PHOTOOXIDATIVE DESTRUCTION OF CHLOROPLASTS AND ITS EFFECT ON NUCLEAR GENE EXPRESSION AND EXTRAPLASTIDIC ENZYME LEVELS *

Abstract

Abstract The cooperation between the nuclear and plastidic genome has been investigated extensively and it is generally accepted that plastidic development is controlled by the genetic information encoded in the nucleus (Ellis, 1981). It was discovered only recently that plastids are also involved in controlling extraplastidic events. If carotenoid‐free plastids are destroyed by photooxidation. expression of plastidic proteins which are encoded in the nucleus is reduced or prevented. Thus is has been postulated that a signal which derives from the plastids controls the expression of these genes in the nucleus. Moreover, extraplastidic enzymes with functions related to intact plastids (such as nitrate reductase and peroxisomal enzymes) are also affected by this treatment, while (photo)morphogenesis and extraplastidic compounds not directly related to plastidic functions seem to be unaffected. Since the damage is restricted exclusively to the plastids and even the outer envelope membrane appears to be unimpaired, photooxidative destruction of carotenoid‐free plastids is often used as a tool to investigate nuclear plastid interaction. This review briefly describes the events occurring during photodamage, analyzes the consequences for extraplastidic events, and discusses the implication of a plastidic signal(s) in controlling the expression of nuclear genes which code for plastidic proteins.