Study Of Physiological And Biochemical Roles Of The Different Forms Of Boron On Wheat Seedlings

The effects of sorbitol-boric acid (SB) and boric acid (BA) on the boron contents of different organs, the activities of major antioxidant enzymes(superoxide dismutase, SOD; peroxidase, POD, and polyphenoloxidase, PPO), soluble proteins content and chlorophyll fluorescence parameters (Fo, Fm, Fv, Fo', Fm', Fv', qP,ΦPSⅡ, ETR and NPQ) of wheat (Triticum aestivum L Huaimai 19) seedlings which were cultured in Hoagland nutrient solution without boron were investigated in the article. Comparative analysis of the effects of these two different forms of B, the differences of absorption, utilization and physiological and biochemical effects of them, as well as the mechanism of boron's function in wheat seedlings were studied. Also we studied the effects of the different concentrations of sorbitol on wheat seedlings. So a scientific basis of developing a new type of boric fertilizer could be provided.The results showed that (1) Wheat seedlings could significantly absorb the two forms of B added in the nutrient solution. B contents in roots, stems and leaves of wheat seedlings were increased significantly with the increasing concentrations of B in culture solution. And the B content in stems was the highest. B contents in roots and leaves treated with SB were increased more greatly than treated with BA. SB significantly improved B contents in wheat seedlings organs, but BA did not improve significantly in the treatments with foliar spraying of them. So we speculated that, compared to BA, SB was more advantageous to be absorbed and transported by wheat seedlings. (2) B deficiency resulted in the increase of SOD, POD and PPO activities and decrease of soluble protein content. Their activities could be significantly reduced and soluble protein content could be significantly increased by two forms of B treatments. The effects were significant in treatments with 0.1-20.0μM SB. But the effect of BA achieved a better result when its concentration was 10.0μM. And 20.0μM BA had poisonous effect on wheat seedlings growth. (3) When the concentrations of the two forms of B in culture solution were less than 20.0μM, the quantum yield of electron transfer at PSⅡ(ΦPSⅡ), photochemical quenching coefficient (qP) and electron transfer rate (ETR) values were increased with the increase of their treatment concentrations. These parameters were increased more significantly in the treatment with SB. These were perhaps because that B could promote the transport of carbohydrates in the phloem, prevent the accumulation of photosynthetic products, and improve the utilization of light energy. And SB was more easily translocated than BA in wheat seedlings. (4) 0.1-20.0μM sorbitol treatments had no impact on biomass of wheat seedlings cultured in Hoagland nutrient solution without B. But also the soluble protein content was significantly improved, and SOD, POD and PPO activities were significantly decreased in the leaves of wheat seedlings.ΦPSⅡand ETR values were also significantly increased in the10.0μM sorbitol treatment. These indicated that the concentrations of sorbitol did not affect the growth of wheat seedlings, but could ameliorate the negative effects of B deficiency on the wheat seedlings to some extent.The effects of different concentrations of SB supplied to the nutrient solution on wheat seedlings grown under salt stress were also investigated in the article. The results showed that: When plants grown at 100 mM NaCl, the fresh weight and water content were significantly decreased, Na+ and K+ concentrations, MDA, SOD and PPO activities were significantly increased significantly, and POD activity did not be changed significantly. And NaCl stress significantly lowered B contents in wheat seedling roots, stems and leaves; especially the decreased degree in the roots was more significant. Under salt stress, supplementary 1.0μM SB significantly reduced Na+ concentration and increased K+ concentration in the wheat seedlings leaves. So it could maintain a certain K+/Na+ in plants. Also the SOD activity was significantly increased; MDA content was significantly reduced in 1.0μM SB treatment. Supplying 10.0μM SB, the fresh weight and water content of wheat seedlings were increased by 11.50% and 11.49% respectively; PPO activity was significantly reduced; andΦPSⅡ, qP values were significantly increased. The results indicated that SB could ameliorate the negative effects of NaCl stress on the wheat seedlings.