bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling the soil‐plant‐atmosphere continuum in a Quercus–Acer stand at Harvard Forest: the regulation of stomatal conductance by light, nitrogen and soil/plant hydraulic properties
Authors: WILLIAMS M. , RASTETTER E. B. , FERNANDES D. N. , GOULDEN M. L. , WOFSY S. C. , SHAVER G. R. , MELILLO J. M. , MUNGER J. W. , FAN S.‐M. , NADELHOFFER K. J.
Published: April 2006

Our objective is to describe a multi‐layer model of C3‐canopy processes that effectively simulates hourly CO2 and latent energy (LE) fluxes in a mixed deciduous Quercus‐Acer (oak–maple) stand in central Massachusetts, USA. The key hypothesis governing the biological component of the model is that stomatal conductance (gs) is varied so that daily carbon uptake per unit of foliar nitrogen is maximized within the limitations of canopy water availability. The hydraulic system is modelled as an analogue to simple electrical circuits in parallel, including a separate soil hydraulic resistance, plant resistance and plant capacitance for each canopy layer. Stomatal opening is initially controlled to conserve plant water stores and delay the onset of water stress. Stomatal closure at a threshold minimum leaf water potential prevents xylem cavitation and controls the maximum rate of water flux through the hydraulic system. We show a strong correlation between predicted hourly CO2 exchange rate (r2= 0.86) and LE (r2= 0.87) with independent whole‐forest measurements made by the eddy correlation method during the summer of 1992. Our theoretical derivation shows that observed relationships between CO2 assimilation and LE flux can be explained on the basis of stomatal behaviour optimizing carbon gain, and provides an explicit link between canopy structure, soil properties, atmospheric conditions and stomatal conductance.
Developmental patterns of above‐ground hydraulic conductance in a Scots pine (Pinus sylvestris L.) age sequence
Authors: MENCUCCINI M. , GRACE J.
Published: April 2006

Hydraulic resistance to water flow was measured in branches and stems of Scots pine trees ranging from 7 to 59 years of age in Thetford (East Anglia, UK). On the basis of these measurements, tree above‐ground conductance was calculated and related to the amount of leaf area sustained by each tree. Branches at the crown bottom had a lower proportion of sapwood area and a lower total hydraulic conductance than branches of the same diameter at the tree top. Within branches, most of the hydraulic resistance was located near the needles. Tree above‐ground conductance was positively related to tree diameter and inversely related to tree height. Compared with young trees, mature trees had about 4 times less above‐ground conductance per unit of leaf area. Apparently, the increase in pathway length associated with tree height growth could be only partially compensated for by the increase in conductive capacities resulting from diameter growth. We argue that this reduction may account for reported decreases of stomatal conductance with tree age. It is suggested that the increase in branchiness associated with tree maturation may represent a compensation mechanism to reduce the overall resistance to water flow in the crowns.
The effect of Albugo Candida (white blister rust) on the photosynthetic and carbohydrate metabolism of leaves of Arabidopsis thaliana
Authors: TANG X. , ROLFE S. A. , SCHOLES J.D.
Published: April 2006

Albugo candida (pers.) O. Kuntze (white blister rust) is a biotrophic fungus which infects cruciferous plants including Arabidopsis thaliana (L) Heynh. We report the effect of this pathogen on the photosynthetic and carbohydrate metabolism of A. thaliana. As infection progressed A. Candida caused a reduction in the rate of photosynthesis when measured at either ambient or saturating concentrations of CO2. These data suggested that both chlorophyll and Rubisco were lost from regions of infected leaves, and measurements of chlorophyll, Rubisco content and activity supported these observations. The reduction in the rate of photosynthesis was not caused by closure of stomata as transpiration was unaffected by the disease. Infected leaves accumulated both soluble carbohydrates and starch. The activities of sucrose‐phosphate synthase, sucrose synthase and ADP glucose pyrophosphorylase did not change in response to infection. However, the activities of both the wall‐bound and soluble acid invertases were higher in infected leaves than in controls; a new soluble invertase isoform with a pl of 5‐1 appeared in infected leaves. The possible origin of the increase in wall‐bound and soluble invertase activities and its effect on the carbohydrate and photosynthetic metabolism of the leaf are discussed.
Long‐ and short‐term responses of leaf carbohydrate levels and photosynthesis to decreased sink demand in soybean
Authors: MORCUENDE R. , PÉREZ P. , MARTÍNEZ‐CARRASCO R. , MARTÍN DEL MOLINO I. , SÁNCHEZ DE LA PUENTE L.
Published: April 2006

Axillary buds and the apical portion of shoots of soybean [Glycine max (L.) Merr. cultivar Turchina] plants were trimmed to investigate long‐term regulation of photosynthesis by sink demand at ambient CO2 and 22 °C. Also, in intact and trimmed shoots, the CO2 level was increased to 660 μmol mol−1 and temperature was lowered to 5°C to examine the superimposed short‐term responses of photosynthesis to low sink demand. Under growth conditions, trimming the shoots increased leaf photosynthesis and the levels of sucrose, glucose‐6‐phosphate (G6P) and 3‐phosphoglycerate (PGA), as well as the G6P/fructose‐6‐phosphate (F6P) and sucrose/starch ratios, while it decreased the level of starch and the triose‐phosphate (glyceraldehyde 3‐phosphate and dihydroxyacetone phosphate, TP)/PGA ratio. Photosynthesis enhancement was accompanied by increased chlorophyll contents and ribulose‐l,5‐bisphosphate carboxylase oxygenase (Rubisco) activity. Sink removal consistently increased photosynthesis measured under a variety of conditions (growth CO2 or a short‐term change to 660 μmol mol‐1 CO2; growth temperature or a short‐term change to 5 °C), except when low temperature was combined with ambient CO2; the increase in photosynthesis was higher under short‐term elevated CO2 than at ambient CO2. In contrast with its effect at ambient CO2, shoot trimming increased the levels of TP and ribulose‐1,5‐bisphosphate (RuBP) and the TP/PGA ratio under high‐CO2 conditions.
A comparison of the composite and repeat pressurization methods of pressure–volume analysis for shoots of four North American conifer species
Authors: PARKER W. C. , COLOMBO S. J.
Published: April 2006

