The Elongation Rate of Wheat Leaves

Abstract

Oscillations of the elongation rate of wheat leaves were observed after sudden illumination and after extinguish the light. The stimulus for these oscillations was perceived by the already mature leaves. The water potential of the plant influences the elongation rate immediaely, and a sudden change in the transpiration rate (opening or closing of stomata owing to light stimulus) changes the water potential. Artificial changes of the water potential, such as those caused by altering the osmotic potential of the root medium to -5×10⁵ Pa or dipping the leaves into water, changed the elongation rate within a few minutes. Reducing the transpiration rates by means of transpiration inhibitors (phenylmercuric acetate (PMA) and abscisic acid (ABA)) down to 60% of the normal transpiration rates prevented the oscillations. Likewise, the oscillations were prevented if the transpiring plant surface was redused by cutting off the two mature leaves while the elongation rate of the 3rd leaf was being recorded.