bluuebunny/crossref_metadata_2025 huggingface dataset:
Soil water matric potential rather than water content determines drought responses in field-grown lupin (Lupinus angustifolius)
Authors: Jensen C.R. , Mogensen V.O. , Poulsen H.-H. , Henson I.E. , Aagot S. , Hansen E. , Ali M. , Wollenweber B.
Published: January 2006

Drought responses in leaves of lupin
(Lupinus angustifolius L., cv. Polonez) were
investigated in plants grown in lysimeters either in a sand or in a loam soil
in the field. Abscisic acid (ABA) content, water
potential (ψl) and conductance to water vapour
(gH2O) were determined in leaves
of both irrigated plants and in plants exposed to gradual soil drying.
Amorning-peak of leaf ABA content was found in both
fully watered and droughted plants. During soil drying which, on both soils
types, only decreased soil water potential of the upper soil layers, mid-day
leaf ABA content increased relative to that in fully
irrigated plants before any appreciable decreases occurred in
ψl. In the part of the soil profile from which water
was taken up (0–60 cm depth),
gH2O decreased when the relative
available soil water content (RASW) on sand was below
12% and RASW on loam, below 30%. At this
point the average soil water matric potential
(ψsoil) on sand was less than –0.13 MPa and
the fraction of roots in ‘wet’ soil was 0.12, while on loam, the
fraction of roots in ‘wet’ soil was 0.44 while y soil was similar
to that on sand. A critical leaf ABA content of 300–400 ng/g
FW was associated with the onset of stomatal closure on
both soil types. We suggest that the initial stomatal closure is controlled by
ABA which originates from the roots where its production
is closely related to ψsoiland the water potential
of the root surface and that ψsoil is a more
important parameter than RASW or the fraction of roots
in ‘wet’ soil for affecting leaf gas exchange. Further drying on
both soils led to further increases in leaf ABA and
declines in ψl and
gH2O. In order to gain further
insight, experiments should be designed which combine signalling studies with
simulation studies, which take account of soil water potential, root contact
area and water flux when calculating the water status at the root surface in
the soil-plant-atmosphere-continuum.
Time-resolved blue-green fluorescence of sugar beet leaves. Temperature-induced changes and consequences for the potential use of blue-green fluorescence as a signature for remote sensing of plants
Authors: Morales Fermín , Cerovic Zoran G. , Moya Ismael
Published: January 2006

Sugar beet (Beta vulgaris L.) leaves emitted blue-green
fluorescence (BGF) and red (chlorophyll a) fluorescence
(RF) when excited with ultraviolet light. The leaf BGF increased when leaf
temperature decreased (5% of BGF change per °C), unlike leaf RF
that remained unchanged. Several lines of evidence indicate that the
temperature-induced changes in the leaf BGF come from the epidermis:
(i) the decrease from 33 to 3°C increased the leaf
and epidermis BGF more than 2-fold, whereas the mesophyll BGF increased only
1.4-fold; (ii) the excitation and emission difference
spectra 3 minus 33°C showed similar maxima in the leaf and in the
epidermis at 340–350 nm and 420–450 nm respectively, whereas in
the mesophyll they were shifted to 320 and 500 nm respectively; and
(iii) time- resolved BGF measurements showed that the
thermal sensitivities of different kinetic components found in leaves matched
with those of the epidermis, unlike those of the mesophyll that were much
lower. All these changes were fully reversible and paralleled the changes in
temperature. Experiments in vitro with ferulic acid
showed that the spectral properties of the BGF and its thermal sensitivity
depend on the solvent in which it is dissolved, suggesting that the origin of
these changes is in the surrounding or the micro-environment of the blue-green
fluorophore. Discussion is focused on the consequences of these findings for
the potential use of BGF as a signature for remote sensing of plants.
Transient expression of maize anthocyanin regulatory genes influences anthocyanin production in white clover and peas
Authors: Majnik John de , Tanner G.J. , Joseph R.G. , Larkin P.J. , Weinman J.J. , Djordjevic M.A. , Rolfe B.G.
Published: January 2006

