Photosynthesis and Chlorophyll Fluorescence Characteristics in Relationship to Changes in Pigment and Element Composition of Leaves of Platanus occidentalis L. during Autumnal Leaf Senescence

The loss of chlorophyll and total leaf nitrogen during autumnal senescence of leaves from the deciduous tree Platanus occidentalis L. was accompanied by a marked decline in the photosynthetic capacity of O₂ evolution on a leaf area basis. When expressed on a chlorophyll basis, however, the capacity for light-and CO₂-saturated O₂ evolution did not decline, but rather increased as leaf chlorophyll content decreased. The photon yield of O₂ evolution in white light (400-700 nanometers) declined markedly with decreases in leaf chlorophyll content below 150 milligrams of chlorophyll per square meter on both an incident and an absorbed basis, due largely to the absorption of light by nonphotosynthetic pigments which were not degraded as rapidly as the chlorophylls. Photon yields measured in, and corrected for the absorptance of, red light (630-700 nanometers) exhibited little change with the loss of chlorophyll. Furthermore, PSII photochemical efficiency, as determined from chlorophyll fluorescence, remained high, and the chlorophyll a/b ratio exhibited no decline except in leaves with extremely low chlorophyll contents. These data indicate that the efficiency for photochemical energy conversion of the remaining functional components was maintained at a high level during the natural course of autumnal senescence, and are consistent with previous studies which have characterized leaf senescence as being a controlled process. The loss of chlorophyll during senescence was also accompanied by a decline in fluorescence emanating from PSI, whereas there was little change in PSII fluorescence (measured at 77 Kelvin), presumably due to decreased reabsorption of PSII fluorescence by chlorophyll. Nitrogen was the only element examined to exhibit a decline with senescence on a dry weight basis. However, on a leaf area basis, all elements (C, Ca, K, Mg, N, P, S) declined in senescent leaves, although the contents of sulfur and calcium, which are not easily retranslocated, decreased to the smallest extent.     

Photosynthetic apparatus of pea thylakoid membranes : response to growth light intensity

We investigated the effect of growth light intensity on the photosynthetic apparatus of pea (Pisum sativum) thylakoid membranes. Plants were grown either in a growth chamber at light intensities that ranged from 8 to 1050 microeinsteins per square meter per second, or outside under natural sunlight. In thylakoid membranes we determined: the amounts of active and inactive photosystem II, photosystem I, cytochrome b/f, and high potential cytochrome b₅₅₉, the rate of uncoupled electron transport, and the ratio of chlorophyll a to b. In leaves we determined: the amounts of the photosynthetic components per leaf area, the fresh weight per leaf area, the rate of electron transport, and the light compensation point. To minimize factors other than growth light intensity that may alter the photosynthetic apparatus, we focused on peas grown above the light compensation point (20-40 microeinsteins per square meter per second), and harvested only the unshaded leaves at the top of the plant. The maximum difference in the concentrations of the photosynthetic components was about 30% in thylakoids isolated from plants grown over a 10-fold range in light intensity, 100 to 1050 microeinsteins per square meter per second. Plants grown under natural sunlight were virtually indistinguishable from plants grown in growth chambers at the higher light intensities. On a leaf area basis, over the same growth light regime, the maximum difference in the concentration of the photosynthetic components was also about 30%. For peas grown at 1050 microeinsteins per square meter per second we found the concentrations of active photosystem II, photosystem I, and cytochrome b/f were about 2.1 millimoles per mol chlorophyll. There were an additional 20 to 33% of photosystem II complexes that were inactive. Over 90% of the heme-containing cytochrome f detected in the thylakoid membranes was active in linear electron transport. Based on these data, we do not find convincing evidence that the stoichiometries of the electron transport components in the thylakoid membrane, the size of the light-harvesting system serving the reaction centers, or the concentration of the photosynthetic components per leaf area, are regulated in response to different growth light intensities. The concept that emerges from this work is of a relatively fixed photosynthetic apparatus in thylakoid membranes of peas grown above the light compensation point.     

