The leaf tonoplast V-H(+)-Atpase activity of a C3 halophyte Suaeda salsa is enhanced by salt stress in a Ca-dependent mode

Multiple linear regression and linear mixed models identify novel traits of salinity tolerance in Olea europaea L

Olive can be considered as moderately tolerant to salinity, with marked differences among cultivars. In the present study, two olive cultivars with different salt tolerance, 'Leccino' (sensitive) and 'Frantoio' (tolerant), were treated with 120 mM of NaCl for 30 days. We measured the expression of genes involved in the management of sodium in the leaves, such as NHX, SOS1 and H+ ATPase, and the concentration of Na+, K+, Mn2+, Mg2+ and Ca2+ in the roots, bark, xylem and leaves of the olive plants. The results were analyzed with multiple linear models and mixed models. Furthermore, we utilized the analysis of covariance to find significant relationships in our data. Both cultivars significantly reduced net photosynthesis and increased water-use efficiency after 30 days of treatment. Sodium accumulated significantly in the roots of both cultivars, and 'Leccino' plants were also able to translocate it to the leaves and the bark. The NHX and vacuolar ATPase subunit E genes were significantly overexpressed in both the cultivars treated with NaCl. The SOS1, ATPase11 and ATPase8 genes were overexpressed in 'Frantoio'. The covariance between gene expression and element concentrations data was analyzed to identify significant interactions between cultivars and treatments. Na+ accumulation in the roots of 'Frantoio' was positively related to the accumulation of K+, Mn2+, Mg2+ and Ca2+ in the xylem, bark and leaves. 'Frantoio' capability to mobilize elements, especially Ca2+, together with the overexpression of key genes for sodium management, could be crucial for salt tolerance.

Cation and Zn Accumulation in Brown Seeds of the Euhalophyte Suaeda salsa Improves Germination Under Saline Conditions

Salinity inhibits plant growth due to salt ion accumulation in plant cells and reduced absorption of other nutrients such as metal ions; however halophyte plants have evolved mechanisms to survive and thrive in high-salt conditions. The euhalophyte Suaeda salsa generates dimorphic seeds (black and brown), which show marked differences in germination and seedling growth under high-salt conditions. However, it is unclear whether their ionic status differs. Here, to provide insight on the role of ions in salt tolerance, we used inductively coupled plasma mass spectrometry to measure the ion contents in the dimorphic seeds from S. salsa plants treated with or without NaCl. We measured the macroelements Na, K, Mg, and Ca, and the microelements Mn, Fe, Zn, Cu, and Mo. NaCl-treated S. salsa plants produced seeds with significantly reduced metallic element contents and significantly increased Na⁺ contents. The brown seeds of S. salsa plants treated with 0 and 200 mM NaCl had much higher contents of K⁺, Ca²⁺, and Fe²⁺ compared with the black seeds. However, the S. salsa seeds (both black and brown) from NaCl-treated plants were significantly larger, and had higher germination rate and higher seedling salt tolerance compared with seeds from plants not treated with NaCl. Interestingly, we measured significantly higher Zn²⁺ contents in the brown seeds from plants treated with NaCl compared with the black seeds. This suggests that the high contents of Zn²⁺ and other cations affected seed development and salt tolerance during germination under high-salt conditions. These observations provide insight into the mechanisms of salt tolerance in this halophyte and inform efforts to increase salt tolerance in salt-sensitive species.

NaCl improves reproduction by enhancing starch accumulation in the ovules of the euhalophyte Suaeda salsa

BACKGROUND

Halophytes show optimal reproduction under high-salinity conditions. However, the role of NaCl in reproduction and its possible mechanisms in the euhalophyte Suaeda salsa remain to be elucidated.

