Destruction Of Chlorophyll Research Articles

Pigment dynamics associated with the grazing of a ciliate and a flagellate feeding on a cyanobacterium

The egestion of particulate material as well as pigment degradation during microzooplankton grazing on phytoplankton are poorly known processes. In an attempt to evaluate these processes, changes in pigment concentrations within various size fractions were monitored in batch cultures of an assemblage of a pelagic ciliate ( Strombidium sulcatum) and a heterotrophic flagellate ( Paraphysomonas sp.) feeding on a cyanobacterium ( Synechococcus sp.) over a 10-day period. Chlorophyll a, carotenoids and phaeopigments were not found in the 0.1–0.7 μm fraction while the pigments originally in the 0.7–3.0 μm fraction (prey) were transferred into the > 3.0 μm size fraction (predator). During this transfer, the carotenoids (zeaxanthin and β-carotene) were not degraded significantly. In contrast, chlorophyll a was degraded into phaeophytin-like compounds which accounted for almost 100% of the recorded phaeopigments. The destruction of chlorophyll a varied with time ranging from 4% (day 3) to almost 100 % (end of the experiment) and this destruction was inversely related to micro-grazer ingestion rates. Microscopic examinations of samples did not reveal any large egested particles > 3.0 μm, suggesting that phaeopigments and carotenoids measured in this size fraction were accumulated inside the protozoa. Zeaxanthin was very stable even when it was within the mico-grazer.

Destruction of chloropigments in copepod guts

In a recent account regarding the destruction of chloropigments within the guts of copepods, Head & Harris (1996) (H&H) presented valuable data on pigment destruction in copepods. However, in one of their main conclusions, the authors invoked 2 enzyme pools to explain the pattern of pigment destruction: one directly derived from copepods, the other one produced by the ingested algae. If this conclusion is correct, it would have tremendous iinpact on the interpretation of data collected by the gut pigment technique. Estimating ingestion rates of copepods in the field would be very difficult, if not impossible, if pigment destruction was dependent upon an unknown food composition in the gut. We therefore felt it necessary to examine the evidence presented in H&H carefully. As we will demonstrate, (1) there is no evidence to postulate the existence of 2 enzyme pools, and (2) the majority of enzymes responsible for pigment destruction are a s likely to originate from copepods a s from the ingested algae. We scanned Fig. 4b of H&H with a HP Scanjet IIC color scanner and digitized the data with the image analysis software 'Data Thief' (by Kees Huyser and Jan van der Laan, National Institute for Nuclear Physics and High Energy Physics, Amsterdam, The Netherlands). We did not directly use the data shown in Fig. 7 of H&H because the data in Fig. 4 had fewer hidden points and could therefore be reproduced more accurately. Fig. 7 was constructed by H&H by multiplying the proportion of pigment destruction by the ingestion rate. Of 102 data points used in Fig. 4 of H&H, only 80 points were visible. However, when calculating the linear regression through these 80 data points, the estimated parameters as well as the calculated coefficient of determination were very similar to the original (Fig. l a ) . H&H estimated enzyme activity by multiplying chlorophyll destruction (y-axis) by ingestion rate (xaxis), and then plotted enzyme activity versus ingestion rate creating an autocorrelation in Fig. 7 . Instead of using the percentage value, H&H multiplied the xaxis from Fig. 4 by the proportion of chlorophyll destruction ranging from ca 0.45 to l . Hence, the units of the Xand y-axes of Fig. 7 are identical (ng mg h-'). Due to this autocorrelation, one would expect a linear relationship to result from any random distribution of a y-variate multiplied by an X-variate and plotted against the X-variate. However, as is already apparent from Fig. 4 , the relationship is not exactly linear, but slightly curved. The curve begins with a slope of ca 1 at low ingestion rates (i.e. 100% chlorophyll destruction) and decreases to ca 0.45 (i.e. 45 % chlorophyll destruction) since the proportion of pigment destruction is decreasing with increasing ingestion rates. Another consequence of the autocorrelated data set is that there cannot be a n intercept, since any product of 0 equals 0. Since ingestion rate is multiplied by chlorophyll destruction to calculate enzyme activity, the product is 0 whenever ingestion rate equals 0. Instead, the positive intercept in H&H is a n artifact caused by data points in the upper part of the curve which 'drive' the linear regression, a common problem in regression analysis (i.e. outliers have more influence on the regression line and rotate the line around the mean). It is therefore no coincidence that the slope of the linear regression (Fig. 7) and the proportion of enzyme destruction at high ingestion rates (Fig. 4 ) are almost identical (i.e. approximately 0.45). In using a linear regression for displaying enzyme kinetics, H&H chose an unconventional approach. In the simplest enzyme-substrate relationship, one would expect the kinetics to follow the classic MichaelisMenten model (Michaelis & Menten 1913) and not a straight line. In this model of regulation of enzyme

