Targeting Glycinebetaine for Abiotic Stress Tolerance in Crop Plants:Physiological Mechanism,Molecular Interaction and Signaling

In the era of climate change,abiotic stresses(e.g.,salinity,drought,extreme temperature,flooding,metal/metalloid(s),UV radiation,ozone,etc.)are considered as one of the most complex environmental constraints that restricts crop production worldwide.Introduction of stress-tolerant crop cultivars is the most auspicious way of surviving this constraint,and to produce these types of tolerant crops.Several bioengineering mechanisms involved in stress signaling are being adopted in this regard.One example of this kind of manipulation is the osmotic adjustment.The quarternary ammonium compound glycinebetaine(GB),also originally referred to as betaine is a methylated glycine derivative.Among the betaines,GB is the most abundant one in plants,which is mostly produced in response to dehydration caused by different abiotic stresses like drought,salinity,and extreme temperature.Glycinebetaine helps in decreased accumulation and detoxification of ROS,thereby restoring photosynthesis and reducing oxidative stress.It takes part in stabilizing membranes and macromolecules.It is also involved in the stabilization and protection of photosynthetic components,such as ribulose-1,5-bisphosphate carboxylase/oxygenase,photosystem II and quarternary enzyme and protein complex structures under environmental stresses.Glycinebetaine was found to perform in chaperone-induced protein disaggregation.In addition,GB can confer stress tolerance in very low concentrations,and it acts in activating defense responsive genes with stress protection.Recently,field application of GB has also shown protective effects against environmental adversities increasing crop yield and quality.In this review,we will focus on the role of GB in conferring abiotic stress tolerance and the possible ways to engineer GB biosynthesis in plants.

Response of Osmotic Adjustment of Lactobacillus bulgaricus to NaCl Stress

Growth and osmotic response of Lactobacillus bulgaricus ATCC 11842 under hyperosmotic constraint were investigated in a chemically defined medium （CDM） and MRS medium. NaCl could inhibit the growth of L. bulgaricus which decreased with increasing NaCl concentration. In the MRS, NaCl of 1.0 mol·L-1 was the biggest salt stress concentration; in the CDM, 0.8 mol·L-1 was the biggest inhibition concentration. In contrast to what was observed in other lactic acid bacteria, proline, glycine betaine and related molecules were unable to relieve inhibition of growth of L. bulgaricus under osmotic constraint. This was correlated to the absence of sequences homologous to the genes coding for glycine-betaine and/or proline transporters described in Lactococcus lactis and Bacillus subtilis. The amino acid aspartate and alanine were proved to be osmoprotective under NaCl stress. Addition of peptone （0.25% w/v） in the presence of salt led to a stimulation of the growth, as the decrease of the lag time and generation time, and the final biomass increased from 0.31 to 0.64.

Effects of cold-hardening on compatible solutes and antioxidant enzyme activities related to freezing tolerance in Ammopiptanthus mongolicus seedlings

Cold acclimation is associated with many metabolic changes that lead to an increase of freezing tolerance. In order to investigate the biochemical process of cold acclimation in Ammopiptanthus mongolicus, seedlings were acclimated at 2℃ under 16-h photoperiod （150 μmol·m^-2·s^-1 photosynthetically active radiation） for 14 d. Freezing tolerance in seedlings increased after 14 d of cold-hardening. Contents of protein, proline and solute carbohydrate in cotyledon increased after cold acclimation. Patterns of isozymes of superoxide dismutase （SOD）, peroxidase, catalase and polyphenol oxidase （PPO） were investigated. The activities of SOD, peroxidase and PPO in cold acclimated plants were increased during cold-hardening. We deduced that compatible solutes and antioxidant enzymes play important roles in development of freezing tolerance during cold acclimation in this evergreen woody plant.

Salt Stress Induced Modulations in Growth, Compatible Solutes and Antioxidant Enzymes Response in Two Cultivars of Safflower (Carthamus tinctorius L. Cultivar TSF1 and Cultivar SM) Differing in Salt Tolerance

