Seasonal influences on early wound reactions in Betulaand Tilia

Seasonal influences on early wound reactions in the xylem of Betula pendula Roth and of Tilia americana L. were investigated by transmission electron microscopy. Wounding induced the synthesis of fibrillar material in the parenchyma with subsequent secretion through the pit membranes into adjacent vessels and fibers. The amount of secreted material after 3-4 weeks served as an indicator for the reaction intensity. Field tests with Betula revealed secretion throughout the year with high intensity between May and November and lowest level in February. Tilia developed intense wound reactions between May and September. In November the intensity appeared moderate, but wounding in February and March did not induce any secretion. Laboratory tests in the summer at 4°C revealed a different temperature sensitivity of Betula and Tilia. Betula retained its capability for secretion, whereas in Tilia secretion ceased completely. Temperature and the physiological stage influence the various steps of early wound reactions and the effectivity of compartmentalization