Peroxidase-catalysed chlorophyll destruction accompanied by the formation of electronically excited states: chlorophyll emission not due to energy transfer from excited substrate metabolites

The peroxidase-catalysed oxidative degradation of chlorophyll- a (chl- a) in the absence or presence of 2,4-dichlorophenol (DCP) is accompanied by the generation of electronically excited states, as indicated by light emission in the red spectral region. A mechanism for the destruction of chl- a is proposed, which takes into account the formation of excited states. As peroxidative chl destruction is believed to be a naturally occurring degradation process, the formation of potentially deleterious excited states during degradation is of physiological importance. Furthermore, it is shown that the red light emission does not originate from energy transfer from a peroxidase substrate metabolite formed in the excited state. As chl- a has been widely utilized as a sensitizer for the detection of triplet excited species in various peroxidasecatalysed transformations in vitro and in vivo, the additional importance of this work is to show that the observation of red light emission in the presence of chl- a does not necessarily indicate the formation of triplet excited state substrate metabolites in peroxidase systems.

Chlorophyll destruction by Calanus spp. grazing on phytoplankton:kinetics, effects of ingestion rate and feeding history, and a mechanistic interpretation

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 135:223-235 (1996) - doi:10.3354/meps135223 Chlorophyll destruction by Calanus spp. grazing on phytoplankton: kinetics, effects of ingestion rate and feeding history, and a mechanistic interpretation Head EJH, Harris LR Chlorophyll destruction by Calanus spp. grazing on phytoplankton (diatoms and Phaeocystis) was assessed at stations in the Labrador Sea and off Labrador and Newfoundland (Canada). Copepods were fed at natural or diluted food concentrations over several (4 to 8) sequential 12 h feeding periods. Initial chlorophyll concentrations were between 0.2 and 19 ug l-1, and degrees of chlorophyll destruction were between 20 and 100%. For replicate incubations, degrees of chlorophyll destruction were similar. Over all experiments degrees of destruction were generally high and variable at low ingestion rates (&LT50 ng chl mg-1 h-1), decreasing to a limit of about 45% at higher ingestion rates. The relationship between ingestion rate and degree of chlorophyll destruction was not obviously affected by differences in in situ conditions (e.g. stage of the spring bloom). Filtration rates, by contrast, did vary, decreasing in the presence of an apparently noxious food (Phaeocystis) and sometimes increasing during experiments, perhaps in response to increasing hunger. Faecal pellets, collected from copepods fed at natural food concentrations, did not leak pigment over a 4 d period, and neither chlorophyll nor phaeopigment was lost as copepods with food in their guts were allowed to defecate for 3 h in filtered seawater. These results suggest that most chlorophyll destruction occurs at an early stage of feeding, and that phaeopigments are not intermediates. When we assumed in a simple model that the 'bleaching' reaction was enzymatically mediated, we found that enzyme activity varied linearly with initial ingestion rate, with a positive y-intercept. One interpretation of this is that there are 2 pools of enzyme activity: one associated with the copepods and the other with the phytoplankton. The algal enzymes are normally latent, but are activated by the physical break-up of cells during ingestion. At low ingestion rates the copepod enzyme can destroy all, or most, of the ingested chlorophyll, whereas at higher ingestion rates more of the destruction is due to the algal enzymes. The high variability in degrees of chlorophyll destruction reported here and elsewhere can be explained partly by differences between algal foods (e.g. differences in levels of the bleaching enzyme), partly by differences in copepod behaviour (e.g. effects on filtration rates), and partly by differences in experimental conditions, which affect the range of ingestion rates exhibited during an incubation (e.g. density of copepods, duration of incubation). Copepod grazing . Chlorophyll destruction . Kinetics . Ingestion rate . Enzyme mediation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 135. Publication date: May 17, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Destruction of a single chlorophyll is correlated with the photoinhibition of photosystem II with a transiently inactive donor side.

