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Published on August 27, 2008; 10.1104/pp.108.124982

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Received June 19, 2008
Accepted August 14, 2008

Regulation of Phosphoenolpyruvate Carboxylase Phosphorylation by Metabolites and ABA During the Development and Germination of Barley Seeds

Ana-Belen Feria , Rosario Alvarez , Ludivine Cochereau , Jean Vidal , Sofia Garcia-Maurino , and Cristina Echevarria *

Departamento de Biologia Vegetal, Facultad de Biologia, Universidad de Sevilla, Avenida Reina Mercedes nº 6, 41012 Seville, Spain; Institut de Biotechnologie des Plantes, UMR8618, Batiment 630, Universite de Paris-Sud 11, 91405 Orsay, Cedex, France

* Corresponding author; email: echeva{at}us.es.

During barley seed development PEPC activity increased and PEPC specific antibodies revealed housekeeping (103 kDa) and inducible (108 kDa) subunits. Bacterial-type PEPC fragments were immunologically detected in denatured protein extracts from dry and imbibed, however, in non-denaturing gels the activity of the recently reported octameric PEPC (in Castor oil seeds) was not detected. The phosphorylation state of the PEPC, as judged by L-malate IC50 values, phosphoprotein chromatography and immunodetection of the phosphorylated N-terminus, was found to be high between 8 and 18 DPA and during imbibition. In contrast, the enzyme appeared to be in a low phosphorylation state from 20 DPA up to dry seed. The time course of 32/36 kDa, Ca2+-independent PEPC kinase activity exhibited a substantial increase after 30 DPA that did not coincide with the PEPC phosphorylation profile. This kinase was found to be inhibited by L-malate, and not by putative protein inhibitors, and the PEPC phosphorylation status correlated with high Glc-6P/malate ratios thereby suggesting an in vivo metabolic control of the kinase. PEPC phosphorylation was also regulated by photosynthate supply at 11 DPA. In addition, when fed exogenously to imbibing seeds, abscissic acid significantly increased PEPC kinase activity. This was further enhanced by the cytosolic protein synthesis inhibitor cycloheximide, but blocked by protease inhibitors, thereby suggesting that the phytohormone acts on the stability of the kinase. We propose that a similar ABA-dependent effect may contribute to produce the increase in PEPC kinase activity during desiccation stages.






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