Chlorophyll Fluorescence Properties Research Articles

Distinct interactions of ericoid mycorrhizae and plant growth-promoting bacteria: impacts on blueberry growth and heat resilience

ABSTRACT Blueberries confront substantial challenges from climate change, such as rising temperatures and extreme heat, necessitating urgent solutions to ensure productivity. We hypothesized that ericoid mycorrhizal fungi (ErM) and plant growth-promoting bacteria (PGPB) would establish symbiotic relationships and increase heat stress tolerance in blueberries. A growth chamber study was designed with low (25/20°C) and high temperature (35/30°C) conditions with micropropagated blueberry plantlets inoculated with ErM, PGPB, and both. Gas exchange and chlorophyll fluorescence properties of the leaves were monitored throughout the growth. At harvest, biochemical assays and biomass analysis were performed to evaluate potential oxidative stress induced by elevated temperatures. ErM application boosted root biomass under 25/20°C conditions but did not impact photosynthetic efficiency. In contrast, PGPB demonstrated a dual role: enhancing photosynthetic capacity and reducing stomatal conductance notably under 35/30°C conditions. Moreover, PGPB showcased conflicting effects, reducing oxidative damage under 25/20°C conditions while intensifying it during 47°C heat shock. A significant highlight lies in the opposing effects of ErM and PGPB on root growth and stomatal conductance, signifying their reciprocal influence on blueberry plant behavior, which may lead to increased water uptake or reduced water use. Understanding these complex interactions holds promise for refining sustainable strategies to overcome climate challenges.

Evaluation of drought stress level in Sargent's cherry (Prunus sargentii Rehder) using photosynthesis and chlorophyll fluorescence parameters and proline content analysis.

Sargent's cherry trees (Prunus sargentiiRehder) are widely planted as an ornamental, climate change-sensing species. This study investigated changes in the soil moisture content, fresh weight, photosynthesis and chlorophyll fluorescence properties, and the chlorophyll and proline content of four-year-old P. sargentii seedlings after 30 days of drought stress. In the trees subjected to drought stress treatment, soil moisture content decreased, and the fresh weight of the aboveground part of the plant decreased. However, there was no significant difference in the root growth of the dried plants. Among the photosynthesis parameters, Pn MAX, E and gs showed a significant (p<0.001) decrease after 15 days in dry-stressed seedlings, but there was no difference between treatments in WUE until 20 days, and there was a significant (p<0.001) difference after 24 days. Chlorophyll fluorescence parameters, Fv/Fm, ΦPSII, Rfd, NPQ, and Pn MAX, also increased after 10 days in dry-stressed seedlings, but these changes did not reach statistical significance compared to the control treatment. These results may suggest that drought stress highly correlates with photosynthesis and chlorophyll fluorescence parameters. Chlorophyll content also significantly decreased in the seedlings under drought stress compared with the control treatment. The proline content decreased until the 10th day of drought stress treatment and increased after the 15th day, showing an increase of 10.9% on the 15th day and 57.1% on the 30th day, compared to the control treatment. These results suggest that photosynthesis, chlorophyll fluorescence parameters, and proline content can be used to evaluate drought stress in trees. The results of this study can contribute to the management of forests, such as the irrigation of trees when pore control ability and photosynthesis ability decrease.

Effects of Shading on the Growth and Photosynthetic Fluorescence Characteristics of Castanopsis hystrix Seedlings of Top Community-Building Species in Southern Subtropical China

