Decrease In Chlorophyll Fluorescence Research Articles

FUNCTIONAL ASPECTS OF SECONDARY CAROTENOIDS IN HAEMATOCOCCUS LACUSTRIS (VOLVOCALES). III. ACTION AS A “SUNSHADE”1

ABSTRACTWe investigated the protection from photoinhibition by different developmental stages of Haematococcus lacustris [Girod] Rostafinski using chlorophyll fluorescence measurements of single cells and suspensions. An overall correlation between higher cellular content of secondary carotenoids and the capacity to withstand excessive irradiation was observed in flagellated cells and aplanospores of H. lacustris. Low‐light‐reversible spreading of extra‐chloroplastic secondary carotenoids occurred in the periphery of the cell during strong irradiation. This process resulted in increased shading of the cup‐shaped chloroplast as demonstrated by a decrease in chlorophyll fluorescence. Extrachloroplastic accumulation of secondary carotenoids in H. lacustris can be interpreted as a specific adaptation to habitats that exhibit strong insolation.

Temperature‐Related Changes in Chlorophyll Fluorescence and Contents of Chlorophyll and Carotenoids in Andean and European Potato Clones

AbstractLow‐temperature adapted Andean potato clones and low‐temperature sensitive European clones cultivated at 20/10°C were compared during stress occuring as the result of low‐temperature treatments.The stress response of leaf tissue was assessed by measuring the decrease in chlorophyll fluorescence (Fv/Fm) in detached leaves during a period of six days. After temperature stress combined with light Fv/Fm decreased only slightly in the Andean clones, but was markedly lower than the initial values in the European clones, However, after a 2°C treatment in darkness no difference between clones of different origins was detected.In general, chlorophyll and carotenoid contents of the Andean clones were higher than those of the European clones. They were markedly lower in all clones in treatments where low temperature was combined with light, than at 20/10°C and at 2°C in the dark. The contents of carotenoids and total chlorophylls decreased more in the European than in the Andean clones when leaves were transferred to a higher light intensity and then the lowest temperature used was combined with light. Thus carotenoids and chlorophylls in the Europeans clones were more sensitive to photo‐oxidation at low temperatures than in the Andean clones.The changes in chlorophyll fluorescence in illuminated, detached leaves induced by a decrease in temperature were found to correlate with the low temperature performance of the genotypes. The correlation between low temperature performance and photosynthetic activity was highly significant and could be used by plant breeders to identify plants that perform well at low temperatures.

Physiological factors determining yield in bread wheat. Effects of introducing dwarfism genes

Improvements in bread wheat productivity have been related to changes in plant morphology and function associated with a large increase in the harvest index for a more or less constant biological yield. The appearance of short genotypes possessing dwarfism genes may modify markedly the objectives of breeding as the upper limits of the harvest index are approached. The aim of the investigations presented here was to identify some contrasts between short and tall genotypes in terms of the physiological characteristics associated with grain yield, so as to orientate more efficiently the selection of genotypes, with or without dwarfism genes, for productivity. Various parameters of flag leaf functioning (photosynthesis rate, chlorophyll fluorescence index, leaf area duration) were related to the biological and economic yields and the harvest index for two groups of genotypes that were differentiated by their height. For all genotypes, the relationships between the various traits and the grain yield were difficult to ascertain. For the tall genotypes without dwarfism genes, the classical relationships between grain yield, harvest index, flag leaf area duration and net photosynthesis rate were confirmed. Moreover, the rate of chlorophyll fluorescence decrease (Rfd) during the slow Kautsky kinetics phase, which is representative of the leaf photosynthesis at low light, was found to be an excellent marker of economic yield. Chlorophyll fluorescence decrease was closely related to grain yield and also with other factors that are known to be important in its expression (harvest index, flag leaf area duration). In very short genotypes, the biological yield and directly related factors (leaf area, plant height) were the main parameters associated with economic yield, since the harvest index had approached its upper limit. The selection of short genotypes must therefore maintain the biological yield through an increase in the size of the aerial organs to counterbalance the decrease in height.

