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Article|17 May 2022|OPEN
Impairment of root auxin–cytokinins homeostasis induces collapse of incompatible melon grafts during fruit ripening
Maria Dolores Camalle1 , Ales Pˇ enˇ cík2 , Ondrej Novák2 , Lina Zhao1 , Udi Zurgil3 , Aaron Fait3 and Noemi Tel-Zur,3 ,
1The Albert Katz International School for Desert Studies, The Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus 8499000, Israel
2Laboratory of Growth Regulators, Faculty of Science, The Czech Academy of Sciences, Palacký University & Institute of Experimental Botany, Slechtitel ˇ u 27, ˚ CZ-783 71 Olomouc, Czech Republic
3French Associates Institute for Agriculture and Biotechnology of Drylands, Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus, P.O.B. 653, Beer Sheva 84104000, Israel
*Corresponding author. E-mail: telzur@bgu.ac.il

Horticulture Research 9,
Article number: uhac110 (2022)
doi: https://doi.org/10.1093/hr/uhac110
Views: 39

Received: 17 Mar 2022
Accepted: 23 Apr 2022
Published online: 17 May 2022

Abstract

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, YUC2YUC6, 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 induces 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.