Starch Changes in Developing and Senescing Tobacco Leaves

Abstract

The quantitative changes in starch content during the growth and senescence of tobacco leaves have been followed. The starch content was low while the leaves were expanding but rapidly increased after expansion stopped,, The maximum was reached when more than half of the original chlorophyll content had gone. The starch content was then reduced rapidly and when the leaf was all yellow there was only a small quantity of starch and this remained when the leaf turned brown. The viscosities, iodine affinites, [beta]-amylolysis limits, and granule sizes of isolated starch granules and the chain lengths of amylopectins at different ages of leaves have been determined. The viscosities and iodine affinities increased with increasing age of the leaf and the [beta]-amylolysis limits of the whole starch and chain length of the amylopectins were constant throughout the growth of the leaf. The average granule size increased as the leaf matured until maximum starch content was reached and decreased as the starch content decreased. It is suggested that in tobacco leaves another starch accumulation pattern of longer duration than diurnal accumulation exists. The degradation of the starch resembles the breakdown of starch in sprouting potato tubers and not that in germinating barley where amylases are the active enzymes. The residue after ethanol extraction of leaves at different stages of growth was fractionated into water-soluble material, a perchloric acid extract precipitated by iodine, and a perchloric acid extract not precipitated by iodine but precipitated by ethanol. Glucan was present in significant concentration only in the perchloric acid extract precipitated by iodine and this had the properties of starch. Paper chromatography indicated that non-starchy extracts were com-posed of galactose, arabinose, xylose, rhamnose, and uronic acid.