Monitoring chilling injury: A comparison of chlorophyll fluorescence measurements, post‐chilling growth and visible symptoms of injury in Zea mays

Changes in chlorophyll fluorescence emission from maize (Zea mays L. cv. Northern Belle) seedlings chilled at 1.5°C in the dark for 3–30 h were compared with the ability of plants to resume growth in the immediate post‐chilling period and with the development of visible symptoms of injury to the leaves. During chilling, the maximal rate of increase of the induced chlorophyll fluorescence rise. FR, was measured on secondary leaf tissue. FR decreased exponentially, at approximately the same rate in plants grown and chilled in hydroponic pots, in leaves detached from similar plants and in plants that were removed from the hydroponic pots and laid on wet filter paper adjacent to the detached leaves. The half‐fall time for FR in the 3 treatments was 7.8 ± 1.3 h, 8.6 ± 0.6 h and 8.8 ± 1.0 h, respectively. Following seedling removal from 1.5°C and return to 25/15°C, relative growth rates were determined from daily measurements of plant fresh weight gain. Compared with non‐chilled seedlings, plants chilled for 3 h and longer showed depressed rates of growth. Inhibition of growth in the immediate post‐chilling period (0–27 h) was linearly related to the duration of the chilling period and had a high positive correlation with the decrease in chlorophyll fluorescence (linearly related to log FR) sustained during the chilling exposure. Visible symptoms of chilling injury developed during the post‐chilling period on seedlings chilled for longer than 3 h. The decrease in log FR during chilling was also linearly correlated with the severity of visual symptoms of chilling injury expressed in the post‐chilling period. It is concluded that the extent of chilling injury in maize can be rapidly and non‐destructively assessed from measurements of chlorophyll fluorescence.

Photoinhibition at Chilling Temperatures

Relative susceptibilities of chilled leaves to photoinhibition were determined for 15 species of crop annuals showing a wide range of chilling tolerance. Leaf tissue at 7°C was exposed to a moderate photon irradiance of 300 �mol m-2 s-1 and photoinhibition was measured by the decrease in chlorophyll fluorescence (Fv/Fm) measured at 77K. All chilling-resistant plants surveyed (barley, broad bean, oat, pea and wheat) were photoinhibited at chilling temperatures. The chilling-sensitive plants (bean, cucumber, lablab, maize, pearl millet, pigeon pea, sesame, sorghum and tomato) were more susceptible, the mean of values for susceptibility to photoinhibition being twice that of the chilling-resistant plants. Rice, however, showed a tolerance to photoinhibition at 7°C comparable to that of some of the chilling- resistant plants. Indica rices were more susceptible than japonica rices. Photoinhibition increased with decreasing temperature and with increasing photon irradiance in both the chilling-resistant and sensitive plants. In pea and cucumber, photoinhibition at 7°C was correlated linearly with the decrease in photosystem II activity assayed in chloroplast thylakoids isolated from similarly treated tissue. Relative tolerances of leaves of the same 15 species to chilling injury in the dark were also measured. No linear correlation was found between susceptibility of chilled leaves to photoinhibition and susceptibility to dark chilling injury. The pattern of differences between species for photoinhibition at 7°C was largely preserved when photoinhibitory treatments were given at a non-chilling temperature (21°C) by increasing the photon irradiance to 900 �mol m-2 s-1. We conclude that, while the chilling-sensitive plants were generally more susceptible than the chilling-resistant ones to photoinhibition at low temperatures, this arose from a greater sensitivity to the irradiance rather than from the chilling sensitivity. Photoinhibition associated with low temperatures was also demonstrated in the tropical fruit species, banana, pawpaw and Monstera. Low values of Fv/Fm recorded in leaves exposed to full sunlight during the winter month of July (range 0.39-0.56 compared with 0.70-0.79 in January) indicated that photoinhibition could adversely affect some tropical perennial fruit species cultivated in semitropical or warm temperate areas experiencing recurrent cool to cold winters.

Are guanine nucleotide-binding proteins involved in regulation of thylakoid protein kinase activity?

