PROTEIN ACCUMULATION POTENTIAL IN BARLEY-SEEDS AS AFFECTED BY SOIL-APPLIED AND PEDUNCLE-APPLIED N AND PEDUNCLE-APPLIED PLANT-GROWTH REGULATORS

Although much investigated, the factors constraining cereal grain prot ein accumulation are not well understood. As a result of the developme nt of a new technique, new approaches to this question are now possibl e. A peduncle perfusion system was used to deliver a range of plant gr owth regulators (PGRs) and/or N solutions into barley (Hordeum vulgare ) plants during the grain-filling period. The perfusion technique floo ds the peduncle interior with a treatment solution for periods of week s to months, allowing the plant to take up administered substances fro m the perfused solution. The objectives of the present work were to de termine: (1) whether some PGRs could alter the overall pattern of N al location within barley plants, perhaps leading to higher protein accum ulation in the seeds, (2) whether the addition of N through the pedunc le could increase the seed N concentration even when the concentration of N in the rooting medium was high, and (3) whether or not PGR stimu lated elevations in grain protein levels and peduncle-added N increase s in grain protein levels were additive. Three experiments were conduc ted to determine the physiological effects of (1) peduncle-administere d PGRs (2) combinations of soil- and peduncle-applied N and (3) select ed combinations of soil- and peduncle-administered N, and peduncle-app lied PGRs on photosynthetic rare, dry matter partitioning and N accumu lation of barley plants during grain filling. The first experiment tes ted four PGRs: abscisic acid (ABA), kinetin, gibberellic acid (GA(3)), and 2,4-dichlorophenoxy acetic acid (2,4-D) each at three concentrati ons. The second experiment tested three levels of soil N (N4NO3) ferti lity, and two concentrations of peduncle-added N (urea). The third exp eriment tested four PGRs: ABA, kinetin, GA(3), and 2,4-D with two soil N concentrations and two concentrations of peduncle-added N. ABA and 2,4-D decreased total seed weight of the perfused spike. The addition of peduncle-perfused N increased seed protein concentration and conten t under conditions of high soil N fertility suggesting that seed prote in accumulation is more limited by the ability of roots to take up N f rom the soil than by the seed to take up N from the rest of the plant. The effects of the PGRs on N allocation among plant parts varied with the amount of N available to the plant. Because it resulted in less p rotein stored in the flag leaf and more in the seeds, GA(3) perfusion caused an overall change in the allocation of N among plant parts. Ped uncle perfusion of kinetin and ABA affected some aspects of photosynth etic physiology.