Photosynthesis, antioxidant system and gene expression of bermudagrass in response to low temperature and salt stress.

There is widespread distribution of salinized lands in northern China. Harnessing such land is essential to environmental health. Bermudagrass [Cynodon dactylon (L.) Pers.] has the potential to improve the salinized lands. However, low temperature remarkably limits the growth of bermudagrass in winter. Currently, there is no information about the interaction of cold and salt in this plant. Hence, the objectives of this study were to figure out the effects of combined cold and salinity stress on bermudagrass. In this study, 4 °C and 200 mM salt solution was used as cold and salt treatments respectively while 4 °C along with 200 mM salt solution were applied as combined stress. After 5 days treatment, bermudagrass displayed a dramatic decline in the turf quality and chlorophyll content, but higher malonaldehyde, electrolyte leakage, hydrogen peroxide content, antioxidant enzyme activity in the combined stress regime as compared to cold or salt treated alone. Analysis of chlorophyll a revealed that the combined stress aggravated stress-induced inhibition of photosystem II. In addition, the expressions of stress-related genes were up-regulated with a lower expression level when cold and salt applied together. In summary, the grass exposed to combined stress presented a relatively lower stress tolerance and suffered a more severe damage than grass grown in the other regimes. These findings are crucial for elucidating the molecular mechanisms of cold and salt combined stress in bermudagrass, and provide information for breeding programs to select and develop bermudagrass cultivars that are suitable for improvement of the northern China salinized land.

Strain-Specific Biostimulant Effects of Chlorella and Chlamydomonas Green Microalgae on Medicago truncatula.

Microalgae have been identified to produce a plethora of bioactive compounds exerting growth stimulating effects on plants. The objective of this study was to investigate the plant-growth-promoting effects of three selected strains of eukaryotic green microalgae. The biostimulatory effects of two Chlorella species (MACC-360 and MACC-38) and a Chlamydomonas reinhardtii strain (cc124) were investigated in a Medicago truncatula model plant grown under controlled greenhouse conditions. The physiological responses of the M. truncatula A17 ecotype to algal biomass addition were characterized thoroughly. The plants were cultivated in pots containing a mixture of vermiculite and soil (1:3) layered with clay at the bottom. The application of live algae cells using the soil drench method significantly increased the plants' shoot length, leaf size, fresh weight, number of flowers and pigment content. For most of the parameters analyzed, the effects of treatment proved to be specific for the applied algae strains. Overall, Chlorella application led to more robust plants with increased fresh biomass, bigger leaves and more flowers/pods compared to the control and Chlamydomonas-treated samples receiving identical total nutrients.

Salinity Stress Responses and Adaptation Mechanisms in Eukaryotic Green Microalgae.

High salinity is a challenging environmental stress for organisms to overcome. Unicellular photosynthetic microalgae are especially vulnerable as they have to grapple not only with ionic imbalance and osmotic stress but also with the generated reactive oxygen species (ROS) interfering with photosynthesis. This review attempts to compare and contrast mechanisms that algae, particularly the eukaryotic Chlamydomonas microalgae, exhibit in order to immediately respond to harsh conditions caused by high salinity. The review also collates adaptation mechanisms of freshwater algae strains under persistent high salt conditions. Understanding both short-term and long-term algal responses to high salinity is integral to further fundamental research in algal biology and biotechnology.

Effects of cadmium-resistant fungi Aspergillus aculeatus on metabolic profiles of bermudagrass [Cynodondactylon (L.)Pers.] under Cd stress.

Plants' tolerance to heavy metal stress may be induced by the exploitation of microbes. The objectives of this study were to investigate the effect of cadmium (Cd)-resistant fungus, Aspergillus aculeatus, on tolerance to Cd and alteration of metabolites in bermudagrass under Cd stress, and identify the predominant metabolites associated with Cd tolerance. Two genotypes of bermudagrass with contrasting Cd tolerance (Cd-sensitive 'WB92' and Cd-tolerant 'WB242') were exposed to 0, 50, 150 and 250 mg kg-1 Cd for 21 days. Physiological responses of bermudagrass to Cd stress were evaluated based on the relative growth rate (RGR) and normalized relative transpiration rate (NRT). Plants inoculated with A. aculeatus exhibited higher RGR and NRT under Cd stress than those of non-inoculated plants, regardless of genotypes. A total of 32 Cd-responsive metabolites in leaves and 21 in roots were identified in the two genotypes, including organic acids, amino acids, sugars, and fatty acids and others. Interestingly, under Cd stress, the leaves of inoculated 'WB92' accumulated less citric acid, aspartic acid, glutamic acid, sucrose, galactose, but more sorbose and glucose, while inoculated 'WB242' leaves had less citric acid, malic acid, sucrose, sorbose, but more fructose and glucose, compared to non-inoculated plants. In 'WB92' roots, the A. aculeatus reduced mannose content, but increased trehalose and citric acid content, while in 'WB242', it decreased sucrose, but enhanced citric acid content, compared to Cd regime. The results of this study suggest that A. aculeatus may induce accumulation of different metabolites associated with Cd tolerance in bermudagrass.

Comparative photosynthetic and metabolic analyses reveal mechanism of improved cold stress tolerance in bermudagrass by exogenous melatonin.

Melatonin (N-acetyl-5-methoxytryptamine) has been reported to participate in plant development and abiotic stress responses. The main objective of this study was to investigate the role of melatonin in the cold-sensitive (S) and the cold-tolerant (T) bermudagrass genotypes' response to cold stress. The genotypes were treated with 100 µM melatonin and exposed to 4 °C temperature for 3 days. In both genotypes, cold stress increased the endogenous melatonin levels, and more prominently in T than S. Physiological responses indicated that exogenous melatonin triggered antioxidant activities in both genotypes, while it alleviated cell damage in the T genotype response to cold stress. Melatonin treatment under cold stress increased fluorescence curve levels for both genotypes, and higher in T than S genotypes. In both genotypes, the alterations in photosynthetic fluorescence parameters after melatonin treatment highlighted the participation of melatonin in improving photosystem response to cold stress, particularly for the cold-tolerant genotype. The metabolic analyses revealed the alterations of 44 cold-responsive metabolites in the two genotypes, mainly including carbohydrates, organic acids and amino acids. After exogenous melatonin treatment under cold condition, there was high accumulation of metabolites in the cold-tolerant regimes than their cold-sensitive counterparts. Collectively, the present study revealed differential modulations of melatonin between the cold-sensitive and the cold-tolerant genotypes in response to cold stress. This was mainly by impacting antioxidant system, photosystem II, as well as metabolic homeostasis.