ORIGINAL ARTICLE Beril Becker Æ Simone Holtgrefe Æ Sabrina Jung Christina Wunrau Æ Andrea Kandlbinder Margarete Baier Æ Karl-Josef Dietz Æ Jan E. Backhausen Renate Scheibe Influence of the photoperiod on redox regulation and stress responses in Arabidopsis thaliana L. (Heynh.) plants under long- and short-day conditions Received: 18 November 2005 / Accepted: 14 December 2005 / Published online: 25 January 2006 Ó Springer-Verlag 2006 Abstract Arabidopsis thaliana L. (Heynh.) plants were grown in low light (150 lmol photons m À2 s À1 and 20°C) either in short days (7.5 h photoperiod) or long days (16 h photoperiod), and then transferred into high light and low temperature (350–800 lmol pho- tons m À2 s À1 at 12°C). Plants grown in short days re- sponded with a rapid increase in NADP-malate dehydrogenase (EC 1.1.1.82) activation state. However, persisting overreduction revealed a new level of regula- tion of the malate valve. Activity measurements and Northern-blot analyses indicated that NADP-malate dehydrogenase transcript and protein levels increased within a few hours. Using macroarrays, additional changes in gene expression were identified. Transcript levels for several enzymes of glutathione metabolism and of some photosynthetic genes increased. The cellular glutathione level increased, but its redox state remained unchanged. A different situation was observed in plants grown in long-day conditions. Neither NADP-malate dehydrogenase nor glutathione content changed, but the expression of several antioxidative enzymes increased strongly. We conclude that the endogenous systems that measure day length interact with redox regulation, and override the interpretation of the signals, i.e. they redi- rect redox-mediated acclimation signals to allow for more efficient light usage and redox poising in short days to systems for the prevention of oxidative damages when grown under long-day conditions. Keywords Glutathione Æ Light acclimation Æ Malate valve Æ Oxidative stress Æ Photoperiod Æ Redox regulation Abbreviations Apx: Ascorbate peroxidase Æ Cat: Catalase Æ DTT: Dithiothreitol Æ GR: Glutathione reductase Æ GS: Glutathione synthase Æ LD: Long day Æ LHC: Light-harvesting complex Æ MDHAR: Monodehydroascorbate reductase Æ MDH: Malate dehydrogenase Æ NTR: NADP-thioredoxin reductase Æ SD: Short day Æ SOD: Superoxide dismutase Æ Trx: Thioredoxin Introduction In their natural environment, plants are subjected to conditions where several parameters such as light or temperature can change dramatically for periods which can last from seconds to days. Plants possess a set of mechanisms, such as Mehler reaction, photorespiration or malate valve (Scheibe 2004), to prevent damages in the short-term, but when environmental alterations persist, a response at the transcriptional level is in- duced (Scheibe et al. 2005). This leads to changes in the ultrastructure of the leaves and in protein and pigment composition (Anderson und Osmond 1987; Das 2004). The chloroplasts of leaves acclimated to low light are characterized by a high content of grana thylakoids, relatively high amounts of photosystems and light harvesting complexes (LHCII) and only low quantities of stromal proteins. Such low-light plants respond to a persisting increase in the light intensity with a very characteristic alteration of gene expression (Rossel et al. 2002; Murchie et al. 2005). Conse- quently, light saturation of photosynthesis is reached at much higher light intensities, the Chl a/b ratio de- creases due to a loss of LHCII, and the content of ATPase and of Calvin-cycle enzymes increases. The B. Becker Æ S. Holtgrefe Æ S. Jung Æ C. Wunrau J. E. Backhausen (&) Æ R. Scheibe Pflanzenphysiologie, Fachbereich Biologie/Chemie, Universita¨t Osnabru¨ck, 49069 Osnabru¨ck, Germany E-mail: backhausen@biologie.uni-osnabrueck.de Tel.: +49-541-9692280 Fax: +49-541-9692265 A. Kandlbinder Æ M. Baier Æ K.-J. Dietz Lehrstuhl fu¨r Biochemie und Physiologie der Pflanzen, Fakulta¨t fu¨r Biologie, Universita¨t Bielefeld, 10 01 31, 33501 Bielefeld, Germany Planta (2006) 224: 380–393 DOI 10.1007/s00425-006-0222-3