Comparative analyses of physiological assays and chlorophyll <Emphasis Type="Italic">a</Emphasis> variable fluorescence parameters: investigating the importance of phosphorus availability in oligotrophic and eutrophic freshwater systems

Diverse measurements of nutrient status indicators were used to test the severity of physiological phosphorus (P) limitation of phytoplankton among lake systems ranging from oligotrophic to eutrophic, based on P and chlorophyll a (Chl a) concentrations. Metabolic assays and particulate nutrient ratios were used to estimate nutrient status at sites located in Lake Erie, Lake Ontario and Lake Huron. Variable fluorescence ratios (F _v/F _m), relative electron transport rates and their response to irradiance were measured by the pulse-amplitude-modulated fluorometer. Under summer stratified conditions, P deficiency was strongest in the oligotrophic sites and nitrogen (N) status indicators and Chl a variable parameters revealed no severe N deficiency. Nutrient amendment assays showed positive associations with P additions and Chl a fluorescence parameters at P-deficient sites. In the most oligotrophic sites, N additions revealed a modest increase only detected by the Chl a fluorescence parameters. Phytoplankton communities were also associated with nutrient status, where chrysophytes and cryptophytes were important in P-deficient sites and cyanobacteria, phyrrophyta, and diatoms were prevalent in nutrient-rich sites. The results confirmed that Chl a fluorescence parameters can reveal P deficiency and indicate its severity among the range of trophic status in aquatic systems.     

Impact of Field Dodder (<Emphasis Type="Italic">Cuscuta campestris</Emphasis> Yunk.) on Chlorophyll Fluorescence and Chlorophyll Content of Alfalfa and Sugar Beet Plants

The impact that the parasitic plant field dodder (Cuscuta campestris Yunk.) has on chlorophyll fluorescence and chlorophyll content of infested alfalfa (Medicago sativa L.) and sugar beet (Beta vulgaris L.) was examined under controlled conditions. Several parameters of chlorophyll fluorescence were measured in infested and non-infested alfalfa and sugar beet plants over a period of twenty days, beginning with the day of infestation. Chlorophyll contents (total, relative and ratio of chlorophyll a to b) were determined 1, 7, 14 and 20 days after infestation (DAI). Field dodder was found to affect both the total and relative chlorophyll contents in infested alfalfa and sugar beet, causing significant reduction in chlorophyll content in both host plants. This parasitic plant also affects a number of parameters of chlorophyll fluorescence (F_o, F_v/F_m, Φ_PSII, F_v and IF), showing that these parameters may be considered sensitive indicators of the impact that field dodder has on its host plants.     

Crop rotation associating a legume and the nickel hyperaccumulator <Emphasis Type="Italic">Alyssum murale</Emphasis> improves the structure and biofunctioning of an ultramafic soil

Nickel (Ni) agromining aims to phytoextract heavy metals using hyperaccumulators whilst at the same time rehabilitating ultramafic soils. After removing the bioavailable metal, ultramafic soils are improved in terms of their agronomic properties with the aim of future agricultural uses. The low fertility of ultramafic soils can be compensated by integrating legumes already used in traditional agro-systems because of their importance in soil nitrogen enrichment. However, few studies have evaluated the potential profits of legumes on Ni agromining and their potential benefits on soil biological fertility. Here, we characterized the effect of a crop rotation with two plants, a legume (Vicia sativa) and a hyperaccumulator (Alyssum murale), on the phytoextraction efficiency and on soil structure and biofunctioning. A pot experiment was set up in controlled conditions to grow A. murale and four treatments were tested: rotation with V. sativa (Ro), fertilized mono-culture (FMo), non-fertilized mono-culture (NFMo) and bare soil without plants (BS). No significant difference was found between the Ro and NFMo treatments for the dry biomass yield. However, the Ro treatment showed the highest Ni concentrations ([Ni]) in A. murale shoots compared to FMo and NFMo treatments. The Ro treatment plants had more than twice as many leaves [Ni] compared to FMo. Soil physico-chemical analyses showed that the Ro treatment was better structured and showed the highest presence of bacterial micro-aggregates, as well as less non-aggregated particles. Legumes integration in Ni-agromining systems could be a pioneering strategy to reduce chemical inputs and to improve soil biofunctioning and thus fertility.     

