The Relationship between Chlorophyllide Accumulation, the Amount of Protochlorophyllide636 and Protochlorophyllide650 in Dark Grown Wheat Leaves Treated with δ-Aminolevulinic Acid

The influence of different amounts of protochlorophyl-lide₆₃₆ and protochlorophyllide₃₅₀ on light Induced chloro-phyllide formation was. studied in wheat leaves treated with δ-aminolevulinic acid. The phototransformation of proto-chlorophyllide was performed with weak red light. This transformation is unaffected by the δ-aminolevulinic acid treatment, whilst the accumulation of chlorophyllide, both the rate and the amount, is greatly stimulated by moderate amounts of protochlorophyllide₆₃₆. The presence of large amounts of protochlorophyllide₆₃₆ decreases the rate of chlorophyllide formation, but increases the final amount of chloro-phyllide formed. A decreased level of protochlorophyllide₆₅₀, obtained by treatment with N_aN₃, results in a decreased transformation rate. Inhibitors; of protein synthesis do not seem to influence the transformation of protochlorophyllide₆₃₆ to chlorophyllide, suggesting that no new synthesis of protein is required. The experimental results indicate that the final steps in chlorophyll biosynthesis are protochlorpnyllide₆₃₆→ protochlorophyllide₆₅₀→ chlorophyllide → chlorophyll.     

The Influence of 8-Hydroxyquinoline on the Accumulation of Porphyrins in Dark-Grown Wheat Leaves Treated with δ-Aminolevulinic Acid

Dark-grown wheat leaves treated with δ-aminolevulinic acid and 8-hydroxyquinoline accumulated porphyrins, most of which were protochlorophyllide and magnesiumprotoporphyrin monomethylester. The ratio between these two components was dependent on the concentration of 8-hydroxyquinoline. Small amounts of other porphyrins could also be detected. The treatment with 8-hydroxyquinoline and the presence of large amounts of porphyrins other than protochlorophyllide did not influence the photoreduction of protochlorophyllide or the Shibata shift. 8-Hydroxyquinoline caused an inhibition of protochlorophyllide biosynthesis, which could be reversed by rinsing the leaves several times with phosphate buffer. Magnesiumprotoporphyrin monomethylester was then converted to protochlorophyllide. The reversal induced by washing was increased if the buffer contained iron. The possible function of iron in the chlorophyll metabolism and its role in the inhibition reactions with 8-hydroxyquinoline are discussed.     

The After-Effect of Water Stress on Chlorophyll Formation during Greening and the Levels of Abscisic Acid and Proline in Dark Grown Wheat Seedlings

Cut seedlings of wheat plants (Triticum aestivum L. cv. Starke II Weibull) between 6 and 7 days old were water stressed in darkness by exposing them to air of 35% relative humidity 2.5 to 20 h. This treatment resulted in a water potential of -11 bars in the leaves after 20 h. The leaves were then rewatered and irradiated. The chlorophyll formation that took place in fully turgid leaves during the greening was markedly decreased in the case of the water-stress pretreatmet. and especially the lag phase was prolonged. The longer the stress pretreatment the more evident was the subsequent effect on chlorophyll formation. However, no linear relationship was found between the amount of stress and the chlorophyll content. Protochlorophyllide regeneration from endogenously formed δ-aminolevulinic acid was markedly decreased even after the shortest water-stress period. However, protochlorophyllide accumulation from exogenously supplied δ-aminolevulinic acid was only slightly decreased following the water-stress pretreatment. Further more, the ratio of protochlorophyllide₆₅₀ to protochlorophyllide₆₂₈ was slightly reduced by the same conditions. During the stress period both abscisic acid and proline were accumulated in the leaves. The content of abscisic acid increased up to six times the normal level during water stress lasting for 20 h. The increase of proline was about three-fold for similar treatment. After rewatering the leaves the levels of both abscisic acid and proline rapidly declined and reached. 10 h later, the levels found in unstressed seedlings. The increase in abscisic acid during water stress associated with impaired chlorophyll metabolism suggested that the after-effect of water stress might be linked to chlorophyll metabolism through abscisic acid or some of its metabolites. The changes in proline content open the possibility that this substance could function as a reserve substance for the formation of chlorophyll after the discon tinuation of the stress.     

Oak Seedlings Grown in Different Light Qualities

Seedlings of oak (Quercus robur) were germinated in darkness for 3 weeks and then given continuous light or short pulses of light (5–8 min every day). The morphological development was followed during 25 days. In continuous white, blue, and red light the stem growth terminated after about 10 days by formation of a resting bud. At that time the seedlings were about 100 mm high. In con tinuous long wavelength farred light (wavelength longer than 700 nm) the stem growth including leaf formation was continuous without the formation of resting buds, and the stem length was about 270 mm after 25 days. The number of nodes developed became twice that of the seedlings grown in while light. The leaves became well developed in all light colours, but leaf areas were largest in plants cultivated in white light. Compared to dark grown seedlings the mean area per leaf was increased about five times in continuous long wavelength far red light. A supplement with short (5 min) pulses of red light each day increased the leaf area up to 20 times. The stem elongation showed a high energy reaction response, i.e. the stem length increased only in continuous long wavelength far-red light but was not influenced by short pulses of red light or far-red light. The leaf expansion, however, was increased by short pulses of red light with a partial reversion of the effect by a subsequent pulse of far-red light. The fraction of the plant covered with periderm was higher in plants given continuous light. In respect to periderm inhibition continuous long wavelength far red light was the most effective. The transfer of seedlings from darkness to continuous white light gave anthocyanin formation in the stem 10–20 mm below the apex. This formation took place in the cortex and was evident in plants grown in darkness or under short pulses of light. Plants grown in continuous red, blue or long wavelength Far red light showed only traces of anthocyanin.     