Pigments destroyed during photoinhibition of water-splitting photosystem II core complexes from the green alga Chlamydomonas reinhardtii were studied. Under conditions of a transiently inactivated donor side, illumination leads to an irreversible inhibition of the electron transfer at the donor side that is paralleled by the destruction of chlorophylls a absorbing maximally around 674 and 682 nm. The observed stochiometry of 1 +/- 0.1 destroyed chlorophyll per inhibited photosystem II suggests that chlorophyll destruction could be the primary photodamage causing the inhibition of photosystem II under these conditions.

Decrease in Activity of Glutathione Reductase Enhances Paraquat Sensitivity in Transgenic Nicotiana tabacum.

Transgenic tobacco (Nicotiana tabacum L. cv SR1) with decreased activity of glutathione reductase exhibited enhanced sensitivity to paraquat in the light as evaluated by chlorophyll destruction and electrolyte leakage from leaf discs. This result indicates the involvement of glutathione reductase in the tolerance of plants to photooxidative stress caused by the herbicide.

Mechanism of photosystem-I photoinhibition in leaves of Cucumis sativus L.

It was recently shown that the site of photoinhibition in leaves of Cucumis sativus L. at low temperatures is Photosystem I (PSI), not PSII (I. Terashima et al. 1994, Planta 193, 300–306). In the present study, the mechanisms of this PSI photoinhibition in vivo were examined. By lowering the photon flux density during the photoinhibitory treatment of leaves at 4°C for 5 h to less than 100 μmol·m−2s−1, we were able to separate the steps of the destruction of the electron-transfer components. Although P-700, the reaction-center chlorophyll, was almost intact in this low-light treatment, the quantum yield of the electron transfer through PSI and photochemically induced absorption change at 701 nm were markedly inhibited. This, along with the results from the measurements of the light-induced absorption changes in the presence of various concentrations of methyl viologen, an artificial electron acceptor, indicates that the component on the acceptor side of the PSI, A1 or Fx, is the first site of inactivation. When the photon flux density during the treatment was increased to 220 μmol·m−2s−1, the destruction of P-700 itself was also observed. Furthermore, the partial degradation of the chlorophyll-binding large subunits was observed in photoinhibited leaves. This degradation of the subunits was not detected when the treatment was carried out under nitrogen atmosphere, the condition in which the electron transfer is not inhibited. Thus, the photoinhibitory processes in the reaction center of PSI go through three steps, the inactivation of the acceptor side, the destruction of the reaction-center chlorophyll and the degradation of the reaction center subunit(s). The similarities and the differences between the mechanisms of PSI photoinhibition and those of PSII photoinhibition are discussed.