Castanopsis hystrix is a major community-building species in the top communities of southern subtropical China, with a high natural regeneration capacity. However, excessive logging and the introduction of exotic tree species have substantially reduced the area of natural forest patches of Castanopsis hystrix, and seedling regeneration is essential for the long-term continuation of Castanopsis hystrix populations. To explore the effects of light intensity on the seedling emergence and early growth of Castanopsis hystrix, shading experiments were conducted under four shading treatments (0%, 40%, 60%, and 80%). The growth, biomass accumulation, and distribution, the quality index of seedlings, the morphology and structure of the root systems of seedlings, and the leaf chlorophyll content and chlorophyll fluorescence properties of seedlings under different shading treatments were analyzed. The results displayed the following: (1) Shade intensity impacts growth of Castanopsis hystrix seedlings and biomass allocation, with optimal results observed at 60% shade, leading to the promotion of organic matter production in leaves and the limitation of stem growth. (2) Using a multi-indicator composite index, it was determined that seedling quality for Castanopsis hystrix peaks at 60% shade intensity. (3) Shade significantly impacts the morphology and structure of Castanopsis hystrix’s root system, with most root characteristics peaking at 60% shade, indicating a substantial increase in root development compared to no-shade conditions. (4) The D-values indicated the most suitable shade intensity for seedling growth to be 60%, suggesting that Castanopsis hystrix seedlings are sensitive to light and excessive light can be detrimental to their growth. (5) The 60% shade treatment showed the maximum values of chlorophyll fluorescence characteristics and photochemical activity, with variations in energy conversion efficiency and dissipation reflected in parameters like photochemical burst coefficient (qP), photochemical burst coefficient (qN), the actual photometric yield of PSII under light acclimation (YII), and the maximum photosynthetic electron transport rate in photoinhibition (ETR), thereby supporting seedling growth and maintaining the normal function of photosynthetic organs. In conclusion, 60% shade treatment can effectively improve the growth and photosynthetic characteristics of Castanopsis hystrix seedlings and promote the accumulation of nutrient elements, ultimately promoting their growth.

Effects of Domestic Sewage on the Photosynthesis and Chromium Migration of Coix lacryma-jobi L. in Chromium-Contaminated Constructed Wetlands

To investigate the effects of domestic sewage on the photosynthesis and chromium migration of plants in chromium-contaminated constructed wetlands, small vertical flow constructed wetlands of Coix lacryma-jobi L. were set up. These wetlands were used to treat wastewater containing 0, 20, and 40 mg/L of hexavalent chromium (Cr (VI)), prepared with domestic sewage (DS), 1/2 Hoagland nutrient solution (NS), and 1/2 Hoagland nutrient solution prepared with domestic wastewater (DN), respectively. The aim was to investigate the effects of domestic sewage on indicators, such as plant growth and chromium accumulation. The results were as follows: (1) Plant heights were significantly inhibited under 20 mg/L and 40 mg/L Cr (VI) treatments, and stem diameters were not significantly affected. The use of domestic sewage in treatment alleviated the inhibition of Cr (VI) on the growth of Coix lacryma-jobi L. (2) Indicators such as root activity, photosynthetic gas exchange, and chlorophyll fluorescence properties significantly decreased with the increase in Cr (VI) concentration. The values of these photosynthetic gas exchange parameters under the DN treatment were the greatest, followed by NS and DS. On the 70th day of Cr (VI) treatment, the net photosynthetic rate (Pn) under the DN treatment was significantly higher than that under NS and DS treatments. (3) Glutathione (GSH) content in roots, stems, and leaves of Coix lacryma-jobi L. significantly increased with the increase in Cr concentration, and it increased more significantly under the DN and DS treatments than under the NS treatment. (4) With the same Cr treatment, the Cr content in roots, stems, and leaves of Coix lacryma-jobi L. under the NS treatment was the highest, followed by DS and DN. The total Cr content in the substrate under the DN treatment was the highest, followed by DS and NS. (5) The addition of domestic sewage reduced the Cr (VI) content in the water sample and increased the organic matter content. The Cr (VI) content in the water sample under the NS treatment was the highest, followed by DS and DN. The addition of domestic sewage increased the accumulation of chromium in the substrate, decreased the absorption of chromium by plants, increased GSH content in roots, stems, and leaves, alleviated the damage of Cr (VI) to plants, and thus benefited the growth of Coix lacryma-jobi L. in the constructed wetlands and ensured the sustainable and stable operation of the wetlands.

