中文摘要：

【目的】从内源赤霉素代谢角度,阐明玉米大豆套作环境下,大豆苗期茎秆发生藤蔓化倒伏的原因。【方法】在大豆单作和玉米大豆套作两种种植方式下,以耐荫抗倒型大豆南豆12和不耐荫抗倒型大豆南032-4为试验材料,采用石蜡切片、液相色谱质谱联用、SYBR？GreenⅡ荧光定量PCR等方法,对茎秆形态、解剖结构、赤霉素含量、赤霉素代谢相关基因表达等进行测定和分析。【结果】与大豆单作相比,玉米大豆套作下,由于受玉米荫蔽的影响,南豆12和南032-4两个大豆材料苗期均出现典型的避荫性反应,即主茎节数减少,节间长和株高显著增加,苗期出现藤蔓化和倒伏,但两大豆材料间反应程度不同,差异极显著。与南032-4比,南豆12受套作荫蔽的影响较小,茎秆藤蔓化程度低,倒伏率仅29.93%,极显著低于南032-4（93.94%）（P〈0.05）;南032-4株高增加32.64 cm,与南豆12（22.95 cm）呈显著差异（P〈0.05）;两材料主茎节数减少,材料间无差异;南032-4中上部节间长度显著长于南豆12,说明套作下植株株高的增加来源于节间的伸长,而非节数的增多,且中部及上部节间过度伸长易导致植株茎秆藤蔓化和倒伏。从茎秆纵切面的解剖结构可知,玉米大豆套作条件下,大豆主茎细胞都有不同程度的伸长,南032-4茎秆髓部、木质部、韧皮部细胞伸长明显,而南豆12在两种种植模式下各部分细胞无明显变化,说明大豆株高的增加源于细胞的伸长,非细胞的分裂。内源赤霉素代谢分析结果表明,套作条件下,两材料茎秆内源赤霉素含量均显著降低,南豆12茎秆内赤霉素A4（GA4）的含量显著低于南032-4;对编码赤霉素代谢途径中关键酶基因表达量的分析表明,除赤霉素合成酶基因Gm GA20ox5、Gm GA3ox6和赤霉素降解酶基因Gm GA2ox4在不同种植方式和不同材料间均保持较低的水平外,茎秆中其他内源赤霉素合成酶GA-20氧化酶基因

英文摘要：

【Objective】 From the perspective of endogenous gibberellins（GAs） metabolism, the reasons of soybean seedling vine lodging under the maize-soybean relay strip intercropping system were studied.【Method】Under maize-soybean relay strip intercropping system and soybean sole cropping system, shade-tolerant and lodging resistant Nandou12 and non-shade tolerant and non- lodging resistant Nan032-4 were taken as experimental materials. The stalk morphology, anatomical structure, the level of gibberellin A4, and the genes that are concerned with gibberellins expression profiles were analyzed with the paraffin section, Gas chromatography-mass spectrometry analyses, real-time q PCR with SYBR？ Green Ⅱ and other. methods.【Result】Compared with soybean monoculture, due to the effects of maize shading at the seeding stage, both Nandou12 and Nan032-4 appeared obvious shade avoidance responses in relay strip intercropping system, including reduction of node number, significant increase of plant height and internode length, vining and lodging of the seedlings. However, the shade avoidance phenotypes were quite different between these two materials. Compared with the shade-tolerant cultivar Nandou12, the shade-sensitive Nan032-4 was influenced more seriously, for which 93.94% of the plants showed a lodging phenotype, much higher than that of Nandou12（29.93%）（P〈0.05）. The height of Nan032-4 was increased by 32.64 cm, different from that of Nandou12（22.95 cm）. The node number of stem reduced, but there was no significance between the two varieties. The upper nodes of Nan032-4 were longer than Nanou12 remarkably, that is to say, in the relay intercropping system, the increase of plant height of these two varieties resulted from internodes elongation, not from the increase of the node number, and the excessive elongation of middle and upper nodes could lead stems to vine and lodge easily. Vertical section of soybean stem revealed that the cell length of stems showed different degrees in elongation between