| The dynamic change of non-structural carbohydrates(NSC) and carbon metabolism enzymes in cotton bolls might have significant impact on lint and seed yields. The objective of this research was to investigate how NSC and carbon metabolism enzymes in the two fractions of cotton boll(fibers,embryos) fluctuated for various nitrogen rates applications(high nitrogen, medium nitrogen, low nitrogen). The difference among the three treatments was compared for NSC concentrations and carbon metabolism enzyme activities, and its relationship to boll characters was evaluated.Cotton line with high fiber quality A001 was chosen in this study, which was bred by Jiangxi Agricultural University. A field experiment was conducted at the Agricultural experimental station,Jiangxi Agricultural University Nanchang in 2014. The experimental design used was a randomized complete block with three replicates. Each plot consisted of five rows, which were 10 m in length and1 m apart from each other. Plant-to-plant distance of 0.4 m was maintained. The three treatments were: high nitrogen(520 kg/hm2), medium nitrogen(260 kg/hm2) and low nitrogen(65 kg/hm2).Control of insects and weeds, and furrow irrigation were given as needed during the growing season with an attempt to minimize plant stress and optimize yield. On the day of anthesis during full-blossom period, white flowers were tagged. Boll samples were brought to the laboratory, where burs, fibers and seeds were immediately separated from the boll samples and dried at 110℃ 30 min and then at 50℃ to constant weight. These tissues were ground with a mill until they could pass through a 32-mesh sieve for analysis of non-structural carbohydrates(glucose, fructose, sucrose and starch). The remaining fresh samples were stored in-80℃ refrigerator in an attempt to measure carbon metabolism enzymes activity. The results were showed as below.(1) single boll weight, lint mass per boll, boll seed weight, seeds per boll and single boll shell weight were greater in high N and medium N than low N. No differ was observed between high N and medium N. there is no significant difference among the three nitrogen rates for lint percentage and lint index.(2) The sucrose concentration in fiber was higher in high N and low N than medium N during fiber cell wall thicken phase( 24 days post anthesis afterwards), but the reverse was true of hexose concentration where it was lower in high N and low N than medium N. Meanwhile, vacuole invertase in fibers exhibited the higher catalyzing activity in medium N than high N and low N. This is in accordance with the change of sucrose and hexose concentrations in fibers.(3) the starch concentration in embryos presented a declining tendency with the maximum occurring at 17 DPA, when it was higher in medium N than high N and low N. no differ was found for those nitrogen rates at 24 DPA afterwards. The sucrose concentration in embryos peaked at 17 or 24 DPA and then declined to a minimum at 31 DPA.Thereafter, the sucrose concentration increaed in linearly, to form a second peak observed at 52 DPA.The sucrose concentration in embryos was the highest in low N, followed by medium N and high N.The reverse was true of the change of vacuole invertase for those nitrogen rates. This is might be one of the reasons of why seed weight per boll was lower in low N than medium N and high N. In addition, the activity of the cell wall invertase in seed coat was placed in order: high N > medium N >low N. |
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