Fructan synthesis is inhibited by phosphate in warm-grown, but not in cold-treated, excised barley leaves.
The inhibition of fructan accumulation by phosphate was investigated in warm-grown and cold-treated barley (Hordeum vulgare) plants. Detached leaves were incubated in water or phosphate for 24 h under lighting or in darkness. Fructosyltransferase, sucrose phosphate synthase (SPS) and cytosolic fructose-1,6-bisphosphatase (FBPase) activities were subsequently analysed, as well as the content of carbohydrates, hexose-phosphates, phosphate, amino acids and protein. In warm-grown leaves, phosphate decreased fructan accumulation and total carbon in carbohydrates and did not affect protein content. Phosphate increased hexose-phosphates, phosphate and amino acids. Fructosyltransferase and FBPase activities were not affected by phosphate feeding, while SPS activity was inhibited by phosphate in incubations in both light and darkness. In cold-treated leaves, which before incubation had higher SPS activities than warm-grown leaves, phosphate had no inhibitory effect on fructan accumulation, carbohydrate content or total C in carbohydrates. The activities of SPS and FBPase were unaffected by phosphate. The results indicate that phosphate decreases fructan accumulation through an inhibition of SPS whenever this activity is not high before a rise in phosphate content.
Morcuende
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R
Institute for Natural Resources and Agricultural Biology of Salamanca, CSIC, Apartado 257, 37071 Salamanca, Spain.
Kostadinova
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S
Pérez
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P
Martínez-Carrasco
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R
D000596:Amino Acids / Q000378:metabolism; D002241:Carbohydrates / Q000032:analysis; D003624:Darkness; D005630:Fructans / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D001467:Hordeum / Q000187:drug effects / Q000378:metabolism*; D008027:Light; D010710:Phosphates / Q000494:pharmacology*; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism; D013403:Sugar Phosphates / Q000378:metabolism; D013696:Temperature; D013816:Thermodynamics
D000596:Amino Acids; D002241:Carbohydrates; D005630:Fructans; D010710:Phosphates; D010940:Plant Proteins; D013403:Sugar Phosphates