Relationships between the physiological and biochemical modifications in soybean seeds under different temperatures

The aim was to analyze the effect of the stress caused by different temperatures, for a period of 24 h, on seed germination and initial growth of soybean seedlings to relate these variables with the antioxidant defense system. For this, three seed lots were exposed for 24 h at temperatures of 15, 25, 35 and 40°C, being evaluated for germination, first germination counting (FGC), germination speed index (GSI), length, dry mass of roots and shoots and electrical conductivity (after three, six and 24 h), respiratory activity, in addition to superoxide dismutase, catalase and ascorbate peroxidase activity. The lot two presented a higher germination (96.72%), followed by the lot three (83.25%) and one (73.25%). Similarly, the FGC (71.79%) and the GSI (50.50) showed highest average in the lot two. This lot also presented higher growth, biomass accumulation and lower loss of leachates during the imbibition period and different temperatures, as well as more constant respiratory activity compared to the other lots, characterizing lot two as more vigorous, which is related to the antioxidant defense system response that, in a general way, demonstrated lower activity of the antioxidant enzymes in the seedlings shoot above 35°C. Thus, the antioxidant defense system activity has relationship with the physiological quality of the soybean seeds exposed to different temperatures.