Acid rain (AR) impacts forest health by leaching calcium (Ca) away from soils and plants. Ca is an essential element and participates in various plant physiological responses. In the present study, the protective role of exogenous Ca in alleviating AR stress in Liquidambar formosana Hance at the physiological and proteomic levels was examined. Our results showed that low Ca condition resulted in the chlorophyll content and photosynthesis decreasing significantly in L. formosana leaves; however, these effects could be reversed by high Ca supplementation. Further proteomic analyses successfully identified 81 differentially expressed proteins in AR-treated L. formosana under different Ca levels. In particular, some of the proteins are involved in primary metabolism, photosynthesis, energy production, antioxidant defense, transcription, and translation. Moreover, quantitative real time polymerase chain reaction (qRT-PCR) results indicated that low Ca significantly increased the expression level of the investigated Ca-related genes, which can be reversed by high Ca supplementation under AR stress. Further, Western blotting analysis revealed that exogenous Ca supply reduced AR damage by elevating the expression of proteins involved in the Calvin cycle, reactive oxygen species (ROS) scavenging system. These findings allowed us to better understand how woody plants respond to AR stress at various Ca levels and the protective role of exogenous Ca against AR stress in forest tree species.

Cadmium sensitivity insultr1;1-sultr1;2double mutant with limiting sulfate supply is attributed to the decreased glutathione content that affected oxidative defense but not phytochelatins’ synthesis.In plants, glutathione (GSH) homeostasis plays pivotal role in cadmium (Cd) detoxification. GSH is synthesized by sulfur (S) assimilation pathway. Many studies have tried to investigate the role of GSH homeostasis on Cd tolerance using mutants; however, most of them have focused on the last few steps of S assimilation. Until now, mutant evidence that explored the relationship between GSH homeostasis on Cd tolerance and S absorption is rare. To further reveal the role of GSH homeostasis on Cd stress, the wild-type and a sultr1;1-sultr1;2 double mutant which had a defect in two distinct high-affinity sulfate transporters were used in this study. Growth parameters, biochemical or zymological indexes and S assimilation-related genes’ expression were compared between the mutant and wild-type Arabidopsis plants. It was found that the mutations of SULTR1;1 and SULTR1;2 did not affect Cd accumulation. Compared to the wild-type, the double mutant was more sensitive to Cd under limited sulfate supply and suffered from stronger oxidative damage. More importantly, under the same condition, lower capacity of S assimilation resulted in decreased GSH content in mutant. Faced to the limited GSH accumulation, mutant seedlings consumed a large majority of GSH in pool for the synthesis of phytochelatins rather than participating in the antioxidative defense. Therefore, homeostasis of GSH, imbalance between antioxidative defense and severe oxidative damage led to hypersensitivity of double mutant to Cd under limited sulfate supply.

Zinc (Zn) is a toxic element for plant at high concentrations. As a biologically active gaseous molecule, hydrogen sulfide (H2S) regulates plant growth and development. The aim of this study is to reveal the ameliorative effects of H2S on the physiological and molecular responses of a hyperaccumulator to Zn toxicity.Growth analysis, biochemical and zymological methods, fluorescent microscopic imaging, western-blot and quantitative real-time PCR analysis were performed to investigate the roles of NaHS (a donor of H2S) on the cadmium (Cd)/Zn hyperaccumulator, Solanum nigrum L.H2S ameliorated excess Zn-induced growth inhibition, especially in roots. H2S decreased free cytosolic Zn2+ content in roots which was correlated well with the down-regulation of Zn uptake and homeostasis related genes expression. Besides, H2S further enhanced the expression of the metallothioneins (MTs). Moreover, Zn-induced oxidative stress was also alleviated by H2S.The alleviation of H2S on excess Zn toxicity in S. nigrum is presumably attributed to: (1) the decrease in Zn accumulation via down-regulation of Zn uptake and homeostasis related genes expression; (2) the enhancement in the expression of MTs which chelate excess Zn; (3) the change in the genes expression of antioxidative enzymes, leading to H2O2 reduction.

Calcium (Ca) is a crucial regulator of plant growth, development and stress responses. Acid rain (AR), a serious environmental issue worldwide, leaches away Ca from surrounding soils and affects vegetation. The objective of this study was to investigate how different Ca levels affect protein and RNA expression of calcium-related genes under AR stress.Pinus massoniana seedlings grown at high, medium, and low Ca levels under AR stress were used for proteomics analysis. Furthermore, relative mRNA levels of eight Ca-related genes and their interaction network were analyzed by quantitative real-time PCR (qRT-PCR) and bioinformatic analysis.Proteomic studies identified 95 differentially expressed proteins which were classified into eight groups, including metabolic processes, photosynthesis, and cell rescue and defense, etc. Moreover, qRT-PCR results indicated that low Ca significantly increased the expression level of the investigated Ca-related genes, which can be reversed by high Ca under AR stress.Defense system, gene transcription and translation, photosynthetic machinery, and substance and energy metabolism may play important roles in the responses of P. massoniana to AR stress. Low Ca increases the abundance of cell rescue and defense-related proteins under AR. High Ca can reduce AR damage by increasing the abundance of proteins involved in the Calvin cycle, glycolysis, TCA cycle, and nitrogen metabolism. Our results indicated a possible mechanism involving Ca in AR tolerance in plants.

