Determination of norflurazon concentration in wheat leaves using a modified QuEChERS method

The aim of this analytical study was to develop and validate an easy-to-use method for measuring the actual level of norflurazon that accumulates in leaves. We amended the QuEChERS method, i.e. Quick, Easy, Cheap, Effective, Rugged, and Safe, which is widely used for pesticide and herbicide analysis in food, and usually combined with HPLC-MS detection. We adapted this method for the detection of norflurazon in leaves or leaf fragments and proposed a useful modification using of HPLC-UV detection. Reproducible retention times of 3.11±0.04 min, precision (RSD<8.0%), LOQ=315 ng∙mL-1 and linearity (R=0.99874) were achieved

The pattern of photosynthetic response and adaptation to changing light conditions in lichens is linked to their ecological range

Epiphytic lichens constitute an important component of biodiversity in both deforested and forest ecosystems. Widespread occurrence is the domain of generalist lichens or those that prefer open areas. While, many stenoecious lichens find shelter only in a shaded interior of forests. Light is one of the factors known to be responsible for lichen distribution. Nevertheless, the effect of light intensity on photosynthesis of lichen photobionts remain largely unknown. We investigated photosynthesis in lichens with different ecological properties in relation to light as the only parameter modified during the experiments. The aim was to find links between this parameter and habitat requirements of a given lichen. We applied the methods based on a saturating light pulse and modulated light to perform comprehensive analyses of fast and slow chlorophyll fluorescence transient (OJIP and PSMT) combined with quenching analysis. We also examined the rate of $CO_{2}$ assimilation. Common or generalist lichens, i.e. Hypogymnia physodes, Flavoparmelia caperata and Parmelia sulcata, are able to adapt to a wide range of light intensity. Moreover, the latter species, which prefers open areas, dissipates the excess energy most efficiently. Conversely, Cetrelia cetrarioides considered an old-growth forest indicator, demonstrates definitely lower range of energy dissipation than other species, although it assimilates $CO_{2}$ efficiently both at low and high light. We conclude that functional plasticity of the thylakoid membranes of photobionts largely determines the dispersal abilities of lichens and light intensity is one of the most important factors determining the specificity of a species to a given habitat

Photoinduction of seed germination in Arabidopsis thaliana is modulated by phototropins

Light exposure is an important environmental factor which breaks seed dormancy in many plant species. Phytochromes have been identified as playing a crucial role in perception of the light signal that releases seed germination in Arabidopsis. Phototropins (Phot1, Phot2) are blue/UV-photoreceptors in plants which mediate phototropic responses, chloroplast relocation, hypocotyl growth inhibition and stomata opening. We studied germination under different light conditions in Arabidopsis Phot1-null and Phot2-null mutants and in a double phot1phot2 mutant. Germination of single phot1 and phot2 mutants in darkness was much lower than in wildtype (WT) seeds, whereas double phot1phot2 mutant lacking both functional phototropins germinated at frequency comparable to WT seeds, irrespective of light and temperature conditions. Light treatment of imbibed seeds was essential for effective germination of phot1, irrespective of low-temperature conditioning. In contrast, cold stratification promoted dark germination of phot2 seeds after imbibition in dim light. Low germination frequency of phot1 seeds under low light intensity suggests that the presence of functional Phot1 might be crucial for effective germination at these conditions. The lower germination frequency of phot2 seeds under continuous light suggests that Phot2 might be responsible for stimulating germination of seeds exposed to direct daylight. Thus, the phototropin system may cooperate with phytochromes regulating the germination competence of seeds under different environmental conditions

Variations in xanthophyll composition in etiolated seedlings of Arabidopsis thaliana correlate with protochlorophyllide accumulation