Significantly different water relations attributes were derived for temperate conifers measured using the repeat pressurization (RP) and composite (CM) pressure–volume (PV) procedures. In the RP method, single shoots were measured 10–20 times for xylem water potential and mass during air‐drying to produce each PV curve. In contrast, for CM PV curves 25–30 shoots were air‐dried to relative water contents (R) ranging from 1.0 to 0.5 before being pressurized once. Aggregation of these 25–30 paired values produced single PV curves. Pinus banksiana, P. resinosa and Picea mariana, but not Pinus strobus, had lower full turgor osmotic potential, shallower slope of the linear segment of the PV curves and higher symplast fraction with the CM method. Data points along the linear segment of PV curves were obtained to lower R using the CM method. Reanalysis using similar R ranges eliminated differences between PV methods for Picea mariana but not Pinus banksiana and P. resinosa.
Carbon and nitrogen economy of four Triticum aestivum cultivars differing in relative growth rate and water use efficiency
Authors: VAN DEN BOOGAARD R. , GOUBITZ S. , VENEKLAAS E. J. , LAMBERS H.
Published: April 2006

We investigated physiological and morphological traits underlying variation in relative growth rate (KGR) among wheat cultivars. Subsequently, we determined whether higher RGR is correlated with higher water demand and lower plant water use efficiency (WUEp). Further, the correlation between water use efficiency and leaf nitrogen concentration was examined. For this purpose we chose lour cultivars contrasting in RGR or WUEp. Gas exchange of shoots and respiration of roots were measured on intact plants over a 24 h period, and total carbon and nitrogen concentrations of all plant parts were determined. The highest RGR was achieved by the cultivars with the highest leaf area ratio. WUEp was strongly dependent on photosynthetic water use efficiency and was highest for the cultivars with the highest rate of photosynthesis, which achieved higher rates of photosynthesis per unit leaf nitrogen. We found no evidence for a functional or genetic link between the physiological traits underlying differences in RGR (specific leaf area and leaf area ratio) and those causing variation in water use efficiency (photosynthetic rate and transpiration rate). These results indicate that, in wheat, it may be possible to select simultaneously for traits associated with a high WUEp and a high RGR.
Effects of nitrogen and phosphorus deficiencies on levels of carbohydrates, respiratory enzymes and metabolites in seedlings of tobacco and their response to exogenous sucrose
Authors: PAUL M. J. , STITT M.
Published: April 2006

A simple method of growing plants in agar was exploited to investigate the effect of long‐term nitrogen (N) and phosphorus (P) deficiencies on respiratory metabolism and growth in shoots and roots of Nicotiana tabacum seedlings, and their interaction with exogenously supplied sucrose. Levels of hexose phosphates and 3‐phosphoglyceric acid (3‐PGA) were low in P‐deficient shoots and roots and high in N‐deficient shoots and roots. The ratio of hexose phosphates to 3‐PGA and levels of fructose‐2,6‐bisphosphate were high in P‐deficient plants and low in N‐deficient plants. These data reflect differences in the way metabolism was perturbed, yet both deficiencies were associated with increased root growth relative to shoot growth, starch accumulation in the shoots, and soluble carbohydrate accumulation, especially hexoses, in the roots. Enzymes for sucrose degradation (sucrose synthase, acid and alkaline invertase) and glycolysis (phosphofructokinase, pyrophosphate‐dependent phospho‐fructokinase and pyruvate kinase) remained unaltered or declined in the shoots and roots. The accumulation of hexoses in roots of N‐ and P‐deficient plants may result from maintenance of high invertase activities relative to sucrose synthase and glycolytic enzymes in the roots. The possibility that hexose accumulation may drive preferential root growth osmotically in N and P deficiencies is discussed. The addition of sucrose to roots to further investigate the interaction of carbohydrates with growth and allocation in low N and low P produced clear effects even though endogenous levels of soluble carbohydrate were already high in the nutrient‐deficient plants. In complete nutrition, growth was stimulated, protein content particularly of the roots was increased and there was a preferential increase in activity of sucrose synthase in roots. At low P, enzyme activities in roots were increased, including sucrose synthase, and protein content increased, particularly in the roots, but there was no increase in growth. In N‐deficient plants, exogenous sucrose led to decreased protein, Rubisco and chlorophyll content in shoots, in contrast to the other conditions, and a higher protein content and a general increase of catabolic enzyme activities and growth in the roots.
The effects of enhanced levels of calcium on the gravireaction of sunflower hypocotyls
Authors: BAGSHAW S. L. , CLELAND R. E.
Published: April 2006

