Comparison of the light-limited growth of the nitrogen-fixing cyanobacteria Anabaena and Aphanizomenon

The effect of simultaneous N₂ fixation and light limitation on the growth of two strains of Anabaena sp. Bory de St. Vincent and Aphanizomenon flos-aquae (L.) Ralfs was investigated using continuous cultures. Under severely light-limited conditions, Aphanizomenon showed a broader absorption spectrum (due to the presence of phycoerythrin), a higher maximum efficiency of photosynthesis, a higher steady-state N₂ fixation activity and a higher growth affinity for light than did Anabaena . On the other hand, under light saturation, Anabaena showed a higher maximum rate of O₂ production and a higher maximum specific growth rate than Aphanizomenon . These monoculture results characterize Anabaena and Aphanizomenon , in relative terms, as a 'sun' and a 'shade' species respectively, and are in accordance with field observations. The difference between the two species in their acclimatory response is discussed in terms of a species-specific alteration of the PSI:PSII stoichiometry. Besides the species-specific modulation of the accessory pigments, such an acclimation would provide a biochemical basis for the observed physiological differences. The monoculture results were used to differentiate the niches of the two species and suggested that Aphanizomenon would competitively displace Anabaena under N₂-fixing, light-limited conditions. However, when both species were grown together, Anabaena became dominant and seemed to be the superior competitor for light. In order to explain this finding, the possible effects of release of allelopathic compounds, or dynamic aspects of light supply, are discussed.     

Enzymatic and Non-Enzymatic Oxygenation of Tyrosine

Tyrosinase isolated from cultured human melanoma cells was studied for tyrosine oxygenation activity. l -Tyrosine and d -tyrosine were used as substrates and dopa was measured with HPLC and electrochemical detection as the product of oxygenation. Incubations were performed in the presence or absence of dopamine as co-substrate. Oxygenation of l -tyrosine occurred only in the presence of dopamine as co-substrate. No oxygenation of d -tyrosine was found, and we conclude that human tyrosinase is characterised by exclusive specificity for the l -isomer of tyrosine in its oxygenase function. It has recently been suggested that superoxide anion is a preferential oxygen substrate for human tyrosinase. Incubations were therefore performed with l - and d -tyrosine, human tyrosinase, and xanthine/xanthine oxidase in the system, generating superoxide anion and hydrogen peroxide. Considerable formation of dopa was observed, but the quantity was the same irrespective of whether d -tyrosine or l -tyrosine was used as the substrate. Furthermore, formation of dopa occurred in a xanthine/xanthine oxidase system when bovine serum albumin (BSA) was substituted for tyrosinase. Our results provide no evidence that superoxide anion is an oxygen substrate for human tyrosinase. In the incubate containing xanthine/xanthine oxidase, catalase completely inhibited dopa formation, and superoxide dismutase and mannitol each strongly inhibited dopa formation. The results are compatible with hydroxyl radicals being responsible for the formation of dopa, since such radicals may be secondarily formed in the presence of superoxide anion and hydrogen peroxide.     

On the ecomorphology of migrants

A multivariate analysis of data from a wide range of avian species revealed that migratory distance was related to a high aspect ratio, long and pointed wings and well-developed distal wing segments. Migration also appeared to set limits on the development of the hind limb and on the wing muscles not involved in forward flight. Among Sylvia warblers it is shown that habitat use and migration may constrain each other.     

Two forms of egg defence in a chrysomelid beetle: egg clumping and excrement cover

Abstract.

• 1 Field experiments demonstrated that the faecal covering that female Microrhopala vittata (Fabr.) (Coleoptera: Chrysomelidae) place over their egg masses significantly reduces egg mortality.
• 2 The bottom egg in the egg mass, which lies against the leaf of the host plant, suffers significantly higher mortality than the other eggs in the egg mass.
• 3 The parasite Chrysonotomyia sp. (Hymenoptera: Eulophidae) generally parasitizes only the bottom egg in the egg mass, while predators rarely penetrate the faecal covering.
• 4 No significant relationship was found between mortality and the number of egg masses per leaf.
• 5 By placing eggs in masses, females may ensure that at least the upper eggs in any egg mass are effectively protected against virtually all natural enemies likely to pose a threat.

     

Immobilization of Ciliates by Concanavalin A*

SYNOPSIS. Interaction of several plant lectins with the ciliates Stylonychia mytilus, Euplotes aediculatus, and Tetrahymena pyriformis GL, was investigated. The motility of Stylonychia is specifically inhibited by treatment with concanavalin A, with which the 2 other ciliates react only weakly. Stylonychia can regain its motility by shedding the lectin-loaded surface components and rebuilding a new pellicle. Other lectins used in this study did not interact with these ciliates.     