The slow ATP-induced decrease in chlorophyll fluorescence associated with the phosphorylation of LHC II seen in spinach thylakoids was inhibited by GTP and its non-hydrolysable analogues β, γ-imidoguanosine 5′-triphosphate and guanosine 5′- O-(3-thiotriphosphate), but not by other nucleotide triphosphates or diphosphates. Inhibition by guanosine 5′- O-(3-thiotriphosphate) appeared to require prior exposure of the thylakoid membranes to the guanine nucleotide under conditions where the protein kinase was active but unable to turnover. Binding studies with thylakoid membranes using [5′,8- 3H]GTP or [ 35S]guanosine 5′- O-(3-thiotriphosphate) show that under similar conditions an increase in specific binding of these radiolabelled nucleotides occurs. The data presented provide evidence for the existence of a guanine nucleotide-binding regulatory protein that is able to interact with the thylakoid protein kinase.

Assessment of the frost sensitivity of wild and cultivated potato species by chlorophyll fluorescence analysis

The potential of the chlorophyll fluoresence technique in screening for frost sensitivity in seedling progenies representing 18 genotypes of wild and cultivated potato from different geographical and altitudinal origins was assessed by measuring the decrease in variable chlorophyll fluorescence (Fvar) of terminal leaflets of hardened and non-hardened plants after freezing at −5°C for 60 min and subsequent re-warming to 20°C. The method was rapid and the results obtained agreed well with a visual assessment of frost injury carried out after leaflets had been returned to optimal growth conditions for 72 hours.Solanum tuberosum CPC 3294 originating from Chile was the most frost-sensitive genotype studied andSolanum albicans CPC 3712 from high-altitude regions of Peru, the most frost-resistant. Frost damage increased with length of exposure to frost and this was associated with a reduction of variable fluorescence and quenching capacity of the thylakoid membranes.

Electro-induced changes of chlorophyll fluorescence in individual intact chloroplasts

The intensity of chlorophyll fluorescence in isolated chloroplasts of Peperomia metallica and in situ chloroplasts of Anthoceros sp. was found to change by 5–10% on passing the electric current through the microelectrode inserted in the intrathylakoid space. The dependence of fluorescence deflections on the direction of a current flow and the absence of electro-induced fluorescence changes in chloroplasts made ion-permeable with gramicidin indicate that the emission was affected by the membrane potential created during the passage of current. A hyperpolarizing displacement of the membrane potential, positive on the inside, produced an increase in the emission in the absence of inhibitors, but has no effect on the fluorescence in chloroplasts treated with DCMU. A stimulation of a variable fluorescence by a positive membrane potential was interpreted as due to slowing down of charge separations and a respective decrease of excitation trapping in Photosystem II. A displacement of the membrane potential to the negative direction resulted in a decrease of chlorophyll fluorescence in both the absence and presence of DCMU. The fluorescence emission seems to be sensitive to variations of the membrane potential of about 100 mV or even less. Possible effects of the light-induced membrane potential on charge separations and the fluorescence emission in Photosystem II are discussed.

Effect of Leaf Detachment on Chlorophyll Fluorescence during Chilling Experiments

The effect of leaf detachment on chlorophyll fluorescence was analyzed for Zea mays, Cucumis sativus, Phaseolus vulgaris, and Echinochloa crus-galli. Results clearly indicate that detachment hastens the decrease in chlorophyll fluorescence during the course of chilling experiments. For maize and bean, the activity of photosystem II of chloroplasts isolated from detached leaves is lower than that of chloroplasts isolated from attached leaves. There are also large differences in ionic loss between detached and attached leaves of barnyard grass which could correlate with changes in leaf water status. The detached leaves lost some 50% of their total ionic content. Finally, detachment alters the ranking of the species with regard to their chilling tolerance.

Phosphorylation of chloroplast thylakoids decreases the maximum capacity of photosystem-II electron transfer

Phosphorylation of chloroplast thylakoid polypeptides by the light-activated protein kinase was found to decrease the light-saturated rate of whole chain and Photosystem-II electron transport. This decrease in electron-transport capacity was reversible and was found to correlate with the phosphorylation-induced decrease in chlorophyll fluorescence.