Estimation of biophysical characteristics for <Emphasis Type="Italic">Chlamydomonas reinhardtii</Emphasis> pigment mutants with an M-PEA-2 fluorometer

Light green pigment mutants with a reduced chlorophyll b content were constructed in the microalga Chlamydomonas reinhardtii Dangeard. A simultaneous recording of the induction curves for prompt and delayed fluorescence and the redox state of P700 in the microsecond range with a M-PEA-2 fluorometer revealed decreases in the quantum yield of electron transport in PS2 (φE₀) and the performance index (PI_ABS) and increases in the quantum efficiency of energy dissipation (φD₀) and ΔpH-dependent nonphotochemical quenching (qE and NPQ). The light-dependence curves of the fluorescence parameters confirmed a decrease in the coefficient of maximum utilization of light energy (α) for the mutants. However, the mutants showed an adequate rate of electron transport at a medium light intensity under steady-state conditions. The mutations did not directly affect the oxidation reactions of the PS1 pigment (P700) and the decrease in delayed fluorescence. Experience in using the mutants to test polluted waters of Kazakhstan confirmed that the mutants are promising for use in biomonitoring for mutagens.     

Intrapopulation heterogeneity of the fluorescence parameters of the marine plankton alga <Emphasis Type="Italic">Thalassiosira weissflogii</Emphasis> at various nitrogen levels

Fluorescence of the marine alga Thalassiosira weissflogii (Grunow) Fryxell et Hasle with open (F _o ) and closed (F _m ) reaction centers of photosystem 2 (PS 2) and its relative variable fluorescence (F _v/F _m ) were measured at various levels of inorganic nitrogen. A significant heterogeneity of the population in terms of these parameters was revealed. Some cells within the population were more sensitive to nitrogen deficiency, and their photosynthetic apparatus was disrupted to a greater extent. The cells within a population also differed in terms of their ability to recover after incubation at low nitrogen levels. Enhancement of nitrogen deficiency resulted in an increase in the variability of the F _o and F _v/F _m values of the cells. Fluorescence variability decreased at a less pronounced deficiency. Fluorescence variability should be taken into consideration in the studies concerning responses of algae to changes in nutrient contents.     

Investigation of the photosynthetic activity of bark phelloderm of arboreous plants using the fluorescent method

Seasonal changes in the characteristics of chlorophyll fluorescence were studied in the bark of several species of trees originating in various climatic zones: Siberian cedar (Pinus sibirica), larch (Larix sibirica), eastern arborvitae (Thuja occidentalis), pendent white birch (Betula pendula), wild black cherry (Padus virginiana), horse chestnut (Aesculus hippocastanum), red oak (Quercus rubra), Manchurian catalpa (Catalpa bungei), linden (Tilia cordata), goat willow (Salix caprea), Amur cherry (Padus maackii), and apple Korichnaya (Malus domestrica B.). Tree bark has a sufficient amount of chlorophyll for measuring the parameters of chlorophyll fluorescence throughout the year. The relative yield of the variable fluorescence of chlorophyll (F _v/F _m) can be used to assess seasonal changes in the physiological state of various trees.     

Nutrient allocation and photochemical responses of <Emphasis Type="Italic">Populus</Emphasis> × <Emphasis Type="Italic">canadensis</Emphasis> ‘Neva’ to nitrogen fertilization and exogenous <Emphasis Type="Italic">Rhizophagus irregularis</Emphasis> inoculation