Oxygen Consumption Stimulated by δ-Aminolevulinic Acid in Darkness and during Irradiation of Dark Grown Wheat Leaves

Dark grown wheat leaves (Triticum aestivum L. cv. Starke II Weibull), treated with δ-aminolevulinic acid in darkness, showed an increased oxygen uptake as measured by a Warburg method. The production of CO₂ was also increased in darkness, giving an RQ ? 1. The increased respiration was dependent on the treatment time as well as on the concentration of the δ-aminolevulinic acid. Potassium cyanide suppressed both the normal and the increased respiration. The treatment with δ-aminolevulinic acid caused accumulation of high amounts of protochlorophyllide. Levulinic acid suppressed the increased oxygen uptake as well as the protochlorophyllide accumulation in δ-aminolevulinic acid treated leaves. Irradiation rapidly decreased the protochlorophyllide content with a simultaneous increase in oxygen uptake over the dark value. The peak value of the increase in oxygen uptake was reached after about 5 min. The light induced oxygen uptake was dependent on the amount of PChlide present at the onset of irradiation. Also the CO₂ production was increased during the first minutes of irradiation but soon fell under the buffer control value. Neither potassium cyanide nor heat denaturation affected the oxygen uptake in light in contrast to the effect on the CO₂ production, which was blocked by heat denaturation. The increased oxygen uptake in light initially seems to be a purely photochemical process leading to a release of CO₂, which release is probably an enzymatic process induced by the photo-oxidative decomposition of pigment.     

Patterns in benthic food webs: a role for omnivorous crayfish?

1. The biomass and species richness of macrophytes and invertebrates in artificial ponds at two sites in southern Sweden (twenty-one ponds at each site) were investigated. Alkalinity was high at one site (H ponds) and low at the other site (L ponds). The ponds chosen had different densities of signal crayfish (Pacifastacus leniusculus), with mean crayfish abundance (estimated by trapping and expressed as catch per unit effort) significantly higher in the L ponds (10.7) than in the H ponds (4.9). Macrophytes, invertebrates, the amount of periphyton on stones and the organic content of the sediment were determined in each pond. 2. Macrophyte biomass, cover and species richness declined with increasing crayfish density. Macrophyte species composition differed between ponds and was related to crayfish abundance. 3. The total biomass of invertebrates and the biomass of herbivorous/detritivorous invertebrates declined with increasing crayfish abundance, but the biomass of predatory invertebrates declined only in the L ponds. The relative biomass of Gastropoda and Odonata declined in ponds where crayfish were abundant. In ponds where crayfish were abundant the invertebrate fauna was dominated by sediment-dwelling taxa (Sialis (H and L ponds) and Chironomidae (H ponds)). 4. The number of invertebrate taxa in macrophytes declined with increasing crayfish abundance. The percentage of macrophyte-associated invertebrate taxa differed between ponds, but also between sites. The relative biomass of Gastropoda declined in H ponds where crayfish were abundant. In H ponds Trichoptera or Gammarus sp. and Heteroptera dominated where crayfish were abundant, whereas Odonata dominated in L ponds with abundant crayfish. 5. The organic content of the sediment decreased in ponds with high crayfish densities, while the amount of periphyton on stones was not related to crayfish density. 6. We conclude that the signal crayfish may play an important role as a keystone consumer in pond ecosystems, but lower trophic levels did not respond to changes in the abundance of the crayfish according to the trophic cascade model. Omnivorous crayfish may decouple the cascading effect.     

pH-Dependent Effects of 2,4-Dinitrophenol (DNP) on Proliferation, Endocytosis, Fine Structure and DNP Resistance in Tetrahymena

ABSTRACT. In view of the importance of external pH on cytotoxic effects of ionizable agents, the pH-dependent effects of 2,4-dinitrophenol (DNP) were investigated. As uncoupler of oxidative phosphorylation. DNP interferes with the proton gradient across the inner mitochondrial membrane. DNP was added to proliferating Tetrahymena pyriformis in media of different initial pH. Effects studied were rates of cell proliferation and endocytosis, and fine structure. Findings correlated with the calculated concentration of undissociated DNP, taking into account that pH changes with time and cell density in Tetrahymena cultures. A linear relationship thus emerged between initial concentrations of undissociated DNP and lengths of the lag preceding cell proliferation. Once resumed, the rate of proliferation corresponded to that of control cells, even in different concentrations of undissociated DNP, presumably indicating an adaptation mechanism. Endocytosis was elevated throughout a wide range of undissociated DNP concentrations with a sharp transition towards inhibition at high DNP concentrations causing lethality with time. Changes in fine structure of DNP-treated cells (mitochondria, peroxisomes, nucleoli) also depended on the concentration of undissociated DNP.     

The effect of climate change on partial migration – the blue tit paradox

Climate change has proven to affect various aspects of the migration of birds. In response to milder winters making the habitat more profitable and increasing the survival of residents, the migratory fraction of partially migratory populations has been predicted to decline. We studied the blue tit Parus caeruleus , a common partial migrant in southern Sweden. The numbers migrating at Falsterbo, a migratory passage site in SW Sweden, has increased during the last decades, in parallel with increasing winter and annual temperatures. Migration data from Falsterbo were compared with yearly indices of the size of the breeding population as estimated by the Swedish National Bird Monitoring Programme. Over the study period 1975–2004, also the breeding population has increased in size. The proportion of blue tits migrating each year did not change over the study period, or possibly even increased slightly, which is in contrast to how climate change has been predicted to influence populations containing both migratory and resident individuals. The most important factors determining the intensity of blue tit migration in a given year was the size of an important winter food source, the beech mast crop (more migrants at lower crops) and the size of the breeding population (more migrants at higher densities).