Transient expression of the maize anthocyanin regulatory genes,
B-Peru and C1, was examined in
maize cell suspensions, and in pea and white clover tissues in order to
determine if these maize regulators can function in legume tissues. Optimal
ratios and amounts of B-Peru and
C1 genes for anthocyanin production were determined in
maize cell suspensions. Activation of anthocyanin biosynthesis in legume
tissues was observed following expression of the B-Peru
and C1 genes, delivered in the pre-determined optimal
ratio and amounts by microparticle bombardment. Tissue-specific expression of
these genes was observed in the legumes tested and the exact sites of
anthocyanin expression in pea depended on the cultivar tested. Maize
anthocyanin regulatory genes can activate anthocyanin biosynthesis in legume
tissues, but appear to be subject to tissue specific controls. Three of the
four varieties of pea tested were able to accumulate anthocyanin when the
B-Peru coding region alone was biolistically expressed.
Response to oxygen deficiency in primary maize roots. I. Development of oxygen deficiency in the stele reduces radial solute transport to the xylem
Authors: Gibbs J. , Turner D.W. , Armstrong W. , Darwent M.J. , Greenway H.
Published: January 2006

A root pressure probe and transport of
36Cl- from the medium to the xylem
were used to test whether development of oxygen deficiency in the stele, but
not the cortex, reduces radial solute transport in excised primary roots of
maize. Oxygen micro-electrodes demonstrated that a core of anoxia developed
within the stele of roots exposed to 0.05 mol m-3
O2 at 25°C, and that oxygen concentrations in the
pericycle were near or below the
Km for O2
uptake by cells, while oxygen concentrations in the endodermis, cortex and
epidermis were sufficient to fully support oxidative phosphorylation.
Decreasing the external O2 concentration from 0.27 mol
m-3 (aerated) to 0.05 mol m-3
decreased root pressure by about 45% to a new steady state over
4–6 h. Uptake of 36Cl- by
roots grown without Cl- demonstrated that the decrease
in root pressure at low O2 concentrations was almost
fully accounted for by a decrease in the rate of net radial energy-dependent
ion transport into the xylem. Even so, some energy-dependent transport
continued at low O2 supply. The data suggest that
energy-dependent solute transport into the xylem is one of the first processes
adversely affected when O2 supply to roots is low, and
provide further evidence against the classical theory of radial solute
transport (Crafts-Broyer hypothesis).
Thermostability of photosystem II is increased in salt-stressed sorghum
Authors: Lu Congming , Zhang Jianhua
Published: January 2006

Modulated chlorophyll fluorescence and rapid fluorescence induction kinetics
were used to evaluate the functions of photosystem II (PSII) photochemsitry in
sorghum leaves exposed to salinity (0–100 mM NaCl) and/or high
temperature stress (30–50°C). No differences were detected in the
steady- state fluorescence parameters and rapid fluorescence induction
kinetics in salt-stressed leaves, indicating that PSII was highly resistant to
salinity stress alone. However, salinity stress modified the responses of PSII
to high temperature. When the temperature was above 45°C, the
thermostability of PSII was strongly enhanced in salt-stressed leaves, which
was reflected in a smaller decrease in maximum efficiency of PSII
photochemistry, coefficients of photochemical and non-photochemical quenching,
and efficiency of excitation capture by open PSII reaction centres, and in a
smaller increase in the proportion of the
QB-non-reducing PSII centres in salt-stressed leaves
than in control leaves. This increased thermostability in salt-stressed leaves
exposed to high temperature seemed to be independent of the imposed salt
concentration since there were no significant variations in the above
fluorescence parameters among the salt-stressed plants treated with different
salt concentrations. The results are discussed in terms of the physiological
significance of such increased resistance of PSII to high temperature.
Effects of water deficits on 13C discrimination and transpiration efficiency of Eucalyptus globulus clones
Authors: Osório Júlio , Osório M. Leonor , Chaves M. Manuela , Pereira João S.
Published: January 2006

