Chlorophyll Fluorescence Assays Research Articles

Salt-Induced Modulation of Ion Transport and PSII Photoprotection Determine the Salinity Tolerance of Amphidiploid Brassicas.

Brassica species show varying levels of resistance to salt stress. To understand the genetics underlying these differential stress tolerance patterns in Brassicas, we exposed two widely cultivated amphidiploid Brassica species having different genomes, Brassica juncea (AABB, n = 18) and Brassica napus (AACC, n = 19), to elevated levels of NaCl concentration (300 mM, half the salinity of seawater). B. juncea produced more biomass, an increased chlorophyll content, and fewer accumulated sodium (Na+) and chloride (Cl-) ions in its photosynthesizing tissues. Chlorophyll fluorescence assays revealed that the reaction centers of PSII of B. juncea were more photoprotected and hence more active than those of B. napus under NaCl stress, which, in turn, resulted in a better PSII quantum efficiency, better utilization of photochemical energy with significantly reduced energy loss, and higher electron transport rates, even under stressful conditions. The expression of key genes responsible for salt tolerance (NHX1 and AVP1, which are nuclear-encoded) and photosynthesis (psbA, psaA, petB, and rbcL, which are chloroplast-encoded) were monitored for their genetic differences underlying stress tolerance. Under NaCl stress, the expression of NHX1, D1, and Rubisco increased several folds in B. juncea plants compared to B. napus, highlighting differences in genetics between these two Brassicas. The higher photosynthetic potential under stress suggests that B. juncea is a promising candidate for genetic modifications and its cultivation on marginal lands.

Evaluating disinfection performance of ultraviolet light-emitting diodes against the microalga Tetraselmis sp.: Assay methods, inactivation efficiencies, and action spectrum

Ultraviolet light-emitting diodes (UV-LEDs) are among the most compact devices and safest technologies in water disinfection systems. However, the validation of different assay methods to evaluate the disinfection performance of different wavelengths (265, 280, 285, and 300 nm) of UV-LEDs toward marine microalgae remains poorly characterized. In this study, several detection assays, namely the culture-based most probable number (MPN) assay, membrane integrity-based vital stain (VS) assay, chlorophyll fluorescence assay, and photochemical efficiency assay, were compared to assess the viability of the marine microalga Tetraselmis sp., with results indicating the MPN assay to be the most sensitive. In addition, this study compared the inactivation kinetics, inactivation efficiency, and energy efficiency of Tetraselmis sp. under different UV wavelengths, as assessed by the VS and MPN assays. The fluence-response curves of Tetraselmis sp. varied with assay and wavelength, with Geeraerd's model fitting all fluence-response microalgal inactivation curves. The results showed a non-significant difference in inactivation efficiency among different wavelengths of UV-LEDs (except for 300 nm) when using the VS assay. On the contrary, significant differences among all wavelengths were observed with respect to inactivation efficiency when using the MPN assay. The wavelength of 265 nm exhibited maximum inactivation efficiency, whereas 285 nm achieved optimal energy efficiency. The UV action spectrum of Tetraselmis sp. exhibited the peak at 265 nm, a finding which matched well with the absorbance spectrum of DNA. The observations from this study provide a theoretical basis and technical support for the application of the emerging UV-LED light sources in the algicidal treatment of marine water.

Colorimetric and Chlorophyll Fluorescence Assays for Fast Detection and Selection of Transgenic Events of Cotton, Cowpea, Soybean and Common Bean Expressing the Atahas Gene

Colorimetric and Chlorophyll Fluorescence Assays for Fast Detection and Selection of Transgenic Events of Cotton, Cowpea, Soybean and Common Bean Expressing the <i>Atahas</i> Gene

Zoysia japonica Chlorophyll b Reductase Gene NOL Participates in Chlorophyll Degradation and Photosynthesis.