Protochlorophyllide (Pchlide) accumulation and xantophyll composition were studied in 5-day old etiolated seedlings of three ecotypes of Arabidopsis thaliana: Columbia (Col-0), Landsberg erecta (Ler) and Wassiliewska (Ws). The total Pchlide level as measured by fluorescence spectroscopy varied significantly between ecotypes. A rapid HPLC method revealed quantitative differences in carotenoid composition. It was found that in the Ler ecotype any enhanced accumulation of Pchlide correlates with an increased level of lutein, suggesting the role of enzymes involved in lutein synthesis in cross-regulation between chlorophyll and carotenoid biosynthetic pathways. The function of the dark-accumulated carotenoid pool in seedling de-etiolation is discussed

Photoactive protochlorophyllide-enzyme complexes reconstituted with PORA, PORB and PORC proteins of A. thaliana : fluorescence and catalytic properties

Photoactive Pchlide-POR-NADPH complexes were reconstituted using protochlorophyllide (Pchlide) and recombinant light-dependent protochlorophyllide oxidoreductase (POR) proteins, His₆-PORA, His₆-PORB and His₆-PORC, from Arabidopsis thaliana. We did not observe any differences in the kinetics of the protochlorophyllide photoreduction at room temperature among the PORA, PORB and PORC proteins. In contrast, the PORC protein showed lower yield of Chlide formation than PORA and PORB when preincubated in the dark for 30 min and then illuminated for a short time. The most significant observation was that reconstituted Pchlide-POR-NADPH complexes showed fluorescence maxima at 77 K similar to those observed for highly aggregated Pchlide-POR-NADPH complexes in prolamellar bodies (PLBs) in vivo. Homology models of PORA, PORB and PORC of Arabidopsis thaliana were developed to compare predicted structures of POR isoforms. There were only slight structural differences, mainly in the organisation of helices and loops, but not in the shape of whole molecules. This is the first comparative analysis of all POR isoforms functioning at different stages of A. thaliana development

Ionic, not the osmotic component, is responsible for the salinity-induced inhibition of greening in etiolated wheat (Triticum aestivum L. cv. Mv Béres) leaves : a comparative study

Main conclusion Greening was partially (in 300 mM NaCl, $CaCl_{2}$, 600 mM $KNO_{3}$ or KCl) or fully inhibited (in 600 mM NaCl, $NaNO_{3}$ or NaCl:KCl) by the ionic and not the osmotic component of salinity. Abstract Although high soil salinity is an increasing global problem, not much is known about how direct exposure to salinity affects etiolated leaves of seedlings germinating in the soil and then reaching the surface. We investigated the effect of various salt treatments on the greening process of leaves in 8- to 11-day-old etiolated wheat (Triticum aestivum L. Mv. Béres) seedlings. Etiolated leaf segments pre-treated on different salt (600 mM NaCl:KCl 1:1, 600 mM NaCl, 600 mM KCl, 600 mM $NaNO_{3}$, 600 mM KNO3, 300 mM KCl, 300 mM NaCl or 300 mM $CaCl_{2}$) or isosmotic polyethylene glycol 6000 (PEG) solutions for 1.5 h in the dark and then greened for 16 h on the same solutions were studied. Leaf segments greened on PEG (osmotic stress) or on 300 mM KCl had similar chloroplasts compared to control samples greened on Hoagland solution. Slightly slower development of chloroplast structure and function (photosynthetic activity) was observed in segments greened on 300 mM NaCl or $CaCl_{2}$, 600 mM KNO3 or KCl. However, etioplast-to-chloroplast transformation and chlorophyll accumulation were fully inhibited and peculiar prothylakoid swelling occurred in segments greened on 600 mM NaCl, $NaNO_{3}$ or NaCl:KCl (1:1) solutions. The data indicate that not the high osmolarity of the used salt solution, but its ions, especially $Na^{+}$, had the strongest negative impact on these processes

Cadmium inhibitory action leads to changes in structure of ferredoxin:NADP+ oxidoreductase

