Carbohydrate metabolism in the developing and maturing wheat embryo in relation to its desiccation tolerance

Embryos of wheat (Triticum aestivum L. cv. Sappo) were studiedthroughout their development and maturation to investigate therelationships among starch, sucrose and raffinose and the onsetof desiccation tolerance. Starch accumulated in axes and scutellafrom about 20 d post anthesis (dpa) to reach a maximum at approximately35 d. The starch content then declined to a very low value inlate maturation. Extractable -amylase activity increased inembryos throughout the period of starch deposition and showeda substantial rise coincident with starch breakdown. In earlymaturation (approximately 26 dpa) sucrose and raffinose appeared,and continued to increase. The rise in the amount of sucroseparalleled the accumulation of starch, but the major increasein raffinose approximated to the fall in starch content. Embryoswere desiccation intolerant prior to the age when free sucroseand raffinose accumulated: the development of desiccation tolerancewas associated with increasing raffinose: sucrose ratios. Possiblemetabolic and physiological relationships among starch, raffinose,sucrose and the onset of desiccation tolerance are discussed. Key words: Wheat embryos, development, maturation, starch, raffinose, sucrose, desiccation tolerance