Temporary reduction of radiation does not permanently reduce flavonoid glycosides and phenolic acids in red lettuce

Abstract

Applying transparent daytime screens in greenhouses in cool seasons reduces the amount of energy needed for heating, but also the solar radiation available for crops. This can reduce yield and product quality of leafy vegetables because of constrained photosynthesis and altered biosynthesis. To study this, we cultivated five-week old red leaf lettuce (Lactuca sativa L.) for four weeks in growth chambers under a photosynthetic photon flux density (PPFD) of 225 and 410 μmol m(-2) s(-1), respectively. Some plants were exchanged between radiation intensities after two weeks. We investigated the concentration of five flavonoid glycosides, three caffeic acid derivatives, reducing sugars as well as plant growth. Remarkably, no significant influence of radiation intensity on the concentration of phenolic acids or anthocyanin glycosides was observed. In contrast, quercetin and luteolin glycoside concentration was between 14 and 34% lower in plants growing under lower compared to higher PPFD. Already after two weeks of cultivation, plants grown under lower PPFD contained less quercetin and luteolin glycosides but they completely compensated if subsequently transferred to higher PPFD until harvest. Hence, marketable lettuce heads which experienced temporary shading followed by an unshaded phase did not contain lower concentrations of flavonoid glycosides or phenolic acids. Also, there was no reduction of head mass in this variant. Our results suggest that saving energy in early growth stages is feasible without losses in yield or health promoting phenolic substances. In addition, there was a close correlation between the concentration of reducing sugars and some flavonoid glycosides, indicating a close metabolic connection between their biosynthesis and the availability of carbohydrates.

Species-specific differences in synthesis of flavonoids and phenolic acids under increasing periods of enhanced blue light

“…The red leaf lettuce is known to be rich in quercetins and chlorogenic acid (Crozier et al, 2000;Arabbi et al, 2004;Becker et al, 2013). Total phenols, chlorogenic acid and anthocyanin concentrations in the seedlings of this cultivar were found to be significantly higher under bluecontaining LEDs (Johkan et al, 2010).…”

“…There may exist a direct link between blue light biosynthesis of certain phenylpropanoids through photosynthesis. Becker et al (2013) showed a close correlation between quercetin-glycosides concentrations with the reducing sugar concentration indicating that glucose might directly increase glucosylation of certain flavonoid aglycones to their glucosides. Accordingly, concentrations of two quercetin-glucosides increased in red leaf lettuce under supplemental blue light ( Table 2).…”

“…Cichoric acid and rosmaric acid exist naturally as major phenolic compounds in lettuce (Rajashekar et al, 2012;Becker et al, 2013) and basil (Lee and Schlagel, 2009;Taulavuori et al, 2013), respectively. In accordance with previous studies, cichoric acid was the most abundant phenolic compound found in red leaf lettuce (Table 2) and similarly rosmaric acid in basil (Table 3).…”

Nutrient solution composition and growing season affect yield and chemical composition of Cichorium spinosum plants

“…This result could be further justified by a previous study of the authors where significant differences between various ecotypes of C. spinosum were reported in terms of nutritional value and chemical composition. Similarly, Becker et al (2014Becker et al ( , 2013 reported that the effect of radiation intensity on phenolic compounds composition of lettuce plants is compound dependent and apart from environmental factors, plant ontogeny is also important. In another study, Pérez-López et al (2015) also observed that lettuce plants treated with high light intensities contained higher concentrations of carotenoids, glutathione, total phenols and anthocyanins, which was also the case in our study regarding total phenolic compounds content.…”

“…Moreover, Bonasia et al (2017) have reported seasonal differences in visual quality and nutritional profile of wild rocket, with colder periods (autumn-winter) resulting in better visual quality, whereas warmer periods (winterspring) were beneficial to nutritional profile in terms of nitrates, total phenols, ascorbic acid and glucosinolates content. According to Becker et al (2014), light intensity and growth stage may affect phenolic compounds composition, such as cyanidin and quercetin glucosides in lettuce plants grown under shading nets, while Becker et al (2013) reported that the reduction of flavonoid glycosides content under low light intensities is fully compensated when plants are subsequently subjected to high photosynthetic photon flux density. Moreover, other phenolic compounds such as caffeic acid derivatives were not affected by shading conditions (Becker et al, 2014), which indicates that apart from environmental factors, ontogeny is also important for chemical composition of leafy vegetables.…”