Effect Of Environment On Photosynthesis In The Photobiont Of Umbilicaria Esculenta Sp.

Lichens, known as the most prominent group of the survivalist symbiosis, arecomposed of mycobiont and photobiont and play a role of pioneer species in theprocess of natural evolution, thus widely distributing in kinds of adverse conditionsand maintaining stable biosphere. Lichens are poikiohydric plants because of alwayssuffering from drought stress, and always survive in severe environments such as hightemperature, strong light and UV, therefore they possessed their defense mechanisms.Umbilicaria esculenta, as a famously edible lichens, is a species of lichens. In thisstudy, it was investigated that the impact of environmental factors on thephotosynthesis in the photoboint of Umbilicaria esculenta.Umbilicaria esculenta could absorb water quickly and RWC immediatelyincreased to over80%in five minutes, and the photosynthetic activity in itsphotoboint rapidly recovered to maximum. Relatively, its desiccation was slower, andthe photosynthetic activity rapidly dropped after10%RWC. Fluoresence image of thephotobiont during recovery of photosynthesis shows that the activities are differentsignificantly in different individuals and in different parts of one individual.Recovery of photosynthetic activity divided into two phase of light dependence and lightindependence, the activation of photosynthetic recovery in the initial phase was lightindependence and the next is light dependence，the harm was slight in hydrate andslighter in dehydrate under strong light. In0-20℃, the photosynthetic activities weregreater, at high temperature the photosynthetic apparatus was greatly influenced onhydration state, and would be caused irreversible damage in40℃over3hours,however, dehydration state of lichens can prevent photosynthetic apparatus fromdamaging in40℃over3days, suggesting that the photoboint could withstand the hightemperature stress in desiccation state. The photoboint showed the greatestphotosynthetic activities at pH6.0-7.0, suggesting Umbilicaria esculenta prefer weakacidic matrix. High UV-A+B had no significant effect on photosynthetic activities of thephotoboint in Umbilicaria esculenta sp., suggesting the lichens may offer someprotection against UV damage. In the wild, the decrease of photosynthetic activities is stronger and therecovery is weaker during the light period in summer than in autumn and winter,suggesting the stress on photosynthetic activities is due to the strong light and hightemperature and the impact of temperature was stronger than strong light. Withcompared to in wetting-dehydration state, the decrease of photosynthetic activitiesis stronger and the recovery is weaker in hydration state, suggesting that waterloss is an important way to resist the stress and to maintain the photosyntheticactivity under condition of strong light and high temperature.The photoboint of Umbilicaria esculenta sp. belong to Trebouxia sp.(Chlorophyta). The cell wall was getting thinner and the cells were smaller afterbeing in vitro cultured; aerating culture was better than stilling culture. In theprocess of in vitro cultivation, the optimal concentration of N, P, Fe is8.8mM,1.615mM,179nM, the optimal temperature is20℃;, the photosynthetic activity ofphotoboint was stressed in40℃; the photoboint of Umbilicaria esculentasp.cultured may grow well in alkalescent medium. Exposure to differentwavelengths of UV, photosynthetic activities were strongly inhibited by UV-A+B,however, there was little effect on its activities by dealing with UV-A or UV-B alone.