Effects of rhizosphere sulfur concentration on sulfur content and sulfate transporter gene expression in Japanese heirloom vegetables of the Brassicaceae family

Several region-specific vegetable varieties in Japan have an extensive cultivation history. Distinct tastes and aromas make them suitable for use in spices and pickles, and varieties with a high content of functional sulfur-containing compounds have been preferentially selected over the years. In the present study, we investigated the effects of different rhizosphere sulfate concentrations (0, 0.2, 0.4, and 0.8 mM) on the dry weight and sulfur content of 40 varieties of Brassicaceae heirloom vegetables. We also analyzed the expression levels of sulfate transporter genes, such as <i>SULTR1s</i> (sum of <i>SULTR1;1, SULTR1;2</i>, and <i>SULTR1;3</i>) and <i>SULTR2;1</i>, in 20 vegetable varieties. At 0 mM sulfate, plants have small leaves, as well as thin and scarce roots, whereas the mean shoot sulfur content per plant was 10% of that in control. Sulfur content increased by 29% at 0.4 mM and by 66% at 0.8 mM sulfate compared with that in control (0.2 mM sulfate); however, dry weight was not significantly affected. Mean shoot sulfur concentration was 0.12% at 0 mM, 0.52% at 0.2 mM, 0.65% at 4 mM, and 0.86% at 0.8 mM of sulfate. Shoot sulfur concentration exceeded 1% at 0.4 mM sulfate in several varieties. Shoot sulfur content and dry weight were positively correlated, suggesting that the capacity for sulfate ion absorption had a strong effect on biomass production in plants of the Brassicaceae family. Sulfur content and <i>SULTR1s</i> and <i>SULTR2;1</i> expression were poorly correlated regardless of rhizosphere sulfur concentration. These genes did not respond to shoot sulfur content but responded to sulfate levels in the rhizosphere. Overall, our data indicated that sulfate absorption response to sulfate concentration in the rhizosphere by sulfate transporters in Brassicaceae plants depends on the inherent characteristics of the variety.

日本多款地域特色蔬菜品种拥有悠久的栽培历史。其独特的风味与香气使其适用于香料制备及腌渍加工，多年来人们优先选育出富含功能性含硫化合物的品种。本研究针对40份十字花科（Brassicaceae）传家宝蔬菜品种，探究了不同根际（rhizosphere）硫酸盐浓度（0、0.2、0.4、0.8 mM）对其干重与硫含量的影响。此外，我们还分析了20份蔬菜品种中硫酸盐转运蛋白基因（sulfate transporter genes）的表达水平，包括SULTR1s（即SULTR1;1、SULTR1;2与SULTR1;3的总和）及SULTR2;1。当硫酸盐浓度为0 mM时，植株叶片偏小，根系纤细且稀疏；此时单株地上部硫含量仅为对照组（0.2 mM硫酸盐）的10%。与对照组相比，0.4 mM硫酸盐处理下植株硫含量提升29%，0.8 mM处理下提升66%；但干重未受显著影响。地上部平均硫浓度在0 mM硫酸盐处理下为0.12%，0.2 mM下为0.52%，4 mM下为0.65%，0.8 mM下为0.86%。部分品种在0.4 mM硫酸盐处理下，地上部硫浓度超过1%。地上部硫含量与干重呈正相关，表明硫酸盐离子吸收能力对十字花科植株的生物量积累具有显著影响。无论根际硫浓度如何，植株硫含量与SULTR1s及SULTR2;1的表达水平均相关性较弱。上述基因并不响应地上部硫含量，而是对根际硫酸盐水平产生应答。综上，本研究数据表明，十字花科植株通过硫酸盐转运蛋白响应根际硫酸盐浓度的能力，取决于品种自身的固有特性。