Abstract
We have shown that chlorophyll biosynthesis was promoted by the application of abscisic acid (ABA) in cucumber plants grown under low nitrogen conditions. Since cytokinin has been well known to promote chlorophyll biosynthesis, we investigated the interaction between ABA and cytokinin in chlorophyll accumulation of cucumber plants under low nitrogen conditions. In addition, we investigated the involvement of reactive oxygen species (ROS) accumulation in chlorophyll degradation.
Chlorophyll contents in the first leaves of cucumber plants grown under low nitrogen conditions were reduced by the application of kinetin (KI). Expression of a rate-limiting enzyme gene in the biosynthesis of chlorophyll which encodes GLUTAMYL-tRNA REDUCTASE was reduced in the first leaves of cucumber treated with KI. On the other hand, the amount of transcripts in relation to ABA biosynthesis was reduced by KI. The amount of H2O2 increased in cucumber plants treated with KI, whereas it decreased in the presence of ABA. These results suggest that ROS is one of the limiting factors in degradation of chlorophyll in cucumber plants under low nitrogen conditions, and ABA suppresses the accumulation of ROS.
