Structural Changes in Phaseolus vulgaris Induced by Atrazine II. Effects on Fine Structure of Chloroplasts

Abstract

1. The fine structure of the chloroplasts of Phaseolus vulgaris is grossly altered by treatment with atrazine when the plants are kept in the light, but atrazine has no effect in the dark. 2. The following progressive changes in chloroplast structure occur: (a) they become spherical rather than discoid; (b) starch disappears from the lamellar system; (c) the frets or parts of frets are destroyed, leading to the disorganization of the granal arrangement; (d) the compartments of the grana swell; and (e) the envelope and the swollen compartments ultimately disintegrate. 3. It is proposed that these changes are brought about by the formation of a toxic substance or substances involving the interaction of atrazine and light in the presence of chlorophyll. 4. The similarity among these modifications and those caused by other substances or mineral deficiencies and the altered chloroplast structure in lutescens mutants of barley and variegated plants of Humulus are discussed.