CARBON UPTAKE IN A MARINE DIATOM DURING ACUTE EXPOSURE TO ULTRAVIOLET B RADIATION: RELATIVE IMPORTANCE OF DAMAGE AND REPAIR1

ABSTRACTExperiments on a marine diatom, Thalassiosira pseudonana (Hustedt) clone 3H, demonstrate that under moderate photon flux densities (75 μmol quanta·m−2·s−1) of visible light the inhibition of photosynthesis by supplemental ultraviolet (UV) radiation (UV‐B: 280–320 nm) is well described as a hyperbolic function of UV‐B irradiance for time scales of 0.5–4 h. Results are consistent with predictions of a recently developed model of photosynthesis under the influence of UV and visible irradiance. Although net destruction of chlorophyll occurs during a 4‐h exposure to UV‐B, and the effect is a function of exposure, the principal effect of UV‐B is a decrease in chlorophyll‐specific photosynthetic rate. The dependence of photoinhibition on dosage rate, rather than cumulative dose, and the hyperbolic shape of the relationship are consistent with net photoinhibition being an equilibrium between damage and repair. The ratio of damage to repair is estimated by a mathematical analysis of the inhibition of photosynthesis during exposures to UV‐B. A nitrate‐limited culture was much more sensitive to UV‐B than were the nutrient‐replete cultures, but the kinetics of photoinhibition were similar. The analysis suggests that the nutrient‐limited culture was more sensitive than the nutrient‐replete cultures because repair or turnover of critical proteins associated with photosynthesis is inhibited. An inhibitor of chloroplast protein synthesis was used to suppress repair processes. Photoinhibition by UV‐B was enhanced, and inhibition was a function of cumulative dose, as would be expected if damage were not countered by repair. The fundamental importance of repair processes should be considered in the design of field experiments and models of UV‐B effects in the environment, especially in the context of vertical mixing. Repair processes must also be considered whenever biological weighting functions are developed.

Fluorescence of wool grease

Wool yolk is highly fluorescent. The amount of wool yolk and intensity of wool yolk fluorescence varies along a Merino wool fibre. The fluorescence intensity of the yolk increases on travelling from tip to the root. Two components-‘grease’ and chlorophyll-contribute to the fluorescence of wool grease. The ‘grease’ fluorescence reveals the presence of a number of chromophores/components. An attempt to separate the chemical constituents and identify them was only partly successful as each of nine fractions obtained by preparatory thin-layer chromatography exhibited similar fluorescence properties. There are two types of chlorophyll presentchlorophyll a and chlorophyll b. Chlorophyll could be detected in all the wool greases examined. Artificial UV irradiation gave rise to a number of complex photochemical reactions including the destruction of chlorophyll. After an initial decrease in fluorescence intensity (for unknown reasons), there is a change of non-fluorescing visible-absorbing species to fluorescing UV-absorbing species before a final change in the latter to the former. The relative size of the changes was different for two different wool greases examined. In-situ studies using blue light as the irradiation source suggest that it also causes a (slower) decrease in fluorescence intensity, but proportionally faster for the ‘grease’ component than for the chlorophyll component.

Physiological Roles of Silicon in Photosynthesis and Dry Matter Production in Rice Plants. I. Effects of silicon and shading treatments.

To investigate the combined effects of silicon application and light intensity on growth characteristics, dry matter production, photosynthetic rate, and transpiration rate, three cultivars (cv. Nipponbare, Koshihikari, Suweon 258) were water cultured, using solutions of +Si (silicon application) and -Si (no-application) under two different light conditions (no shade and shade). Silicon application promoted growth and dry matter production in the three cultivars. The greatest effect was found in a japonica-type cultivar, Koshihikari, grown under the shade condition. Silicon application prevented overtranspiration and increased water use efficiency in leaves. This was effective in curbing photosynthetic depression and chlorophyll destruction in aged leaves. The maintenance of photosynthetic activity was regarded as one of the main reasons for the dry matter production increase by silicon application.

