Protective Effect of Triacontanol Against Acidic Mists in Samanea saman (Jacq.) Merrill Seedlings: Differential Responses in Growth, 14CO2 Fixation,Ribulose-1,5-Bisphosphate Carboxylase,and Electron Transport Activities

Seedlings of tropical leguminous tree Samanea saman (Jacq.) Merrill were exposed for 7 d to acidic mist (AM, induced by H₂SO₄) of pH 5.6, 4.0, and 2.0. AM significantly reduced seedling growth (root and shoot length, leaf density, leaf area, fresh and dry mass accumulation) and photosynthetic activities. In thylakoids isolated from leaves treated at pH 4.0 and 2.0 a decrease in the activities of photosystem (PS) 2 and whole chain electron transport was observed, but PS1 activity did not change. When the seedlings were subsequently sprayed with triacontanol (TRIA), the AM effect was partially or completely reversed indicating that TRIA can protect from AM effects. The artificial electron donors, di-phenylcarbazide (DPC) and hydroxylamine (NH₂OH), markedly restored the loss of PS2 activity in AM (pH 2.0) treated leaves. This is the first report of alleviating the AM by TRIA in tropical tree seedlings.