Jezerní sedimenty jsou ideálním přírodním archivem, který zachycuje minulé změny nejen samotného jezera, ale i okolního prostředí. Jsou zároveň jedinečné tím, že se v nich zachovávají zbytky těl různých organismů, z čehož lze zrekonstruovat druhové složení celého jezerního ekosystému. Zjištěné druhy nám také poskytují informace o životním prostředí v minulosti. Díky postupnému usazování jezerního sedimentu v průběhu holocénu tak můžeme zaznamenat nejen dlouhodobý vývoj rostlinných společenstev, ale i přírodních podmínek v horizontu tisíců let. V jezeře Šúr se během pozdního glaciálu vyskytovaly vodní rostliny rdesty, stolístky a parožnatky. Od časného holocénu se začaly objevovat na živiny a teplo náročnější druhy, jako např. šejdračka bahenní či růžkatce a během středního holocénu v jezeře expandovala kotvice plovoucí a lekníny. Na konci středního holocénu a během pozdního holocénu postupně došlo k zaplnění jezera organickým materiálem a vzniku ostřicové slatiny a posléze olšového lesa., Lake sediments are natural archives of past changes not only in the lake itself, but also in its surroundings. They preserve remains of numerous organisms, from which the species composition of the entire lake ecosystem can be reconstructed, providing information about the past environment. Thanks to gradual deposition of sediment in the lake Šúr (western Slovakia) during the Holocene period, both the long-term development of plant communities and the environmental conditions over thousands of years can be reconstructed. During the succession, aquatic communities were replaced by sedge fen and alder forest., and Anna Potůčková.
The influence of arbuscular mycorrhizal (AM) fungus Glomus deserticola (Trappe and John) on plant growth, nutrition, flower yield, water relations, chlorophyll (Chl) contents and water-use efficiency (WUE) of snapdragon (Antirhinum majus cv. butterfly) plants were studied in potted culture under well-watered (WW) and water-stress (WS) conditions. The imposed water stress condition significantly reduced all growth parameters, nutrient contents, flower yield, water relations, and Chl pigment content and increased the electrolyte leakage of the plants comparing to those of nonstressed plants. Regardless of the WS level, the mycorrhizal snapdragon plants had significantly higher shoot and root dry mass (DM), WUE, flower yield, nutrient (P, N, K, Mg, and Ca) and Chl contents than those nonmycorrhizal plants grown both under WW or WS conditions. Under WS conditions, the AM colonization had greatly improved the leaf water potential (Ψw), leaf relative water content (RWC) and reduced the leaf electrolyte leakage (EL) of the plants. Although the WS conditions had markedly increased the proline content of the leaves, this increase was significantly higher in nonmycorrhizal than in mycorrhizal plants. This suggests that AM colonization enhances the host plant WS tolerance. Values of benefit and potential dry matter for AM-root associations were highest when plants were stressed and reduced under WW conditions. As a result, the snapdragon plants showed a high degree of dependency on AM fungi which improve plant growth, flower yield, water relations particularly under WS conditions, and these improvements were increased as WS level had increased. This study confirms that AM colonization can mitigate the deleterious effect of water stress on growth and flower yield of the snapdragon ornamental plant., A. A. Asrar, G. M. Abdel-Fattah, K. M. Elhindi., and Obsahuje bibliografii
