ABSTRACT
Four variants of arcelin, an insecticidal seed storage protein of bean, Phaseolus vulgaris L., were investigated. Each variant (arcelin-1, -2, -3, and -4) was purified, and solubilities and M(r)s were determined. For arcelins-1, -2, and -4, the isoelectric points, hemagglutinating activities, immunological cross-reactivities, and N-terminal amino acid sequences were determined. On the basis of native and denatured M(r)s, the variants were classified as being composed of dimer protein (arcelin-2), tetramer protein (arcelins-3 and -4), or both dimer and tetramer proteins (arcelin-1). Although the dimer proteins (arcelins-1d and -2) could be distinguished by M(r)s and isoelectric points, they were identical for their first 37 N-terminal amino acids and had similar immunological cross-reactions, and bean lines containing these variants had a DNA restriction fragment in common. The tetramer proteins arcelin-1t and arcelin-4 also could be distinguished from each other based on M(r)s and isoelectric points; however, they had similar immunological cross-reactions and they were 77 to 93% identical for N-terminal amino acid composition. The similarities among arcelin variants, phytohemagglutinin, and a bean alpha-amylase inhibitor suggest that they are all encoded by related members of a lectin gene family.
ABSTRACT
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 C(2)H(2) reduction rates of 0.2 micromoles per minute per plant. Rates of C(2)H(2) 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 C(2)H(2) reduction by whole plants indicated a large increase in the energy of activation below the inflection at 15 C. Highest C(2)H(2) 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 C(2)H(2) 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.