A current hypothesis states that there is a redistribution of wall calcium from the lower to the upper sides of horizontal shoots during gravireaction, and because calcium stiffens walls, the unequal calcium distribution results in differential wall extensibility on the upper and lower sides, and thus, causes unequal growth. If this hypothesis is valid, then saturating the cell walls with calcium should minimize the effect of calcium redistribution, and thereby inhibit gravicurvature and stiffen the walls. To test this hypothesis, sunflower seedlings were grown on agar containing 0 to 50molm‐3 CaCl2. The wall‐bound calcium content of the tissues increased as the external concentration of CaCl2 increased, and the epidermal layers were saturated with calcium by the 10molm‐3 CaCl2 treatment. Contrary to the predictions from the hypothesis, the vertical growth and the gravicurvature rate of plants grown in 10molm‐3 CaCl2 were actually accelerated, and wall extensibility, as measured by the Instron technique, was unaffected. These results contradict the hypothesis, and provide further evidence that wall‐bound calcium is not involved in the reaction phase of gravicurvature.
Temperature and growth‐induced water potential
Authors: BOYER J. S.
Published: April 2006

When the steins of dark‐grown soybean [Glycine max (L.) Merr.] seedlings grew rapidly at favorable temperatures in saturating humidities, a water potential of about 0·2 MPa was induced by growth ($pSo‐$pSw, where $pSo is the water potential of the basal nonelongating tissue and $pSw is the water potential of the elongating tissue). If this water potential was caused by high concentrations of solute in the apoplast, as has been proposed, lowering the temperature should have little effect on the potential. On the other hand, if the water potential was caused by apoplast tensions generated by growth, then the tensions should disappear as growth is inhibited by low temperatures. We observed that the growth‐induced water potential became too small to detect when growth was inhibited by temperatures as low as 13—5 °C. The disappearance was observed as a rise in apoplast water potential using a thermocouple psychrometer for intact plants, a rise in cell turgor using a miniature pressure probe and a decrease in apoplast tensions using a pressure chamber. The disappearance was not caused by a loss of solute from the apoplast because the tensions fully accounted for the growth‐induced water potential at all temperatures. The results are consistent with the lack of solute measured directly in the apoplast solutions at high temperatures (Nonami & Boyer 1987). Therefore, it was concluded that little solute was present in the apoplast at any temperature, and the growth‐induced water potential was associated mostly with a tension that moved water from the xylem and into the surrounding cells to meet the demand of cell enlargement.
Rapid and reversible modifications of extension capacity of cell walls in elongating maize leaf tissues responding to root addition and removal of NaCl
Authors: NEUMANN P. M.
Published: April 2006

A creep extensiometer technique was used to provide direct evidence that short (20 min) and long‐term (3d) exposures of roots to growth inhibitory levels of salinity (100mol m‐3 NaCl) induce reductions in the irreversible extension capacity of cell walls in the leaf elongation zone of intact maize seedlings (Zea mays L.). The long‐term inhibition of cell wall extension capacity was reversed within 20 min of salt withdrawal from the root medium. Inhibited elongation of leaf epidermal tissues was also reversed after salt removal. The salt‐induced changes in wall extension capacity were detected using in vivo and in vitro assays (shortly after localized freeze/thaw treatment of the basal elongation zone). The rapid reversal of the inhibition of wall extensibility and leaf growth after salt removal from root medium of long‐term salinized plants, suggested that neither deficiencies in growth essential mineral nutrients nor toxic effects of NaCl on plasmamembrane viability were directly involved in the inhibition of leaf growth. There was consistent agreement between the scale, direction and timing of salinity‐induced changes in leaf elongation growth and wall extension capacity. Rapid metabolically regulated changes in the physical properties of growing cell walls, caused by osmotic (or other) effects, appear to be a factor regulating maize leaf growth responses to root salinization.
Stomatal and nonstomatal limitations of photosynthesis in 19 temperate tree species on contrasting sites during wet and dry years
Authors: KUBISKEM M. E. , ABRAMS M. D.
Published: April 2006

A unique approach was used to evaluate stomatal and nonstomatal constraints to photosynthesis in 19 naturally occurring, deciduous tree species on xeric, mesic and wetmesic sites in central Pennsylvania, USA, during relatively wet (1990) and dry (1991) growing seasons. All species exhibited significantly decreased stomatal conductance to CO2(gc) in 1991 compared to 1990. The mesic species had drought related decreases in photosynthesis (A) attributed primarily to increased absolute stomatal limitation toA(Lg), whereas in the wet‐mesic species, the absolute mesophyll limitation (Lm) was at least as important asLgin limitingAduring drought. The xeric species maintained relatively highAduring drought despite decreasedgc.In the xeric and mesic species,Lmdecreased andLgincreased during drought due to stomatal closure. From xeric to mesic to wet‐mesic, the relative stomatal limitation (Ig) generally decreased faster, and relative mesophyll limitations toAincreased faster, with increasinggcsuggesting greater photosynthetic capacity (i.e. greater potential maximumA) with increasing drought tolerance rank of species. Few species exhibited a significant drought‐related decrease in photosynthetic capacity. The results of this landscape‐based study indicate that the interaction of stomatal and nonstomatal limitations ofAvary in a manner consistent with species' drought tolerance and site conditions, and that nonstomatal constraints toAin field plants during a moderate, season‐long drought were generally not as severe as reported in controlled studies.
A branch bag technique for simultaneous CO2 enrichment and assimilation measurements on beech (Fagus sylvatica L.)
Authors: DUFRENE E. , PONTAILLER J.‐Y. , SAUGIER B.
Published: April 2006

