Regulation of Plant Cell Growth: The Changing Perspective

S ummary This article outlines the main features of growth regulation by auxin and places them side‐by‐side with the physiological properties of fusicoccin. The fundamental role of the plasma membrane located H + /K + ATPase in growth responses is examined and the information about this enzyme briefly reviewed. The effects of wounding on the activity of this enzyme are detailed and it is concluded that growth in excised tissue segments ceases not from lack of hormone but from impairment of ATPase function. An additional conclusion of major importance for hormone studies is reached; that is, that the experimentally‐realized reactivation of growth by auxin in excised tissues represents largely an accelerated recovery from injury. Furthermore the calmodulin/Ca 2+ system may be an essential intermediary in this recovery step. Finally, the major area of ignorance, predisposition to growth, is considered.