RESULTS

We performed transcript profiling of S. salsa flowers and measured starch accumulation in ovules, sugar contents in flowers, and photosynthetic parameters in the leaves of plants supplied with 0 and 200 mM NaCl. Starch accumulation in ovules, sugar contents in flowers and ovules, and net photosynthetic rate and photochemical efficiency in leaves were significantly higher in NaCl-treated plants vs. the control. We identified 14,348 differentially expressed genes in flowers of NaCl-treated vs. control plants. Many of these genes were predicted to be associated with photosynthesis, carbon utilization, and sugar and starch metabolism. These genes are crucial for maintaining photosystem structure, regulating electron transport, and improving photosynthetic efficiency in NaCl-treated plants. In addition, genes encoding fructokinase and sucrose phosphate synthase were upregulated in flowers of NaCl-treated plants.

CONCLUSIONS

The higher starch and sugar contents in the ovules and flowers of S. salsa in response to NaCl treatment are likely due to the upregulation of genes involved in photosynthesis and carbohydrate metabolism, which increase photosynthetic efficiency and accumulation of photosynthetic products under these conditions.

Chinese wheat mosaic virus-derived vsiRNA-20 can regulate virus infection in wheat through inhibition of vacuolar- (H+ )-PPase induced cell death

Vacuolar (H⁺ )-PPases (VPs), are key regulators of active proton (H⁺ ) transport across membranes using the energy generated from PPi hydrolysis. The VPs also play vital roles in plant responses to various abiotic stresses. Their functions in plant responses to pathogen infections are unknown. Here, we show that TaVP, a VP of wheat (Triticum aestivum) is important for wheat resistance to Chinese wheat mosaic virus (CWMV) infection. Furthermore, overexpression of TaVP in plants induces the activity of PPi hydrolysis, leading to plants cell death. A virus-derived small interfering RNA (vsiRNA-20) generated from CWMV RNA1 can regulate the mRNA accumulation of TaVP in wheat. The accumulation of vsiRNA-20 can suppress cell death induced by TaVP in a dosage-dependent manner. Moreover, we show that the accumulation of vsiRNA-20 can affect PPi hydrolysis and the concentration of H⁺ in CWMV-infected wheat cells to create a more favorable cellular environment for CWMV replication. We propose that vsiRNA-20 regulates TaVP expression to prevent cell death and to maintain a weak alkaline environment in cytoplasm to enhance CWMV infection in wheat. This finding may be used as a novel strategy to minimize virus pathogenicity and to develop new antiviral stratagems.

Salt-Enhanced Reproductive Development of Suaeda salsa L. Coincided With Ion Transporter Gene Upregulation in Flowers and Increased Pollen K+ Content

Halophytes are adapted to saline environments and demonstrate optimal reproductive growth under high salinity. To gain insight into the salt tolerance mechanism and effects of salinity in the halophyte Suaeda salsa, the number of flowers and seeds, seed size, anther development, ion content, and flower transcript profiles, as well as the relative expression levels of genes involved in ion transport, were analyzed in S. salsa plants treated with 0 or 200 mM NaCl. The seed size, flower number, seed number per leaf axil, and anther fertility were all significantly increased by 200 mM NaCl treatment. The Na+ and Cl- contents in the leaves, stems, and pollen of NaCl-treated plants were all markedly higher, and the K+ content in the leaves and stems was significantly lower, than those in untreated control plants. By contrast, the K+ content in pollen grains did not decrease, but rather increased, upon NaCl treatment. Genes related to Na+, K+ and, Cl- transport, such as SOS1, KEA, AKT1, NHX1, and CHX, showed increased expression in the flowers of NaCl-treated plants. These results suggest that ionic homeostasis in reproductive organs, especially in pollen grains under salt-treated conditions, involves increased expression of ion transport-related genes.

