bluuebunny/crossref_metadata_2025 huggingface dataset:
Catalase Is Not Involved in Control of Germination of Cocklebur Seeds
Authors: Esashi Y , Sakai Y , Ushizawa R , Tazaki S
Published: January 2006

Treatment of unimbibed, dry non-dormant upper seeds of Xanthium pensylvanicum Wallr, with KCN, NH2OH, NaNO3 or CS(NH2)2, at optimal concentration for stimulating germination, inhibited catalase activity in extracts from treated seeds. KNO3 was also inhibitory to catalase, although ineffective in stimulating germination. Catalase inhibition by these chemicals, except NaN3, was not observed in seeds presoaked for 7 days, although the seeds were still responsive in germmation. NaN3-treated seeds showed lowered catalase activity even at the secondary dormancy stage, although NaN3 failed to cause germination; CS(NH2)2, however, elicited higher catalase activity at the secondary dormancy stage. Oxygen enrichment, application of ethylene, anaerobiosis, and chilling, which were very effective in stimulating germination, gave conflicting results in regulating catalase activity. Thus, evidence does not favor a role for catalase in the control of cocklebur seed germination.
Relationship Between Grain Nitrogen, Non-Protein Nitrogen and Nucleic Acids During Wheat Grain Development
Authors: Donovan GR
Published: January 2006

Eight wheat varieties which normally produce grain of different final percentage nitrogen content were grown under field and glasshouse conditions. The final percentage grain nitrogen of the field grown varieties ranked in the expected order; however, total nitrogen/grain, DNAIgrain, RNA/grain and non-protein nitrogen/grain during grain development differed between varieties. DNA/grain reached a maximum value in all varieties between 21 and 28 days post- anthesis, suggesting a longer period of cell division than previously reported. There was no apparent relationship between final percentage grain nitrogen and either DNA, total grain RNA or the concentration of grain amino acids during development. Heads from glasshouse grown wheat were detached at 8 days postanthesis and grown in liquid culture under conditions where the nitrogen concentration of the culture medium was varied. Fresh weight/grain, DNA/grain, RNA/grain and total grain nitrogen all increased with increasing nitrogen concentration in the culture medium, but grain dry weight remained constant at the different nitrogen concentrations. The changes in fresh weight/grain, DNA/grain and RNA/grain were not the same for all varieties. A possible relationship between total grain nitrogen and DNA/grain and RNA/grain during seed development exists for heads grown in culture for individual varieties. This apparent relationship for individual varieties cannot be used to explain intervarietal differences in total grain nitrogen because in some cases different varieties grown under identical culture conditions, although producing grain of equivalent total nitrogen, had widely differing levels of both DNA and RNA per grain.
Amino Acid Uptake by Tomato Leaf Tissue Under Chilling Stress: Uptake Conditions and a Comparison of Lycopersicon Species of Different Chilling Resistance
Authors: Paull RE , Patterson BD , Graham D
Published: January 2006

Uptake of [3H]leucine by leaf fragments and roots from Lycopersicon esculentum (domestic tomato) and L. hirsutum (a wild tomato) was compared. Uptake of amino acids was affected by metabolic inhibitors and temperature. The L. esculentum cultivars studied, Rutgers and PI.341985, showed similar uptake rates above 12°C. After preincubation at the uptake temperatures below 12°C, the Q10 for uptake for PI.341985 was about 25 while for Rutgers it was about 125. The temperature response was similar for root and leaf material and for material grown at different temperatures (24/18 and 15/5°C). The temperature response of the uptake by leaf fragments of the wild races of L. hirsutum was related to the altitude of origin. The race from the highest altitude (3100 m) showed little change in slope in a plot of tog uptake rate versus temperature over the range 4-20°C. The race from the lowest altitude (30 m) resembled the cultivars of L. esculentum in its response to temperature and showed an increasing slope below 10°C. The race of L. hirsutum from 1500 m responded to temperature in an intermediate fashion. It is concluded that the decrease in the rate of uptake of amino acids during incubation at chilling temperatures can be related to genetic adaptation to the temperature of the native habitat and chilling resistance of the variety of Lycopersicon used.
Observations on the Scutellum. III. Ferulic Acid as a Component of the Cell Wall in Wheat and Barley
Authors: Smart MG , O'brien TP
Published: January 2006

Fractions enriched in the cell walls of wheat and barley scutella were prepared from isolated, ungerminated scutella. The cell-wall fractions were subjected to hot, alkaline extraction under an inert atmosphere. An ether extract was investigated for phenolic compounds by thin-layer chromatography using three solvent systems and by ultraviolet spectroscopy. The major autofluorescent component of the scutella of both wheat and barley is ferulic acid. There is apparently no p-coumaric acid.
Photosynthesis in the Aquatic Macrophyte Egeria densa. III. Gas Exchange Studies
Authors: Browse JA , Dromgoole FI , Brown JMA
Published: January 2006

