qN Values Research Articles

Trait coordination at leaf level explains the resistance to excess light stress in shade-tolerant tropical tree species.

Plant functioning in response to the environment is an important issue for vegetation reassembly of degraded lands because of both low and excessive sunlight influence the performance of young plants. However, how shade-tolerant tree species deal with excess of light energy remains unclear due to the contrasting results among studies and the subjective classifications of species shade tolerance. From a quantitative classification of shade tolerance of 12 tropical tree species planted in the field under contrasting light conditions, we hypothesized that shade-tolerant species are capable of effective long-term acclimation to high-light conditions. Plant size and survival of species were measured at the beginning and 38months after planting. We also measured functional traits associated with carbon economy and non-photochemical energy dissipation. Under high-light condition, more light-demanding species showed higher growth rates associated with higher values of functional traits that improve the CO2 assimilation capacity. By contrast, more shade-tolerant species showed higher survival that was associated with higher values of qN, leaf K contents and leaf thickness. The concomitant increase in these traits, as well as their greater plasticity to light in WUEi, Fv/Fm and qN, confers on these species strong photoprotection to avoid high-light stress and to persist under open field conditions. The results challenge the common assumption that only fast-growing and light-demanding tree species are suitable for vegetation reassembly in full sunlight conditions and to improve the environmental conditions for other species.

Drought response of cowpea (Vigna unguiculata (L.) Walp.) landraces at leaf physiological and metabolite profile levels

Drought threatens the world’s food production, particularly in Sub Saharan Africa low external input and rain fed agricultural systems, where cowpea (Vigna unguiculata (L.) Walp.) is an important food crop. In the context of growing concerns regarding climate changes implications on water availability, this study aimed at 1) to evaluate the drought responses in cowpea landraces with contrasting drought tolerance levels (A55 – high sensitivity; A80 - mild sensitivity; A116 - tolerant), 2) using an integrated physiological (leaf gas exchanges; chlorophyll a fluorescence) and biochemical (photoprotective pigments; RuBisCO activity; primary metabolite profiling) analysis to identify drought tolerance probes, in plants submitted to three water availability levels (well-watered, WW; mild drought, MD; severe drought, SD). A116 plants maintained a better water status under drought, what could justify the higher Pn and Pnmax values in MD, as well as higher photochemical use of energy (reflected in the photochemical quenching (qL) and in the quantum yield of non-cyclic electron transport (Y(II))), and the lower need of photoprotective thermal dissipation mechanisms (given by the non-photochemical quenching (qN), and the quantum yield of regulated energy dissipation at photosystem PSII (Y(NPQ))), in MD and SD plants. Greater declines of net (Pn) and potential (Pnmax) photosynthesis were observed in A55 plants, which frequently showed significant impacts already under MD conditions in most parameters, whereas A80 usually displayed and intermediate behaviour. Still, even A55 showed some acclimation response, regarding photoprotective mechanisms associated with high contents of zeaxanthin, lutein, and carotenes, and high Y(NPQ), and qN values, supporting the absence of an increase in the non-regulated energy dissipation at PSII (Y(NO) did not increased) even in SD plants. Additionally, A55 was not significantly affected in RuBisCO activity, which showed to be quite resilient in cowpea. A primary metabolite profiling, complemented with a partial least square discrimination analysis (PLS-DA), allowed a better separation of A116 and A55 plants according to their degree of drought tolerance. In response to drought, A116 showed the greatest accumulation of most responsive metabolites, 14 in total, with sucrose, fucose, urea, alanine and putrescine being exclusively increased in this genotype, suggesting that they can be candidates as drought tolerance proxies. Other compounds, as proline, valine, isoleucine (among amino acids), and rhamnose and raffinose (among sugars) showed close increase patterns across landraces, thus they would be involved in the common drought response of cowpea plants. This pioneer approach to characterize Africa’s and Central Mozambique highly diverse cowpea germplasm, highlights the advantages of an integrated physiological and biochemical analysis, to identify response mechanisms and potential probes for drought tolerance in cowpea, aiming at to support selection and breeding strategies to obtain high yield and drought tolerant elite varieties.