The degradation of chlorophyll is of great significance to plant growth. The chlorophyll b reductase NOL (NYC1-like) is in charge of catalyzing the degradation of chlorophyll b and maintaining the stability of the photosystem. However, the molecular mechanisms of NOL-mediated chlorophyll degradation, senescence, and photosynthesis and its functions in other metabolic pathways remain unclear, especially in warm-season turfgrass. In this study, ZjNOL was cloned from Zoysia japonica. It is highly expressed in senescent leaves. Subcellular localization investigation showed ZjNOL is localized in the chloroplast and the bimolecular fluorescence complementation (BiFC) results proved ZjNOL interacts with ZjNYC1 in vivo. ZjNOL promoted the accumulation of abscisic acid (ABA) and carbohydrates, and the increase of SAG14 at the transcriptional level. ZjNOL simultaneously led to the excessive accumulation of reactive oxygen species (ROS), the activation of antioxidant enzymes, and the generation of oxidative stress, which in turn accelerated senescence. Chlorophyll fluorescence assay (JIP-test) analysis showed that ZjNOL inhibited photosynthetic efficiency mainly through damage to the oxygen-evolving complex. In total, these results suggest that ZjNOL promotes chlorophyll degradation and senescence and negatively affects the integrity and functionality of the photosystem. It could be a valuable candidate gene for genome editing to cultivate Z. japonica germplasm with prolonged green period and improved photosynthesis efficiency.

Impact of exogenous growth regulators on growth and photosynthetic activity in dwarf mandarin plants (Citrus unshiu Marc.)

The impact of synthetic regulators on the growth and development of mandarin plants was investigated. It was shown that the exposure of plants to growth regulators had no effect on leaf chlorophyll content. Non-root application of nanoelicitor and siliplant synthetic regulators elevated the carotenoid content to 2.69-3.11 mg/g (control, water: 2.57 mg/g) and stimulated protective response. The total chlorophyll- carotenoid ratio in plants treated with nanoelicitor (4.29 mg/g) and siliplant (4.12 mg/g) was less than in the control, reflecting the degree of plant adaptation to adverse conditions in the growing season. Exposure to growth regulators improved photosynthetic activity and overall functionality. Chlorophyll fluorescence assays were used to evaluate photosynthetic activity coefficient as falling within a range of 0.54-0.57, which exceeded the control by 1.2-fold. Nanoelicitor was shown to induce active shooting and reduce fruit shedding. Compared to the control, growth regulators increased the retained fruit value by 1.5-1.9-fold and improved plantation productivity. Phytoregulators have shown promise in both improving the functional condition and reducing preharvest shedding in dwarf mandarin plants.

Cysts of the Snow Alga Chloromonas krienitzii (Chlorophyceae) Show Increased Tolerance to Ultraviolet Radiation and Elevated Visible Light.

Melting mountainous snowfields are populated by extremophilic microorganisms. An alga causing orange snow above timberline in the High Tatra Mountains (Poland) was characterised using multiple methods examining its ultrastructure, genetics, life cycle, photosynthesis and ecophysiology. Based on light and electron microscopy and ITS2 rDNA, the species was identified as Chloromonas krienitzii (Chlorophyceae). Recently, the taxon was described from Japan. However, cellular adaptations to its harsh environment and details about the life cycle were so far unknown. In this study, the snow surface population consisted of egg-shaped cysts containing large numbers of lipid bodies filled presumably with the secondary carotenoid astaxanthin. The outer, spiked cell wall was shed during cell maturation. Before this developmental step, the cysts resembled a different snow alga, Chloromonas brevispina. The remaining, long-lasting smooth cell wall showed a striking UV-induced blue autofluorescence, indicating the presence of short wavelengths absorbing, protective compounds, potentially sporopollenin containing polyphenolic components. Applying a chlorophyll fluorescence assay on intact cells, a significant UV-A and UV-B screening capability of about 30 and 50%, respectively, was measured. Moreover, intracellular secondary carotenoids were responsible for a reduction of blue-green light absorbed by chloroplasts by about 50%. These results revealed the high capacity of cysts to reduce the impact of harmful UV and high visible irradiation to the chloroplast and nucleus when exposed at alpine snow surfaces during melting. Consistently, the observed photosynthetic performance of photosystem II (evaluated by fluorometry) showed no decline up to 2100 μmol photons m–2 s–1. Cysts accumulated high contents of polyunsaturated fatty acids (about 60% of fatty acids), which are advantageous at low temperatures. In the course of this study, C. krienitzii was found also in Slovakia, Italy, Greece and the United States, indicating a widespread distribution in the Northern Hemisphere.

