柠条适应极端干旱的生理生态机制——叶片脱落和枝条中叶绿体保持完整性

Eco-physiological Mechanism of Caragana korshinskii Kom Adaptation to Extreme Drought Stress: Leaf abscission and keeping chloroplast integrity in stem

为了探讨柠条适应极端干旱的生理生态机制,对盆栽柠条停止浇水造成土壤持续干旱直到叶片完全脱落,然后复水。干旱和复水期间,对土壤、叶片和枝条的相对含水量、叶片和枝条中的叶绿素含量以及超微结构进行了测定和观察。结果表明,干旱脱水过程中叶片中的色素含量下降,枝条中类胡萝卜素含量下降。复水4d后,叶片中色素含量和枝条中类胡萝卜素含量上升并逐步达到正常水平。超微结构研究表明,柠条嫩枝的亚细胞组织中普遍含有叶绿体。正常条件下,无论是枝条还是叶片的亚细胞组织,叶绿体紧贴细胞壁。叶绿体中的类囊体排列整体有序。随着干旱的加剧,叶绿体脱离细胞壁,向细胞中央靠近。严重干旱造成了叶片叶肉细胞和叶绿体结构不可恢复性的破坏,包括外膜和膜片层结构,类囊体膜解体,淀粉粒消失,部分细胞器裂解成碎片。而嫩枝的亚细胞组织和叶绿体都保持完整。因此,柠条通过叶片脱落减少光照面积来适应极端干旱对自身造成的伤害,通过保持枝条中叶绿体的完整性和一部分叶绿素为复水条件下光合作用的快速恢复提供了保证。

In order to study the eco-physiological mechanism of C. korshinskii adaptation to extreme drought stress, we investigated variations of relative water content, Chlorophyll a and b, and carotenoid contents in leaves and stems of 2-year-old C. korshinskii and its chloroplast ultrastructure change during progressive soil drought and rehydration process, and also investigated the variation of soil relative water content during the process. Results showed that during dehydration process, contents of Chlorophyll a and b, and carotenoid in leaf decreased, and carotenoid contents in stem decreased too. After rehydration for a- bout 4 days, the contents of Chlorophyll a and b, and carotenoid in leaves and stems reached normal level a- gain. In most case, chloroplasts appear in subcellular organization of C. korshinskii and choroplasts cling the cell wall, and chloroplasts are surrounded by a persistent envelope and with abundant and ordered thyla- koid system. With the ongoing of drought stress, chloroplasts in leaves broke away from the cell wall and appeared in the center of the cell. The mesophyll ultrastructure and chloroplasts configuration in leaves were disturbed beyond retrieve in the leaves under severe drought stress, and the inner and outer membranes is destroyed, hylakoid is disintegrated, starch grain disappeared and parts of cell tissue dismantled into debris. But the mesophyll ultrastructure and chloroplasts configuration in stems remained complete. Caragana kor- shinskii utilizes leaf abscission to reduce the surface area exposed to light to avoid the hurt from the ex- treme drought stress, and retains chloroplast integrity and a considerable amount of chlorophyll to enable a rapid recovery of photosynthesis under rehydration process.