Mild water stress-induced priming enhance tolerance to Rosellinia necatrix in susceptible avocado rootstocks

BackgroundWhite root rot (WRR) disease caused by Rosellinia necatrix is one of the most important threats affecting avocado orchards in temperate regions. The eradication of WRR is a difficult task and environmentally friendly control methods are needed to lessen its impact. Priming plants with a stressor (biotic or abiotic) can be a strategy to enhance plant defense/tolerance against future stress episodes but, despite the known underlying common mechanisms, few studies use abiotic-priming for improving tolerance to forthcoming biotic-stress and vice versa (‘cross-factor priming’). To assess whether cross-factor priming can be a potential method for enhancing avocado tolerance to WRR disease, ‘Dusa’ avocado rootstocks, susceptible to R. necatrix, were subjected to two levels of water stress (mild-WS and severe-WS) and, after drought-recovery, inoculated with R. necatrix. Physiological response and expression of plant defense related genes after drought-priming as well as the disease progression were evaluated.ResultsWater-stressed avocado plants showed lower water potential and stomatal limitations of photosynthesis compared to control plants. In addition, NPQ and qN values increased, indicating the activation of energy dissipating mechanisms closely related to the relief of oxidative stress. This response was proportional to the severity of the water stress and was accompanied by the deregulation of pathogen defense-related genes in the roots. After re-watering, leaf photosynthesis and plant water status recovered rapidly in both treatments, but roots of mild-WS primed plants showed a higher number of overexpressed genes related with plant defense than severe-WS primed plants. Disease progression after inoculating primed plants with R. necatrix was significantly delayed in mild-WS primed plants.ConclusionsThese findings demonstrate that mild-WS can induce a primed state in the WRR susceptible avocado rootstock ‘Dusa’ and reveal that ‘cross-factor priming’ with water stress (abiotic stressor) is effective for increasing avocado tolerance against R. necatrix (biotic stressor), underpinning that plant responses against biotic and abiotic stress rely on common mechanisms. Potential applications of these results may involve an enhancement of WRR tolerance of current avocado groves and optimization of water use via low frequency deficit irrigation strategies.

Understanding the Structure and Structural Effects on the Properties of Blast Furnace Slag (BFS)

Evolving knowledge of the structure and physical properties of metallurgical slags is summarized in current review. Slag structure, compositional effects, role of cations in structural modifications, parameters used to represent the structure, structural analysis techniques and effects of structure on properties of blast furnace slag (BFS) studied in details. The basicity, polymerization (Q) or depolymerization (NBO/T), optical basicity, Qn values, concentrations of bridging O’s (Oo), non-bridging O’s (O−) and free O’s (O2−) in slag are useful to represent the structure of slag. Methods and techniques utilized to study the slags are also discussed. The BFS is characterized by using X-ray Diffraction and Spectroscopy, Raman Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Photoelectron Spectroscopy (XPS) and Nuclear Magnetic Resonance (NMR) Spectroscopy. The physical properties such as surface tension, viscosity, density, thermal expansion and diffusion, electrical conductivity and resistivity of slags are reviewed thoroughly which are heavily dependent on structure of slag. Viscosity is affected by polymerization or depolymerization of slag structure and cation size; electrical resistivity depends on Q, size of cations and number of available cations; thermal expansion depends on Q and cation field strength (i.e. z/r2); thermal conductivity is linked with rigidity of slag network which is also dependent on Q and metal-oxygen (M–O) bond strength. Degree of polymerization or depolymerization of slag structure also effect the surface and interfacial tension, it decreases as metal-oxygen (M–O) bond strengths (i.e. z/r2, cation field strength) decrease.

Analysis of stress-strain state of RVS-20000 tank under non-axisymmetric wind load action

In modern reference documentation, it is customary to set the wind load as uniformly distributed pressure over the area and wall of the tank. Experimental studies in the wind tunnel for various designs of the VST carried out under the guidance of professors V.E. Shutov and V.L. Berezin showed that when wind acts on the shell, there occur rarefaction zones, which must be taken into account during strain analysis of tanks. A finite-element model of the RVS-20000 tank was developed to calculate the wind load in a non-axisymmetric setting, taking into account the array of differentiated values of the aerodynamic coefficient. The distribution of stresses and strains of RVS-20000 metal structures under the effect of unevenly distributed wind pressure with a normal value of Qn = 600 Pa is obtained. It is established that the greatest strains and stresses occur at the interface of the wall and the fixed floor.

