Distribution of gramine and hydroxamic acids in barley and wheat leaves

Abstract

The first leaf of 12-day-old barley seedlings, contained 1.3 μmol/g fr. wt gramine while the concentrations were 2.2, 2.0 and 3.1 μmol/g fr. wt in lower and upper epidermis and mesophyll parenchyma, respectively. Gramine was not detected in the vascular bundles, nor in xylem exudates or guttation drops. Thus, about 70% of total gramine in the leaf was found in the mesophyll parenchyma and 30% in epidermal tissue. The content of hydroxamic acids was 3.0 μmol/g fr. wt in the first leaf of 12-day-old wheat plants, while the concentrations were 6.8 and 4.1 μmol/g fresh wt in the vascular bundle and mesophyll parenchyma, respectively. These compounds were not detected in epidermis, xylem exudates and guttation drops. About 50% of total hydroxamic acids were found in the vascular bundles. The significance of these results in plant protection against aphids is discussed.