Exogenous application of Ca2+ mitigates simulated acid rain stress on soybean productivity and quality by maintaining nutrient absorption

Role of root plasma membrane H+-ATPase in enhancing Cucumis sativus adaptation to microcystins

Microcystins (MCs) are the most widespread and hazardous cyanotoxins posing a huge threat to agro-ecosystem by irrigation. Some adaptive metabolisms can be initiated at the cellular and molecular levels of plant to survive environmental change. To find ways to improve plant tolerance to MCs after recognizing adaptive mechanism in plant, we studied effects of MCs on root morphology, mineral element contents, root activity, H+-ATPase activity, and its gene expression level in cucumber during exposure and recovery (without MCs) periods. After being exposed to MCs (1, 10, 100 and 1000 μg L-1) for 7 days, we found 1 μg L-1 MCs did not affect growth and mineral elements in cucumber. MCs at 10 μg ·L-1 increased root activity and H+-ATPase activity partly from upregulation of genes (CsHA2, CsHA3, CsHA8, and CsHA9) expression, to promote nutrient uptake. Then, the increase in NO3-, Fe, Zn, and Mn contents could contribute to maintaining root growth and morphology. Higher concentration MCs (100 or 1000 µg L-1) inhibited root activity and H+-ATPase activity by downregulating expression of genes (CsHA2, CsHA3, CsHA4, CsHA8, CsHA9, and CsHA10), decreased contents of nutrient elements except Ca largely, and caused root growing worse. After a recovery, the absorption activity and H+-ATPase activity in cucumber treated with10 μg L-1 MCs were closed to the control whereas all parameters in cucumber treated 1000 μg L-1 MCs were even worse. All results indicate that the increase in H+-ATPase activity can enhance cucumber tolerance to MC stress by regulating nutrient uptake, especially when the MCs occur at low concentrations.

Improving yield and quality of rice under acid rain stress by regulating nitrogen assimilation with exogenous Ca2

Acid rain threatens crop yield and nutritional quality, and Ca²⁺ can regulate plant responses to abiotic stresses. To improve the yield and nutritional quality of crops under acid rain stress, we applied exogenous Ca²⁺ to regulate nitrogen assimilation in rice seedlings under simulated acid rain stress (pH 4.5 or 3.0), taking yield and nutritional quality of rice as evaluation criteria. We found that Ca²⁺ (5 mM) maintained the total nitrogen content of rice at the seedling and booting stages to alleviate the inhibitory effect of simulated acid rain on rice yield. Meanwhile, Ca²⁺ improved the activity of glutamate synthase to eliminate the disruption of glutamine synthetase/glutamate synthase balance under simulated acid rain. It decreased the efficiency of nitrogen assimilation, thereby reducing the inhibition of essential amino acid content in rice. The mitigation effect on simulated acid rain at pH 4.5 was better than that of simulated acid rain at pH 3.0. Overall, Ca²⁺ may reduce the negative effect of acid rain on the yield and nutritional quality of crops.

Modification of plasma membrane H+-ATPase in Masson pine (Pinus massoniana Lamb.) seedling roots adapting to acid deposition

To understand the regulation of roots plasma membrane H+-ATPase in Masson pine responding to acid deposition, the changes in biomass, plant morphology, intracellular H+, enzyme activity and H+-ATPase genes expression in Masson pine seedlings exposed to simulated acid rain (SAR, pH 5.6 and 4.6) with and without vanadate were studied. Simulated acid rain exposure for 60 days increased the intracellular H+ in pine roots whether added with 0.1 mM Na3VO4 or not. The growth of seedlings treated with SAR was maintained well, even the primary lateral root length, root dry weight and number of root tips in seedlings exposed to SAR at pH 4.6 were higher than that of the control (pH 6.6). However, the addition of vanadate resulted in severe growth inhibition and obvious decline in morphological parameters. Similarly, ATP hydrolytic activity and H+ transport activity of roots plasma membrane H+-ATPase, both were stimulated by SAR whereas they were inhibited by vanadate, and the highest activity stimulation was observed in pine roots subjected to SAR at pH 4.6. In addition, SAR also induced the expression of the investigated H+-ATPase subunits (atpB, atpE, atpF, atpH and atpI). Therefore, the roots plasma membrane H+-ATPase is instrumental in the growth of Masson pine seedlings adapting to acid rain by a manner of pumping more protons across the membrane through enhancing its activity, and which involves the upregulated gene expression of roots H+-ATPase subunits at transcriptional level.

Effects of acid rain on plant growth: A meta-analysis

Anthropogenic driven acid gases emission has caused acid rain in many regions globally. Although efforts have been made to assess the effects of acid rain on terrestrial ecosystems, a systematic assessment of growth-related traits across plant aboveground and belowground is lacking. Hence, we performed a phylogenetically controlled meta-analysis of 755 observations from 69 independent studies to quantify the effects of acid rain on six growth-related traits of plant. We estimated the inhibitory effects of acid rain on plant growth in general and found that aboveground and belowground plant parts responded differently. The acidity of acid rain and acid rain interval had direct modulation effects on plant growth. We also found that there were interactions between acid rain pH and other acid rain characteristics (i.e., acid rain interval, mole ratio of S:N, and acid rain rate) and experimental characteristics (i.e., initial soil pH and plant exposure part), indicating that there were pH-dependent interaction patterns. Thus, an effective approach to evaluate and predict the effects of acid rain on plant growth is to fully consider the direct effects of acid rain pH and the interactions between acid rain pH and other factors.

