Kinetics of phosphorus absorption by mycorrhizal and nonmycorrhizal tomato roots.

Kinetics of P absorption were investigated in mycorrhizal (Glomus fasciculatus) and nonmycorrhizal tomato (Lycopersicon esculentum) roots to determine why increased ion absorption by mycorrhizae occurs. Initial rates of absorption of (32)P were measured at 1 to 100 micromolar KH(2)PO(4) (pH 4.6). Absorption rates of mycorrhizae were about twice those of control roots. Augustinsson-Hofstee analysis yielded two linear phases; V(max) and K(m) were calculated for each phase. In the low phase (1 to 20 micromolar), V(max) values for the mycorrhizal and nonmycorrhizal roots were each 0.10 micromoles P per gram fresh weight per hour while K(m) values were 1.6 and 3.9 micromolar KH(2)PO(4), respectively. For the high phase (30 to 100 micromolar), V(max) values for mycorrhizal and nonmycorrhizal roots were 0.32 and 0.25 micromoles P per gram fresh weight per hour and K(m) values were 35 and 42 micromolar, respectively. These results indicate that at the lower phase concentrations, similar to those expected in most soil solutions, a major factor contributing to the increased uptake was an apparent greater affinity of the absorbing sites for H(2)PO(4) (-) (lower K(m)).

Effects of adenine and cytokinins on growth and protein kinase activity of Verticillium albo-atrum.

Growth of Verticillium albo-atrum in liquid Czapek-Dox broth was stimulated about four-fold by added 10 mM adenine, N6-benzyladenine, or kinetin. Less stimulation was evident at lower concentrations. With none of these included in the basal growth medium, detectable protein kinase activity in cell-free extracts was low and responded minimally to cAMP (adenosine 3',5'-cyclic monophosphate) in the reaction mixture. With each of these compounds as an additive to the growth medium, protein kinase activity was not only greater but also responded markedly (several fold) to cAMP. These results demonstrate a strong correlation between exogenously supplied adenine and related compounds, increased growth, increased protein kinase activity, and kinase response to cAMP in this organism.

Relative Activities and Characteristics of Some Oxidative Respiratory Enzymes from Conidia of Verticillium albo-atrum.

Conidia of Verticillium albo-atrum Reinke and Berthold, collected from shake cultures grown in Czapek broth, were sonified for 4 or 8 minutes or ground frozen in a mortar to obtain cell-free homogenates. These were assayed for certain enzymes associated with respiratory pathways. Malic dehydrogenase was the most active, glucose-6-P and NADH dehydrogenase were less active, NADH-cytochrome c reductase, NADPH dehydrogenase, and cytochrome oxidase were low in activity, and succinic dehydrogenase and succinic cytochrome c reductase were very low to negligible in activity. No NADH oxidase activity was detected.With the exception of NADH-cytochrome c reductase and possibly succinic dehydrogenase and cytochrome c reductase, there was no evident increase in specific activity of the enzymes during germination. Some NADH-cytochrome c reductase and a small amount of succinic-dehydrogenase and cytochrome c reductase were associated with the particulate fraction from 105,000 x g centrifugation. The other enzymes, including cytochrome oxidase, almost completely remained in the supernatant fraction.Menadione and vitamin K-S(II) markedly stimulated NADH-cytochrome c reductase activity in the supernatant fraction but had much less effect on NADPH-cytochrome c reductase in this fraction or on either of these enzyme systems in the particulate fraction. Electron transport inhibitors affected particulate NADH- and NADPH-cytochrome c reductase activity but had no effect on these in the supernatant fraction.

Effect of gossypol on some oxidative respiratory enzymes.

Gossypol was examined in relation to its effect on certain enzymes and enzyme complexes associated with the tricarboxylic acid cycle and the electron transport system. Succinic dehydrogenase and cytochrome oxidase activity from sweet potato was completely inhibited by gossypol at 7.5 x 10(-3)m and 2.0 x 10(-3)m, respectively. Succinoxidase activity of the same preparations was fully inhibited at a lower concentration, 2.5 x 10(-4)m. This concentration did not affect either succinic dehydrogenase or cytochrome oxidase, the primary and terminal enzymes of the succinoxidase complex. The nature of the intermediate step or steps inhibited at this concentration is not yet known. Gossypol was further shown to inhibit phosphorylation at concentrations having no appreciable effect on oxidation. Inhibition in general was not reduced by increased substrate concentrations in the enzyme systems examined, with the exception of cytochrome c for cytochrome oxidase. Bovine serum albumin was partially effective in reducing gossypol inhibition, provided that it was present before enzyme exposure to gossypol.