When free CO2 alone was present in the ambient medium, photosynthesis by Egeria densa Planch displayed an apparent Km of 77 μM. A light- and CO2-saturated rate of 100 μmol C (mg Chl)-1 h-1 was achieved only in 400 μM CO2(aq) [c. 1% CO2(g)]. The CO2 response data and other considerations suggest that, although the carboxylation and mesophyll resistances (3800 s m-1 and <9000 s m-1 respectively) are considerably higher than in aerial plant leaves, the boundary layer is the highest component (> 27 000 s m-1) of the total resistance. An increase in the total resistance of 7200 s m-1 between 0.02 and 0.21 atm O2 (2 and 21 kPa O2) is attributed to photorespiration.
Closed and open circuit gas exchange experiments demonstrated that bicarbonate is taken up by the plant cells and does not act merely as a reservoir of inorganic carbon for production of CO2 at the plasmalemma. Bicarbonate stimulated photosynthesis, even when the free CO2 concentration was below the CO2 compensation point. The total resistance to bicarbonate uptake appears to be 8-12 times that for CO2 uptake presumably due to the processes of active uptake, transport and/or conversion to CO2 involved in bicarbonate but not CO2 assimilation.
Crassulacean Acid Metabolism and Diurnal Variations of Internal CO2 and O2 Concentrations in Sedum praealtum DC
Authors: Spalding MH , Stumpf DK , Ku MSB , Burris RH , Edwards GE
Published: January 2006

Internal CO2 and O2 concentrations in Sedum praealtum DC. were determined by gas chromatography of 200-�l gas samples. Day-night monitoring showed that internal CO2 varied from a high of approximately 4000 �l/l during periods of daytime stomatal closure to a low of 270-280 �l/l during the dark period (stomata open). Internal O2 concentrations varied from a high of approximately 26 % at midday to a low of 20.8 % during the dark period. The calculated internal O2/CO2 ratio varied about 12-15-fold from 50-60 near midday to approximately 750 during the dark period (ratio in normal air is roughly 600). Day-night patterns of CO2 exchange and malic acid concentration were typical for a plant with crassulacean acid metabolism (CAM). Influx of CO2 during the late light period was inhibited by O2, but dark CO2 influx was O2-insensitive. Gas samples taken near midday from several CAM plants all showed elevated internal CO2 and O2 concentrations. Ratios of O2/CO2 in these plants ranged from 81 in Sedum praealtum to 285 in Hoya carnosa. The highest internal O2 concentration observed was 41.5% in Kalanchoe gastonis-bonnieri. The high CO2 concentration in leaves of CAM plants during daytime stomatal closure should provide a near- saturating level of this substrate for photosynthesis. In comparison to C3 plants, the relatively low O2/CO2 ratio in the CAM leaf during malic acid decarboxylation should be favourable for photosynthesis and unfavourable for O2 inhibition of photosynthesis.
Distribution and Characteristics of Aminoacyl β-Naphthylamidase Activities in Wheat Seedlings
Authors: Waters SP , Dalling MJ
Published: January 2006

Gel electrophoretic studies have revealed that crude extracts from various tissues of wheat seedlings contain two major enzymes capable of hydrolysing aminoacyl �-naphthylamides. A third enzyme which exclusively hydrolyses the �-naphthylamides of the imino acids proline and hydroxyproline has also been demonstrated in wheat leaves. The pH optimum for �-naphthylamidase activity against phenylalanine �-naphthylamide in crude extracts was 7.4. The two major enzymes differ with respect to their substrate specificities; the more anionic enzyme, APl, hydrolyses a relatively narrow range of hydrophobic aminoacyl substrates including the �-naphthyIamides of leucine, phenylalanine, methionine, tyrosine and tryptophan, while the enzyme of lower electrophoretic mobility, AP2, hydrolyses a broad range of substrates. The two enzymes also differ in their sensitivity to the metal chelator 1,10-phenanthroline. The AP2 enzyme from wheat, like that from pea, appears to be a metallo-enzyme, but APl does not show any sensitivity to phenanthroline. The results of developmental studies performed with wheat seedling tissues are consistent with the view that the naphthylamidase enzymes function as aminopeptidases in vivo. A close association was observed between total enzyme activity and soluble protein content, with the highest naphthylamidase activities being found in actively growing tissues.
Aluminium Uptake by Excised Roots of Cabbage, Lettuce and Kikuyu Grass
Authors: Huett DO , Menary RC
Published: January 2006

Uptake of aluminium by excised roots of cabbage, lettuce, kikuyu grass and by a weakly acidic cation exchange resin was studied. The role of metabolism was also investigated, using a range of temperatures and a metabolic inhibitor. The time course of uptake had two phases: an initial rapid phase of about 60 min duration for all species and a slower accumulation phase that was pronounced for cabbage and lettuce and almost absent for kikuyu grass. During the initial phase, calcium was exchanged by aluminium. A small fraction of the aluminium taken up by excised roots could not be desorbed by dilute buffer; this was thought to result from irreversible binding of aluminium directly to exchange sites. Evidence is also presented for a third component for aluminium uptake involving diffusion through the plasmalemma. The non-metabolic nature of the entire uptake process was confirmed by the negligible effect of temperature (1-30°C) and enhancement by 2,4-dinitrophenol on the rate of uptake. Aluminium uptake at pH 4.2 exceeded that at pH 4.0, probably due to the lowering of net charge density of aluminium ions as pH is increased.
Analytical Approach to the Study of Circadian Leaf Oscillations in Clover. II. Responses to Continuous Light and to Sinusoidal Light Oscillations
Authors: Robinson GR , Scott BIH
Published: January 2006

