Impact of osmotic stress on physiological and bioc

Authors: Izabela Marcińska Ilona CzyczyłoMysza Edyta Skrzypek Maria Filek Stanisław Grzesiak Maciej T Grzesiak Franciszek Janowiak Tomasz Hura Michał Dziurka Kinga Dziurka Agata Nowakowska Steve A Quarrie

Publish Date: 2012/09/14

Volume: 35, Issue: 2, Pages: 451-461

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Abstract

In this study the seedlings of two wheat cultivars were used droughtresistant Chinese Spring CS and droughtsusceptible SQ1 Seedlings were subjected to osmotic stress in order to assess the differences in response to drought stress between resistant and susceptible genotype The aim of the experiment was to evaluate the changes in physiological and biochemical characteristics and to establish the optimum osmotic stress level in which differences in drought resistance between the genotypes could be revealed Plants were subjected to osmotic stress by supplementing the root medium with three concentrations of PEG 6000 Seedlings were grown for 21 days in control conditions and then the plants were subjected to osmotic stress for 7 days by supplementing the root medium with three concentrations of PEG 6000 D1 D2 D3 applied in two steps during the first 3 days of treatment −050 −075 and −100 and next −075 −125 and −15 MPa respectively Measurements of gas exchange parameters chlorophyll content height of seedlings length of root leaf and root water content leaf osmotic potential lipid peroxidation and contents of soluble carbohydrates and proline were taken The results highlighted statistically significant differences in most traits for treatment D2 and emphasized that these conditions were optimum for expressing differences in the responses to osmotic stress between SQ1 and CS wheat genotypes The level of osmotic stress defined in this study as most suitable for differentiating drought resistance of wheat genotypes will be used in further research for genetic characterization of this trait in wheat through QTL analysis of mapping population of doubled haploid lines derived from CS and SQ1It is known that water is an important environmental factor and a major limitation for plant growth development and yield Plants usually experience a fluctuating water supply during their life cycle due to continuously changing climatic factors Blum 1998 Bohnert et al 1995 Chaves et al 2002 Passioura et al 1993 Tan et al 2006 Variability of resistance to drought within plants belonging to the same species has not been completely explained The responses of plants to water stress depend on plant species plant age phase of growth and development level and duration of drought and physical parameters Differences in resistance to drought stress are known to exist amongst genotypes of plant species eg in maize Martiniello and Lorenzoni 1985 Lorens et al 1987 wheat Winter et al 1988 and triticale Grzesiak et al 2003 Plants develop different mechanisms morphological physiological and biochemical which inhibit or remove the harmful effects of stressesWater deficit caused by drought and osmotic stress effects changes in morphology water status gas exchange and chlorophyll content which are connected with the onset of protective mechanisms in the plant Blum and Ebercon 1981 Mansfield and Davies 1981 Jackson et al 1996 Application of polyethylene glycol PEG in a hydroponic solution causes osmotic stress which results in changes in the water status of the tissues and a decrease of plant growth and biomass production Berkowitz et al 1983 Kicheva et al 1994 P’erezAlfocea and Larcher 1995 Grzesiak et al 2003 Usually droughtresistant genotypes accumulate more biomass in leaves than susceptible ones Kerepesi and Galiba 2000 Leaf water content and gas exchange are physiological processes very susceptible to drought stress Under moderate drought a decrease in photosynthesis is generally considered to be the result of reduced availability of CO2 due to stomatal closure Mansfield and Davies 1981 However when drought is prolonged a decrease in photosynthesis is caused by “nonstomatal” mechanisms The changes in photosynthetic activity are connected with membrane damage in mesophyll cells decrease in chlorophyll content and disturbance in synthesis and transport of assimilates Cornic and Massacci 1996 Limitations of photosynthesis by stomatal as well as nonstomatal mechanisms depend not only on the duration and intensity of drought stress but also on plant species stage of plant development and leaf age Berkowitz et al 1983 Kicheva et al 1994 Passioura et al 1993A decrease in net photosynthetic rate under water stress is also related to disturbances in biochemical processes of a nonstomatal nature caused by oxidation of chloroplast lipids and changes in the structure of pigments and proteins Drought stress causes an increase in the content of reactive oxygen species ROS Dhanda et al 2004 Li et al 2004 Miller et al 2010 Rauf et al 2007 Shao et al 2005a In response to droughtinduced oxidative stress plants increase the activity of antioxidative peroxidases or glutathione reductase Gill and Tuteja 2010 Miller et al 2010 Neill et al 2002 In photosystem 2 PS2 the occurrence of ROS is caused by damage to thylakoid membranes when electrons from water are transferred to oxygen Chloroplasts are very susceptible to oxidative stress mainly due to high oxygen concentrations inside these organelles which is a result of irradiation generating singlet oxygen Baker 1993 Cornic and Briantais 1991 When water is not available to the leaves in sufficient quantity higher water use efficiency WUE appears to be an alternative strategy to improve crop performance Araus et al 2002 WUE may be modified not only through a decrease in stomata conductance but also through an increase in photosynthetic capacityOsmotic adjustment in plants subjected to water deficit may occur through an accumulation of low molecular weight organic solutes The compatible osmolytes found in higher plants are soluble carbohydrates and proline The accumulation of soluble carbohydrates in plants has been widely reported as a response to salinity Ashraf and Harris 2004 and drought Zhang et al 2009 in addition to a significant decrease in the net CO2 assimilation rate Proline which is widely found in higher plants accumulates in stressed plants in larger amounts than other amino acids Ghaderi and Siosemardeh 2011 Proline accumulation is one of the common characteristics in many monocotyledons under water deficit Proline regulates the accumulation of useable nitrogen is osmotically active and contributes to membrane stability Bandurska 2000 Bandurska et al 2008 DaCosta and Huang 2006 Javadi et al 2008 It may also act as a signaling regulatory molecule able to activate multiple responses that are components of the adaptation process Maggio et al 2002The wheat genotype Chinese Spring CS used in this study has been shown to be relatively droughtresistant Galiba et al 1989 and to maintain relatively high yields under drought field conditions compared to those of the breeding line SQ1 Dodig and Quarrie data unpublished CS and SQ1 have been used to make a mapping population of doubled haploid lines for quantitative trait locus QTL analysis of stress responses Quarrie et al 2005 As a prerequisite for future work on the genetic control of these physiological and biochemical responses to osmotic stress the experiment described here was performed under PEGinduced osmotic stress on the two parents The objective of this experiment was to determine the optimum concentration of PEG to expose the differences in the physiological and biochemical traits described above between CS and SQ1 grown under osmotic stressSeedlings of droughtresistant Chinese Spring CS and droughtsusceptible SQ1 hexaploid wheat Triticum aestivum L were examined in the experiment The genotype SQ1 was selected at the Plant Breeding Institute UK from the seventh cross generation F7 between two wheat genotypes Highbury × TW269/9/3/4 CS and SQ1 differ significantly in their physiological morphological and developmental traits In comparison to CS SQ1 is shorter with a smaller leaf surface area and fewer spikes which have awns Quarrie et al 1991

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