Water Supply, Evaporation, and Vapour Diffusion in Leaves

On the basis of experimental results published during the last25 years, but more particularly during the last 5 years andincluding some results presented here, the hypothesis is proposedthat an important portion of the water supply from major veinsin leaves travels within the epidermal tissue to sites of evaporationclose to the stomatal pores. These evaporation sites are innerepidermal walls especially subsidiary and guard cell walls becausethese are closest to air spaces with the highest water vapourdeficits. Less water than is traditionally supposed evaporatesfrom mesophyll cell walls. Low osmotic potentials of guard cells(large negative) are not required in building up high turgorpressures. However, they are required in competing for wateragainst the process of evaporation which causes low matric potentialsto develop in subsidiary and guard cell walls so that guardcolls can maintain the comparatively low turgor pressures whichhave been shown to operate the stomatal apparatus. Traditionalviews about leaf water relations and methods of estimating mesophyllresistances for carbon dioxide diffusion into leaves must bemodified.     

The Role of Compartmentalization in the Activation of Particular Control Genes and in the Generation of Proximo-Distal Positional Information in Appendages

SYNOPSIS. A mechanism is proposed for the activation of particulargenes during interpretation of positional information and duringsequential addition of new structures during outgrowth. Theprimary event is assumed to be an alternation between two states.The alternation of anterior-posterior-anterior compartmentsin insects or bone-joint-bone in the chicken wing is assumedto be a trace of this primary subdivision into two alternativestates. Each (or each second) transition from one state to theother causes a switch from one structure-controlling gene tothe next. This enables a counting of alternations on the DNA-leveland a high resolution in the corresponding activation of controlgenes. The model explains the formation of compartments andsegmental specification in perfect register. The elements ofthe bithorax gene complex become understandable assuming thismechanism. It is shown further that such a "compartmentalization" can beused for the reproducible generation of subpatterns for thefiner subdivision of a developing embryo. By "cooperation ofcompartments," a cone-shaped morphogen distribution can be generated,accounting, e.g., for the circular arrangement of structuresin the fate map of the leg disk of Drosophila. The most distalstructures are formed at the intersection of compartments anddistal transformation occurs whenever cells of all three orfour major compartments are close to each other.     

Effects of Photoperiodic Induction and Debudding in Xanthium pennsylvanicum and of Partial Defoliation in Phaseolus vulgaris on Rates of Net Photosynthesis and Stomatal Conductances

Xanthium pennsylvanicum plants received four treatments in thefactorial experiment (a) debudded v. not debudded, and (b) longdays . photoinductive short days. Rates of net photosynthesis,carbon dioxide compensation points (), and stomatal conductanceswere assessed after 8 days and before leaf growth or stomatalsize were appreciably affected. Leaf size, stomatal frequencies,and lengths of guard cells were estimated at this time and again22 flays after treatment. Debudding alone slightly Increased stomatal conductance; inductionalone had a similar but larger effect. Debudding and inductiontogether caused a more than additive increase in net photosynthesisat 8 days, with marked decreases in . At 22 days this combinationcaused more than additive increases in leaf size and guard-celllengths while stomatal frequencies had decreased. Induction alone directly increased stomatal conductance andthis may be responsible for the increase in photosynthesis;but debudding alone may directly affect photosynthesis by increasingthe supply of cytokinins to the leaves. The positive interactionof these factors in photosynthesis could not be explained interms of stomatal conductance and a synergism between cytokininsand a photoperiodically induced hormone is suggested. In Phaseolus vulgaris plants, 4 days after partial defoliation,stomatal conductances and rates of net photosynthesis increasedgreatly in the remaining leaflets.     

Spectroscopic Investigation of the Inhibitory Effect of Fatty Acids on Photosynthetic Systems

Fatty acids have a reversible inhibitory effect on respiration and on photo-synthetic action. Investigation of the influence of octanoic acid on the photo-synthetic bacterium Rhodopseudomonas spheroides R-26 indicates that a less efficient energy transfer and decoupling of the light-gathering pigment system from the energy converting reaction centre is responsible for the inhibitory effect.     

Rates of Photosynthesis and Respiration in Relation to Stomatal Movements in Leaves Treated with {alpha}-Hydroxysulphonate and Glycollate

Leaves of tobacco and Xanthium pennsylvanicum were treated withsolutions of -hydroxysulphonate and glycollate in normal air.During the treatment with -hydroxysulphonate the intercellular-spacecarbon dioxide concentration of the leaves increased owing toa decrease in photosynthetic activity. It seems probable thatthese increases in internal carbon dioxide concentration werethe cause of stomatal closure, because when treated leaves wereflushed with carbon dioxide free air the stomata reopened. Experimentalresults also showed that the accumulation of glycollate, resultingfrom treatment with -hydroxysulphonate, could not be held responsiblefor stomatal closure because treatment with glycollate alonehad no influence on either the internal carbon dioxide concentrationor on the stomata of the leaves.