Decrease In Chlorophyll Fluorescence Research Articles

Analysis of in vivo chlorophyll fluorescence spectra to monitor physiological state of tomato plants growing under zinc stress

The effects of zinc (Zn) on plant chlorophyll fluorescence were investigated in 10-day-old tomato ( Solanum lycopersicum) seedlings subjected for 7 days to a series of zinc (10, 50, 100 and 150 μM) applied via the nutrient solution. The chlorophyll fluorescence spectra of leaves were recorded in the spectral region 650–800 nm using the spectroscopic technique of ultraviolet light emitting diode induced fluorescence spectroscopy (UV-LED IFS). These spectra have been used to analyze the effect of several doses of zinc on the photosynthetic activities of tomato plants. The fluorescence intensity ratios (FIR) at the two maxima ( F 690/ F 735) of control as well as treated tomato plants were calculated by evaluating curve-fitted parameters using a Gaussian spectral function. The variable chlorophyll fluorescence decrease ratio ( R Fd) values were determined from the fluorescence induction kinetics curves recorded at 690 nm and 735 nm. In addition, Zn accumulation in plants, plant growth, photosynthetic pigments content and malondialdehyde level (MDA, an index of lipid peroxidation) were also estimated. The results indicated that the plants treated with 10 μM of zinc exhibited better growth, however, higher concentrations of zinc were harmful for plants. Excess Zn induced a decrease in the R Fd values, which was associated with a strong decline of the total chlorophylls content and an increase of MDA level. The total chlorophylls content decline could also be followed via an increase of the chlorophyll fluorescence ratio F 690/ F 735.

Effects of fungus inoculation and salt stress on physiology and biochemistry of in vitro grapevines: Emphasis on sugar composition changes by FT-IR analyses

The impacts of salt stress and inoculation in in vitro grapevine ( Vitis vinifera L.) growth, nutrient accumulation, osmoregulation, photosynthesis and membrane integrity were evaluated. One month exposure to 100 mM NaCl as well as to inoculation with Phaeomoniella chlamydospora reduced relative growth rate (RGR) and induced senescence in grapevine plants, shown by: (1) decrease of Ψ π without osmoregulation, (2) decrease of chlorophyll content and fluorescence, (3) loss of membrane integrity and (4) nutritional disorders. To assess putative changes in structural and/or non-structural carbohydrates induced by these two stress conditions, alcohol insoluble residues from the roots, stems and leaves were also characterised by FT-IR and GC with respect to the sugar composition. The referred organs were distinguished based on: (1) higher proportion of uronic acid residues in leaves which diagnose the presence of pectic polysaccharides (wavenumbers 1100, 1150 and 1018 cm −1 in FT-IR spectra), (2) higher proportion of xylose and glucose on stems and FT-IR spectra diagnostic of xylose-rich polysaccharides (1041 cm −1) and cellulose (1060 cm −1), (3) higher proportion of glucose residues, xylose and arabinose on roots and a FT-IR spectra characteristic of xylose-rich polysaccharides (1041 cm −1). The main alterations induced by salt stress and inoculation were more visible in leaves, where the content of uronic acid decreased showing that changes in cell wall composition occurred, mostly at the pectic fraction. Besides, an accumulation of insoluble glucose was found, and FT-IR spectra showed that this glucose-based material was starch (maximum absorption at 998 cm −1), accumulated as a non-specific response to salt stress and P. chlamydospora inoculation.