The spectral characteristics of the circadian leaf oscillation of Trifolium repens L. were investigated in constant illumination from 1-10 000 lux. The natural frequency was found to fall from 0.92 cycles/day at 1 lux to 0.84 cycles/day at 10 000 lux, with a corresponding fall in damping coefficient from 0.29 day-1 to 0.10 day-1. Spectral characteristics of the leaf responses to rectangular wave light variations, and to sinusoidal variations in the logarithm of light intensity were also compared. The response to sinusoidal light variations was measured over the frequency range 0.67-20 cycles/day and Bode amplitude and phase plots indicated resonances at 0.85 cycles/day (the circadian frequency) and also at 9.5 cycles/day. A model consisting of two feedback loops and two phase advance elements was developed and its frequency characteristics approximated to those of the leaf. The physiological implications of the proposed model are considered.
Sorbitol Metabolism in Nectaries From Flowers of Rosaceae
Authors: Bieleski RL , Redgwell RJ
Published: January 2006

Although sorbitol is the major soluble carbohydrate in plants of the woody Rosaceae, the floral nectars contained virtually no sorbitol. Glucose and fructose occurred in approximately equal proportions, with sucrose making up the balance.
Nectar secretion was studied using excised flowers. Extensive conversion of sorbitol to other sugars occurred within the flower, at least partly within the nectary itself. Cutting the nectary tissue into slices greatly reduced its ability to transform sorbitol to other sugars. It is suggested that during nectar secretion sorbitol conversion occurs mainly during phloem unloading.
Changes in sugar composition of nectars were studied. There was no evidence that sucrose was secreted then subsequently hydrolysed by invertase or by a microbial flora. There was bidirectional movement of sugars: radioactive sucrose and other sugars added to the nectar entered the nectary tissue, were metabolized there to other sugars, and were secreted again to the nectar. Composition of the nectar was therefore a product of both secretion and uptake processes.
Effects of Osmotica Around the Roots on Water Uptake by Maize Plants
Authors: Nulsen RA , Thurtell GW
Published: January 2006

Nutrient solutions with osmotic potentials of -70, -190 and -380 kPa were supplied to maize plants whose roots were enclosed in a pressure chamber. The plants were stressed and then rewatered with the same nutrient solution. Sap flow rate from the detopped root system was measured at 400 kPa applied pressure. The lower was the osmotic potential of the pretreatment solution, the lower was the initial flow rate. Flow rates rapidly decreased to zero and did not recover for up to 90 min.
Different responses in leaf water potential of unstressed, intact plants occurred when the nutrient solution bathing the root was replaced by either a more concentrated nutrient solution or a solution of sucrose or polyethylene glycol 6000. For nutrient solution replacement the change in leaf water potential was less than the difference in solution osmotic potentials; for sucrose the difference was greater, and for polyethylene glycol the change was equal to the osmotic potential difference. Osmotic effects observed were due to differential accumulations at different barriers in the root. The zero-flow periods seen during recovery of severely stressed plants may have been due to a decrease in the osmotic potential of the solution external to the plasmalemma of root cortical cells.
Partial Characterization of Pyruvate Decarboxylase Isolated From Germinating Pea Seeds
Authors: Leblova S , Valik J
Published: January 2006

Pyruvate decarboxylase (EC 4.1.1.1), isolated from 4-day-old germinating peas, was precipitated from a sodium phosphate extract when (NH4)2SO4 was increased from 15 to 30% saturation, desalted on Sephadex G-25 or by dialysis for 24 h, and then chromatographed on a DEAE-cellulose column. This procedure increased the specific activity of the enzyme 120-fold compared with the sodium phosphate extract. The behaviour of the enzyme during gel filtration indicates that it has a high molecular weight. The pea enzyme exhibits a sigmoid dependence on the pyruvate concentration; reaction velocity is half-maximal at a substrate concentration of 1.8 mM and the Hill coefficient is 1.8. Thiamin pyrophosphate (TPP) is the coenzyme, which is relatively firmly bound to the apoenzyme, but can be removed by dialysis for 48 h. The apoenzyme is activated optimally at 2 mM TPP and inhibited by concentrations above 4 mM. The pH optimum for pea pyruvate decarboxylase is 5.8 and maximal temperature stability occurs at 48°C.
A Common Feature of the Uptake of Solutes by Root Parenchyma Cells
Authors: Cram WJ
Published: January 2006

After carrot root tissue has accumulated KCl for 4 days or more, the internal KCl concentration rises from 10 to over 100 �mol g-1. In the KCl-loaded state, the influxes of a range of solutes are reduced by up to 90%. These solutes are the anions Cl-, NO3-, ClO3-, H2PO4-, benzenesulfonate, and malate; the cation K+ ; and the neutral molecules glucose and urea. The influx of mannitol is not affected, The fall in influx with KCl loading is not due to increased turgor or decreased sugar concentration in the tissue.
The question of what feature the various transport systems share in common is discussed. A common signal is thought to be more likely than a common mechanism of transport. The main implication of the findings is that the system regulating the accumulation of Cl- (which was recognized in earlier work) must in fact be only a part of a more complex regulatory system which operates naturally, in vivo, on a range of solutes, but whose significance is not yet otherwise understood.
Response in Plant Water Status to Integrated Values of Soil Matric Potential Calculated From Soil Water Depletion by a Field Bean Crop
Authors: Karamanos AJ
Published: January 2006

