are cultivated.