Study On Heterosis Mechanism Of CCRI63 Based On Sink-source Relationship

By using hybrid cotton CCRI63 and its parents with exceeding close relationship as materials, this study systematically investigated physiological index difference in leaf subtending to cotton boll, boll shell and cotton fiber of CCRI63 and its parents from the―source‖and ―sink‖ to provide a theoretical basis about heterosis mechanism from physiological and biochemical aspects. The main results were as follows:1. The heterosis physiological indexes of leaf subtending to cotton boll were analyzed. The results showed that the soluble sugar content of CCRI63 had significant heterosis in the whole cotton boll development period. In addition, the net photosynthetic rate(Pn), transpiration rate(Tr), chlorophyll content(CHL), starch content, soluble protein content, amino acid content, C/N, the activity of sucrose synthase(SS), sucrose phosphate synthase(SPS), superoxide dismutase(SOD) and malondialdehyde content(MDA) of CCRI63 also had significant heterosis in the late development stage of cotton boll. The results proved the mechanism of heterosis of CCRI63’s leaf subtending to cotton boll: there were higher physiological activity and function in the late cotton boll development stage, so the leaf subtending to cotton boll could synthesize more photosynthetic products and efficiently transport to cotton bolls.2. The heterosis physiological indexes of boll shell were analyzed. The results showed that the boll shell weight of CCRI63 and its parents were all rising rapidly at early stage and then declining slowly. The boll shell weight of CCRI63 didn’t had obvious heterosis and the boll shell rate of CCRI63 was lower than the parents. Through analysis of soluble sugar, sucrose and starch content of boll shell, CCRI63 significantly lower than its parents and had significant difference in the late cotton boll development stage. The results could be inferred that the most nutrients of CCRI63’s boll shell transported to the seed cotton in the late cotton boll development stage. It proved that the boll shell of the CCRI63 had higher nutrient transport efficiency than its parents.3. The heterosis of physiological indexes of boll fiber were analyzed. The results showed that CCRI63’s single boll weight, soluble sugar and sucrose content were significantly higher than its parents but malondialdehyde content was lower than its parents in the whole cotton boll development period. In addition, the soluble protein content, the activity of sucrose synthase(SS), sucrose phosphate synthase(SPS) and superoxide dismutase(SOD) of CCRI63 significantly higher than its parents in the late cotton fiber development period. The result implied that CCRI63’ cotton fiber had higher physiological activity, lower degree of membrane lipid peroxidation and longer function period. So, CCRI63 can be more durably and efficiently absorb the nutrients from leaf subtending to cotton boll and finally obtain higher fiber production.In summary, the high yield heterosis mechanism of CCRI63 was inferred from the "source" and "sink" level. Compared with its parents, the leaf subtending to cotton boll of CCRI63 had higher physiological activity, lower degree of membrane lipid peroxidation and longer function period in the late cotton boll development stage. These advantages of leaf subtending to cotton boll can make them more durable compound photosynthetic products. The photosynthetic products transport to the cotton fiber through boll shell which can be called "transfer station". Cotton fiber of CCRI63 also had higher physiological activity, lower degree of membrane lipid peroxidation and longer function period in the late cotton boll development stage. Therefore, it can be more durably and efficiently absorb the nutrients from leaf subtending to cotton boll and bollshell. Which all of those made CCRI63’s high boll weight and its significant heterosis in high yielding.