The Measurement and Prediction of Organ Growth in a Uniculm Barley

Measurements of leaf areas, net rates of photosynthesis, patterns of assimilate translocation, and of some aspects of respiration were made at leaf-increment intervals during the expansion of leaves 5, 6, 7, 8, and 9 on the single axis of a uniculm barley (Kindred Uniculm 97) grown in controlled environments. These data were used as the primary inputs in a computer programme developed to simulate the carbon metabolism and consequent weight changes of the organs in the single-axis barley plant. The total weight of plant tissue increased threefold between the expansion of the fifth and ninth leaves; during this period the simulation model generally predicted the daily growth increments to within 10 per cent of the observed values. The predictions of daily growth increments in new leaf, stem, and root were less accurate. The simulation indicated that the proportion of photosynthetic products incorporated in new growth at the meristems declined from some 54 per cent of the assimilate at the fifth leaf stage to 42–3 per cent at the ninth leaf stage. This decline in the efficiency of conversion of photosynthetic products appeared to be the result of an increase in maintenance respiration, which in turn stemmed from an approximately linear increase in total tissue weight; the proportion of photosynthetic products lost in the respiration associated with synthetic processes remained approximately constant throughout the growth period.