Low root temperature effects on soybean nitrogen metabolism and photosynthesis [Inhibition of growth and of nodulation by roots inoculated with Rhizobium japonicum]

• Published in: Plant physiology (Bethesda) 1979-05, Vol.63 (5), p.956-962
• Main Authors: Duke, S H, Schrader, L E, Henson, C A, Servaites, J C, Vogelzang, R D, Pendleton, J W
• Format: Article
• Language: English
• Subjects: Alkynes; Enzymes; Imbibition; Low temperature; Nodules; Photosynthesis; Plant roots; Plants; Respiration; Soybeans
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.63.5.956

The influences of low root temperature on soybeans (Glycine max [L.] Merr. cv. Wells) were studied by germinating and maintaining plants at root temperatures of 13 and 20 C through maturity. At 42 days from the beginning of imbibition, 13 and 20 C plants were switched to 20 and 13 C, respectively. Plants were harvested after 63 days. Control plants (13 C) did not nodulate, whereas those switched to 20 C did and at harvest had C2H2 reduction rates of 0.2 micromoles per minute per plant. Rates of C2H2 reduction decreased rapidly in plants switched from 20 to 13 C; however, after 2 days, rates recovered to original levels (0.8 micromoles per minute per plant) and then began a slow decline until harvest. Arrhenius plots of C2H2 reduction by whole plants indicated a large increase in the energy of activation below the inflection at 15 C. Highest C2H2 reduction rates (1.6 micromoles per minute per plant) were at 58 days for the 20 C control. Root respiration rates followed much the same pattern as C2H2 reduction in the 20 C control and transferred plants. At harvest, roots from 13 C-treated plants had the highest activities for malate dehydrogenase, glutamate oxaloacetate transaminase, and phosphoenolpyruvate carboxylase. Roots from transferred plants had intermediate activities and those from the 20 C treatment the lowest activities. Newly formed nodules from plants switched from 13 to 20 C had much higher glutamate dehydrogenase than glutamine synthetase activity. Photosynthetic rates on a leaf area basis were about three times as high in the 20 C control as compared to 13 C control plants. Photosynthetic rates of plants switched from 20 to 13 C decreased to less than half the original rate within 2 days. Photosynthetic rates of plants switched from 13 to 20 C recovered to rates near those of the 20 C control plants within 2 weeks. All leaf enzymes assayed at harvest, with the exception of nitrate reductase, were highest in activity in the 20 C control plants.