Sucrose metabolism in the subtending leaf to cotton boll at different fruiting branch nodes and the relationship to boll weight

SUMMARY 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 sucrose-metabolizing 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.