Potted cuttings of three Eucalyptus globulus Labill.
clones (AR3, CN44, MP11) were grown over 6 months in a greenhouse under three
watering regimes: well watered (HW), moderate soil water deficit (MS) and
severe soil water deficit (SS). Transpiration efficiency
(W = total dry matter/water transpired) and
leaf intrinsic gas exchange efficiency
(A/gs = carbon assimilation
rate/stomatal conductance) increased under water stress and were
positively correlated with the stable carbon isotope composition of leaf
tissue (δ13C). The clones did not vary
significantly with respect to A/gs
and W. However, statistically significant differences were detected among
clones in δ13C, A and
biomass. W did not differ between the MS and SS regimes,
probably due to plant acclimation to increasing soil water deficits. The
increase in W with soil water deficits relative to the
well watered control was primarily associated with stomatal closure, but was
also influenced by differences in respiratory carbon losses
(?c) and variation in the leaf-to-air water vapour
difference (v). Variance in
?c and v may explain
partially why the two levels of soil water deficit were different in regard to
δ13C but not in terms of W.
The Induction of Nitrate Reductase in Mung Bean Seedlings
Authors: Higgins TJV , Goodwin PB , Carr DJ
Published: January 2006

Nitrate reductase is induced by its substrate in the root and hypocotyl of mung bean seedlings (Phaseolus aureus Roxb.). This induction is considerably enhanced by NH4+ and to a lesser extent by an amino acid mixture, and is also promoted by the presence of sucrose in the incubation medium. There is a lag period between the addition of nitrate and the establishment of a steady rate of increase in enzyme activity. The lag period decreases with increasing temperature. The enzyme activity continues to increase only in the continued presence of nitrate in the incubation medium. However, a constant level of activity is maintained for at least 6 h after removal of substrate. Re-addition of substrate causes an immediate resumption of the normal rate of increase without manifestation of a lag period. A number of inhibitors of RNA and protein synthesis inhibit the induction. However, chloramphenicol and 5-fluorouracil at appropriate concentrations promote induction. The inhibitor of DNA synthesis, fluorodeoxyuridine, is without effect. Gibberellic acid, naphthaleneacetic acid, benzyladenine and abscisic acid have no effect in the induction process in the absence of substrate. However, abscisic acid and high concentrations of naphthaleneacetic acid (10-6M) and benzyladenine (10-5M) inhibit the response to nitrate. Cyclic 3',5'-AMP slightly enhances the induction of the enzyme. Related nucleotides cause varying degrees of inhibition: cyclic 2',3'-AMP is strongly inhibitory. The distribution of enzyme activity and nitrate along the roots after growth in the induction medium has been examined. Maximum enzyme activity is associated with minimum internal nitrate concen- tration. The highest nitrate reductase activity occurs at the root tip.
Influence of Flooding on the Alcohol Dehydrogenase Activity of Roots of Trifolium subterraneum L.
Authors: Francis CM , Devitt AC , Steele P
Published: January 2006

Flooding the roots of T. subterraneum grown in sand culture induced large (often 30-fold) increases in alcohol dehydrogenase (ADH) activity, indicative of anaerobic respiration. In pot culture the levels of ADH activity were lower in varieties of subspecies yanninicum than in varieties of subspecies brachycalycinum and subterraneum. The varieties took 6–9 days to reach maximum ADH values, indicating a flooding period of this order is suitable in varietal testing for flooding tolerance. Lower ADH levels in subspecies yanninicum were not evident when the roots were tested after 3 days in anaerobic solution culture.
Stress Metabolism. VI.* Temperature Stress and the Accumulation of Proline in Barley and Radish
Authors: Chu TM , Aspinall D , Paleg LG
Published: January 2006