Arbuscular mycorrhizal fungi (AMF) can promote plant growth performance, but their effectiveness varies depending on soil nitrogen (N) availability. To clarify the effectiveness of exogenous AMF along an N-fertilization gradient (0, 2, 10, 20, and 30 mM), the impacts of exogenous Rhizophagus irregularis and N on the growth, photochemical activity, and nutritional status of Populus?×?canadensis ‘Neva’ in natural soil were evaluated in a pot experiment. The results showed that the 10 mM N level was the optimal fertilization regime with the highest promotion effect on plant growth and the maximum quantum yield of photosystem II (PSII) (F_v/F_m). Excess N (20 and 30 mM) fertilization reduced the actual quantum yield of PSII (ФPSII) and the F_v/F_m of the plants. Regardless of the N availability, inoculated plants exhibited greater F_v/F_m values than did non-inoculated plants. The biomass of inoculated plants was significantly higher compared with the control under low N levels (0 and 2 mM). Under high N levels, inoculated plants showed significant increases in ФPSII. Moreover, the nutrient imbalance of plants inoculated with exogenous R. irregularis was eased by increasing P, Fe, Mn and Cu uptake in roots and higher P, Ca, Mg, Fe, Mn and Zn concentrations in leaves. Moreover, the F_v/F_m and ФPSII exhibited positive correlations with P, Ca, Mg and Zn concentrations in leaves. In conclusion, inoculation with exogenous R. irregularis can benefit plant fitness by improving the photochemical capacity and nutrient composition of poplar under different N levels.     

Intelligent image analysis (IIA) using artificial neural network (ANN) for non-invasive estimation of chlorophyll content in micropropagated plants of potato

An artificial neural network (ANN) was used to analyze photometric features extracted from the digitized images of leaves from in vitro-regenerated potato plants for non-invasive estimation of chlorophyll content. A MATLAB®-based, feed-forward, backpropagation-type network was developed for an input layer (three input elements), with one hidden layer (one node) and one output layer representing the predicted chlorophyll content. A significant influence of training function during optimization of ANN modeling was observed. Among the 11 training functions tested, “trainlm” was found to be the best on the basis of comparative analysis of root-mean-square error (RMSE) at zero epoch. A significant correlation between the model-predicted and Soil-Plant Analysis Development (SPAD) meter-measured relative chlorophyll contents was obtained when the mean brightness ratio (rgb) parameters were used. Compared to a red (R), green (G), and blue (B) color space model, the rgb model exhibited better performance with a significant correlation (R ² = 0.85). Incorporation of photometric features, such as luminosity (L), blue (B)/L, and green (G)/L, with rgb failed to improve the performance of the network. The developed Intelligent image analysis (IIA) system was able to estimate in real time the chlorophyll content of in vitro-regenerated leaves for assessment of plant nutrient status during micropropagation.     

Nutrient concentration in wheat and soil under allelopathy treatments

Allelopathy is related to soil nutrient availability and allelochemicals can change the soil and therefore the plant nutrient status. Wheat is one of the most important crops for the production of human food in the world. Alhagi maurorum and Cardaria draba are the most important weeds in wheat fields. We performed experiments to assess the allelopathic effect of A. maurorum and C. draba shoots on mineral nutrient concentrations in pot-grown wheat plants and soil. The presence of dry powder of A. maurorum and C. draba shoots reduced concentrations of macronutrients (NO₃ ^?, K⁺, Ca²⁺ and P) and micronutrients (Fe²⁺ and Cu²⁺) in roots and shoots of wheat plants, whereas it did not affect concentrations of Mg²⁺, Mn²⁺ and Zn²⁺. Allelopathic effect of A. maurorum was significantly greater than that of C. draba. There was a significantly positive correlation between wheat growth and ion concentration. There was a significantly negative correlation between the soil nutrient concentration and plant nutrient concentration across the treatments. These results suggest that allelopathy increases the nutrient availability in the soil because of the decrease in absorption by plants.     

