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 about 4 days, the contents of Chlorophyll a and b, and carotenoid in leaves and stems reached normal level again. 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 thylakoid 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 korshinskii utilizes leaf abscission to reduce the surface area exposed to light to avoid the hurt from the extreme drought stress, and retains chloroplast integrity and a considerable amount of chlorophyll to enable a rapid recovery of photosynthesis under rehydration process.

Transmission electron microscopy of mesophyll cells in leaves and epidermis cell in stems of C.korshinski

Transmission electron microscopy of chloroplasts in leaves and stems of C.korshinskii

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