Abstract
We have previously shown that the transgenic moss Physcommitrella patens that overexpress Arabidopsis ABA 8'-hydroxylase resulted in the spontaneous appearance of macrochloroplasts in protonemal cells. To analyze the effect of ABA on plastids in detail, we applied various concentration of ABA to ptotonemal tissue and followed the plastids under confocal microscope. We noticed that the number of cloroplasts in a cell increased two folds within three days compared to the untreated control. Since ABA is known to induce cell division of protpnemal cells to form brood cells, it was possible that the increase of chloroplast numbers is a secondary effect of ABA. To exclude the possibility, we evaluate the ABA effect on gametophore leaf cells that do not show cell division by ABA treatment. As the result, we observed increase of the chloroplast numbers in these gametophore cells. Moreover, transgenic P. patens that lacks Group A PP2C genes, which are major negative regulators of ABA signal transduction, also exhibited increased chloroplast numbers compared to the wild type without exogenous ABA. These result suggest that ABA is involved in regulation of plastid division in the moss.