Water deficits were induced in a field bean crop using Polythene rainout shelters to study the crop response to changes in soil matric potential integrated over the zone of soil water extraction. Integrated values of soil matric potential (Ψm,s) were derived from the values of matric potential (Ψm,s) at four separate depths weighted according to the corresponding rates of water depletion at the time of measurement. Linear relationships existed between Ψm,s and variations in leaf water potential before sunrise (Ψd) and in the afternoon (Ψa). The total resistance to daily water flow in the soil-plant system was found to increase linearly with falling Ψm,s. The water flux from separate soil layers indicated that the deeper the layer, the greater the resistance to water uptake from soils at a given value of soil water potential. Such an increase in resistance with soil depth, which considerably reduced the availability of soil water in the deeper soil layers, was attributed mainly to plant factors.
Effects of Shading or Removing Spikelets in Wheat: Testing Assumptions.
Authors: Jenner CF
Published: January 2006

Shading for 10 days reduces the supply of sucrose available for distribution to the grains, and the amounts of sucrose in the endosperm, but has no effect on the delivery of soluble amino compounds to the grain. Soon after returning shaded plants to full illumination, the supply of sucrose to the ear is restored to unshaded levels. In addition, shading affects the amounts of ethanol-insoluble material in the peduncle and the rachis, and the nitrogen content of this material in the peduncle.
Trimming ears to four spikelets (10 days after anthesis) results in an increased supply of sucrose and soluble amino compounds available for distribution to the remaining grains. More nitrogen enters the grains of trimmed ears than intact ones, but inflow of sucrose is not increased by trimming the ear, and no more starch is deposited in grains developing in trimmed ears.
While the responses to shading observed in this work indicate that the interpretation of the effects of shading on the growth of cereal grains may not be straightforward, the use of shading as a treatment for investigating physiological processes such as grain growth is not disqualified. However, as removing spikelets results in several unpredicted, and inexplicable, responses in the grain itself, the value of such a treatment as a means of investigating mechanisms regulating the accumulation of dry matter in the cereal grain is questionable.
Endogenous gibberellin content does not correlate with photoperiod-induced growth changes in strawberry petioles
Authors: Wiseman Nadine J. , Turnbull Colin G. N.
Published: January 2006

We have examined whether gibberellins (GAs) mediate photoperiodic growth
responses in strawberry (Fragaria ×
ananassa) by measuring GA content and GA metabolism in
petioles with accurately defined growth rates. Gibberellin
A1 , GA8 ,
GA19 , GA20 ,
GA29 , GA34 , and tentatively
GA17 , were identified by gas chromatography–mass
spectrometry, and GA4 was detected by selected ion
monitoring. Although petiole growth rates were reduced within 2 d of a
long-day to short-day transfer, we found no consistent changes in GA content
until 8 d, when GA1 , GA8 ,
GA29 and GA34 were reduced by
about two-fold in short days. GA20 concentration was
always low regardless of age or treatment, typically 10-fold less than
GA1 and 40-fold less than GA19 .
Application of paclobutrazol (25 g plant–1 )
reduced growth rate by 43%, somewhat greater than the effect of short
days (23%), but resulted in a six-fold decrease in
GA1 content, much greater than the maximum two-fold
effect of short days. However, paclobutrazol-treated petioles in long and
short days differed in growth rate by 30%, yet had no difference in
GA1 content.
[2H]GA19 and
[2H]GA20 were
metabolised to GA1 , GA8 and
GA29 , although conversion of GA19
was slow. GA4 was converted to GA 34 but not to
GA1 or GA8 . Photoperiod had
little effect on any of these metabolic steps. For the following reasons, we
suggest that the photoperiod growth response is not mediated primarily through
altered GA concentrations: (1) a lack of a rapid photoperiod effect on GA
concentrations or metabolism, (2) changes in growth before or independent of
changes in GA concentrations and (3) a normal photoperiod effect on growth in
petioles with artificially lowered GA content.
Adaptation to Water Stress of the Leaf Water Relations of Four Tropical Forage Species
Authors: Wilson JR , Ludlow MM , Fisher MJ , Schulze E
Published: January 2006

