How do Cr and Zn modify cucumber plant re-establishment after grafting?

Abstract

Plant grafting is a propagation technique that uses two plant individuals to optimize crop production. Although physiological traits defining the growth of grafted plants have been investigated, physiological changes caused by excessive metal nutrients or non-essential metals during the early stages of grafting have been poorly characterized. Understanding such changes would contribute to the selection of rootstocks and scions more tolerant to environmental contamination with heavy metals. Our study evaluated the responses of cucumber plants (Cucumis sativus L.) grafted onto pumpkin rootstocks (Duchesne x Cucurbita moschata Duch.); and exposed to root applications of fertigation solutions with varying concentrations of zinc (10 µM [low] or 2.44 mM [excessive]), chromium (30 µM Cr [low] or 100 µM Cr [excessive]) or both metals (30 µM Cr and 10 µM Zn). Grafted plants exposed to Cr and excess Zn increased enzyme ascorbate peroxidase activity. Plants exposed to Cr exhibited lower magnesium and manganese concentrations in leaves than both the control and Zn treatments, which were associated to low carbon assimilation. On the other hand, low Zn availability improved plant growth after grafting and superoxide dismutase in stems. We verified that the heavy metals Cr and Zn did not impair cucumber plant re-establishment immediately after grafting onto pumpkin rootstock. Our study demonstrated that grafted cucumber plants can grow in environments contaminated with Cr, but will not express their complete physiological potential.