Preliminary investigation into the uneven ripening of banana (Musa sp.) peel

Mature green bananas (Musa sp., AAA group, Cavendish subgroup, cultivar ‘Williams') were used to examine the uneven de‐greening of banana peel treated with 1‐methylcyclopropene (1‐MCP). After ethylene treatment (200 μl litre−1 for 24h at 20°C) bananas were allocated different treatment units: 1‐MCP treatment (200 nl litre−1, 20°C, 24h); nitrogen treatment (O2<0.1%, 20°C, 24h); ethanol treatment (0.3 ml litre−1, 20°C, 24h); chilling treatment (1±1°C, 24h); and untreated control (20°C). After these post‐ripening treatments (24h), fruit were stored in perforated plastic bags at 20°C. Ethylene, respiration, ethanol and acetaldehyde production, skin colour, chlorophyll fluorescence, chlorophyll content, and flesh firmness were assessed at regular intervals. The post‐ripening nitrogen atmosphere and chilling treatment (24h) led to a transient delay of ripening compared to ethanol ‐treated fruit and untreated control fruit. However by 1 week of shelf life at 20°C, there were no differences between non‐1‐MCP treated fruit. No differences in the accumulation of acetaldehyde and ethanol were detected during storage. Ethylene production was not affected by the 1‐MCP treatment 24h after initiating ripening. However peel de‐greening, the decrease in chlorophyll content and chlorophyll fluorescence were delayed with 1‐MCP treatment. There was some general browning throughout the 1‐MCP treated peel in both the green and yellow areas of the ripening peel. It appears the 1‐MCP treated peel 24h after ethylene treatment may still undertake some normal senescence that occurs during banana ripening.

Chlorophyll fluorescence imaging of photosynthetic activity in sun and shade leaves of trees

The differences in pigment levels, photosynthetic activity and the chlorophyll fluorescence decrease ratio R (Fd) (as indicator of photosynthetic rates) of green sun and shade leaves of three broadleaf trees (Platanus acerifolia Willd., Populus alba L., Tilia cordata Mill.) were compared. Sun leaves were characterized by higher levels of total chlorophylls a + b and total carotenoids x + c as well as higher values for the weight ratio chlorophyll (Chl) a/b (sun leaves 3.23-3.45; shade leaves: 2.74-2.81), and lower values for the ratio chlorophylls to carotenoids (a + b)/(x + c) (with 4.44-4.70 in sun leaves and 5.04-5.72 in shade leaves). Sun leaves exhibited higher photosynthetic rates P (N )on a leaf area basis (mean of 9.1-10.1 micromol CO(2) m(-2 )s(-1)) and Chl basis, which correlated well with the higher values of stomatal conductance G (s) (range 105-180 mmol m(-2 )s(-1)), as compared to shade leaves (G (s) range 25-77 mmol m(-2 )s(-1); P (N): 3.2-3.7 micromol CO(2) m(-2 )s(-1)). The higher photosynthetic rates could also be detected via imaging the Chl fluorescence decrease ratio R (Fd), which possessed higher values in sun leaves (2.8-3.0) as compared to shade leaves (1.4-1.8). In addition, via R (Fd) images it was shown that the photosynthetic activity of the leaves of all trees exhibits a large heterogeneity across the leaf area, and in general to a higher extent in sun leaves than in shade leaves.

Morphological and physiological responses of canola ( Brassica napus) siliquas and seeds to UVB and CO 2 under controlled environment conditions

Combined effects of UVB radiation and CO 2 concentration on plant reproductive parts have received little attention. We studied morphological and physiological responses of siliquas and seeds of canola ( Brassica napus L. cv. 46A65) to UVB and CO 2 under four controlled experimental conditions: UVB radiation (4.2 kJ m −2 d −1) with ambient level of CO 2 (370 μmol mol −1) (control); UVB radiation (4.2 kJ m −2 d −1) with elevated level of CO 2 (740 μmol mol −1); no UVB radiation (0 kJ m −2 d −1) with ambient level of CO 2 (370 μmol mol −1); and no UVB radiation (0 kJ m −2 d −1) with elevated level of CO 2 (740 μmol mol −1). UVB radiation affected the outer appearance of siliquas, such as colour, as well as their anatomical structures. At both CO 2 levels, the UVB radiation of 4.2 kJ m −2 d −1 reduced the size of seeds, which had different surface patterns than those from no UVB radiation. At both CO 2 levels, 4.2 kJ m −2 d −1 of UVB decreased net CO 2 assimilation ( A N) and water use efficiency (WUE), but had no effect on transpiration ( E). Elevated CO 2 increased A N and WUE, but decreased E, under both UVB conditions. At both CO 2 levels, the UVB radiation of 4.2 kJ m −2 d −1 decreased chlorophyll fluorescence, total chlorophyll (Chl), Chl a and Chl b, but had no effect on the ratio of Chl a/ b and the concentration of UV-screening pigments. Elevated CO 2 increased total Chl and the concentration of UV-screening pigments under 4.2 kJ m −2 d −1 of UVB radiation. Neither UVB nor CO 2 affected wax content of siliqua surface. Many significant relationships were found between the above-mentioned parameters. This study revealed that UVB radiation exerts an adverse effect on canola siliquas and seeds, and some of the detrimental effects of UVB on these reproductive parts can partially be mitigated by CO 2.

