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The study was conducted on dry maize seed and seed subjected to sub optimal germination temperature. Four lines of maize seeds were used, two were classified as susceptible to low temperature (44 and 54) and two tolerant to low temperature (64 and 91°C). Water content and germination tests were performed at different temperatures (10 and 25°C) to evaluate the physical and physiological quality of maize seeds. For molecular study, activity of heat-resistant proteins, esterase, superoxide dismutase, catalase and α-amylase enzymes were assessed. Study of AOX1, ZmMPK5, SOD, APX, SAD, ENR and LEA genes with real time polymerase chain reaction (PCR) were carried out. AOX, SAD and LEA genes that are related as tolerant to abiotic stress showed higher expression in line 64, which was classified as tolerant to low germination temperature. The ZmMPK5 gene is associated with increased production of abscisic acid and expressed more in line 54, which was considered as susceptible to low germination temperature. Key words: Zea mays, seed vigor, abiotic stress.

With the increased demand for high quality maize seeds, the market absorbs innovations that add speed and reliability in the tests that enable differentiation of potential performance of seed lots. This study aims to evaluate the combination of the physiological tests with the expression of enzymes of respiratory route for differences in vigor levels in lots of hybrid seed corn. The percentage of germination, germination first count, emergence on tray, index of emergency speed, accelerated aging and respiration rate were evaluated by Pettenkoffer and Titulation method. Furthermore, the expression of alpha amylase, alcohol dehydrogenase, malate dehydrogenase and pyruvate decarboxylase was analyzed. With the results, it is determined that the vigor tests analyzed, together with the tests of enzymatic expressions of respiratory route were efficient to detect different levels of force in hybrid seed corn. Lot 1 had higher physiological quality while lot 2 had the lowest vigor compared to the other lots. With the vigor tests and expression of enzymes, it was possible to differentiate the quality of the seeds and therefore it can be recommended as reliable tests for defining the quality of seed lots. Key words: Respiration, enzyme expression, vigor, viability.

Plants are frequently exposed to various biotic and abiotic stresses that impair their growth, development and limit the productivity. In the present work the objective was to evaluate the effect of saline stress on the germination and biochemical alterations by the expression of enzymatic systems in corn seeds treated with different concentrations of NaCl. Hybrid maize seeds (H1, H2, H3) were used during 2013 cropping season and solutions of sodium chloride (NaCl) to simulate the saline stress. The respective concentrations of NaCl (mol.m-3) were zero (0.0 g/L); 25 (1.46 g/L); 50 (2.93 g/L); 75 (4.39 g/L) and 100 mol.m-3 (5.85 g/L), diluted into water. In order to evaluate the physiological potential of these seeds, we realized the germination test with four replications of 50 seeds, distributed between three germitest papers moistened with NaCl solutions, described above. The evaluation was performed on the seventh day, with the first count realized determining the percentage of normal seedlings on the fourth day after planting. The biochemical evaluation was performed by the expression of isoenzymes superoxide dismutase (SOD), esterase (EST), catalase (CAT), alcohol dehydrogenase (ADH), malate dehydrogenase (MDH) and alpha amylase. Seeds of the three tested hybrids have lower germination when placed in conditions of greater concentration of salinity. The hybrid H3 that presents higher tolerance to salinity and hybrid H1 are most susceptible during the germination process. The hybrid with higher vigor, H3 had higher activity of alpha amylase and catalase enzyme groups. Esterase and alcoholic dehydrogenase were not effective in measuring the quality of maize grains under salt stress conditions. Key words: Zea mays, physiological quality enzyme.

This study evaluated the effect of water and salt stresses on the physiological quality and on the electrophoresis patterns of heat resistant proteins in corn seeds. The experiments were carried out in the laboratories of seed analysis and biotechnology at the Universidade Federal de Lavras. Corn seeds of the hybrid GNZ 2004 and the inbred line LE 57 were used. The seeds were produced in soils with an electric conductivity of 3 dS m-1 (under stress) and 0.4 dS m-1 (without stress) and in pots containing substrate with a water holding capacity of 40% (with stress) and 70% (without stress). The randomized complete block design with treatments arranged in a split-plot scheme was used with four replications . Seeds were harvested at different stages of development. Seed physiological quality was evaluated using the tests of germination, artificial aging and cold test. The patterns of heat resistant proteins were evaluated by electrophoresis. The results showed that depending on seed developmental stage there was an effect of water and salt stresses on the seed vigor. The electrophoretical patterns of heat resistant proteins were stable in seeds produced under different stress conditions. Key words: Zea mays, developmental stages, late embryogenesis abundant proteins (LEA proteins).