Desiccation-Tolerance And Resurrection Mechanisms Of Photosynthesis Of Boea Hygrometrica

Leaves detached from mature plant of resurrection plant Boea hygrometrica (Bunge) R.Br. were used to investigate the dehydration protection in the physiological and chemical levels represented by the changes of photosynthesis, sucrose, antioxidants and electrolyte leakage during desiccation and subsequent rehydration, and molecular mechanisms of dehydration tolerance by means of mRNA differential display based on the studies of Deng's.Deng et al. (2000) found an obvious increase in carotenoids content in detached Boea leaves during dehydration, indicating a protective role of xanthophylls cycle in dehydrated Boea leaves. The results of changes in photochemical activity parameters and chloroplast pigments in the present study indicated that xanthophylls cycle was induced in leaves of Boea hygrometrica when they were dehydrated for 8 days undervery weak light condition (3u mol.m-2.s-1), xanthophylls cycle may play a photoprotective role in dehydrated Boea leaves.Desiccation-sensitive plants and/or different resurrection ones were often used in previous studies on desiccation tolerant mechanisms of resurrection plants, which often resulted in similar findings among desiccation-sensitive plants and resurrection ones. It didn't reveal the exact desiccation tolerant mechanisms of resurrection plants. The results of treatments with different concentration of phosphate in the present study indicated, whether Boea leaves were treated before desiccation or during rehydration, and whether they were intact leaves, leaf halves or leaf discs, the Boea leaves were injured and their photochemical activity of PSII were serious affected by treatment with 0.1mol/L phosphate or over, thus resulted in poor resurrection for dehydrated Boea leaves. The photochemical activity of PSII was a sensitive parameter of physiological activities for Boea leaves during dehydration and rehydration. This is a new idea in the study, which lays a foundation for the further studies on molecularmechanisms of desiccation tolerance and resurrection in resurrection plants.Obvious increases in AsA, GSH and sucrose content during dehydration and steep declines in subsequent rehydration indicated that AsA, as well as GSH and sucrose, might be involved in protection of dehydrated Boea leaves, but not for rehydrated ones. In addition, the well retained stability and integrity of cell membrane of Boea leaves might also be an important mechanism which make them resurrect well.By using mRNA differential display, 5 desiccation sensitive cDNAs, 52 desiccation-induced cDNAs, 21 up-regulated cDNAs, 14 down-regulated cDNAs and 16 phosphate induced cDNAs were obtained. The cloning, sequencing, homological blasting and Northern blotting results of 5 desiccation-induced cDNAs and 3 phosphate induced cDNAs implied that signal transduction induced by desiccation, regulatory gene cascades and functional genes such as G protein, protein kinase, VP3-and MAD3- like genes might be involved in dehydration in the resurrection plant Boea hygrometrica.