RELATIONSHIP BETWEEN GROWTH, IMPORT OF ASSIMILATES, AND CONTENT OF PHYTOHORMONES IN BARLEY EARS

The growth of barley (Hordeum vulgare L.) ears was studied as a functi on of import and utilization of assimilates and the hormonal status of the ear. Photoassimilate transport from leaves into the ear was studi ed using (CO2)-C-14 and was considered an indicator of ear sink activi ty evaluated from the uptake of exogenous C-14-glucose by the ear. The content of IAA, ABA, and cytokinins was studied with ELISA. Both sour ce-sink relations and ear sink activity changed during plant growth. T he most active consumption of assimilates and exogenous C-14-glucose b y ears was noted at the booting (I) and milky ripeness stages (II). At stage I, the initiation and growth of elements of ear structure occur red, and cell wall polysaccharides-cellulose and hemicellulose-were sy nthesized in the ear from incoming assimilates. At stage II, during gr ain filling, incoming assimilates and exogenous glucose incorporated i nto starch and proteins. At stages I and II, the rate of ear growth wa s high, 34 and 65-70 mg/day, respectively, and zeatin content achieved its highest values of 10 and 23 ng/g dry wt, respectively. Contents o f other phytohormones studied and their ratios varied: at stage I, the IAA level was at its highest, 8.8 mu g/g dr wt, whereas, at stage II, the content of ABA was the highest, 6.7 mu g/g dr wt. At the final st ages of caryopsis maturation, ABA content decreased. It is proposed th at, at these stages, the high sink activity and fast dry matter produc tion in the ear could be related to its specific hormonal status, whic h determined photosynthate demand and their transport, partitioning, a nd metabolism.