Cu and Cd affect distinctly the physiology of a cosmopolitan tropical freshwater phytoplankton

Copper and Cd are natural constituents of freshwater ecosystems, both cycling influenced by microbial communities. The present research examined the impacts of environmentally relevant concentrations of Cu and Cd on the growth, viability, cell size, chlorophyll a (Chl a) content and photochemical efficiency of the tropical freshwater phytoplankton Chlorolobion braunii. Cell growth was significantly impaired by Cu and Cd, with EC50 occurring at 33.6 and 1.6µM, respectively. At sublethal levels (< EC50), cell death was already induced at 5µM Cu and 1µMCd. Average cell volume significantly increased as metal concentrations increased, as did the Chl a content per cell, although the Chl a content per unit volume decreased. Copper did not affect both the photosystem II (PSII) maximum quantum yield (ΦM) or the operational quantum yield (ΦE), while Cd significantly impacted ΦE, with EC50 occurring at 18.4µM. Different responses for Cu and Cd were obtained whether the photochemical fluorescence quenching (Qp) or non-photochemical quenching (Qn) were considered. Qp decreased after Cd addition, but was not altered after Cu addition. Qn values significantly increased after the addition of either metal. Non-photochemical quenching due to heat dissipation (NPQ) significantly increased in response to both metals, but it was more pronounced in the case of Cd. Overall, Cd was more toxic to C. braunii than Cu.

Absorption correction and phase function shape effects on the closure of apparent optical properties.

We present a closure experiment between new inherent optical properties (IOPs: absorption a, scattering b, backscattering b_b) and apparent optical properties (AOPs: remote-sensing reflectance R_rs, irradiance reflectance R, and anisotropic factor at nadir Q_n) data of Ionian and Adriatic seawaters, from very clear to turbid waters, ranging across one order of magnitude in R_rs. The internal consistency of the IOP-AOP matchups was investigated though radiative transfer closure. Using the in situ IOPs, we predicted the AOPs with the commercial radiative transfer solver Hydrolight. Closure was limited by two unresolved issues, one regarding processing of in situ data and the other related to radiative transfer modeling. First, different correction methods of the absorption data measured by the Wetlabs ac-s produced high variations in simulated reflectances, reaching 40% for the highest reflectances in our dataset. Second, the lack of detailed volume scattering function measurements forces us to adopt analytical functions that are consistent with a given particle backscattering ratio. The analytical phase functions named Fournier-Forand and two-term Kopelevich presented reasonable angular shapes with respect to measurements at a few backward angles. Between these phase functions, induced changes were within 4% for R_rs, within 11% for R, and within 10% for Q_n. Additionally, closure of Q_n was generally not successful considering radiometric uncertainties. Simulated Q_n overestimated low values and underestimated high values, especially at 665 nm, where Hydrolight was unable to predict measured Q_n values greater than 6 sr. The physical nature of Q_n makes this mismatch almost independent of the measured IOPs, thus precluding Q_n tuning by varying the former. The non-closure of Q_n might be caused by an inaccurate phase function and, to a lesser extent, by the modeling of the incoming radiance. For the future, this remains the task of accurate absorption and phase function measurements, especially at red wavelengths.

Photosynthetic gas exchange and water utilization of flag leaf of spring wheat with bunch sowing and field plastic mulching below soil on semi-arid rain-fed area.

