The Physiological And Biochemical Mechanisms Of Adaption To Salt Stress In Two High Yield Jatropha Curcas L.

In recent years, the physic nut (Jatropha curcas L.) has received special attention as a biodiesel feedstock, because of its high seed oil content and quality. Large-scale investments and expansions of physic nut plantations have been triggered. If the physic nut competes for land with food crops or high carbon stocks, its acclaimed sustainability advantages are lost. The seeds of physic nut plants represent a promising bio-energy source and current research is mainly focused on their oil content, characteristics and composition and their use and application to biodiesel production. Knowledge of the physic nut agronomic properties and the plant’s physiological responses to biotic and abiotic stress are not thoroughly understood. For example, there is limited information on how the physic nut responds to salt stress.These knowledge gaps imply that developing large scale plantations is not without socio-economic and ecological risk. In order to selected salt-tolerant, high yield physic nut ecotypes, we analyzed the chemical and physical characteristics of seeds and seed oils of three physic nut ecotypes (Nanyou1,2and3) with relatively high capsule yield, which were initially screened from fifteen physic nut ecotypes. Furthermore, In order to clarify the salt tolerance of physic nut and its salt tolerance mechanisms, we analyzed the growth and physiological and biochemical responses to salt stress between the Nanyou2and3. The Nanyou2was also exposed to different concentrations of seawater to clarify the seawater-tolerance in physic nut and the effect of sea water on physic nut growth, seed oil content and the fatty acid compositions. All these basic reasearch would help to develop strategies for improving understanding the physic nut plants response to salt stress, screen high yield and salt-tolerant strains of physic nut, cultivate for salt-tolerant cultivars in the future. The main results obtained were shown as follows:1. The kernel oil content of three physic nut ecotypes was more than60%. Moreover, the fatty acid compositions in three physic nut seed oils were mainly oleic acid (C18:1), palm itic acid (C16:0), linoleic acid (C18:2), stearic acid (C18:0) and margaric acid (C17:0), and were dominated by unsaturated fatty acids. Thus, they were all good biodiesel feedstocks. Among these three physic nut ecotypes, the kernel oil content and biological yield of the Nanyou3was highest. Therefore, it had the greatest potential for biodiesel feedstock. There was no significant difference in kernel oil content and biological yield between the Nanyou1and2. However, the Nanyou2was with excellent fruit characters and excellent physical and genetic characteristics, which were helpful for reducing the cost of biodiesel production. Thus, compared with the Nanyou1, the Nanyou2had a greater potential for biodiesel feedstock.2. Seedlings of Nanyou2and Nanyou3were subjected to different concentrations of NaCl (0,50,100and200mmol-L"1) treatment for24days. Compared with the control leaves, both the leaf RWC had no significant difference in two ecotypes, suggested that physic nut plants has a strong capacity to maintain cell water balance under salt stress. Under50mmol-L-1NaCl treatment, compared with the control, the Pn,Fv/Fm and the totally photosynthetic area had no significant difference, indicated the photosynthetic performance remained stable. Thus, the whole plant dry weight was not affected by50mmol-L"1NaCl in both Nanyou2and Nanyou3. Under100and200mmol·L-1NaCl treatment, both the dry weights of Nanyou2and Nanyou3were reduced significantly, especially that of Nanyou3, indicated50mmol·L-1NaCl had no significant effect on the physic nut growth. The Nanyou2had a strong capacity of resistance to salt stress than the Nanyou3under mid-high salt stress.3. The SOD activity of Nanyou2increased under50mmol-L-1NaCl treatment and decreased significantly under200mmol-L-1NaCl treatment, while that of Nanyou3decreased continuously with a significant degree. The POD activity in both Nanyou2and3maintained stable under50mmol-L"1NaCl treatment, with the increasing NaCl treatment, the POD activity in Nanyou2increased significantly, while that in Nanyou3significantly decreased but maitained stable. The CAT activities of both ecotypes increased significantly when treated with50mmol-L’1NaCl, and then showed similar trend as the SOD activities did in both ecotypes. These results suggested that the activity of antioxidant enzymes in physic nut seedling leaves could be activated under salt stress. Compared with the Nanyou3, the Nanyou2could maitain higher antioxidant enzyme activities and had a better ability to increase coordinately and remain higher activity.4.With