Photosynthetic response and adaptation to high temperature in desert plants : a comparison of gas exchange and fluorescence methods for studies of thermal tolerance

The temperature threshold for the onset of irreversible loss of photosynthetic capacity of leaves was examined in studies of net CO₂ exchange and by chlorophyll fluorescence techniques. Close agreement was found between the temperature threshold for a dramatic increase in the fluorescence of chlorophyll from intact leaves and the leaf temperature at which the capacity for photosynthetic CO₂ fixation (measured at rate saturating light intensity by infrared gas analysis) began to be temperature unstable (i.e. decline with time of exposure to a constant temperature). This decline in CO₂ uptake was not a result of a stomatal response yielding a reduced intercellular CO₂ concentration at high temperature, and it is interpreted as an indication of progressive damage to some essential component(s) of the leaf. The temperature-dependent change in chlorophyll fluorescence apparently also indicated the onset of this damage. The fluorescence assay could be conducted with discs of leaves collected from remote locations and kept moist while they were transported to a central location, allowing assessment of the high temperature tolerance of leaves which developed under natural field conditions. These assays were verified using a mobile laboratory to study gas exchange of attached leaves in situ. The high temperature sensitivity of leaves of plants growing under natural conditions were similar to those of the same species grown in controlled environments of similar thermal regimes. High temperature in controlled environment studies brought about acclimation responses which increased the threshold for high temperature damage as measured by gas exchange. Studies of fluorescence versus temperature confirmed that this method could be used to quantify these responses, and permitted the kinetics of the acclimation response to be examined. Gas exchange studies, while providing similar estimates of thermal stability, required more time, more elaborate instrumentation, and are particularly difficult to conduct with field plants growing in situ.     

Variation of photosynthetic capacity with leaf age in an alpine orchid, Cypripedium flavum

Photosynthetic rate, chlorophyll fluorescence, leaf nitrogen and chlorophyll content of Cypripedium flavum were studied at different leaf ages. The photosynthetic capacity changed significantly with leaf age. Net photosynthesis and chlorophyll content peaked when leaf age was 60 days, decreasing at 30, 90 and 120 days. Stomatal conductance showed the highest value at 60 days, while mesophyll conductance decreased with increasing leaf age. Both leaf nitrogen content per unit area and leaf nitrogen content per unit mass decreased with increasing leaf age. The age-dependent variation in photosynthetic capacity could be linked to the changes in biochemical efficiency, leaf nitrogen content and CO₂ diffusion limitation.     

Age-dependent changes in the functions and compositions of photosynthetic complexes in the thylakoid membranes of Arabidopsis thaliana

Photosynthetic complexes in the thylakoid membrane of plant leaves primarily function as energy-harvesting machinery during the growth period. However, leaves undergo developmental and functional transitions along aging and, at the senescence stage, these complexes become major sources for nutrients to be remobilized to other organs such as developing seeds. Here, we investigated age-dependent changes in the functions and compositions of photosynthetic complexes during natural leaf senescence in Arabidopsis thaliana. We found that Chl a/b ratios decreased during the natural leaf senescence along with decrease of the total chlorophyll content. The photosynthetic parameters measured by the chlorophyll fluorescence, photochemical efficiency (F _v/F _m) of photosystem II, non-photochemical quenching, and the electron transfer rate, showed a differential decline in the senescing part of the leaves. The CO₂ assimilation rate and the activity of PSI activity measured from whole senescing leaves remained relatively intact until 28 days of leaf age but declined sharply thereafter. Examination of the behaviors of the individual components in the photosynthetic complex showed that the components on the whole are decreased, but again showed differential decline during leaf senescence. Notably, D1, a PSII reaction center protein, was almost not present but PsaA/B, a PSI reaction center protein is still remained at the senescence stage. Taken together, our results indicate that the compositions and structures of the photosynthetic complexes are differentially utilized at different stages of leaf, but the most dramatic change was observed at the senescence stage, possibly to comply with the physiological states of the senescence process.     

