The formation of cotton fiber strength largely relies on continuous and steady sucrose supply to cellulose synthesis and is greatly impaired by drought. However, the effects of drought on sucrose import into fiber and its involvement in cellulose biosynthesis within fiber remain unclear. To end this, moisture deficiency experiments were conducted using two Gossypium hirsutum cultivars of Dexiamian 1 (drought-tolerant) and Yuzaomian 9110 (drought-sensitive). Fiber strength was significantly decreased under drought. The results of ¹³C isotope labeling indicated that drought notably reduced sucrose efflux from cottonseed coat to fiber, and this was caused by down-regulation of sucrose transporter genes (GhSWEET10 and GhSWEET15) in the outer cottonseed coat, finally leading to decreased sucrose accumulation in fiber. Further, under drought, the balance of sucrose allocation within fiber was disrupted by increasing the flow of sucrose into β-1,3-glucan synthesis and lignin synthesis but hindering that into cellulose synthesis in both cultivars. Additionally, glycolysis and starch synthesis were specifically enhanced by drought in Yuzaomian 9110, which further reduced the flow of sucrose into cellulose synthesis. Under drought, the cellulose deposition was decreased due to promoted cellulose degrading process in Dexiamian 1 and stunted cellulose synthesis in Yuzaomian 9110. Consequently, reduced cellulose content was measured in drought-stressed fibers for both cultivars. In summary, the inhibited cellulose accumulation caused by drought was mainly due to reduced sucrose translocation from the outer cottonseed coat to fiber, and less sucrose partitioned to cellulose synthesis pathway under the condition of intensified competition for sucrose by different metabolic pathways within fiber, finally degrading the fiber strength.

中文翻译：

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干旱限制了蔗糖从棉籽外皮到纤维的转运，并进一步抑制了棉纤维增稠过程中的纤维素合成

棉花纤维强度的形成很大程度上依赖于纤维素合成的连续稳定的蔗糖供应，并且受到干旱的极大影响。然而，干旱对蔗糖进入纤维及其参与纤维内纤维素生物合成的影响仍不清楚。为此，使用德夏棉1（耐旱）和玉早棉 9110（耐旱）两个陆地棉品种进行了缺水试验。干旱时纤维强度显着降低。¹³ C同位素标记结果表明，干旱显着减少了从棉籽皮到纤维的蔗糖外排，这是由于蔗糖转运蛋白基因（GhSWEET10和GhSWEET15）的下调引起的。) 在外棉籽皮中，最终导致纤维中蔗糖积累减少。此外，在干旱条件下，通过增加蔗糖进入 β-1,3- 葡聚糖合成和木质素合成的流量，但阻碍了这两种栽培品种的纤维素合成，从而破坏了纤维内蔗糖分配的平衡。此外，玉枣面 9110 的糖酵解和淀粉合成特别受干旱增强，这进一步减少了蔗糖进入纤维素合成的流量。在干旱条件下，由于德夏面 1 的纤维素降解过程促进和玉早面 9110 的纤维素合成受阻，纤维素沉积减少。因此，两个品种的干旱胁迫纤维中的纤维素含量均降低。总之，