The correlation between forest decline and calcium (Ca) depletion under long-term acid deposition remains elusive in China due to the high level of Ca deposition. We compared two species (Abies fabri and Rhododendron calophytum) for their growth pattern and base elements concentration in both polluted (Mt. Emei) and unpolluted (Mt. Gongga) sites in Sichuan, southwestern China. A. fabri grown at Mt. Emei had poorer crown condition, slower radial growth rate, and lower seedling density under long-term acid deposition, which correlated closely with the reduced Ca concentration in foliage and tree-ring, in comparison with those at Mt. Gongga. In contrast, R. calophytum showed a stable Ca level and thus displayed normal growth between the two sites. The differential capability of these two species to acclimate to poor Ca environment is one of the keys to understanding the long-term ecological effect of changing atmospheric acid and Ca deposition in the subalpine forest in southwestern China.

A proteomic study using 2-D gel electrophoresis and MALDI-TOF MS was performed to characterize the responses of Arabidopsis thaliana plants to simulated acid rain (SiAR) stress, which is a global environmental problem and has become a serious issue in China in recent years. The emphasis of the present study was to investigate the overall protein expression changes when exposed to SiAR. Out of over 1000 protein spots reproducibly resolved, 50 of them changed their abundance by at least 2-fold. Analysis of protein expression patterns revealed that a set of proteins associated with energy production, metabolism, cell rescue, cell defense and protein folding, etc., could play important roles in mediating plant response to SiAR. In addition to this, some proteins involved in stress responses and jasmonic acid pathway are also involved in plant response to SiAR. More interestingly, the expression of several ubiquitination-related proteins changed dramatically after 32-h SiAR treatment, suggesting that they may act as a molecular marker for the injury phenotype caused by SiAR. Based on our results, we proposed a schematic model to explain the mechanisms associated with the systematic response of Arabidopsis plants to SiAR.

To elucidate the osmotic adjustment characteristics of mangrove plants, inorganic ion and organic solute contents of intermediate leaves were investigated in 3-month-old Kandelia candel (L.) Druce seedlings during 45 days of NaCl treatments (0, 200, and 500 mM NaCl). The contents of Na+, Cl−, total free amino acids, proline, total soluble sugars, pinitol and mannitol increased to different degree by salinity, whereas, K+ content decreased by salinity compared with control. NaCl treatment induced an increase of inorganic ion contribution while a decrease of organic solute contribution. It was concluded that accumulating a large amount of inorganic ions was used as the main osmotic adjustment mechanism under salinity treatment. However, accumulation of organic osmolytes might be considered to play much more important role in osmoregulation under severe salinity (500 mM NaCl) than under moderate salinity (200 mM NaCl), thus the damage caused by high toxic ions (Na+ and Cl−) concentration in K. candel leaves could be avoided.

Changes in the physiological and biochemical characteristics of the leaves of Kandelia candel (L.) Druce seedlings in response to short-term (7 days) and long-term (60 days) treatments with two NaCl concentrations (250 and 500 mM) were studied. The growth rates were measured in terms of plant height, leaf area, and dry weight and were greater in the culture treated with 250 mM NaCl. Photosynthetic pigments also showed a preference for salinity growth conditions. The content of soluble sugars increased under any salinity during continuous treatments, whereas the proline level increased by the end of long-term culture. Further, during the treatment with 500 mM NaCl, the contents of hydrogen peroxide increased dramatically, whereas the levels of MDA, a measure of lipid peroxidation, decreased. The intactness of membrane integrity under this salinity condition may be explained by the activities of superoxide dismutase (SOD) and peroxidase (POD) which increased during the long-term experiment. It is concluded that the ability of K. candel to tolerate salt may occur mainly by inducing biosynthesis of soluble sugars and proline and increasing the activities of SOD and POD. The results imply that K. candel can survive well at 250 mM NaCl conditions and become acclimated to seawater salinity (∼500 mM) for 60 days of exposure.

•Nitric oxide-overproducing mutant (nox1) compared to the wild-type Arabidopsis.•59 differentially expressed proteins were identified.•Metabolism, energy and post-translational modification disorder in nox1 mutant.•Enhanced level of oxidative stress in nox1 mutant.Nitric oxide (NO) as a ubiquitous signal molecule plays an important role in plant development and growth. Here, we compared the proteomic changes between NO-overproducing mutant (nox1) and wild-type (WT) of Arabidopsis thaliana using two-dimensional electrophoresis coupled with MALDI-TOF MS. We successfully identified 59 differentially expressed proteins in nox1 mutant, which are predicted to play potential roles in specific cellular processes, such as post-translational modification, energy production and conversion, metabolism, transcription and signal transduction, cell rescue and defense, development and differentiation. Particularly, expression levels of five anti-oxidative enzymes were altered by the mutation; and assays of their respective enzymatic activities indicated an enhanced level of oxidative stress in nox1 mutant. Finally, some important proteins were further confirmed at transcriptional level using quantitative real-time PCR revealing the systemic changes between WT and nox1. The result suggests that obvious morphological changes in the nox1 mutant may be regulated by different mechanisms and factors, while excess endogenous NO maybe one of the possible reasons.