Abiotic stresses effects on expression of two genes of ZmPIP family in leaves of maize (Zea mays cv 704)

IntroductionPlants continuously face several environmental and stressing factors. Among these factors, salinity, drought are the major environmental stimuli that can greatly influence plant growth and productivity. Plant water relations are disturbed by drought or high salinity due to the lowered water potential in the environment hampering water uptake or favouring loss of water from plants. These stresses impose osmotic stress on plants, causing a series of morphological, physiological, biochemical and molecular changes in plants. To survive these stresses, plants have evolved complex mechanisms to perceive external signals and to manifest adaptive responses with proper physiological, morphological and molecular changes (Zhu, 2002). In addition to, Closing of stomata reduces transpirational losses of water from leaves. The uptake and the biosynthesis of compatible solutes and the regulation of membrane permeability and transport are further measures that either hold back water within the plant or facilitate further uptake of water (Zhu, 2001; Sharp et al., 2004). AQPs are present in the tonoplast, the plasma membrane, and possibly in other internal membranes. In addition to water, individual MIP members may mediate the movement of small non-charged molecules, for example glycerol,urea, CO2, or formaldehyde(Tyerman et al., 2002; Gaspar et al., 2003; Uehlein et al., 2003). Furthermore, a role as osmotic or turgor sensors has been suggested for MIPs (Hill et al., 2004).
Materials and methodsSeeds of maize (Zea mays L. cv. SC. 704) were obtained from Urmia Agriculture Research Centre. Seeds were graded and the big uniform shaped ones selected. Seeds were surface sterilized with 2% sodium hypochlorite for 10 min then washed with sterile distilled water three times. Following vernalization, seeds were placed in growth chamber and transferred to the plastic pot containing a soil mixture of sand (30%) and compost (70%). Plant experienced the following growth conditions for 21 days: the light regime of 16/8 h light/dark with 80% humidity and 22°C temperature. After 21 days of culture, began treatment plants, were applied For short (4 days) and long (8 days) period treatment for three salinity stress NaCl(200mM), CaCl2(40mM) and drought PEG6000(10%). 21 day-old-maize plants were divided into 8 groups and undergone following treatment for wounding and 4 and 8 days.
Results and discussionThe RT-PCR result of all stressed leaves indicated no significant difference in PEG6000(10%) treatment in comparison to the others treatment. ZmPIP1,2 expression had been increased in NaCl-4 , NaCl-8, CaCl2-4 and especially CaCl2-8 plants compared to control plants. This indication showed the effect of salinity stresses (NaCl and CaCl2) on the ZmPIP1,2 suppression. Semi-quantitative RT-PCR analysis of ZmPIP1,5 gene expression showed significant reduction in NaCl-8 plants while undergoing treatment of plants with CaCl2-4, PEG-4 and PEG-8 increase in gene expression observed. Other treated plants did not show significant changes in gene expression. Our results propose these genes are necessary for efficient sensing of environmental changes.
Plasma membrane intrinsic proteins belonging to the aquaporin family have been reported to function in water transport in many plant species (Katsuhara et al., 2002; Chaumont et al., 2001; Tester and Bacic, 2005).
ConclusionsFrom the results of this experiment, it can be concluded that Semi-quantitative RT-PCR analysis of ZmPIPs genes expression in maize showed differential response and significant down or up regulation under applied adverse conditions. Further studies must be carried out to investigate the mechanism by which plant gene expression is controlled by abiotic stresses.