NaCl markedly improved the reproductive capacity of the euhalophyte Suaeda salsa

The effect of NaCl on reproductive development was investigated in euhalophyte Suaeda salsa L. under controlled conditions. Results showed that NaCl promoted the reproductive growth of S. salsa and 200mM NaCl was optimal. This was reflected in the increases of seed yield, seed number, flower number per plant and leaf axil, 1000 seed weight, as well as a decrease in flower abortion percentage with supply of NaCl. NaCl reduced the flower abortion percentage by increasing stigma receptivity instead of pollen viability. The Na+ and Cl- concentration in petals, stems and leaves were increased significantly but slightly in stamen and pistil. In contrast, the K+ concentration decreased markedly in leaves, stems and petals but a little in stamen and pistil. The Na+ and Cl- concentrations also increased significantly in seed from mother plants exposed to NaCl, whereas K+ decreased. However, seed quality was not influenced. Our results showed that high concentration of NaCl markedly increases the seed number and quality of S. salsa primarily via increasing flower number and fertility and S. salsa develops strategy to maintain ion homeostasis in reproductive organs for the generation. These factors play a pivotal role in setting up plant populations in saline environment.

Temporal variations and bioaccumulation of heavy metals in different Suaeda salsa marshes of the Yellow River estuary, China

To understand the temporal variations and bioaccumulation of heavy metals in the coastal marshes, the concentrations of heavy metals (Cr, Ni, Pb, and Cu) in the two Suaeda salsa marshes [middle S. salsa marsh (MM) and low S. salsa marsh (LM)] of the Yellow River estuary were determined from May to November in 2008 by in situ sampling and inductively coupled plasma mass spectrometry (ICP-MS) analysis. Results showed that heavy metal concentrations in S. salsa of MM and LM were generally in the order of Cu > Cr > Pb > Ni, while those in sediments fell in the order of Cr > Ni > Cu > Pb. Heavy metal concentrations of S. salsa in MM and LM were different, and significant differences were observed in stems (F = 4.797, p = 0.046) and litters (F = 6.799, p = 0.026) for Ni. Litter was the main stock of heavy metals, and the allocations of Cr, Ni, and Pb reached 31.25-51.31, 28.49-42.58, and 29.55-66.79 % (in MM) and 36.73-48.60, 41.70-57.87, and 33.30-60.64 % (in LM), respectively. The ratios of roots/leaves (R/L) and roots/stems (R/S) for Cr and Ni in MM were mostly greater than 1, while those ratios in LM were mostly less than 1, indicating that Cr and Ni in S. salsa at LM had greater mobility compared with those at MM. Moreover, the [accumulation factor, AF]plant of Cr, Ni, Cu, and Pb in LM, especially [AF]root and [AF]stem of Cr and [AF]litter of Ni, was also higher than that in MM. These indicated that S. salsa grown in LM was more suitable for potential biomonitor or phytoremediation of Cr, Ni, Cu, and Pb if intertidal sediments were seriously contaminated with an increase of pollutant loading (especially heavy metals) in the Yellow River estuary. The use of biomonitor (S. salsa) living and growing in LM could yield valuable information not only on the presence of anthropogenic stressors, but, more importantly, on the adverse influence the stressors are having on the environment.

Spatial and temporal variations of nitrous oxide flux between coastal marsh and the atmosphere in the Yellow River estuary of China