Barley (cv.Prior) and radish (cv.White Icicle) plants were subjected to heat stress (39�C) for 1–5 days when growing in either a high (90–95 %) or low (50%) relative humidity environment. Although the plants were watered daily, leaf water potential (ψw) in heat-stressed plants at low relative humidity fell to a low level (– 30 bars, day 5) whereas there was no such decrease in the leaves of those maintained at a high humidity (– 4.6 bars). Growth in height was inhibited and leaf chlorophyll concentration decreased by high temperature, these effects being accentuated by accompanying water-stress in the leaves. On the other hand, proline only accumulated in the leaves when (ψw) fell, there being apparently no direct response to elevated temperature. These effects were confirmed for a range of temperatures extending to a maximum of 41�C. Proline accumulated rapidly, after an initial lag phase, in both barley and radish plants exposed to a low temperature (4�C). This accumulation was unrelated to any changes in the leaf water relationships. Neither leaf water potential, osmotic potential nor turgor demonstrated changes with low temperature sufficient to account for the accumulation of proline. The characteristics of this cold- induced accumulation of proline are compared with those of water stress-induced accumulation. * Part V, Aust. J. Biol. Sci., 1973, 26, 319–27.
Some Physical Factors Affecting the Formation and/or Net Accumulation of Medicarpin in Infection Droplets on White Clover Leaflets
Authors: Cruickshank IAM , Veeraraghavan J , Perrin DR
Published: January 2006

A quantitative study was made of the effect of several physical factors in the environment on the formation and/or net accumulation of medicarpin in infection droplets on excised white clover leaflets following inoculation with Monilinia fructicola (Wint.) Honey. Incubation experiments (duration 40 h) showed that the optimum temperature for medicarpin formation was 25�C. Medicarpin was first detected at 6 h and rose to a maximum concentration in the infection droplet at 30 h following inoculation. Predisposition experiments showed that medicarpin concentrations were highest where plants had been grown under high temperature regimes (day/night 30/25 and 33/28�C). It was formed in significantly greater concentration where plants had been grown under long-day rather than short-day treatments. Level of light intensity was found to have no effect. Time of day of leaf detachment from a plant significantly affected the level of medicarpin formed. *Part XI11 of 'Studies on Phytoalexins' (Part XU, PI. Physiol., Lancaster, 1972, 50, 660–6).
Biosynthesis of Gibberellins in Barley and Dwarf Rice Seedlings
Authors: Faull KF , Coombe BG , Paleg LG
Published: January 2006

Incorporation studies with 14 CO2 suggested that 11-day-old barley seedlings biosynthesized an A1- like gibberellin de novo and that the biosynthesized gibberellin completely turned over within 12 h. Exogenous [14C]mevalonic acid, supplied in a variety of ways, was not incorporated into the gibberellins of barley seedlings. Barley seedlings, which failed to elongate in response to exogenous ent-kaurenoic acid, metabolized exogenous [17-14C]ent-kaurenoic acid to a few compounds, but not to a biologically active gibberellin. Dwarf rice seedlings (cv. Tan-ginbozu), which elongated in response to exogenous ent-kaurenoic acid, metabolized exogenous [17-14C]ent-kaurenoic acid to a number of radioactive compounds, one of which behaved like [14C]gibberellin A1 in that it showed radioactivity and biological activity at the expected retention time during gas-liquid chromatography.
Relationship Between Thermoinduction and Photoinduction of Flowering and Dormancy in Hordeum bulbosum L., a Perennial Grass
Authors: Ofir M , Koller D
Published: January 2006

