LHCB TRANSCRIPTION IS COORDINATED WITH CELL-SIZE AND CHLOROPHYLL ACCUMULATION - STUDIES ON FLUORESCENCE-ACTIVATED, CELL-SORTER-PURIFIED SINGLE CELLS FROM WILD-TYPE AND IMMUTANS ARABIDOPSIS-THALIANA

To study the mechanisms that integrate pigment and chlorophyll a/b-bin ding apoprotein biosynthesis during light-harvesting complex II assemb ly, we have examined beta-glucuronidase (GUS) enzyme activities, chlor ophyll contents, and cell sizes in fluorescence-activated, cell-sortin g-separated single cells from transgenic Arabidopsis thaliana wild-typ e and immutans variegation mutant plants that express an Lhcb (photosy stem II chlorophyll a/b-binding polypeptide gene)/GUS promoter fusion. We found that GUS activities are positively correlated with chlorophy ll content and cell size in green cells from the control and immutans plants, indicating that Lhcb gene transcription is coordinated with ce ll size in this species. Compared with the control plants, however, ch lorophyll production is enhanced in the green cells of immutans; this may represent part of a strategy to maximize photosynthesis in the gre en sectors to compensate for a lack of photosynthesis in the white sec tors of the mutant. Lhcb transcription is significantly higher in pure -white cells of the transgenic immutans plants than in pure-white cell s from norflurazon-treated, photooxidized A. thaliana leaves. This sug gests that immutans partially uncouples Lhcb transcription from its no rmal dependence on chlorophyll accumulation and chloroplast developmen t. We conclude that immutans may play a role in regulating Lhcb transc ription, and may be a key component in the signal transduction pathway s that control chloroplast biogenesis.