Abstract
UV radiation plays an important role not only in plant growth and development but also in the accumulation of essential nutrients and health-promoting phytochemicals in plants. The main objective of this study was to examine the effects of supplemental UV-A, UV-B, and UV-AB on the nutritional quality of lettuce (Lactuca sativa, cv. red leaf “New Red Fire” and green leaf “Two Star”) and tomato (Solanum lycopersicum L., cv. BHN-589) grown in a greenhouse. Supplemental UV radiation was provided by UV lamps 5 - 6 days prior to harvest. Supplemental UV-A produced higher accumulation of total phenolic compounds and higher antioxidant capacity in red leaf lettuce compared to other treatments. Overall, supplemental UV-A produced a stronger response than other UV treatments and control in the accumulation of many phenolic compounds including luteolin-7-glucoside, quecetin-3-glucoside, and apigenin-3-glucoside in red leaf lettuce. However, UV-B and UV-AB had a negative response in the accumulation of many phenolic compounds including chlorogenic acid, luteolin-7-glucoside, quercetin-3-glucoside, and apigenin-3-glucoside in both red and green leaf lettuce varieties. In tomato fruits, supplemental UV-A had no effect on their total phenolic concentration. However, supplemental UV-B radiation for 3 h or UV-AB radiation for 9 h exposure produced higher total phenolic concentration in the fruits compared to other supplemental UV treatments. Supplemental UV-AB (3 hexposure) was generally more effective than other UV treatments in increasing the accumulation of a number of phenolic compounds including chlorogenic acid, caffeic acid, chicoric acid, luteolin-7-glucoside, and other flavonoids in ripe tomato fruits. Supplemental UV-A produced higher accumulation of carotenoids including lutein and β-carotene than other supplemental UV treatments, while supplemental UV-AB increased the accumulation of lycopene in fully ripe tomatoes. With regard to the essential nutrients, green leaf lettuce was more responsive to the supplemental UV treatments than red leaf lettuce. All the supplemental UV treatments produced an increase in protein concentration in the leaves of green leaf lettuce. However, supplemental UV-AB produced a stronger response compared to the control and other UV treatments in increasing the accumulation of many nutrients including protein, phosphorus, potassium, sulfur, and zinc in green leaf lettuce “Two Star”. Supplemental UV-treatments did not affect the accumulation of any essential nutrients in fully ripe tomato fruits. The results show that supplemental UV enhances the nutritional quality of lettuce in relation to both health-promoting phytochemicals and essential nutrients. Similarly, supplemental UV enhances nutritional quality in tomato fruits with higher accumulation of both phenolic compounds and carotenoids than does the control treatment.
Highlights
UV radiation (UV-A and UV-B) plays an important role in the growth and development of plants [1] [2]
The results from our study suggest that supplemental UV treatment, especially (UV-A and UV-AB), of tomato plants just prior to harvest has a beneficial impact on the accumulations of key carotenoids such as lycopene, lutein and β-carotene that play an important role in maintaining eye health, in reducing the risks of some cancers, and in maintaining the overall health and wellbeing in humans [41] [42]
Supplemental UV-A enhanced the accumulation of many phenolic compounds such as chlorogenic acid, luteolin-7-glu, quercetin-3-glu, and apigenin-3-gluc in red leaf lettuce
Summary
UV radiation (UV-A and UV-B) plays an important role in the growth and development of plants [1] [2]. UV-radiation, especially UV-B, can induce reactive oxygen species, which can be damaging to many organelles and macromolecules and impair photosynthetic function leading to reduced growth [7] [8]. UV radiation can induce a plethora of phenolic compounds, especially flavonoids which protect plants against high doses of UV-B but as they are antioxidants they have health-promoting qualities. They are known to reduce the risk of many common chronic and degenerative diseases including cardiovascular diseases, cancers, diabetes, and arthritis; more importantly they promote overall health in humans [10] [11].
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