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  • Author or Editor: Masafumi Johkan x
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With the increase in dialysis patients worldwide, the demand for low-K vegetables is growing. Thus, a type of lettuce with a low-K content has been marketed in Japan. To learn more about low-K vegetables, information is needed on the physiological differences between these vegetables and those with typical levels of potassium (K). In this study, lettuces (Lactuca sativa L.) were cultivated using two low-K management methods in an environment-controlled system. One method was based on electrical conductivity (EC) management, and the K was replaced by sodium (Na) at the end of cultivation. The other method was based on quantitative nutrient management, and the nutrients required for low-K lettuce were quantitatively supplied, but no extra Na was added. Meanwhile, lettuce with normal K concentration was cultivated with EC management as the control. Plant growth indices, leaf photosynthesis traits, chlorophyll fluorescence characteristics, concentrations of secondary metabolites (SMs), and antioxidant activity were examined to investigate the physiological effects of low-K and high-Na concentrations during low-K lettuce cultivation. Both low-K treatments significantly restrained the growth of lettuce and increased the concentration of soluble sugar. However, photosynthesis and fluorescence characteristics remained unchanged. This indicates that the biomass reduction of low-K lettuce was due to the wasteful accumulation of carbohydrates rather than the decline in photosynthesis. Concentrations of SMs were increased in the low-K lettuce. In addition, higher concentrations of Na influenced the concentration of SMs, indicating that SMs were more sensitive to environmental stress.

Open Access

The aim of this study was to establish an alternative method to produce clones of tomato plants by modification of the complete decapitation method, which regenerates multiple shoots from the cut surfaces of the main and lateral stems of plants grown in vivo. Shading the stems of tomato plants drastically increased the number of regenerated shoots from 2.4 in controls with unshaded stems to 36.2 in shaded stems. In shaded stems, the concentrations of chlorophyll and phenolic compounds were stable for 3 weeks after cutting, whereas these amounts increased in unshaded stems. Inhibiting the production of phenolic compounds in the shaded stem tissues was associated with an acceleration of shoot formation in vivo.

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