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Ontogenic changes of thioredoxins f and m, and of their targets fructose-1,6-bisphosphatase and NAD(P)-malate dehydrogenase, of pea plants grown under light stress conditions

Published online by Cambridge University Press:  01 January 2000

EDUARDO A. PAGANO
Affiliation:
Faculty of Agronomy, Universidad de Buenos Aires, Argentine
ANA CHUECA
Affiliation:
Department of Plant Biochemistry, Estación Experimental del Zaidín, Prof. Albareda 1, 18008-Granada, Spain
ROSARIO HERMOSO
Affiliation:
Department of Plant Biochemistry, Estación Experimental del Zaidín, Prof. Albareda 1, 18008-Granada, Spain
JUAN JOSE LAZARO
Affiliation:
Department of Plant Biochemistry, Estación Experimental del Zaidín, Prof. Albareda 1, 18008-Granada, Spain
JULIO LOPEZ-GORGE
Affiliation:
Department of Plant Biochemistry, Estación Experimental del Zaidín, Prof. Albareda 1, 18008-Granada, Spain Present address: Estación Experimental del Zaidín, Profesor Albareda 1, 18008 Granada, Spain (fax +34 58 129600; e-mail jlgorge@eez.csic.es).
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Abstract

The transcript (mRNA) level and the protein content (as determined by enzyme-linked immunosorbent assay) of thioredoxins (Trx) f and m, and of their targets, chloroplast fructose-1,6-bisphosphatase (FBPase) and NAD(P)- malate dehydrogenase (NADP-MDH), increase over the ontogeny of pea plants grown under normal conditions, showing their highest values before flowering (40 d growth). The clearest results appear in apical, but also in middle leaves. Enzyme activites of FBPase and NADP-MDH were lowest just before flowering. In the case of FBPase this was probably a mechanism to facilitate triose-phosphate export to the cytosol for sucrose synthesis. The likely function of NADP-MDH is to supply the cytosol, via the malate translocator, with the NAD(P)H necessary for UTP regeneration in the sucrose biosynthetic pathway. Both the Fv/Fm ratio and the net photosynthetic rate (IRGA) decreased at saturating irradiance (16 h photoperiod) and under sub-saturating continuous light. However, the Fv/Fm quotient recovered to normal values after several days adaptation to high light. A similar recovery was also observed in net photosynthesis, although normal levels were never obtained. Under light-stress conditions the concentration of Trxs f and m, and of the targets FBPase and NADP-MDH, were somewhat lower than those of unstressed plants. Even though the levels of the corresponding transcripts (mRNAs) are similar in upper leaves from control and light-stressed plants, those of the middle and basal leaves from plants grown under high light were substantially higher than those of the control plants. In addition to the well-documented transcriptional regulation of nuclear-coded chloroplast proteins, these results seem to indicate the existence of an additional post-transcriptional control.

Type
Research Article
Copyright
© Trustees of the New Phytologist 2000

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