Effects of water and nutrient availability on morphological, physiological, and biochemical traits of one invasive and one native grass of a Neotropical savanna

• The invasive species accumulates biomass by using resources more efficiently • The invasive species showed higher photon fluxes and lower pigment concentrations • The invasive species showed a weaker oxidative response to water stress • The species grow similarly in scenarios of low water and nutrient availability • Unnatural nutrient inputs and high-water availability benefit the invasive species The cerrado is a Neotropical savanna characterized by a soil and vegetation mosaic where plants endure dystrophic soils and seasonal drought. Dry spells or flooding are the main environmental stress native species face in their growth period. African grasses are common invasive species, jeopardizing the biodiversity by displacing native species and outgrowing them. Invasive species may benefit from human interventions that increase nutrient availability in natural areas and may respond differently than natives to environmental conditions. Therefore, we compared the performance of one native ( Schizachyrium microstachyum ) and one invasive ( Melinis minutiflora ) grass in different conditions of water and nutrient availability simulating possible cerrado scenarios. Five-week-old seedlings were submitted to different irrigation treatments (simulating dry spells, normal rainfall, and flooding) and fertilization treatments (high or low nutrient availability) for four weeks, and were analyzed for morphological (leaf area, length of the shoot, number of tillers, seedling dry weight, and root:shoot ratio) and physiological parameters (chlorophyll fluorescence, pigment concentration, nutrient content, and biochemical assays). There was a trend for the invasive species to show better responses to water stress by growing more profusely, showing an even higher effect when the soil was richer in nutrients. The invasive species may outcompete the native species by using nutrients and water more efficiently, showing a weaker oxidative response to drought and fertilization. The native species would perform at a similar pace to the invasive species in conditions of less water and nutrient availability, whereas unnatural fertilization inputs and high-water availability would benefit the invasive species.

Lutein-mediated photoprotection of photosynthetic machinery in Arabidopsis thaliana exposed to chronic low ultraviolet-B radiation

Ecologically relevant low UV-B is reported to alter reactive oxygen species metabolism and anti-oxidative systems through an up-regulation of enzymes of the phenylpropanoid pathway. However, little is known about low UV-B-induced changes in carotenoid profile and their impacts on light harvesting and photoprotection of photosystem II (PSII) in plants. We investigated carotenoids profile, chlorophyll pigments, phenolics, photosynthetic efficiency and growth in Arabidopsis thaliana (Col-0) plants grown under photosynthetically active radiation (PAR), PAR+ ultraviolet (UV)-A and PAR+UV-A+B regimes for 10 days in order to assess plant acclimation to low UV-B radiation. A chlorophyll fluorescence assay was used to examine UV-B tolerance in plants further exposed to acute high UV-B for 4 and 6 h following a 10-day growth under different PAR and UV regimes. We found that both PAR+ UV-A and PAR+UV-A+B regimes had no negative effect on quantum efficiency, electron transport rate, rosette diameter, relative growth rate and shoot dry weight of plants. Chronic PAR+ UV-A regime considerably (P < 0.05) increased violaxanthin (26 %) and neoxanthin (92 %) content in plants. Plant exposure to chronic PAR+UV-A+B significantly (P < 0.05) increased violaxanthin (48 %), neoxanthin (63 %), lutein (33 %), 9-cis ß-carotene (28 %), total ß-carotene (29 %) and total phenolics (108 %). The maximum photochemical efficiency (Fv/Fm) in leaves was found to be positively correlated with total phenolics (rho = 0.81 and rho = 0.91, P < 0.05 for 4 and 6 h, respectively) and non-photochemical quenching (qN) (rho = 0.81 and rho = 0.84, P < 0.05 for 4 and 6 h, respectively) in plants exposed to acute high UV-B for 4 and 6 h following a 10-day growth under chronic PAR+UV-A+B. There was also a significant positive correlation (rho = 0.93, P < 0.01) between qN and lutein content in the plants exposed to acute high UV-B stress for 4 h following plant exposure to chronic PAR+UV-A+B. The findings from our study indicate that plants grown under chronic PAR+UV-A+B displayed higher photoprotection of PSII against acute high UV-B stress than those grown under PAR and PAR+ UV-A regimes. An induction of phenolics and lutein-mediated development of qN were involved in the photoprotection of PSII against UV-B-induced oxidative stress.