The cation-dependence of the degree of protein phosphorylation-induced unstacking of pea thylakoids

Experiments are presented to show that the phosphorylation of the light-harvesting chlorophyll a b - protein complex (LHC) induces structural reorganisation within the thylakoid membrane in response to the introduction of additional negative surface charges. The effect of cations of different valency on chlorophyll fluorescence measurements indicates that LHC-phosphorylation-induced reorganisation involves a change in the electrostatic screening capability of the added cation. At intermediate levels of cations (e.g., 1 or 2 mM Mg 2+), which substantially stack non-phosphorylated membranes, it was found that membrane phosphorylation caused considerable unstacking as monitored by light scattering and electron microscopy. Concomitant with this was a large decrease in chlorophyll fluorescence indicative of randomisation of chlorophyll protein complexes which would result in an increase in energy transfer between the photosystems as well as an absorption cross-section change. At higher concentrations (e.g., above 5 mM Mg 2+) a persistent ATP-induced decrease in chlorophyll fluorescence has been attributed to the displacement of charged phosphorylated LHC from the appressed granal to the non-appressed stromal lamellae, thus decreasing the absorption cross-section of Photosystem II. Under these circumstances only a small degree of unstacking was detected by light scattering and measurements of the percentage of thylakoid length which is stacked to form grana. However, when considered on a surface area basis, the structural changes observed can qualitatively account for the magnitude of the chlorophyll fluorescence quenching due to the lateral diffusion of LHC.

Assessment of the frost sensitivity of Trifolium species by chlorophyll fluorescence analysis

SUMMARYThe potential of the chlorophyll fluorescence technique in screening for frost sensitivity in a range of Trifolium species from different geographical origins was assessed by measuring the decrease in variable chlorophyll fluorescence (Fvar) of leaves after freezing at ‐ 5°C for 60 min. The method was rapid and the results obtained agreed well with a visual assessment of freezing injury carried out after leaves were returned to optimal growth conditions for 72 h. Trifolium alexandrinum (Berseem clover) cv. Tabor originating from Israel was shown to be the most frost sensitive species studied and Trifolium subterraneum (subterranean clover) cv. Mt. Barker, from temperate regions of Australia, the most frost resistant. On extended periods of freezing, frost damage increased and this was associated with a further reduction in variable chlorophyll fluorescence and in quenching capacity of the thylakoid membranes. These results thus indicate that substantial thylakoid membrane dysfunction is induced at freezing temperatures. Furthermore, it was found that frost hardening of the frost sensitive species T. alexandrinum for 21 days at 5°C reduced the extent of damage sustained by the thylakoid membranes as shown by higher fluorescence quenching capacity, smaller reduction in variable fluorescence (Fvar) and higher initial fluorescence (Fo) when leaves of hardened plants were frozen at ‐5°C and ‐7°C.

The effect of magnesium and phosphorylation of light-harvesting chlorophyll [formula omitted] on the yield of P-700-photooxidation in pea chloroplasts

The yield of P-700 photooxidation has been studied in isolated chloroplast membranes by measuring the extent of the flash-induced absorption increase at 820 nm ( ΔA 820) in the microsecond time range. The extent of ΔA 820 induced by non-saturating laser flashes was increased by the following treatments. (1) Suspension of chloroplast membranes in Mg 2+ free medium (plus 15 mM K +) which leads to unstacking of grana (as detected by a decrease in chlorophyll fluorescence). (2) Reduction of Q, the primary acceptor of Photosystem II, in the presence of 20 μM 3-(3,4 dichlorophenyl)-1,1-dimethylurea by a saturating xenon flash, fired 300 ms before the laser flash. (3) Phosphorylation of light harvesting chlorophyll a b - protein complex, which occurs in the presence of ATP after activation of protein kinase in the dark with NADPH and ferredoxin. We conclude that the Mg 2+ concentration, the redox state of Q and the protein-phosphorylation all can control the photochemical efficiency of P-700 photooxidation in isolated chloroplasts, and we discuss these results in relation to control of excitation energy distribution between the two photosystems. We also discuss the significance of these results in relation to the regulation of photosynthetic electron transport in vivo.