Based on the field experiment which was conducted in Dingxi County of Gansu Province, and involved in the three treatments: (1) plastic mulching on entire land with soil coverage and bunching (PMS), (2) plastic mulching on entire land and bunching (PM), and (3) direct bunching without mulching (CK). The parameters of SPAD values, chlorophyll fluorescence parameters, photosynthetic gas exchange parameters, as well as leaf area index (LAI), yield, evapotranspiration, and water use efficiency in flag leaves of spring wheat were recorded and analyzed from 2012 to 2013 continuously. The results showed that SPAD values of wheat flag leaves increased in PMS by 10.0%-21.5% and 3.2%-21.6% compared to PM and CK in post-flowering stage, respectively. The maximum photochemical efficiency (Fv/Fm) , actual photochemical efficiency (ΦPS2) of photosystem 2 (PS2), and photochemical quenching coefficient (qP) of PMS were higher than those of PM and CK, the maximum increment values were 6.1%, 9.6% and 30.9% as compared with PM, and significant differences were observed in filling stage (P＜0.05). The values of qN in PMS were lowest among the three treatments, and it decreased significantly by 23.8% and 15.4% in heading stage in 2012 and 2013 respectively, as compared with PM. The stoma conductance (gs) of wheat flag leaves in PMS was higher than that of PM and CK, with significant difference being observed in filling stage, and it increased by 17.1% and 21.1% in 2012 and 2013 respectively, as compared with PM. The transpiration rate (Tr), net photosynthetic rate (Pn), and leaf instantaneous water use efficiency (WUEi) except heading stage in 2013 of PMS increased by 5.4%-16.7%, 11.2%-23.7%, and 5.6%-7.2%, respectively, as compared with PM, and significant difference of WUEi was observed in flowering stage in 2012. The leaf area index (LAI) of PMS was higher than that of PM and CK, especially, it differed significantly in seasonal drought of 2013. Consequently, the PMS increased the SPAD values in flag leaves of spring wheat, and the capacity of flag leaves for photo energy assimilation and photosynthetic gas exchange were enhanced, caused more photosynthetic energy flowing into photochemical process, as well as decreased the heat dissipation, resulted in the increment of Pn and WUEi. Based on the higher Pn and LAI, the yield and WUE of PMS increased.

Effects of low irradiation on photosynthesis and antioxidant enzyme activities in cucumber during ripening stage

In order to investigate the effects of low irradiation (LI) on cucumber (Cucumis sativus L. cv. Jinyou 35) during a ripening stage, our experiment was carried out in a climate chamber. Two levels of PAR were set for plants: normal irradiation [NI, 600 μmol(photon) m−2 s−1] and low irradiation [LI, 100 μmol(photon) m−2 s−1], respectively. The experiments lasted for 9 d; then both groups of plants were transferred under NI to recover for 16 d. The plants showed severe chlorosis after the LI treatment. Chlorophyll (Chl) a, initial slope, photosynthetic rate at saturating irradiation (P max), light saturation point, maximal photochemical efficiency of PSII (Fv/Fm), electron transport rate of PSII (ETR), soluble protein content, and catalase (CAT) activity in cucumber leaves decreased under LI stress, while Chl b, carotenoids, light compensation point, nonphotochemical quenching (qN), superoxide dismutase (SOD), and malondialdehyde (MDA) exhibited an increasing trend under LI. After 16 d of recovery, values of P max, Fv/Fm, ETR, qN, SOD, CAT, MDA, and soluble protein were close to those of the control after one, three, and five days of the LI treatment, while those kept under LI for 7 and 9 d could not return to the control level. Therefore, 7 d of LI stress was a meteorological disaster index for LI in cucumber at the fruit stage.

Longitudinal Photosynthetic Gradient in Crust Lichens’ Thalli

In order to evaluate the self-shading protection for inner photobionts, the photosynthetic activities of three crust lichens were detected using Microscope-Imaging-PAM. The false color images showed that longitudinal photosynthetic gradient was found in both the green algal lichen Placidium sp. and the cyanolichen Peltula sp. In longitudinal direction, all the four chlorophyll fluorescence parameters Fv/Fm, Yield, qP, and rETR gradually decreased with depth in the thalli of both of these two lichens. In Placidium sp., qN values decreased with depth, whereas an opposite trend was found in Peltula sp. However, no such photosynthetic heterogeneity was found in the thalli of Collema sp. in longitudinal direction. Microscope observation showed that photobiont cells are compactly arranged in Placidium sp. and Peltula sp. while loosely distributed in Collema sp. It was considered that the longitudinal photosynthetic heterogeneity was ascribed to the result of gradual decrease of incidence caused by the compact arrangement of photobiont cells in the thalli. The results indicate a good protection from the self-shading for the inner photobionts against high radiation in crust lichens.