To investigate the spatial and seasonal variations of nitrous oxide (N2O) fluxes and understand the key controlling factors, we explored N2O fluxes and environmental variables in high marsh (HM), middle marsh (MM), low marsh (LM), and mudflat (MF) in the Yellow River estuary throughout a year. Fluxes of N2O differed significantly between sampling periods as well as between sampling positions. During all times of day and the seasons measured, N2O fluxes ranged from -0.0051 to 0.0805 mg N2O m(-2) h(-1), and high N2O emissions occurred during spring (0.0278 mg N2O m(-2) h(-1)) and winter (0.0139 mg N2O m(-2) h(-1)) while low fluxes were observed during summer (0.0065 mg N2O m(-2) h(-1)) and autumn (0.0060 mg N2O m(-2) h(-1)). The annual average N2O flux from the intertidal zone was 0.0117 mg N2O m(-2) h(-1), and the cumulative N2O emission throughout a year was 113.03 mg N2O m(-2), indicating that coastal marsh acted as N2O source. Over all seasons, N2O fluxes from the four marshes were significantly different (p < 0.05), in the order of HM (0.0256 ± 0.0040 mg N2O m(-2) h(-1)) > MF (0.0107 ± 0.0027 mg N2O m(-2) h(-1)) > LM (0.0073 ± 0.0020 mg N2O m(-2) h(-1)) > MM (0.0026 ± 0.0011 mg N2O m(-2) h(-1)). Temporal variations of N2O emissions were related to the vegetations (Suaeda salsa, Phragmites australis, and Tamarix chinensis) and the limited C and mineral N in soils during summer and autumn and the frequent freeze/thaw cycles in soils during spring and winter, while spatial variations were mainly affected by tidal fluctuation and plant composition at spatial scale. This study indicated the importance of seasonal N2O contributions (particularly during non-growing season) to the estimation of local N2O inventory, and highlighted both the large spatial variation of N2O fluxes across the coastal marsh (CV = 158.31%) and the potential effect of exogenous nitrogen loading to the Yellow River estuary on N2O emission should be considered before the annual or local N2O inventory was evaluated accurately.

Energization of vacuolar transport in plant cells and its significance under stress

The plant vacuole is of prime importance in buffering environmental perturbations and in coping with abiotic stress caused by, for example, drought, salinity, cold, or UV. The large volume, the efficient integration in anterograde and retrograde vesicular trafficking, and the dynamic equipment with tonoplast transporters enable the vacuole to fulfill indispensible functions in cell biology, for example, transient and permanent storage, detoxification, recycling, pH and redox homeostasis, cell expansion, biotic defence, and cell death. This review first focuses on endomembrane dynamics and then summarizes the functions, assembly, and regulation of secretory and vacuolar proton pumps: (i) the vacuolar H(+)-ATPase (V-ATPase) which represents a multimeric complex of approximately 800 kDa, (ii) the vacuolar H(+)-pyrophosphatase, and (iii) the plasma membrane H(+)-ATPase. These primary proton pumps regulate the cytosolic pH and provide the driving force for secondary active transport. Carriers and ion channels modulate the proton motif force and catalyze uptake and vacuolar compartmentation of solutes and deposition of xenobiotics or secondary compounds such as flavonoids. ABC-type transporters directly energized by MgATP complement the transport portfolio that realizes the multiple functions in stress tolerance of plants.

Fluxes of nitrous oxide and methane in different coastal Suaeda salsa marshes of the Yellow River estuary, China

The spatial and temporal variations of the fluxes of nitrous oxide (N(2)O) and methane (CH(4)) and associated abiotic sediment parameters were quantified for the first time across the coastal marsh dominated by Suaeda salsa in the Yellow River estuary during 2009/2010. During all times of day and the seasons measured, N(2)O and CH(4) fluxes from coastal marsh ranged from -0.0147 mg N(2)O m(-2) h(-1) to 0.0982 mg N(2)O m(-2) h(-1) and -0.7421 mg CH(4) m(-2) h(-1) to 0.4242 mg CH(4) m(-2) h(-1), respectively. The mean N(2)O fluxes in spring, summer, autumn and winter were 0.0325 mg N(2)O m(-2) h(-1), 0.0089 mg N(2)O m(-2) h(-1), 0.0119 mg N(2)O m(-2) h(-1) and 0.0140 mg N(2)O m(-2) h(-1), and the average CH(4) fluxes were -0.0109 mg CH(4) m(-2) h(-1), -0.0174 mg CH(4) m(-2) h(-1), -0.0141 mg CH(4) m(-2) h(-1) and -0.0089 mg CH(4) m(-2) h(-1), respectively, indicating that the coastal marsh acted as N(2)O source and CH(4) sink. Both N(2)O and CH(4) fluxes differed significantly between times of day of sampling. N(2)O fluxes differed significantly between sampling seasons as well as between sampling positions, while CH(4) fluxes had no significant differences between seasons or positions. Temporal variations of N(2)O emissions were probably related to the effects of vegetation (S. salsa) during summer and autumn and the frequent freeze/thaw cycle of sediment during spring and winter, while those of CH(4) fluxes were controlled by the interactions of thermal conditions and other abiotic factors (soil moisture and salinity). Spatial variations of N(2)O and CH(4) fluxes were primarily affected by soil moisture fluctuation derived from astronomic tide, sediment substrate and vegetation composition. N(2)O and CH(4) fluxes, expressed as CO(2)-equivaltent (CO(2)-e) emissions, showed that N(2)O comprised the principal part of total calculated CO(2)-e emissions during spring and winter, while the contributions of CH(4) could not be ignored during summer and autumn. This study highlights the importance of seasonal N(2)O and CH(4) contributions, particularly during times of significant CH(4) consumption. For the accurate up-scaling of N(2)O and CH(4) fluxes to annual rates, a careful sampling design at site-level is required to capture the potentially considerable temporal and spatial variations of N(2)O and CH(4) emissions.

