Abstract
Plants have evolved various adaptive mechanisms to environmental stresses, such as sensory mechanisms to detect mechanical stimuli. This plant adaptation has been successfully used in the production practice of leafy vegetables, called mechanical conditioning, for many years, but there is still a lack of research on the effects of mechanically-induced stress on the content of specialized metabolites, or phytochemicals with significant antioxidant activity. Therefore, the aim of this study was to determine the content of specialized metabolites and antioxidant capacity of lettuce and green chicory under the influence of mechanical stimulation by brushing. Mechanically-induced stress had a positive effect on the content of major antioxidants in plant cells, specifically vitamin C, total phenols, and flavonoids. In contrast, no effect of mechanical stimulation was found on the content of pigments, total chlorophylls, and carotenoids. Based on the obtained results, it can be concluded that induced mechanical stress is a good practice in the cultivation of leafy vegetables, the application of which provides high quality plant material with high nutritional potential and significantly higher content of antioxidants and phytochemicals important for human health.
Highlights
Consumer interest in cut leafy vegetables with distinct functional value is increasing, as is the need for a continuous supply to the market
The significant effect of mechanically-induced stress (MIS) on ascorbic acid (AsA) content in lettuce (Table 1) is most pronounced in the first harvest period (L-MC101, L-MC201 ), with the highest AsA content (24.39 mg/100 g fw) determined in a sample treated with 20 brushings per day (L-MC201 )
The mechanically-induced stress in the form of brushing per day (10 and 20) did not cause damage to plant tissue and did not significantly affect the processes of primary metabolism, i.e., photosynthesis, as shown by the higher contents of total chlorophylls and carotenoids in lettuce in both harvest periods; with an average of 22% higher TCh in plants treated with 20 brushings per day in the first harvest period and 18% higher TCh in the second harvest period compared to the non-treated plants, and 33% higher total carotenoids (TCA) in the first and 24% higher in the second harvest period in plants treated with 20 brushings per day compared to the non-treated plants
Summary
Consumer interest in cut leafy vegetables with distinct functional value is increasing, as is the need for a continuous supply to the market. Growing leafy vegetables in greenhouses allows them to be grown throughout the year, even in the cold months, ensuring the supply and availability of various leafy vegetables, especially lettuce, in the off-season [1,2]. The cultivation of leafy vegetables in greenhouses has been increasingly oriented towards hydroponic cultivation, mainly because of a number of advantages that this type of cultivation has over the conventional one: significant yield, high quality and healthy plant material, lower incidence of pathogens, less use of pesticides, less pollution, conservation of groundwater (closed hydroponic systems), high degree of automation, less physical labor, better control of water and nutrient supply to plants, fewer weeds, etc. The benefits are many and include faster growth, earlier harvest, more production cycles, and higher yield per unit area due to better control of plant nutrients [5,6]. To produce the strongest and most resistant plant, different treatments can be
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