The Effects of Calcium and the Ionophore A23I87 on Modulation, Nitrogen Fixation and Growth of Soybeans

Abstract

AbstractThe calcium ionophore A23187 was used to separate the processes of infection and nodule development from nitrogen fixation in soybeans. Seedlings of Glycine max (L.) Merr. cv. Williams were grown in solution cultures containing three concentrations of Ca2+ (0.1, 0.5 or 1.0 mM) with or without 0.5 μM ionophore A23187. Three weeks after inoculation with Rhizobium japonicum, strain B1. plants were harvested. Low Ca2+ (0.1 mM) significantly reduced nodule number and weight, acetylene reduction, fresh weight of roots and shoots and increased lengths of 2nd and 3rd internodes. There were no significant differences between 0.5 and 1.0 mM Ca2 in their influence on any parameters measured, except for Ca2+ concentration in the tissue. The ionophore A23187 significantly reduced nodule number and weight, and increased internode lengths, but it had no effect on acetylene reduction or fresh weight of roots and tops. The ionophore did not affect the Ca2+ concentration of roots, tops or nodules. Therefore, nitrogen fixation rate is partially independent of number and weight of nodules. The single most important result of this study is that the ionophore A23187 affected critical steps in the infection process or nodule development without influencing subsequent nitrogen fixation.