Photosynthetic activity,chloroplast ultrastructure,and leaf characteristics of high-light and low-light plants and of sun and shade leaves

The photosynthetic CO₂-fixation rates, chlorophyll content, chloroplast ultrastructure and other leaf characteristics (e.g. variable fluorescence, stomata density, soluble carbohydrate content) were studied in a comparative way in sun and shade leaves of beech (Fagus sylvatica) and in high-light and low-light seedlings.

1. Sun leaves of the beech possess a smaller leaf area, higher dry weight, lower water content, higher stomata density, higher chlorophyll a/b ratios and are thicker than the shade leaves. Sun leaves on the average contain more chlorophyll in a leaf area unit; the shade leaf exhibits more chlorophyll on a dry weight basis. Sun leaves show higher rates for dark respiration and a higher light saturation of photosynthetic CO₂-fixation. Above 2000 lux they are more efficient in photosynthetic quantum conversion than the shade leaves.
2. The development of HL-radish plants proceeds much faster than that of LL-plants. The cotyledons of HL-plants show a higher dry weight, lower water content, a higher ratio of chlorophyll a/b and a higher gross photosynthesis rate than the cotyledons of the LL-plants, which possess a higher chlorophyll content per dry weight basis. The large area of the HL-cotyledon on the one hand, as well as the higher stomata density and the higher respiration rate in the LL-cotyledon on the other hand, are not in agreement with the characteristics of sun and shade leaves respectively.
3. The development, growth and wilting of wheat leaves and the appearance of the following leaves (leaf succession) is much faster at high quanta fluence rates than in weak light. The chlorophyll content is higher in the HL-leaf per unit leaf area and in the LL-leaf per g dry weight. There are no differences in the stomata density and leaf area between the HL- and LL-leaf. There are fewer differences between HL- and LL-leaves than in beech or radish leaves.
4. The chloroplast ultrastructure of shade-type chloroplasts (shade leaves, LL-leaves) is not only characterized by a much higher number of thylakoids per granum and a higher stacking degree of thylakoids, but also by broader grana than in sun-type chloroplasts (sun leaves, HL-leaves). The chloroplasts of sun leaves and of HL-leaves exhibit large starch grains.
5. Shade leaves and LL-leaves exhibit a higher maximum chlorophyll fluorescence and it takes more time for the fluorescence to decline to the steady state than in sun and HL-leaves. The variable fluorescence VF (ratio of fluorescence decrease to steady state fluorescence) is always higher in the sun and HL-leaf of the same physiological stage (maximum chlorophyll content of the leaf) than in the shade and LL-leaf. The fluorescence emission spectra of sun and HL-leaves show a higher proportion of chlorophyli fluorescence in the second emission maximum F₂ than shade and LL-leaves.
6. The level of soluble carbohydrates (reducing sugars) is significantly higher in sun and HL-leaves than in shade and LL-leaves and even reflects changes in the amounts of the daily incident light.
7. Some but not all characteristics of mature sun and shade leaves are found in HL- and LL-leaves of seedlings. Leaf thickness, dry weight, chlorophyll content, soluble carbohydrate level, photosynthetic CO₂-fixation, height and width of grana stacks and starch content, are good parameters to describe the differences between LL- and HL-leaves; with some reservations concerning age and physiological stage of leaf, a/b ratios, chlorophyll content per leaf area unit and the variable fluorescence are also suitable.

     

Remote sensing of heterogeneity in photosynthetic efficiency, electron transport and dissipation of excess light in Populus deltoides stands under ambient and elevated CO2 concentrations, and in a tropical forest canopy, using a new laser-induced fluorescence transient device