Physiological and proteomic analysis of plant growth enhancement by the rhizobacteria <Emphasis Type="Italic">Bacillus</Emphasis> sp. JS

In this study, the effects of the plant growth-promoting rhizobacterium (PGPR), Bacillus sp. JS on the growth of tobacco (Nicotiana tabacum ‘Xanthi’) and lettuce (Lactuca sativa ‘Crispa’), were evaluated by comparing various growth parameters between plants treated with the bacterium and those exposed to water or nutrient broth as control. In both tobacco and lettuce, fresh weight and length of shoots were increased upon exposure to Bacillus sp. JS. To explain the overall de novo expression of plant proteins by bacterial volatiles, two-dimensional gel electrophoresis was performed on samples from PGPR-treated tobacco plants. Our results showed that chlorophyll a/b binding proteins were significantly up-regulated, and total chlorophyll content was also increased. Our findings indicate the potential benefits of using Bacillus sp. JS as a growth-promoting factor in agricultural practice, and highlight the need for further research to explore these benefits.     

A note on imitative behavior

In a preceding paper (Bull. Math. Biophysics,27, 175–185) the distribution function ofφ=? ₁-? ₂,—the difference of excitations in the two mutually inhibiting centers, has been derived in terms of the distribution functionsf ₁(? ₁) andf ₂(? ₂) of the two excitations. In the present note some properties of the distribution functionf(?) in terms of the propertiesf ₁(? ₁) andf ₂(? ₂) are derived.     

Kinetin Regulates UV-B-Induced Damage to Growth,Photosystem II Photochemistry,and Nitrogen Metabolism in Tomato Seedlings

Cytokinins are a class of plant growth regulators that regulate several developmental processes in plants, and recently their role in counteracting the deleterious effects of abiotic stresses has been noted. The impacts of kinetin (10 µM, KN; an artificial cytokinin) on growth, photosystem II photochemistry, and nitrogen metabolism in tomato seedlings exposed to two levels (UV-B₁, ambient+?1.2 kJ m^?2 day^?1, and UV-B₂, ambient+?2.4 kJ m^?2 day^?1) of enhanced UV-B radiation were analyzed under open field condition. The growth, pigment contents, carbonic anhydrase activity, photosynthetic O₂ yield, and values of chlorophyll a fluorescence parameters: F _v/F ₀, F _v/F _m or φP₀, ψ ₀, φE ₀, and PI_ABS declined, whereas the values of energy flux parameters (ABS/RC, TR₀/RC, ET₀/RC, and DI₀/RC) of PS II, efficiency of water splitting complex (F ₀/F _v), and respiratory rate of O₂ uptake increased under UV-B stress. Likewise, UV-B exposure at both doses significantly inhibited the activity of enzymes involved in nitrogen metabolism: nitrate reductase, nitrite reductase, glutamine synthetase, and glutamate synthase. In contrast, an enhancing effect on glutamate dehydrogenase activity was observed under UV-B stress. Exogenous KN resulted in a significant attenuation in UV-B-induced negative effects on growth, pigments, photosynthesis, and nitrogen metabolism. The study concludes that exogenous KN improved the growth performance of tomato seedlings by attenuating the damaging effects of UV-B radiation on photochemistry of PS II and nitrogen metabolism, and the alleviating effect against the low dose (UV-B₁) of UV-B was more pronounced.     

Solute patterns and diurnal variation of photosynthesis and chlorophyll fluorescence in Korean coastal sand dune plants

Four plant species, Elymus mollis Trin., Carex kobomugi Ohwi, Glehnia littoralis F. Schmidt ex Miq., and Vitex rotundifolia L.f., are dominant perennial species in coastal sand dunes of Korea. We examined a physiological adaptation of these species by measurements of diurnal variation in photosynthesis and chlorophyll (Chl) fluorescence and solute patterns in leaves during one season (June), which is favorable for plant growth of all four species. All four species adopted different strategies in order to utilize radiation and to maintain water status under a fluctuating microclimate. Although the lowest water contents among four plant species was found, E. mollis with a high Chl and K⁺ content showed better photosynthetic performance, with high stomatal conductance (g _s), net photosynthetic rate (P _N), instantaneous carboxylation efficiency (CE), and water-use efficiency. Midday depression of P _N in E. mollis and G. littoralis, without a reduction of gs, was associated with a reduction in CE and maximum photochemical efficiency of PSII, indicating nonstomatal limitation. Photosynthesis depression in both C. kobomugi and V. rotundifolia, with relatively low g _s values, could be attributed to both stomatal and nonstomatal limitations. The high storage capacity for inorganic ions in E. molli, C. kobomugi, and G. littoralis may play an efficient role in regulating photosynthesis and maintaining leaf water status through stomatal control, and can also play an important role in osmotic adjustment.     