A cheap CO2 enrichment system was designed to perform continuous gas exchange measurements of branches of mature European beech trees (Fagus sylvatica L.). Branches were grown at ambient (350 cm3 m‐3) and elevated CO2 (700cm3 m‐3) during the whole 1992 leafy period. Leaks resulting from airtightness defaults in the system appeared to be low enough to measure accurately net CO2 assimilation and transpiration rates during the day. However, the CO2 exchange rates during the night (respiration) were too low to allow accurate measurements. Elevated CO2 had a great effect on the net assimilation rate of branches via its influence on both the C3 photosynthetic pathway and the shade‐tolerance of beech trees (85% increase). The A/Ca curves showed no acclimation effect to high CO2, both control and enriched branches increasing their net assimilation in the same way. The decrease of net assimilation rates in mature leaves was similar for both control and enriched branches. The pattern of daily transpiration rates remained the same for both control and enriched branches, hence we can assume that there was no visible CO2 effect on stomata.
Action du glycocolle sur le développement in vitro des colonies prothalliennes de Gymnogramme calomelanos, Filicinée Polypodiacée.
Authors: Sossountzov I.
Published: April 2006

Dans les colonies prothalliennes de Gymnogramme calomelanos, le glycocolle (glycine), comme source unique d'azote, augmente le nombre de prothalles filiformes aux dépens du nombre de prothalles cordiformes.

Le nombre moyen d'anthéridies est le même quelle que soit la concentration des milieux cu azote (la prolifération des prothalles n'est possible (qu'entre 0,5 el 10 mM/glycocolle). La sexualité archégoniale est fortement maxima en présence de 5 mM/glycocolle ou davantage. La longueur moyenne des prothalles est faiblement maxima sur les milieux à 5 et à 6 mM. La largeur moyenne varie à mesure qu'augmente la concentration des milieux en glycocolle (trios maximums: au niveau de 0,5 de 3 à 5 et de 8 à 10 mM). La variabilité des moynnes est toujours plus élevée sur les prothalles des cultures normales que sur ceux des cultures aberrantes.

Entre le 1er et le 6e repiquages, la sexualité et les dimension des prothalles cordes demeurent, dans l'ensemble, constantes. Leur variabilité s'atténue.

Comparés a la solution de Knop normale (10.94 mA/azote), les milieux à glycocolle qui assurent une croissance normale des cultures (1,5 à 5 mM) stimulent la prolifération des prothalles filamenteux aux dépens des prothalles cordés, inhibent le développement des anthéridies et des dimensions prothalliennes, mais exaltent la sexualité archégoniale. Il en est de même si la comparaison est faite à concentration en azote égale (cultures aberrantes et normales).
Action de quelques acides amiués aliphatiques sur le délveloppement in vitro des colonies prothalliennes de Gymnogramme calomelanos, Filicinée Polypodiacée
Authors: Sossountzov Iaroslav
Published: April 2006

L'étude présentée ici compléte celle qui a été précédemment consacrée à l'action du glycocollo sur le développement in vitro des colonies prothallinnes de Gymnogramme calomelanos (10. 11).
Der Verlauf der endogenen Tagesrhythmik bei photo‐periodisehen Storlieht‐Versuchen mit Soja
Authors: Bünning E.
Published: April 2006

Zusainmenfassung

Es wird bei Soja mit Hilfe der tagesperiodischen Blattbewegungen der Verlauf der endogenen Tagesrbytbmik unter Licht‐Dunkel‐Zyklen untersucht, die denen In Wareings Experimenten entsprechen.

Bei den langen Dunkel‐Periodeu zwischen 39–51 Stunden Dauer, die mit Haupt‐Lichtperioden von 6 oder 9 Stunden alternieren, tritt etwa 20 Stunden nach deren Beginn eine Dunkelstarre ein. Die nächste Lichtperiode induziert erneut eine nicht mehr als etwa 30 Stunden andauenide Rhythmik, der dann wieder eine Dunkelstarre folgt.

Störlicht von 30 Minuten Dauer hat während der Zeit, in der die Rhythmik läuft, einen relativ geringen Einfluß auf den Zeitpunkt von Hebung und Senkung. Wirkt es aber wäbrend der Dunkelstarre, so bedingl es ebenso wie eine Haupt‐Lichtperiode einen neuen Start der endogenen Tagesrhythmik.

Aus diesen Befunden lassen sich die Ergebnisse Wareings über die Wirkung des zu verschiedenen Zeiten der Duukelperiode gebotenen Störlichts erklären.
Studies on the Physiology of the Soil Yeast Cryptococcus terricolus
Authors: Pedersen T. A.
Published: April 2006

A new species of yeast, belonging to the genis Cryptococcus, and named Cryptococcus terricolus nov. spec., was recently isolated from different Norwegian forest soils (Pedersen 1958). Besides being of taxonomic interest, this yeast was found to produce lipids in great quantities. The presence of lipids could easily be estahlished by microscopical examination, owing to the formatinn of a large lipid globule in every cell. In the present paper, investigations on the growth conditions of the organism are presented. The factors influencing the lipid synthesis will be treated in a future article.
Investigations of Ion Uptake by Tissue Slices II. The effect of 2,4‐diuitrophenol on the uptake of calcium hy potato slices
Authors: Chasson Robert M.
Published: April 2006

DNP (2,4‐dinitrophenol) has been found by a number of investigators to inhibit both anion and cation uptake in a variety of plant tissues (Arisz 1953, Hopkins 1956, Middleton 1955, Ordin and Jacobson 1955, Robertson et al. 1951, Russell and Ayland 1955). Following some preliminary investigations, Chasson and Levitt (1956) reported in a brief note that calcium uptake by potato slices was stimulated by the addition of DNP. Presented below are the results of a more thorough study of these initial observations.
Studies on Mono‐ and Di‐caryotic Mycelia of Collybia velutipes
Authors: Aschan‐Åberg Karin
Published: April 2006

