黄土高原旱塬区短枝型苹果对N素的吸收规律及对果实C代谢的调控机理

Longdong Loess Plateau is one of the high-quality producing areas of apple production in China. Tianshui is the largest area in the field of Red Delicious spur type apple cultivation in China, and the mode of dry dwarf culture and compact planting of “rooted stock + spur type” was established. However, the application of nitrogen fertilizer is high, the utilization rate is low, the fruit quality is reduced, etc. In this study, based on the special climate and soil conditions, the spur apple cultivar "Qregan spur II" was used as the experimental material, and the 15-N isotope tracer method was used to determine its absorption and utilization of nitrogen. The effects of nitrogen application rate and nitrogen application time on nitrogen metabolism and carbon metabolism related enzymes, endogenous hormones, growth and development, yield and quality were studied to determine the suitable nitrogen application rate and nitrogen application period. The mechanism of the regulation of C metabolism in fruit was clarified by the modern biological means such as fruit transcriptome (RNA-seq) and metabolomics (Non-targeted LC-MS), which was provided a theoretical basis for the quality of spur type apple in the arid Loess Plateau.

陇东黄土高原是我国苹果生产的优质产区之一，天水是我国元帅系短枝型苹果栽培面积最大的区域，该区域已建立“乔化砧+短枝型品种”的旱作矮化密植栽培模式。然而，氮肥施用量高、利用率低、果实品质降低等生产问题突出。本研究针对该区特殊的气候与土壤条件，以短枝型苹果品种‘俄矮2号’为试验材料，采用15-N同位素示踪法，明确短枝型品种对氮素的吸收和利用规律。通过施氮量和施氮时期对果实氮代谢和碳代谢相关酶、内源激素、生长发育、产量与品质等方面的影响，确定适宜的施氮量和施氮时期。结合果实转录组（RNA-seq）、代谢组学（非靶向LC-MS）等现代生物学手段，阐明N素对果实C代谢的调控机制，为黄土高原旱塬区短枝型苹果品质提升提供理论依据。

为揭示黄土高原地区氮素对短枝型苹果果实品质形成的调控机理，设置不同施氮量和施用时期，基于转录组学和分子生物学技术手段，揭示旱作条件下苹果氮素对品质的调控机制。结果表明，300 kg/hm-2的氮肥处理可显著提高膨大期和成熟期苹果的果糖和葡萄糖含量。600 kg/hm-2的氮肥处理可显著整个生育期的蔗糖含量。150和300 kg/hm-2的氮肥处理可显著提高幼果期山梨醇含量。此外，300 kg/hm-2的氮肥处理可显著提高苹果产量。幼果期、果实膨大初期和果实膨大后期施氮肥，均不同程度提高了单果重、果实硬度和果形指数，在采收期时，单果重和果实硬度均以果实膨大初期施氮肥最高，果形指数在果实膨大后期施氮肥最高。果实膨大后期施氮肥，采收期果实可溶性固形物、果糖、葡萄糖和山梨醇含量最高。转录组数据中筛选到响应氮素且调控糖代谢的转录因子MdbZIP44，亚细胞定位分析发现，MdbZIP44是核定位蛋白。组织特异性表明，它在苹果果实中的表达量最高。通过转化番茄和苹果愈伤，发现氮素处理可显著提高 MdbZIP44过表达植株的淀粉含量，降低其葡萄糖含量。此外，还可提高糖代谢相关酶的活性和糖代谢相关基因的表达量。通过蛋白与DNA互作试验，发现MdbZIP44会调控Mdα-GP2基因的表达；通过蛋白与蛋白互作试验，发现MdbZIP44的互作蛋白是MdCPRF2-like,且它们会共同调控Mdα-GP2基因的表达。从分子水平上揭示了N 素对短枝型苹果果实碳水化合物积累的分子调控机理。