Chlorophyll and carotenoid transformation and destruction by Calanus spp. grazing on diatoms

Chlorophyll and carotenoid transformation and destruction by Calanus spp. grazing on diatoms

The role of ascorbate in drought‐treated Cochlearia atlantica Pobed. and Armeria maritima (Mill.) Willd.

Cochlearia atlantica is a species rich in ascorbic acid. After 4 days of intermittent drought treatment, there was a large decrease in the concentration of ascorbate and glutathione, functioning probably as radical scavengers (anti-oxidants). Although there was no increase in lipid peroxidation (a marker of oxygen radical damage), drought treatment did result in the destruction of chlorophyll and a decrease in protein. This species showed little or no change in the activities of five enzymes usually associated with the processing of, and protection from, activated forms of oxygen. Armeria maritima showed similar decreases in relative water content and dry weight after droughting, but a quantitatively smaller decrease in ascorbate with no loss of glutathione. Instead a major response to drought, in this species, was the marked increases in the activities of superoxide dismutasc and peroxidase. Despite these increases in enzymic defences against oxygen radicals, drought treatment resulted in increased lipid peroxidation. in A. maritima. It is concluded that ascorbic acid and glutathione may play a significant role in the response to drought in C. atlantica but protection in A. maritima is largely through enzymic processing of activated farms of oxygen.

Iron‐catalysed oxygen radical formation and its possible contribution to drought damage in nine native grasses and three cereals

Abstract. The origin, sequence and location of molecular damage arising during sub‐lethal drought is described in 4‐week‐old wheat (Triticum aestivum L.). Short episodes of water deprivation increased the uptake of iron within 6h of drought. Superoxide, precursor of the highly reactive hydroxyl radical in the presence of iron, was formed in the thylakoid membranes. Further draughting promoted destruction of chlorophylls (but not carotenoids), which was detectable after 14 h and preceded significant losses in relative water content. Peroxidation of lipids and a decreased protein content occurred after 26h of cumulative water deprivation but was confined to the shoots. In contrast, there was no significant loss of protein nor peroxidation of lipids in the root tissue, despite quantitatively larger, more rapid, losses in water content. These results indicate that damage arising in the early phases of drought appears to be initiated within the chloroplast and to be largely confined to the photosynthetic tissue. The pattern of drought‐induced damage in 11 other non‐xerophytes of the north temperate region was qualitatively similar to wheat, although the response to drought of the three cereals was more extreme than in the indigenous grasses and less extreme in ecologically stress‐tolerant species. A method for the simultaneous quantification of carotenoids in the presence of chlorophylls is provided.

Radical formation and accumulation in vivo, in desiccation tolerant and intolerant mosses.

Water loss in a desiccation-sensitive moss resulted in destruction of chlorophyll, loss of carotenoids and increased lipid peroxidation, indicating the presence of damaging forms of activated oxygen. These effects were exaggerated when the plants were desiccated at high light intensities. During water-deprivation there was a build up of a free radical, detected in vivo, with a close correlation between molecular damage and radical accumulation. In contrast, in a desiccation-tolerant moss there was almost no indication of molecular (oxidative) damage. However a stable radical similar in type and concentration to that found in the desiccation-sensitive species accumulated, particularly under high irradiances. The stable radical appears to be one of the end-products of a process initiated by environmental stress, desiccation and high irradiance: its association with molecular damage depending on the degree to which the species is tolerant of desiccation. Identification of the radical in intact tissue from EPR and ENDOR studies, suggests that this is not a short-lived peroxy-radical but instead is relatively stable and carbon-centred.

