Journal Article

Evidence of active NADP<sup>+</sup> phosphatase in dormant seeds of <i>Avena sativa</i> L.

Stéphane Gallais, Marie‐Anne Pou de Crescenzo and Danielle L. Laval‐Martin

in Journal of Experimental Botany

Volume 51, issue 349, pages 1389-1394
Published in print August 2000 | ISSN: 0022-0957
Published online August 2000 | e-ISSN: 1460-2431 | DOI: http://dx.doi.org/10.1093/jexbot/51.349.1389
Evidence of active NADP+ phosphatase in dormant seeds of Avena sativa L.

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Freshly‐harvested seeds of Avena sativa L. do not germinate when imbibed at temperatures higher than 25 °C. This high temperature dormancy is due to the seed coats, and to the low activities of glycolysis and the oxidative pentose phosphate pathway (OPP) in the embryo. The analysis by exclusion chromatography of soluble NADP+ phosphatase activities of embryos revealed two isoforms: a 37 kDa isoform present in both dormant and after‐ripened caryopses, and a second isoform, with an apparent molecular weight of 160 kDa, five times more active in embryos of dormant seeds than in the after‐ripened ones, after 6 h of imbibition at 30 °C. Moreover, the activity of this 160 kDa isoform was three times less in embryos from dormant caryopses when they were grown at 10 °C, a permissive temperature for radicle protrusion. These results suggest a correlation between the activity of the 160 kDa NADP+ phosphatase and the dormancy state of the caryopsis. The two isoforms differed in the pH required for optimal activity: pH 5.7 and 6.5 for the 37 kDa and the 160 kDa phosphatases, respectively. Furthermore, the 160 kDa NADP+ phosphatase displayed a strong specificity for NADP+, whereas the 37 kDa isoform was able to hydrolyse numerous other phosphorylated compounds.

Keywords: Avena sativa; dormancy; germination; NADP+phosphatase.; ADH, alcohol dehydrogenase; AR, after‐ripened; D, dormant; DTT, dithiothreitol; EDTA, ethylenediamine tetraacetic acid; EGTA, ethylene glycol‐bis(aminoethyl ether)‐N,N,N′,N′‐tetraacetic acid; G6PDH, glucose‐6‐phosphate dehydrogenase; MTT, 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide; OPP, oxidative pentose phosphate pathway; PES, phenazine ethosulphate; PMSF, phenylmethylsulphonyl fluoride; pNPP, p‐nitrophenyl phosphate; PVP, polyvinylpyrrolidone; S0.5, S20, S105, supernatants of 500 g, 20 000 g, and 105 000 g centrifugations, respectively.

Journal Article.  3734 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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