The factors underlying the plant collapse of certain melon-pumpkin graft combinations are not fully understood. Our working hypothesis was that impairment of photoassimilates transport in incompatible combinations induces an imbalance in the homeostasis of root auxin (indole-3-acetic acid; IAA) and of cytokinins, probably triggering plant collapse. Root IAA and cytokinins levels in the presence and absence of fruit and changes in root and scion metabolites were investigated in compatible and incompatible combinations. We showed elevated levels of IAA, 2-oxoindole-3-acetic acid (IAA catabolite), indole-3-acetylaspartate (IAA conjugate), and cis-zeatin-type cytokinins, but low levels of trans-zeatin-type cytokinins in the roots of plants of the incompatible combination during fruit ripening. Similarly, during fruit ripening, the expression of the YUCCA genes, YUC2, YUC6, and YUC11 (required for auxin biosynthesis), the GRETCHEN-HAGEN3 gene (required for auxin conjugation), and the cytokinin oxidase/dehydrogenase 7 (CKX7) gene (regulates the irreversible degradation of cytokinin) was enhanced in the roots of plants of the incompatible combination. Moreover, in the incompatible combination the fruiting process restricted transport of photoassimilates to the rootstock and reduced their accumulation in the scion. In addition, high levels of hydrogen peroxide and malondialdehyde and reduced activity of antioxidant enzymes were observed in the roots of the incompatible graft. Our results showed that the collapse of the incompatible graft combination during fruit ripening is closely associated with a dramatic accumulation of IAA in the roots, which probably elicits oxidative damage and disturbs the balance of IAA and cytokinins that is of critical importance in melon-pumpkin graft compatibility.

中文翻译：

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根系生长素-细胞分裂素稳态受损导致果实成熟过程中不相容的甜瓜移植物塌陷

某些甜瓜-南瓜嫁接组合导致植物倒塌的因素尚未完全清楚。我们的工作假设是，不相容组合中光同化物运输的损害会导致根生长素（吲哚-3-乙酸；IAA）和细胞分裂素的稳态失衡，可能引发植物崩溃。在相容和不相容组合中研究了果实存在和不存在时的根 IAA 和细胞分裂素水平以及根和接穗代谢物的变化。我们发现 IAA、2-氧吲哚-3-乙酸（IAA 分解代谢物）、吲哚-3-乙酰天冬氨酸（IAA 偶联物）和顺式玉米素型细胞分裂素水平升高，但反式玉米素型细胞分裂素水平较低。不相容组合的植物在果实成熟过程中的根部。同样，在果实成熟过程中，YUCCA 基因、YUC2、YUC6 和 YUC11（生长素生物合成所需）、GRETCHEN-HAGEN3 基因（生长素结合所需）和细胞分裂素氧化酶/脱氢酶 7 (CKX7) 基因（调节细胞分裂素不可逆降解）的表达) 在不相容组合的植物的根中得到增强。此外，在不相容的组合中，结果过程限制了光同化物向砧木的运输，并减少了它们在接穗中的积累。此外，在不相容移植物的根部观察到高水平的过氧化氢和丙二醛以及抗氧化酶活性降低。我们的研究结果表明，果实成熟过程中不相容嫁接组合的崩溃与根中 IAA 的急剧积累密切相关，