Reaction of Tomato Cultivars to a Sublethal Dose of Glyphosate

-1 64 m to the south. The air was at 21.5C and wind speed was 1.9 to 3 km·hr -1 from the south. All plants exhibited chlorosis of new leaves and of the terminal bud, indicating damage from spray drift. Two weeks after exposure, no plants had died, so the concentration was judged to be sublethal. The original plot design consisted of the three cultivars in three treatments in three completely randomized blocks with plants on 46cm centers. Plants were fertilized in-row before bed formation, and water was supplied by drip irrigation. The original objective of the field experiment was terminated and effects of a sublethal dose of glyphosate, applied before flowering, on growth and yield of the cultivars noted was examined. Harvests were begun 10 weeks after transplanting. ‘Sunny’ had higher total and marketable yields than the other cultivars (Table 1). Only 38% (range 37% to 41%) of fruit were marketable. On average, 46% of fruit in this study were rejected due to small size (39%, ‘Jet Star’; 48%, ‘Sunny’; .50%, ‘FloraDade’). Of the remaining ≈16% of fruit, which were of marketable size, ≈10% were rejected for cracks and ≈3% each for insect damage or disease. A greenhouse experiment was conducted to determine the amount of the glyphosate solution necessary to cause the symptoms observed in the field. Five 7-week-old seedlings of each cultivar/dosage were transplanted in Terra-lite Redi-earth (Grace Prod., Cambridge, Mass.) potting soil in 0.946-liter pots. After 1 week, an artist’s airbrush (Toler and Herbert, 1965) was used to apply 0.075, 0.1, 0.2, 0.4, 0.6, 0.8, or 1.0 ml of the 4.5% glyphosate solution uniformly to plants, including the terminal bud and new leaves. Received for publication 2 Apr. 1990. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. Plants treated with 1.0 ml of water were used as controls. Color change was monitored using a calorimeter (Minolta CR-200, Minolta Camera, Japan). Values were measured as A (change green to red), and B (change blue to yellow). Before application (0 hr), five readings per plant were made on leaves that would receive treatment. At 5 hr after application, before symptom expression, five readings per plant for all dosages were made on treated leaves. Subsequent readings were made on symptomatic leaves. A and B values described significant cubic distributions (Fig. 1) with no differences among cultivars due to treatment, A values for all dosages had increased by 5 hr after application and again by 20 hr and then stabilized. Values of B increased between 20 and 72 hr after application of all dosages; by that time, leaves sprayed with dosages subsequently determined to be lethal exhibited necrosis. After 72 hr, readings were only from chlorotic leaves. By 90 hr, B values were still greater than initial values. These findings represent destruction of chlorophyll and onset of necrosis, and indicate that dam

Bleaching Herbicide Flurtamone Interferes with Phytoene Desaturase

The mode of action of the furanone herbicide flurtamone and derivatives was investigated with cress seedlings and with the unicellular cyanobacterium Anacystis. Either in the light or in the dark these compounds inhibited the formation of alpha- and beta-carotene and all of the xanthophylls in the seedlings. Instead, phytoene, a precursor of colored carotenoids, was accumulated. In illuminated seedlings photooxidative destruction of chlorophyll was observed. The I(50) value of flurtamone inhibition of carotenoid biosynthesis in intact Anacystis cells and the K(1) value for interaction of flurtamone with phytoene desaturase with Anacystis thylakoids were 30 and 18 nanomoles, respectively. Concentrations of flurtamone which strongly inhibited carotenoid synthesis had no direct peroxidative activities and did not inhibit photosynthetic electron transport.

Photobleaching in the unicellular green alga Dunaliella parva 19/9

The change in the pigment composition of the unicellular alga Dunaliella parva 19/9 during exposure to high light (4000 μmol m(-2) s(-1)) has been investigated. During photobleaching the carotenoids were lost at a greater rate than the chlorophylls. In these photoinhibitory conditions, β-carotene and especially the minor carotenes, δ- and γ-carotene, were more susceptible to oxidative destriction than the xanthophylls. Lutein, the major carotenoid present, was the most stable of the carotenoids in these conditions. In addition to the direct photobleaching of carotenoids and chlorophylls, high light treatment induced the de-epoxidation of violaxanthin to antheraxantin and zeaxanthin. Small amounts of zeaxanthin were present in cells prior to illumination but the amount increased 2.4 fold following high light treatment. The effects of extremes of temperature during exposure to high light intensities were also investigated. The destruction of chlorophylls was found to be more temperature sensitive than that of the carotenoids. The general pattern of loss for the individual carotenoids was similar to that found at 25°C, i.e., the carotenes were more readily degraded than the xanthophylls.

