A Cytological Study Of Drought Tolerance Mechanisms Of The Resurrection Plant Boea Hygrometrica (Bunge) R.Br.

The resurrection plant B. hygrometrica (Bunge) R.Br. distributed in China uniquely were used to investigate the cytological mechanisms of the desiccation-tolerance. To provide experimental basis for understanding plant drought tolerance mechanisms and improving crop agromonic traits related to environment.On set of dehydration the stomata of B. hygrometrica leaves rapidly closed, however, gradually reopened when RWC dropped further. ABA pretreatment was able to induce the closure of stomata, but failed to prevent the reopening during the subsequential dehydration. Photosystem II activity was inhibited during dehydration, as shown by the decrease of the quantum yields. It was observed that mesophyll cells shrank, central vacuoles disappeared, and numerous small vacuoles emerged in dehydrated leaves. It was also found that the arrangement of chloroplast grana altered, electron density of nucleolus became ununiform. nucleole disappeared after dehydration. However, plasma membrane, chloroplast membrane and nuclear membrane kept intact and cellular structure remained integral during the process of dehydration. It was important to note that cell wall folding was observed in many place of the mesophyll cells upon dehydration. FTIR revealed that the composition of cell wall was altered after dehydration, as protein and pectin underwent a marked increase. Using two-dimensional electrophoresis, it was showed that the pattern of salt soluble and covalently bound cell wall proteins changed to a different degree in dehydrated leaves. All these changes were inversed upon rehydration.Results demonstrated above had dropped a hint that the alteration in wall composition during dehydration may have an effect on the cell wall flexibility and extensibility, resulting in commensurate folding of the cell wall. Such folding will contribute greatly to preventing mechanical injury of plasma membrane tear resulted from the severe plasmolysis as plasma shrink to a significant extent during dehydration, so that the integration of the cell structure was ensured. This hypothesis may explain the extraordinary ability of B. hygrometrica being dehydration tolerant and rehydration resurrectable.