Abstract
We have already reported that chlorophyll levels in cucumber plants grown under low nitrogen conditions are preserved by abscisic acid (ABA). In this study, we investigated expression of chlorophyll biosynthesis and degradation genes in cucumber plants under low nitrogen conditions. In contrast to the reduction of expression of chlorophyll biosynthesis genes in older cucumber plants grown without ABA, ABA maintained relative high levels of transcripts until 20 days after treatment. The transcript levels of chlorophyll degradation genes in cucumber plants applied ABA were smaller than that in drug free plants. In addition, the transcript level of chlorophyll a/b binding protein reduced in cucumber plants grown under low nitrogen conditions in the absence of ABA compared to those applied ABA. Although the structure of thylakoid stack was disordered in drug free plants, it was well defined in plants in the presence of ABA under low nitrogen conditions. These results suggest that ABA promotes chlorophyll biosynthesis and suppresses chlorophyll degradation in cucumber plants grown under low nitrogen conditions. ABA also allows chlorophyll to be stable in thylakoid membrane.