The present paper forms part of a series which was begun with mainly genetical aims in view (Aschan 1952). It was soon found that morphologically different strains of Collybia velutipes could not be sufficiently characterized by such simple means as the determination of their dry weight production under constant conditions, and other methods for quantitative description of the strains were sought, e.g. the measurement of their cellulolytic activity (Norkrans and Aschan 1953. Aschan and Norkrans 1953). Measurements of the linear growth rate of the mycelia, of the temperature dependence of their growth, and of their nitrogen and phosphorous content are now presented. Some of the experiments were also planned in the hope of finding some clue to the factors which regulate fructification and the phenomenon of incompatibility.
Maleic Hydrazide and Isonicotinyl Hydrazide as Carbonyl Reagents
Authors: Suzuki Yonezo
Published: April 2006

The effects of maleic hydrazide (MH) and isonicotinyl hydrazide (INH) on the reactions catalyzed by pea cotyledon amine oxidase, carrot root l‐glutamic decarboxylase, and wheat seedling transaminase have been studied.

The activity of amine oxidase is inhibited if it is incubated with MH or INH before the addition of substrate, and it is also dependent on the time of preincubation.

The effect of MH and INH is depressed or prevented by α‐ketoglutarate, pyruvate, pyridoxal phosphate, and pyridoxal but not pyridoxine, reduced glutathione, cysteine, or CuCl2.

MH and INH inhibit the l‐aspartate transamination by wheat mitochondria. They only slightly inhibit the decarboxylation of l‐glutamate by the carrot root enzyme.

The role of MH and INH is discussed as carbonyl reagents in plant metabolism. decarboxylase. Thus, the mechanism by which Mh and INH inhibit action of l‐glutamic decarboxylase is rather complicated and will not be elucidated very soon. The inhibition of aspartate transamination by MH and INH can be interpreted in terms of two processes: the combination of the inhibitors with α‐ketogultarate and pyridoxal phosphate which is a coenzyme of the transaminase. Since transamination is one of the most important reactions in the amino acid metabolism controlling the protein level in living cells, the effect of MH and INH should be noticed as shown above. Kim and Greulach (1963) report that MH and 5‐fluorouracil markedly reduce the content of free amino acids and DNA in Chlorella pyrenoideas; this in interesting in view of the present results concerning the transamination.
The Influence of CO2 Concentration and pH on Two Chlorella Species Grown in Continuous Light
Authors: Nielsen E. Steemann , Willemoes M.
Published: April 2006

Both Chlorella pyrenoidosa and Chlorella vulgaris grow equally well at 20°C aerated with ordinary air or mixtures of air with 5 or 12 per cent CO2 (5 klux continuous light). Whereas C. vulgaris relatively rapidly adapts to a higher CO2 tension, adaptation takes about 24 hours for C. pyrenoidosa.

In Chlorella vulgaris pH in the range 3.6–7.6 has no apparent influence on the rate of photosynthesis in experiments having a duration of two hours. This is true both for algae grown aerated by ordinary air and for algae grown with a mixture of 5 per cent CO2 in air. The adaptation time must be short. In Chlorella pyrenoidosa the same is found for algae in ordinary air, whereas an influence of pH is seen in some experiments where the aeration was by 5 per cent CO2 in air.

As is to be expected, the rate of photosynthesis in C. pyrenoidosa during the first two hours is very much influenced by the concentration of free CO2. The highest rate is found at the CO2 concentration at which the algae had been growing previously. The influence on the rate of photosynthesis in C. vulgaris is very much less, although in principle the same.

The investigation of the corresponding influence on the rate of respiration is complicated by considerable variation from one series to another. In C. vulgaris this is particularly of importance. In C. pyrenoidosa, the highest rate of respiration is generally found at the CO2‐concentration at which the alga had been growing before the experiment.

It seems probable that variations between similar series is due to the fact that the algae were grown in continuous light but with dilution with fresh culture medium when the optical density had reached a certain magnitude. Algae grown in this way are neither synchronized nor non‐synchronized.Our thanks are due to the Danish State Research Foundation for financial support.
Effects of Gibberellic Acid on Growth and Parthenocarpy in the Dwarf Telephone Pea
Authors: Bonde Erik K.
Published: April 2006

Growth in height and production of seedless pods wore studied in Dwarf Telephone pea seedlings treated with relatively large amounts of the potassium salt of gibberellic acid applied in solution to leaflets. Such treatment produced a saturation in growth in height with 2 mg or more per plant when the plants were allowed to grow to maturity. Larger amounts caused no inhibitory effects on growth. Maximum growth with 1 mg per plant was attained only if the treated leaflets were left on the plant for about 14 days, at least, but increasing numbers of weekly 10‐mg applications produced no additional growth affects beyond two applications. Increasing age of plants from 10 to 59 days of age at the time of single 10‐mg applications per plant resulted in decreasing final heights.

