A study of geotropism in roots of pisum sativum through the use of transmission and light microscopy

Abstract

A current theory of graviperception in roots is the settling of starch grains in the columella tissue of the root cap. This settling against the endoplasmic reticulum or other cell components may induce calcium release along the lower cell membrane, which sets up an auxin sink; thereby allowing differential growth on that wall. In order to more thoroughly elucidate the role of starch grains (staloliths) in the graviperception mechanism knowledge of the structures and subcellular organelles found in the pea root tip in and adjacent to the region of graviperception in newly differentiated cells under conditions of gravitational change is needed. This presentation addresses some of these areas.Seeds of Pisum sativum - Dwarf Gray Sugar were surface sterilized in one percent sodium hypochlorite for twenty minutes followed by a twenty minute rinse in running tap water. The seeds were placed on two sheets of filter paper in one hundred mm plastic petri dishes containing five ml of free water. They were dark germinated for three days. One to one and one-half mm tips were harvested and dropped into solution A which contained twenty-five mis each of 8% Paraformaldehyde, 0.2 M cacodylate buffer adjusted to pH 7.6, and distilled water 1-1/2 hours at 4° C.