The early morphogenesis of Glycine max and Pisum sativum root nodules

Abstract

The development of pre-emergent and early emergent stages of soybean (G. max) and garden pea (P. sativum) root nodules was studied utilizing the superior preservation and resolution obtained by noncoagulative fixatives and subsequent embedding in plastic. In both species, extensive mitotic activity and cytological changes occur in the root cortical cells while the infection thread (Rhizobium leguminosarum) is restricted to the infected root hair cell. In soybean the central mass of infected tissue is derived mainly from the outer layer of cortical cells whereas the inner cortical cells contribute extensively to the infected tissue of the pea nodules. The temporal and spatial patterns of mitosis differ in the nodules of the 2 spp. Mitotic activity is restricted to a nodule meristem and occurs over many weeks in pea nodules. In soybean nodules, mitotic activity occurs throughout the central zone and before decreasing, persists over a few weeks. The timing and distribution of mitotic activity affect nodule morphogenesis.