Substrate Gradients and Regional Patterns of Dry Matter Deposition Within Developing Wheat Endosperm. I. Carbohydrates

Abstract

Starch and protein content of wheat endosperm are important factors determining yield and grain quality. Experiments were conducted using microsectioning, HPLC, analysis, and radiotracer techniques to describe regional patterns of deposition of starch and protein throughout wheat endosperm, and to test whether these patterns of deposition could be due to regional patterns of substrate supply. This paper describes the distribution patterns of starch and soluble carbohydrates.

Carbohydrate entered the grain as sucrose. It was transported to and through the endosperm mostly as sucrose, even though sucrose accounted for only 40-45% (w/w) of the total soluble carbohydrates in the endosperm cavity and endosperm. The concentration of hexose was low, equivalent to only 1.6% and 7% (w/w) of the amount of sucrose in the endosperm cavity and endosperm respectively.

The endosperm cavity and endosperm contained appreciable amounts of a glucose disaccharide, appearing in a number of tests as maltose. These regions also contained oligosaccharides appearing as a fructan series. There was no evidence for ribose or raffinose. Other soluble carbohydrates were identified.

Turnover of sucrose in the grain is rapid. Sucrose in the endosperm and endosperm cavity was equivalent to only 3.1 h and 1.0 h of starch deposition respectively.

Starch was deposited evenly from the endosperm cavity to the endosperm periphery on the dorsal side except for a decrease in the outermost section. Any gradient of protein percentage across the endosperm is not due to changes in the concentration of starch. There was a 2-fold gradient of sucrose across the same region, decreasing in an outward direction. The gradient was steepest near the endosperm cavity. The pattern of starch deposition throughout wheat endosperm cannot be attributed to a regional pattern of sucrose concentration. We conclude that transport of sucrose across the endosperm is not a factor regulating the distribution of starch.