Three tropical grasses, green panic (Panicum maximum var, trichoglume), spear grass (Heteropogon contortus) and buffel grass (Cenchrus ciliaris) and the tropical legume siratro (Macroptilium atropurpureum), were grown in plots in a semi-arid field environment. The water relations characteristics of leaves from plants subjected to a soil drying cycle were compared with those of unstressed leaves from plants in irrigated plots. Minimum water potentials attained in the stressed leaves were c. -44, - 38, - 33 and - 13 bar for the four species, respectively.
The grass leaves adjusted osmotically to water stress, apparently through accumulation of solutes, so that there was a decrease in osmotic potential at full turgor (Ψπ100) of 5.5, 3.9 and 7.1 bar, and in water potential at zero turgor (Ψ0) of 8.6, 6.5 and 8.6 bar for green panic, spear grass and buffel respectively. Water stress appeared to increase slightly the proportion of bound water (B) and the bulk modulus of elasticity (ε) of the grass leaves, but it did not alter the relative water content at zero turgor (RWC0) or the ratio of turgid water content to dry weight of the tissue.
The Ψπ100 and Ψ0 of stressed siratro leaves decreased by 2.5-4 bar and 3-5 bar respectively when subjected to soil drying cycles. These changes could be explained by the marked decrease in the ratio of turgid water content to dry weight of the leaf tissue rather than by accumulation of solutes. The values of RWC0 and ε for siratro leaves were not altered by stress but, in contrast to the grasses, B was apparently decreased although the data exhibited high variability.
Adjustments in Ψπ100 and Ψ0 of stressed leaves of buffel grass and siratro were largely lost within 10 days of rewatering.
Chloride Accumulation as a Homeostatic System: Negative Feedback Signals for Concentration and Turgor Maintenance Differ in a Glycophyte and a Halophyte
Authors: Cram WJ
Published: January 2006

Carrot tissue is taken as a representative glycophilic tissue. It accumulates K+, Cl- and total osmotica to a steady level after 10-15 days. This level of Cl- is nearly constant and is independent of external KCl concentration and of turgor. Cl- influx is also independent of turgor. It therefore appears that the Cl- accumulating system in carrot (and possibly in other glycophytes) can, under artificial conditions, act as a homeostat for intracellular C- concentration, and is not the basis of turgor maintenance. It is suggested that turgor might be maintained by controlled accumulation of K+ carboxylates in glycophytes. Beet tissue is taken as a representative halophilic tissue. It accumulates K+, Cl-, and total osmotica to a steady level after about 4 days. At this stage turgor is constant, due to differences in the levels of KCl accumulated. Cl- influx is stimulated by reducing turgor after a lag of 3-5 h. The relationship of Cl- influx to turgor is non-linear. It therefore appears that in beet (and possibly in other halophytes) turgor maintenance is based on the turgor-sensitive accumulation of Cl- salts.
Cl- influx in beet is also affected by changes in intracellular Cl- concentration, as in carrot. It is suggested that this feedback relationship may primarily be part of a system for the controlled uptake of nutrients rather than of Cl- in both tissues.
Responses to Humidity by Stomata of Nicotiana glauca L. And Corylus avellana L. Are Consistent With the Optimization of Carbon Dioxide Uptake With Respect to Water Loss
Authors: Farquhar GD , Schulze ED , Kuppers M
Published: January 2006

Intact leaves of N. glauca and C. avellana were exposed to a range of humidities and their gas exchange monitored. Rates of transpiration and assimilation of carbon dioxide, and their sensitivities to changes in total conductance (leaf and boundary layer) were determined. The ratio of these sensitivities, δE/δA, remained substantially constant over the range of humidities. The results represent the first experimental support for a recent hypothesis that stomata vary their apertures in such a manner as to keep δE/δA constant, which optimizes carbon gain with respect to water loss.
Structural Aspects of Protein Accumulation in Developing Pea Cotyledons. II. Three-Dimensional Reconstructions of Vacuoles and Protein Bodies From Serial Sections
Authors: Craig S , Goodchild DJ , Miller C
Published: January 2006

The three-dimensional structure of vacuoles and protein bodies seen in developing cotyledons from pea (Pisum sativum L.) have been reconstructed from serial sections. At days 12 and 15 after flowering, serial sections 1 �m thick of epoxy-embedded seed tissue were used to determine vacuole morphology while, at day 20, serial sections 0.25 �m thick were examined by electron microscopy to ascertain protein body morphology. At day 12 there are one or two large vacuoles having extremely complex protrusions emanating from a larger central vacuolar volume. This gives rise to up to 20 apparently discrete vacuole profiles in a given section through a cell. By day 15, there are many smaller, approximately spherical, vacuoles and also some that are more complex. At day 20 most protein bodies are discrete, spherical structures, although a few irregularly shaped bodies are seen. The results support the concept of a large highly convoluted central vacuole fragmenting to give rise to the protein bodies seen towards seed maturity.
Architecture of Individual Plants in a Field-Grown Tobacco Crop
Authors: Whitfield DM , Connor DJ
Published: January 2006

The three-dimensional display of each leaf of a number of adjacent plants was measured with a spatial coordinate apparatus on five occasions during the growth of a tobacco crop. Several architectural characteristics of the foliage display were estimated from these data.
A truncated ellipsoid adequately described plant extent and allowed the calculation and analysis of vertical profiles of leaf area distribution within the plant volume. Foliage densities ranged between 5 and 12 m-1 in small plants and in the upper regions of larger plants. Plants with leaf areas in excess of 0.8 m2 had a leaf area density of approximately 3.2 m-1.
In mature crops, the foliage extended further into the inter-row space than into the space occupied by neighbouring plants in the row.
Mean leaf angle was 40° and elevation distributions were remarkably similar throughout growth and development. Foliage inclination consistently decreased with depth in the canopy. Azimuth distributions of foliage were not significantly different from that of a uniform distribution.
The data are discussed in the context of assumptions that are commonly used in representations of canopy structure.
Interaction of Single Tobacco Plants With Direct-Beam Light
Authors: Whitfield DM , Connor DJ
Published: January 2006

