Abstract
Silicon (Si) has an important function in reducing the damage of environmental stress on plants. Acid rain is a serious abiotic stress factor, and Si can alleviate the stress induced by acid rain on plants. Based on these assumptions, we investigated the effects of silicon on the growth, root phenotype, mineral element contents, hydrogen peroxide (H2O2) and antioxidative enzymes of rice (Oryza sativa L.) seedling roots under simulated acid rain (SAR) stress. The results showed that the combined or single effects of Si and/or SAR on rice roots depend on the concentration of Si and the pH of the SAR. The combined or single effects of a low or moderate concentration of Si (1.0 or 2.0 mM) and light SAR (pH 4.0) enhanced the growth of rice roots, and the combined effects were stronger than those of the single treatment. A high concentration of Si (4.0 mM) or severe SAR (pH 2.0) exerted deleterious effects. The incorporation of Si (1.0, 2.0 or 4.0 mM) into SAR with pH 3.0 or 2.0 promoted the rice root growth, decreased the H2O2 content, increased the Si concentration and the superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX) activities, maintained the balance of mineral element (K, Ca, Mg, Fe, Zn, and Cu) concentrations in the roots of rice seedlings compared with SAR alone. The alleviatory effects observed with a moderate concentration of Si (2.0 mM) were better than the effects obtained with a low or high concentration of Si (1.0 or 4.0 mM). The observed effects were due to disruptions in the absorption and utilization of mineral nutrients and impacts on the activity of antioxidant enzymes in roots, and this conclusion suggests that the degree of rice root damage caused by acid rain might be attributed to not only acid rain but also the level of Si in the soil.
Highlights
As a result of rapid worldwide economic growth, acid rain is becoming an increasingly serious environmental issue [1,2]
These treatments significantly increased the total root length (TRL), root surface area (RSA), root volume (RV) and root tip number (RTN) in rice seedlings compared with the control treatment, the average diameter (AD) was unchanged (Table 2)
The roots of the rice seedlings treated with 4 mM Si were smaller than those of the control (Fig 1M); in addition, the TRL, RSA, RV and RTN observed in the 4 mM Si-treated seedlings were significantly decreased by 23.64%, 22.13%, 23.40% and 21.35%, respectively, whereas the AD was significantly increased by 19.97% (Table 2)
Summary
As a result of rapid worldwide economic growth, acid rain is becoming an increasingly serious environmental issue [1,2]. The average pH value of acid rain in China ranges from 3.0 to 4.5 [5], it can be as low as 1.3 [6]. Both the area affected by acid rain and the acidity of rainwater are increasing, and the frequency. The consequences of acid rain in plants include damage to the cell membrane system and negative impacts on respiration, photosynthesis, and the antioxidative enzyme system [8,9,10,11], and low yields, low germination rates, thin roots, premature abscission, branch dieback, necrosis, and morphological changes have been reported [3,8,12,13]. Some studies have indicated that acid rain effects on the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) on plant species depend on the pH and duration of the acid rain treatments [9,10,11,14,15]
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