Determining the spatial and temporal diversity of photosynthetic processes in forest canopies presents a challenge to the evaluation of biological feedbacks needed for improvement of carbon and climate models. Limited access with portable instrumentation, especially in the outer canopy, makes remote sensing of these processes a priority in experimental ecosystem and climate change research. Here, we describe the application of a new, active, chlorophyll fluorescence measurement system for remote sensing of light use efficiency, based on analysis of laser‐induced fluorescence transients (LIFT). We used mature stands of Populus grown at ambient (380 ppm) and elevated CO₂ (1220 ppm) in the enclosed agriforests of the Biosphere 2 Laboratory (B2L) to compare parameters of photosynthetic efficiency, photosynthetic electron transport, and dissipation of excess light measured by LIFT and by standard on‐the‐leaf saturating flash methods using a commercially available pulse‐modulated chlorophyll fluorescence instrument (Mini‐PAM). We also used LIFT to observe the diel courses of these parameters in leaves of two tropical forest dominants, Inga and Pterocarpus, growing in the enclosed model tropical forest of B2L. Midcanopy leaves of both trees showed the expected relationships among chlorophyll fluorescence‐derived photosynthetic parameters in response to sun exposure, but, unusually, both displayed an afternoon increase in nonphotochemical quenching in the shade, which was ascribed to reversible inhibition of photosynthesis at high leaf temperatures in the enclosed canopy. Inga generally showed higher rates of photosynthetic electron transport, but greater afternoon reduction in photosynthetic efficiency. The potential for estimation of the contribution of outer canopy photosynthesis to forest CO₂ assimilation, and assessment of its response to environmental stress using remote sensing devices such as LIFT, is briefly discussed.     

CO(2) Concentrating Mechanism of C(4) Photosynthesis: Permeability of Isolated Bundle Sheath Cells to Inorganic Carbon

Diffusion of inorganic carbon into isolated bundle sheath cells from a variety of C₄ species was characterized by coupling inward diffusion of CO₂ to photosynthetic carbon assimilation. The average permeability coefficient for CO₂ (P_CO2) for five representatives from the three decarboxylation types was approximately 20 micromoles per minute per milligram chlorophyll per millimolar, on a leaf chlorophyll basis. The average value for the NAD-ME species Panicum miliaceum (10 determinations) was 26 with a standard deviation of 6 micromoles per minute per milligram chlorophyll per millimolar, on a leaf chlorophyll basis. A P_CO2 of at least 500 micromoles per minute per milligram chlorophyll per millimolar was determined for cells isolated from the C₃ plant Xanthium strumarium. It is concluded that bundle sheath cells are one to two orders of magnitude less permeable to CO₂ than C₃ photosynthetic cells. These data also suggest that CO₂ diffusion in bundle sheath cells may be made up of two components, one involving an apoplastic path and the other a symplastic (plasmodesmatal) path, each contributing approximately equally.     

Photosynthetic and stomatal responses of spinach leaves to salt stress

The gas exchange of spinach plants, salt-stressed by adding NaCl to the nutrient solution in increments of 25 millimolar per day to a final concentration of 200 millimolar, was studied 3 weeks after starting NaCl treatment. Photosynthesis became light saturated at 1100 to 1400 micromoles per square meter per second in salt-treated plants and at approximately 2000 micromoles per square meter per second in control plants. Photosynthetic capacity of the mesophyll measured as a function of intercellular partial pressure of CO₂ at the light intensity prevailing during growth and at light saturation were both decreased in the salttreated plants. The CO₂ compensation points and relative enhancements of photosynthesis at low O₂ were not affected by salinity. The lower photosynthetic rates in salt-treated leaves at 450 micromoles per square meter per second were associated with a 70% reduction in stomatal conductance and low intercellular CO₂ (219 microbars; cf. 285 microbars for controls). Increasing photon flux density to light saturation extended the linear portions of the CO₂ response curves, increased stomatal conductances, increased intercellular CO₂ in the salt-treated plants, but lowered it in controls, and accentuated differences in photosynthetic rate (area basis) between the treatments.

Leaves from salt-treated plants were thicker but contained about 73% of the chlorophyll per unit area of control plants. When photosynthetic rates were expressed on a chlorophyll basis there was no difference in initial slope of assimilation versus intercellular CO₂ between treatments. Photosynthetic rates (chlorophyll basis) at light saturation differed only by 20% which was also observed earlier with isolated, intact chloroplasts (Robinson et al. 1983 Plant Physiol 73: 238-242).

