The Measurement and Prediction of Organ Growth in a Uniculm Barley

Measurements of leaf areas, net rates of photosynthesis, patternsof assimilate translocation, and of some aspects of respirationwere made at leaf-increment intervals during the expansion ofleaves 5, 6, 7, 8, and 9 on the single axis of a uniculm barley(Kindred Uniculm 97) grown in controlled environments. Thesedata were used as the primary inputs in a computer programmedeveloped to simulate the carbon metabolism and consequent weightchanges of the organs in the single-axis barley plant. The totalweight of plant tissue increased threefold between the expansionof the fifth and ninth leaves; during this period the simulationmodel generally predicted the daily growth increments to within10 per cent of the observed values. The predictions of dailygrowth increments in new leaf, stem, and root were less accurate.The simulation indicated that the proportion of photosyntheticproducts incorporated in new growth at the meristems declinedfrom some 54 per cent of the assimilate at the fifth leaf stageto 42–3 per cent at the ninth leaf stage. This declinein the efficiency of conversion of photosynthetic products appearedto be the result of an increase in maintenance respiration,which in turn stemmed from an approximately linear increasein total tissue weight; the proportion of photosynthetic productslost in the respiration associated with synthetic processesremained approximately constant throughout the growth period.