Acid-induced growth and the geotropic response of the wheat node.

Growth is initiated in segments of the leaf sheath base of Triticum aestivum by gravitational stimulation and by incubation in buffer solutions of pH 3. Both responses involve only an increase in segment length, are rapidly terminated on removal of the stimulus, have a similar Q10 and are dependent upon cell turgor. They differ, however, in that the response to acid solutions is rapid and unaffected by anoxia. Acid-induced growth can be stopped and started repeatedly by changing the pH, an increase in pH from 3 to 5 or 7 being sufficient to terminate the response. The maximum growth induced by low pH is not increased by simultaneous stimulation by gravity.