Reproduction Characteristics Of The Typical Desert Moss And Mechanisms Of Physiological And Biochemical Tolerance To Environmental Dehydration And Thermostress

In this study, the factors influencing in the tissue culture of a typical desert moss Tortula desertorum were investigated and the possibility of macropropagating the desert moss was assessed. These works were the foundational data for scale of cultivation of desert mosses and for artificial construction of biological soil crusts (BSCs). Through investigation of the changes of water content, Chlorophyll fluorescence, electron conductivity of solution leakage, pigment content, ultrastructure and regeneration potential, some traditional responses of the desert moss was studied, including morphology and physiology and asexual reproduction to different dehydration rates and temperatures. Those indexes could help establish suitable methods for BSCs restoration in semi-arid and arid regions. Some new biophysical methods such as Scanning electron microscopy (SEM), Atomic force microscopy (AFM), Differentiate scanning calorimeter (DSC), Fourier Transform Infrared Spectroscopy (FTIR), Gas chromatography (GC) and Electron paramagnetic resonance (EPR) were firstly used in study of the desiccation tolerance and thermotolerance in desiccation tolerant mosses. The changes of surface structure and wax chemical characteristics, chemical components and state transition, membrane permeability and cytoplasmic molecular mobility under desiccation and heat stress were studied by those instruments. Those methods and results brought a new path for the study of lower and little size of biomaterial. Furthermore, the proteomics of the desert moss T. desertorum under different water content was studied by 2-demension gel electrophoresis (2-D gel). Some expressed proteins were found and identified, and the functions of these proteins were searched in protein database (NCBI and EBI). This step was crucial of choosing right genes relative with desiccation tolerance and thermotolerance and utilizing these genes for improve crops abiotic tolerances.At first, effects of media, explants and culture temperatures on regeneration potential of T. desertorum were investigated respectively in this study. The factors of relative humidity, light intensity and photoperiod were optimized through orthogonal test design. The life cycle of desert moss T. desertorum in cultivation was investigated according to the several factors on asexual reproduction. The protocol for macropropagation of T. desertorum according the following: detached leaves→day/night temperature 25/15℃→nutrient source Knop solid-agar medium→RH 65-80%→photoperiod 16h→light intensity 85-120 PPFD→2 months cultivation. No sterilized materials were used in cultivation. An incipient moss-dominated crust was constructed using detached green leaves cultivated at 20/10℃in Knop agar-solid medium for one month and transplanted in river sand under 25/15℃for other month. This process proved that it was feasibility to artificial construction of BSCs for desert restoration.In order to improve the abiotic tolerances and ecological functions of BSCs, the main component of BSCs, the desert moss T. desertorum, the responses in morphology, physiology and reproduction to the extreme environment, especially water and temperature, were investigated. The elder tissues had more advantages in cellular structure to cope with environmental stresses. In dehydration and thermostress and the combined stress test, cellular wall and membrane were not penetrated under fast dry. Only did chloroplasts change loose under 45℃treatment. Plenty of bladders emerged in chloroplasts and membranes were penetrated resulting in lipids transferred from cell inner after tissues were exposed to a combined stress of desiccation and thermostress. Increase of solution leakage, decrease of chlorophyll fluorescence activity, intense responses of pigment and sugars were observed when tissues were subjected to fast dry or higher temperatures. However, the fast recovery could be seen in tissues treated with desiccation or the combined stress after being re-irrigated. Meanwhile, higher temperature (> 30℃) could depressed the leaf regeneration potential but the combined stress (<60℃) have not significant effect on reproduction. These results indicated T. desertorum have desiccation tolerance and thermotolerance.To grasp the root cause of desiccation tolerance and thermotolerance of T. desertorum, the structure functions and structural chemistry were studied. There overloaded waxes in the surface between cell membrane and environment. Cell wall stretched outside and formed closed papilla, which could retard water loss and alleviate the damage of hot air. All these information proved the ecological advantages of T. desertorum. The relationship between the changes of chemical components in moss tissues and the mechanisms of thermotolerance were investigated by micro-FTIR. Increase of lipids in hydrophilic regions and proteins content, improvement the structure content ofα-helix in the younger was employed in coping with thermal stress and sustaining the stability of cell structures. The elder engaged with thermostress by promoting the content of carbohydrate and lipids in hydrophobic regions to stabilize the normal structures of proteins and cells. Using different spin labels, the changes of membrane permeability and fluidity and cytoplasmic molecular mobility under desiccation and heat were monitored by EPR. The results elucidated the mechanism of structure stability of cellular membrane and subcellular organelles. T. desertorum depended on high content of sugars and other bio-macromolecules to changes the cytoplasmic state from liquid crystalline to vitrification rapidly after cell lost majority of free water. The rate of metabolism and the activity among molecules were suppressed in glass state, and the substances in cytoplasm were sustained. The partitioning behaviors of amphiphiles could transfer some antioxidants into membrane and eliminated the damage of free radicals. Those processes could maintain the cellular damage within recovery regimes during fast dry.Because of vitrification, the cellular structure was stability and the solution leakage during rehydration became serious. There need powerful recovery mechanism to resume the normal function of cell. The former reports had proposed that the proteins expressed in rehydration were the key to repair the damage of moss in dehydration and rehydration. Some different expression proteins were found between dried and re-wet materials using 2-D gel. Especially, the content of dehydrin (13.1kDa), rehydrin (67.5 kDa), HSP 70 (71.4 kDa和71.2 kDa) and sHSP (36.7 kDa) were up regulation during rehydration and we believed those proteins and corresponding genes had a role in repair mechanism.