The interaction of single plants of tobacco with direct-beam light was investigated using coordinate data describing the three-dimensional display of foliage. The projection of unit leaf area of single plants showed little variation with either plant size or azimuth angle of sight but showed a major dependence on the zenith angle. In contrast, the beam-lit area of foliage varied with each of these factors. Zenith angle also had the largest effects on the distribution of beam-lit foliage area with respect to the leaf-beam angle.
These variables were also estimated with a model which took account of the basic structural features of the plants. The assumption of a uniform distribution of the leaf projections on the plane normal to the beam led to systematic errors in estimates of the proportion of beam-lit foliage. These deviations were used for estimates of an empirical index of the dispersion of the projections of the elements of foliage. The index varied with plant size and zenith angle of sight. Satisfactory estimates of the projections of unit leaf area and of distributions of the beam-lit foliage with respect to the leaf-beam angle were obtained from the model orientation distributions and assuming that foliage intercepts light in proportion to its frequency in the orientation distributions. Results are discussed in terms of changes in the structure of the plant associated with growth and development.
Diurnal Variation in Physical Attributes Associated With Photosynthesis of a Tobacco Canopy
Authors: Whitfield DM , Connor DJ
Published: January 2006

Diurnal changes in vertical profiles of sunlit foliage and distributions of the angle between the leaves and the sun were derived from computer representations of the actual foliage display of a tobacco crop. The crop was analysed at five stages of development.
Diurnal variations in the proportion of sunlit leaf area were significant only at lower solar elevations. For a large part of the day, most of the foliage of small, isolated plants was directly lit, whereas the proportion of beam-lit foliage fell to approximately 0.4 in larger crops.
The distributions of sunlit foliage with respect to the leaf-beam angle were used to assess the efficiency with which photosynthetically active radiation was captured by the component layers of the crop. At each stage of development, larger proportions of sunlit foliage at intermediate and higher leaf-beam angles coincided with higher solar elevations. These results are discussed in the context of the photosynthetic response of tobacco leaves.
Sunlit leaf area and its distribution with respect to the leaf-beam angle were also estimated with a model of the foliage display of tobacco plants. The model accounted for the presence and influence of neighbouring plants in the crop. Comparisons between model estimates and those from geometrical representations of the crop are discussed in assessing model performance.
Growth Responses of Dactylis glomerata, Lolium perenne and Phalaris aquatica to Chronic Ozone Exposure
Authors: Horsman DC , Nicholls AO , Calder DM
Published: January 2006

D. glomerata, L. perenne and P. aquatica were exposed to 9 parts per hundred million ozone for 4 h per day on 5 days per week for 5 weeks. The grasses responded similarly and significant changes in growth were generally observed only at the end of the exposure. The changes in growth were accompanied by slight leaf chlorosis. Total dry weight and yield (above-ground dry weight) were significantly reduced (14-21%) by the treatment. Root growth was impaired the most, followed by stem and then leaves. Specific leaf area was generally lower in ozone-treated plants but the difference was not significant. Effects on relative growth rate were mainly due to the decrease in net assimilation rate, leaf area ratio remaining relatively unchanged.
Water Relations of the Developing Wheat Grain
Authors: Barlow EWR , Lee JW , Munns R , Smart MG
Published: January 2006

The physiological and anatomical mechanisms underlying the reduced sensitivity of wheat grain growth to water deficits in the post anthesis period have been investigated. The water potential (Ψ) and water content of the developing wheat grain and of other tissues within the wheat spike and flag leaf were compared under controlled environment and field conditions. In the 14 days following anthesis when the amount of water in each grain was increasing, the Ψ gradient between the grain and the rest of the plant was most pronounced. This Ψ gradient disappeared when the water per grain reached its maximum level (15 days after anthesis). The apparent turgor potential (P) of the wheat grain was very small (less than 0.2 MPa) throughout the grain filling period. When water was withheld 10 and 20 days after anthesis, the grain Ψ changed little despite a large decrease in the Ψ of the glumes, rachis and flag leaf. Grain Ψ showed the same independence during a diurnal cycle of water deficit. The independence of grain Ψ under water deficit conditions may be related initially to the xylem discontinuity in the floral axis and, in longer-term water stress situations, to the deposition of lipid in the pigment strand of the grain itself.
Carbon Production and Utilization in Cotton: Inferences From a Carbon Budget
Authors: Constable GA , Rawson HM
Published: January 2006

A carbon budget for cotton plants at the single leaf, node and whole plant level was constructed using data from four glasshouse experiments. Data were collected on leaf expansion and dry weight growth, net photosynthesis, dark respiration of leaves and stems and on responses of photosynthesis to light in tissues of different age. The potential export of carbon by leaves was calculated as daily net photosynthesis less requirements for growth and dark respiration.
The carbon budget for the single leaf showed that the leaf's maximum requirement occurred 7-8 days after unfolding, at the same time as it became a net carbon exporter. Dark respiration used most carbon at days 12-15 but even then the amount was only about 10% of the carbon fixation by the leaf during the day. Potential carbon export reached a peak in 22-day-old leaves, approximating 1 mg C cm-2 day -1 on a sunny day.
The main finding from the budget was that carbon production and its utilization by bolls is out of phase both at the node and whole plant level which necessitates considerable movement of carbon among nodes and into and out of storage. This finding was confirmed in a study using 14CO2 which, while supporting the general hypothesis that the plant's carbon is fed into a pool available to all organs, indicated that there are preferred links between node positions in vertical alignment.
Carbon Production of Sunflower Cultivars in Field and Controlled Environments. I. Photosynthesis and Transpiration of Leaves, Stems and Heads
Authors: Rawson HM , Constable GA
Published: January 2006

