Trossat C, Rathinasabapathi B, Weretilnyk E A, Shen T L, Huang Z H, Gage D A, Hanson A D
Horticultural Sciences Department, University of Florida, Gainesville 32611, USA.
Plant Physiol. 1998 Jan;116(1):165-71. doi: 10.1104/pp.116.1.165.
Wollastonia biflora (L.) DC. plants accumulate the osmoprotectant 3-dimethylsulfoniopropionate (DMSP), particularly when salinized. DMSP is known to be synthesized in the chloroplast from S-methylmethionine (SMM) imported from the cytosol, but the sizes of the chloroplastic and extrachloroplastic pools of these compounds are unknown. We therefore determined DMSP and SMM in mesophyll protoplasts and chloroplasts. Salinization with 30% (v/v) artificial seawater increased protoplast DMSP levels from 4.6 to 6.0 mumol mg-1 chlorophyll (Chl), and chloroplast levels from 0.9 to 1.9 mumol mg-1 Chl. The latter are minimum values because intact chloroplasts leaked DMSP during isolation. Correcting for this leakage, it was estimated that in vivo about one-half of the DMSP is chloroplastic and that stromal DMSP concentrations in control and salinized plants are about 60 and 130 mM, respectively. Such concentrations would contribute significantly to chloroplast osmoregulation and could protect photosynthetic processes from stress injury. SMM levels were measured using a novel mass-spectrometric method. About 40% of the SMM was located in the chloroplast in unsalinized W. biflora plants, as was about 80% in salinized plants; the chloroplastic pool in both cases was approximately 0.1 mumol mg-1 Chl. In contrast, > or = 85% of the SMM was extrachloroplastic in pea (Pisum sativum L.) and spinach (Spinacia oleracea L.), which lack DMSP. DMSP synthesis may be associated with enhanced accumulation of SMM in the chloroplasm.
双花黄细心（Wollastonia biflora (L.) DC.）植株会积累渗透保护剂3-二甲基巯基丙酸内盐（DMSP），尤其是在盐渍化条件下。已知DMSP是由从细胞质中导入的S-甲基甲硫氨酸（SMM）在叶绿体中合成的，但这些化合物在叶绿体和叶绿体以外部分的含量尚不清楚。因此，我们测定了叶肉原生质体和叶绿体中的DMSP和SMM。用30%（v/v）人工海水进行盐渍化处理后，原生质体中的DMSP含量从4.6增加到6.0 μmol mg-1叶绿素（Chl），叶绿体中的含量从0.9增加到1.9 μmol mg-1 Chl。后者是最小值，因为完整的叶绿体在分离过程中会泄漏DMSP。校正这种泄漏后，据估计，在体内约一半的DMSP存在于叶绿体中，对照植株和盐渍化植株中叶绿体基质中的DMSP浓度分别约为60 mM和130 mM。这样的浓度将对叶绿体渗透调节有显著贡献，并可保护光合过程免受胁迫伤害。SMM含量采用一种新的质谱方法进行测定。在未盐渍化的双花黄细心植株中，约40%的SMM位于叶绿体中，在盐渍化植株中约为80%；在这两种情况下，叶绿体中的含量约为０.1 μmol mg-1 Chl。相比之下，在缺乏DMSP的豌豆（Pisum sativum L.）和菠菜（Spinacia oleracea L.）中，≥85%的SMM位于叶绿体以外部分。DMSP的合成可能与叶绿体中SMM积累的增加有关。