Air pollution effects on the leaf structure ofLaurus nobilis, an injury resistant species

N. S. Christodoutakis and C. Fasseas Institute of General Botany, University of Athens, Athens 157 84, Greece The emiseion of air pollutants from the various indus- trial, domestic and social activities of man create a serious problem by turning the atmosphere in te a mix- ture of toxic and suf™ gases wich are disastrous te both plants and animale. The action of air pollutants te plants has long ago been the matter of several inves- tigations. Btructural modifications oG plant cell orga- nelles <Wellburn et al. 1972; Fishsr et ai. 1973; Rei- nert et al. 1975; Lentzian and Unsworth 1983; Patel and Devi 1984), inhibition of photosynthesis (White et al 1974; Capron and Mansfield 1976; Ormrod et al 1981) and finally, elimination of primary productivity (Fisher et al 1973; Winnsr 1981; Margaris et al 1985) have been reported by environmental scientists. Concerning plant responses ai the ultrastructura] leve] it is well documented that chrenic injury is displayed as chlorosis and subsequent nscrosis due te chlorophyll destruction which is also followed by thylakoid swelling and chloroplast lysis (Lendzian and Unsworth 1983, Psaras and Christodoulakis 1987; 1987a). Mereover it was also observed that ultrastructural injuries appear prier te any other visible modification on the leaf (Lendzian and Unsworth 1983). Although the problems caused by the long-tsrm exposure te air pollution are serious for the existence e™ plants, the support of plant lire in heavily polluted areas is essential Eor the improvement of man's lire in a hard-te-breath atmosphere. In Athens the problem of photochemical smog is se serious that li™ in ths metro- politan area becomes dangerous (Margaris et ai.1985). That is why the Laurus nobilis (laurel) plante growing on the partition isle of a continuously tra™ and heavily polluted main street in Athens, attracted out attention and became the eubject oG our investigation Send reprint requests te N.S. Christodoulakis at the above address.

Mutagenesis and Triazine Herbicide Effects in Strawberry Shoot Cultures

The effects of simazine on shoot culture of two varieties of strawberry were investigated with a view to establishing a system for in vitro selection of resistant mutants. In single shoots some chlorophyll loss occurred at herbicide levels producing little growth inhibition, but efficient bleaching was associated with severe suppression of growth. Varying simazine and sucrose levels, in both single and multiple shoot cultures did not reveal any conditions where chlorophyll destruction and growth inhibition could be separated. A protective effect, against bleaching, of high sucrose levels was not linked to suppression of photosynthesis, as assessed by CO2-fixation measurements. Mutagenesis with nitrosomethyl urea resulted in chlorophyll deficiencies in about 10% of shoots arising from axillary buds, but no resistant sectors emerged from 8000 and 400 mutagenized explants placed on medium containing inhibitory levels of simazine and streptomycin sulphate, respectively.

Plants Under Drought-Stress Generate Activated Oxygen

Lysed chloroplasts prepared from droughted wheat plants generate O2- on illumination as detected by electron spin resonance spectroscopy, the amplitude of the signal increasing with the severity of water deprivation. Following a similar time-course as radical formation and chlorophyll destruction, there was a significant increase in the accumulation of iron in the droughted shoots to reach an estimated concentration in the cell sap of about 2.5 mM. The evidence suggests that superoxide generated as a result of impaired electron transport in the chloroplasts reacts with the high concentration of accumulating iron resulting in the formation of hydroxyl radical, the probable cause of the primary pathologies observed in droughted plants.