Regulation of Chloroplast Gene Expression is Affected in ali, a Novel Tobacco Albino Mutant

Abstract

An albino mutant designated ali was isolated from an M 2 population derived from a tobacco (Nicotiana tabacum L. `BY-4') plant which had been irradiated with a 14 N-ion beam at an early stage of embryonic development. Leaf mesophyll cells of ali were devoid of developed chloroplasts, and no stacked thylakoid membranes could be detected in the plastids. The reduction of pigment and the arrest of chloroplast development in ali were associated with distinct alterations in gene expression. Expression of plastid-encoded genes for the photosynthesis system (rbcL, psbA) was greatly reduced in ali, but at the transcript level plastid-encoded genes for 23S rDNA and 16S rDNA expression were only slightly reduced. Transcription of the nuclear-encoded Lhc and rbcS genes in the mutant was similar to that in the wild-type. There was no accumulation of Rubisco-L, Rubisco-S, and PSII-D1 polypeptides in the ali mutant. The number of chloroplasts per cell was similar in both ali and wild-type plants. These results suggest that ali is a novel albino mutant in which chloroplast gene expression is aected.