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The protein concentration of cereal grains is low and the production of cereal crops with increased grain protein concentrations is desirable. This work investigates the physiological aspects of protein accumulation potential in barley grain. A recently developed perfusion system was used in four experiments conducted in 1993 and 1994. In the field experiment, plants were allowed to take up urea at 15 or 30 mM N, or ethephon at 15 $ mu$ M. Abscisic acid and 2,4-D decreased total seed weight spike$ sp{-1}$. Gibberellic acid and 2,4-D increased seed protein concentration and content, while ABA decreased both of these. Kinetin and abscisic acid treatments resulted in the highest and lowest levels, respectively for flag leaf photosynthesis, stomatal conductance, transpiration and intercellular CO$ sb2$ concentration. Both protein content spike$ sp{-1}$ and seed protein concentration were elevated in plants fertilized with 10.7 mM N via the soil and plants perfused with 30 mM N via the peduncle. Plants receiving treatments of 10.7 mM N from the soil and mixture of 30 mM N and GA$ sb3$ or 2,4-D through the peduncle had increased protein content seed$ sp{-1}$, and the highest seed weight spike$ sp{-1}$, respectively. Peduncle perfusion with 30 mM N increased spike protein concentration and content and grain protein concentration without affecting seed weight spike$ sp{-1}$. Grain protein concentration was increased by peduncle perfusion with ethephon. The perfusion technique worked well under field conditions. (Abstract shortened by UMI.)

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