The aim of the current work was to determine whether grafting could improve salinity tolerance of melon and cucumber, and whether possible induction of tolerance to salt stress was associated with the protection of the photosynthetic apparatus. Two greenhouse experiments were carried out to determine gas exchange, mineral composition, growth and yield of melon (Cucumis melo L. cv. Cyrano) and cucumber (Cucumis sativus L. cv. Akito) plants, either ungrafted or grafted onto the Cucurbita hybrid rootstocks (Cucurbita maxima Duch. × Cucurbita moschata Duch.), ‘P360’, and ‘PS1313’, respectively. Plants were grown hydroponically and supplied with two nutrient solutions - a nonsalinized control and a salinized solution which contained 40 mmol L-1 of NaCl. Salinity induced a smaller decrease in leaf area index (LAI), in grafted-compared to ungrafted plants. Similarly, the
PN and gs reduction in NaCl treatment compared to control were significantly lower in grafted plants (34% and 34%, respectively, for melon and 14% and 15.5%, respectively, for cucumber) compared to ungrafted plants (42% and 40%, respectively, for melon and 30% and 21%, respectively, for cucumber). In all grafting combinations, negative correlations were recorded between Na+ and Cl- in the leaf tissue and PN. Grafting reduced concentrations of sodium, but not chloride, in leaves. Under saline conditions a smaller reduction in melon and cucumber shoot biomass dry mass and fruit yield were recorded, with positive correlations between shoot biomass, yield and PN. These results suggest that the use of salt tolerant Cucurbita rootstock can improve melon and cucumber photosynthetic capacity under salt stress and consequently crop performance., Y. Rouphael ... [et al.]., and Obsahuje bibliografii
To investigate the effect of low CO2 on the expression and activity of ferredoxin-NADP+ oxidoreductase (FNR) and this enzyme-mediated cyclic electron flow around photosystem I (cyclic PSI), the activity staining, immunoblotting and initial rate of P700 + reduction were measured in high- or low-CO2-grown (H or L)-cells of wild-type Synechocystis sp. strain PCC 6803 (WT) and its ΔndhB mutant (M55). Major results were depicted as follows. (1) The protein levels and activity of FNR were remarkably stimulated in L-cells of both WT and M55 relative to that in their H-cells. (2) The rate of cyclic PSI was significantly increased in L-cells of WT, not M55, when compared to that in respective H-cells. (3) N-ethylmaleimide, an inhibitor of FNR, partially inhibited the increase in the rate of cyclic PSI induced by low CO2 in both WT and M55. These findings indicated that low CO2 enhanced the expression and activity of FNR and the cyclic PSI mediated by FNR. The contribution of FNR to cyclic PSI is shortly discussed. and Y. R. Liu, W. M. Ma, H. L. Mi.
In the terrestrial bromeliad, Puya floccosa, a value of carbon isotopic composition (δ13C) of -22‰ has been previously reported, suggesting the operation of weak and/or intermediate (C3-CAM) crassulacean acid metabolism (CAM). In order to characterize the operation of CAM in P. floccosa and its possible induction by drought, plants were grown in Caracas and subjected to four independent drought cycles. Additionally, since plants of this species grow in Venezuela in a large range of elevations, leaf samples were collected at elevations ranging from 725 to 2,100 m a.s.l. in the Venezuelan Andes and the Coastal Range, in order to evaluate the effect of elevation on CAM performance. Even though nocturnal acid accumulation occurred in both watered and droughted plants, mean ΔH+ was higher in droughted than watered plants [ΔH+ = 60.17.5 and 22.9 ± 5.2 μmol g-1(FM), respectively]. The majority of plants from all the natural populations sampled had low values of δ13C not differing significantly from those of C3 plants collected as standards and δ13C did not change with elevation. We conclude that P. floccosa is capable of a weak CAM activity, with a large variability among populations and drought experiments probably due to local and temporal differences in microclimatic variables and drought stress; elevation bears no influence on values of δ13C in this species. and A. Herrera ... [et al.].
