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). and H. Nagy-Déri ... [et al.].
The effect of high temperature (HT) and dehydration on the activity of photosynthetic apparatus and its ability to restore membrane properties, oxygen evolution, and energy distribution upon rehydration were investigated in a resurrection plant, Haberlea rhodopensis. Plants growing under low irradiance in their natural habitat were desiccated to air-dry state at a similar light intensity [about 30 μol(photon) m-2 s-1] under optimal day/night (23/20°C) or high (38/30°C) temperature. Our results showed that HT alone reduced the photosynthetic activity and desiccation of plants at 38°C and it had more detrimental effect compared with desiccation at 23°C. The study on isolated thylakoids demonstrated increased distribution of excitation energy to PSI as a result of the HT treatment, which was enhanced upon the desiccation. It could be related to partial destacking of thylakoid membranes, which was confirmed by electron microscopy data. In addition, the surface charge density of thylakoid membranes isolated from plants desiccated at 38°C was higher in comparison with those at 23°C, which was in agreement with the decreased membrane stacking. Dehydration led to a decrease of amplitudes of oxygen yields and to a loss of the oscillation pattern. Following rehydration, the recovery of CO2 assimilation and fluorescence properties were better when desiccation was performed at optimal temperature compared to high temperature. Rehydration resulted in partial recovery of the amplitudes of flash oxygen yields as well as of population of S0 state in plants desiccated at 23°C. However, it was not observed in plants dehydrated at 38°C. and M. Velitchkova ... [et al.].
Photosynthetic activity of leaf disks from chlortoluron (2 µmol per plant) treated and non-treated non-transgenic and transgenic (PGF-6) tobacco plants was measured from 1 up to 21 d after treatment under greenhouse conditions. PGF-6 plants, expressing the fused rat cytochrome P4501A1/yeast reductase genes were used. PGF-6 plants were much more chlortoluron-resistant than control plants. In non-transgenic tobacco plants the electron transport flow to PQ pool was strongly inhibited 1 d after treatment with herbicide whereas it was still existing in PGF-6 plants although some reduction was observed. The quantum yield of photosystem 2 (ΦPS2) which is related to the quantum yield of whole-chain electron transfer was much more inhibited by chlortoluron than the primary PS2 photochemistry, measured by the ratio Fv/Fm. Lower PS2 activity was found for herbicide-treated non-transgenic plants up to the 9th day. Then it started to increase in both control and PGF-6 plants, but more rapidly in PGF-6 ones, and its values were near to the control level at the 21st d after chlortoluron treatment. and E. Yordanova ... [et al.].
Haberlea rhodopensis Friv. is unique with its ability to survive desiccation to an air-dry state during periods of extreme drought and freezing temperatures. To understand its survival strategies, it is important to examine the protective mechanisms not only during desiccation but also during rehydration. We investigated the involvement of alternative cyclic electron pathways during the recovery of photosynthetic functions after freezing-induced desiccation. Using electron transport inhibitors, the role of PGR5-dependent and NDH-dependent PSI-cyclic electron flows and plastid terminal oxidase were assessed during rehydration of desiccated leaves. Recovery of PSII and PSI, the capacity of PSI-driven cyclic electron flow, the redox state of plastoquinone pool, and the intersystem electron pool were analyzed. Data showed that the effect of alternative flows is more pronounced in the first hours of rehydration. In addition, the NDH-dependent cyclic pathway played a more determining role in the recovery of PSI than in the recovery of PSII.