POSTHARVEST N-PROPYL DIHYDROJASMONATE AND ABSCISIC ACID APPLICATION ON REDUCING CHILLING INJURY IN BANANA PEEL

ISHS IV International Conference on Managing Quality in Chains - The Integrated View on Fruits and Vegetables Quality POSTHARVEST N-PROPYL DIHYDROJASMONATE AND ABSCISIC ACID APPLICATION ON REDUCING CHILLING INJURY IN BANANA PEEL

Biochemical responses of the aquatic moss Fontinalis antipyretica to Cd, Cu, Pb and Zn determined by chlorophyll fluorescence and protein levels

Biochemical reactions to Cu, Cd, Zn and Pb in the aquatic moss Fontinalis antipyretica were studied in order to characterize the physiological background of the metal response. Chlorophyll fluorescence and intracellular metal localization and stress protein levels were measured. Exposure to 25 or 100 μM Cu over a 7-day period resulted in a decline of chlorophyll fluorescence to about 70% and 52%, respectively. Up to 100 μM Cd caused a decrease in chlorophyll fluorescence to 75%. With all metals used at 25–100 μM concentrations, the intracellular uptake increased. For all metals investigated at 25–100 μM, the intracellular uptake increased. Maximum values were reached at 100 μM Cu, Pb, Zn or Cd exposure. As shown by analytical electron microscopy (EDX, EELS) moss material treated with 50 μM Cu exhibited reduced sulphur levels in the cytoplasm and an increase in phosphate in vacuolar dense particles. EEL-spectra indicated that Cu is chelated in the cytoplasm by SH-groups and coprecipitated with orthophosphate in vacuoles. To monitor the stress response at the protein level, heavy metal induced heat shock protein 70 (hsp70) was measured. An antibody was raised against conserved plant metallothionein p2 motifs derived from Brassica juncea. In all metal-treated samples the antibody bound to proteins of about 8 kDa. However, sequencing failed to reveal significant homologies to known proteins. These experiments provide for the first time results on protein level after heavy metal stress in the aquatic bioindicator moss.

ETHANOL PRODUCTION AND CHLOROPHYLL FLUORESCENCE IN HEAT-STRESSED APPLE FRUIT DURING STORAGE

Ethanol concentration and chlorophyll fluorescence were measured as signs of heat stress in apple fruit [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.]. 'Mclntosh', 'Cortland', 'Jonagold', and 'Northern Spy' apples were held at 46°C for 0, 4, 8, or 12 h. Following treatments, fruit were stored at 0°C in air and evaluated after 0, 4, 8, or 12 weeks. Peel and flesh browning, headspace ethanol concentration, and chlorophyll fluorescence (Fv/Fm) were measured. Peel browning became apparent in all 4 cultivars 4 weeks after treatment and increased during storage. Exposure to 46°C for 12 h caused severe flesh browning in all cultivars. Severity of flesh browning increased with increasing heat treatment time and storage time. Headspace ethanol concentrations immediately following 12 h heat treatments increased and were 48-, 70-, 9-, and 170- fold higher in 'Mclntosh', 'Cortland', 'Jonagold', and 'Northern Spy' apples than in the controls, respectively. Ethanol concentrations also increased in fruit treated for 8 h but not in those treated for 4 h. Ethanol concentrations were maintained or increased during the 12 weeks of storage. Heat treatments reduced chlorophyll fluorescence (Fv/Fm). One day following treatment, fruit exposed to 46°C for 12 h had Fv/Fm values that were 36%, 59%, 63%, and 36% of the control values in 'Mclntosh', 'Cortland', 'Jonagold', and 'Northern Spy', respectively. The 8 h heat treatment also decreased Fv/Fm in treated fruit, but the 4 h treatment had no effect. Fv/Fm decreased in all treatments during storage. Correlations between flesh browning and ethanol concentration ranged from 0.87 to 0.78, and flesh browning and Fv/Fm ranged from -0.91 to -0.67 depending on cultivar. The increase in ethanol production and decrease in chlorophyll fluorescence were apparent before browning was visually apparent and have the potential to predict injury that develops during storage.