Effects of exogenous calcium on growth, chlorophyll fluorescence characteristics and antioxidant system of Fraxinus malacophylla seedlings

Karst ecosystems are becoming increasingly problematic, and high calcium is one of the main characteristics of soils in rocky desertification areas. Chlorophyll fluorescence is one of the most important indicators of the extent to which plants are affected by their environment. There are few reports on the effects of changes in exogenous calcium levels on the chlorophyll fluorescence properties of Fraxinus malacophylla seedlings. In the present study, we investigated the growth, chlorophyll fluorescence properties and antioxidant system of Fraxinus malacophylla seedlings in response to exogenous calcium (as the concentrations of 0, 25, 50, 75 mmol L−1). The results showed that Ca2+ concentration (25–50 mmol L−1) treatment mainly promoted the growth, biomass accumulation, root activity, and chlorophyll synthesis and effect on chlorophyll fluorescence in Fraxinus malacophylla; the developed root system became a strong linking hub for calcium adaptation. In addition, the activities of the antioxidant enzymes peroxidase (POD) and catalase (CAT) are upregulated and play an important role in preventing excessive oxidative damage. OJIP test parameters changed significantly with the addition of exogenous calcium, and parameters related to each photosystem II (PSII) reaction centre, such as ABS/RC and DIo/RC, increased significantly in the OJIP test, with enhanced function of the PSII electron donor lateral oxygen evolution complex. In conclusion, the addition of exogenous calcium (25–50 mmol L−1) had an important protective effect on the photosynthetic mechanism of Fraxinus malacophylla, promoting photosynthesis, better growth and better adaptability.

Seed maturation and its practical implications

The use of high vigour seeds for crop production is increasing in importance. Seed vigour develops during the late maturation phase, after deposition of reserves and attainment of maximum dry weight. During this phase, various protective mechanisms are imposed in the seeds that will aid survival after release from the mother plant. These mechanisms include the production of protective metabolites such as antioxidants and pigments, specific proteins and degradation of chlorophyll. All are essential for maximum quality of seeds used as propagation material, since they aid in providing increased tolerance to diverse biotic and abiotic stresses. Physical sanitation treatments, ageing during storage and threat by pathogens are some of the stresses that the seeds can experience during production, processing and germination. However, harvesting seeds at the fully mature stage and with maximum vigour is a big challenge in seed production. For most seeds, analysis of chlorophyll levels can be used as a measure of relative maturity. This is a rather sensitive technique as it uses the fluorescence properties of chlorophyll, and can also be used for upgrading seed lots containing relatively large fractions of less mature seeds. Sorted seed fractions are also useful to study processes during late seed maturation and the different seed vigour aspects gained during late seed maturation.

Differential responses of leaf photosynthesis to insect and pathogen outbreaks: A global synthesis

Outbreak of insects or pathogens (referred to as biotic disturbance), which is projected to continually increase in a warmer climate, may profoundly affect plant photosynthesis and production. However, the response of plant photosynthesis to biotic disturbance remains unclear, especially differences in response between insects and pathogens, which hinders the prediction of plant productivity in future climate. In this study, a meta-analysis approach was used to examine effects of insects and pathogens on photosynthetic rate per unit leaf area (Pn) and the associated characteristics from 115 studies. Our results showed that biotic disturbance significantly decreased Pn by 34.8% but increased Rd by 26.2%. Most of parameters associated with Pn were significantly reduced by biotic disturbance, including gs, Tr, photosynthetic pigments (e.g., a+b, a, and b), and chlorophyll fluorescence properties (Fv/Fm, qp). The disturbance type (insects vs pathogens) was the most important factor affecting the response of Pn, with a greater decrease in Pn by pathogens (−37.5%) than insects (−28.0%). The response ratio of Pn was positively correlated with that of gs and Tr for both insects and pathogens, while negatively with Ci and positively with Chl a+b, ΦPSII, and qp for only pathogens. In addition, the higher sensitivity of Pn to biotic disturbance in crop than non-crop plants poses a great challenge to agricultural system in the future. The weighted response ratio of Pn and relationships of Pn with other associated paramerters under insect and pathogen disturbance will facilitate vegetation models to integrate the effects of biotic disturbance on primary production, improving predicition of the ecosystem carbon cyling in combining with leaf area measurement.

