ALBERT

Notes: 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.

Notes: Glycine max (L.) Merr.]; (ii) whether the temporal pattern of FD for soybean structure is altered by population density or intercropping with corn (Zea mays L.); and (iii) how the FD for soybean structure compares with other quantitative measures of shoot development. Soybean plants were randomly sampled in monocropped soybean and intercropped corn-soybean plots grown at the same site in three successive years. Sampled plants were cut at the stem base, and leaf blades were immediately detached. Leafless plant structure was photographed from the side which allowed maximum appearance of branches and petioles. The FD was estimated two-dimensionally from the scanned and processed images. Fractal dimension of soybean leafless structure increased with time for all treatments, coincident with the increasing complexity of structure as shoots developed. The rate of linear increase of FD with time varied among treatments. Leaf area per plant, plant height, and number of leaves per plant increased with time for all treatments, indicating a positive correlation with FD. In contrast, light penetration decreased during canopy development, and was negatively correlated with FD. Whereas leaf area evaluates the surface available for light interception, FD characterizes its geometric distribution in space.