Toxicological effects of environmentally relevant lead and zinc in halophyte Suaeda salsa by NMR-based metabolomics

Lead (Pb) and zinc (Zn) are two typical metal contaminants with high levels in both seawater and sediment in the intertidal zones of the Bohai Sea. Suaeda salsa is the pioneer halophyte plant in the intertidal zones of the Bohai Sea. In the present work, the short (1 week) and long term (1 month) toxicological effects of environmentally relevant concentrations of Pb and Zn were characterized in S. salsa using NMR-based metabolomics combined with antioxidant enzyme activities. After metal exposure for 1 week, no significant metabolic responses were detected in root tissues of S. salsa. The significant metabolic responses included the increase of isocaproate, glucose and fructose, and decrease of malate, citrate and sucrose in root tissues of S. salsa exposed to Pb for 1 month. The increased phosphocholine and betaine, and decreased choline were uniquely found in Zn-exposed samples. The metabolic changes including decreased malate, citrate and sucrose were detected in both Pb and Zn-exposed groups. These metabolic biomarkers revealed that both Pb and Zn exposures could induce osmotic stress and disturbances in energy metabolism in S. salsa after exposures for 1 month. Overall, this work demonstrates that metabolomics can be used to elucidate toxicological effects of environmentally relevant metal contaminants using halophyte S. salsa as the bioindicator.

Metabolic profiling of cadmium-induced effects in one pioneer intertidal halophyte Suaeda salsa by NMR-based metabolomics

Cadmium is a non-essential element to living organisms and has become the severe contaminant in both seawater and sediment in the intertidal zones of the Bohai Sea. The halophyte, Suaeda salsa is the pioneer plant in the intertidal zones of Bohai Sea and has been widely applied in environmental sciences. In this study, the dose- and time-dependent effects induced by environmentally relevant concentrations (2, 10 and 50 μg l(-1)) of cadmium were characterized in S. salsa using NMR-based metabolomics. The levels of amino acids (valine, leucine, glutamate, tyrosine, etc.), carbohydrates (glucose, sucrose and fructose), intermediates of tricarboxylic acid cycle (succinate, citrate, etc.) and osmolyte (betaine) were altered in the S. salsa samples after cadmium exposures. These metabolic biomarkers indicated the elevated protein degradation and disturbances in the osmotic regulation and energy metabolism caused by cadmium in S. salsa. Overall, our results demonstrated the applicability of NMR-based metabolomics for the detection of metabolic biomarkers that could be used for the interpretation of toxicological effects induced by contaminants in the pioneer plant S. salsa in the intertidal zones. In addition, the metabolic biomarkers could be potentially useful for the bio-monitoring of contaminants in the intertidal zones.