TEMPORARY REMOVAL: Effects of oxathiapiprolin on photosynthetic activity of Chlorella pyrenoidosa probed by chlorophyll fluorescence and thermoluminescence assays

Oxathiapiprolin is the first member of the piperidinyl thiazole isoxazoline fungicides developed globally as DuPont™ Zorvec™ for the control of plant diseases caused by Oomycete pathogens. Although they have great application potential, ecotoxicological data, especially their non-target effects on photosynthesis of algae and higher plants are completely lacking. Effects of a novel oxathiapiprolin biocide on the photosynthesis of Chlorella pyrenoidosa were therefore investigated using chlorophyll a fluorescence and thermoluminescence techniques. Effects of the bioicide on photosynthetic electron transport and energy absorption and dissipation were concentration dependent. Inhibition of the electron donor side of PSII significantly increased as oxathiapiprolin concentration increased from 0 to 100 μM. The oxathiapiprolin treatment increased the effective antenna size per reaction center and the dissipated energy flux per reaction center. It damaged PSII reaction centers and blocked the electron transport flux, thus inhibiting photochemical activity in Chlorella pyrenoidosa. Exposure to oxathiapiprolin at concentrations up to 50 μM had little effect on QA− reoxidation kinetics on the electron acceptor side. Only a higher concentration (100 μM) of the oxathiapiprolin biocide exerted obvious inhibitory effects on QA− reoxidation. At 100 μM, electron transport beyond QA was drastically blocked, and more QA was reoxidized through S2(QAQB)− charge combination. As the concentration increased from 0 to 100 μM, the thermoluminescence C band decreased with increasing oxathiapiprolin concentration, whereas the intensity of the Q band increased which was associated with the decrease of B1 and B2 band intensity. This confirmed that the bioicide hindered electron transfer after QA and caused an increase of S2/S3QB− and TyrD+ QA− recombination. This study implies that when oxathiapiprolin biocides are applied to farmlands, they may pose a potential risk to algae and higher plants.

Leaf chlorophyll fluorescence discriminates herbicide resistance in Echinochloa species

SummaryTimely detection of herbicide resistance at an early stage of crop cultivation is essential to help farmers find alternative solutions to manage herbicide resistance in their fields. In this study, maximum quantum yield of PS II [Fv/Fm = (Fm – Fo)/Fm] was measured at the 4–5 leaf stage to discriminate between herbicide‐resistant and susceptible biotypes of Echinochloa species. The differences in Fv/Fm between herbicide‐resistant and susceptible Echinochloa spp. were consistent with the whole‐plant assay based on I50 (herbicide doses causing a 50% inhibition of Fv/Fm) and GR50 (herbicide doses causing a 50% reduction in plant fresh weight) values and R/S ratios (herbicide resistance index), regardless of the mode of action of the tested herbicides. A PS II inhibitor caused the fastest inhibition of Fv/Fm, compared with ACCase and ALS inhibitors, after herbicide treatment. The required time for discrimination between herbicide‐resistant and susceptible Echinochloa spp. was 64 h after PS II inhibitor treatment, much shorter than those of ACCase and ALS inhibitor‐treated plants, which required 168 and 192 h respectively. The leaf chlorophyll fluorescence assay provided reliable diagnostics of herbicide resistance in Echinochloa spp. with significant time savings and convenient measurement in field conditions compared with the conventional whole‐plant assay.