Tolerance of Borya nitida, a poikilohydrous angiosperm, to heat, cold and high-light stress in the hydrated state

Borya nitida Labill., a plant able to colonize rock outcrops and shallow sands in areas of high incident solar radiation in Western Australia, was examined for its tolerance to extremes of temperature, and to intense visible radiation. Stress injury to the leaves from heat, chilling or photoinhibitory light was followed by the decrease in in-vivo variable chlorophyll fluorescence. Heat injury was also ascertained by an increase in the "constant" fluorescence. Borya nitida leaves were extremely heat tolerant when heated at 1° C min(-1). In-vivo variable chlorophyll fluorescence was detectable up to 55° C, several degrees higher than either maize or barley which are, respectively, adapted to warm and cool climates. An increase in "constant" fluorescence occurred above 50° C in B. nitida. This compares with values in the literature of 48-49° C for three desert plants from Death Valley, California, and 44-48° C for ten species of tropical plants. Unlike the Death-Valley plants, the high degree of heat tolerance found in B. nitida did not require prior acclimation by growth at high temperatures. Borya nitida was also tolerant of a chilling temperature of 0° C. Plants grown at a low photon fluence rate (120 μmol m(-2)s(-1)) were irreversibly photoinhibited by light at 650 μmol m(-2)s(-1). Plants grown in sunlight resisted photoinhibition; however, the capacity to withstand photoinhibition was no greater than that of plants from less extreme environments.

Light-dependent quenching of chlorophyll fluorescence in pea chloroplasts induced by adenosine 5′-triphosphate

Addition of ATP to chloroplasts causes a reversible 25–30% decrease in chlorophyll fluorescence. This quenching is light-dependent, uncoupler insensitive but inhibited by DCMU and electron acceptors and has a half-time of 3 minutes. Electron donors to Photosystem I can not overcome the inhibitory effect of DCMU, suggesting that light activation depends on the reduced state of plastoquinone. Fluorescence emission spectra recorded at −196°C indicate that ATP treatment increases the amount of excitation energy transferred to Photosystem I. Examination of fluorescence induction curves indicate that ATP treatment decreases both the initial ( F o) and variable ( F v) fluorescence such that the ratio of F v to the maximum ( F m) yield is unchanged. The initial sigmoidal phase of induction is slowed down by ATP treatment and is quenched 3-fold more than the exponential slow phase, the rate of which is unchanged. A plot of F v against area above the induction curve was identical plus or minus ATP. Thus ATP treatment can alter quantal distribution between Photosystems II and I without altering Photosystem II-Photosystem II interaction. The effect of ATP strongly resembles in its properties the phosphorylation of the light-harvesting complex by a light activated, ATP-dependent protein kinase found in chloroplast membranes and could be the basis of physiological mechanisms which contribute to slow fluorescence quenching in vivo and regulate excitation energy distribution between Photosystem I and II. It is suggested that the sensor for this regulation is the redox state of plastoquinone.

Photooxidative damage to the photosynthetic apparatus during chilling

AbstractShort periods of chilling in the presence of light (up to 6 h: 1°C; 270 W/m2) decreased the subsequent apparent photosynthesis and chlorophyll fluorescence of leaf discs of Cucumis sativus L. cv. Kleine Groene Scherpe. The extent of the injury depended on the duration of the chilling pretreatment. After 6 h the subsequent apparent photosynthesis even reached a negative value, and it increased only slightly during the next 2 1/2 h. The decrease of apparent photosynthesis was not a consequence of increased dark respiration but was of photooxidative origin since the presence of both light and oxygen was required. Preincubation in the light for 2 h at 20°C sensitized leaf discs to subsequent photooxidation during chilling. Prompt and delayed chlorophyll fluorescence decreased simultaneously after chilling and light treatment. The corresponding decrease of photosynthesis and chlorophyll fluorescence is discussed in relation to primary photooxidative damage to the photosystems in the chloroplast membrane.