Measurement of carbon isotope ratio revealed less discrimination against ¹³C with salt treatment and confirmed the persistence of low intercellular partial pressures of CO₂ during plant growth. The development of a thicker leaf with less chlorophyll per unit area during salt treatment permitted stomatal conductance and intercellular partial pressure of CO₂ to decline without restricting photosynthesis and had the benefit of greatly increasing water use efficiency.

     

Limiting Factors in Photosynthesis: II. IRON STRESS DIMINISHES PHOTOCHEMICAL CAPACITY BY REDUCING THE NUMBER OF PHOTOSYNTHETIC UNITS

It has been proposed that Fe stress may be used in the study of limiting factors in photosynthesis as an experimental means of varying photochemical capacity in vivo (Plant Physiol 1980 65: 114-120). In this paper the effect of Fe stress on photosynthetic unit number, size, and composition was investigated by measuring P₇₀₀, cytochrome (Cyt) f, chlorophyll (Chl) a, and Chl b in sugar beet leaves. The results show that when Fe stress reduced Chl per unit area by 80% (from 60 to 12 micrograms per square centimeter), it decreased the number of P₇₀₀ molecules per unit area by 88% and Cyt f per unit area by 86%; over the same range the Chl to P₇₀₀ ratio increased by 37% but there was no significant change in the Chl to Cyt f ratio. These data suggest that Fe stress decreases photochemical capacity and Chl per unit area by diminishing the number of photosynthetic units per unit leaf area.     

Maturation in Larch : II. Effects of Age on Photosynthesis and Gene Expression in Developing Foliage

The effect of maturation on the morphological and photosynthetic characteristics, as well as the expression of two genes involved in photosynthesis in the developing, current year foliage of Eastern larch (Larix laricina [Du Roi]) is described. These effects were observed on foliage during the third growing season after grafting of scions from trees of different ages onto 2 year old rootstock. Specific leaf weight (gram dry weight per square meter), leaf cross-sectional area (per square millimeter), and chlorophyll content (milligram per gram dry weight) all increase with increasing age in long shoot foliage from both indoor- and outdoor-grown trees. Net photosynthesis (NPS) (mole of CO₂ per square millimeter per second) increases with age on indoor- but not outdoor-grown trees. NPS also increases with increased chlorophyll content, but outdoor-grown scions of all ages had higher chlorophyll content, and chlorophyll does not appear to be limiting for NPS outdoors. To extend these studies of maturation-related differences in foliar morphology and physiology to the molecular genetic level, sequences were cloned from the cab and rbsS gene families of larch. Both cab and rbcS gene families are expressed in foliage but not in roots, and they are expressed in light-grown seedlings of larch but only at very low levels in dark-grown seedlings (~2% of light-grown seedlings). Steady-state cab mRNA levels are relatively higher (~40%) in newly expanding short shoot foliage from juvenile plants compared to mature plants. Unlike cab, the expression of the rbcS gene family did not seem to vary with age. These data show that the maturation-related changes in morphological and physiological phenotypes are associated with changes in gene expression. No causal relationship has been established, however. Indeed, we conclude that the faster growth of juvenile scions reported previously (MS Greenwood, CA Hopper, KW Hutchison [1989] Plant Physiol 90: 406-412) is not due to increased NPS or cab expression. Long shoot foliage is the dominant foliar type on young trees and its lower specific leaf weight will permit production of more photosynthetic surface area per unit of leaf biomass.     