Induction of axillary bud dormancy (as manifested by initiation of the bulb which is associated with the dormant buds) and of reproductive development in H. bulbosum are closely linked processes. Both are potentiated by thermoinduction (vernalization of the seed) and express themselves as a result of subsequent photoinduction in long (16-h) photoperiods. Partial photoinduction of vernalized plants, which sufficed for bulb initiation, was insufficient for full expression of flowering: the reproductive development of the shoot apex was arrested and reverted to vegetative development. This was terminated by formation of a second bulb and a normal inflorescence, both typical of non- induced plants. Intercalation of as many as 30 short (8-h) photoperiods after the end of thermoinduction did not diminish the developmental response of the shoot apex to subsequent photo- induction. On the contrary, intercalation of short photoperiods after vernalization increased the effectiveness of subsequent photoinduction, with respect to the bulb-forming response and to the reproductive development of the shoot apex. Both photoperiodic regimes in this sequence were effective in promoting bulb initiation, However, effectiveness of short photoperiods was much smaller than that of long photoperiods and was progressively decreasing as their number increased. The position of the bulb internode showed remarkable parallelism with the number of leaves which had emerged by the start of photoinduction, but the intensity of photoinduction had no effect. No parallelism was found with the total number of leaves produced by the apex (i.e. including leaf primordia). The significance of these results is discussed.
An Exploration of the Carbon Economy of the Tobacco Plant. II. Patterns of Leaf Growth and Dry Matter Partitioning
Authors: Hackett C , Rawson HM
Published: January 2006

As a sequel to calculations made in Part I about the carbon economy of the tobacco plant, a short-day variety of tobacco (Nicotiana tabacum L. cv. Mammoth 17L) was grown at controlled temperatures in two contrasting photoperiods (13 and 9 h) and the growth and gas exchange of the plants were determined as frequently as possible during the period 30–100 days from sowing. This paper describes aspects of the leaf emergence, leaf expansion, floral development, and dry matter partitioning in these plants. Part III will present the gas-exchange data. The most striking finding from the growth data concerned leaf expansion. The application of curve-fitting techniques showed that the expansion of each leaf studied could be accurately described by the Gompertz growth function, which implied that the maximum absolute rate of expansion had been achieved quite early in the leaf's development, at about 37% of full expansion. Furthermore, in all but the juvenile leaves, the time-spread of expansion was similar, despite up to 10-fold differences in the final area of the leaves due to photoperiod and position on the stem. Other relationships observed in the data seemed of fundamental interest. Attention is drawn (1) to the smooth progression in final leaf size with progress up the stem, and (2) to the changes with time in the ratio of the relative growth rates of the major plant parts, but whether these relationships, and those between leaf expansion and time, are typical of tobacco will remain uncertain until comparable studies are performed. * Part I, Aust. J. Biol. Sci., 1973, 26, 1057–71.
An Investigation of the Association Between the Hydrolysis of Sucrose and Its Absorption by Grains of Wheat
Authors: Jenner CF
Published: January 2006

The possibility of a linkage between the hydrolysis of sucrose and its uptake by wheat grain was investigated by culturing isolated grain in solutions of sugar. The grain hydrolyses sucrose to glucose and fructose, the catalyst seems to be extracellular acid invertase (�-fructofuranosidase), and the rate of hydrolysis is at least as fast as the deposition of starch. However, tris-HCl buffers inhibit hydrolysis but have no effect on the uptake of sucrose or on the speed of its conversion to starch.
The grains absorb invert sugar (glucose and fructose) faster than sucrose, but more sucrose accumulates and less starch is produced from invert sugar than from sucrose. Culturing grain in a mixture of non-radioactive glucose or fructose and symmetrically labelled sucrose introduces very little asymmetry into the sucrose taken up, but sucrose accumulated from [fructosyl-14C]sucrose loses half the asymmetry, while sucrose produced from a mixture of [12C]glucose and [14C]fructose is not completely symmetrical. Both moieties of sucrose are converted into starch.
It is concluded that absorption of sucrose is not dependent on extracellular hydrolysis, and intracellular hydrolysis of sucrose prior to conversion to starch is unlikely.
Gibberellic Acid and Rna Synthesis in Barley Aleurone Layers: Metabolism of rRNA and tRNA and of RNA Containing Polyadenylic Acid Sequences
Authors: Jacobsen JV , Zwar JA
Published: January 2006

