Leaf Photosynthesis and Respiration of High CO(2)-Grown Tobacco Plants Selected for Survival under CO(2) Compensation Point Conditions

Four self-pollinated, doubled-haploid tobacco, (Nicotiana tabacum L.) lines (SP422, SP432, SP435, and SP451), selected as haploids by survival in a low CO₂ atmosphere, and the parental cv Wisconsin-38 were grown from seed in a growth room kept at high CO₂ levels (600-700 parts per million). The selected plants were much larger (especially SP422, SP432, and SP451) than Wisconsin-38 nine weeks after planting. The specific leaf dry weight and the carbon (but not nitrogen and sulfur) content per unit area were also higher in the selected plants. However, the chlorophyll, carotenoid, and alkaloid contents and the chlorophyll a/b ratio varied little. The net CO₂ assimilation rate per unit area measured in the growth room at high CO₂ was not higher in the selected plants. The CO₂ assimilation rate versus intercellular CO₂ curve and the CO₂ compensation point showed no substantial differences among the different lines, even though these plants were selected for survival under CO₂ compensation point conditions. Adult leaf respiration rates were similar when expressed per unit area but were lower in the selected lines when expressed per unit dry weight. Leaf respiration rates were negatively correlated with specific leaf dry weight and with the carbon content per unit area and were positively correlated with nitrogen and sulfur content of the dry matter. The alternative pathway was not involved in respiration in the dark in these leaves. The better carbon economy of tobacco lines selected for low CO₂ survival was not apparently related to an improvement of photosynthesis rate but could be related, at least partially, to a significantly reduced respiration (mainly cytochrome pathway) rate per unit carbon.     

Role of external carbonic anhydrase in light-dependent alkalization byFucus serratus L. andLaminaria saccharina (L.) Lamour. (Phaeophyta)

It has been proposed that many marine macroalgae are able to utilize HCO ₃ ^– for photosynthesis and growth, and that energy-dependent ion pumping is involved in this process. We have therefore studied the light-dependent alkalization of the surrounding medium by two species of marine macroscopic brown algae,Fucus serratus L. andLaminaria saccharina (L.) Lamour. with the aim of investigating the role of extracellular carbonic anhydrase (EC 4.2.1.1.) in the assimilation of inorganic carbon from the seawater medium. In particular, the influence of membrane-impermeable or slowly permeable carbonic-anhydrase inhibitors on the rate of alkalization of the seawater has been investigated. Inhibition of the alkalization rate occurred in both species at an alkaline pH (pH 8.0) but no inhibition was observed at an acidic pH (pH 6.0). The alkalization was found to be light-dependent and inhibited by 3-(3,4-dichlorophenyl)-1, 1-dimethylurea and, thus, correlated with photosynthesis. Alkalization by macroalgae has previously been shown to be proportional to inorganiccarbon uptake. We suggest that alkalization of the medium at alkaline pH in both of the species examined is mainly the consequence of an extracellular reaction. The reaction is catalyzed by extracellular carbonic anhydrase which converts HCO ₃ ^– to OH^– and CO₂; CO₂ is then taken up through the plasmalemma. However, we do not exclude the involvement of other mechanisms of inorganic-carbon uptake.Abbreviations AZ acetazolamide - CA carbonic anhydrase - CAext extracellular carbonic anhydrase - C_i inorganic carbon - DBS dextran-bound sulfonamide - DCMU 3-(3,4-dichloro-phenyl)-1,1-dimethylurea - PPFD photosynthetic photon flux density This study was carried out with financial support by SAREC (Swedish Agency for Research Cooperation with Developing Countries), Carl Trygger's Fund for Scientific Research (Sweden), SJFR (Swedish Council for Forestry and Agricultural Research) and CICYT (Spain). Z. Ramazanov is an invited professor of Ministerio de Educación y Ciencia, Spain.     

