Effects of borax and sucrose on the non-structural carbohydrate content in Chinese chestnut fruit

Abstract:【Objective】Boron and sucrose are essential to plants. Boron participates in the transport of the carbohydrates in plant and thus improves the supply of organic matters. Sucrose provides materials and energy for plant growth and development and serves as a signal molecule that regulates carbohydrate metabolism. Boron and sucrose have an impact on the accumulation of the non-structural carbohydrates. Chinese chestnut (Castanea mollissima Bl.) is a major traditional commercial nut-bearing tree in China. The development of chestnut industry in China is of significant economic and ecological importance. In this study, we examined the effect of spraying borax and sucrose on the contents of boron in different forms, photosynthesis in leaves and non-structural carbohydrate content in the fruit of Chinese chestnut.【Methods】The experiment was conducted in Qianxi, Hebei province using a complete randomized block design. Fourteen-year-old Chinese chestnut‘Yanshanzaofeng'trees were selected as the experimental material. All the trees received conventional orchard care. 0.2% borax, 4% sucrose, or 0.2%borax + 4% sucrose was sprayed to the trees through during fruit set for three times. The leaves on the fruit-bearing branches in different directions of the canopy were selected 7 days after spraying. Contents of boron in different forms, photosynthesis in leaves and non-structural carbohydrate content infruit of Chinese chestnut were tested. The experimental data were processed and analyzed statistically using Microsoft Excel and SPSS 20.0.【Results】Boron in plant can be divided into three forms: soluble B, semi-bound B and bound B. The three B forms are in a dynamic balance in plants. There were significant differences in the contents of different B forms in different treatments, which had the similar pattern of soluble B > semi-bound B > bound B. The contents of the three B forms in leaves were increased at various degrees by different treatments. The contents of the three B forms were highest in borax+sucrose treatment, and those in sucrose treatment had the least difference with CK. Total B had the same trend with the three B forms. Correlation analysis showed that net photosynthetic rate was significantly positively correlated to the contents of the three B forms. Transpiration rate was significantly positively correlated to soluble B and to semi-bound B. No significant correlation existed between transpiration rate and bound B. There were significant differences in net photosynthetic rate and transpiration rate in different treatments. The highest soluble sugar content in fruit was in borax+sucrose treatment, and the soluble sugar content was increased by 64.09% compared with the control. The order of treatments according to fruit amylopectin content from high to low were borax + sucrose treatment > borax treatment > sucrose treatment, which increased anylopectin by 8.34%, 5.28%, 3.53% compared with the control, respectively. The amylose content in fruit under different treatments showed the same trend.Net photosynthetic rate and transpiration rate in leaves and the non-structural carbohydrate content in fruit in borax+sucrose treatment were the highest. Correlation analysis showed that the contents of soluble sugars, amylose and amylopectin in fruit were significantly positively correlated to net photosynthetic rate and transpiration rate in leaves. This was because that the main source of the accumulated nonstructural carbohydrates in fruit was the photosynthetic leaves. The treatments with net photosynthetic rate and transpiration rate from high to low were borax+sucrose treatment, borax treatment and sucrose treatment. The non-structural carbohydrate content in fruit was significantly positively correlated to the contents of different forms of B as well as to net photosynthetic rate and transpiration rate. The nonstructural carbohydrate content in fruit reflects the carbon supply of the whole plant. The above results showed that borax and sucrose enhanced photosynthesis in leaves of Chinese chestnut, which led to an increase in assimilation products. Spraying borax and/or sucrose improved non-structural carbohydrate content in fruit, and the highest content of non-structural carbohydrates in fruit was found in borax +sucrose treatment.【Conclusion】Spraying borax and/or sucrose increases B contents in different forms, photosynthesis in leaves, and thus non-structural carbohydrate content in fruit. Borax+sucrose treatment has the best effect on accumulation of non-structural carbohydrates in Chinese chestnut fruit.