RESUMO
The effect of exogenously applied silicon (Si) on plant growth, lipid peroxidation, total phenolic compounds and non-protein thiols was studied in two maize varieties (Zea mays L. vars. Kneja 605, 434) differing in sensitivity to excess manganese (Mn). Based on the density of brown spots per leaf area and relative shoot weight (RSW) used to define Mn tolerance var. Kneja 434 was found to be more Mn-tolerant than Kneja 605. The lipid peroxidation level and total phenolic compounds were enhanced with increasing Mn concentration in the nutrient solution. In addition, the Mn-sensitive var. Kneja 605 with markedly expressed first visible Mn toxicity symptoms had higher levels of total phenolic acids than var. Kneja 434 thus supporting the hypothesis that a stimulating effect of Mn on phenol content reflected rather a stress response to Mn excess than a tolerance mechanism. In contrast, non-protein SH content increased to a higher extent in the Mn-tolerant var. Kneja 434. The increased amount of non-protein SH compounds was accompanied by a much stronger oxidative stress in the Mn-sensitive plants when compared with the Mn-tolerant variety, thus suggesting that non-protein SH compounds may play a role in Mn tolerance in maize. The addition of silicon (Si) reduced the density of brown spots per leaf area as well as lipid peroxidation level and improved plant growth in Mn-treated plants.
