The influence of low temperature on soybean ( Glycine 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 C (control) by submergence in H 2 O for 6 hours and maintenance for an additional 42 hours 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 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 C. Energies of activation for mitochondrial respiration between 20 and 30 C for the cold and control treatments were 7.8 and 15.6 kcal/mole, respectively. These data indicate possible differences in mitochondrial membranes, degree of mitochondrial integrity, and mitochondrial enzyme complement between the two 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 hours of temperature treatments. Activity of these dehydrogenases decreased during the first 6 hours with the exception of MDH. After germination at 23 C (48 hours) all five dehydrogenases increased in activity. Arrhenius plots of cotyledon dehydrogenase activities indicated that one inflection temperature between 6 and 18 C was present for each enzyme assayed. Differences were seen in Arrhenius plots of axes dehydrogenase activities with the two temperature treatments in the cases of GDH and MDH from mitochondrial pellets and with differences in enzyme extraction media. These data suggest that 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 C treatment) suggesting that this enzyme may limit mitochondrial respiration at low temperature in soybean tissues grown at moderate temperatures.

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

Effect of Cultivar, Temperature and Seed Size on the Germination and Emergence of Soya Beans (Glycine max (L.) Merr.)

6 – Management and Production

Functionality of soybean CBF/DREB1 transcription factors

Canola emergence and stand establishment are adversely affected by low soil temperature conditions which frequently occur in the Canadian prairies at seeding time. A technique, based on rapid germination of seeds on moist filter paper at 10 °C, was developed and used to screen canola genotypes suitable for low temperature propagation. Broad sense heritability estimates for rapid germination and growth at low temperatures were about 60% for Brassica napus L., and about 90% for B. campestris L., indicating complex inheritance (possibly polygenic) of these characters. Selection within canola cultivars for rapid germination was successful. However, canola genotypes presently available displayed limited variability for germination and seedling vigor at low temperatures. Thus, without bringing in new germplasm, rapid progress within the populations surveyed could not be expected.Key words: Brassica napus L., Brassica campestris L., low temperature germination selection, heritability

Selection and heritability studies on canola/rapeseed for low temperature germination.

Emergence experiments were conducted on 32 soybean (Glycine max (L.) Merrill) cultivars at a 2.5-cm depth in Guelph loam soil at 10, 20 and 30 C. Differences in emergence were found among cultivars at 10 C but not at 20 and 30 C. Results of the emergence experiment at 10 C permitted classification of cultivars into cold tolerant, intermediate and intolerant groupings. There was no close relationship between maturity group and degree of cold tolerance. Differences in speed of germination were found among cultivars at 10 C. A correlation coefficient (r = +0.616) between germination and emergence indicates that germination at 10 C would be effective in the selection of cold tolerant types. Growth analysis studies on seedlings up to the unifoliolate leaf stage showed that cold tolerant cultivars had a higher fresh weight at a specific age at 10 C. This was attributed to the faster emergence of the cold tolerant cultivars.

J. W. Tanner

Papers

Preliminary studies on the cold tolerance of soybean seedlings