Photochemical reactions in dehydrated photosynthetic organisms, leaves, chloroplasts and photosystem II particles: reversible reduction of pheophytin and chlorophyll and oxidation of β-carotene

Abstract Photoreactions of dehydrated leaves, isolated broken chloroplasts and PSII membrane fragments of spinach ( Spinacia oleracea ) were studied at different air humidities and compared with photoreactions of dry fronds of a fern, Polypodium vulgare , and a dry lichen, Parmelia sulcata , which in contrast to spinach are insensitive to photoinactivation in the dry state. Even in very dry air, P700 in the reaction center of photosystem I of dry leaves was oxidized, and the primary quinone acceptor Q A in the reaction center of photosystem II was photoreduced by low light. These reactions were only very slowly reversed in the dark and saturated under low light intensity. Light-minus-dark difference absorption spectra of the dry leaves, isolated chloroplasts and PSII membrane fragments measured at higher light intensities revealed absorbance changes of β-carotene at 500 nm (light-dependent bleaching) and 980 nm (light-dependent band formation) and bleaching of chlorophyll at 436 and 680 nm with appearance of bands at 450 and 800 nm. Decrease of chlorophyll fluorescence upon strong illumination indicated photoaccumulation of a quencher. All these changes were kinetically related and readily reversible. They are interpreted to show light-induced oxidation of β-carotene (Car) and reduction of chlorophyll-680 (Chl-680) in the reaction center of photosystem II of the dried leaves, chloroplasts and photosystem II particles. The fluorescence quencher was suggested to be Chl-680 − or Car + in close proximity to P680, the primary electron donor. Appreciable photoaccumulation of reduced pheophytin was only observed in dry leaves after Q A reduction had been lost during heat treatment of hydrated leaves prior to dehydration. The observations are interpreted to show light-dependent cyclic electron flow within the reaction center of photosystem II in which Chl-680 (or Pheo) is reduced by P680 * and Car is oxidized by P680 + with consequent recombination of Car + and Chl-680 − (or Pheo − ). Cyclic electron flow is thought to be moderately photoprotective by reducing the concentration of the strong oxidant P680 + . Nevertheless, prolonged strong illumination caused considerable photodamage in the dry spinach leaves, much less damage in dry fern fronds and no damage in the dry lichen in which distinct photoreactions were not expressed at light intensities which were effective in dry leaves and fern fronds.

Inhibition of catalase activity by oxidative stress and its relationship to salicylic acid accumulation in plants

The decrease in catalase activity and its relationship to change in salicylic acid content were investigated in rice, wheat, and cucumber seedlings exposed to oxidative stresses. A decrease in chlorophyll fluorescence (ΔF/Fm′), measured as an indicator of the oxidative stress, and a drop in catalase activity were observed following treatment with NaCl in all plant seedlings tested . Furthermore, such decreases in ΔF/Fm′ and catalase activity were also observed under low temperature conditions in both rice cultivars, whereas the degrees of decrease were dependent on their low temperature tolerance . Although the content of salicylic acid increased in rice seedlings stressed by NaCl treatment, it was inversely correlated with the decrease in the catalase activity . Such a relationship between the decrease in catalase activity and increase in salicylic acid content was confirmed with paraquat treatment of the rice seedlings . These results suggested that the fall in catalase activity is a phenomenon occurring in many plant species under oxidative stress and is related to the accumulation of salicylic acid in oxidatively-stressed plants.

