Silicon alleviates oxidative damage of wheat plants in pots under drought
Introduction
Drought stress usually causes a decrease in crop production. It inhibits the photosynthesis of plants, causes changes of chlorophyll contents and components and damage of photosynthetic apparatus [1]. It also inhibits the photochemical activities and decreases the activities of enzymes in the Calvin cycle [2]. One of the important reasons that environmental stress inhibits the growth and photosynthetic abilities of plants is the breakdown of the balance between the production of reactive oxygen species (ROS) and the antioxidant defense [1], causing accumulation of ROS which induces oxidative stress to proteins, membrane lipids and other cellular components [1], [3].
The antioxidant defense system in the plant cell includes both enzymatic [superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), POD peroxidase (POD, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.6.4.2), etc.] and non-enzymatic constituents [cystein (Cys), reduced glutathione (GSH), ascorbic acid (Asc), etc.]. SOD removes superoxide anion free radicals accompanying with formation of hydrogen peroxide (H2O2), which is then detoxified by CAT and POD [4]. In the ascorbate–glutathione cycle, APX reduces H2O2 using ascorbate as an electron donor. Oxidized ascorbate is then reduced by GSH generated from GSSG catalyzed by GR at the expense of NADPH [5]. In environmental stresses conditions such as drought, high activities of antioxidant enzymes and high contents of non-enzymatic constituents are important for plants to tolerate stresses.
Silicon has not yet been considered a generally essential element for higher plants, partly because its roles in plant biology are poorly understood [6], [7], [8], and our knowledge of silicon metabolism in higher plants lags behind that in other organisms (such as diatoms) [9]. However, numerous studies have demonstrated that silicon is one of the important elements of plants, and plays an important role in tolerance of plants to environmental stresses [6], [10]. Relatively more attention has been paid to roles of silicon in controlling disease [11], [12] and pest [13], [14], alleviation in toxicity of heavy metal [15], [16] and salt stress [7], [8], [17].
With respect to drought stress, relevant work is limited. Agarie et al. [18] reported that silicon could decrease the transpiration rate and membrane permeability of rice (Oryza sativa L.) under water deficit induced by polyethylene glycerol. In sorghum (Sorghum bicolor Moench), plants grown in pots applied with silicon had higher relative water content and dry materials [19]. Lux et al. [20] believed that high root endodermal silicification might be related to a higher drought resistance of sorghum. In our previous work, we have also observed that wheat (Triticum aestivum L.) plants applied with silicon could maintain better water status and higher content of dry materials compared with non-silicon treatment under drought [21]. These studies show that application of silicon is useful for drought tolerance improvement of plants. However, the mechanism remains unclear, e.g. whether silicon is involved in physiological responses of plants to drought stress and how it is involved, etc. In this work, the effects of silicon on the oxidative stress of wheat plants in pots under drought are investigated, which maybe help elucidate the physiological mechanism of silicon in improvement of drought tolerance of plants.
Section snippets
Plant materials
After sterilization of the surface with 1% sodium hypochlorite for 10 min and germinated for 24 h, seeds of the wheat (Triticum aestivum L. Longchun 8139, provided by the Institute of Agriculture, Dingxi County, Gansu Province, PR China) were sown in plastic pots (45 cm × 32 cm × 13 cm) each filled with 16.95 Kg soil. Before sowing, the soil was mingled sufficiently, divided into several parts each with 16.95 Kg weight, and then sodium silicate or sodium sulfate (in order to supplement Na introduced by
Effects of silicon on the water status of wheat leaves under drought
As shown in Table 2, the water potential and water content of wheat leaves were decreased under drought stress. And the silicon applied plants still maintain higher water potential and water content with compared to those without application of silicon under drought, which indicated that application of silicon improved the water status of stressed wheat plants.
Effects of silicon on some enzymes activities and H2O2 contents of wheat leaves under drought
Compared with well watered treatments, the activities of SOD, CAT and GR in stressed plants without silicon applied were obviously
Discussion
It was suggested that silicon could increase drought tolerance of plants [18], [19], [20], [21]. In order to elucidate the physiological mechanism, in this work, we investigated the effect of silicon on the oxidative stress of wheat plants.
Even under normal growth conditions, many metabolic processes produce ROS in plants, such as superoxide (O2−), hydrogen peroxide (H2O2), and the hydroxyl radical (OH) [4]. Meanwhile, plants possess efficient antioxidant defense systems for scavenging ROS [8].
Acknowledgements
This work was supported by the National Key Basic Research Special Funds of P R China (No. G1999011705).
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