Physiology of Cereal Grain I. the Source of Carbon for the Developing Barley Kernel

Abstract

Organic substrate for development of the barley kernel rises mainly from current assimilation of carbon dioxide. This paper describes a study of the relative importance of the several potential sources of substrate using ear shading, carbon-14 as tracer, and kernel-competition techniques. The application of the ear-shading technique to awnless, single-awned, and triple-awned varieties of barley led to significant reductions in yield of 9, 23, and 18 per cent. respectively, although the differences between the reductions themselves were not significant. Carbon-14 was supplied either to attached ears as 14C02 or to detached ears through the peduncle as 14C-sucrose. Whichever source of carbon-14 was supplied, radioactivity was incorporated in the kernel from anthesis through to maturity, and its subsequent distribution in the kernel was similar. Translocation following 14C02 feeding was also examined, and it is concluded that little movement occurred except at an early stage of ear development. Competition between kernels was not evident, although it was induced when carbohydrate supply was artificially depleted. A scheme to accommodate the results is discussed, and a new method for calculating the maximum contribution of photosynthesis within the ear to kernel yield is presented.