Age-dependent response of maize leaf segments to cadmium treatment: Effect on chlorophyll fluorescence and phytochelatin accumulation

The relationship between the age of leaf tissue and response of the photosynthetic apparatus and phytochelatin accumulation to Cd treatment was studied. Studies were carried out with seedlings of Zea mays L. cv. Hidosil grown in the presence of 100-200 mumol/L Cd for 14 days under low light conditions. The third leaf was divided into 3 segments of equal length differing in the stage of tissue maturity and used for measurements of chlorophyll content, chlorophyll fluorescence, glutathione and phytochelatin content and Cd accumulation. A close relationship between the age of leaf tissue and response of the photosynthetic apparatus to Cd was shown. Cadmium (200 mumol/L) reduced photochemical processes more in older than younger leaf segments as seen in the Chl fluorescence parameters Fv/F0, and t1/2, while the chlorophyll fluorescence decrease ratio (Rfd) was inhibited more strongly in younger ones. Fv/Fm was slightly affected. Cd-induced enhancement of GSH content was correlated with higher phytochelatin accumulation to a greater extent in younger than in older leaf segments. Phytochelatin level corresponded to changes of photochemical processes in older leaves. The peptide thiol:Cd molar ratio for the phytochelatins varied depending on Cd concentration and age of leaf segments. The protective role of phytochelatins for the photosynthetic apparatus is discussed.

Response of Olea europaea ssp. maderensis in vitro shoots exposed to osmotic stress

Olea europaea ssp. maderensis shoots (2.5 cm) were grown for 2 months on Driver and Kuniyuki medium (DKW) supplemented with 4.4 μM benzyladenine (BA) and 0.4 μM indole-3-butyric acid (IBA). Osmotic stress was induced for 1 month in shoots by the addition of sorbitol (0.1 and 0.2 M) to DKW. Moderate stress (0.1 M) did not affect shoot growth, and induced osmotic adjustment by increasing K content without water lost. Also no decrease in chlorophyll fluorescence was detected although chlorophyll content decreased. However, at 0.2 M sorbitol (a more severe stress) growth was reduced. This sorbitol concentration increased tissue osmolality and lipid peroxidation, but decreased water and soluble protein contents. It also decreased chlorophyll content and chlorophyll fluorescence, by increasing basal fluorescence ( F o) and decreasing maximal fluorescence ( F m) values. Both sorbitol concentrations decreased Mg and Zn contents while 0.2 M decreased K and Cu contents in shoots. Rooting was reduced by moderate stress (0.1 M) and completely inhibited by 0.2 M sorbitol.

Phototolerance of lichens, mosses and higher plants in an alpine environment: analysis of photoreactions.

Adaptation to excessive light is one of the requirements of survival in an alpine environment particularly for poikilohydric organisms which in contrast to the leaves of higher plants tolerate full dehydration. Changes in modulated chlorophyll fluorescence and 820-nm absorption were investigated in the lichens Xanthoria elegans (Link) Th. Fr. and Rhizocarpon geographicum (L.) DC, in the moss Grimmia alpestris Limpr. and the higher plants Geum montanum L., Gentiana lutea L. and Pisum sativum L., all collected at altitudes higher than 2000 m above sea level. In the dehydrated state, chlorophyll fluorescence was very low in the lichens and the moss, but high in the higher plants. It increased on rehydration in the lichens and the moss, but decreased in the higher plants. Light-induced charge separation in photosystem II was indicated by pulse-induced fluorescence increases only in dried leaves, not in the dry moss and dry lichens. Strong illumination caused photodamage in the dried leaves, but not in the dry moss and dry lichens. Light-dependent increases in 820-nm absorption revealed formation of potential quenchers of chlorophyll fluorescence in all dehydrated plants, but energy transfer to quenchers decreased chlorophyll fluorescence only in the moss and the lichens, not in the higher plants. In hydrated systems, coupled cyclic electron transport is suggested to occur concurrently with linear electron transport under strong actinic illumination particularly in the lichens because far more electrons became available after actinic illumination for the reduction of photo-oxidized P700 than were available in the pool of electron carriers between photosystems II and I. In the moss Grimmia, but not in the lichens or in leaves, light-dependent quenching of chlorophyll fluorescence was extensive even under nitrogen, indicating anaerobic thylakoid acidification by persistent cyclic electron transport. In the absence of actinic illumination, acidification by ca. 8% CO2 in air quenched the initial chlorophyll fluorescence yield Fo only in the hydrated moss and the lichens, not in leaves of the higher plants. Under the same conditions, 8% CO2 reduced the maximal fluorescence yield Fm strongly in the poikilohydric organisms, but only weakly or not at all in leaves. The data indicate the existence of deactivation pathways which enable poikilohydric organisms to avoid photodamage not only in the hydrated but also in the dehydrated state. In the hydrated state, strong nonphotochemical quenching of chlorophyll fluorescence indicated highly sensitive responses to excess light which facilitated the harmless dissipation of absorbed excitation energy into heat. Protonation-dependent fluorescence quenching by cyclic electron transport, P700 oxidation and, possibly, excitation transfer between the photosystems were effectively combined to produce phototolerance.