The thermo-sensitivity of two new pea (Pisum sativum L.) cultivars-Afila (mutant in the gene transforming leaves into mustaches) and Ranen (mutant for early ripening)-as compared to the control cultivar Pleven-4 to either low (4 °C, T4) or high temperature (38 °C, T38) was investigated by means of chlorophyll (Chl) fluorescence kinetics. The low temperature treatment decreased the photosynthetic activity, measured via a decline of the Chl fluorescence decrease ratios RFd690 and RFd735, and this was mainly due to a decline of the Chl fluorescence decrease parameter Fd and maximum Chl fluorescence Fm. In the new cv. Ranen the RFd ratios at first decreased and increased again after 24-h exposure to 4 °C, indicating its good acclimation ability to low temperature. The cold-induced changes in the photosynthetic performance of all cultivars were reversed after transferring plants back to 23 °C for 48 h. In the Chl and carotenoid (Car) contents no or little changes occurred during the T4 treatment, except for a slight but clear increase of the ratio Chl a/b and a decrease in the ratio Chl/Car. In contrast to this, the T38 treatment for 72 h decreased the RFd ratios more strongly than the T4 exposure did. In fact, an irreversible injury of the photosynthetic apparatus was caused in the control pea cv. Pleven-4 by a 48-h T38 exposure and for the new cv. Afila after a 72-h T38 exposure. In contrast, the cv. Ranen was less and little sensitive to the T38 exposure. In the heat-sensitive cvs. Pleven-4 and Afila, the decrease in RFd values at T38 was associated with a strong decline of the Chl a+b and total Car contents. The Chl a+b decline could also be followed via an increase of the Chl fluorescence ratio F690/F735. Parallel to this, a strong decline of Chl a/b from ca. 3.0 (range 2.85-3.15) to ca. 1.9 (range 1.85-1.95) occurred indicating a preferential decline of the Chl a-pigment proteins but not of the Chl a/b-pigment protein LHC2. In the relatively heat-tolerant cv. Ranen, however, the ratio Chl a/b declined only partially. After the T4 treatment the stress adaptation index Ap was higher in cv. Ranen than in controls and reached in heat-treated Ranen plants almost the starting value indicating a cold and heat stress hardening of the treated plants. The Chl fluorescence parameters and pigment contents were influenced by T38 and T4 treatments in various ways indicating that the mechanisms of low and high temperature injury of the photosynthetic apparatus are different. The new cv. Ranen exhibited a cross tolerance showing a fairly good acclimation ability to both T4 and T38, hence it is a very suitable plant for outdoor growth and for clarification of the accl, imation mechanisms to unfavourable temperatures., and K. Georgieva, H. K. Lichtenthaler.
Alterations in photosynthetic performance of lutein-deficient mutant lut2 and wild type (wt) of Arabidopsis thaliana were followed after treatment with low temperature and high light for 6 d. The obtained results indicated lower electrolyte leakage, lower excitation pressure, and higher actual photochemical efficiency of PSII in lut2 plants exposed to combined stress compared to wt plants. This implies that lut2 is less susceptible to the applied stress conditions. The observed lower values of quantum efficiency of nonphotochemical quenching and energy-dependent component of nonphotochemical quenching in lut2 suggest that nonphotochemical quenching mechanism(s) localized within LHCII could not be involved in the acquisition of higher stress tolerance of lut2 and alternatives to nonphotochemical quenching mechanisms are involved for dissipation of excess absorbed light. We suggest that the observed enhanced capacity for cyclic electron flow and the higher oxidation state of P700 (P700+), which suggests PSI-dependent energy quenching in lut2 plants may serve as efficient photoprotective mechanisms, thus explaining the lower susceptibility of lut2 to the combined stress treatments.
The effect of high irradiance (HI) during desiccation and subsequent rehydration of the homoiochlorophyllous desiccation-tolerant shade plant Haberlea rhodopensis was investigated. Plants were irradiated with a high quantum fluence rate (HI; 350 µmol m-2 s-1 compared to ca. 30 µmol m-2 s-1 at the natural rock habitat below trees) and subjected either to fast desiccation (tufts dehydrated with naturally occurring thin soil layers) or slow desiccation (tufts planted in pots in peat-soil dehydrated by withholding irrigation). Leaf water content was 5 % of the control after 4 d of fast and 19 d of slow desiccation. Haberlea was very sensitive to HI under all conditions. After 19 d at HI, even in well-watered plants there was a strong reduction of rates of net photosynthesis and transpiration, contents of chlorophyll (Chl) and carotenoids, as well as photosystem 2 activity (detected by the Chl fluorescence ratio RFd). Simultaneously, the blue/red and green/red fluorescence ratios increased considerably suggesting increased synthesis of polyphenolic compounds. Desiccation of plants in HI induced irreversible changes in the photosynthetic apparatus and leaves did not recover after rehydration regardless of fast or slow desiccation. Only young leaves survived desiccation. and K. Georgieva, S. Lenk, C. Buschmann.