Electron Microscope Observation on the Development of Chloroplasts of <i>Avena</i> and Chlorophyll-deficient Mutants

Abstract

1. Development of Avena chloroplasts in normal, etiolated and chlorophyll-deficient mutant plants, are observed with an electron microscope.2. Normal proplastids in green plants have one or two plastid centers, from which fine double lamellae of about 80A in thickness protrude radially, fused each other at the end and formed a sack-like structure. Then the lamellae arrange parallel through the plastid and form ordered layers composed of the fine lamellae. As the number of lamellae in one layer increases, grana are differentiated within certain areas of these layers. Grana are composed of staks of discs of double membranes (grana-lamellae, each of which is about a 80A in thickness). Each disc is connected with one stroma-lamella of about 300A in thickness which is often resolvable as doublet.3. In etiolated and albino leaves, plastid developments are stopped at certain stages of differentiation, and grana can not be formed. This suggests that these structural blockings may be associated with the failure of chlorophyll synthesis.4. In both pale green mutants, mutant 602-15 which is a hybrid between A. strigosa and A. barbata and mutant 3250 caused by X-ray irradiation, plastids develop and grana differentiate, but plastid development is somewhat different between them. While in the mutant 602-15, the completion of lamellar system is followed by destruction caused by vacuolization, in mutant 3250 arrangement of lamellae is abnormal from the early stages and grana arrange irregularly in direction and in localization in mature chloroplasts.