Separation of Spinach Thylakoid Protein Complexes by Native Green Gel Electrophoresis and Band Characterization using Time-Correlated Single Photon Counting.

The light reactions of photosynthesis are carried out by a series of pigmented protein complexes in the thylakoid membranes. The stoichiometry and organization of these complexes is highly dynamic on both long and short time scales due to processes that adapt photosynthesis to changing environmental conditions (i.e., non-photochemical quenching, state transitions, and the long-term response). Historically, these processes have been described spectroscopically in terms of changes in chlorophyll fluorescence, and spectroscopy remains a vital method for monitoring photosynthetic parameters. There are a limited number of ways in which the underlying protein complex dynamics can be visualized. Here we describe a fast and simple method for the high-resolution separation and visualization of thylakoid complexes, native green gel electrophoresis. This method is coupled with time-correlated single photon counting for detailed characterization of the chlorophyll fluorescence properties of bands separated on the green gel.

Divergence in Life-History and Developmental Traits in Silvery-Thread Moss (Bryum argenteumHedw.) Genotypes between Golf Course Putting Greens and Native Habitats

AbstractSilvery-Thread Moss (Bryum argenteumHedw.) is an undesirable invader of golf course putting greens across North America, establishing colonies and proliferating despite practices to suppress it. The goal was to grow genotypes ofgreen(growing in putting greens) andnative(growing in habitats outside of putting greens)B. argenteumin a common garden experiment, allowing an experimental test of life-history traits between genotypes from these two habitats. Seventeen collections ofgreenand 17 collections ofnative B. argenteumwere cloned to single genotypes and raised through a minimum of two asexual generations in the lab. A culture of each genotype was initiated using a single detached shoot apex and was allowed to grow for 6 mo under conditions of inorganic nutrients present and absent. Compared with genotypes from native habitats, genotypes ofB. argenteumfrom putting greens exhibited earlier shoot regeneration and shoot induction, faster protonemal extension, longer (higher) shoots, lower production of gemmae and bulbils, and greater aerial rhizoid cover, and showed similar tendencies of chlorophyll fluorescence properties and chlorophyll content. Cultures receiving no inorganic nutrients produced less chlorophyll content, greatly reduced growth, and bleaching of shoots. Mosses from putting greens establish more quickly, grow faster, produce more abundant rhizoids, and yet do not produce as many specialized asexual propagules compared with mosses of the same species from native habitats. The highly managed putting green environment has either selected for a suite of traits that allow the moss to effectively compete with grasses, or genotypic diversity is very high in this species, allowing a set of specialized genotypes to colonize the putting green from native habitats. Successful golf course weeds have been able to adapt to this highly competitive environment by selection acting on traits or genotypes to produce plants more successful in competing with golf course grasses.

Changes in winter snow depth affects photosynthesis and physiological characteristics of biological soil crusts in the Tengger Desert

Water availability is a major limiting factor in desert ecosystems. However, a winter snowfall role in the growth of biological soil crusts is still less investigated. Here, four snow treatments were designed to evaluate the effects of snow depth on photosynthesis and physiological characteristics of biological soil crusts. Results showed that snow strongly affected the chlorophyll fluorescence properties. The increased snow depth led to increased contents of photosynthetic pigments and soluble proteins. However, all biological soil crusts also exhibited a decline in malondialdehyde and soluble sugar contents as snow increased. Results demonstrated that different biological soil crusts exhibited different responses to snow depth treatment due to differences in their morphological characteristics and microhabitat. In addition, interspecies differentiation in response to snow depth treatment might affect the survival of some biological soil crusts. Further, this influence might lead to changes in the structural composition and functional communities of biological soil crusts.

