Drought appears at flowering and boll formation for cotton frequently. However, reports on the impact of carbon dynamics in the subtending leaf on boll biomass under periodic droughts are limited. To investigate this, experiments were carried out with two cultivars (drought-tolerant: Dexiamian 1; drought-sensitive: Yuzaomian 9110), three water levels [soil relative water content (SRWC): control (75 ± 5)%, moderate drought (60 ± 5)%, severe drought (45 ± 5)%] and five drought durations (10, 17, 24, 31 and 38 days). A 38-day drought declined the net photosynthetic rate of subtending leaf, which could be collectively attributed to the reduction in carboxylation with reduced ribulose-1,5-bisphosphate carboxylase activity, and stomal limitation with decreased stomatal conductance, along with the damage of photosynthetic apparatus with depressed maximum and actual photochemical quantum yield, leading to lower starch content. A 38-day drought also increased the activities of sucrose phosphate synthase (SPS), sucrose synthase (Susy) and expressions of genes (GhSPS1, GhSPS2, GhSusA and GhSusB) associated with these enzymes, causing the accumulation of sucrose content, finally resulting in lower boll biomass. Some of the above parameters fully recovered under more than 17-day moderate drought or over 10-day severe drought, but boll biomass still decreased after re-watering. Under 10-day moderate drought, all aforementioned indices and boll biomass were completely recovered within 7 days of re-watering, and the recovery capacity of Yuzaomian 9110 was lower than that of Dexiamian 1. Therefore, rapid recovery of photosynthesis and decline in the subtending leaf sucrose content to pre-stress levels are important factors in lessening the impacts of drought on boll biomass and are indicative of cultivar tolerance to short-term moderate water deficit.

中文翻译：

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土壤干旱持续时间和严重程度通过改变恢复时间和对向叶的碳动态影响棉铃生物量

棉花开花结铃期经常出现干旱。然而，关于周期性干旱下对向叶中碳动态对棉铃生物量影响的报道有限。为了研究这一点，对两个品种（耐旱：德霞棉 1；干旱敏感：玉早棉 9110）、三个水分水平 [土壤相对含水量 (SRWC)：对照 (75 ± 5)]、中度干旱（ 60 ± 5)%，严重干旱 (45 ± 5)%] 和五个干旱持续时间（10、17、24、31 和 38 天）。38 天的干旱降低了对向叶的净光合速率，这可以共同归因于羧化作用的减少和核酮糖-1,5-二磷酸羧化酶活性的降低，以及气孔受限和气孔导度的降低，随着最大和实际光化学量子产率降低的光合作用装置的损坏，导致淀粉含量降低。38 天的干旱也增加了蔗糖磷酸合酶 (SPS)、蔗糖合酶 (Susy) 和基因表达的活性 (GhSPS1、GhSPS2、GhSusA和GhSusB) 与这些酶相关，导致蔗糖含量的积累，最终导致较低的棉铃生物量。上述部分参数在17天以上中度干旱或10天以上重度干旱下完全恢复，但复水后棉铃生物量仍有下降。在10天的中度干旱条件下，上述指标和棉铃生物量在复水7天后全部恢复，玉早棉9110的恢复能力低于德霞棉1号，因此光合作用恢复快，对向性下降叶片蔗糖含量达到胁迫前水平是减轻干旱对棉铃生物量影响的重要因素，并且表明品种对短期中度缺水的耐受性。