Nitrate assimilatory properties of barley grown under long-term N limitation: Effects of local nitrate supply in split-root cultures

The effect of nitrate availability on characteristics of the nitrate assimilatory system was investigated in N-limited barley (Hordeum valgare L. cv. Golf), grown with the seminal root system split into initially equal-sized halves. The cultures were continuously supplied with nitrate-N at a relative addition rate (RA) of 0.09 day^?1, which resulted in relative growth rates (RG) that were ca 85% of those observed under surplus nitrate nutrition. The total N addition was divided between the subroots in ratios of 100:0, 80:20, 70:30, 60:40, and 50:50. For comparison, standard cultures were grown at RAs ranging from 0.03 to 0.18 day^?1. Initially, biomass and N partitioning to the subroots responded strongly and proportionally to the nitrate distribution ratio. After 12-14 days no further effect was observed. The V_max for net nitrate uptake and in vitro nitrate reductase (NR) activity were measured in acclimated plants, i.e., after > 14 days under a certain nitrate regime. In subroots fed from 20 to 100% of the total N addition, V_max for net nitrate uptake increased slightly, whereas NR activity was unaffected. Uptake and NR activities were insignificant in the 0%-subroot. Uneven nitrate supply to individual subroots had negligible effect on the whole-plant ability for nitrate uptake, and the relative V_max (unit N taken up per unit N in whole plant tissue and time) remained about 7-fold in excess of the demand set by growth. Balancing nitrate concentrations (the resulting external nitrate concentrations at a certain RA) generally ranged between 2 and 10 μM at growth-limiting RA, both when predicted from uptake kinetics and when actually measured. When comparing split root and standard cultures when acclimated, it appears that uptake and NR activities in roots respond more strongly to over-all nitrate availability than to nitrate availability to individual subroots.     

A clinical comparison of the tendency to capsular contracture between smooth and textured gel-filled silicone mammary implants.

The aim of this prospective, controlled clinical investigation was to find out if there is a difference in the capsular contracture rate between silicone implants with a smooth or textured surface as the only difference. Twenty-five women with bilateral mammary hypoplasia underwent mammary augmentation. All got a textured implant on one side and a smooth implant on the other. The implants were placed subglandularly. Follow-up examinations were done on six occasions. Three parameters were used for estimation of the tendency to capsular contracture: (1) the patient's opinion on differences in hardness of the breasts, (2) the investigator's classification of capsular contracture, and (3) applanation tonometry. At the end of the follow-up period, after 1 year, all parameters showed with no doubt that the breasts augmented with textured implants had a lower tendency to develop contracting capsules than the breasts augmented with smooth implants.     

On the multiplicity of sugar transport systems in guinea pig jejunum.

A study has been made in everted sacs of guinea pig jejunum to see if the two transport systems of glucose analogues characterized at the brush border membrane vesicles are operative. The transport kinetics of D-galactose and alpha-methylglucoside up to 80 mM concentrations has been studied, as well as the mutual inhibitions between them at low and high concentrations of the substrate and at different concentrations of the inhibitor. Low temperature (20 degrees C) inhibits galactose transport at 0.1 mM (70%) and 40 mM (78%) concentrations. A mass transfer coefficient, KD, somewhat higher for galactose than for alpha-methylglucoside, was obtained when the transport component was abolished by phlorizin. The transport of D-galactose and alpha-methylglucoside seemed to be compatible with the function of one system shared by both substrates, which presents greater affinity for alpha-methylglucoside. The functional existence of two systems of active transport at the brush border of guinea pig was not evidenced in intestinal preparations of whole tissue, due perhaps to the effect of the unstirred water layers. However, differences in KD values and some results of the mutual inhibitions may suggest a second system.     

Absence of limbs and gross body wall defects: an epidemiological study of related rare malformation conditions.

The study is based on almost 10 million births and reports on 215 infants with two unusual malformations: amelia and gross body wall defect. Amelia without body wall defect was present in 116 cases, 67 had body wall defects without amelia, and 32 had both. The total rate was 2.2 per 100,000 births. The infants were divided into five mutually exclusive groups. There were 40 infants (0.4 per 100,000) with agenesis of the body stalk, 18 with amelia and other types of gross body wall defects (0.2 per 100,000), 56 with amelia and malformations other than gross body wall defects (0.6 per 100,000), 41 with amelia (with or without other limb reduction defects) but no nonlimb malformations (0.4 per 100,000), and 60 infants with gross body wall defects of a type other than agenesis of body stalk and without amelia (0.6 per 100,000). A weak trend of decreasing prevalence of these malformations was found during the observation period. Infants with agenesis of the body stalk and infants with amelia combined with other types of gross body wall defects occurred at an increased rate in infants of young women. This maternal age effect is also found with gastroschisis, but not with omphalocele, and may indicate etiological or pathogenetic similarities between gastroschisis and the two former groups of defect. In infants with amelia, additional limb reduction defects could be of any type: transverse, longitudinal, or intercalary. Therefore, amelia may be the end result of different types of disturbances of limb morphogenesis. There was an increased rate of twinning. The relationship with amniotic band syndrome is discussed.     