Calcium regulates antioxidative isozyme activity for enhancing rice adaption to acid rain stress

Acid rain, as a typical abiotic stress, damages plant growth and production. Calcium (Ca) mediates plant growth and links the signal transduction in plants for adapting to abiotic stresses. To understand the effect of Ca²⁺ on plant adaptable response to acid rain, we investigated changes in activities and gene expression of antioxidative enzymes and fatty acid composition of membrane lipid in rice seedlings treated with exogenous Ca²⁺ (5 mM) or/and simulated acid rain (SAR, pH 3.5 / 2.5). Exogenous Ca²⁺ enhanced activities of superoxide dismutase, catalase and peroxidase isozymes in rice leaves under SAR stress by promoting activation of existing isoforms and up-regulation of Cu/Zn-SOD1, Cu/Zn-SOD2, Cu/Zn-SOD3, CAT1, CAT2 and POD1. Compared to SAR treatment alone, exogenous Ca²⁺ alleviated SAR-induced oxidative damage to cell membrane by enhancing antioxidative capacity, as shown by the decrease in concentrations of H₂O₂, O₂^- and malondialdehyde in rice leaves. Meanwhile, Ca²⁺ alleviated SAR-induced decrease in unsaturation of membrane lipid for maintaining membrane fluidity. Finally, exogenous Ca²⁺ alleviated SAR-induced inhibition on relative growth rate of rice. Therefore, Ca²⁺ could play a role in regulating activities of antioxidative enzymes as well as maintaining unsaturation of membrane lipid for enhancing tolerance in rice seedlings to acid rain stress.

Physiological and biochemical responses of tea seedlings (Camellia sinensis) to simulated acid rain conditions

Tea (Camellia sinensis), widely planted in the south of China, and often exposed to acid rain. However, research concerning the impacts of acid rain on physiology and biochemistry of tea plants is still scarce. In this study, we investigated the influence of simulated acid rain (SAR) on plant height, root length, photosynthetic pigment, Fv/Fm, proline, malondialdehyde, antioxidant enzyme activity, total nitrogen, caffeine, catechins, and free amino acids. Our results showed that SAR at pH 4.5 did not hinder plant development because growth characteristics, photosynthesis, and ascorbate peroxidase and catalase activities did not decrease at this pH compared to those at the other investigated pH values. However, at pH 3.5 and pH 2.5, the activities of antioxidase and concentrations of malondialdehyde and proline increased significantly in response to the decrease of photosynthetic pigments and Fv/Fm. In addition, the increase in acidity increased total nitrogen, certain amino acid content (theanine, cysteine), and decreased catechin and caffeine contents, resulting in an imbalance of the carbon and nitrogen metabolisms. Our results indicated that SAR at pH 3.5 and pH 2.5 could restrict photosynthesis and the antioxidant defense system, causing metabolic disorders and ultimately affecting plant development and growth, but SAR at pH 4.5 had no toxic effects on tea seedlings when no other stress factors are involved.

Comparison of plasma membrane H+-ATPase response to acid rain stress between rice and soybean

Acid rain is a global environmental issue due to inhibiting severely plant growth and productivity. To discover the tolerant mechanism in plants under acid rain stress, we studied the difference in response of two crops (rice and soybean) to simulated acid rain (pH 5.0 ~ 2.5) at growth and physiological, biochemical and molecular levels during exposure and recovery periods by hydroponics. By analyzing the change in relative growth rate, chlorophyll content and plasma permeability in rice and soybean, we found that rice could tolerate acid rain above pH 3.0 whereas soybean could tolerate acid rain above pH 4.5. By RT-PCR analyses, immunoprecipitation and enzyme kinetics study, we observed that pH 4.5 acid rain promoted the transcriptional expression of H+-ATPase genes and the phosphorylation of H+-ATPase and increased H+-ATPase activity in the two crops for resisting acid stress. The increased degree in soybean was larger than that in rice. Acid rain at pH 3.0 still promoted the transcription regulation to maintain H+-ATPase activity higher in rice for resisting stress but caused irreversible inhibition on express of H+-ATPase and decreased H+-ATPase activity in soybean. All results suggest that the different tolerance in rice and soybean to acid rain stress could be associated with difference in plasma membrane H+-ATPase at transcriptional regulation, post-translational modification and the substrate affinity.

Random walk particle tracking simulation on scalar diffusion with irreversible first-order absorption boundaries

Scalar transport in an open channel with irreversible first-order absorption boundaries is investigated through random walk particle tracking method (RWPT). We provide the pre-asymptotic behavior of scalar transport as well as a comparison with existing asymptotic formulations. The RWPT method is based on the development of the probability that a particle is absorbed at the boundary. The random walk model is applied to simulate three main parameters of the scalar transport in the laminar flow with sorption boundaries. The three parameters are (1) the attenuation coefficient reflecting the depletion rate of the total mass; (2) the effective velocity coefficient representing the effective advection of the total mass; and (3) the effective longitudinal dispersion coefficient expressing the effective spreading rate of the solute plume. When the Peclet number is large, numerical results agree well with previous theoretical solutions. Results show that (1) the three coefficients reach their asymptotic values when the dimensionless time τ (= Dt/H²) is about 0.5, where t is the time, H is the water depth, and D is the molecular diffusion coefficient and (2) when the Damkohler number reaches a value around 100, the boundary can be treated as a totally absorptive boundary.