117 Ethanol Production and Chlorophyll Fluorescence Indicate Freezing and Heat Stress in Apple Fruit During Storage

Ethanol production and chlorophyll fluorescence were measured as signals of freezing and heat stress in apple fruit. `Cortland' and `Jonagold' apples were held at –8.5 °C for 0, 6, 12 or 24 h (freezing treatments), or at 46 °C for 0, 4, 8 or 12 h (heat treatments). Following treatments, fruit were stored at 0 °C and evaluated after 0, 1, 2, or 3 months. Following storage, fruit samples were kept for 12 h at 20 °C and then analyzed for ethanol production, chlorophyll fluorescence, and visible injury. Severity of flesh browning increased with increasing treatment time for both freezing and heat treatments. Freezing for 24 h and heating for 12 h caused severe flesh browning in both cultivars. Severity of heat-induced browning increased during storage. Increases in ethanol production were apparent 12 h following treatments and reflected the degree of stress-induced fruit injury. After 2 months of storage, ethanol concentrations peaked and were as much as 400-fold greater than that of controls. These stress treatments also reduced ethylene production and chlorophyll fluorescence. The degree of increase in stress-induced ethanol production and decrease in chlorophyll fluorescence correlated with stress-induced injury and could be used to predict the severity of injury that develops during storage. Other volatile production and their relationship to fruit stress will also be discussed.

Degradation of photosynthetic activity of saintpaulia leaf by sudden temperature drop

On contact with 5°C water for 3 s, photosynthesis of Saintpaulia leaf stopped with concomitant drop of delayed luminescence, followed by the decrease in chlorophyll (Chl) fluorescence to the F 0 level within 20 s. In the chloroplasts isolated from chill-treated leaves, the PS I activity became hardly detectable within 3 min while the PS II activity stayed less affected for several hours after chilling. Neither the photosynthetic activity of oxygen evolution nor the variable fluorescence (F v) was any more restored in the chill-treated leaves. Chill-induced decay in Chl fluorescence occurred in anaerobiosis, in darkness and even in the presence of DCMU. The decay was also seen with the Chl fluorescence at 77K. Disintegration of intergrana lamellae occurred within 10 s, followed by a disarrangement of the grana lamellae. These results suggest that primary event is degradation of the membrane structures leading to loss of the ΔpH and the cessation of electron flow between the two photosystems. Chill-injured leaves of this plant were found to show an abundant oxygen absorption which ceased in a few minutes after the chilling, but the decrease in Chl fluorescence in anaerobiosis indicates that the oxygen absorption is another event induced by the injured organelles other than the chloroplasts.

Photosynthetic and stomatal responses to high temperature and light in two oaks at the western limit of their range.

