Section 7
Chapter 6,107

Phosphorus nutrition of barley hordeum vulgare buckwheat fagopyrum esculentum and rape brassica napus ssp napus cultivar line seedlings 1. influence of seed borne phosphorus and external phosphorus levels on growth phosphorus content and phosphorus 32 phosphorus 31 fractionation in shoots and roots

Schjorring, J.K.; Jensen, P.

Physiologia Plantarum 61(4): 577-583


ISSN/ISBN: 0031-9317
DOI: 10.1111/j.1399-3054.1984.tb05173.x
Accession: 006106889

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Seedlings of barley (H. vulgare L. 'Salka' and 'Zita'), buckwheat (F. esculentum Moench) and rape (B. napus L. ssp. napus cv. Line) were grown at 8 or 10 different external P levels in the range 0-2000 .mu.M. Apart from P, the nutrient solutions were complete. In some experiments with barley and rape, 32P-labeled phosphate was used. Root fresh weights of buckwheat and rape decreased when the external P supply exceeded the level required for maximal root development. In all 3 spp., the roots constituted a decreasing proportion of the total plant fresh weignt as the external P level increased. The shoot/root fresh weight ratio increased linearly with the P concentration of the roots. The ratio between the P concentration in shoots and roots increased with the P status of the seedlings grown at low to intermediate external P levels, but decreased at higher P levels. The proportion of total seedling-P held in roots consequently reached a minimum value and thereafter increased as the P status of the seedlings increased. Some control mechanism counteracted the accumulation of harmful P levels in the shoots. 32P-Phosphate uptake by seedlings of barley and rape grown in solutions with 2 mM P overestimated the actual net P uptake by a factor of 6-7, indicating a marked fractionation of 32P and 31P. For seedlings grown in solutions with 25 .mu.M P (barley) or 50 .mu.M (rape) no fractionation occurred. The relative excess of 32P in high P seedlings accumulated in the roots. The fractionation was probably caused by efflux of low specific activity P and by diffusion of free phosphate ions across the plasmalemma of the root cells in response to a difference in the concentration gradient between the 2 P isotopes.

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