CHANGES IN CARBOHYDRATES AND NITROGENOUS COMPOUNDS IN THE ROOT NODULES OF ALNUS GLUTINOSA IN RELATION TO DORMANCY

Abstract

SUMMARYCarbohydrate reserves for overwintering accumulate in the root nodules from late summer and begin to be utilized when leaf fall is virtually complete. It is probable that metabolism of these carbohydrate reserves supports in part the low nitrogenase activity which develops as buds swell and flush in early March, before substantial new photosynthates are translocated to the nodules. Higher rates of photosynthesis as leaves expand, and a reduction in the proportion of photosynthates retained by or translocated to buds as they flush, makes available more photosynthates for translocation to the nodules to support higher nitrogenase activity.Soluble nitrogenous reserves also accumulate as leaves expand. Ammonia accumulates in the spring during early leaf expansion and could be of importance in repressing nitrogenase synthesis in the endophyte, reducing the demands of the nodule for limited supplies of photosynthates until leaf expansion is more advanced.Sections of nodules show that the vesicular form of the endophyte largely degenerates during the winter months and new nitrogenase activity probably develops in new vesicles. Nodule meristematic activity recommences about bud burst. Earlier findings have shown high cytokinin activity in the nodules at this time.