Commercial cultivars of sunflower were grown either with adequate water in glasshouses, or in the field using stored moisture or with supplementary irrigation. Diurnal measurements of photosynthesis, transpiration, respiration and water use efficiency were made as leaves expanded and aged: several leaf positions of each cultivar and treatment were examined throughout the season. Responses to quantum flux density were also determined.
Comparable treatments in the field and glasshouse gave similar results and any differences in gas exchange per unit leaf area among cultivars were very small. All leaves, regardless of position on the plant had the same age-determined pattern of gas exchange per unit leaf area. Rates peaked some 10-12 days after leaves were 5 cm2 and had fallen to 50% of these values 50 days later: the decline was slightly faster in field canopies. Instantaneous rates of photosynthesis were occasionally reduced in plants growing on stored moisture when leaf water potential fell below 1.0 MPa, but on a diurnal scale these reductions were small. Water use efficiency declined with leaf age though under saturating light the decline was only 13% in 60 days: efficiency was markedly reduced at quantum flux densities below 800 �E m-2 s-1. The contribution of heads and stems to photosynthesis and transpiration throughout grain growth is discussed.
It is concluded that the water use efficiency of sunflower in the short term is similar to that of other C3 species in spite of the high rates of gas exchange of sunflower. On a diurnal basis, its characteristic of maintaining open stomata under conditions of high evaporative demand results in poor water economy. Sunflower appears to be set to maximize carbon fixation per unit leaf area almost regardless of conditions.
Chloride and Nitrate Stimulate Stomatal Opening and Decrease Potassium Uptake and Malate Production in Epidermal Tissues of Commelina benghalensis
Authors: Raghavendra AS
Published: January 2006

The effect of chloride, nitrate and sulfate on stomatal opening in epidermal strips of C. benghalensis was examined in relation to phosphoenolpyruvate (PEP) carboxylation and malate production. Inclusion of malate, oxalacetate or bisulfite in the medium inhibited PEP carboxylase activity in epidermal tissues, suppressed malate formation and restricted stomatal opening. Malate ions therefore seem to favour potassium uptake even in presence of chloride. Stomata could open when supplied with K+ (K-Tricine); additional presence of chloride or nitrate enhanced further K+ - stimulated stomatal opening but reduced malate production and potassium content of epidermal tissues. Potassium content of epidermal tissues was higher when no inorganic anion was supplied than that in the presence of chloride or nitrate. The relative stimulation of stomatal opening by chloride or nitrate was greater in the presence of 10 m-equiv. K+ than at 100 m-equiv. K+. It is suggested that chloride as well as nitrate is taken up by guard cells: (i) to contribute with K+ to the turgor of guard cells and (ii) to act as a counterion for malate ions.
Environmental Effects on Peppermint (Mentha piperita L.). I. Effect of Daylength, Photon Flux Density, Night Temperature and Day Temperature on the Yield and Composition of Peppermint Oil
Authors: Clark RJ , Menary RC
Published: January 2006

Long days (16 h light), high photon flux density (1200 �Em-2 s-1.) and high night temperature (20°C) resulted in the highest oil yield. :
Daylength, night temperature, day temperature and photon flux density were important interacting factors determining oil composition. The photosynthate model proposed by Burbott and Loomis (Plant Physiol., 1967, <B.42, 20-8) explained the effect of environmental factors with respect to pulegone, menthone and menthofuran. Factors favouring the maintenance of high levels of photosynthate resulted in high concentrations of menthone and low concentrations of pulegone and menthofuran. The photosynthate model does not explain the effect of environmental factors on several other monoterpenes.
Production and Distribution of Assimilate in Chickpea (Cicer arietinum L.)
Authors: Singh BK , Pandey RK
Published: January 2006

Chickpea plants were supplied with 14CO2 to various organs and the assimilation and distribution of 14C was measured in order to investigate the sources of assimilate for pod development and the distribution of assimilate within the plant.
Leaves were the main photosynthetic organ and pod wall photosynthesis was not a significant source of assimilate for seed development. However, the pod wall contributed a significant amount of photosynthate to its own growth.
Individual branches on the plant acted as independent units in terms of photosynthate production and utilization. Attempts to create a gradient by selective defoliation or pod removal did not result in movement of assimilate from one branch to others.
Within the individual branch, photosynthate was utilized close to its site of production. The export of 14C-labelled photosynthate was not dependent on the age of a leaf but was regulated by the presence or absence of an axillary pod. The amount of assimilate drawn by a pod from the subtending leaf was dependent on the size of the pod.
Photoinhibition of Intact Attached Leaves of C4 Plants: Dependence on CO2 and O2 Partial Pressures
Authors: Powles SB , Chapman KSR , Osmond CB
Published: January 2006