New evidence for primordial action site of Fluazifop-P-butyl on Acanthospermum hispidum seedlings: From the effects on chlorophyll fluorescence characteristics and histological observation

Acanthospermum hispidum DC, an Asteraceae weed species, was very susceptible to fluazifop-P-butyl, but tolerant to other aryloxyphenoxypropionate herbicides, such as haloxyfop-P-methyl. However, other Asteraceae weeds including Bidens pilosa were all tolerant to fluazifop-P-butyl. Membrane lipid peroxidation by increasing the levels of reactive oxygen species (ROS) was proposed as an action mechanism of fluazifop-P-butyl in A. hispidum. To further clarify the primordial action site of fluazifop-P-butyl in this species, the effects on chlorophyll fluorescence characteristics and cytohistology of apical meristems were studied. Chlorophyll fluorescence characteristics (CFC) in sensitive A. hispidum seedlings were markedly affected by 10μM fluazifop-P-butyl, with the dark fluorescence yield (Fo), maximal fluorescence yield (Fm), maximal PS II quantum yield (Fv/Fm), effective photosystem II (PS II) quantum yield [Y(II)], and quantum yield of regulated energy dissipation [Y(NPQ)] declining, quantum yield of nonregulated energy dissipation [Y(NO)] rising, but these measures were not affected in Bidens pilosa. The effects of fluazifop-P-butyl on chlorophyll fluorescence properties were observed on the growing point before the mature leaves by about 4–6h. Haloxyfop-P-methyl, a control herbicide, had no effects on CFC of either A. hispidum or B. pilosa. In addition, damage to apical meristem cells of A. hispidum was observed at 6 HAT prior to changes in chlorophyll fluorescence parameters suggesting that the primary action site of fluazifop-P-butyl in this species is in the apical meristem and the effects on CFC may be the results of secondary action.

The optical, absorptive and chlorophyll fluorescence properties of young stems of five woody species

To reveal the roles of stems in responding to the surrounding light environment, the optical properties of stem tissues of five woody species and their effect on bark, xylem and pith photosynthesis were investigated. Species-specific bark morphology and the distribution of pigments along the stem cross-section altered the radial conduction of light to a different degree, but in all investigated species light gradients within stems were markedly steep and visible light was largely depleted within the outer bark and cortex of the stems. Thereby, optical properties of the outer and inner bark resulted in an internal light environment, which is very different from outside according to intensity and spectral composition. Among species PAR-transmittance of outer bark or periderm varied in quantity between mean values of 8.5 and 42% and PAR-transmittance of total bark between 2.2 and 6.2%. The blue-band of the spectrum was totally absorbed by the outer and inner bark tissues. In the red-band total bark transmittance varied between 2 and 11%. Thus, blue light can only trigger photosynthetic electron transport in the cell layers of the cortex near the stem surface, whereas in the underlying cell layers of the xylem or pith the energy for photosynthesis can only be provided by longer wavelengths (green and particularly red light). In all species, the internal light gradient matched well with the chlorophyll fluorescence properties of the respective stem tissues. The maximum and effective quantum efficiencies of PSII clearly decreased from the cortex toward the innermost stem tissues (xylem, pith), which showed also a lower capability of photosynthetic electron transport of PSII. Our results indicate not only that light signals can enter the interior of stems and are modified in quantity and quality by its path through the stem. There is evidence to suggest that the light regime within stems has also profound effects on plastid differentiation and thus the photosynthetic properties of the respective stem tissues.

