镉胁迫对甜瓜幼苗叶片叶绿体超微结构及光合色素质量分数的影响

为挖掘甜瓜抗镉种质资源,以野生、薄皮和厚皮甜瓜为试材,幼苗三叶一心时用不同质量浓度(0～100 mg·L~(-1))的镉溶液培养3 d后取第2片真叶制片,透射电镜观察叶绿体超微结构;培养7 d后测定光合色素质量分数。结果表明,正常生长条件下,叶绿体紧贴细胞内壁,呈梭形。而随着Cd~(2+)质量浓度增加,叶绿体逐渐呈离壁不规则形状,叶绿体膜部分缺失,淀粉粒体积明显变大。Cd~(2+)质量浓度最大时,薄皮和厚皮甜瓜叶绿体超微结构受损较重,片层结构排列无序、疏松,叶绿体膜部分裂解;野生甜瓜叶绿体结构相对稳定,淀粉粒体积明显增大,片层结构疏松解体。同等Cd~(2+)质量浓度对野生甜瓜叶绿体超微结构的影响最小,厚皮甜瓜叶绿体超微结构损伤最严重。Cd~(2+)质量浓度为25 mg·L~(-1)时,薄皮甜瓜叶片各色素质量分数均高于对照,Cd~(2+)质量浓度50 mg·L~(-1)时,光合色素质量分数低于对照;野生甜瓜和厚皮甜瓜各光合色素质量分数均逐步递减,且厚皮甜瓜降幅最大,野生甜瓜降幅最小。高浓度镉胁迫降低了甜瓜叶片光合色素质量分数,损坏了叶绿体结构,进而影响叶片的光合作用。供试的野生甜瓜幼苗抗镉性最强,厚皮甜瓜幼苗受镉胁迫最重。

Effects of Cadmium Stress on Leaf Chloroplast Ultrastructure and Chlorophyll Mass Fraction of Three Melon Varieties

Wild melon, thin skin melon and musk melon were used as materials to investigate the effect of cadmium stress on melon leaf chloroplast ultrastructure and chlorophyll content. The second true leaf was cultured with different mass concentrations of cadmium (0-100 mg·L^-1) for 3 days at one time in three leaves of seedlings. The ultra structure of chloroplast was observed by transmission electron microscopy. Photosynthetic pigment mass fraction was determined after 7 days of culture. The results showed that the chloroplasts of the leaves of muskmelon were attached to the inner wall of the mesophyll cells in a spindle shape. With the increase of the mass concentration of Cd²⁺, chloroplast gradually showed irregular shape from the wall, chloroplast membrane was partially absent, starch granule volume increased significantly, and when the mass concentration of Cd²⁺ reached the maximum level, the chloroplast ultra structure of thin skin melon and thick skin melon were seriously damaged, the lamellar structure was disordered and loose, and the chloroplast membrane was partially cracked. The chloroplast structure of wild melon was relatively stable, the volume of starch granule obviously increased, and the lamellar structure was loose and disintegrated. The effect of cadmium stress at the same concentration on chloroplast ultrastructure of wild muskmelon was the least, followed by thin rind, and the damage of thick rind muskmelon chloroplast ultrastructure was the mostly serious. At the Cd²⁺ mass concentration of 25 mg·L^-1, the pigment mass fraction in the leaves of thin-skinned melon was higher than that of the control, and at the Cd²⁺ mass concentration of 50 mg·L^-1, the photosynthetic pigment mass fraction was lower than that of the control and gradually decreased, while the photosynthetic pigment mass fraction in wild melon and thick-skinned melon gradually decreased, and the decrease was the greatest in thick-skinned melon and the smallest in wild melon. High concentration of cadmium stress reduced the photosynthetic pigment mass fraction in the leaves of melon, damaged the chloroplast structure of the photosynthetic organ, and then affected the photosynthesis of the leaves. However, there were differences among varieties. Among the three tested varieties, wild melon had the strongest cadmium resistance, and thick-skin melon had poor cadmium resistance.