ONTOGENY OF ANNUAL GRASS GRAIN PROTEIN FRACTIONS AND AMINO ACIDS AFFECTED BY NITROGEN SUPPLY

Abstract

Mechanisms involved in uptake, assimilation, and distribution of nitrogen (N) in plants may reflect the effectiveness of various physiological functions developed under the conditions a species was evolved. The purpose of these studies was to determine the influences of N nutrition on the partitioning of different N forms within the Avena sativa grain during its maturation. Plants were grown in a glasshouse using nutrient solution sand culture with four N treatments: two high-N (5.33 mM), a mid-N (2.67 mM) and a low-N (5.33mM before anthesis and no N after anthesis). One high-N series was labeled with ¹⁵N at anthesis to distinguish the N in the grain taken up after anthesis (exogenous N) from that absorbed prior to anthesis and translocated to the grain (endogenous N). Exogenous N accumulated in a sigmoidal pattern for the measured grain protein fractions and total grain- N, reaching 35–40% of the N for these three fractions/classes of N. The grain prolamin-glutelin protein fraction responds more to differences in N provided after anthesis than does the albumin- globulin protein fraction. A measure of constituent deposition in the grain, relative accumulation rate, is represented as RAR = 1/x · dx/dt, where x is the concentration of a fraction and t is time. Albumin-globulin RAR had two increases, while prolamin-globulin RAR had a single longer increase during grain maturation. At individual samplings the distribution of exogenous N between the two protein fractions coincided with their RAR's. For oat grain uptake, exogenous N was the most important source of N in the fastest accumulating protein fraction. When comparing grain of high-N with mid-N, individual amino acid concentrations ranged from an increase of 16.3% to a decrease of 17%. The average glucose requirement for the synthesis of amino acids which increased at high-N was less than that of the amino acids which decreased. The bisynthethic efficiency and production values (reciprocal of construction cost referenced to glucose required by the metabolic product synthesis) were significantly related to the significantly skewed distribution of amino acids in the grain protein. The most bioenergetically efficient amino acids were the most utilized in the grain proteins; energy expenditure regulation is a possible reason.

ACKNOWLEDGMENTS

This research was partially supported by Hatch and University of California funds for Experiment Station project 3194-H. Cindy Bergens helped with the glasshouse harvest. F. Broadbent provided the ¹⁵N label together with the use of his mass spectrometry instrumentation for the isotope determinations. C. Stuart. Pettygrove, Charles Tyson, and James H. Richards generously made suggestions to earlier versions of the ms. Robert S. Loomis provided helpful comments with the amino acid bioenergetics. Valentino M. Tiangco helped with the proofreading.