Predicted future climatic changes for the Mediterranean region give additional importance to the study of photooxidative stress in local economic species subjected to combined drought and
high-temperature conditions. Under this context, the impact of these stresses on photosynthesis, energy partitioning, and membrane lipids, as well as the potential ability to attenuate oxidative damage, were investigated in Ceratonia siliqua L. Two thermal regimes (LT: 25/18°C; HT: 32/21°C) and three soil water conditions (control, water stress, and rewetting) were considered. HT exacerbated the adverse effects of water shortage on photosynthetic rates (PN) and PSII function. The decrease in PN was 33% at LT whereas at HT it was 84%. In spite of this, the electron transport rate (ETR) was not affected, which points to an increased allocation of reductants to sinks other than CO2 assimilation. Under LT conditions, water stress had no significant effects on yield of PSII photochemistry (ΦPSII) and yields of regulated (ΦNPQ) and nonregulated (ΦNO) energy dissipation. Conversely, drought induced a significant decrease of ΦPSII and a concomitant increase of ΦNO in HT plants, thereby favouring the overproduction of reactive oxygen species (ROS). Moreover, signs of lipid peroxidation damage were detected in HT plants, in which drought caused an increase of 40% in malondialdehyde (MDA) content. Concurrently, a marked increase in proline content was observed, while the activities of catalase (CAT) and ascorbate peroxidase (APX) were unaffected. Despite the generation of a moderate oxidative stress response, C. siliqua revealed a great capability for photosynthetic recovery 36 h after rewatering, which suggests that the species can cope with predicted climate change. and M. L. Osório ... [et al.].
This work aimed to evaluate if gas exchange and PSII photochemical activity in maize are affected by different irradiance levels during short-term exposure to elevated CO2. For this purpose gas exchange and chlorophyll a fluorescence were measured on maize plants grown at ambient CO2 concentration (control CO2) and exposed for 4 h to short-term treatments at 800 μmol(CO2) mol-1 (high CO2) at a photosynthetic photon flux density (PPFD) of either 1,000 μmol m-2 s-1 (control light) or 1,900 μmol m-2 s-1 (high light). At control light, high-CO2 leaves showed a significant decrease of net photosynthetic rate (PN) and a rise in the ratio of intercellular to ambient CO2 concentration (Ci/Ca) and water-use efficiency (WUE) compared to control CO2 leaves. No difference between CO2 concentrations for PSII effective photochemistry (ΦPSII), photochemical quenching (qp) and nonphotochemical quenching (NPQ) was detected. Under high light, high-CO2 leaves did not differ in PN, Ci/Ca, ΦPSII and NPQ, but showed an increase of WUE. These results suggest that at control light photosynthetic apparatus is negatively affected by high CO2 concentration in terms of carbon gain by limitations in photosynthetic dark reaction rather than in photochemistry. At high light, the elevated CO2 concentration did not promote an increase of photosynthesis and photochemistry but only an improvement of water balance due to increased WUE. and C. Arena, L. Vitale, A. Virzo de Santo.
Low temperature significantly influences chloroplast development and chlorophyll (Chl) biosynthesis, so effect of coldness on Chl content and Chl fluorescence characteristics was investigated in C. bungeana (Chorispora bungeana Fisch. & C.A. Mey). The levels of transcript and protein of an enzymatic step during Chl biosynthesis in response to chilling (4°C) and freezing (-4°C) were also examined in this work. Significant reduction in total Chl content was observed, but the reduction was much less at 4°C than that at -4°C. Moreover, the maximal quantum efficiency of photosystem II (PSII) photochemistry, indicated by Fv/Fm, decreased in the first 12 h, but then started to increase and reached higher levels than the control at 24 h and 48 h at 4°C, but decreased continuously at -4°C. Whereas quantum yield of PSII (ΦPSII) showed no significant difference between the chilling-stressed and the control seedlings, at -4°C, ΦPSII was markedly reduced with the prolonged treatment. In general, there were no significant responses of photochemical quenching (qP) and non-photochemical quenching (NPQ) to cold treatment. Meanwhile, the full-length cDNA of NADPH:protochlorophyllide oxidoreductase (POR, EC 1.3.1.33) was isolated and termed CbPORB (GenBank Accession No. FJ390503). Its transcript and protein content only slightly declined at 4°C, but dramatically reduced at -4°C with the time. These results strongly suggest that CbPORB possesses certain resistant characteristics and is a major player in Chl biosynthesis process involved in plant growth and development of C. bungeana under cold environmental conditions. and Y. H. Li ... [et al.].