Visual Analysis for Detection and Quantification of Pseudomonas cichorii Disease Severity in Tomato Plants.

Pathogen infection in plants induces complex responses ranging from gene expression to metabolic processes in infected plants. In spite of many studies on biotic stress-related changes in host plants, little is known about the metabolic and phenotypic responses of the host plants to Pseudomonas cichorii infection based on image-based analysis. To investigate alterations in tomato plants according to disease severity, we inoculated plants with different cell densities of P. cichorii using dipping and syringe infiltration methods. High-dose inocula (≥ 106 cfu/ml) induced evident necrotic lesions within one day that corresponded to bacterial growth in the infected tissues. Among the chlorophyll fluorescence parameters analyzed, changes in quantum yield of PSII (ΦPSII) and non-photochemical quenching (NPQ) preceded the appearance of visible symptoms, but maximum quantum efficiency of PSII (Fv/Fm) was altered well after symptom development. Visible/near infrared and chlorophyll fluorescence hyperspectral images detected changes before symptom appearance at low-density inoculation. The results of this study indicate that the P. cichorii infection severity can be detected by chlorophyll fluorescence assay and hyperspectral images prior to the onset of visible symptoms, indicating the feasibility of early detection of diseases. However, to detect disease development by hyperspectral imaging, more detailed protocols and analyses are necessary. Taken together, change in chlorophyll fluorescence is a good parameter for early detection of P. cichorii infection in tomato plants. In addition, image-based visualization of infection severity before visual damage appearance will contribute to effective management of plant diseases.

Early physiological and biochemical responses of rice seedlings to low concentration of microcystin-LR

Microcystin-leucine and arginine (microcystin-LR) is a cyanotoxin produced by cyanobacteria like Microcystis aeruginosa, and it's considered a threat to water quality, agriculture, and human health. Rice (Oryza sativa) is a plant of great importance in human food consumption and economy, with extensive use around the world. It is therefore important to assess the possible effects of using water contaminated with microcystin-LR to irrigate rice crops, in order to ensure a safe, high quality product to consumers. In this study, 12 and 20-day-old plants were exposed during 2 or 7days to a M. aeruginosa extract containing environmentally relevant microcystin-LR concentrations, 0.26-78μg/L. Fresh and dry weight of roots and leaves, chlorophyll fluorescence, glutathione S-transferase and glutathione peroxidase activities, and protein identification by mass spectrometry through two-dimensional gel electrophoresis from root and leaf tissues, were evaluated in order to gauge the plant's physiological condition and biochemical response after toxin exposure. Results obtained from plant biomass, chlorophyll fluorescence, and enzyme activity assays showed no significant differences between control and treatment groups. However, proteomics data indicates that plants respond to M. aeruginosa extract containing environmentally relevant microcystin-LR concentrations by changing their metabolism, responding differently to different toxin concentrations. Biological processes most affected were related to protein folding and stress response, protein biosynthesis, cell signalling and gene expression regulation, and energy and carbohydrate metabolism which may denote a toxic effect induced by M. aeruginosa extract and microcystin-LR. The implications of the metabolic alterations in plant physiology and growth require further elucidation.

Are the fluorescence parameters of German chamomile leaves the first indicators of the anthodia yield in drought conditions?

