Polyols in the crustose lichen Rhizocarpon geographicum

A lichen is an intimate association between an alga and a fungus and is regarded as one of the best examples of ‘mutualism’ or ‘symbiosis’ involving microorganisms. In lichens which have Trebouxia as the algal partner, photosynthesis by the algae results in the production of the soluble polyol ribitol which is then transported to the fungus where it is converted to arabitol and mannitol. Within the fungus, arabitol may act as a short-term carbohydrate reserve while mannitol may be involved in stress resistance. The crustose lichen Rhizocarpon geographicum (L.) DC., has an unusual thallus structure consisting of discrete granules (areolae) containing the algal component growing in association with a non-lichenised fungal hypothallus that extends beyond the areolae to form a marginal ring. The concentrations of ribitol, arabitol, and mannitol were measured, using gas chromatography, in the central areolae and marginal hypothallus of the crustose lichen Rhizocarpon geographicum (L.) DC. growing on slate rocks in north Wales, UK. The concentrations of all three polyols were greater in the central areolae than in the marginal hypothallus. In addition, the ratios of polyols in the marginal hypothallus to that in the central areolae varied through the year. The concentration of an individual poyol in the hypothallus was correlated primarily with the concentrations of the other polyols in the hypothallus and not to their concentrations in the areolae. Low concentration of ribitol, arabitol, and mannitol in the marginal hypothallus compared with the central areolae suggests either a lower demand for carbohydrate by the hypothallus or limited transport of polyols from areolae to hypothallus, and may explain the low growth rates of this species. In addition, polyols appear to be partitioned differently through the year with an increase in mannitol compared with arabitol in more stressful periods.

Concentration of mannitol and other soluble carbohydrates in the crustose lichen Rhizocarpon geographicum

In symbiotic lichens which have Trebouxia as the algal partner, photosynthesis by the algae results in the production of the soluble carbohydrate ribitol which is then transported to the fungus where it is converted to arabitol and mannitol. Within the fungus, arabitol may act as a short-term carbohydrate reserve while mannitol may have a more protective function and be important in stress resistance. The concentrations of ribitol, arabitol, and mannitol were measured, using gas chromatography, in the central areolae and marginal hypothallus of the crustose lichen Rhizocarpon geographicum (L.) DC. growing on slate rocks in north Wales, UK. The concentrations of all three soluble carbohydrates were greater in the central areolae than in the marginal prothallus. In addition, the ratio of mannitol in the prothallus to that in the areolae was least in July. The concentration of an individual carbohydrate in the prothallus was correlated primarily with the concentrations of the other carbohydrates in the prothallus and not to their concentrations in the areolae. Low concentration of ribitol, arabitol, and mannitol in the marginal prothallus compared with the central areolae suggests either a lower demand for carbohydrate by the prothallus or limited transport from areolae to prothallus and may explain the low growth rates of this species. In addition, soluble carbohydrates appear to be partitioned differently through the year with an increase in mannitol compared with arabitol in more stressful periods.

Polyols in the crustose lichen rhizocarpon geographicum

A lichen is an intimate association between an alga and a fungus and is regarded as one of the best examples of ‘mutualism’ or ‘symbiosis’ involving microorganisms. In lichens which have Trebouxia as the algal partner, photosynthesis by the algae results in the production of the soluble polyol ribitol which is then transported to the fungus where it is converted to arabitol and mannitol. Within the fungus, arabitol may act as a short-term carbohydrate reserve while mannitol may be involved in stress resistance. The crustose lichen Rhizocarpon geographicum (L.) DC., has an unusual thallus structure consisting of discrete granules (areolae) containing the algal component growing in association with a non-lichenised fungal hypothallus that extends beyond the areolae to form a marginal ring. The concentrations of ribitol, arabitol, and mannitol were measured, using gas chromatography, in the central areolae and marginal hypothallus of the crustose lichen Rhizocarpon geographicum (L.) DC. growing on slate rocks in north Wales, UK. The concentrations of all three polyols were greater in the central areolae than in the marginal hypothallus. In addition, the ratios of polyols in the marginal hypothallus to that in the central areolae varied through the year. The concentration of an individual poyol in the hypothallus was correlated primarily with the concentrations of the other polyols in the hypothallus and not to their concentrations in the areolae. Low concentration of ribitol, arabitol, and mannitol in the marginal hypothallus compared with the central areolae suggests either a lower demand for carbohydrate by the hypothallus or limited transport of polyols from areolae to hypothallus, and may explain the low growth rates of this species. In addition, polyols appear to be partitioned differently through the year with an increase in mannitol compared with arabitol in more stressful periods.

