Evelin Ramóna Péli

Photosynthetic activity of homoiochlorophyllous desiccation tolerant plant Haberlea rhodopensis during dehydration and rehydration

The functional state of the photosynthetic apparatus of flowering homoiochlorophyllous desiccation tolerant plant Haberlea rhodopensis during dehydration and subsequent rehydration was investigated in order to characterize some of the mechanisms by which resurrection plants survive drought stress. The changes in the CO2 assimilation rate, chlorophyll fluorescence parameters, thermoluminescence, fluorescence imaging and electrophoretic characteristics of the chloroplast proteins were measured in control, moderately dehydrated (50% water content), desiccated (5% water content) and rehydrated plants. During the first phase of desiccation the net CO2 assimilation decline was influenced by stomatal closure. Further lowering of net CO2 assimilation was caused by both the decrease in stomatal conductance and in the photochemical activity of photosystem II. Severe dehydration caused inhibition of quantum yield of PSII electron transport, disappearance of thermoluminescence B band and mainly charge recombination related to S2QA− takes place. The blue and green fluorescence emission in desiccated leaves strongly increased. It could be suggested that unchanged chlorophyll content and amounts of chlorophyll–proteins, reversible modifications in PSII electron transport and enhanced probability for non-radiative energy dissipation as well as increased polyphenolic synthesis during desiccation of Haberlea contribute to drought resistance and fast recovery after rehydration.

Copper tolerance in the macrolichens Cladonia furcata and Cladina arbuscula subsp. mitis is constitutive rather than inducible.

In this study we assessed the degree of copper (Cu) tolerance in two common lichen species (Cladonia furcata and Cladina arbuscula subsp. mitis) that grow on both uncontaminated substrata and the surface of waste heaps from abandoned old Cu-mines. Regardless of their locality, populations of these lichens contain identical strains of photobionts (Asterochloris clade A in C. arbuscula subsp. mitis and clade D in C. furcata). Therefore, it was expected that if there were differences in Cu toxicity or tolerance between populations, that the photobiont could not be a key element of Cu tolerance in these two lichen species. In laboratory experiments samples of both lichen species (from contaminated and control sites) were incubated in Cu solutions (500 μM) for 24 h. We attempted to determine whether Cu tolerance in these lichens was constitutive, or inducible form. Based on measurements of Cu accumulation, chlorophyll a integrity, chlorophyll a fluorescence, photosynthesis, respiration, measurements of the content of thiobarbituric acid reactive substances (TBARS), the content of soluble proteins, reactive oxygen species (ROS) and the amount of extracellular secondary metabolites of both lichens we found that there were no significant differences in the response of all selected populations of both lichen species to short-term exposure to these high levels of Cu. As a result, we conclude that Cu tolerance in these two lichen species is the constitutive rather than the inducible.

Changes in chloroplast morphology of different parenchyma cells in leaves of Haberlea rhodopensis Friv. during desiccation and following rehydration

The size, shape, and number of chloroplasts in the palisade and spongy parenchyma layers of Haberlea rhodopensis leaves changed significantly during desiccation and following rehydration. The chloroplasts became smaller and more rounded during desiccation, and aggregated in the middle of the cell. The size and number of chloroplasts in the palisade parenchyma cells were higher than in spongy parenchyma. The good correlation observed between the size or number of chloroplasts and the cross-sectional area of mesophyll cells, the cross-sectional width of the leaf and its water content suggested that the palisade cells were more responsive to water availability than the spongy cells. Changes in chloroplast number during desiccation and rehydration process are characteristic features for desiccation-tolerant plants (especially in homoiochlorophyllous strategy).

Ecophysiological responses of desiccation-tolerant cryptobiotic crusts

In our present studies, the recovery of photosynthetic activity after rehydration was demonstrated. We measured chlorophyll fluorescence, CO2 gas exchange and the pigment composition in the previously long-term air-dried cryptogamic inselberg crusts collected from two tropical areas. The cryptobiotic crusts were collected from different localities on similar ecological and climatic conditions from extreme habitats of inselbergs (outcrops). These inselbergs are characterized by a dry microclimate and are covered by scarce soil. We found that the ecophysiological responses of both cryptogamic inselberg crusts showed an extremely high degree of desiccation-tolerance due to the fast and full recovery during rehydration. The photosynthetic activity of the cryptobiotic crusts were restored and regained within 15 and 40 min, respectively, after rehydration. Photosynthetic activity of the crusts was retained at all applied light intensities when enough water was available, however the degree of the recovery was different between the crusts. Photosynthetic pigment contents were strongly and positively correlated with water content. Our results indicated that tropical desiccation-tolerant cryptogamic crusts found on inselberg rock surfaces have CO2 fixation ability in the range of cyanobacteria and lichens, suggesting that at a global scale they can assimilate CO2 in a significant amount.

Decomposition Rate, and Carbon and Nitrogen Dynamics of Sphagnum Litter: Lessons from a Peat Bog

ABSTRACT Decomposition rates and changes of carbon and nitrogen contents of Sphagnum litter in mire vegetation can help to explore the ecological effects of climate change and the role of environmental factors from a local to an ecosystem scale. The objective of the study was to determine the relationship between mentioned parameters in small and isolated Sphagnum dominated mires. Measurements had been conducted throughout a year by placing litterbags filled with Sphagnum biomass in three vegetation types (open peat bog, poor fen, alder carr) of a mire ecosystem in Hungary. Peat decomposition rates differed to a great extent; the slowest decomposition rate (39.1±9.52%) was in the alder carr, indicating that slower decomposition could be characteristic for this kind of vegetation type of mire. Between Sphagnum dominated microhabitats, open peat bog showed medium (65.57±4.05) while poor fen the fastest (68.61±5.5) rates in decomposition. The C/N ratio of the Sphagnum litter showed significant decrease (P <0.005) in all studied micro-environments. Slower N release was observed from litter of Alnus dominated association (31.3±6.9%) compared to Sphagnum dominated ones (56.5±8.3%). Our findings showed that the decomposition rates were more dependent on vegetation type than C/N ratio and this relationship was also revealed at a small spatial scale.

Differences in histological and physiological traits of ozone sensitive and resistant bean strains

An examination of possible histological causes of differences in ozone sensitivity between ozone sensitive (R123) and resistant (S156) Phaseolus vulgaris strains was carried out. A distinction between the causes and effects of ozone sensitivity was also performed. We studied several morphological and histological traits, which included stomata number and size and also looked at different cell characteristics, such as stomatal index; leaf tissue thickness, fraction and gaseous conductance of intercellular air spaces. Together with this, we made gas-exchange measurements and found inner CO2 levels to be higher in the ozone sensitive strain. We also found several quantitative morphological parameters between the two strains to be initially different, however, these differences changed after exposure to summer climate and ozone. Stomatal function between the two strains was also differently altered by the pollutant, which was apparent from differences in stomatal openness when investigated in summer. According to our histological data, epidermal cells of the ozone sensitive strain grew larger on leaves that developed after exposure to cumulative considerable phytotoxic ozone doses; moderately decreasing the number of stomata and epidermal cells per mm2 epidermal area despite the originally higher number of epidermal cells in sensitive plants. Cross sections of injured sensitive leaves revealed disorganisation of mesophyllum tissues.