Route of Substrate Movement Into Wheat Endosperm. I. Carbohydrates

Abstract

Experiments were conducted to define the routes of soluble carbohydrate movement within developing wheat grains. Radioactive soluble carbohydrates originating from photosynthetic activity in the ear moved longitudinally in the tissues at the base of the crease, into the endosperm cavity, and radially across the endosperm in an outward direction. Surgical treatments were used to disrupt transport pathways. Their effects on delivery of carbohydrates to the endosperm were determined mainly by time-dependent profiles of radioactivity across the grain. Disruption to longitudinal movement within tissues at the base of the crease prevented any detectable transfer of radioactive carbohydrates to the grain's main vascular bundle, the endosperm cavity, and the endosperm distal to the site of the block. Disrupting movement in the stalk showed that soluble carbohydrates deriving from photosynthetic activity in the inner pericarp move to the endosperm also via the endosperm cavity. There was no evidence for a direct inward radial pathway from the inner pericarp. The nucellar epidermis and aleurone layer lie on the inside of the developing cuticular layers. Disrupting any circumferential movement of soluble carbohydrates around the grain in these or any other tissues had no noticeable effect on delivery of soluble carbohydrates to the endosperm. The results are discussed in relation to the anatomy of tissues that appear to have the potential for a transport function.