Diurnal Carbohydrate Metabolism of Barley Primary Leaves

Abstract

The carbohydrate content of barley (H. vulgare L.) leaves was measured over a 24 h cycle. Nonstructural carbohydrate accumulation was linear after the 1st h of light, whereas utilization in the dark was fast initially and slowed as stored reserves were depleted. Sucrose was the most abundant storage form of carbohydrate in the primary leaf. Lesser amounts of starch, fructans and hexoses were also present. Leaf reserves were almost completely remobilized by the end of the dark transition. Lower rates of starch accumulation were observed at the beginning and at the end of the day. Fructan synthesis occurred primarily towards the end of the light period as rates of sucrose and starch synthesis decreased. Carbohydrate metabolism in primary barley leaves apparently was controlled by light and by endogenous factors such as foliar sucrose levels. Measurements of specific [14C]sucrose activity in steady state labeled 7-day old barley primary leaves suggested the presence of at least 2 kinetically separate pools. Sucrose levels were higher and apparent turnover rates were lower in barley leaves in comparison to previous studies with other species.