This study deals with the influence of cadmium on the structure and function of ferredoxin:NADP(+) oxidoreductase (FNR), one of the key photosynthetic enzymes. We describe changes in the secondary and tertiary structure of the enzyme upon the action of metal ions using circular dichroism measurements, Fourier transform infrared spectroscopy and fluorometry, both steady-state and time resolved. The decrease in FNR activity corresponds to a gentle unfolding of the protein, caused mostly by a nonspecific binding of metal ions to multiple sites all over the enzyme molecule. The final inhibition event is most probably related to a bond created between cadmium and cysteine in close proximity to the FNR active center. As a result, the flavin cofactor is released. The cadmium effect is compared to changes related to ionic strength and other ions known to interact with cysteine. The complete molecular mechanism of FNR inhibition by heavy metals is discussed. Electronic supplementary material The online version of this article (doi:10.1007/s10867-012-9262-z) contains supplementary material, which is available to authorized users

Non-typical fluorescence effects and biological activity in selected 1,3,4-thiadiazole derivatives : spectroscopic and theoretical studies on substituent, molecular aggregation, and pH effects

The below article presents the results of spectroscopic research, theoretical (time-dependent density functional theory (TD-DFT)), microbiological, and antioxidative calculations for three compounds from the group of 1,3,4-thiadiazoles: 2-amino-5-phenyl-1,3,4-thiadiazole (TB), 2-amino-5-(2-hydroxyphenyl)-1,3,4-thiadiazole (TS), 2-amino-5-(2-hydroxy-5-sulfobenzoyl)-1,3,4-thiadiazole (TSF). In the fluorescence emission spectra (TS) of solutions with varying concentrations of hydrogen ions, a particularly interesting effect of dual fluorescence was observed. The aforementioned effect was observed even more clearly in the environment of butan-1-ol, relative to the compound&rsquo;s concentration. Depending on the modification of the resorcylic substituent (TS and TSF), we observed the emergence of two separate, partially overlapping, fluorescence emission spectra or a single emission spectrum. Interpretation of the obtained spectra using stationary and time-resolved spectroscopy allowed the correlation of the effect&rsquo;s emergence with the phenomenon of molecular aggregation (of a particular type) as well as, above all, the structure of the substituent system. The overlap of said effects most likely induces the processes related to the phenomenon of charge transfer (in TS) and is responsible for the observed fluorescence effects. Also, the position of the &ndash;OH group (in the resorcylic ring) is significant and can facilitate the charge transfer (CT). The determinations of the changes in the dipole moment and TD-DFT calculations further corroborate the above assumption. The following paper presents the analysis (the first for this particular group of analogues) of the fluorescence effects relative to the changes in the structure of the resorcylic group combined with pH effects. The results of biological studies also indicate the highest pharmacological potential of the analogue in the case where the effects of dual fluorescence emission are observed, which predisposes this particular group of fluorophores as effective fluorescence probes or potential pharmaceuticals with antimycotic properties

Origin of Chlorophyll Fluorescence in Plants at 55–75°C ¶

The origin of heat-induced chlorophyll fluorescence rise that appears at about 55–60°C during linear heating of leaves, chloroplasts or thylakoids (especially with a reduced content of grana thylakoids) was studied. This fluorescence rise was earlier attributed to photosystem I (PSI) emission. Our data show that the fluorescence rise originates from chlorophyll a (Chl a ) molecules released from chlorophyll-containing protein complexes denaturing at 55–60°C. This conclusion results mainly from Chl a fluorescence lifetime measurements with barley leaves of different Chl a content and absorption and emission spectra measurements with barley leaves preheated to selected temperatures. These data, supported by measurements of liposomes with different Chl a /lipid ratios, suggest that the released Chl a is dissolved in lipids of thylakoid membranes and that with increasing Chl a content in the lipid phase, the released Chl a tends to form low-fluorescing aggregates. This is probably the reason for the suppressed fluorescence rise at 55–60°C and the decreasing fluorescence course at 60–75°C, which are observable during linear heating of plant material with a high Chl a /lipid ratio ( e.g. green leaves, grana thylakoids, isolated PSII particles).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74574/1/0031-8655_2003_0770068OOCFIP2.0.CO2.pd