DROUGHT STRESS Changes in Water Status, Membrane Stability and Antioxidant Capacity of Wheat Seedlings Carrying Different Rht-B1 Dwarfing Alleles under Drought Stress K. Kocheva 1 , V. Nenova 1 , T. Karceva 1 , P. Petrov 1 , G. I. Georgiev 1 ,A. B € orner 2 & S. Landjeva 1 1 Institute of Plant Physiology and Genetics, Bulgarian Academy of Sciences Sofia, Bulgaria 2 Leibniz Institute of Plant Genetics and Crop Plant Research (IPK) Gatersleben, Germany Keywords antioxidant enzymes; cell membrane stability; DELLA proteins; drought; osmoregulation; reduced height genes; wheat Correspondence S. Landjeva Institute of Plant Physiology and Genetics Bulgarian Academy of Sciences Acad. Georgi Bonchev str. bl. 21 1113 Sofia Bulgaria Tel.: +359 2 9793677 Fax: +359 2 8739952 Email: s_landjeva@mail.bg; slandjeva@gmail. com Accepted November 14, 2013 doi:10.1111/jac.12047 Abstract Water deficiency is a major constraint to wheat productivity in drought prone regions. The wheat DELLA-encoding height-reducing genes (Rht) are associated with significant increase in grain yield. However, the knowledge of their benefit in dry environments is insufficient. The objective of the study was to examine the effect of induced drought on leaf water content, level of oxidative stress, cell membrane stability, accumulation of osmoprotectants and activity of some anti- oxidant enzymes in wheat near-isogenic lines carrying the alleles Rht-B1b (semi- dwarfing) and Rht-B1c (dwarfing) in comparison with the tall control Rht-B1a. Six-day-long water deprivation was imposed at seedling stage. Plants carrying Rht-B1c and, to a lesser extent, those carrying Rht-B1b performed better under stress compared with Rht-B1a in terms of more sustained membrane integrity, enhanced osmoregulation and better antioxidant defence. These differential responses could reflect pleiotropic effects of the Rht-B1 gene associated with the accumulation of the mutant gene product, that is, altered DELLA proteins, or might be related to allelic variations at neighbouring loci carrying candidate genes for proteins with a major role in plant water regulations and stress adaptation. These findings might be of importance to breeders when introducing Rht-B1 alleles into wheat cultivars designed to be grown in drought liable regions. Introduction Water deficiency is a major stress factor affecting plants at different developmental stages and at various levels of their organization. In continental climate environments, autumn-sown wheat frequently experiences early season drought stress during seedling establishment. Such early setbacks can constrain the subsequent growth and develop- ment and may finally result in a substantial yield reduction (Blum 2011). At the organ and tissue level, the harmful consequences of drought include disturbed balance between water uptake by roots and loss of shoot water through transpiration flow, causing tissue water deficiency and associated osmotic stress. Generation of reactive oxygen species (ROS), such as hydrogen peroxide (H 2 O 2 ) (Sairam and Saxena 2000, Apel and Hirt 2004, Singh et al. 2012), and accumulation of malondialdehyde (MDA), a secondary by-product of the oxidation of polyunsaturated fatty acids in cell membranes, are typical symptoms of the development of the accompanying oxidative stress (Selote and Khanna-Chopra 2006). Subsequent lipid peroxidation may disturb membrane integrity and thus lead to loss of selective permeability causing ion leakage from damaged tissues (Blum and Ebercon 1981). The plant adaptive responses to drought are mainly focused to maintain water homeostasis and membrane sta- bility, and limit the consequences of the developing oxida- tive stress. A general biochemical adaptation at the cellular level is the accumulation of organic solutes such as amino acids, sugars and polyols which improve osmotic potential and water uptake ability (Chen and Jing 2010, Sperdouli and Moustakas 2012). Besides acting as osmoprotectants, these low molecular weight and highly soluble substances may contribute for maintaining membrane integrity, stabi- lizing enzymes or proteins and minimizing oxidative dam- age (Matysik et al. 2002, Chen and Jing 2010). In addition, © 2013 Blackwell Verlag GmbH, 200 (2014) 83–91 83 J Agro Crop Sci (2014) ISSN 0931-2250