Increased salinity and groundwater levels lead to degradation of the Robinia pseudoacacia forest in the Yellow River Delta

Forest degradation is a worldwide problem,although its causes vary due to geographical and climatic differences and man-made causes.In recent years,the Robinia pseudoacacia forest in the Yellow River Delta has suffered severe degradation.The causative mechanisms were investigated in the field over two years,and the results show that increased forest degradation was reflected by increased tree mortality,high leaf and soil sodium salt levels and groundwater depth.Average tree diameters decreased,and leaf chlorophyll and soil microbial contents decreased.Redundancy discriminate analysis(RDA)showed that degradation of the forest was correlated positively with soil salt content,but negatively with groundwater depth.Correlation analysis showed that 0.79%–0.95%soil salt content and above 1.20 m groundwater depth caused the death of R.pseudoacacia trees due to localized anthropogenic economic activities,such as rice farming,that disrupted the original water–salt balance.Measures are recommended to prevent further degradation and restore degraded forests.

Sodium Stress in the Halophyte Thellungiella halophila and Transcriptional Changes in a thsos1-RNA Interference Line

The plasma membrane Na＋/H＋-antiporter salt overly sensitive1 （SOS1） from the halophytic Arabidopsis-relative Thellungiella halophila （ThSOS1） shows conserved sequence and domain structure with the orthologous genes from Arabidopsis thaliana and other plants. When expression of ThSOSt was reduced by RNA interference （RNAi）, pronounced characteristics of salt-sensitivity were observed. We were interested in monitoring altered transcriptional responses between Thellungiella wild type and thsost-4, a representative RNAi line with particular emphasis on root responses to salt stress at 350 mmol/L NaCI, a concentration that is only moderately stressful for mature wild type plants. Transcript profiling revealed several functional categories of genes that were differently affected in wild-type and RNAi plants. Down-regulation of SOS1 resulted in different gene expression even in the absence of stress. The pattern of gene induction in the RNAi plant under salt stress was similar to that of glycophytic Arabidopsis rather than that of wild type Thellungiella. The RNAi plants failed to down-regulate functions that are normally reduced in wild type Thellungiella upon stress and did not up-regulate functions that characterize the Thellungiella salt stress response. Metabolite changes observed in wild type Thellungiella after salt stress were less pronounced or absent in RNAi plants. Transcript and metabolite behavior suggested SOS1 functions including but also extending its established function as a sodium transporter. The down-regulation of ThSOS1 converted the halophyte Thellungiella into a salt-sensitive plant.

Enhancement of Superoxide Dismutase and Catalase Activities and Salt Tolerance of Euhalophyte Suaeda salsa L. by Mycorrhizal Fungus Glomus mosseae

Arbuscular mycorrhizal （AM）-mediated plant physiological activities could contribute to plant salt tolerance. However, the biochemical mechanism by which AM fungi enhance salt tolerance of halophytie plants is unclear. A pot experiment was conducted to determine whether salt tolerance of the C3 halophyte Suaeda salsa was enhanced by the AM fungus Glomus rnosseae. When 60-day-old S. salsa seedlings were subjected to 400 mmol L-1 NaC1 stress for 35 days, plant height, number of leaves and branches, shoot and root biomass, and root length of G. mosseae-colonized seedlings were significantly greater than those of the nonmycorrizal seedlings. Leaf superoxide dismutase （SOD） activity at all sampling times （weekly for 35 days after salt stress was initiated） and leaf catalase （CAT） activity at 2 and 3 weeks after salt stress was initiated were also significantly enhanced in G. mosseae-colonized S. salsa seedlings, while the content of leaf malondialdehyde （MDA）, a product of membrane lipid peroxidation, was significantly reduced, indicating an alleviation of oxidative damage. The corresponding leaf isoenzymes of SOD （Fe-SOD, Cu/Zn-SOD1, and Cu/Zn-SOD2） and CAT （CAT1 and CAT2） were also significantly increased in the mycorrhizal seedlings after 14 days of 400 mmol L-1 NaC1 stress. Our results suggested that G. rnosseae increased salt tolerance by increasing SOD and CAT activities and forming SOD and CAT isoforms in S. salsa seedlings.

Organ-Specific Responses of Vacuolar H^+-ATPase in the Shoots and Roots of C_3 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 NaCI within the shoots and roots. The growth of shoots, but not roots, was dramatically stimulated by NaCI. CI^- and Na^＋ were mainly accumulated in shoots. V-ATPase activity was significantly increased by NaCI in roots and especially in shoots. Interestingly, antisera ATP95 and ATP88b detected three V1 subunits （66, 55 and 36 KDa） of V-ATPase only in shoots, while an 18 kDa V0 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.

Overexpression of a Chloroplast-located Peroxiredoxin Q Gene, SsPrxQ, Increases the Salt and Low-temperature Tolerance of Arabidopsis

Ablotlc stress, such as salt, drought and extreme temperature, can result in enhanced production of reactive oxygen species （ROS）. Plants have developed both enzymatic ROS-scavenging and non-enzymatic ROS-scavenging systems. The major ROS-scavenging enzymes of plants include superoxide dismutase （SOD）, ascorbate peroxldaae （APX）, catalaae （CAT）, glutathione peroxldaae （GPX） and peroxiredoxina （Prxa）. In the present work, we identified a gene encoding chloroplast-located peroxiredoxin Q, SsPrxQ, from Suaeda salsa L. located at chloroplast. Overexpression of SsPrxQ In Arabidopsis leads to an increase In salt and low-temperature tolerance.

Petal Development in Lotus japonicus

Previous studies have demonstrated that petal shape and size in legume flowers are determined by two separate mechanisms, dorsoventral （DV） and organ internal （IN） asymmetric mechanisms, respectively. However, little is known about the molecular mechanisms controlling petal development in legumes. To address this question, we investigated petal development along the floral DV axis in Lotus japonicus with respect to cell and developmental biology by comparing wild-type legumes to mutants. Based on morphological markers, the entire course of petal development, from initiation to maturity, was grouped to define 3 phases or 13 stages. In terms of epidermal micromorphology from adaxial surface, mature petals were divided into several distinct domains, and characteristic epidermal cells of each petal differentiated at stage 9, while epidermal cells of all domains were observed until stage 12. TCP and MIXTA-like genes were found to be differentially expressed in various domains of petals at stages 9 and 12. Our results suggest that DV and IN mechanisms interplay at different stages of petal development, and their interaction at the cellular and molecular level guides the elaboration of domains within petals to achieve their ideal shape, and further suggest that TCP genes determine petal identity along the DV axis by regulatincl MIXTA-like clene expression.