Abstract
Potential alleviation effects of Homobrassinosteroid (HBR) (0.5 and 1 µM HBR) on root germination, cell division and antioxidant system enzymes (superoxide dismutase and catalase) of barley (Hordeum vulgare L. cv. ‘Hilal’) roots grown under different salt concentrations (150 mM and 250 mM) were investigated during 48 and 72 h at dark with their controls. Salt applications decreased primary root lengths, seminal root lengths, number of roots from one seed, mitotic activity and induced mitotic abnormalities. In addition, salt application decreased protein content but increased enzyme activities both at 48 h and 72 h when compared to control. Roots treated with HBR enhanced root lengths and root number. HBR-treated roots showed more mitotic activity, mitotic abnormalities and significant enlargements at the root tips when compared to controls and only salt-treated samples. Salt + HBR applications stimulated root lengths and showed more mitotic activity and mitotic abnormalities when compared to only salt-treated samples. Salt application increased superoxide dismutase and catalase activities both at 48 h and 72 h. However, HBR application decreased total soluble protein content and increased enzyme activities especially at 48 h compared to control. Depending on concentration and timing, salt + HBR treatments showed varying results in total soluble protein content and enzyme activities. There was also a significant change in protein banding patterns of experimental groups separated by SDS-PAGE. These findings are expected to contribute to understanding of how HBR affect barley roots grown under different salt concentrations.
Highlights
Brassinosteroids (BRs) are a special class of plant polyhydroxysteroids that play essential roles during normal plant growth and development. They bind to a small family of leucine-rich repeat receptor kinases (BRI1) at the cell surface, initiating an intracellular signal transduction cascade that results in the altered expression of hundreds of genes which are implicated for diverse functions including increased adaptation to various abiotic stresses such as those induced by salts, drought, low and high temperature and heavy metals (Abdullahi et al, 2002; Sharma and Bhardwaj, 2007; Bajguz and Hayat, 2009; Farooq et al, 2009)
Barley seeds grown under control, salt stress (150 mM and 250 mM), HBR application (0.5 μM and 1 μM) and salt + HBR application showed different root lengths at 48 h and 72 h (Fig. 1 and 2, respectively). 0.5 and 1 μM HBR
Determination of protein content and antioxidant enzyme activities Controls and treated roots were first homogenized in a sterile mortar and pestle with liquid nitrogen, subsequently 1 ml extraction buffer (50 mM PBS [0.2 M monobasic sodium phosphate, 0.2 mM dibasic sodium phosphate pH 7.0], 0.1 mM EDTA, 4% polyvinylpyrrolidone) was used per 0.01 mg plant material
Summary
Activity of major cytosolic enzymes by disturbing intracellular potassium homeostasis, causing oxidative stress and programmed cell death, reduced nutrient uptake, metabolic toxicity, inhibition of photosynthesis, reduced CO2 assimilation and reduced root respiration (Sairam and Srivastava, 2002; Cuin and Shabala, 2007; Chen et al, 2007; Shabala, 2009; Abogadallah, 2010; Demirkiran et al, 2013; Liu et al, 2014).Reactive Oxygen Species (ROS) are highly toxic and can greatly disrupt normal metabolism through membrane lipid peroxidation, DNA/RNA nicking, protein oxidation and enzyme inhibition (Tanou et al, 2009). Brassinosteroids (BRs) are a special class of plant polyhydroxysteroids that play essential roles during normal plant growth and development. They bind to a small family of leucine-rich repeat receptor kinases (BRI1) at the cell surface, initiating an intracellular signal transduction cascade that results in the altered expression of hundreds of genes which are implicated for diverse functions including increased adaptation to various abiotic stresses such as those induced by salts, drought, low and high temperature and heavy metals (Abdullahi et al, 2002; Sharma and Bhardwaj, 2007; Bajguz and Hayat, 2009; Farooq et al, 2009). Some researchers have suggested that brassinosteroids promote root elongation and mitosis in a wide range in low concentrations but not high concentrations (Hu et al., 2000; Howell et al, 2007; Kartal et al, 2009)
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