The Regulation of Carbon Transport and the Carbon Balance of Mature Tomato Leaves

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Abstract
Rates of carbon transport from a single mature tomato leaf in the light period (day transport) and the dark period (night transport) were estimated from the rate of carbon fixation in the light period, the rate of respiration in the dark period and the changes in carbon contents over these two periods. Plants were grown initially at 40 W m−2 light intensity with either 350 vpm (nonenriched plants) or 1000 vpm CO2 (enriched plants). Various light flux densities or CO2 concentrations were then applied to the experimental leaves in the light period during the experiment When leaves were temporarily exposed to contrasting light flux densities both day transport and night transport were linearly related to the rate of carbon fixation. If leaves were shaded below the light compensation point for up to five days, or transferred to contrasting CO2 concentrations for up to ten days, the linear relationship between carbon fixation and carbon transport no longer held. During acclimatization, therate of wbon fixation was simply related to thecurrent light flux density and CO2 concentration, but the rate of carbon transport changed with time. Day and night transports responded differently to changes in environment: night transport was more related to the content of reserve, particularly starch, than to the rate of concurrent wbon fixation. It is concluded that the rate of carbon transport of a mature tomato leaf in a single photoperiod is regulated not merely by the rate of concurrent carbon fixation but by the content of reserve in the leaf. The latter results from previous cumulative wbon fixation and carbon transport. As a result of changing the rate of carbon transport, a balance of carbon input and output was achieved within 10 days of acclimatization in a mature tomato leaf.

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