the increasing NaCl concentration, the increasing trend of Na+and Cl-content in physic nut roots, stems and leaves was observed. The increase of Na+and Cl-content in physic nut shoots and roots was more conspicuous than that in leaves under50mmol-L-1NaCl treatment. Moreover, the Na+and Cl-were mainly distributed in the cortex of root and stem as well stem pith, so it could reduce the damage to the leaf. Under200mmol-L-1NaCl treatment, the increasing rate of Na+and Cl-content in leaves and stems was higher than that of roots, and the Na+and Cl-were mianly distributed to the cortex and xylem of the leaf main vein to reduce the injury for palisade and spongy tissue. Thus, the leaf could maintain photosynthetic capacity. Compared with the Nanyou3, the decreasing rate of K+and Ca2+in Nanyou2was lower, so it could maitain higher K+/Na+andCa2+/Na+ratio than the Nanyou3did. Thus, its ability to maintain ion balance was stronger than that of the Nanyou3.5. This study investigates the acclimation of PM-H+-ATPase of Nanyou2physic nut roots and leaves treated with0,50and200mmol-L-1NaCl for5days. Upon comparison with control roots, the PM H+-ATPase hydrolytic activity, Vmax, Km, H+-pumping activity and pH gradient potential across the plasma membrane were significantly higher in roots treated with NaCl, especially under mild salt stress. The translational activation of PM-H+-ATPase of physic nut roots helped to maintain nitrogen and phosphorus uptake as well as soluble sugar acquisition in root, thus promoting root growth and increasing root shoot ratio and increasing the salt tolerance of physic nut. Compared with the control leaves, with NaCl treatment, lower Km values for the PM H+-ATPase of leaves were observed, suggested that the affinity of PM H+-ATPase towards ATP increases as a function of salt treatment. The maintenance of H+transport under50mmol-L"1NaCl was attributed to a modification of the lipid membrane, and the increase in H+transport under200mmol-L-1NaCl could be because of an acid-mediated activation. Under salt stress, the activity of V-H+-ATPase and V-H+-PPase of roots and leaves was also activated in varying degrees in two physic nut ecotypes.These modulations of PM H+-ATPase, V-H+-ATPase and V-H+-PPase in the roots and leaves of physic nut, could represent a set of adaptive mechanisms to salinity. Compared with the Nanyou3, the Nanyou2maintained higher activity of theses enzymes in roots and leaves under salt stress, indirectly suggested that the ability of ionic and nutritional balance and the compartmentation Na+and Cl-into the vacuole was relatively stronger than that of the Nanyou3. Thus its ability to resist salt stress was relatively stronger than that of the Nanyou3.The results (2-5) indicate that young physic nut plants are able to cope with salt stress by maintaining stable integrity of the photochemical activity and stable leaf water status associated with stable Pn, maintaining higher antioxidant enzyme activities associated with stable membrane, activating root PM-H+-ATPase mainly through translational regulation and leaf PM-H+-ATPase mainly through transcriptional and/or post-translational regulation, associated with nutrients absorbtion and ion homeostasis, activating leaf V-H+-ATPase and V-H+-PPase associated with compartmentation the toxic ions and cytosolic pH homeostasis etc. These responses might represent a set of adaptive mechanisms employed by physic nut to cope with salt stressful conditions. Compared with the Nanyou3, the Nanyou2had better response strategies.6.10%seawater treatment had no significant effect on the growth of the Nanyou2seedling, but it enhanced the vegetative growth of the Nanyou2, and the seed production of per plant.20%sea water treatment had no significant effect on the vegetative growth and the production of per plant. However, it reduced the linolenic acid and linoleic acid content of the fatty acid, which helped to improve the quality of biodiesel feedstock.In conclusion, the kernel oil content of three physic nut ecotypes was more than60%. Thus, they were all good biodiesel feedstocks. Among these three physic nut ecotypes, the kernel oil content and biological yield of the Nanyou3was highest, and the Nanyou2was with excellent fruit characters and excellent physical and genetic characteristics, which were helpful for reducing the cost of biodiesel production.Therefore, the Nanyou3and2had the greater potential for biodiesel feedstock. Compared with the Nanyou3, the Nanyou2had a relatively high salt tolerance. Further research showed that physic nut can adapt to10%～20%sea water treatment. It has the potential to adapt to grow in the coastal area, so we can further cultivate the salt-tolerant physic nut cultivar, as the coastal mixed forest tree species for the ecological and economic use.