Effect of canopy structure on sun-induced chlorophyll fluorescence

We investigated the impact of canopy structure on chlorophyll fluorescence properties. For this purpose, we developed SpectroFLEX, an instrument for quantitative measurements of canopy fluorescence in O2A and O2B atmospheric absorption bands. The fluorescence emission of a natural grass canopy was compared with the leaf level fluorescence spectrum acquired simultaneously. It was found that the red-to-far-red fluorescence ratio decreased by a factor of two from the leaf to the canopy level. In addition, this ratio decreased under high light conditions. FluoSAIL simulations were conducted to study the impact of canopy density and geometry on this decrease. This effect has been attributed to a preferential re-absorption of red fluorescence emission during radiative transfer within the canopy compared to far-red emission.

Inversion of total suspended matter concentration in turbid water based on the characteristic of chlorophyll fluorescence peak

The optical property of inland water is very complex, and inversion of water components concentration of inland water body is hotspot and difficulty problem in water quality remote sensing. The remote sensing reflectance and water qualities of 67 stations were acquired in the Lake Taihu in October, 2004. Basing on the characteristic spectral analysis, it was obvious that the water body spectral character in Lake Taihu in autumn was dominated by the total suspended matter (TSM). The properties of the chlorophyll fluorescence peak mainly reflect the variation of the concentration of TSM. Hereby, we established the relation between the properties of the chlorophyll fluorescence peak and the concentration of TSM based on in-situ remote sensing reflectance with 1nm bandwith and water quality measurements. There were good response relationships between them. Making a concrete analysis ofthe correlation relationship between the absolute height of fluoresce peak, the height above the reference baseline, the normalized height referred to the maximum reflectance about 560nm in green band and 810nm in infrared band, the integral area (including the total integral area, the integral area between the spectral curve and the reference baseline, the integral area below the reference baseline and the wavelength axis) and the concentration of TSM. Their correlation coefficients were 0.8822, 0.7483, 0.8901, 0.8547, 0.8927, 0.8877 and 0.8632 respectively, and the average relative error were 27.25%, 41.03%, 27.11%, 25.75%, 24.91%, 25.47% and 27.54% respectively. The inversion accuracy of the total integral area method is obvious better than the reference baseline height method. No outstanding correlation relationship between chlorophyll concentration and fluorescence peak position were found based on reflectance spectra. The results show that chlorophyll fluorescence properties are effective in detecting TSM concentration in turbid inland water body, which provide a new optional sensitive band to retrieval TSM concentration in complex waters.

Effects of Cd 2+ on seedling growth of garlic ( Allium sativum L.) and selected physiological and biochemical characters

In this study, we determined the effects of Cd 2+ (from 10 −5 to 10 −3 M) on the growth of leaves and roots of garlic seedlings in Hoagland’s nutrient solution. We also characterized the influences of Cd 2+ on a few key cellular activities, e.g., antioxidant enzymes, content of malondialdehyde (MDA), composition of photosynthetic pigments and fluorescence properties of chlorophyll on day 5, 10 and 15. The results indicated that the presence of 10 −3 M Cd 2+, but not other tested Cd 2+ concentrations, significantly decreased the development of leaves and roots of the seedlings. This level of Cd 2+ increased the activities of antioxidant enzymes and the level of MDA. With the exception of carotenoid on day 5, the presence of 10 −3 M Cd 2+ showed no significant effects on the contents of photosynthetic pigments. Intermediate concentrations of Cd 2+ caused variable effects, ranging from lowering to increasing the pigments in garlic seedlings. The presence of 10 −3 M Cd 2+, but not other tested concentrations, decreased efficiency of energy harvesting associated with photosystem II as measured by the ratio of variable to maximum chlorophyll fluorescence of intact leaves. However, Cd 2+ generated no definitive trends on photochemical quenching. Possible significance of experimental findings in relation to Cd 2+ level in garlic seedling is discussed.