Gibberellic acid caused the formation of seedless pods a number of weeks after application, and deformed flower petals, elongated peduncles, and conspicuously inflated pods were associated with seedlessness. GA was most effective in inducing parthenocarpy when applied to the first true leaves of young seedlings and became progressively less effective with age. A complete absence of seeds in pods formed on the main plant axis was produced by one application of 10 mg GA per plant, while six applications were required for the suppression of seed formation on side branches.
The in vitro Germination of Pollen of Setaria sphacelata
Authors: de Bruyn J. A.
Published: April 2006

The effects of various substances upon germination and tube growth of pollen of Setaria sphacelata were investigated in hanging‐drop culture. Both sucrose (0.6–0.7 M) and boron (1–5 ppm, as borate) are essential for germination. Comparable results were obtained with boric acid, sodium tetraborate and tri‐n‐butyl borate as boron sources, but sodium tetraphenylboron was inhibitory.

Good germination and growth were obtained with raffinose and cellobiose, alone or in combination with sucrose (total 0.5 M); 0.25 M rhamnose, lactose and glycerol were without effect, and xylose, galactose and glucose were slightly inhibitory in the presence of 0.25 M sucrose; 0.25 M arabinose, fructose, mannose, sorbose, maltose, mannitol and sorbitol completely inhibited germination, even in the presence of 0.25 M sucrose.

IAA and GA (0.01–10 ppm) could not replace or supplement the effects of borate on germination and growth, indicating the pollen to be self‐sufficient in this respect. Riboflavin (0.1–10 ppm) and calcium pantothenate (1–100 ppm) stimulated germination and growth, whereas 0.01–10 ppm of thiamine, pyridoxine, nicotinic acid and ascorbic acid were generally without effect.

Although copper sulphate, manganese sulphate, zinc sulphate and ammonium molybdate could not replace boric acid, 1.0 ppm of copper, manganese and zinc stimulated germination and growth in the presence of boron.

In no instance were tubes found comparable in length to those required for fertilisation in vivo. It was concluded that the pollen probably requires a complex mixture of substances, including sucrose and borate, before this can be achieved in vitro.
Further Observations on the Inhibition of Prototheca zopfii Growth by 3‐Amino‐l,2,4‐triazole
Authors: Casselton P. J.
Published: April 2006

The concentration of amitrole (3‐amino‐l,2,4‐triazole) causing 50 per cent inhibition of Prototheca zopfii growth is 1.25 mg/100 g at 25°C. This inhibition is not reversed by adenine. 50 per cent inhibition of growth is also caused by 100–120 mg/ 100 g 2‐aminopurine and this inhibition is partially reversed by 40 mg/100 g adenine, the highest adenine concentration tested due to solubility problems. Imidazoleglycerol accumulation occurs in the medium of cells grown in the presence of amitrole.
Active and Passive Components of Sulfate Uptake in Sunflower Plants
Authors: Pettersson Sune
Published: April 2006

The aim of the investigation was to identify components of active and passive ion uptake and transport in roots of plants and to assess their quantitative relations under different external and internal conditions.

The uptake of radiosulfate and water by young sunflower plants from complete nutrient solutions labelled with 35S was studied.

The metabolism‐linked nature of the sulfate uptake in the root following the passive migration into the apparent free space (AFS) was demonstrated by the addition of sodium. selenate, 2,4‐dinitrophenol, potassium cyanide, and sodium azide to the nutrient solutions.

The magnitude of the AFS measured on a root volume basis varied between 14 and 57 per cent depending on the pretreatment of the plants and the sulfate concentration of the nutrient solution. The variations were supposed to be due to different capacity to bind sulfate by exchange‐adsorption within the AFS.

The amounts of sulfate in different fractions of the total AFS‐uptake were computed under certain theoretical assumptions.

A quantitative connection was proposed between the magnitude of the adsorbed sulfate fraction in the AFS and the rate of active uptake into the symplasm. The exchange‐adsorption probably constitutes the initial stage of active ion uptake. The stimulating effect by water on ion uptake would be an increase of the speed of transporting ions to, from, or along the adsorption sites in the AFS.

Experiments conducted at temperatures in the nutrient solution between 5 and 35 C elucidated the multistep nature of ion transport within a root.
A Comparison of Phenolic Constituents of Pinus monticola Resistant and Susceptible to Cronartium ribicola
Authors: Hanover J. W. , Hoff R. J.
Published: April 2006

Polyphenols and simple phenols in Pinus monticola Dougl. foliage and hark were studied in relation to host resistance to Cronartium ribicola J. C. Fisch. ex Rabenh. More than 50 phenolic substances were detected but no qualitative differences were found between resistant and susceptible trees. Some evidence is given for a quantitative relationship between one polyphenol in white pine foliage and resistance to blister rust. This compound may be a guaiacyl derivative. Differences in phenolics due to tree‐to‐tree variation, needle age, tissue (foliage versus bark), and season of year are also reported.
Artificially Induced Water and Sulfate Transport through Sunflower Roots
Authors: Pettersson Sune
Published: April 2006

A new experimental method is used to determine simultaneously the quantity and composition of the sap exuded by a detopped root system at the same time that a pressure deficit of desired magnitude can be applied to the stem stump.

The technique was used in a study of the transport of radioactive sulfate through the roots of young sunflower plants placed on complete nutrient solutions labelled with35S.

The complications by the time factor on the composition and rate of the sap stream in experiments of this type were observed and discussed. The time of detopping the roots was very critical as the conditions of sulfate transport were greatly changed some time after the excision.