Bur oak (Quercus macrocarpa Michx.) and chinquapin oak (Q. muehlenbergii Engl.) leaves were exposed to high temperatures at various photosynthetic photon flux densities under laboratory conditions to determine if species-specific responses to these factors were consistent with the distribution of these oaks in gallery forests in the tallgrass prairies of northeastern Kansas, USA. Measurements of the ratio of chlorophyll fluorescence decrease, R(fd), indicated that chinquapin oak maintained greater photosynthetic capacity than bur oak across all tested combinations of irradiance (100, 400, 700 and 1000 micro mol m(-2) s(-1)) and temperature (40, 42, 44, 46 and 48 degrees C). In both oak species, manipulation of leaf temperature to about 47 degrees C for 45 min in the field led to a 45% decrease in carbon assimilation up to one week after the heat treatment, and to sharp reductions in stomatal conductance. Photosynthetic recovery patterns indicated that bur oak took longer to recover from heat stress than chinquapin oak, suggesting that heat stress may be important in determining distribution patterns of these oak species. Based on a comparison of the results with data from other forest species, we conclude that the photosynthetic temperature tolerances of bur oak and chinquapin oaks facilitate their dominance at the western limit of the eastern deciduous forest.

Changes of Chlorophyll Fluorescence Signatures during Greening of Etiolated Barley Seedlings as Measured with the CCD-OMA Fluorometer

In greening barley seedlings the chlorophyll fluorescence emmission spectra were recorded by the Karlsruhe CCD-OMA spectrofluorometer during the fast rise (fast component of Kautsky effect) and the slow decline (slow component of Kautsky effect) of the chlorophyll fluorescence kinetics. The relationships between fluorescence signatures and photosynthetic pigments were used to characterize the development of photosynthetic activity in 7d old etiolated barley seedlings during illumination with continuous white light, The shape of the chlorophyll fluorescence spectra exhibited characteristic changes during the greening of etiolated barley seedlings. At the onset of greening and a very low chlorophyll content only one fluorescence peak near 690 nm was detectable, whereas the second fluorescence peak near 735 nm, initially expressed only as a shoulder, was developed during the chlorophyll accumulation to a separate fluorescence maximum. The time course of the fluorescence intensity near 690 nm and 735 nm at maximum (fm) and steady-state of the chlorophyll fluorescence (fs) can be explained on the basis of a partial reabsorption of the emitted red chlorophyll fluorescence band F690 by the leaf chlorophyll. The chlorophyll fluorescence ratios F690/F735 at fm and fs were determined from the CCD-OMA spectra. The decreasing of the chlorophyll fluorescence ratio F690/F735 with increasing chlorophyll content during greening of the etiolated barley leaves can be expressed by a power function (curvilinear relationship): y=ax-b. The variable chlorophyll fluorescence decrease ratios (Rfd-values) as vitality index were calculated from the fluorescence intensities measured at 690 nm and 735 nm of the CCD fluorescence spectra. The Rdf690 and Rfd735 values increased during greening and exhibited the characteristics of a saturation curve. The latter was reached for Rfd690 after 24 h of illumination (chlorophyll content 14 μm-2) and for Rfd735 already after 6h of illumination (chlorophyll content 8 μ cm-2). The Karlsruhe CCD-OMA spectrofluorometer is excellently suited for photosynthetic studies as well as stress detection in plants.

End-product Inhibition of Photosynthesis in Prunus cerasus L. in Response to Whole-plant Source-Sink Manipulation

