硫是植物必需的大量元素，发挥众多的生物学功能。但我们对硫营养如何影响根系生长发育的认知还很欠缺。在前期项目的资助下，我们对外源硫营养水平对根系生长发育进行了较系统的研究，发现拟南芥主根伸长与硫度呈负相关；根系内源半胱氨酸，IAA和ABA含量与硫浓度呈正相关。根系对硫营养水平的这种响应，与土壤中硫酸盐的流动性相吻合，因为硫酸盐和硝酸盐在土壤中容易被淋溶到较深的土壤层面，为了应对这样的根际营养变化，根系需要调整其生长发育使其能较快延伸主根，以追寻和吸收被淋溶到较深土壤曾的硫酸盐。根系对硫酸盐浓度变化的响应极有可能是在漫长的进化过程中逐渐形成的一种适应性机制，但这种适应性的分子机理仍不清楚。该项目拟应用耐低硫突变体sue4D（低硫条件下主根比野生型显著增长）进一步解析SUE4功能，以及在根系适应根际低硫环境中作用，研究结果将为科学施肥和农作物根系改良提供理论依据和指南。

Sulfur is an essential macronutrient for plants with numerous biological functions. However, the influence of sulfur availability on the regulation of root development remains largely unknown. In our previous NNSFC-funded projects, we studied the impact of sulfur availability on root growth and development and found that Arabidopsis primary root elongation was negatively correlated with sulfate levels while the cysteine, IAA and ABA contents in the root were positively correlated with sulfate levels. This response of roots to sulfur availability fits well with the mobility of sulfate as well as nitrate in the soil, which are easily leached down to the deeper soil profiles. Under such a circumstance, roots must adjust their growth and development to elongate the primary root faster to catch up the leached nutrients in the deeper soil profiles. This adaptive response of roots to sulfur availability must be developed in evolution. However, little is known about the underlying mechanisms. We propose to further study the low-sulfur tolerant mutant sue4D isolated in our lab (under low sulfur condition, the primary root of sue4D elongates much faster than that of the wild type) and analyze the function of SUE4 in the adaptive response. The results from this study will provide guidelines for proper fertilization in agriculture and for improvement of crop roots.