7-day soil drought followed by 7-day rehydration was applied to potted German chamomile (Chamomilla recutita) plants at the beginning of their generative stage. Plants of a wild type (WT), plus two diploid (2n) and two tetraploid (4n) genotypes were studied, in order to examine the alterations in chlorophyll (Chl) and carotenoids (Car) contents, and chlorophyll fluorescence (CF) parameters during water shortage and rehydration. The fresh mass of the anthodia after the recovery was also studied.WT plants adjust better to water stress than modern breeding genotypes, because drought resulted in the low fall in leaf water content of WT, the lowest decrease in the fresh mass of its anthodia (a 41% decrease from the control), and the most elastic response of the photosynthetic apparatus. 4n C11/2 strain plants suffered from the highest reduction in anthodia yield (87%), and had the lowest constitutive pigment contents. It was also the only genotype which revealed nontypical alterations in various CF parameters obtained on a dark- and light-adapted leaf. During drought, a big increase was noticed in minimal, maximal, and variable fluorescence of PSII reaction centres in the dark- adapted (F0, Fm and Fv, respectively), and in the light-adapted state (F0', Fm' and Fv'). It was accompanied by the biggest decline in linear electron transport rate (ETR), quantum efficiency of PSII electron transport (ΦPSII) and photochemical quenching coefficient (qP). These alterations were prolonged to the stage when the normal leaf water content was retained. On the contrary, C6/2 strain plants had the highest constitutive Chl and Car contents, which additionally increased after rehydration, similarly to the values of F0, Fm and Fv, which reflects the high photosynthetic potential of this genotype. It was accompanied by the relatively high yield of its anthodia after drought. Considering the drop in the yield triggered by drought, it seems to be the only parameter which may be linked with the ploidy level.Although the yield formation of chamomile strains cannot simply be estimated by CF assay, this technique may serve as an additional tool in the selection of plants to drought. The following circumstances should be submitted; namely: measurement at the proper developmental stage of plants, in different water regimes, and an analysis of various CF parameters. The increase in F0 and F0', and the reduction in ETR, Fv'/Fm', ΦPSII and qP values in response to water deficit should be an indicator of the impairment of the photosynthetic apparatus through drought.

Shedding light on the role of photosynthesis in pathogen colonization and host defense

The role of photosynthesis in plant defense is a fundamental question awaiting further molecular and physiological elucidation. To this end we investigated host responses to infection with the bacterial pathogen Xanthomonas axonopodis pv. citri, the pathogen responsible for citrus canker. This pathogen encodes a plant-like natriuretic peptide (XacPNP) that is expressed specifically during the infection process and prevents deterioration of the physiological condition of the infected tissue. Proteomic assays of citrus leaves infected with a XacPNP deletion mutant (∆XacPNP) resulted in a major reduction in photosynthetic proteins such as Rubisco, Rubisco activase and ATP synthase as a compared with infection with wild type bacteria. In contrast, infiltration of citrus leaves with recombinant XacPNP caused an increase in these host proteins and a concomitant increase in photosynthetic efficiency as measured by chlorophyll fluorescence assays. Reversion of the reduction in photosynthetic efficiency in citrus leaves infected with ∆XacPNP was achieved by the application of XacPNP or Citrus sinensis PNP lending support to a case of molecular mimicry. Finally, given that ∆XacPNP infection is less successful than infection with the wild type, it appears that reducing photosynthesis is an effective plant defense mechanism against biotrophic pathogens.

