Low Temperature Effects on Soybean (Glycine max [L.] Merr. cv. Wells) Mitochondrial Respiration and Several Dehydrogenases during Imbibition and Germination

Abstract

The influence of low temperature on soybean (G. max [L.] Merr. cv. Wells) energy transduction via mitochondrial respiration and dehydrogenases was investigated in this study during imbibition and germination. Mitochondria were isolated from embryonic axes of seeds treated at 10 and 23.degree. C (control) by submergence in H2O for 6 h and maintenance for an additional 42 h in a moist environment. Arrhenius plots of initial respiration rates revealed that those from cold-treated axes had respiratory control (RC) ratios of near 1.0 above an inflection in the plot at 8.degree. C. Arrhenius plots of control axes mitochondrial respiration showed RC ratios of 2.8 above and 5.0 below an inflection temperature of 12.5.degree. C. Energies of activation for mitochondrial respiration between 20 and 30.degree. C for the cold and control treatments were 7.8 and 15.6 kcal/mol, respectively. These data indicate possible differences in mitochondrial membranes, degree of mitochondrial integrity and mitochondrial enzyme complement between the 2 treatments. Glutamate dehydrogenase (GDH), malate dehydrogenase (MDH), alcohol dehydrogenase (ADH), glucose-6-phosphate dehydrogenase (G6P-DH) and NADP-isocitrate dehydrogenase (NADP-ICDH) were assayed from whole seeds and axes (after germination) during the 48 h of temperature treatments. Activity of these dehydrogenases decreased during the first 6 h with the exception of MDH. After germination at 23.degree. C (48 h) all 5 dehydrogenases increased in activity. Arrhenius plots of cotyledon dehydrogenase activities indicated that 1 inflection temperature between 6 and 18.degree. C was present for each enzyme assayed. Differences were seen in Arrhenius plots of axes dehydrogenase activities with the 2 temperature treatments in the cases of GDH and MDH from mitochondrial pellets and with differences in enzyme extraction media. Apparently the temperature treatments yield differences in mitochondrial enzyme complement. There were no detectable inflection temperatures for the activities of G6P-DH and ADH extracted from axes. Arrhenius plots of NADP-ICDH activity indicated extreme cold sensitivity. The slopes of the plots for axes NADP-ICDH were very similar to those for mitochondrial respiration (23.degree. C treatment) suggesting that this enzyme may limit mitochondrial respiration at low temperature in soybean tissues grown at moderate temperatures.