Tissue and cellular phosphorus storage during development of phosphorus toxicity in Hakea prostrata (Proteaceae).
Storage of phosphorus (P) in stem tissue is important in Mediterranean Proteaceae, because proteoid root growth and P uptake is greatest during winter, whereas shoot growth occurs mostly in summer. This has prompted the present investigation of the P distribution amongst roots, stems, and leaves of Hakea prostrata R.Br. (Proteaceae) when grown in nutrient solutions at ten P-supply rates. Glasshouse experiments were carried out during both winter and summer months. For plants grown in the low-P range (0, 0.3, 1.2, 3.0, or 6.0 micromol d(-1)) the root [P] was > stem and leaf [P]. In contrast, leaf [P] > stem and root [P] for plants grown in the high-P range (6.0, 30, 60, 150, or 300 micromol P d(-1)). At the highest P-supply rates, the capacity for P storage in stems and roots appears to have been exceeded, and leaf [P] thereafter increased dramatically to approximately 10 mg P g(-1) dry mass. This high leaf [P] was coincident with foliar symptoms of P toxicity which were similar to those described for many other species, including non-Proteaceae. The published values (tissue [P]) at which P toxicity occurs in a range of species are summarized. X-ray microanalysis of frozen, full-hydrated leaves revealed that the [P] in vacuoles of epidermal, palisade and bundle-sheath cells were in the mM range when plants were grown at low P-supply, even though very low leaf [P] was measured in bulk leaf samples. At higher P-supply rates, P accumulated in vacuoles of palisade cells which were associated with decreased photosynthetic rates.
Shane
Michael W
MW
School of Plant Biology, Faculty of Natural and Agricultural Sciences, University of Western Australia, Crawley, WA 6009, Australia.
McCully
Margaret E
ME
Lambers
Hans
H
D002478:Cells, Cultured; D003300:Copper / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D010758:Phosphorus / Q000378:metabolism* / Q000633:toxicity*; D018515:Plant Leaves / Q000187:drug effects / Q000254:growth & development; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development; D018547:Plant Stems / Q000187:drug effects / Q000254:growth & development; D039105:Proteaceae / Q000166:cytology / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D013045:Species Specificity; D015032:Zinc / Q000378:metabolism
D010758:Phosphorus; D008345:Manganese; D003300:Copper; D007501:Iron; D015032:Zinc