A rectilinear connection existed between the rate of sulfate transport in the sap and the water flow at sap flow velocities comparable with transpiration rates. When the transport of water was very slow, the rate of sulfate transport became constant and independent of the water stream. It was suggested that diffusion or water flow could act as motive force for the ion transport in some non‐metabolic phase of transfer in the roots. The addition of 2,4‐DNP to the test solution severely interfered with the water and sulfate transport conditions in the roots.
The Influence of Photosynthetic Factors and Metaholic Inhibitors on the Uptake of Phosphate in P‐Deficient Scenedesmus
Authors: Kylin Anders
Published: April 2006

The cells used in the present investigation had a phosphate content of about 20 per cent as compared with the status in normal cultures. The uptake of phosphate during a period of 4 hours was determined at a pH of 6,5, kept constant with the aid of a citrate buffer.

In the absence of CO2, light increased the uptake of phosphate with saturation around 14,000 erg/cm2s. With 5 per cent CO2 in the air the relationship was more complicated, and the uptake of phosphate must he related to more than one process during active photosynthesis.

The inhibiting effect of CO2 in air was noticeable already at low concentrations both in light and in darkness. With the system used, this supports earlier indications for internal recycling of orthophosphate, CO2 was inhibiting also in nitrogen in the light.

Selenate in a concentration of 2 mM gave a slight and rather irregular inhibition.—Anaerobiosis had no effect in the light but gave a large decrease in the dark.—DNP (0.1 mM) was somewhat more active in the dark than in the light. The lower concentrations tested had no effect in either case.—Menadione (0.1 mM) inhibited strongly, and more in illuminated than in non‐illuminated cells.
The Implication of Auxin in the UV Promoted Expansion of Etiolated Bean Leaf Disks
Authors: Spang Henry A.
Published: April 2006

A promotion of expansion of etiolated bean leaf disks by ultraviolet (UV) radiation was confirmed. The optimum conditions for the effeet were found to be 5 seconds UV exposure followed by 24 hours of incubation at 25°C and pH 6.2. Macerations and sections of the treated and control disks indicated that the basis of the response was an increase in the number of cells in the UV treated disks. Experiments with indolebutyric acid (IBA) and p‐chlorophenoxyisobutyric acid (PCIB) indicated that the UV apparently acted to reduce a superoptimal endogenous auxin level to an optimum level which resulted in promotion of the expansion.
An Improvement in the Sensitivity of the Salkowski Reagent for Tryptamine, Tryptophan and Indoleacetic Acid
Authors: Perley James E. , Stowe Bruce B.
Published: April 2006

The reaction of indoles with the Salkowski reagent has been examined. It was found that the concentration of acid as well as the concentration and anionic component of the iron salt employed are critical factors in the choice of a reagent that will fail to react—or will react maximally with a given indole. Tryptamine can be reproducibly assayed with a reagent containing 0.01 M Fe(NO3)3 in 7.0 M HCIO4. Two ml of this reagent are added to two ml of the sample. The absorbancy is read at 450 nm after 90 minutes under uniform light conditions. Versions of this reagent can also be used for the quantitative colorimetric determination of tryptophan or indoleacetic acid.
Effect of Oxygen on the Rate of Photorespiration in Detached Tobacco Leaves
Authors: Tregunna E. B. , Krotkov G. , Nelson C. D.
Published: April 2006

The rate of carbon dioxide exchange in both light and darkness by detached tobacco leaves placed at various oxygen concentrations was measured by an Infra‐Red CO2 Analyzer and a Clark oxygen electrode. It was observed that during illumination oxygen had two different effects. One was to stimulate carbon dioxide evolution and the other to inhibit carbon dioxide absorption.

Concentration of carbon dioxide at compensation point was found to be a linear function of oxygen concentration and this has been explained as due mainly to an increased evolution of carbon dioxide. Such an evolution during illumination has been called photorespiration. Increased concentrations of oxygen also had a stimulating effect on the magnitude of the initial post‐illumination burst of carbon dioxide in darkness, but no effect on the subsequent steady rates.

These data have been explained as due to the suspension of regular respiration in darkness and its replacement by a different process, tentatively called photorespiration.

A second effect of oxygen was to reduce the efficiency (called “carboxylation efficiency”) with which a leaf was able to remove carbon dioxide from the atmosphere.
Transport of Kinetin‐814C in Petioles
Authors: Lagerstedt H. B. , Langston R. G.
Published: April 2006

Several differences in the translocation pattern of radioactive kinetin in plant petioles were determined. Radioactivity from kinetin‐8‐14C (Kn*) moved from donor agar blocks through petioles of bean and cocklebur but not of cotton. There was no difference in basipetal or acropetal movement of radioactivity from Kn* in cocklebnr petioles, but there was in bean petioles. In bean petioles this movement was preferentially basipetal, but it was influenced by the age of the petiole and by the presence of added indoleactic acid. The combination treatment accelerated the basipetal movement of radioactivity from Kn* in young bean petioles and not in old ones.

All data is based on radioactivity translocated into receiver agar blocks which were assayed individually in a liquid scintillation spectrometer. The results show that plant species, direction of transport, age of tissue, and presence of IAA can all influence the translocation of Kn* in petioles.
Stimulation of abscission of Petioles of Phaseolusavulg ris by Sucrose and Gibberellic acid
Authors: Devlin Robert M. , McIntyre Owen M.
Published: April 2006

The influence of Grand sucrose, alone and in combination, on the abscissionarate of petioles of the common be n plant was investigated. application of either Gaorasucrose to the distalatip of one of apair of opposite petiolesa celebrated the abscission of the treated petiole. When the two compounds were applied simult neously less than additive effect was observed. The abscission rate of untreated petioles remain ed practically unchanged by treatment of their opposite partners with G a or sucrose or combinations of these two compounds.
Active Water Transport in Plants
Authors: Oertli J. J.
Published: April 2006

There is no unanimous agreement about a definition of active water transport. The following definition was accepted: During an active transport or process, the water potential must increase and this gain must depend on the decrease in free energy in some metabolic process (5, 10).

