【摘要】 电镜观察结果表明，不同种类植物生长在相同倍增的高ＣＯ２ 浓度条件下，其叶绿体超微结构彼此呈现出明显的差异． 最醒目的特征是淀粉粒的积累比对照的增加很多；类囊体膜系发生异变． 总体上，（１）淀粉粒，Ｃ４ 植物谷子（Ｓｅｔａｒｉａ ｉｔａｌｉｃａ）叶绿体比Ｃ３ 植物紫花苜蓿（Ｍｅｄｉｃａｇｏ ｓａｔｉｖａ）积累的更多． （２）淀粉粒较小且较少时，紫花苜蓿叶绿体基粒类囊体膜增多，与基质类囊体膜相间排列有序；谷子叶绿体的基粒垛及基粒类囊体膜数均增多，但基粒变小，基质类囊体膜变长，且有些膜出现膨胀甚至破损． （３）淀粉粒较大且积累过多时，紫花苜蓿叶绿体中尚可隐约见到由４～８ 个类囊体膜组成的短小基粒零星分布于淀粉粒间；谷子叶绿体中几乎找不到可辨认的基粒和基质类囊体膜更多还原

【Abstract】 It has been reported in quite a number of literatures that doubled CO 2 concentration increased the photosynthetic rate and dry matter production of C 3 plants, but substantially affected C 4 plants little. However, why may CO 2 enrichment promote growth and either no change or decrease reproductive allocation of the C 3 species, but having no effects on growth characteristics of the C 4 plants? So far,there has been no satisfactory explanation on that mentioned above,except the differences in their CO 2 compensatory points. In the past,although some studies on ultrastructure of the chloroplasts under doubled CO 2 concentration were limitedly conducted. Almost all the relevant experimental materials were only from C 3 plants not from C 4 plants,and even though the results were of inconsistancy.Thereby,it needs to verify whether the differences in photosynthesis of C 3 and C 4 plants at doubled CO 2 level is caused by the difference in their chloroplast deterioration. Experiments to this subject were conducted at the Botanical Garden of Institute of Botany, Academia Sinica in 1993～1994. Both experimental materials from C 3 plant alfalfa (Medicago sativa) and C 4 plant foxtail millet (Setaria italica) were cultivated in the cylindrical open top chambers (2 2 m in diameter × 2.4 m in height) with aluminum frames covered by polyethylene film. Natural air or air with 350×10 -6 CO 2 were blown from the bottom of the chamber space with constant temperature between inside and outside of the chamber(<0.2 ℃). Electron microscopic observation revealed that the ultrastructure of the chloroplasts from C 3 plant Medicago sativa and C 4 plant Seteria italica growing under the same doubled CO 2 concentration were quite different from each other. The differential characteristics in ultrastructure of chloroplasts displayed mainly in the configuration of thylakoid membrances and the accumulation of starch grains. They were as follows: 1. The most striking feature was the building up of starch grains in the chloroplasts of the bundle sheath cells (BSCs) and the mesophyll cells (MCs) at doubled CO 2 concentration. The starch grains appeared centrifugally first in the BSCs and then in the chloroplast of the other MCs. It was worthy to note that the starch grains in the chloroplasts of C 4 plant Setaria italica were much more than those of the C 3 plant Medicago sativa . The decline of photosynthesis in the doubled CO 2 grown C 4 plants might be caused by an over accumulation of starch grains,that deformed the chloroplast even demaged the stroma thylakoids and grana. There might exsist a correlation between the comformation of thylakoid system and starch grain accumulation, namely conversion and transfer of starch need energy from ATP, and coupling factor (CF) for ATP formation distributed mainly on protoplastic surface (PSu) of stroma thylakoid membranes, as well as end and margin membranes of grana thylakoids. Thereby, these results could provide a conclusive evidence for the reason of non effectiveness on growth characteristics of C 4 plant. 2. Under normal condition ,the mature chlolroplats of higher plants usually develop complete and regularly arranged photosynthetic membrane systems . Chloroplasts from the C 4 plant Setaria italica, however, exerted significant changes on stacking degree, grana width and stroma thylakoid length under doubled CO 2 concentration. In these changes, the grana stacks were smaller and more numerous,and the number of thylakoids per granum was greatly increased, and the stroma thylakoid was greatly lengthened as compared to those of the control chloroplasts. But the grana were mutually intertwined by stroma thylakoid. The integrity of some of the grana were damaged due to the augmentation of the intrathylakoid space .Similarly, the stroma thylakoids were also expanded. In case, the plant was seriously effected by doubled CO 2 concentration as observed in C 4 plant Setaria italica , its chloroplasts contained merely the stroma(matrix) with abund更多还原