Two modes of bicarbonate utilization in the marine green macroalga Ulva lactuca

The green marine macroalga Ulva lactuca L. was found to be able to utilize HCO₃^? from sea water in two ways. When grown in flowing natural sea water at 16°C under constant dim irradiance, photosynthesis at pH8.4 was suppressed by acetazolamide but unaffected by 4,4′-diisothiocyanostilbene-2,2′-disulphonate. These responses indicate that photosynthetic HCO₃^? utilization was via extracellular carbonic anhydrase (CA) -mediated dehydration followed by CO₂ uptake. The algae were therefore described as being in a ‘CA state’. If treated for more than 10 h in a sea water flow-through system at pH9.8, these thalli became insensitive to acetazolamide but sensitive to 4,4′-diisothiocyanostilbene-2,2′-disulphonate. This suggests the involvement of an anion exchanger (AE) in the direct uptake of HCO₃^?, and these plants were accordingly described as being in an ‘AE state’. Such thalli showed an approximately 10-fold higher apparent affinity for HCO₃^? (at pH9.4) than those in the ‘CA state’, while thalli of both states showed a very high apparent affinity for CO₂. These results suggest that the two modes of HCO₃^? utilization constitute two ways in which inorganic carbon may enter the Ulva lactuca cells, with the direct entry of HCO₃^?, characterizing the ‘AE state’, being inducible and possibly functioning as a complementary uptake system at high external pH values (e.g. under conditions conducive to high photosynthetic rates). Both mechanisms of entry appear to be connected to concentrating CO₂ inside the cell, probably via a separate mechanism operating intracellularly.     

Changes in Cell Wall Polysaccharides During the Growth of Phaseolus vulgaris Leaves

The changes in pectic and hemicellulosic polysaccharides, and-cellulose during the expansion growth of the primary leavesof Phaseolus vulgaris L. var. Pinta have been studied. -Celluloseincreased continuously with age, while pectic and water-solublehemicellulose extracted with 4% KOH fractions slightly decreased.The water-soluble hemicelluloses extracted with 24% KOH showedthe most conspicuous changes, increasing until the 8th day,when the absolute growth rate was maximal, and thereafter decreasing.Furthermore, the study of the molecular mass distribution ofpectin, and water-soluble polysaccharides extracted with 4%and 24% KOH, showed an increase in the degree of polymerizationof polyuronic acid and xylan, and an important depolymerizationof galactan and xyloglucan. Accordingly, the mechanism of cellwall loosening in the leaf cell walls is similar to that describedfor plant axes. Key words: Cell wall, growth, leaf     

ATPase Activity in Flagella from Euglena gracilis. Localization of the Enzyme and Effects of Detergents*

SYNOPSIS. The biochemical effects of some detergents on the ATPase activity of isolated flagella from Euglena gracilis are related to morphologic obliterations induced by those detergents. Enzymic activity can be localized by electron microscopy along the microtubules and also on the paraflagellar rod. The nonionic detergent digitonin solubilizes the enzyme linked to dyneinic arms, whereas the activity linked to residual structures appears enhanced. These results support the hypothesis that the paraflagellar rod may be a structure actively related to the motility of this type of flagellum.     

Chlorophyll b accumulation and grana formation in low intensities of red light

Abstract When dark grown leaves of wheat (Triticum aesivum L.) were given a brief irradiation, there was an immediate onset of chlorophyll (Chl) b synthesis in the dark. This synthesis led to a rather slow accumulation of Chl b, which ceased when the Chl b/Chl a ratio had reached a value of about 0.1. The Chl b synthesis occurred also when the seedlings were treated with the herbicide SAN 9789. Leaves grown under different intensities of red light accumulated Chl b and Chl a, resulting in a ratio Chl b/Chl a which depended on the light intensity. If the light intensity was low, Chl a accumulated to a level about ten times the level of PChlide of the dark grown leaves. This occurred without any increase in the Chl b/Chl a ratio. There was no difference between SAN 9789-treated seedlings and water controls in this respect. Above a certain threshold of irradiance, the Chl b/Chl a ratio in the control leaves increased rapidly with the irradiation intensity. The increase in Chl b/Chl a ratio coincided with formation of grana in the plastids. This increase was not found and grana formation was completely absent in the seedlings treated with SAN 9789. The possibility of two different stages in the Chl b synthesis is discussed.     

ATPase Activity in Isolated Flagella from Euglena gracilis

SYNOPSIS. The ATPase activity of isolated flagella was studied in Euglena gracilis strain Z in the presence of Mg⁺⁺ or Ca⁺⁺. With Mg⁺⁺, the optimum activity was at pH 7 and with Ca⁺⁺, at pH 9. The K _m values were respectively 6.6 × 10⁻⁴ and 3.6 × 10⁻⁴. Activity was influenced also by temperature and ionic strength. Results with inhibitors of membrane ATPase suggest the presence of a specific contractile system in the flagella. Our results are compatible with a multicomponent enzymic system containing 2 active ATPases.     

