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Changes of sucrose metabolism in the subtending leaf to cotton (Gossypium hirsutum L.) boll at different fruiting branch nodes (FBN) were investigated. Two cotton cultivars, Kemian 1 and Sumian 15, were grown in the field at three planting dates in 2009 and 2011. Cotton planted on different dates but experiencing similar climatic factors flowered on the same date and had similar boll opening dates, but had different FBN. In the present study, boll weight and carbohydrate content were significantly affected by both flowering date (FD) and FBN. However, only cystolic fructose-1,6-bisphosphatase (cy-FBPase) and sucrose-phosphate synthase (SPS) activities of the sucrosemetabolizing enzymes were influenced significantly by FBN, and the influence of FBN was lower with delayed FD. In general, effects of FBN on boll weight and sucrose metabolism in the subtending leaf were higher at the optimal FD (13 August) than those at later FD (9 September 2009 and 2 September 2011), and total fruiting branches were used to characterize cotton physiological age in the current study. Sucrose transport capacity (Tn) and SPS in the subtending leaf had significantly positive correlations with boll weight at 17-24 days post anthesis (DPA), a crucial period when boll weight was significantly affected. In addition, higher SPS activity was favourable for sucrose export and boll weight during boll development.

Reduced radiation from air pollutants has become a major challenge to cotton (Gossypium hirsutum L.) production. Field experiments were conducted using two cotton cultivars at three shading levels during boll development in Nanjing (32°02′ N, 118°50′ E), China, to determine the effect of shading on cotton yield and quality. Lint yield, distributions of yield within the plant and that of biomass within bolls, and the quality of fiber and seed were analyzed. Shading reduced lint yield (decreased by 17–22% and 35–38% under shading conditions S1 and S2, respectively) through reducing boll number and boll weight, but increased proportion of lint yield on the bottom five fruiting branches (FB1–5) by 2.1 to 2.4% and 3.4 to 4.3% under S1 and S2, respectively. The proportion of fiber biomass in the boll decreased significantly, whereas proportion of seed biomass increased with enhanced shading. Fiber was the most sensitive boll component to shading, the biomass of which under shading condition (S1, S2) decreased by 5.9 to 6.9% and 8.8 to 11.9%, respectively. Shading increased oil content but decreased protein content of the seed on FB3. Seed oil and protein contents on FB7 and FB12 responded opposite to those on FB3. Simultaneously, shading was advantageous to fiber length and micronaire but disadvantageous to fiber strength. The greater the shading enhanced, the more the abovementioned measurements were affected. Shading due to air pollutants alters biomass distribution within bolls and lint yield distribution within the plant. Bolls on the bottom fruiting branches are more tolerant of shading.

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