Linking leaf chlorophyll fluorescence properties to physiological responses for detection of salt and drought stress in coastal plant species

Effects of salinity and drought on physiology and chlorophyll fluorescence were used to evaluate stress in two coastal plants, Myrica cerifera (L.) and Phragmites australis (Cav.) Trin. ex Steud. Drought and salinity stress were induced and measurements of stomatal conductance, photosynthesis, xylem pressure potential (psi) and fluorescence were conducted following treatment. The onset of stress began at 2 g l(-1) for M. cerifera, and 5 g l(-1) for P. australis, as seen by significant decreases in physiological measurements. Despite the physiological effects of salinity, there was no significant difference in dark-adapted fluorescence (F(v)/F(m), where F(m) is the maximal fluorescence in dark-adapted leaves) for either species at any salinity level. Significant decreases in the light-adapted measurement Delta F/F'(m) (F'(m) is maximal fluorescence in light-adapted leaves) occurred at 10 g l(-1) in M. cerifera and P. australis, days before visible stress was evident. The quantum yield of xanthophyll-regulated thermal energy dissipation (Phi(NPQ), where NPQ is non-photochemical quenching of chlorophyll fluorescence) increased with decreasing Delta F/F'(m). Drought studies showed similar results, with significant decreases in physiological measurements occurring by day 2 in M. cerifera and day 4 in P. australis. Differences in Delta F/F'(m) were seen by day 5 for both species, whereas F(v)/F(m) showed no indication of stress, despite apparent visible signs. Xanthophyll-cycle-dependent energy dissipation may be the underlying mechanism in protecting photosystem II from excess energy in salinity- and drought-treated plants.

Longitudinal leaf gradients of UV-absorbing screening pigments in barley (Hordeum vulgare).

In vivo leaf characteristics were examined to describe longitudinal gradients of UV-absorbing screening pigments in barley. Chlorophyll fluorescence properties and in vivo absorption spectra (210-750 nm) of leaves were measured from the base to the tip. Barley leaves showed strong longitudinal gradients of chlorophyll, where chlorophyll concentration increased within the first 5-8 cm from the leaf base, and did not significantly change for the remaining part of the leaf. Fluorescence microscopy was used to localize cell wall bound screening pigments different from flavonoids, since flavonoids lack a blue-green fluorescence emission (Lichtenthaler and Schweiger 1998). Measurements of in vivo chlorophyll fluorescence indicated that the ratio of UV-absorbing screening pigments per leaf area increases from the leaf base to the tip. These gradients were confirmed by in vivo absorption spectra. It is demonstrated that leaves in the early stage of development are less protected against UV-radiation than fully developed mature leaf regions. The experiments show that measurements of in vivo chlorophyll fluorescence are ideally suited as a fast non-invasive tool to estimate the epidermal UV-transmittance in different leaf sections.

Carbon Fixation Profiles Do Reflect Light Absorption Profiles in Leaves

Bifacial leaves contain an array of chloroplasts which are aligned along cell walls adjacent to intercellular airspaces. Cells beneath the adaxial (upper) surface are generally cylindrical in shape, forming palisade tissue and contain chloroplasts that have characteristics associated with acclimation to high irradiance. Conversely, cells near the abaxial (lower) surface are irregular in shape, forming spongy tissue and contain chloroplasts that have characteristics associated with acclimation to low irradiance. This results in a gradient of declining photosynthetic capacity per unit chlorophyll with increasing depth into the leaf. Space irradiance declines dramatically through the leaf. The profile of light absorption through the leaf has yet to be measured, but should approximate the product of space irradiance and pigment profiles. Since pigment content is highest in the middle of the leaf, light absorption peaks about one quarter of the way through the leaf. The response of leaf photosynthetic rate to irradiance reflects the interaction between the profiles of light absorption and chloroplast characteristics. Quantum yield (mol CO2 mol-1 quanta absorbed) varies for different layers in the leaf because the profile of Rubisco content per unit chlorophyll is not as steep as the light absorption profile. This skews the profile of carbon fixation away from the light absorption profile, favouring greater fixation in deeper layers. Nishio, Sun and Vogelmann (1993, Plant Cell 5, 953-961) measured profiles of 14C fixation across spinach leaves and concluded that carbon fixation was disconnected from the light gradient. Reanalysis of their data shows that carbon fixation is remarkably consistent with light absorption obeying the Beer- Lambert law when allowance is made for chlorophyll and Rubisco profiles through the leaf. This interpretation is supported by chlorophyll fluorescence properties of adaxial and abaxial surfaces. An apparent extinction coefficient of about 1500 m2 (mol Chl)-1 could be derived from leaf data which compares with 2230 m2 (mol Chl)-1 for pigment-protein complexes in solution. A possible test for this analysis would be to measure the 14C fixation profile of leaves illuminated on their abaxial surface.