Field assessment of sub-epidermal leaf anthocyanin, PSII photochemistry, and the xanthophyll-cycle as photoprotective mechanisms in two morphs of Agave striata

We tested the hypothesis that leaf epidermal pigments screen light of particular wavelengths from reaching the photosynthetic machinery, reducing dependence on the xanthophyll-cycle as an energy dissipation process. Under field conditions, photosynthesis and water relations were studied in two morphs of Agave striata that differ in leaf coloration (green vs. reddish-purple). Titratable acidity, chlorophyll fluorescence, and internal and surface leaf temperatures were measured under low irradiance by shading (30%) and full sunlight (100%) for six days. We also measured the reflectance ratio (RRED: RGREEN), an index of anthocyanin content and the change in photochemical reflectance index (ΔPRI), an index of xanthophyll-cycle de-epoxidation state (xanthophyll conversion). Our results showed that both morphs expressed typical CAM-activity with no significant differences under sun vs. shade. However, shading did reduce titratable acids in both morphs. Both morphs were well hydrated, with the relative water content (RWC) being greater than 93%. Leaf surface temperature was found to be significantly higher during the day in the green morph compared to the red morph under sun and shade. Dark level fluorescence (Fo), photochemical efficiency of PSII (Fv/Fm), and the quantum yield of PSII electron transport (ΦPSII) were higher in the red morph under sun compared to the green morph. The value of qN (non-photochemical quenching) was significantly higher during the day for the green morph compared to the red morph and this higher qN value was associated with a greater xanthophyll conversion and surface leaf temperature. However, sunlight did not predispose either of the morphs to photoinhibition. It is clear that the sub-epidermal anthocyanins serve as a photoprotective mechanism in the red morph, screening light energy from reaching the photosynthetic machinery and reducing dependence on the xanthophyll-cycle. We concluded that under natural light conditions the leaves of two morphs tested utilized differential photoprotective mechanisms.

Effects of extracellular ATP on the characteristics of photochemical reaction in bean (Phaseolus vulgaris) leaves under different light intensities

Aims Although adenosine 5′-triphosphate (ATP) is usually considered to be localized in intracellular spaces, plant and animal cells can secrete ATP from the cytosol into the extracellular matrix. This extracellular ATP (eATP) is an important signal molecule for many physiological responses in plants. However, whether eATP could also have effects on photosynthesis in plants has not been extensively studied. Methods With bean (Phaseolus vulgaris) leaves as experiment material, the effects of eATP on the chlorophyll fluorescence characteristics and photosynthetic O2 evolution rate were studied under different light intensities. Important findings The maximal photosystem II (PSII) quantum yield in light adaptation (Fv′/Fm′), effective photochemical quantum yield of PSII (Y(II)), and photochemical quenching coefficient (qP) gradually decreased, and the electron transport rate (ETR), non-photochemical quenching coefficient (qN), and the quantum yield of regulated energy dissipation (Y(NPQ)) increased, with increases in light intensity. Treatment of leaves with eATP significantly increased the values of the potential maximal photochemical efficiency of PSII (Fv/Fm), Fv′/Fm′, Y(II), qP, ETR, and photosynthetic O2 evolution rate, but did not affect the values of qN and Y(NPQ). In contrast, treatment of leaves with β,γ-methyleneadenosine triphosphate (AMP-PCP, an inhibitor of eATP receptors) significantly reduced the values of Fv/Fm, Fv′/Fm′, Y(II), ETR, and photosynthetic O2 evolution rate, but increased the values of qN and Y(NPQ). These results show that the levels of eATP exert important influences on the photochemical reaction in photosynthesis.

The Total Charge of Carbon and Nitrogen Atoms in the Amide Bonds Acts as a New Approach to Understand the Mobile Proton Model

ABSTRACT The mobile proton model has been the main theory to describe peptide fragmentation in mass spectrometry (MS). In this study, Gly-Ala-Tyr (GAY) was used to research the mass spectrometry cleavage mechanism. The hydroxyl radical oxidation technique was applied to change the charge distribution of the peptide. We applied MS/MS technique to obtain the tandem mass spectrum of the peptide and then obtained fragmentation efficiency curves, which indicated that the cleavage of GAY became more and more difficult as more O atoms were added. The charge distribution was obtained from quantum chemical calculations at the B3LYP/6-31G(d) level using the Gaussian 03 W program. By analyzing the charge distribution around the amide bonds, we found that the total charge of C and N atoms (QC + QN) in the amide bonds provided a reasonable prediction of peptide fragmentation efficiency. A decrease of the QC + QN value in the amide bonds leads to a low fragmentation efficiency of GAY, and vice versa. Through comparing experimental data with calculation results to research the relationship between charge distribution and the mass spectrometry cleavage mechanism, this work provides a new way to understand the mobile proton model for peptide fragmentation.