Effects of light intensity on leaf photosynthetic characteristics,chloroplast structure,and alkaloid content of <Emphasis Type="Italic">Mahonia bodinieri</Emphasis> (Gagnep.) Laferr.

The variation of light intensity has obvious effects on leaf external morphology, internal anatomy, and physiological characteristics; it even induces changes in secondary metabolite production. The effects of different irradiance levels on biomass, gas exchange parameters, and photosynthetic pigment contents in Mahonia bodinieri (Gagnep.) Laferr. were analyzed here. Combined analyses of physiology, cytology, and HPLC were used to study the differences in leaf morphology, structure, physiological characters, and alkaloid content in response to different irradiances. The results indicated that the highest foliar biomass was observed under I ₅₀ (50 % of full sunlight) followed by I ₃₀ (30 % of full sunlight), the highest net photosynthetic rate, stomatal conductance, transpiration rate values were observed under I ₃₀ followed by I ₅₀, and lower values occurred in I ₁₀ (10 % of full sunlight) and I ₁₀₀ (full sunlight). With increased light intensity, total leaf area and the contents of chlorophyll a (Chl a), chlorophyll b (Chl b), and chlorophyll (Chl a+b) per unit leaf area were clearly reduced, whereas leaf mass per area, carotenoid content, leaf thickness, thickness of palisade and spongy parenchyma, and stomatal density were all significantly increased. Electron microscopic observation revealed that the number of grana, stroma lamellae and the number of starch grains in chloroplasts were decreased, the number of plastoglobuli was increased when irradiance levels increased. The estimated total yield of alkaloids in a single plant was higher under I ₃₀ and I ₅₀ than under I ₁₀ or I ₁₀₀ as a result of the higher biomass of the plants. Therefore, I ₃₀ and I ₅₀ were not only beneficial to increase biomass, but also suitable for the synthesis and accumulation of the major secondary metabolites (alkaloids). Our findings provide valuable data for the determination and regulation of irradiance levels during artificial cultivation of M. bodinieri.     

Mesophyll conductance to CO<Subscript>2</Subscript> in leaves of Siebold’s beech (<Emphasis Type="Italic">Fagus crenata</Emphasis>) seedlings under elevated ozone

Ozone is an air pollutant that negatively affects photosynthesis in woody plants. Previous studies suggested that ozone-induced reduction in photosynthetic rates is mainly attributable to a decrease of maximum carboxylation rate (V_cmax) and/or maximum electron transport rate (J_max) estimated from response of net photosynthetic rate (A) to intercellular CO₂ concentration (C_i) (A/C_i curve) assuming that mesophyll conductance for CO₂ diffusion (g_m) is infinite. Although it is known that C_i-based V_cmax and J_max are potentially influenced by g_m, its contribution to ozone responses in C_i-based V_cmax and J_max is still unclear. In the present study, therefore, we analysed photosynthetic processes including g_m in leaves of Siebold’s beech (Fagus crenata) seedlings grown under three levels of ozone (charcoal-filtered air or ozone at 1.0- or 1.5-times ambient concentration) for two growing seasons in 2016–2017. Leaf gas exchange and chlorophyll fluorescence were simultaneously measured in July and September of the second growing season. We determined the A, stomatal conductance to water vapor and g_m, and analysed A/C_i curve and A/C_c curve (C_c: chloroplast CO₂ concentration). We also determined the Rubisco and chlorophyll contents in leaves. In September, ozone significantly decreased C_i-based V_cmax. At the same time, ozone decreased g_m, whereas there was no significant effect of ozone on C_c-based V_cmax or the contents of Rubisco and chlorophyll in leaves. These results suggest that ozone-induced reduction in C_i-based V_cmax is a result of the decrease in g_m rather than in carboxylation capacity. The decrease in g_m by elevated ozone was offset by an increase in C_i, and C_c did not differ depending on ozone treatment. Since C_c-based V_cmax was also similar, A was not changed by elevated ozone. We conclude that g_m is an important factor for reduction in C_i-based V_cmax of Siebold’s beech under elevated ozone.     