The influence of bird droppings on the growth of lichen fragments transplanted to slate and cement substrates

The influence of bird droppings on the growth and fragmentation of five lichen species transplanted to slate and cement substrates was studied over a period of 15 months in South Gwynedd, Wales. The results suggested that at 15 months (1) thallus areas of Parmelia conspersa (Ehrh. Ex Ach.)Ach. were greater on both substrates with the addition of bird droppings with a greater increase on cement; (2) In Parmelia saxatilis (L.)Ach. And Parmelia glabratula ssp. fuliginosa (Fr. ex Duby)Laund., thallus areas were greatest on slate alone and least on cement with bird droppings; (3) in Physcia orbicularis (Neck.)Poetsch, thallus area was significantly reduced on cement alone compared with slate and cement treated with bird droppings; and (4) in Xanthoria parietina (L.)Th.Fr., thallus area was significantly greater on cement with bird droppings compared with slate and cement alone. These responses were attributable to the effect of the substrate and bird droppings on radial growth and the degree of fragmentation of the thalli. The results suggested that nutrient enrichment was more important than the substrate in determining the distribution of P. conspersa and Ph. orbicularis. However, the substrate and bird droppings were important in the remaining species, the data suggesting that P. saxatilis and P. glabratula ssp. fuliginosa would prefer nutrient-poor, siliceous rocks and X. parietina calcareous, nutrient enriched rocks in South Gwynedd.

Mesozoic to recent evolution of the Andean forearc of northern Chile (22-24 s)

The Andean forearc of northern Chile comprises four morphotectonic units, which include from east to west: 1) The Cordillera de la Costa: composed of Jurassic granites and andesites, thought to represent a volcanic arc, the Mejillones terrane, an accreted allochthonous terrane, and the Lower Cretaceous Coloso basin, which formed through forearc extension along the suture between the Mejillones terrane and the Jurassic arc. Palaeomagnetic studies of the above units have identified approximately 29+/-11 degrees of clockwise rotation. Rotation is due to extension (caused by subduction roll back and slab pull), at an angle to the direction of absolute motion of the South American Plate. 2) The Central Depression: a large arid basin containing isolated fault-bounded blocks of pre-Mesozoic metamorphosed igneous rocks, Triassic sediments and volcanics, and Jurassic carbonates, deposited in a. back-arc basin setting. The isolated blocks formed through extension along previous thrust faults, these originated through compression of the back-arc basin due to accretion of the Jurassic volcanic arc. 3) The Precordillera.: composed of Permian-Triassic rift-related sediments and volcanics, Jurassic continental sediments synchronous with back-arc basin sedimentation, and Cretaceous and Oligo-Miocene continental sediments deposited in foreland basins. Palaeomagnetism has identified clockwise rotation in rocks ranging in age from Jurassic-Miocene. Rotation in the Precordillera. affected larger structural blocks than in the Cordillera de la Costa. 4) The Salar Depression: a. series of arid continental basins developed on continental crust. These basins nay have originated in the Triassic, when rifting of the South American craton is thought to have taken place. In conclusion, palaeomagnetic and geological evidence is consistent with the view that the north Chilean forearc was largely under an extensional stress regime. However, the presence of extensive compressional structures in Palaeocene and older rocks in the forearc together with the currently active foreland thrust belt of Argentina. indicate that throughout the evolution of the Andean Orogen, a delicate balance between compressional and extensional tectonic regimes has existed.