Long-term changes in the phytoplankton of large lakes in response to changes in nutrient loading

In Sweden the recovery process of the four largest lakes (<500 km²) has been followed since the mid-1970's when the phosphorus loading was reduced by approximately 50%. A ten-year investigation period before that acts as a basis of comparison. The response of the dominating species in the phytoplankton communities in the eutrophic Lake Mälaren and the oligotrophic Lake Vättern is discussed also in relation to a pristine state of the lakes. The long-term investigations with monthly sampling make a natural phytoplankton biomass variation range possible to establish - a range that is mainly due to effects of weather fluctuations. In order to get a tool for water management where disturbing and highly disturbing total phytoplankton volumes can be anticipated from a certain phosphorus concentration, a model is suggested based on experiences from more than 50 Swedish lakes investigated during a series of years.     

Gramicidin channels: a new mechanism for transmembrane transfer of ions (from high resolution x-ray structural studies of the antibiotic)]

The crystal structure of the membrane-active antibiotic-cyclopeptide gramicidin S complex with urea was determined by the X-ray structure analysis. The gramicidin S molecule possesses an antiparallel beta-structure, its slightly twisted 30-membered cycle has a roughly rectangular form about 4.8 x 13.6 A in size, with the lesser side being formed by the main chain atoms of Phe and Pro residues. The maximum size of the molecule is 22.9 A. A characteristic feature of the molecule is the position of the extended side chains of the Orn residues on one side of the molecular cycle in the form of peculiar "legs--tentacles". One of these legs is "fastened" by the intramolecular H-bond to O atom of the nearer Phe4 residue, the other being free. The distance between the terminal NE atoms of the Orn residues is 5.7 A. The side chains of the Phe and Orn2 residues have trans-orientation, those of the Val, Orn7, Leu residues gauche-orientation. For Val1 and Leu3 side chains statistical disorder of the terminal C atoms is realized. The pyrrolidine rings of the Pro residues adopt Cs-C beta-exo conformation. There are one urea and 20 water molecules per one antibiotic molecule in the structure. The positions of three water molecules are fully occupied, the others with the probability of 0.56-0.20. One of the "water" positions is occupied on 2/3 by water, and on 1/3 by the O atom of the alcohol. There is a complicated system of intra- and intermolecular H-bonds in the structure, with and without the participation of water, alcohol and urea molecules. The gramicidin S molecules, collecting around 3(1) axis according to the left-handed double helix, form the channels whose outside hydrophobic surface is built of the side uncharged radicals, the inside surface being built of the main chain atoms, mainly of the O and N atoms and of the ornithine "tails" with uncharged NE atoms at the termini. The outer diameter of the channel is 29-43 A, inner (without ornithine "tails") is about 12.7 A. At the expense of the change of these "tails" conformation, the inner diameter of the channel filled with water molecules may change from 3.4 up to 6.3 A. Thus, the ions and particles of a rather large size may pass through the channel. The gramicidin channels are discovered and described for the first time. The channels in the crystal structure are close-packed under the hexagonal law.(ABSTRACT TRUNCATED AT 400 WORDS)     

One-step synthesis of Gly-Gly-PheNH2 from N-unprotected amino acid derivatives by papain in one-phase liquid media

Summary Papain was able to catalyze the one-step synthesis of Gly-Gly-PheNH₂, from N-unprotected amino acid derivatives. Maximum synthetic activity was obtained for a pH value of 6.5 and for a ]PheNH₂]/[Gly-GlyOEt] ratio of 6. The presence of an organic cosolvent, such as ethylene glycol, influenced the synthetic activity. Synthetic yield was higher than 65% for a 12.5 M cosolvent concentration.     

Engineering of lactose metabolism inE. coli by introducing β-galactosidase/galactokinase fusion enzymes

Summary A series of plasmids encoding -galactosidase/galactokinase fusion proteins with connecting linkers of different lengths and properties separating the enzyme moieties were made.E. coli cells harbouring the genes for these bifunctional enzymes were grown on minimal media with lactose as carbon source in order to asses possible metabolic effects. Differences in growth rates were observed when the cells contained a scavenger enzyme, galactose dehydrogenase, competing with galactokinase for the galactose formed by -galactosidase.E. coli cells coding for fusion proteins with long linkers then reflected markedly slower growth rates.