The passage of water from soil through plants to atmosphere can involve several active steps. A removal of solutes from the water represents a gain of osmotic water potential and this gain can exceed concurrent losses of other water potential components, resulting in a net gain of water potential.

An increase of water potential was demonstrated in barley seedlings. Bleeding and guttation liquids were usually found to be more dilute than the external solution. Osmotic and gravitational potential components in exudates, thus, increased while other components remained virtually constant relative to the external solutions. The gain in osmotic potential depends most likely on a metabolic removal of salts: hence, the requirements for an active transport are satisfied. Active water transports, however, are not dependent or connected with the development of root pressure.

The existence of active water transports disproves the rule that water flows only along water potential gradients (only against diffusion pressure deficit gradients).

A gain in leaf water potential has a physiological significance since the range of soil water potentials a plant can withstand without wilting is extended.
Aflatoxins of Aspergillus flavus Grown on Cassava
Authors: Nartey Frederick
Published: April 2006

Aspergillus flavus Link ex Fries was grown on cassava (Manihot utilissima) and Czapek‐Dox media at 31±1°C and 90 per cent relative humidity for 8 weeks. Isolation and purification of the toxic and carcinogenic metabolic products of the mould by paper and thin layer chromatography are described. High concentrations of aflatoxin B1, B2, G1 and G2 were synthesized by the mould grown on cassava for 4 weeks. In addition to these four major toxic components, 9 other fluorescent materials were observed on the chromatograms of crude products from cassava.

It is concluded that the high moisture, high polysaccharide and low nitrogen content of cassava constitute a favourable nutritional condition at high temperatures and high relative humidity for the growth of A. flavus and the synthesis of relatively high concentrations of aflatoxin. This conld represent a serious health hazard in the moist tropics.
Experimental Studies on the Physiology of the Phycobiont and Mycobiont Ramalina ecklonii By
Authors: Fox Cecil H.
Published: April 2006

The lichenized fungus and alga of the fruticose lichen Ramalini ecklonii were isolated into pure cultures. The ascospores of the fungus failed to germinate in less than five weeks incubation in spite of the use of a variety of cultural conditions. The fungus showed a considerable increase in growth on malt extract agar. Both organisms showed a marked tolerance for high concentrations of glucose although growth was quantitatively reduced. The fungus was able to use a variety of carbon and nitrogen sources as well as an extract of algal cells. Cultivation in the absence of biotin and thiamine failed to yield significant amounts of growth. The alga yielded 27 mg of dry weight after three weeks in a synthetic medium under low light intensities. The alga could be grown in satisfactory amounts on CO2 and inorganic salts with moderate light intensities. Experiments using 14CO2 showed the fungus able to incorporate the extra‐cellular and intra‐cellular products of algal metabolism. The rate of incorporation of extra‐cellular products was inhibited by high concentrations of biotin and thiamine. The alga assimilated l4CO2 which was retained by the cells over a period of 14 days, at which time 78 per cent of the activity was insoluble in 80 per cent ethanol. An extract of the fungus labelled with 14C glucose was partially taken up by the alga and 50 per cent of the label was insoluble in 80 per cent after three days incubation in the light. No lichen acids were found in either the fungal cultures or the algal cultures although large amounts (e.g. 2 liters) of material were extracted and chromatographed. Usnic acid was produced by the intact lichen thallus.
Substrate Dependent Reversibility of Inhibition by β‐Thujaplicin of Glucose and Acetate Respiration in Saccharomyces cerevisiae
Authors: Raa Jan , Goksøyr Jostein
Published: April 2006

Attempts to determine the rate of uptake of β‐thujaplicin (TH) and its 1:1 rupric chelate (CuT+) in yeast cells showed in both cases a very rapid equilibration. In the concentration range where respiration is inhibited, most of the TH added was still present in the extracellular fluid, while CuT+ was almost completely removed.

The inhibition of glucose respiration by TH was Completely removed when the cells were repeatedly washed, while inhibition of acetate respiration remained. Washing of CuT+ inhibited cells did not release the inhibition of either glucose or acetate respiration.

The succinic acid dehydrogenase activity was the same in homogenates of both CuT+ and TH inhibited cells as in homogenates of non‐inhibited cells. Prior to homogenization acetate respiration was inhibited by 60 to 70 per cent by both inhibitors. Alcohol dehydrogenase activity was likewise not affected by TH and CuT+.

The formation of acetyl coenzyme A was inhibited by both TH and CuT+ to about the same extent as the respiration of acetate.

It is concluded that TH inhibits the acetate respiration by inhibiting the formation of acetyl coenzyme A from acetate. The same site of action is plausible also for CuT+ but in that case, additional sites of inhibition may also be located in the reactions in the Krebs cycle.
The Effect of Light on the Phytolization of Chlorophyllide α and the Spectral Dependence of the Process
Authors: Lilijenberg Conny
Published: April 2006

Seven days old dark‐grown etiolated seedlings of wheat cultivated on nutrition solution were given short light impulses of high intensity followed by a dark period, during which the phytolization of chlorophyllic α was studied.

If the leaves prior to the short light impulses were given a pretreatment consisting of a light impulse followed by three hours of darkness the phytolization rate increased.

Monochromatic light as pretreatment gave a response which was mainly restricted to the red region with a peak around 660 nm.