Effects of blue light supplementation to red light on nitrate reductase activity in leaves of rice seedlings.

摘要

Rice plants grown under red light supplemented with blue light, recorded higher whole-plant N content and N content per unit dry weight compared to plants grown under red light alone (unpublished data). This observation suggested that supplementation with blue light promotes the uptake or assimilation of N in rice cv. Sasanishiki plants. We focused on NADH nitrate reductase (NR), which functions as a key enzyme in nitrate assimilation in rice leaves; the effects of irradiation with red light alone (R), red light supplemented with blue light (red/blue-light photosynthetic photon flux density (PPFD) ratio 4/1; RB) and blue light alone (B) on NADH NR activity were examined. Rice seedlings were irradiated for 5 minutes or 12 h by R, RB or B at 200 micro mol m-2 s-1 PPFD. Irrespective of the irradiation period, the activation rate of NADH NR was higher under RB than under R and B. Supplemental blue light play important roles in promoting reactivation of NR. Total NADH NR activity was higher under RB than under R and B when the plants were irradiated continuously for 12 h, although there was no significant difference in the total NADH NR activity among light treatments for a 5-minute irradiation. Thus, supplemental blue light led to increased NR activity, as seen both in the amount of NADH NR and in its activation rate. The total activity and the activation rate of NADH NR under B were not necessarily as high as those under RB, which was plausibly due to the small phytochrome photostationary state ( Phi ) of B..