American Journal of Botany, Vol 85, 17, Copyright © 1998 by Botanical Society of America, Inc.

STRUCTURE AND DEVELOPMENT

Regeneration of tissue following cavity formation in the vascular cylinders of Pisum sativum (Fabaceae) primary roots

T Niki, TL Rost and DK Gladish

The reorganization of vascular cylinders of pea (Pisum sativum, cv. Alaska) primary roots following the formation of vascular cavities was examined by light and electron microscopy. Cavities usually began forming ~20 mm from the root tip and were continuous to ~90 mm from the tips in roots 150 mm long, where they began filling with specialized parenchyma cells (SP cells). SP cells were usually produced by enlargement of parenchymous cells of the primary xylem at cavity margins. Depending on the extent and shape of the cavity, they were also sometimes produced by primary phloem parenchyma and early derivatives of the vascular cambium. Enlargement and some divisions of SP cells continued until a cavity was completely filled by them. SP cells proceeded through a series of cytoplasmic changes as they developed. First the cytoplasmic layer became thicker and more electron dense than surrounding cells. As SP cells enlarged there was an increase in vesicular traffic and the cytoplasm became less electron dense. Ultimately the cytoplasm thinned further, organelles degenerated, and the tonoplast sometimes broke down. SP cells did not form secondary walls. X­ray microanalysis revealed that SP cells accumulated potassium and rubidium to the same degree as cortical and xylem parenchyma cells and to a greater degree than immature secondary and late-maturing tracheary elements.

This article has been cited by other articles:

				T. Niki and D. K. Gladish Changes in Growth and Structure of Pea Primary Roots (Pisum sativum L. cv. Alaska) as a Result of Sudden Flooding Plant Cell Physiol., July 1, 2001; 42(7): 694 - 702. [Abstract] [Full Text] [PDF]