Safflower is an important, traditional, multipurpose oil crop. This was to investigate the effect of different salinity levels on morphological, physiological, biochemical and antioxidant response of two safflower cultivars (Carthamus tinctorius L. cultivar TSF1 and cultivar SM) differing in salt tolerance. Salinity stress (0.0%, 1.0%, 1.5% and 2.0% of NaCl) was induced to safflower plants after 19 days of vegetative growth. After 12 days of stress impositions, plants were harvested and analysed for various parameters. The results revealed that cultivar TSF1 showed maximum growth, dry weight, cell membrane stability and more water content in both root and leaf tissues at higher salinity levels than cultivar SM. Salt stress resulted an accumulation of more soluble sugars, amino acids, proline and glycine betaine at high salinity level confers the tolerance potential of cultivar TSF1 over cultivar SM. Salt stress induces more increase in the enzyme activity of superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase and catalase in tolerant cultivar than sensitive one. The results indicate that each cultivar adopt specific strategy at distinct salinity level for resistance against salinity. The possible conclusion is that improved tolerance in cultivar TSF1 to salinity may be accomplished by better management of growth, physiological attributes and antioxidative defence mechanisms.

Osmotic Adjustment of Soil Biocrust Mosses in Response to Desiccation Stress

Biological soil crusts(biocrusts) widely occur in semiarid and arid regions throughout the world and play important roles in many desert ecosystems: protecting soil from wind erosion and detaining nutrient-rich dust and organic carbon. An experiment was conducted in the Shapotou revegetated area of the Tengger Desert, Ningxia Hui Autonomous Region of China to investigate the physiological responses of the dominant biocrust mosses, Bryum argenteum and Didymodon vinealis, to desiccant stress using different osmotic adjustments. B. argenteum and D. vinealis accumulated K+, total soluble sugar, sucrose, trehalose, proline, and glycine betaine during desiccation. The proline content of B. argenteum was about two times higher than that of D. vinealis. The K+and glycine betaine contents in B. argenteum were slightly higher than those in D. vinealis. In contrast, the total soluble sugar, sucrose,and trehalose contents in D. vinealis were about 3 to 5 times higher than those in B. argenteum. With gradual desiccation stress,the Na+content of B. argenteum was low and did not significantly change. On the contrary, the Na+content of D. vinealis sharply increased and reached a very high level of about 10 to 18 times higher than that of B. argenteum, indicating that B. argenteum and D. vinealis gradually adapted to desiccation stress by osmotic substances accumulation to different degrees.

Solutes in native plants in the Arabian Gulf region and the role of microorganisms: future research

Aims One of the outstanding challenges facing humankind is increas-ing crop production under various types of severe environmental conditions.Many measures have been taken to adopt molecular and biotechnological approaches that lead to the development of transgenic plants able to deal with such harsh and polluted envi-ronments.However,such solutions could be very expensive and require considerable efforts and time to achieve these objectives.The main objective of this review is to discuss the new biological solutions that have emerged in the last decade,as environmentally friendly approaches,perhaps to support and/or replace the present efforts.These solutions based on plant-microbe interactions could be a lifeline and promising alternative strategy to create plants with a high resistance to the extreme environments.Methods During the last two decades research projects have been conducted to study the ecology,identify the features,and the ecophysiology of native plants and the associated microorganisms in the Arabian Gulf region and particularly in Qatar.Many physiological and bio-chemical parameters have been determined,including organic sol-utes(amino acids like proline,glycinebetaine,soluble sugars,etc.),photosynthetic pigments,organic acids and inorganic ions espe-cially heavy metals,along with the physical and chemical proper-ties of the soil in various locations of the State of Qatar.Also,the microorganisms adjacent to and associated with these native plants were identified to elucidate the possible roles in the soil biota in supporting these plants against extreme environmental conditions.Important Findings Investigations of native plants in the Arabian Gulf states during the last decade have shown that wild plants exhibit different abili-ties to accumulate organic solutes to cope with the harsh natural environments.Pollution is a major factor stressing wildlife in this region due to the expansion of urban sectors and industrial activi-ties of oil and gas.Compatible osmolytes,like proline,accumu-late in wild plants in response to severe environmental conditions and heavy metal contaminated soil.Accumulation of these solutes in plant tissues could provide some level of adaptation and resist-ance against all these types of environmental stresses.We present some promising efforts in the Arabian Gulf region to remediate desert soil and water polluted with heavy metals and petroleum hydrocarbons.Substantial evidence is introduced about the roles of microorganisms associated with wild plants in natural habitats,such association may help them cope with the extreme stresses.Possible mechanisms adopted by microorganisms in alleviating the harsh abiotic stresses facing the wild life are discussed,one of which is the promotion of biosynthesis and transport of organic solutes to the plants.Also,the main possibilities of the origin of activities of the accumulation of compatible organic solutes are suggested and the objectives of the future research are discussed.