The distribution of ¹⁴C-labelled assimilates in mature lemon trees

Abstract

The translocation of 14C assimilates within fruiting branches was examined by supplying 14CO2 to selected leaves and then collecting the respiratory CO2evolved by the importing fruit. The distribution pattern of labelled photosynthate within the tree was then established by autoradiography. Developing fruits obtained photosynthate mainly from the leaves on the same growth cycle that produced the fruit. Adjacent foliage, corresponding to the previous growth cycle, supplied 14C photosynthate to terminal fruits and to the basipetal translocation stream. Leaves on an earlier growth cycle (two cycles earlier than that of the fruits) did not supply labelled assimilates to the fruit; translocation was entirely basipetal. Similarly, lateral shoots made no photosynthetic contribution to fruits, but 14C assimilates were translocated into the root system of the tree.