Temporary drought can selectively suppress Schoenoplectus mucronatus in rice

Abstract Outdoor pot experiments were conducted in California to quantify differences in rice and Schoenoplectus mucronatus susceptibility to drought and to identify morphological and physiological traits that would favor rice over S. mucronatus under drought. Plants were grown in flooded soil for approximately 5 weeks, and then subjected to different drought periods after which pots were re-flooded. Chlorophyll fluorescence assays revealed that rice and S. mucronatus Fv/Fm first became Ψ leaf ) had decreased to approximately −4 MPa and −2 MPa, respectively. Thus, by suffering less photosynthetic damage from drought, rice had better recovery after re-flooding than S. mucronatus . When drought reduced Ψ leaf to −3 MPa, S. mucronatus re-growth was nearly suppressed but that of rice was unaffected. Rice plants depleted soil moisture 1.6 faster than S. mucronatus due to larger and deeper roots and a high water-spending strategy (when Ψ leaf decreased from approximately −0.5 MPa to −2.5 MPa, 13 δ increased from −27.8 to −27.4 and from −28.1 to −26.0 for rice and S. mucronatus , respectively). Rice under interspecific competition sustained its Ψ leaf by extracting more water from greater depths, while causing severe moisture stress and photosynthetic damage to S. mucronatus . Thus temporary drought enhanced rice competitiveness over S. mucronatus , supporting the concept of using brief drought as a tool for S. mucronatus suppression in rice. The Ψ leaf developed by the end of the drought period predicted rice yields ( R 2 = 0.77, P S. mucronatus to recover from drought upon irrigation resumption ( R 2 = 0.62, P S. mucronatus never fully recovered from drought. Rice yields were only reduced after Ψ leaf reached values below approximately −2.5 MPa. Longer drought (∼20 d) delayed maturity and reduced rice yields by approximately 60–80%. The dry-down approach could help suppress weeds similar to S. mucronatus in organic rice where premium prices can compensate for lower grain yield.

Comparative proteomics of thylakoid membrane from a chlorophyll b-less rice mutant and its wild type

A novel rice mutant ( Oryza sativa L. var. Zhenhui 249Y) was identified as a low chlorophyll b mutant with a chlorophyll a/ b ratio of 4.7. Chloroplast ultrastructure showed decreased grana lamellae and slightly swelling thylakoid in the mutant. Chlorophyll fluorescence assay demonstrated that the mutant noticeably reduced PSII thermostability. However, heat-induced PsbO release from thylakoid membrane indicated an increased thermo-resistance of PSII structure in the mutant. In order to explain these phenomena, two different 2D electrophoresis approaches have been used to compare the thylakoid proteome between the mutant and the wild type: two-dimensional blue native–SDS-PAGE and isoelectric focusing–SDS-PAGE, which was followed by MS identification. Totally, 52 proteins were identified. The results indicated that the LHC-IIb in the mutant was about 40% less than that in wild type. However, both LHC-Ia and LHC-Ib decreased more greatly in this mutant, only 20% remaining. IEF–SDS-PAGE showed that H +-transporting ATP synthase, fructose-bisphosphate aldolase, PSII assembly/stability factor HCF136 increased in the mutant, while PsaE and 8.7 kDa Fe-S protein, decreased. The results suggest that in our mutant, maintenance of the water-oxidizing system is not the major reason of LHC-II stabilization effect on PSII complexes. In addition, the reduction of Chl b affected LHC-I assembly more severely than LHC-II.

PsbA mutation (Asn266 to Thr) in Senecio vulgaris L. confers resistance to several PS II‐inhibiting herbicides

DNA sequence analysis of the psbA gene encoding the D1 protein of photosystem II (PS II), the target site of PS II-inhibiting herbicides, identified a point mutation (Asn266 to Thr) in a bromoxynil-resistant Senecio vulgaris L. population collected from peppermint fields in Oregon. Although this mutation has been previously reported in Synechocystis, this is the first report of this particular point mutation in a higher plant exhibiting resistance to PS II-inhibiting herbicides. The resistant population displayed high-level resistance to bromoxynil and terbacil (R/S ratio 10.1 and 9.3, respectively) and low-level resistance to metribuzin and hexazinone (R/S ratio 4.2 and 2.6, respectively) when compared with the susceptible population. However, the population was not resistant to the triazine herbicides atrazine and simazine or to the urea herbicide diuron. A chlorophyll fluorescence assay confirmed the resistance levels and patterns of cross-resistance of the whole-plant studies. The resistant S. vulgaris plants produced fewer seeds. Differences in cross-resistance patterns to PS II-inhibiting herbicides and the difference in fitness cost could be exploited in a weed management program.

