Xylem plays an important role in regulating the leaf water potential and fruit quality of Meiwa kumquat (Fortunella crassifolia Swingle) trees under drought conditions.

Highlights • Soil water deficit treatment significantly increase the number of first-flush summertime flowers in Meiwa kumquat. • Transpiration occurred from the stem surface but the rate was approximately one-eighth of that from the leaf under non-stressed conditions. • Despite the rapid decrease in the transpiration of the leaves, that of the stem remained unchanged during soil water deficit treatment. • Increase in the monosaccharides due to the soil water deficit treatment also occurred even in the xylem of scaffold branches. Abstract Drought induce various physiological changes such as flowering advancement and carbohydrate accumulation in many plants. Soil water deficit (SWD) has been shown to significantly increase the number of first-flush summertime flowers in the ever-flowering Meiwa kumquat (Fortunella crassifolia Swingle). In this study, we examined how SWD affects transpiration and the accumulation of soluble sugars in various parts of the plant as a result of osmoregulation. Despite the rapid decrease in the transpiration of the leaves, that of the stem remained unchanged during SWD treatment at one-eighth of that from the leaves under non-stressed conditions. The SWD treatment increased the total soluble sugar content in all plant parts, except the leaves. Increase in the monosaccharides such as glucose and fructose being greater than for the disaccharide sucrose, in the stems of shoots more than 3 years of age as well as in the xylem of scaffold branches, is suggesting that these increased sugar levels were due to osmoregulation. The sucrose content decreased markedly during the 4 months after SWD treatment in the xylem of scaffold branches but was significantly higher in the fruit that were harvested from SWD-treated trees at 4 months after SWD treatment. These results suggest that the sugars that are accumulated in the xylem positively affect fruit growth after SWD treatment. [ABSTRACT FROM AUTHOR]