The relationship between the phosphorus status of subterranean clover plants and the dry weight responses of detached leaves in solutions with and without phosphate

In four experiments subterranean clover plants (Trifolium subterraneum L., cv. Mt. Barker) were grown at different levels of phosphorus applied to solution cultures, to Perlite and to pots containing phosphorus-deficient soil. Leaves detached from deficient plants, placed in 3mM fructose 1,6-diphosphate or in 6mM NaH2PO4.2H2O for periods of 8–12 hr and then in distilled water under fluorescent lights (31,000–33,000 lx) for total light periods of 75–115 hr (18 hr light per 24 hr), showed greater increases in dry weight than corresponding leaves placed in distilled water without an initial phosphate treatment. By contrast, there were no differences in dry weight increases between similarly treated leaves from non-deficient plants; thus a clear distinction could be made between deficient and non-deficient plants. Dry weight increases of deficient leaves during the light period were markedly dependent on the length of the preceding period in phosphate solutions. Maximum increases occurred after periods of 8–12 hr, depending on the degree of phosphorus stress of the leaves. For non-deficient leaves initial uptake periods of up to 12 hr gave dry weight increases under the lights close to or the same as those of leaves in distilled water only, while periods of 24 and 48 hr resulted in greatly reduced dry weight increases. The possible application of the results as the basis for a simple diagnostic technique is discussed.