Limits imposed by salt to the growth of the halophyte Sesuvium portulacastrum

The growth of the halophyte Sesuvium portulacastrum, commonly known as sea purslane, is impeded by NaCl only at high (600–1000 mM) concentration. Therefore, the goal of this investigation was to identify the mechanisms which set the limit of the salt resistance of S. portulacastrum. 21‐day‐old cuttings were grown for 45–50 d under split‐root conditions in which one half of the root system was immersed in complete nutrient solution supplemented with 800 mM NaCl, while the other half was immersed in a NaCl‐free medium, containing all nutrients or being deprived of potassium or calcium or nitrogen. Using this approach, we demonstrate that K⁺ and N uptake was impaired in roots exposed to NaCl. Concerning Ca²⁺, there was no indication of uptake inhibition by NaCl. However, restriction of K⁺ uptake by roots was compensated by an increase in the K⁺‐use efficiency, so that growth was not inhibited. Concerning N, our analysis shows that NO and/or NH uptake, but not their assimilation, was limited by salt treatment. Thus, we conclude that at high salinity levels, the growth of S. portulacastrum is limited by the restrictions imposed by NaCl on N uptake, perhaps in addition to inhibiting effects of excessive Na⁺ accumulation in shoot.     

海马齿胚胎发育晚期丰富蛋白基因SpLea5的克隆与表达分析

根据筛选文库时获得的EST序列信息,利用RACE技术从海马齿根中分离获得了一个海马齿胚胎发育晚期丰富蛋白基因的全长cDNA,命名为SpLea5。序列分析结果表明,SpLea5基因cDNA全长685 bp,含有一个294 bp的完整开放阅读框,编码97个氨基酸残基;推测编码的氨基酸序列与柽柳、杨木樨、烟草、甜橙、温州蜜柑、麻风树和陆地棉中相应基因的氨基酸序列一致性为54%、52%、48%、47%、47%、46%、44%、41%,在聚类分析时与高等植物聚为一类。SpLea5在海马齿植株中呈组成型表达,但根中表达最为丰富,茎和叶次之;海水、NaCl、PEG、ABA处理均能够诱导根部SpLea5基因的表达。这些结果表明,SpLea5基因可能参与了海马齿对盐和干旱胁迫的分子响应。     

盐胁迫下海马齿叶肉细胞超微结构观察

通过透射电镜,在超显微结构水平上对淡水和海水栽培的海马齿(Sesuvium portulacastrumL.)植物叶肉细胞结构进行了比较。结果显示:海水栽培的海马齿叶肉细胞质膜明显向内折叠,出现大量大小、形状各异的质膜突起,以及质膜片层;而淡水栽培的海马齿叶肉细胞质膜向内折叠不明显,质膜突起少见。相对于淡水栽培,海水栽培的海马齿植物叶肉细胞叶绿体变小、数量增多;形状变短,由肾形、梭形或弓形变成椭圆形或一端膨大的不规则形状;叶绿体基粒片层结构清晰完整,垛叠程度增加,叶绿体没有受到明显伤害;叶绿体中淀粉粒数量增多,体积变大,淀粉粒表面出现皱褶,形状由长椭圆型变成短椭圆形或不规则形状,电子密度变低;叶绿体上脂质体增多且体积变大。线粒体数量增加,但体积变小;形状由圆球状或棒状变成椭圆体状;线粒体内膜向内折叠所形成的嵴清晰,但海水栽培的海马齿叶肉细胞线粒体外膜模糊,受到轻微伤害。