Concentration, Size Distribution and Electrostatic Charge of Laying Hen House Particulate Matter

Published data on indoor air contaminants in livestock buildings in Saudi Arabia are relatively scarce. The main objective of this study was to determine the airborne concentrations of particles and electrostatic charge acquired by airborne particles in a multiple tier housing system (Manure Belt Cage System) under the climatic conditions of Saudi Arabia. In this house, the mean of total suspended particle (TSP) concentration was 0.99 mg/m3, the PM10 concentration (particulate matter with a diameter less than or equal to 10 µm) was 0.47 mg/m3, and the PM2.5 concentration (particulate matter with a diameter less than or equal to 2.5 µm) was 0.05 mg/m3. The particle size distribution results obtained from the layer house revealed that the GMD (geometric mean diameter) was 6.95 µm, based on the mass concentration of the particles. Alternatively, based on the number concentration of particles, the GMD was 0.82 µm. The cumulative percentage of mass concentration for the particles ranging from 0.3–10 ?m showed that the major fraction of the particles was larger than 2.5 ?m (>85%). The net charge-to-mass ratio (qN) of airborne particles was -0.86 mC/kg (s.d.=0.27). The measured qN value of airborne particles in the layer house varied due to the nature of the particles in addition to the environmental conditions and high concentration of airborne particles inside the poultry housing. In general, PM concentrations did not exceed the recommended values and those cited in literature.

土壤逐渐干旱对菖蒲生长及光合荧光特性的影响

In the process of soil gradual drought,the growth of typical wetland plant Acorus calamus in dry condition and control condition were investigated.The soil water contents of dry group were about 55%(0th day),40%(3th day),30%(6th day),20%(9th day),10%(11th day) and 5%(12th day) and average soil water content of the control group was(53.49±0.6)% during the experiment period.Meanwhile,Photosystem Ⅱ(PSⅡ) photochemical efficiency(Fv/Fm),quantum yield(Yield),photochemical quenching(qP),non-photochemical quenching(qN) were also measured by a submersible,pulse-amplitude modulated(PAM) fluorometer: Diving-PAM. The results showed that the decline of soil water content in a short term(soil water content declined from 53.86% to 42.6%,on the 0th —3th day) was beneficial to the growth of dry group Acorus calamus.Fv/Fm,Yield,qP were much high than those of the control group(P0.05),while qN was lower than control group.Compared with control group,average plant height,leaf width and leaf biomass,root biomass of dry group increased by 4.35%,3.13%,12.50%,17.82%,respectively. With soil becoming drought gradually(soil water content declined from 42.6% to 18.02%,on the 3th —9th day),the growth of drought group Acorus calamus was restrained gradually and yield and qP value began to decrease.The qN value rose from 0 to 0.403 quickly and was much higher than those of control group(P0.05).The dry group plant began to suffer from soil drought stress and presented low photo-inhibition phenomenon.High qN value detected in the study demonstrated that they could protect PSⅡ by increasing heat dissipating.At the same time,there was no significant difference of Fv/Fm between drought group and control group,which also indicated that photosynthesis structure of PSⅡ was unspoiled.At the same time,Acorus calamus plant reduced water transpiration and promoted water absorption to protect itself from soil drought pressure by reducing leaf area,leaf water content and root water content.On the 9th day,the leaf width,leaf water content and root water content of dry group declined to 89.1%,92.5% and 95.8% of control group respectively. With more serious soil drought degree(soil water content declined from 18.02% to 4.5%,on the 9th —12th day),the growth of dry group plant was significantly restrained.The yield and qP value decreased quickly and were much lower than those of the control group.The photosynthetic efficiency decreased significantly.Meanwhile,Fv/Fm value began to be much less than that of the control group and qN value reduced to 0,which indicated that photosynthesis structure of PSⅡ has begun to be destroyed and the capacity of dissipating heat has disappeared.On the 11th and 12th day,leaf water content of dry group declined to 75.79% and 68.78% respectively.The small leaf began to wither and decline,followed by the big leaf.The above phenomenon indicated that high plant biomass was weak to keep plant water content in the process of soil gradual drought,80% of leaf water content was the critical value to maintain Acorus calamus plant survival.