The source-sink ratio of l-year-old, potted `Montmorency' sour cherry (Prunus cerasus) trees was manipulated by partial defoliation (D) or continuous lighting (CL) to investigate the phenomenon of end-product inhibition of photosynthesis. Within 24 hours of D, net CO2 assimilation rate (A) of the most recently expanded source leaves of D plants was significantly higher than nondefoliated (control) plants throughout the diurnal photoperiod. Between 2 and 7 days after D, A was 30% to 50% higher and stomatal conductance rate (g,) was 50% to 100% higher than in controls. Estimated carboxylation efficiency(k) and ribulose-1,5-bisphosphate (RuBP) regeneration rate increased significantly within 2 days and remained consistently higher for up to 9 days after D. Leaf starch concentration and dark respiration rate decreased but sorbitol and sucrose concentration increased after D. The diurnal decline in A in the afternoon after D may have been due to feedback inhibition from accumulation of soluble carbohydrates (sucrose and sorbitol) in the cytosol. This diurnal decline indicated that trees were sink limited. By 9 days after D, photochemical efficiency was significantly higher than in control plants. In the long term, leaf senescence was delayed as indicated by higher A and gs in combination with higher chlorophyll content up to 32 days after D. CL resulted in a significant reduction of A, gs, k, variable chlorophyll fluorescence (Fv), photochemical efficiency, and estimated RuBP regeneration rate of the most recently expanded source leaves within 1 day. During the exposure to CL, A was reduced 2- to 3-fold and k was reduced up to 4-fold. The normal linear relationship between A and gs was uncoupled under CL indicating that A was not primarily limited by gs and since internal CO2 concentration was not significantly affected, the physical limitation to A imposed by the stomata was negligible. The decrease in Fv and photochemical efficiency indicated that leaves were photoinhibited within 1 day. The decrease in instantaneous chlorophyll fluorescence after at least 1 day of CL indicated that there was a reversible regulatory mechanism whereby the damage to photosystem II reaction centers was repaired. Leaf chlorophyll content was not altered by 1,2, or 3 days of exposure to CL, indicating that photooxidation of chlorophytl did not occur. The time to full photosynthetic recovery from CL increased as the duration of exposure increased. CL plants that were photoinhibited accumulated significant starch in the chloroplast in a companion study (Layne and Flore, 1993) and it is possible that an orthophosphate limitation in the chloroplast stroma was occurring. D plants that were continuously illuminated were not photosynthetically inhibited. After 7 days of CL, plants that were then partially defoliated yet remained in CL photosynthetically recovered within 5 days to pre-CL values. Under the conditions of this investigation, end-product inhibition of A occurred in young, potted sour cherry trees but the mechanism of action in D plants was different than in CL plants.

Salinity Tolerance of Rice (Oryza sativa L.) with Reference to Endogenous and Exogenous Abscisic Acid

AbstractExperiments conducted m a phytotron on three rice varieties of different salinity tolerance revealed an increase in the content of endogenous abscisic acid (ABA) with increasing NaCl salinity in IR20 (semi salt‐tolerant), but in Pokkali (salt‐tolerant) and IR28 (salt‐sensitive) the increase in ABA content was marginal. Under sahnity stress, in general, 5 weekly sprayings of ABA (10‐4 mol L‐1) decreased Na and K concentrations in the shoot to the extent of 29.5 % and 3.3 %, respectively. However, ABA application significantly improved the K/Na ratio as well as the chlorophyll fluorescence decrease ratio (Rfd, indicator for potential photosynthetic activity), the number of green leaves per plant and the shoot dry weight. The response of IR20 and IR28 to ABA application was significantly better than that of Pokkali. Increasing salinity caused marked nutrient imbalances, decreased Rfd values and shoot dry weight. The results are discussed in relation to possible mechanism of salinity tolerance.

Xanthophyll Cycle Patterns and in vivo Photoinhibition in Herbicide-Resistant Biotypes of Conyza canadensis

Summary The xanthophyll cycle and in vivo photoinhibition were investigated in the herbicide-susceptible (S), paraquat-resistant (PQ-R), atrazine-resistant (Atr-R) and paraquat-atrazine co-resistant (PQAtr-R) biotypes of Conyza canadensis using both low-(LLG) and high-light-grown (HLG) plants. HPLC revealed markedly reduced levels of zeaxanthin under photoinhibitory conditions in atrazine-resistant (Atr-R and PQAtr-R) biotypes as compared with the S and PQ-R biotypes. The variable chlorophyll fluorescence (F v ) decrease and constant fluorescence (F o ) increase revealed an enhanced susceptibility to in vivo photoinhibition in Atr-R and PQAtr-R biotypes. LLG plants were more susceptible than HLG plants to in vivo photoinhibitory treatment. It is suggested that the increased susceptibility to photoinhibition in Atr-R and PQAtr-R biotypes of C. canadensis is a consequence not only of D1 protein mutation, but also possibly of a lower rate of violaxanthin to zeaxanthin de-epoxidation.