Abstract
Physiological, biochemical, metabolite changes, and gene expression analysis of greenhouse tomato (Solanum lycopersicum L.) were investigated in two grafting combinations (self-grafted ‘Ikram’ and ‘Ikram’ grafted onto interspecific hybrid rootstock `Maxifort'), with and without arbuscular mycorrhizal (AM), exposed to 0 and 25 μM Cd. Tomato plants responded to moderate Cadmium (Cd) concentration by decreasing yield and crop growth parameters due to the accumulation of Cd in leaf tissue, inhibition of the PS II activity, reduced nutrients translocation, and also to the oxidative stress as evidenced by enhanced hydrogen peroxide (H2O2) generation, ion leakage, and lipid peroxidation. AM inoculation significantly enhanced the metal concentration in shoots and reduced growth and yield. The Ikram/Maxifort combination induced higher antioxidant enzymes, higher accumulation of proline and reduction of lipid peroxidation products. This suggests that the use of Maxifort rootstock in tomato has a high reactive oxygen species scavenging activity since lower H2O2 concentrations were observed in the presence of Cd. The higher crop performance of Ikram/Maxifort in comparison to Ikram/Ikram combination was also due to the improved nutritional status (higher P, K, Ca, Fe, Mn, and Zn) and increased availability of metabolites involved in cadmium tolerance (phytochelatin PC2, fructans, and inulins). The up-regulation of LeNRAMP3 gene in leaf of Ikram/Maxifort could explain the better nutritional status of interspecific grafting combination (higher Fe, Mn, and Zn).
Highlights
Cadmium (Cd) is the most hazardous heavy metal element for plant growth with high toxicity even at low level (5–10 μg g−1dry weight; Dong et al, 2006; White and Brown, 2010)
When averaged over Cd concentration, tomato plants grafted onto Maxifort rootstock had more root colonization (77%) than self-grafted inoculated ones (67%)
Growth and yield of tomato was restricted by the application of moderate levels of Cd, which could occur in vegetable production systems
Summary
Cadmium (Cd) is the most hazardous heavy metal element for plant growth with high toxicity even at low level (5–10 μg g−1dry weight; Dong et al, 2006; White and Brown, 2010). In tomato plants, excess Cd causes inhibition of chlorophyll and carotenoids biosynthesis and substantial inhibition of the photosystem (PS) II activity. It causes significant alteration in nutrient uptake and translocation of K, Ca, Mg, Mn, Fe, and Zn (Djebali et al, 2005; Dong et al, 2006; Hèdiji et al, 2010; Bertoli et al, 2012). At low Cd concentrations in soil or water, these visible symptoms are less marked, but various cellular processes may still be affected (Smeets et al, 2005; Gratão et al, 2008; Hèdiji et al, 2010). These include, among others, proline, ascorbate, carotenoids, glucosinolates, and phytochelatinsas well as phytohormones
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