INDUCTION OF TOLERANCE TO HIGH DRYING TEMPERATURE IN CORN SEEDS THROUGH PRE-CONDITIONING AT LOW TEMPERATURE
STTELA DELLYZETE VEIGA FRANCO DA ROSA | ÉDILA VILELA RESENDE VON PINHO | MARIA DAS GRAÇAS GUIMARÃES C. VIEIRA | RUBEN DELLY VEIGA
Mature corn seeds, under natural drying conditions, lose water slowly and become more tolerant to higher drying temperatures in consequence of the occurrence of physical, physiological and biochemical changes. The aim of the present work was to investigate the effect of the pre-conditioning of corn seeds by means of pre-drying, undertemperature of 35ºC on the drying tolerance at 50ºC. So, corn seeds of three cultivars harvested with water contents of 42.3%, 37.2% and 34.2%, were submitted to pre-drying at 35ºC (pre-conditioning) for periods of 0, 4, 8 16, 24, 32, 40, 48 and 56 hours before the drying, conducted at 50ºC up to 12% of water content. After the pre-conditioning periods, embryos were analyzed as to the contents of glucose, sucrose and stachiose. After drying at 50ºC, the seeds were evaluated trough tests of germination, first count, cold test, test of electric conductivity, dry weight and seedling length. In one of the cultivars, the activity of the α-amilase enzyme was determined. The freshly collected seeds are tolerant at 35ºC and intolerant at 50ºC but they become tolerant to that temperature after pre-drying at 35ºC (pre-conditioning) till they reach water contents between 25.3 and 28.5%. The seeds intolerant at 50ºC present poorer germination, vigor and enzyme activity. Concomitantly with the acquisition of tolerance at 50ºC, the decrease of glucose and the increase of raffinose take place. Sucrose content seems not to suffer any changes during the transition of the state of intolerance to that of tolerance.
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