Interaction between selenium and sulfur promotes alteration in the internal quality traits in green and red lettuce

The interaction between selenium (Se) and sulfur (S) was investigated in green and red lettuce grown in a hydroponic system contain-ing a basal mineral complement at contrasting levels of Se and S. The experiment aimed to evaluate the impact of Se and S supplementation on the quality traits of the lettuce, including soluble sugars, organic acids, total protein and nitrate (NO3−) to result in better lettuce yield with improving quality. The Se and S concentrations determined in the lettuce leaves showed complex dependence on the various levels of selenate (SeO42−) and sulfate (SO42−) supplied via the foliar application and the nutrient solution, respectively. The foliar application of Se resulted in a synergistic interaction between both elements. With elevated Se and S (Se2/S2), Se accumulation was enhanced drastically in red lettuce, and in green lettuce, the S concentration increased significantly. Regarding carbohydrate accumulation, including water-soluble sugars, a lower Se dose under adequate S conditions enhanced glucose levels significantly by 3.2 and 2.1-fold in green and red lettuce, respectively. A synergistic interaction between Se and S was found following higher Se and S treatment (Se2/S2), resulting in a significant (p ≤ 0.05) reduction in glucose and fructose concentrations. However, higher S strikingly increased the accumulation of the reducing sugars (glucose and fructose) by 5.3 and 3.0-fold for glucose and 3.7 and 5.6-fold for fructose in green and red lettuce, respectively. Meanwhile, sucrose increased by 2.0-fold in red lettuce and remained unaltered in green lettuce. A low nitrate level (NO3−) was maintained in response to adequate or elevated S and Se levels. Se levels (Se1 and Se2) did not affect total protein concentration under contrasting sulfate/selenate. However, potential effects in terms of protein accumulation were associated with an adequate or increased S concentration. The data suggest that lower Se and sufficient S doses significantly increase glucose levels in both pigmented lettuce cultivars. Additionally, the synergistic interaction between Se and S could benefit the final nutritional value and quality of lettuce, especially for nitrate, where Se and S enrichment can ensure low nitrate levels

The Interplay of Sulfur and Selenium Enabling Variations in Micronutrient Accumulation in Red Spinach

Aside from its importance in human and animal health, low levels of foliar-applied selenate (SeO4) can be advantageous in the presence of sulfur (S), contributing to improved growth, nutrient uptake, and crop quality. A hydroponic experiment in a growth chamber explored the interactive influence of Se and S on micronutrients and several quality indices, such as soluble sugars, organic acids, and total protein concentrations in spinach (Spinacia oleracea L.). Three levels of S (deprivation, adequate, and excessive) with varying quantities of Se (deficient, moderate, and higher) were examined in combination. Under S starvation and along with S nourishment in plant parts, Se treatments were found to cause noticeable variations in plant biomass and the concentrations of the examined elements and other quality parameters. Both Se levels promoted S accumulation in S-treated plants. Although the Se treatment had the opposite effect in shoots, it had a favorable impact on minerals (apart from Mn) in roots grown under S-limiting conditions. The S and Se relationship highlighted beneficial and/or synergistic effects for Mn and Fe in edible spinach portions. Reducing sugars were synergistically boosted by adequate S and moderate Se levels in roots, while in shoots, they were accumulated under moderate-or-higher Se and excessive S. Furthermore, the concentration of the quantified organic acids under S-deficient conditions was aided by various Se levels. In roots, moderate Se under high S application enhanced both malic acid and citric acid, while in the edible parts, higher Se under both adequate and elevated S levels were found to be advantageous in malic acid accumulation. Moreover, by elevating S levels in plant tissues, total protein concentration increased, whereas both moderate and high Se levels (Se1 and Se2) did not alter total protein accumulation in high S-applied roots and shoots. Our findings show that the high S and medium Se dose together benefit nutrient uptake; additionally, their combinations support soluble sugars and organic acids accumulation, contributing ultimately to the nutritional quality of spinach plants. Moreover, consuming 100 g of fresh red spinach shoot enriched with different Se and S levels can contribute to humans’ daily micronutrients intake