Nitrogen cycle of a typical Suaeda salsa marsh ecosystem in the Yellow River estuary

The nitrogen (N) biological cycle of the Suaeda salsa marsh ecosystem in the Yellow River estuary was studied during 2008 to 2009. Results showed that soil N had significant seasonal fluctuations and vertical distribution. The N/P ratio (15.73 +/- 1.77) of S. salsa was less than 16, indicating that plant growth was limited by both N and P. The N absorption coefficient of S. salsa was very low (0.007), while the N utilization and cycle coefficients were high (0.824 and 0.331, respectively). The N turnover among compartments of S. salsa marsh showed that N uptake from aboveground parts and roots were 2.539 and 0.622 g/m2, respectively. The N translocation from aboveground parts to roots and from roots to soil were 2.042 and 0.076 g/m2, respectively. The N translocation from aboveground living bodies to litter was 0.497 g/m2, the annual N return from litter to soil was far less than 0.368 g/m2, and the net N mineralization in topsoil during the growing season was 0.033 g/m2. N was an important limiting factor in S. salsa marsh, and the ecosystem was classified as unstable and vulnerable. S. salsa was seemingly well adapted to the low-nutrient status and vulnerable habitat, and the nutrient enrichment due to N import from the Yellow River estuary would be a potential threat to the S. salsa marsh. Excessive nutrient loading might favor invasive species and induce severe long-term degradation of the ecosystem if human intervention measures were not taken. The N quantitative relationships determined in our study might provide a scientific basis for the establishment of effective measures.

Organ-specific responses of vacuolar H-ATPase in the shoots and roots of C halophyte Suaeda salsa to NaCl

Suaeda salsa L. is a halophytic species that is well adapted to high salinity. In order to understand its salt tolerance mechanism, we examined the growth and vacuolar H(+)-ATPase (V-ATPase) response to NaCl within the shoots and roots. The growth of shoots, but not roots, was dramatically stimulated by NaCl. Cl(-) and Na(+) were mainly accumulated in shoots. V-ATPase activity was significantly increased by NaCl in roots and especially in shoots. Interestingly, antisera ATP95 and ATP88b detected three V(1) subunits (66, 55 and 36 KDa) of V-ATPase only in shoots, while an 18 kDa V(0) subunit of V-ATPase was detected by both antisera in shoots and roots. It suggested that the tissue-specific characteristics of V-ATPase were related to the different patterns of growth and ion accumulation in shoots and roots of S. salsa.

Synthetic reactive dye wastewater treatment by narrow-leaved cattails (Typha angustifolia Linn.): effects of dye, salinity and metals

Narrow-leaved cattails were studied in synthetic reactive dye wastewater (SRDW) under caustic conditions. The effects of the toxic dye were expressed in terms of relative plant growth rate and the appearance of symptoms such as necrosis, and chronic or acute wilting. The dye toxicity was 25.33 mg l(-1) which was close to approximate the concentration of dye residue from the textile effluent in the public stream. The system pH and % color removal were decreased, indicating that narrow-leaved cattail can treat wastewater. The average system pH decreased from 9 to 7. The maximum color removal was approximately 60% when cultured under soil conditions. The SEM image of narrow-leaved cattail root after treatment with SRDW indicated that the root cortex was damaged and the crystalline sodium salts deposited in the root cells which caused evaporation and transpiration decreased in SRDW. The salinity under caustic conditions also affects the growth of the plants. The maximum sodium removal was approximately 44% and was found in the SRDW under soil conditions within 14 days. A small amount of sodium could enhance the relative growth rate. However, the sodium removal of the plants was limited after the third week of treatment. It should be noted that narrow-leaved cattails are known to avoid the textile dye and salt stress conditions during SRDW treatment through special mechanisms such as salt accumulation in the roots or shedding of older leaves. In addition, elements such as silicon, calcium and iron in plants might help the plant to detoxify by forming complexes with dye molecules.

