Protein accumulation potential in barley seeds as affected by soil‐ and peduncle‐applied N and peduncle‐applied plant growth regulators

Abstract

Although much investigated, the factors constraining cereal grain protein accumulation are not well understood. As a result of the development of a new technique, new approaches to this question are now possible. A peduncle perfusion system was used to deliver a range of plant growth regulators (PGRs) and/or N solutions into barley (Hordeum vulgare) plants during the grain‐filling period. The perfusion technique floods the peduncle interior with a treatment solution for periods of weeks to months, allowing the plant to take up administered substances from the perfused solution. The objectives of the present work were to determine: (1) whether some PGRs could alter the overall pattern of N allocation within barley plants, perhaps leading to higher protein accumulation in the seeds, (2) whether the addition of N through the peduncle could increase the seed N concentration even when the concentration of N in the rooting medium was high, and (3) whether or not PGR‐stimulated elevations in grain protein levels and peduncle‐added N increases in grain protein levels were additive. Three experiments were conducted to determine the physiological effects of (1) peduncle‐administered PGRs (2) combinations of soil‐ and peduncle‐applied N and (3) selected combinations of soil‐ and peduncle‐administered N, and peduncle‐applied PGRs on photosynthetic rate, dry matter partitioning and N accumulation of barley plants during grain filling. The first experiment tested four PGRs: abscisic acid (ABA), kinetin, gibberellic acid (GA3), and 2,4‐dichlorophenoxy acetic acid (2,4‐D) each at three concentrations. The second experiment tested three levels of soil N (NH4NO3) fertility, and two concentrations of peduncle‐added N (urea). The third experiment tested four PGRs: ABA, kinetin, GA3, 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 content under conditions of high soil N fertility, suggesting that seed protein accumulation is more limited by the ability of roots to take up N from 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 protein stored in the flag leaf and more in the seeds, GA3 perfusion caused an overall change in the allocation of N among plant parts. Peduncle perfusion of kinetin and ABA affected some aspects of photosynthetic physiology.