Chemical Synthesis Of 5-Aminolevulinic Acid (ALA) And Its Effects On Salt Tolerance Of Strawberry And Watermelon Plants

In recent years, as a new photodynamic compound, it has been proposed that 5-aminolevulinic acid (ALA) has a very important role in medicine and agriculture. For example , it is helpful to diagnose or cure skin and ophthalmic diseases as well as some kinds of cancers, such as bladder cancer, enteron cancer, lung cancer etc. In addition, ALA level can be used as the standard to estimate lead poisoning. In agriculture, ALA may act as insecticide and herbicide; and it can also increase crop yield, enhance resistance of plants to environmental stresses, so it is regarded as a new plant growth regulator and attracting more and more attention. Overseas scholars once reported that when ALA was dissolved, it was found to be unstable, however, the stability properties were not presently well described in the literature. Salt tolerance of cotton, cowpea and spinach could be improved by ALA treatment, but up to now, articles about effects of ALA on fruit plants can not be easily seen yet.In this work, firstly, chemical synthesis of ALA was tested and it's stability was studied in aqueous solution as a function of concentration, pH and temperature, and then whether ALA treatment could enhance salt tolerance of strawberry and improve germination of watermelon seeds and growth of its seedlings were investigated. The main results were as follows:1 Synthesis of 5-aminolevulinic acid from levulinic acid The route for the synthesis of ALA from levulinic acid was introduced accompanied with mild reaction conditions, low toxicty, simply manipulation and environment friendly. It was a simple way to synthesize ALA.2 Stability of 5-aminolevulinic acid The results showed that the higher the concentration, pH and storage temperature, the faster the degradating rate of ALA, the more unstable ALA was. Therefore, ALA should be stored in the form of original crystal or powder and kept in dry, shady and cool place with package tightly closed. When ALA was dissolved, the pH and concentration of solution should be as low as possible, and used in one time, especially not mixed with alkaline reagents.3 Effects of ALA on strawberry under salt stress Under normal (0 mmol ? L-1 NaCl Conditions, 3 day after 150 mg · L-1 ALA pretreatment, CAT, POD activities and net photosynthetic rate of leaves were significantly increased; 3rd day after 0.3% NaCl treatment, compare to ALA pre-treated ones, in the leaves of non-ALA pre-treated, SOD activity significantly decreased while production rate of O2- increased remarkably; 9th day after NaCl treatment, CAT, POD activities and net photosynthesis rate of ALA pre-treated young plant leaves were significantly higher than that of non-ALA pre-treated. These results indicated that the protection against oxidative damage by higher levels of enzyme activities, and by increase of the photosynthesis, could be involved in the increased salt tolerance observed in strawberry by treatment with 150 mg ? L-1 ALA with NaCl.4 Effects of ALA on watermelon seed germination under salt stress When NaCl concentration was high up to 100 mmol ? L-1, seed germination and seedling growth of watermelon were significantly inhibited. However, treatment with 30 mg ? L-1ALA could promote seed germination and seedling growth even under higher salt stress (125 mmol ·L-1 NaCl ). The results also showed that the activities of SOD and POD in hypocotyls and radicles were increased, while the production rate of O2-, MDA content and LOX activity were decreased remarkably when treated with 30 mg ? L-1 ALA. Adding with AsA (lg · L-1), a POD activity inhibitor, the promotion of ALA was significantly inhibited. These results indicated that the promotion of exogenous ALA treatment on germination under salt stress might be associated with the increased activities of the antioxidases.