Quantitative Role of Glycine Betaine and DMSP in Cellular Nitrogen and Sulfur Budgets of Marine Phytoplankton

海洋浮游植物产生多种有机渗透物，包括含氮化合物甘氨酸甜菜碱（GBT）及其硫类似物二甲基磺丙酸酯（DMSP）。GBT和DMSP似乎对许多海洋浮游植物的细胞氮和硫库以及表层海水中的颗粒有机氮（PON）和颗粒有机硫（POS）库做出了巨大的贡献，但迄今尚未被认识到。人们对这些不稳定的生物化合物的产生、分布和循环知之甚少。文献资料和初步研究表明，许多种类的浮游植物同时产生GBT和DMSP，氮的有效性可能影响GBT和DMSP的相对比例。本项目将进行实验室和实地研究，以验证以下假设：1)GBT在某些海洋浮游植物的细胞氮中占重要（5-20%）的比例，DMSP是细胞硫的主要成分；2)分类学与GBT和DMSP的产生存在一定的关系；3)浮游植物中GBT和GMSP含量是氮有效性的函数，在限氮条件下，DMSP更受青睐；4)浮游植物从其周围环境中吸收并在一定条件下释放GBT和DMSP；5)在高氮环境下，GBT的产量大于DMSP，或产生GBT的物种的选择将更有利。该研究将为甲基化氮和硫渗透物对浮游植物细胞氮和硫收支以及海洋中PON和POS的定量作用提供新的重要数据。这些信息将有助于更好地了解海洋中氮和硫的生物循环。

Marine phytoplankton produce a variety of organic osmolytes including the nitrogenous compound glycine betaine (GBT) and its sulfur analog, dimethylsulfoniopropionate (DMSP). It appears that GBT and DMSP make large and hitherto unrecognized contributions to the cellular nitrogen and sulfur pools in many species of marine phytoplankton and to particulate organic nitrogen (PON) and particulate organic sulfur (POS) pools in surface sea water. Very little is known about the production, distribution and cycling of these labile biogenic compounds. Information from the literature and from preliminary studies suggests that many species of phytoplankton produce both GBT and DMSP simultaneously and that nitrogen availability may affect the relative proportions of GBT and DMSP. This project will conduct laboratory and field studies to test the following hypotheses: 1) GBT makes up a significant (5-20%) fraction of cellular nitrogen in certain species of marine phytoplankton and DMSP is a major constituent of cellular sulfur; 2) There is a relationship between taxonomy and GBT and DMSP production; 3) The levels of GBT and GMSP in phytoplankton are a function of nitrogen availability, with DMSP favored under N-limitation; 4) Phytoplankton take up GBT and DMSP from their surroundings and release them under certain conditions; 5) Production of GBT over DMSP, or selection of species which produce GBT, will be favored in high nitrogen environments. This study will provide new and important data on the quantitative role of methylated nitrogen and sulfur osmolytes to the cellular nitrogen and sulfur budgets of phytoplankton and to PON and POS in the sea. This information will lead to a better understanding of the biological cycling of nitrogen and sulfur in the ocean.