Molecular Plant Advance Access originally published online on March 23, 2009
Molecular Plant 2009 2(3):442-456; doi:10.1093/mp/ssp008
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Pyridine Nucleotide Cycling and Control of Intracellular Redox State in Relation to Poly (ADP-Ribose) Polymerase Activity and Nuclear Localization of Glutathione during Exponential Growth of Arabidopsis Cells in Culture
a Plant Sciences, Rothamsted Research, Harpenden, Herts, AL5 2 JQ, UK
b CIR Università Campus Bio-Medico, V. A. Del Portillo 21, 00128 Roma, Italy
c School of Agriculture, Food and Rural Development, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK
d Depto. de Fisiología, Av. Blasco Ibañez 15, 46010 Valencia, Spain
e Dipartimento di Biologia e Patologia Vegetale, V. E. Orabona 4, 70125 Bari, Italy
1 To whom correspondence should be addressed. E-mail christine.foyer{at}ncl.ac.uk, fax +44 (0) 191 2227811, tel. +44 (0) 191 2226932.
Pyridine nucleotides, ascorbate and glutathione are major redox metabolites in plant cells, with specific roles in cellular redox homeostasis and the regulation of the cell cycle. However, the regulation of these metabolite pools during exponential growth and their precise functions in the cell cycle remain to be characterized. The present analysis of the abundance of ascorbate, glutathione, and pyridine nucleotides during exponential growth of Arabidopsis cells in culture provides evidence for the differential regulation of each of these redox pools. Ascorbate was most abundant early in the growth cycle, but glutathione was low at this point. The cellular ascorbate to dehydroascorbate and reduced glutathione (GSH) to glutathione disulphide ratios were high and constant but the pyridine nucleotide pools were largely oxidized over the period of exponential growth and only became more reduced once growth had ceased. The glutathione pool increased in parallel with poly (ADP-ribose) polymerase (PARP) activities and with increases in the abundance of PARP1 and PARP2 mRNAs at a time of high cell cycle activity as indicated by transcriptome information. Marked changes in the intracellular partitioning of GSH between the cytoplasm and nucleus were observed. Extension of the exponential growth phase by dilution or changing the media led to increases in the glutathione and nicotinamide adenine dinucleotide, oxidized form (NAD)-plus-nicotinamide adenine dinucleotide, reduced form (NADH) pools and to higher NAD/NADH ratios but the nicotinamide adenine dinucleotide phosphate, oxidized form (NADP)-plus-nicotinamide adenine dinucleotide phosphate, reduced form (NADPH) pool sizes, and NAPD/NADPH ratios were much less affected. The ascorbate, glutathione, and pyridine nucleotide pools and PARP activity decreased before the exponential growth phase ended. We conclude that there are marked changes in intracellular redox state during the growth cycle but that redox homeostasis is maintained by interplay of the major redox pyridine nucleotides, glutathione, and ascorbate pools. The correlation between PARP expression and activity and GSH accumulation and the finding that GSH can be recruited to the nucleus suggest a relationship between redox regulation and nuclear enzyme activity.
Key Words: glutathione • ascorbate • Redox control • cell cycle • cell signaling • cell redox state