Light-stimulated leaf growth on intact and excised bean plants (Phaseolus vulgaris L). IV. Effect of light quality on leaf and stem pH, peroxidase, and elongation

Intact and excised 10-day-old bean plants grown in red light were subjected for 96 h to red, green, blue, and comparable intensive white lights. Leaf elongation was only partially dependent on light intensity. Blue or green light induced considerably less leaf elongation than red and white light at the same intensity (mmol m-2 s-1). Blue light enhanced epicotyl, stem, and petiole elongation. The pH of stem sap in plants exposed to white light was significantly lower than in all other light treatments. On the other hand, white light caused a rapid and significant increase in surface pH of leaves. The pH of the hypocotyl sap was always higher than that of the epicotyl sap. Peroxidase activity of leaf sap was negatively correlated with the rate of leaf elongation and was independent of the light source or excision.