Overexpression of Tomato Homolog of Glycolate/Glycerate Transporter Gene <Emphasis Type="Italic">PLGG1/AtLrgB</Emphasis> Leads to Reduced Chlorophyll Biosynthesis

LrgA and LrgB genes have been identified as new components in regulation of programmed cell death (PCD) in bacteria. While in Arabidopsis, it has been documented that AtLrgB plays a crucial role in chloroplast development and photorespiration by acting as a glycolate/glycerate translocator (PLGG1) in the chloroplast inner membrane. However, little is known about LrgB homologs in other plant species, especially those with fleshy fruits. In this study, a homologous gene of AtLrgB, here designated SlLrgB, was identified in tomato. Similar to AtLrgB, structure analysis suggests that the LrgA and LrgB genes have evolved into two domains of the SlLrgB protein. Expression pattern analysis showed that SlLrgB accumulated mainly in green tissues and could be regulated by light, hormone, and abiotic stress treatments. Compared to wild-type plants, parts of SlLrgB overexpression plants displayed etiolated leaves and a growth retardation phenotype, with significantly reduced chlorophyll content both in leaves and fruits. The qPCR results revealed that the SGR gene, which was associated with chlorophyll degradation, was severely repressed. Two key genes in the chlorophyll biosynthesis pathway, CAO and POR, were also suppressed in the SlLrgB overexpression plants. Taken together, we suggest that SlLrgB may play important roles in the regulation of chlorophyll metabolism pathways in tomato.     

Physiological and biochemical responses of <Emphasis Type="Italic">Camellia sinensis</Emphasis> to stress associated with <Emphasis Type="Italic">Empoasca vitis</Emphasis> feeding

The tea green leafhopper, Empoasca vitis, is the most serious pest in plantations of tea, Camellia sinensis. Beyond physical damage to the leaves, tea yields may be affected if feeding stress causes physiological and biochemical changes in the tea plant, which affected the quality and flavor of the tea. Yet the effect of feeding stress, induced by E. vitis, is largely unknown. We measured the injury index and the physiological and biochemical responses of C. sinensis to stress by E. vitis feeding in a series of laboratory trials. Using 2-year-old C. sinensis plants, we tested the effects of leafhopper feeding at different densities—0, 5, 10, and 20 leafhoppers—and different durations of exposure—1, 4, 7, and 10 days—on potential changes in chlorophyll, tea polyphenols, nutrient content, activities of protective enzymes (peroxidase, POD; superoxide dismutase, SOD; and catalase, CAT), and the lipid peroxidation (MDA). We found that the injury indices for tea leaves increased continuously as the density of E. vitis increased in the same day, and simultaneously, as the time of leafhoppers damage increased, the injury indices for tea leaves also increased. Our results also indicated that feeding by E. vitis caused a considerable decline in chlorophyll a, chlorophyll b, total chlorophyll in tea leaves and soluble carbohydrate content, and an increase in tea polyphenols. Soluble protein content showed a direct increasing relationship with the increasing leafhopper density and the duration of exposure. Throughout the period of E. vitis exposure, there was highly significant difference in the activities of protective enzymes and MDA content. Additionally, POD, SOD, and CAT activities in tea leaves were elevated significantly with the increase of leafhopper density. Lipid peroxidation (MDA) content also increased after the exposure to leafhopper feeding. Overall, our results indicate that although C. sinensis displays a certain level of tolerance to E. vitis feeding stress, higher density of leafhoppers, and longer exposure duration, can cause severe damage to tea leaves and also a decline in plant defense of tea, so as to affect the tea quality.