The induction of soluble peroxidase activity in bean leaves by wind-induced mechanical perturbation

The induction of defense-related peroxidase (POD) activity in plants occurs in response to many biotic and abiotic stimuli. This controlled greenhouse study was an attempt to provide insight into the nature of the induction of soluble POD activity by noninjurious wind-induced mechanical perturbation (MP). In a time course study, exposure of common bean (Phaseolus vulgaris) seedlings to daily periods of fan-produced wind induced a significant and sustained increase in soluble POD activity in primary leaves of 7-9-d-old seedlings. In a wind-gradient study, wind-induced MP led to increases in soluble POD activity in leaves that were proportionally related to the wind speed experienced by individual seedlings. Wind-induced MP enhanced soluble POD activity to a degree similar to treatment with 5 mmol/L HgCl2, a potent oxidizing elicitor of POD activity in plants. However, no further increases in POD activity were induced by HgCl2 on plants that were preconditioned with wind-induced MP. Finally, shea periods of brushing-induced MP enhanced soluble POD activity to the same degree as longer periods of wind-induced MS, suggesting a greater sensitivity to thigmic stimuli than to seismic stimuli in leaves of bean seedlings. This study illustrates the potential importance of wind and other mechanical stimuli as inducers of POD activity and interacting factors in the elicitation of POD activity by other environmental stimuli.