SOS2 promotes salt tolerance in part by interacting with the vacuolar H+-ATPase and upregulating its transport activity

The salt overly sensitive (SOS) pathway is critical for plant salt stress tolerance and has a key role in regulating ion transport under salt stress. To further investigate salt tolerance factors regulated by the SOS pathway, we expressed an N-terminal fusion of the improved tandem affinity purification tag to SOS2 (NTAP-SOS2) in sos2-2 mutant plants. Expression of NTAP-SOS2 rescued the salt tolerance defect of sos2-2 plants, indicating that the fusion protein was functional in vivo. Tandem affinity purification of NTAP-SOS2-containing protein complexes and subsequent liquid chromatography-tandem mass spectrometry analysis indicated that subunits A, B, C, E, and G of the peripheral cytoplasmic domain of the vacuolar H+-ATPase (V-ATPase) were present in a SOS2-containing protein complex. Parallel purification of samples from control and salt-stressed NTAP-SOS2/sos2-2 plants demonstrated that each of these V-ATPase subunits was more abundant in NTAP-SOS2 complexes isolated from salt-stressed plants, suggesting that the interaction may be enhanced by salt stress. Yeast two-hybrid analysis showed that SOS2 interacted directly with V-ATPase regulatory subunits B1 and B2. The importance of the SOS2 interaction with the V-ATPase was shown at the cellular level by reduced H+ transport activity of tonoplast vesicles isolated from sos2-2 cells relative to vesicles from wild-type cells. In addition, seedlings of the det3 mutant, which has reduced V-ATPase activity, were found to be severely salt sensitive. Our results suggest that regulation of V-ATPase activity is an additional key function of SOS2 in coordinating changes in ion transport during salt stress and in promoting salt tolerance.

Cryptochrome 2 is involved in betacyanin decomposition induced by blue light in Suaeda salsa

Seeds of the halophyte Suaeda salsa (L.) Pall. were cultured in 24 h dark and 14 h blue light / 10 h dark to examine the role of blue light and the blue-light-absorbing photoreceptor cryptochrome 2 (CRY2) in betacyanin accumulation, hypocotyl elongation and cotyledon opening in S. salsa seedlings. Darkness significantly promoted betacyanin accumulation and hypocotyl elongation but inhibited cotyledon opening. Blue light suppressed betacyanin accumulation and hypocotyl elongation but stimulated cotyledon opening. Betacyanin in S. salsa seedlings decomposed with time in blue light. Western blot analysis showed that CRY2 protein accumulated both in hypocotyls and cotyledons of S. salsa seedlings grown in dark, but degraded with time in blue light, which was paralleled by a decrease of tyrosine hydroxylation activity of tyrosinase, a key enzyme involved in the betalain biosynthesis pathway. These results suggest that CRY2 protein mediates betacyanin decomposition via inactivation of tyrosinase in S. salsa seedlings, and the blue-light-dependent degradation of CRY2 protein is crucial to its function.

Analysis of the physiological mechanism of salt-tolerant transgenic rice carrying a vacuolar Na+/H + antiporter gene from Suaeda salsa

Salt stress is one of the most serious factors limiting the productivity of agricultural crops. Increasing evidence has demonstrated that vacuolar Na+/H+ antiporters play a crucial role in plant salt tolerance. In the present study, we expressed the Suaeda salsa vacuolar Na+/H+ antiporter SsNHX1 in transgenic rice to investigate whether this can increase the salt tolerance of rice, and to study how overexpression of this gene affected other salt-tolerant mechanisms. It was found that transgenic rice plants showed markedly enhanced tolerance to salt stress and to water deprivation compared with non-transgenic controls upon salt stress imposition under outdoor conditions. Measurements of ion levels indicated that K+, Ca2+ and Mg2+ contents were all higher in transgenic plants than in non-transformed controls. Furthermore, shoot V-ATPase hydrolytic activity was dramatically increased in transgenics compared to that of non-transformed controls under salt stress conditions. Physiological analysis also showed that the photosynthetic activity of the transformed plants was higher whereas the same plants had reduced reactive oxygen species generation. In addition, the soluble sugar content increased in the transgenics compared with that in non-transgenics. These results imply that up-regulation of a vacuolar Na+/H+ antiporter gene in transgenic rice might cause pleiotropic up-regulation of other salt-resistance-related mechanisms to improve salt tolerance.