Fully expanded intact attached leaves of Zea mays and other C4 plants illuminated at 2000 �E m-2 s-1 in CO2-free N2 containing 10 mbar O2 for a 3-h treatment period showed substantial inhibition of the capacity for both CO2-dependent and light-dependent CO2 assimilation. This photoinhibition was reflected at the chloroplast level as substantial inhibition of photosystem II activity of the mesophyll chloroplasts. Photoinhibition was largely insensitive to the O2 partial pressure maintained throughout the treatment period. This result suggests that internal CO2 generation by photorespiration with subsequent carbon cycling, or O2 uptake in a Mehler-type reaction are largely unable to alleviate photoinhibition. The extent of photoinhibition was, however, markedly affected by the CO2 partial pressure present throughout the treatment period. This result is consistent with the CO2-concentrating function of C4 photosynthesis, which allows substantial rates of CO2 assimilation even at low mesophyll CO2 partial pressures. Apparently, a certain level of CO2 turn- over is beneficial in providing a sink for photochemically generated energy, thereby maintaining the ability of illuminated leaves to transduce and dissipate light energy.
Brassinosteroid-induced de-etiolation of Arabidopsis thaliana seedlings resembles the long-term effects of cytokinins
Authors: Luo Jie , Chen Ji-Chu , Zhao Yu-Ju
Published: January 2006

Cytokinins can cause de-etiolation of
Arabidopsis thaliana (L.) Heynh. seedlings growing in
the dark. Brassinosteroids (BRs) have been considered to regulate negatively
the de-etiolation in dark-grown Arabidopsis seedlings. We show here that
epi-brassinolide (epi-BL) can partially produce the phenotype of de-etiolation
as caused by treatment with cytokinins in the dark, including the development
of leaves and epicotyls in the wild-type and the BR-deficient mutant
det2. But BRs cannot inhibit hypocotyl elongation, nor
restore all the inhibition caused by cytokinins and light. We have found that
there are distinct short term and long term phases of induction of
de-etiolation by cytokinins. The short-term effect is probably coupled to
ethylene in the inhibition of the hypocotyl elongation; the long-term effect
causes morphogenesis of leaves and epicotyls. BRs can only regulate
de-etiolation in the long term. We propose that the inhibition of hypocotyl
elongation of det2 in darkness is caused by the absence
of BR-dependent elongation rather than the inhibition caused by the expression
of genes for photomorphogenesis. We propose that BRs resemble cytokinins in
regulating de-etiolation as positive regulators, and that the inhibition of
hypocotyl elongation and the development of leaves and epicotyls in
de-etiolation are independent processes.
T-DNA tagging and characterisation of a novel meristem-specific promoter from tobacco
Authors: Mudge Stephen R. , Birch Robert G.
Published: January 2006

We have evaluated T-DNA mediated plant promoter tagging, with a
left-border-linked promoterless firefly luciferase (luc)
construct, as a strategy for the isolation of novel plant promoters. In a
population of approximately 300 transformed tobacco plants, 10 lines showed
LUC activity, including novel tissue-specific and developmental patterns of
expression. One line, showing LUC activity only in the shoot and root apical
meristems, was further characterised. Inverse PCR was used to amplify a 1.5 kb
fragment of plant DNA flanking the single-copy T-DNA insertion in this line.
With the exception of a 249 bp highly repetitive element, this sequence is
present as a single copy in the tobacco genome, and is not homologous to any
previously characterised DNA sequences. Sequence analysis revealed the
presence of several motifs that may be involved in transcriptional regulation.
Transgenic tobacco plants transformed with a transcriptional fusion of this
putative promoter sequence to the β-glucuronidase
(uidA) reporter gene, showed GUS activity confined to
the shoot tip and mature pollen. This promoter may be useful to direct the
expression of genes controlling the transition to flowering, or genes to
reduce losses due to pests and stresses damaging plant apical meristems.
Root xylem embolisms: implications for water flow to the shoot in single-rooted maize plants
Authors: Shane M. W. , McCully M. E.
Published: January 2006

The recent measurements of high percentage embolized vessels in a sample of
maize axile roots during the day raised the question whether such
interruptions to water flow could occur in plants that had only a single
water-supplying root. Zea mays L. plants were grown in
the field on a root system developed entirely from the single primary root.
The formation of vessel embolisms in this root was monitored by cryo-scanning
electron microscopy. Vessels were sap-filled at dawn, but 60% of late
metaxylem (LMX) vessels were embolized by 0830 h. This high percentage
persisted until early afternoon, then declined to reach 30% by 1800 h.
Leaf balance pressures rose from about 0.3 MPa at dawn to a peak mean of 1.2
MPa at 1300 h, then declined to 0.5 MPa by 1800 h. Peak embolism in LMX
vessels was reached in the early morning at balance pressures of 0.7–0.8
MPa. Some refilled in the afternoon while balance pressures were 0.5–0.7
MPa. The six to eight LMX vessels at the root base would deliver most of the
transpiration stream to the shoot. Our finding that up to 60% were
embolized during the day, while the plants continue to transpire, suggests
that the mean flow velocity in the vessels is higher than the value of 270 m
h–1 estimated recently by others for completely
full vessels in the mesocotyl of single-rooted corn plants.