甜菊不同叶龄细胞结构及其甜菊糖甙含量分布的研究

本文报道甜菊(Stevia rebaudiana Bertoni)不同叶龄细胞结构与甜菊糖苷含量分布。应用电镜技术观察表明,现蕾期成叶细胞内具有内含物丰富的巨大液泡,这些内含物呈大小不一的颗粒或小泡。应用差速离心法,对甜菊成叶的叶肉细胞进行亚细胞分离,并对各部分进行甜菊糖苷的提取与微量测定。结果表明,甜菊糖苷主要存在于12000g的上清液(这部分主要包括液泡内含物和可溶性细胞质)。结合细胞结构和细胞化学研究结果,表明细胞质是合成UDPG的主要场所,在甜菊糖苷合成中具有重要作用。对不同叶龄叶片甜菊糖苷测定表明,现蕾期成叶的甜菊糖苷含量最高。从甜菊不同叶龄细胞结构和甜菊糖苷含量测定结果,现蕾期是甜菊叶片收割的最适时期。

STUDY ON STRUCTURE OF DIFFERENT-STAGED LEAF CELLS OF STEVIA REBAUDIANA BERTONI AND-DISTRIBUTION OF STEVIOSIDE CONTENT

This paper reports the relationship between the structures of different-staged leaf cells of Stevia rebaudiana Bertoni and distribution of stevioside content.The electron microscopy observation shows that mature leaf cell, du- ring its floral initiation period, contains a huge vacuole with a lot of inelusions which appear as different-sized granules or vesicles.Furthermore, the suhcellular separation of mature leaf of S. rebaudiana is performed with differential centrifugation, and the stevioside in various parts is respectively extracted out and microanalyzed. The results show that most of stevioside is in 12000 Xg supernatant (this part mainly contains vacuolar inclusions and soluble cytoplasm). Relating these results with the result of cytochemical study, we think that soluble cytoplasm may be the main site of the synthesis of UDPG, which is critical in the synthesis of stevioside, and stevioside is stored in vacuoles.The analysis of stevioside for the different-staged leaf cells shows that its cntent of stevioside in floral initiation period is the highest. Considering the relationship between the content of stevioside and th leaf-age, we may conclude that the floral initiation period is exactly the suitablest reaping time.