Ammonium ion, ethylene, and abscisic acid in polyethylene glycol-treated rice leaves

Polyethylene glycol (PEG)-treatment decreased chlorophyll and protein contents and increased NH4+ content due to decreased glutamine synthetase activity in detached rice leaves. PEG-treatment also increased abscisic acid (ABA) content and decreased ethylene production. Addition of fluridone, an inhibitor of ABA biosynthesis, reduced ABA content in rice leaves but did not prevent chlorophyll and protein loss in rice leaves induced by PEG. Silver thiosulfate, an inhibitor of ethylene action, was effective in preventing PEG-promoted chlorophyll and protein loss, but had no effect on PEG-induced NH4+ accumulation. The current results suggest that NH4+ accumulation in rice leaves induced by PEG increases leaf sensitivity to ethylene, which in turn results in an enhancement of chlorophyll and protein loss.