Chlorophyll fluorescence imaging of photosynthetic activity with the flash-lamp fluorescence imaging system

A flash-lamp chlorophyll (Chl) fluorescence imaging system (FL-FIS) is described that allows to screen and image the photosynthetic activity of several thousand leaf points (pixels) of intact leaves in a non-destructive way within a few seconds. This includes also the registration of several thousand leaf point images of the four natural fluorescence bands of plants in the blue (440 nm) and green (520 nm) regions as well as the red (near 690 nm) and far-red (near 740 nm) Chl fluorescence. The latest components of this Karlsruhe FL-FIS are presented as well as its advantage as compared to the classical single leaf point measurements where only the fluorescence information of one leaf point is sensed per each measurement. Moreover, using the conventional He-Ne-laser induced two-wavelengths Chl fluorometer LITWaF, we demonstrated that the photosynthetic activity of leaves can be determined measuring the Chl fluorescence decrease ratio, R_Fd (defined as Chl fluorescence decrease F_d from maximum to steady state fluorescence F_s:F_d/F_s), that is determined by the Chl fluorescence induction kinetics (Kautsky effect). The height of the values of the Chl fluorescence decrease ratio R_Fd is linearly correlated to the net photosynthetic CO₂ fixation rate P _N as is indicated here for sun and shade leaves of various trees that considerably differ in their P _N. Imaging the R_Fd-ratio of intact leaves permitted the detection of considerable gradients in photosynthetic capacity across the leaf area as well as the spatial heterogeneity and patchiness of photosynthetic quantum conversion within the control leaf and the stressed plants. The higher photosynthetic capacity of sun versus shade leaves was screened by Chl fluorescence imaging. Profile analysis of fluoresence signals (along a line across the leaf area) and histograms (the signal frequency distribution of the fluorescence information of all measured leaf pixels) of Chl fluorescence yield and Chl fluorescence ratios allow, with a high statistical significance, the quantification of the differences in photosynthetic activity between various areas of the leaf as well as between control leaves and water stressed leaves. The progressive uptake and transfer of the herbicide diuron via the petiole into the leaf of an intact plant and the concomitant loss of photosynthetic quantum conversion was followed with high precision by imaging the increase of the red Chl fluorescence F₆₉₀. Differences in the availability and absorption of soil nitrogen of crop plants can be documented via this flash-lamp fluorescence imaging technique by imaging the blue/red ratio image F₄₄₀/F₆₉₀, whereas differences in Chl content are detected by collecting images of the fluorescence ratio red/far-red, F₆₉₀/F₇₄₀.     

Studies on genetic male-sterile soybeans : v. Effects of male-sterility on the function and glycerolipid composition of chloroplast thylakoids

Soybean (Glycine max L. Merr.) germplasm, isogenic except for loci controlling male sterility (ms₁), was utilized to study the effects of reproductive development on certain aspects of photosynthesis. Plants were sampled at various times between flowering (77 days after transplanting) and maturity (147 days after transplanting). During that period photosynthetic rates declined more rapidly in the male-sterile genotypes than male-fertile genotypes; and after 105 days, the sterile genotypes maintained low but relatively constant carbon exchange rates. The decline of leaf photosynthesis in the male-sterile genotype occurred concomitantly with an inhibition of the photosynthetic electron transport chain associated with photosystem II. Changes in photosystem I activities, cytochrome f levels, and chlorophyll a/b ratios per se were not responsible for the decline in whole leaf photosynthesis. These conditions were independent of the source of nitrogen nutrition. Lipid analyses of the thylakoids revealed that a loss of phosphatidylglycerol was highly correlated with the inhibition of photosystem II activity. These results suggested a relation between the decline in leaf carbon exchange and the decline in photosynthetic electron transport activity.     

Effect of transient accumulation of anthocyanin on leaf development and photoprotection of Fagopyrum dibotrys mutant

Changes in pigments contents, leaf area, leaf dry mass per unit area (LMA), photosynthetic rate and chlorophyll a fluorescence were investigated in developing leaves of Fagopyrum dibotrys Hara. mutant. Anthocyanins transiently accumulate below the upper epidermis during leaf ontogeny of this mutant. Red leaves possessed lower Chl content, LMA, photosynthetic rate and apparent carboxylation efficiency than green leaves. However, content of anthocyanins declined and above mentioned parameters increased during further leaf development. In both red and green leaves, chronic photoinhibition did not take place according to variable to maximum chlorophyll fluorescence ratio (F_v/F_m). Red leaves had higher non-photochemical quenching (NPQ) and higher PS 2 efficiency.     

