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This study examined the inorganic and total phosphorus in wheat plant tops, along with the phosphatase activity and the phosphatase isozymes occurring in the youngest fully expanded leaves, from two field experiments done in 1983 and I984 at two sites in South Australia. Twelve levels of phosphorus were used in the first year, and split plots in the second year allowed the effects of current and/or residual phosphorus treatments to be determined.The inorganic or total phosphorus concentration, or content per plant, could be related to plant and grain yield, but values relative to phosphorus deficiency varied between different stages of growth and between sites. Relationships with inorganic phosphorus were no better than those with total phosphorus.Leaf acid phosphatase assays were a better measure, providing similar values relative to plant deficiency between sites, between seasons and irrespective of whether current or residual phosphorus was the source, but the values varied with plant age.The phosphatase zymograms identified an isozyme which appeared when plants were deficient in phosphorus. It did not appear when they were adequately supplied. The isozyme appeared at all stages of growth to anthesis, and from late tillering through to heading was related to grain yield at both sites, in both seasons and whether freshly applied or residual phosphorus was the source of supply. For diagnostic purposes, specific sets of standards would be required for the phosphorus and phosphatase assays. They would not be required for the phosphatase zymograms. |
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