Wound signals in plants: A systemic plant wound signal alters plasma membrane integrity

Within 4 hr after wounding the lower leaves of young potato and tomato plants, a rapid and remarkable change is induced in the cells of upper undamaged leaves that results in extensive lysis of protoplasts during their isolation. Protoplast yields from unwounded upper leaves, 4 hr after wounding a lower leaf by crushing with a hemostat, decreased 25% below yields from leaves of unwounded plants. From 8 to >20 hr after wounding, protoplast yields were less than half of those from control plants. Multiple woundings decreased yields even further, as did chewing of the lower leaves by tobacco hornworms over a period of several minutes. In addition, within 4 hr of excising young tomato plants at their base with a razor blade, a 90% decrease in leaf protoplast yields was recorded. The major loss of protoplasts induced by wounding was primarily due to an increased cell lysis during protoplast isolation. Cell lysis was apparently due to a weakened cell membrane, because newly recovered protoplasts released from leaves of wounded plants were extremely fragile and exhibited 70% lysis during low speed centrifugation, compared to 20% lysis of protoplasts recovered from control plants. We conclude that a signal is released by wounding that is rapidly transmitted or transported through the plants to induce a profound change in the leaf cell membranes that renders them fragile during protoplast isolation. It is proposed that this signal may play a role in inducing cellular changes in the plant cells as part of their responses to environmental stress such as pest attacks.