Chlorophyll fluorescence induction and estimation of plant resistance to stress factors

The usage of chlorophyll fluorescence induction (CFI) for estimating various types of plant resistance (primary, general, initial, adaptive) to stress factors is reviewed. The necessity of ontogenetic approach (considering the age-specific properties of the photosynthetic apparatus) in determining general and adaptive resistance of plants to prolonged action of stress factors by the CFI method is argued. In the plant Cucumbis sativus L., the possibility is shown of using age-specific qualitative and quantitative traits of leaf CFI (changes in the shape of chlorophyll fluorescence induction curves and in the dynamics of CFI parameters in the course of leaf ontogeny) for comparative study of differences between fully active and stressed plants. Possible criteria are suggested for estimating the effect of outer stress factors by the presence or absence of a steady-state phase in the dynamics of CFI parameters during leaf ontogeny. It is also suggested to use the duration of the steady-state phase following the termination of leaf growth (estimated by the dynamics of the slow phase of CFI as the ratio of fluorescence intensity at the peak P and the steady-state fluorescence intensity, Fp/Fs, or as the viability index Rfd) and the variability of CFI parameters during this period as qualitative estimates of plant resistance to prolonged action of stress factors.     

Cotton genotypic variation in the photosynthetic response to irradiance

The photosynthetic response of 8 cotton (Gossypium hirsutum L.) genotypes to changing irradiance was investigated under field conditions during the 1998 through 2000 growing seasons. Equations developed to describe the response of net photosynthetic rate (P_N) to photosynthetic photon flux density (PPFD) demonstrated that, across all irradiances, the two okra leaf-type genotypes photosynthesized at a greater rate per unit leaf area than all of the six normal leaf-type genotypes. This superior photosynthetic performance of the okra leaf-type genotypes can be partially explained by their 13 % greater leaf chlorophyll content relative to that of the normal leaf-type genotypes. The 37 % reduction in leaf size brought upon by the okra leaf trait may have concentrated the amount of photosynthetic machinery per unit leaf area. Nevertheless, the lack of sufficient canopy leaf surface area suppressed the potential yield development that could accompany the higher P_N per unit leaf area.     

Submerged versus air-exposed intertidal macrophyte productivity: from physiological to community-level assessments

The photosynthetic productivity of the intertidal communities dominated by the seagrass Zostera noltii and the cordgrass Spartina maritima was assessed in two contrasting situations during a tidal cycle, i.e., air exposure and water immersion. Two complementary methods were used: infra red gas analysis of CO₂ flux measurements in whole communities and chlorophyll a fluorescence measurements of individual plants photosynthetic activity. Higher photosynthetic rates of Z. noltii in air were observed both at the individual plants response level determined by chlorophyll fluorescence and at the community level measured as gas exchange (CO₂ uptake). S. maritima plants consistently showed low photosynthetic response when immersed. Gross community production (GCP) measured as carbon dioxide uptake was always higher in air than in water for both communities. When immersed, the GCP of both communities was similar. However, when exposed to the air, the GCP of the S. maritima community was higher than the one of Z. noltii's. The key factor in CO₂ assimilation by air-exposed Z. noltii was the retention of water in sediment microdepressions. During low tide, depressions in the sediment retain a considerable amount of water, enough to maintain leaf hydration. In these conditions, rapid air-water CO₂ diffusion occurs, making it readily available to plants. The community gas exchange measurements compared well with the fluorescence indications. Both Z. noltii and S. maritima were shown to be responsible for the overall pattern of photosynthetic carbon fixation within their respective communities, both during submersion and emersion periods. The short-term incubations method described in this report proved to be a valuable tool for field measurements of intertidal lagoon productivity. It provides fast and precise values of carbon dioxide fixation, both in submerged and air-exposed communities.     