Functional plasticity of photosynthetic apparatus and its resistance to photoinhibition in Plantago media

Morphological and functional characteristics of Plantago media L. leaves were compared for plants growing at different light regimes on limestone outcrops in Southern Timan (62°45′N, 55°49′E). The plants grown in open areas under exposure to full sunlight had small leaves with low pigment content and high specific leaf weight; these leaves exhibited high photosynthetic capacity and elevated water use efficiency at high irradiance. The maximum photochemical activity of photosystem II (Fv/Fm) in leaves of sun plants remained at the level of about 0.8 throughout the day. The photosynthetic apparatus of sun plants was resistant to excess photosynthetically active radiation, mostly due to non-photochemical quenching of chlorophyll fluorescence (qN). This quenching was promoted by elevated deepoxiation of violaxanthin cycle pigments. Accumulation of zeaxanthin, a photoprotective pigment in sun plant leaves was observed already in the morning hours. The plant leaves grown in the shade of dense herbage were significantly larger than the sun leaves, with pigment content 1.5–2.0 times greater than in sun leaves; these leaves had low qN values and did not need extensive deepoxidation of violaxanthin cycle pigments. The data reveal the morphophysiological plasticity of plantain plants in relation to lighting regime. Environmental conditions can facilitate the formation of the ecotype with photosynthetic apparatus resistant to photoinhibition. Owing to this adjustment, hoary plantain plants are capable of surviving in ecotopes with high insolation.

The combined effect of anthracene and cadmium on photosynthetic activity of three Desmodesmus (Chlorophyta) species

Individual toxicity of heavy metals (HM) and polycyclic aromatic hydrocarbons (PAH) to plants living in water bodies is well-documented. In view of frequent joint occurrence of these compounds in the environment, plants are subjected to damage from their combined action. Cadmium and anthracene can generate production of reactive oxygen species (ROS). We have recently detected elevated activity of Fe- and Mn-SOD isoforms, indicating chloroplast and mitochondrion as the main sites of combined toxicity of HM and PAH. In the present paper, short-term (1–24h) experiments on the mechanism of combined toxicity of anthracene and cadmium to the photosynthesis of three Desmodesmus species are reported. Inhibition, stimulation or no effect on the oxygen evolution was observed following the treatment with the contaminants when applied either separately or jointly. The response pattern was both strongly species- and time-dependent. In contrast, the photosynthetic activity of cells, expressed by chlorophyll fluorescence parameters, was substantially unaffected, since no effect or, in several cases, a slight stimulation of PS II quantum efficiency (Φ PS II) were noted. A characteristic relationship between the SOD activity and the qN values was observed. The treatment of Desmodesmus cells with anthracene or cadmium had either no effect or slightly enhanced either the SOD activity or the qN value, whereas the mixture of the contaminants resulted in a multifold increase in both the SOD activity and the qN values. The results suggest that chloroplasts of algae are well protected against the combined action of the two contaminants the toxicity of which should be attributed to nucleocytoplasmic compartments and reproductive processes of the cell cycle.

Photosystem 2 activity of Citrus volkameriana (L.) leaves as affected by Mn nutrition and irradiance

Citrus volkameriana (L.) plants were grown for 43 d in nutrient solutions containing 0, 2, 14, 98, or 686 µM Mn (Mn0, Mn2, Mn14, Mn98, and Mn686, respectively). To adequately investigate the combined effects of Mn nutrition and irradiance on photosystem 2 (PS2) activity, irradiance response curves for electron transport rate (ETR), nonphotochemical quenching (qN), photochemical quenching (qP), and real photochemical efficiency of PS2 (ΦPS2) were recorded under 10 different irradiances (66, 96, 136, 226, 336, 536, 811, 1 211, 1 911, and 3 111 µmol m−2 s−1, I66 to I3111, respectively) generated with the PAM-2000 fluorometer. Leaf chlorophyll content was significantly lower under Mn excess (Mn686) compared to Mn0; its highest values were recorded in the treatments Mn2-Mn98. However, ETR and ΦPS2 values were significantly lower under Mn0 compared to the other Mn treatments, when plants were exposed to irradiances ≥96 µmol m−2 s−1. Furthermore, Mn0 plants had significantly higher values of qN and lower values of qP at irradiances ≤226 and ≥336 µmol m−2 s−1, respectively, than those grown under Mn2-Mn686. Irrespective of Mn treatment, the values of ΦPS2 and qN decreased, while those of qP increased progressively by increasing irradiance from I136 to I3111. Finally, Mn2-Mn98 plants were less sensitive to photoinhibition of photosynthesis (≥811 µmol m−2 s−1) than the Mn686 (≥536 µmol m−2 s−1) and Mn0 (≥336 µmol m−2 s−1) ones.