Visible absorption and fluorescence properties of chlorophyll a and b and pheophytin a and b in the nonionic surfactant-nonaqueous solvent system.

クロロフィルa,b及びフェオフィチンa,bの非イオン性界面活性剤非水溶液中での吸収並びに蛍光特性を検討し,クロロフィル分子と非イオン性界面活性剤分子間の相互作用について考察した.その結果,無極性溶媒を用いた場合,界面活性剤の添加によりモル吸光係数は1.5~2倍に,蛍光の量子収率はクロロフィルaで約6倍,クロロフィルbは約2倍に増加した.しかし,クロロフィルの中心金属であるマグネシウムが脱離したフェオフィチンa,bは添加前後ではモル吸光係数及び蛍光の量子収率は変化しなかった.又,蛍光の偏光度を測定し,ペラン-ウェーバー式を用いて溶媒和分子の体積を求めた.その結果,界面活性剤の添加によるクロロフィルの溶媒和体積の増加を確認し,クロロフィルのマグネシウムとエチレンオキシド(EO)鎖の酸素原子との相互作用が示唆された.

GROWTH AND PHOTOSYNTHESIS OF ULVA ROTUNDATA (CHLOROPHYTA) AS A FUNCTION OF TEMPERATURE AND SQUARE WAVE IRRADIANCE IN INDOOR CULTURE1

ABSTRACTTemperature and photon flux density (PFD) vary independently in estuaries, e.g. high PFD may occur at any temperature, so it is necessary to consider synergistic effects of these factors on algal growth. Because natural PFD is highly variable and daylength changes confound seasonal temperature cycles, it is easier to interpret factorial experiments in controlled laboratory conditions. Clonal Ulva rotundata Blid. (Chlorophyta) has been studied extensively in outdoor culture. In this study it was maintained indoors under square wave photoperiods at five PFDs and three temperatures. Growth rate, photqsynthetic light response (P‐I) curves, and photosystem II chlorophyll fluorescence properties were measured at the growth temperature following acclimation. Interactions between PFD and growth temperature were strongly indicated in all physiological parameters measured. Greatest PFD response occurred at the highest temperature, and the largest temperature response occurred at the highest PFD. Light‐saturated photosynthesis (Pm) dark respiration (Rd), and light‐limited quantum yield (Φm) were sufficient to describe acclimation status. The light‐saturation parameter (Ik) was redundant and potentially misleading. Although U. rotundata exhibits a great amplitude of photoacclimation, it apparently has little capacity for temperature acclimation compared to the kelp, Laminaria saccharina, for which published data indicate similar photosynthetic rates over a broad range of growth temperatures. Diurnal variation of Pm and Rd at a growth PFD of ∼ 1700 ± 200 μmol photons · m−2· s−1 was similar to the pattern observed previously in outdoor culture, suggesting endogenous control of these parameters. Quantum yield and the ratio of variable to maximum chlorophyll fluorescence (Fv/Fm), which were depressed in midday sunlight exceeding ∼ 1500 μmol photons · m−2· s−1, were relatively invariant through the day in indoor culture, indicating that these parameters are controlled primarily by instantaneous PFD. Growth and fluorescence data are also presented for some other macroalgae for comparative purposes.