Chlorophyll fluorescence induction,chlorophyll content,and chromaticity characteristics of leaves as indicators of photosynthetic apparatus senescence in arboreous plants

Parameters of chlorophyll fluorescence induction (CFI) are widely used for assessment of the physiological state of higher plant leaves in biochemical, physiological, and ecological studies and in agricultural applications. In this work we have analyzed data on variability of some CFI parameters — Φ _PSII ^max = F _v/F _m (relative value of variable fluorescence), q _NPQ (non-photochemical quenching coefficient), R _Fd (“vitality index”) — in autumnal leaves of ten arboreous plant species of the temperate climatic zone. The correlation between the chlorophyll content in the leaves and fluorescence parameters characterizing photosynthetic activity is shown for two representative species, the small-leaved linden Tilia cordata and the rowan tree Sorbus aucuparia. During the period of mass yellowing of the leaves, the Φ _PSII ^max value can be used as an adequate characteristic of their photochemical activity, while in summer the q _NPQ or R _Fd values are more informative. We have established a correlation between the Φ _PSII ^max value, which characterizes the maximal photochemical activity of the photosystem II, and “chromaticity coordinates” of a leaf characterizing its color features. The chromaticity coordinates determined from the optical reflection spectra of the leaves serve as a quantitative measure of their hues, and this creates certain prerequisites for a visual expert assessment of the physiological state of the leaves.     

Changes of endogenous ABA and ACC,and their correlations to photosynthesis and water relations in mungbean (Vigna radiata (L.) Wilczak cv. KPS1) during waterlogging

The effects of waterlogging on the dynamics of leaf abscisic acid (ABA) and root 1-aminocyclopropane-1-carboxilic acid (ACC, a precursor of ethylene) contents together with those on photosynthetic rate, leaf water potential and chlorophyll fluorescence were studied in mungbean (Vigna radiata (L.) Wilczak cv. KPS1) plants under greenhouse conditions. Waterlogging reduced the photosynthetic rate and water use efficiency rapidly without any changes of stomatal conductance, transpiration rate and ABA concentrations. Rapid reduction of photosynthetic rate and Fv/Fm ratio of chlorophyll fluorescence without increase of ABA indicates that early reduction of photosynthetic rate may not be related to ABA. In addition, the slower recovery of P, P/T_r and Fv/Fm values than ABA implies that ABA is not completely involved in photosynthetic reduction. Increased concentration of ACC during the waterlogging period and after the end of waterlogging may indicate the involvement of ethylene in photosynthetic reduction through the reduction of PSII activities, although early reduction of photosynthesis could not be explained by ethylene. After 2 days of waterlogging, ABA was increased concomitantly with the rapid reduction of P, T_r and g_s. It may suggest that ABA reduces photosynthesis through some ABA-related reactions, such as stomatal closure.     

Analysis of salinity effects on basil leaf surface area, photosynthetic activity, and growth

Basil (Ocimum basilicum L.) seedlings were cultured on liquid medium in controlled conditions. Two varieties differing in leaf size were compared. When plants were 30?days old, the medium was supplemented with 50?mM NaCl. After 15?days of treatment, root, stem and leaf biomass, leaf number, and leaf surface area were measured. Ion accumulation was determined in roots, stems, and leaves. Photosynthetic parameters (CO₂ fixation rate, internal CO₂ concentration, stomatal conductance) as well as transpiration rate were determined on separate leaves. Electrolyte leakage and malondialdehyde content were used to estimate damage to membranes and lipid peroxidation, respectively. Several antioxidant enzymatic activities were used as proxies of oxidative stress. High Na⁺ concentration was reached in leaf tissues. Salt restricted whole plant biomass deposition rate by diminishing leaf number and leaf expansion, as well as photosynthetic activity were estimated from whole plant biomass production per unit leaf surface area. Diminished stomatal conductance restricted CO₂ fixation rate, and decrease in chlorophyll content presumably limited photosynthetic activity. Lipid peroxidation revealed damages to membranes. The magnitude of these responses differed between the two varieties, indicating that an intraspecific variability in salt response exists in basil.