Boron availability alters its distribution in plant parts of tomato

Abstract

This study was performed to investigate boron (B) distribution within various parts of tomato plants (Solanum lycopersicum L. ‘Super Momotarou’) grown under either B supply (adequate, 0.5 mg·L−1) or no B (0 mg·L−1) condition. The objective was to examine how B supply affects plant growth, photosynthetic activity and the morphological response of the entire root system. When the plants were grown for 36 days under the B supply treatment, B concentration was greatest in the order of the leaf (54.3 μg·g−1), fruit cluster (27.8 μg·g−1), petiole (24.7 μg·g−1), and stem (14.1 μg·g−1). However, B deficient supply altered the B distribution so that the greatest concentration was found in the stem (7.82 μg·g−1); then the petiole (8.20 μg·g−1), the fruit cluster (5.5 μg·g−1), and lastly in the leaf (4.11 μg·g−1). No B treatment resulted an approximately 46% decrease in the calcium content of the leaf and an 87% decrease in the potassium content of the fruit cluster. No B treatment also led to a severe decrease in photosynthetic rate, stomatal conductance and transpiration, with an increase in the water vapor saturation deficit at the leaf surface. Microscopic investigation of the stomata 36 days after transplant revealed that a majority of the stomata in the epidermal layer of B-deficit leaves were closing. The total dry weights of the leaves, leaf petioles and stems of B-deficit leaves decreased by 36, 43, and 27%, respectively, at 22 days after transplant, and decreased by 60, 69, and 60%, respectively, at 36 days after transplant, compared to the values for the B-sufficient leaves. A 10-fold lower fruit cluster dry weight was also observed in the B-deficit plants. Under no B supply, the total root length at 35 days after transplant decreased by about 56%, while the average root diameter increased by 20%. This was associated with a significant decrease in the root length, which ranged between 0 and 0.2 mm in diameter, alongside a significant increase in the root length, which ranged larger than 0.9 mm in diameter. One explanation for this finding is that limited B availability leads to a lack of translocation of B to the leaf and reproductive tissues, and this alteration of B partitioning may then affect fruit quality as well as root growth. An improved understanding of B partitioning in plant tissues may help to improve B management and, in the long term, improve crop yields.