Effects of Drought Stress on Ultrastructure of Mesophyll and Stem Cells in Two Potato Varieties

In order to find change relationship of potato mesophyll and stem cells ultrastructure under water stress, plantlets in vitro of drought-sensitive variety Favorita and drought-tolerant variety Dongnong 308 were cultured in MS liquid medium. 20%PEG-6000 was added to MS liquid medium as drought stress. The results indicated that drought stress affected ultrastructure of potato plantlets seriously, and harm degree intensified with the extension of time. Dongnong 308 was damaged significantly lighter than Favorita. Chloroplasts of mesophyll were the most sensitive and the most seriously damaged under water stress. Chloroplast morphology turned to swollen and became more round firstly, lamellae became loosed, the interspaces between lamellar structures became larger or occurred with some holes, even completely disintegrated. The membrane of the mitochondria was disrupted, and the cristae were partially degraded. Nuclei were relatively stable. Ultrastructure of mesophyll was more sensitive than that of stem cells to water stress. Nuclei were the most sensitive among organelles of stem cells.