Adaptations by macroalgae to low carbon availability. I. A buffer system in Ascophyllum nodosum, associated with photosynthesis

Abstract The exchange of CO₂, H⁺ and O₂ between seawater and the intertidal brown macroalga Ascophyllum nodosum (L.) Le Jolis were measured in a flowthrough system. While the algae were kept in darkness, seawater with artificially increased alkalinity and pH at 9.85, was alternated with ‘normal’ seawater at pH 8.0. A proton buffering system, with capacity to release and reabsorb about 20 μmol protons per gram alga (fresh weight) was revealed. As the algae were returned to the ‘normal’ seawater, the kinetics of proton reabsorbtion indicated that a proton uptake was gradually induced. This proton uptake, which was not connected to ion exchange in the cell wall, reached its maximum after 12 h. If subjected to high alkalinity seawater in the light, A. Nodosum for a certain period of time was capable of carrying out O, evolution in excess of the import of inorganic carbon. This ‘photosynthetic buffering capacity’ amounted to about 17 μmol O; per gram alga. Besides depending on a buffer of photorcducible substances, this ‘photosynthetic buffering capacity’ appeared to be functionally connected with the proton buffer. The time course for the discharge of the ‘photosynthetic buffer system’ and for the reabsorbtion of protons into the proton buffer (about 6h for 90× of the capacity at a temperature of 6°C) suggests that the ‘photosynthetic buffer system’ has a functional importance in the adaptation of A. nodosum to intertidal regions. The function of the buffer system is discussed in relation to the crassulacean acid metabolism (CAM)-like characteristics recently shown for the intertidal brown algal family Fucaceae.     

Adaptations by macroalgae to low carbon availability. II. Ultrastructural specializations, related to the function of a photosynthetic buffer system in the Fucaceae

Abstract Among the brown algae, species of the Fucaceae (Pelvetia, Fucus and Ascophyllum) were found to have a ‘photosynthetic buffering’ system, allowing the algae to carry out oxygen production without a concomitant uptake of inorganic carbon. This system was not found in other brown algae examined (e.g. Halidrys, Laminaria and Desmarestia) nor in 16 examined species of red and green algae. Pelvetia, Fucus and Ascophyllum belong to the littoral algae which are periodically emersed. In the Fucaceae, the meristodermal cells were found to have a special organization of organelles. Towards the outer cell wall there was a prominent layer of mitochondria while the chloroplasts were concentrated towards the inner and side walls. Between the mitochondria and the chloroplasts there was a large number of physodes. This arrangement of organelles was not found in the other brown algae examined nor in red or green algae. The significance of this organization of the mitochondria is discussed in connection with the function of the ‘photosynthetic buffering’ system.     

Structure of Protochlorophyll-containing Plastids in the Inner Seed Coat of Pumpkin Seeds (Cucurbita pepo)

The inner seed coat of seeds of Cucurbita pepo L. cv. Ohlsens Enke Köks was used to study the development of protochlorophyll-containing plastids with an abnormal ultrastructural composition. The pumpkins were harvested at different stages during fruit development and they thus contained seeds with different developmental stages. The dry weight of seeds of the developmental stages used varied from 0.04 g to 0.3 g. Such a series of seeds with decreasing water content indicating increasing maturity contained different amounts of protochlorophyll, from 0.20 μg/g fresh weight to 500 μg/g fresh weight. The ultrastructure of the protochlorophyll containing plastids changed greatly during development. In young seeds with a low content of protochlorophyll, regular prolamellar bodies were found and starch grains filled most of the plastids. During development the starch content decreased and the prolamellar bodies increased in size and lost their regularity. During maturation the plastids accumulated plastoglobuli, probably containing protochlorophyll, and finally the internal structure of the prolamellar body tubular complex was lost.     

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.     

Alterations of NADPH:protochlorophyllide oxidoreductase quantity and lipid composition in etiolated barley seedlings infected by Barley stripe mosaic virus (BSMV)

To understand the phenomenon by which infection of seed-transmitted Barley stripe mosaic virus (BSMV) alters membrane structures and inhibits protochlorophyllide biosynthesis of dark-grown barley ( Hordeum vulgare L.) plants, we analysed the presence of NADPH:protochlorophyllide oxidoreductase (POR, EC 1.3.1.33) and the galactolipid content and fatty acid composition. The amount of POR in etioplasts of infected leaves, compared with non-infected leaves, was reduced, as measured by immunoelectron microscopy and Western blot. These results are in agreement with the previously described reduction of the ratio of the photoactive 650 nm to non-photoactive 630 nm absorbing protochlorophyllide forms ( Harsányi et al. , 2002 . Physiol. Plant 114 , 149–155). The galactolipid content was lower in infected leaves. Monogalactosyl-diacylglycerol (MGDG) content was reduced to 40% and digalactosyl-diacylglycerol to 55% of control plants on a fresh weight basis. In infected plants, the proportion of linolenic acid decreased in both galactolipids. The lower amount of highly unsaturated fatty acids and the reduced abundance of MGDG correlated well with the previously detected reduction in the membrane ratio of prolamellar body (PLB) to prothylakoid ( Harsányi et al. , 2002 . Physiol. Plant 114 , 149–155). The reduced amount of POR and the above described alterations in the lipid composition resulted in a disturbed structure of PLBs. As a consequence, pigment synthesis and the greening process were inhibited in infected cells, in turn explaining the appearance of chlorotic stripes of BSMV-infected barley leaves. Our results show that BSMV infection can be detected at a very early stage of leaf development.