Evidence for Signal Transduction in the Stimulation of Nitrate Uptake by Blue Light in Chlorella saccharophila*

Abstract— In Chlorella saccharophila blue light supplementary to red light stimulated the nitrate uptake rate by a factor of two. This stimulation was independent of photosynthesis as it occurred in cells where photosynthesis was totally inhibited by DCMU. The effect of blue light (2 min 25 μE m ^?2 s^?1 are sufficient) led to an event that persisted for 50 min (memory effect) as an enhanced nitrate uptake. However, the addition of ocadaic acid extended the effect of blue light over 90 min. Blue light alone also led to the phosphorylation of distinct proteins (120 kDa and 34 kDa) bound to the plasma membrane with that at 34 kDa being the most prominent. This phosphorylation was inhibited by staurosporine and was stimulated after the plasma membrane vesicles were treated with several freeze-thawing cycles.