Augmentation of Antioxidant Constituents by Drought Stress to Roots in Leafy Vegetables

Abstract

<jats:p>Plants can synthesize some antioxidants, including L-ascorbic acid (AsA) and polyphenol, in response to environmental stresses. Antioxidants detoxify reactive oxygen species in plants and also aid in human health. In this study, we demonstrate that a novel hydroponic treatment can increase leafy vegetable nutritional quality without retarding growth. Leaf lettuce (<jats:italic>Lactuca sativa</jats:italic>) was grown hydroponically and subjected to rhizosphere drought stress by lowering the water level in the solution tub before harvesting. Appropriate drought stress using this method could increase AsA, polyphenol, and sugar content by 24%, 50%, and 17%, respectively, and decrease nitrate nitrogen content by 18% without reducing yield. Similar effects of drought stress on AsA content were observed in four other plant species. This hydroponic method has a universal potential to increase leafy vegetable quality without reducing yield in controlled environments such as plant factories.</jats:p>

Alterations in the Chemical Composition of Spinach (Spinacia oleracea L.) as Provoked by Season and Moderately Limited Water Supply in Open Field Cultivation

“…The significant increase of dry biomass-related ascorbic acid levels in spinach grown in 2015 (p = 0.0493) was in agreement with findings of Koyama et al [6], who demonstrated an augmentation of ascorbic acid by lower water supply in hydroponically grown leafy vegetables such as lettuce and spinach. In contrast to our study, Koyama et al [6] did not observe significant alterations in the water content.…”

“…The significant increase of dry biomass-related ascorbic acid levels in spinach grown in 2015 (p = 0.0493) was in agreement with findings of Koyama et al [6], who demonstrated an augmentation of ascorbic acid by lower water supply in hydroponically grown leafy vegetables such as lettuce and spinach. In contrast to our study, Koyama et al [6] did not observe significant alterations in the water content. In our study, by analogy to polyols, ascorbic acid levels were highest in the relatively "low light, dry" cultivation set in 2015, both in dry and fresh biomass, possibly being related to lower global irradiation, which has previously been shown to enhance ascorbic acid contents in spinach [40].…”

“…The fresh biomass-based contents of all of the studied carotenoids, i.e., violaxanthin, lutein and ß-carotene, showed significant and rather uniform increases (Table 3, Supplementary Table S1). [6] did not observe significant alterations in the water content. In our study, by analogy to polyols, ascorbic acid levels were highest in the relatively "low light, dry" cultivation set in 2015, both in dry and fresh biomass, possibly being related to lower global irradiation, which has previously been shown to enhance ascorbic acid contents in spinach [40].…”

“…Plants respond to drought stress with physiological and biochemical changes, aiming at the retention of water against a high external osmotic pressure and the maintenance of photosynthetic activity, while stomatal opening is reduced to counteract water loss [5]. While severe drought stress often results in clearly unmarketable crops, mild and moderate limitations in water supply induce more subtle changes and have earlier been considered to even enhance the formation of health-promoting antioxidant constituents in leafy vegetables [6]. However, this effect is highly plant-specific.…”

Tolerance of Seedlings From Different Lettuce Genotypes to Irrigation With Water of High Salt Content

“…Por otro lado se ha encontrado que cuando las plantas de lechuga son sometidas a estrés salino (Kohler et al, 2009) o sequía (Koyama et al, 2012) se observan variaciones en el contenido de sustancias antioxidantes. Así una variedad de lechuga tolerante al NaCl muestra un mejor comportamiento en su crecimiento y en su capa cidad antioxidante que una variedad sensible.…”