Ultrastructure and development of phenolic-storing cells in cotton roots

Abstract

The development of phenolics in the radicle of cotton was determined with the nitroso reaction and light microscopy. In all cotton cultivars tested, phenolics could be detected in the endodermis at a distance of 1.0-2.0 mm from the root tip and in the root cap 0.5 mm from the root tip. By 3.0 mm the phenolic-storing cells in the endodermis were mature. The rate of development of the phenolic-storing endodermal cells was similar in all cultivars but varied with temperature, with maximum rates at 35.degree. C. At this temperature, development and maturation of the phenolic-storing cells occurred in 30 min. Phenolics could first be detected by EM in the vacuoles of endodermal cells 1.0 mm from the root tip; these cells were essentially mature 3.0 mm from the root tip. Except for the phenolics in the vacuoles, developing phenolic-storing cells were identical with surrounding parenchyma and contained abundant endoplasmic reticulum and ribosomes, mitochondria, dictyosomes and large, variable plastids. Although several fixation methods were used and the appearance of the cells varied according to the fixation procedure, no positive origin for the phenolic material could be detected in the electron micrographs.