The effect of current photosynthesis on the origin of translocates in old tomato leaves
1976
Ho, L.C.
The rate of carbon transport from an old tomato leaf (54 days), grown at 80 W m−2, was measured under light flux densities between 7 and 90 W m−2. Under low light, the rate of carbon transport over a 6 h period was about 1 mg C dm−2 h−1, well in excess of the concurrent photosynthetic rate. The loss from these leaves of 14C-leaf assimilate which was fixed before the experimental period amounted to 62 per cent of the total initial uptake and was higher than that from leaves with higher concurrent photosynthetic rates. The higher loss of 14C from leaves with low photosynthetic rates was due to a greater contribution of 14C from the starch and residue fractions. The rate of transport appeared to be determined by the concentration of the labile sucrose, not the total sucrose concentration. In comparison with young fully-expanded tomato leaves (Ho, 1976) the size of the labile sucrose pool appeared to decrease with age. The photosynthesistranslocation coefficient was low (k1k2=0⋅21) for an old tomato leaf. Based on these results a scheme of carbon partitioning in relation to translocation is proposed. Criteria for assessing the efficiency of translocation in leaves are discussed.
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