Screening Pecan Cultivars for Drought Tolerance Using Physiological Parameters

Pecan is a riparian species distributed over an area of geographic and climatic variation; such a wide distribution produces exposure to varied environmental conditions, providing a potential for genetic adaptation within the cultivars. Genotypes can be screened in order to obtain more drought tolerant cultivars using indirect screening parameters (chlorophyll fluorescence, osmotic adjustment, and abscisic acid assay) based on physiological responses of plants to abiotic stress conditions. A study was established at Texas A&amp;M University, College Station, using a mixture of fritted clay (Quick dry) and pure sand in 1:1 (by weight) ratio to study the effects of drought on pecan rootstocks. The experiment was set up with the three water potential levels as treatments (–0.033 MPa, –0.1 MPa, –0.3 MPa) in a randomized complete-block design with three blocks. Measurements will include leaf water relations (relative water content, leaf water potential, osmotic adjustments, etc.), gas exchange parameters [net carbon dioxide assimilation rate (A), transpiration rate (E), stomatal conductance (gs)], chlorophyll fluorescence measurements [minimum (Fo), maximum (Fm), and variable fluorescence (Fv), quantum efficiency], water use efficiency, and abscisic acid assay on roots. Statistical analysis systems (SAS) package will be used for analysis. PROC GLM of the SAS will be used for statistical analysis of study involving plant response to water potential levels.

The emergence of a atrazine resistant black nightshade (Solanum nigrum L.) biotype and molecular basis of the resistance

Seeds from atrazine resistant plants of black nightshade (&lt;I&gt;Solanum nigrum &lt;/I&gt;L.)&lt;I&gt; &lt;/I&gt;were collected at the railway station Prague-Vršovice, seeds from susceptible plants in Vyšehořovice (Prague East district). Tests on emergence showed that in both resistant and susceptible biotypes it was highest at a seeding depth of 1 mm, and that at the same seeding depth there were statistically significant differences in emergence between the resistant and susceptible biotypes. The resistance or susceptibility to atrazine was tested by both a chlorophyll fluorescence assay and spraying with atrazine. A region of the gene encoding D1 protein of photosystem II was sequenced and compared between the resistant and susceptible biotypes. Resistance to atrazine in the &lt;I&gt;S. nigrum&lt;/I&gt; biotype from Vršovice was conferred by a glycine for serine substitution at residue 264 of the D1 protein. In the plants of the biotypes there was excellent correspondence between the presence of the mutation and herbicide resistance. The assay based on restriction analysis of PCR products can be used for rapid detection of the mutation in populations of black nightshade.

Amaranthus hybridus populations resistant to triazine and acetolactate synthase‐inhibiting herbicides

Summary Amaranthus hybridus L. populations (A, B and C) obtained from escapes in Massac County and Pope County fields in southern Illinois, USA were subjected to greenhouse and laboratory experiments to measure multiple resistance to triazine and acetolactate synthase (ALS)‐inhibiting herbicides and cross‐resistance between sulfonylurea and imidazolinone herbicides. Phytotoxicity responses of the three populations revealed that only population B exhibited multiple resistances to triazine and ALS‐inhibiting herbicides. This population was &gt;167‐, &gt;152‐ and &gt;189‐fold resistant to atrazine, imazamox and thifensulfuron, respectively, at the whole plant level compared with the susceptible population. Population A was only resistant to triazines and population C was only resistant to ALS‐inhibiting herbicides. Results from in vivo ALS enzyme and chlorophyll fluorescence assays confirmed these findings and indicated that an altered site‐of‐action mediated resistance to both triazine and ALS‐inhibiting herbicides. Gene sequencing revealed that a glycine for serine substitution at residue 264 of the D1 protein, and a leucine for tryptophan substitution at residue 574 of ALS were the causes of resistance for the three populations.