Eficiência fotoquímica de gramíneas forrageiras tropicais submetidas à deficiência hídrica

Neste estudo, as espécies capim-setária (Setaria anceps Stapf.), capim-hemárthria (Hemarthria altissima [Poir] Stapf. &amp; Hubbard), capim-do-nilo (Acroceras macrum Stapf.) e capim-angola (Brachiaria purpurascens [Raddi] Henr.) foram submetidos à deficiência hídrica moderada a seca com o objetivo de avaliar o efeito do déficit hídrico sobre as características de fluorescência da clorofila. O experimento foi realizado em casa de vegetação, em blocos ao acaso, constituídos pelas quatro espécies cultivadas sob dois regimes hídricos (irrigado e não-irrigado), em três repetições. Durante a indução da deficiência hídrica, foram monitoradas as seguintes variáveis de fluorescência da clorofila a: fluorescência inicial (F0), fluorescência máxima (Fm), rendimento quântico máximo do PSII (Fv/Fm), taxa relativa de transporte de elétrons (ETR), quenching fotoquímico (qP) e quenching não fotoquímico (qN). Após dez dias de submissão ao estresse hídrico, os valores de Fo e Fm decresceram em todas as espécies. Os menores valores de Fv/Fm foram encontrados no capim-do-nilo e no capim-setária, o que configura baixo rendimento fotoquímico nessas espécies sob déficit hídrico, ao contrário do capim-hemárthria, que apresentou valores similares em ambos os tratamentos. Os valores mais altos de qN foram registrados no capim-hemárthria e no capim-angola, demonstrando boa capacidade dessas espécies em dissipar a energia luminosa absorvida em excesso para manter baixo estado de redução nos aceptores primários de elétrons do PSII. Em geral, as curvas de ETR em resposta ao fluxo de fótons fotossintéticos mostraram-se distintas entre os tratamentos, sendo mais pronunciadas no capim-do-nilo. Nessa espécie, a eficiência dos transportadores de elétrons do PSII foi seriamente comprometida pelo déficit hídrico.

Interplay between initial carbohydrate availability, current photosynthesis, and adventitious root formation in Pelargonium cuttings

Pelargonium was used to explore the interrelation between initial carbohydrate reserves and current photosynthesis in adventitious root formation (ARF) of leafy stem cuttings. The effects of pre-severance light intensity, short-term storage, and current light intensity were studied. Initial carbohydrate levels in the basal stems (BS) were positively correlated with pre-severance photosynthetic photon flux density (PPFD) and were only marginally reduced by storage. The storage-induced decrease in non-photochemical quenching (qN) of chlorophyll fluorescence (CF) and carbohydrate levels in leaves was compensated during the early rooting period. Concurrently, qN values, sugar levels in leaves, and sugar accumulation in the BS were lower for the high-light-adapted cuttings that received low light compared with their counterparts that were exposed to higher light or with low-light-adapted cuttings receiving the same light. The number of roots was positively correlated with initial concentrations of leaf sugars, especially sucrose, but only with a current PPFD ≤ 100 μmol m −2 s −1. When the PPFD was higher, the root number was dependent on the mean qN, which reflected the short-term adaptation of the photosynthetic apparatus to current PPFD. The entire variation in ARF was explained by the mean leaf sucrose concentrations of days 0 + 7, which reflected the stability of early leaf carbohydrate export. It is suggested that the leaf-derived influx of sugars or other co-transported molecules determines the intensity of ARF in leafy stem cuttings.