Effects of Some Metabolic Phosphorus Compounds on Rates of Photosynthesis of detached Phosphorus-deficient Subterranean Clover Leaves

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Abstract
Rates of photosynthesis (net CO2 uptake in saturating light) of leaves sampled from phosphorusdeficient subterranean clover plants (Trifolium subterraneum L. cv. Mt. Barker) were lower than those of non-deficient leaves. When comparable deficient leaves were placed in solutions containing 0.13 mM Pi1, there were no responses in photosynthesis, even though earlier results had established these solutions as optimal for responses for intact deficient plants. Deficient leaves, placed for the first 12 h after detachment in solutions of increasing Pi1 concentrations (0.15, 0.70, 2.0, and 6.0 mM) and then in distilled water, showed marked increases in photosynthesis in the three higher phosphate treatments on the first day after detachment. During the following 6 d the decline in photosynthesis was less the higher the initial phosphate treatment. By contrast, non-deficient leaves in the same treatments showed a decline in photosynthesis with increasing phosphate levels, due to leaf damage in the two highest treatments (phosphorus toxicity). Rates of photosynthesis of deficient leaves kept for 3 h in 3 or 6 mM FDP1 or G-6-P1 increased within 24 h and remained higher than those for corresponding leaves in 0.13 mM Pi or distilled water. There were no differences between the same treatments for non-deficient leaves, thus enabling a clear distinction between leaves that were deficient and those that were not. There was no leaf damage in these solutions, even after 48 h. AMP1 or ADP1 had no effect. ATP1 and 3-PGA1 caused toxicity symptoms. Fructose itself (6 mM) had no effect on photosynthesis.

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