Ines Eichholz

Interaction of drought stress and UV-B radiation - impact on biomass production and flavonoid metabolism in lettuce (Lactuca sativa L.)

The response of plants to stress such as UV-radiation or drought highly depends on the species, cultivar, plant organ, developmental stage, and furthermore, is influenced by ecophysiological interactions. Drought stress as well as UV irradiation are the most adverse factors for plant growth and productivity. In the present study, the interactive effect of UV-B and drought stress on biomass, primary and secondary metabolites, and mediated enzyme activity of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) was investigated in lettuce (Lactuca sativa L.). It was found that biomass production decreased in response to both stressors, while dry matter, total phenolic contents and the flavonol quercetin were not significantly affected by UV-B and drought stress, neither solely nor in combination. In contrast, anthocyanins and luteolin accumulated only in response to drought stress. However, the precursor amino acid proline as well as the activity of PAL increased under conditions of increased UV-B and water deficit. Thus, the present results deduce that both stressors acted either synergistically or to some extent antagonistically in terms of inducing plant protective mechanisms.

Blueberry Phenolic Compounds: Fruit Maturation, Ripening and Post-Harvest Effects

Abstract Currently, there is great momentum in research on phytochemicals, such as polyphenols, in fruit and vegetables. In this context, berry crops have drawn much attention. Blueberries score extraordinarily well in rankings among polyphenol-rich berry fruits. For blueberries, research has focused primarily on the phenolic compound profiles and antioxidant activities. However, little is reported on the development of phenolic compounds during the process of fruit maturation and ripening as well as during post-harvest. Maturation and ripening of blueberries are accompanied by characteristic physiological changes, which include color change, tissue softening, increasing maturity index. etc. During the different physiological stages shifting within the phenolic compound profile occurs as follows: anthocyanins increase during successive ripening, meanwhile flavonols and hydroxycinnamic acids decrease from unripe green to ripe blue berries. Depending on the harvest date, this trend continues during post-harvest. However, while earlier-harvested berries continue phenol accumulation, all phenolic compounds are degraded in stored full-ripe berries.

Survey of bioactive metabolites in selected cultivars and varieties of Lactuca sativa L. under water stress

Plants respond to water stress with a variety of physiological and biochemical changes, but their response vary between species, varieties and cultivars. The present study focused on changes of bio-functional phytochemicals (phenolic compounds, chlorophyll, carotenoids, dietary fiber) in commercial cultivars and old, traditional varieties of lettuce under different water regimes (water-deficit, well-watered and water-logged). Results revealed lettuce varieties and cultivars with a different response behavior to water stress. Biomass production under drought conditions was reduced significantly. Carotenoid and chlorophyll contents decreased in both water extremes, while total phenols were accumulated under limited water availability. Dietary fiber content was not influenced by different water regimes. Water stress reduces biomass production and led to a change of phytochemicals in lettuce, however, old and traditional varieties did not show a different water stress adaptation compared to commercial cultivars.