Abstract
We have already reported that abscisic acid (ABA) promoted chlorophyll accumulation in cucumber plants under low nitrogen conditions. In this study, we focused on the effect of ABA on the accumulation of aminolevulinic acid (ALA) under low nitrogen conditions since ALA is a key compound in the pathway of chlorophyll biosynthesis. The total amount of ALA was increased by ABA treatment, especially in cotyledon, as ABA treated period was longer. And ALA suppressed the reduction in the total amount of chlorophyll in cucumber cotyledons and promoted the chlorophyll accumulation in the first leaves under low nitrogen conditions. These results suggest that ABA promotes ALA biosynthesis, resulting in chlorophyll accumulation in cucumber plants. In addition, ABA promoted nitrate reductase activity under low nitrogen conditions, but ALA did not. Consequently, ABA promotes not only ALA biosynthesis but also nitrate reductase activity in cucumber plants grown under low nitrogen conditions.
