Nutritional status and root morphology of tomato under Cd-induced stress: Comparing contrasting genotypes for metal-tolerance

Cadmium (Cd) is an environmental pollutant that limits crop production. Among the deleterious effects by metal induced stress on plant development, cell leakage and nutrient losses have been observed, whereas root morphology is severely affected. However, the mechanisms by which genotypes contrasting in tolerance level to heavy metal excess maintain root cells integrity and nutrient absorption are still unclear. In this work, tomato (Salaam lycopersicum) genotypes with contrasting tolerance to Cd toxicity, Calabash Rouge (sensitive) and Pusa Ruby (tolerant), were used to shed some light on possible tolerance mechanisms against Cd toxicity. For this purpose, plants were grown in hydroponics containing 0 or 35 mu M CdCl2 for 7 days. Temporal variations (on the 1st, 4th and 7th days of Cd exposure) in nutrient management (absorption and use efficiency), relative plant growth, biomass partitioning, root morphology and Cd accumulation were evaluated in control and Cd-treated plants. Furthermore, multivariate analyses, in which information about the antioxidant machinery was also included, were performed in order to identify the set of parameters related to plant tolerance. The results showed that Pusa Ruby was able to improve biomass allocation to roots, further increasing their capacity to accumulate this metal. The tolerant genotype was also more capable to modulate nutrient uptake by roots under Cd excess. In conclusion, the current study revealed that Pusa Ruby is more tolerant to Cd exposure than Calabash Rouge due to its ability in reducing Cd-induced damages on root morphology and on nutrient absorption and use efficiency.