RNA containing polyadenylic acid sequences [poly(A)-RNA] was detected in and isolated from barley aleurone layers. Gibberellic acid (GA3) stimulated the synthesis of this RNA by about 70% over a 16-h period during which amylase induction occurred. The poly(A)-RNA was polydisperse on polyacrylamide gels and the effect of GA3 was to enhance synthesis of poly(A)-RNA species with a wide range of molecular weights.
GA3 had no major effects on the synthesis of rRNA, 5 S RNA and tRNA species, and since it also had no effect on levels of total RNA in aleurone, it probably had no effect on RNA breakdown. Furthermore, rRNA synthesis could be essentially stopped with 5-fluorouracil with no effect on amylase synthesis, indicating that synthesis of new ribosomes was unnecessary for normal amylase induction.
These results indicate that for amylase synthesis to occur in response to GA3, regulation of synthesis of mRNA but not that of the major species would appear to be necessary.
Effect of Previous Water Stress on Ion Uptake and Transport in Barley Seedlings
Authors: Pitman MG , Luttge U , Lauchli A , Ball E
Published: January 2006

Measurements of ion transport through roots and ion uptake into roots were made following a brief period of water stress induced by wilting in air. The basic processes of photosynthesis, respiration and protein sinthesis did not appear to be affected by this treatment, and uptake of 86Rb and L-leucine to the roots was not reduced. However, transport of 86Rb and L-leucine from root to shoot wasinhibited. Thus the response of the plants to water stress resembles the response to inhibitors of protein synthesis and to abscisic acid, which has been found to be produced in plants subject to water stress.
Retranslocation of Potassium in Beta vulgaris L. Under Conditions of Low Sodium Supply
Authors: Graham RD , Ulrich A
Published: January 2006

Potassium retranslocation was studied in B. vulgaris by sequential harvests of plants following transfer to a potassium-deficient medium. Absolute amounts of potassium in each blade and petiole and in other plant parts were calculated. There was a net retranslocation of 37.5% of the plant potassium in the 15 days following potassium cutoff. Blades and fibrous roots exported potassium readily, but petioles and beet tissue accumulated potassium even as the degree of deficiency increased. The eight oldest leaves (blade plus petiole) exported potassium throughout while the potassium in leaf 9 was relatively unchanged. Younger leaves were net importers of potassium. It is suggested that the redistribution is of survival value under conditions of potassium stress.
Internal Control of Stomatal Physiology and Photosynthesis. I. Stomatal Regulation and Associated Changes in Endogenous Levels of Abscisic and Phaseic Acids
Authors: Loveys BR , Kriedemann PE
Published: January 2006

Both environmental factors and manipulative treatments (such as fruit excision or stem cincturing) were found to alter gaseous diffusion resistances in grape vine foliage. These responses have been analysed in terms of the hormonal physiology of Vitis vinifera L. leaf tissue.
Environmental factors such as moisture stress or photoperiod alterations which contributed towards an increase in stomatal resistance (rs) were correlated with increased levels of endogenous abscisic acid (ABA) and phaseic acid (PA) in mature foliage. Conversely, treatments which elicited a decrease in rs were associated with lower levels of both ABA and PA. For example, rs had increased from 1.41 to 7.14 s cm-1 7 days after fruit removal and stem cincturing, while ABA and PA levels rose by 50 and 370 % respectively. This increase in endogenous ABA was not a consequence of decreased leaf water potential; moisture status was actually improved after treatment.
It is proposed that changes in endogenous levels of ABA, and possibly PA, constitute a mechanism for regulating gas exchange in these perennial plants.
Effects of Sodium and Potassium on Starch Synthesis in Leaves
Authors: Hawker JS , Marschner H , Downton WJS
Published: January 2006

The growth rate of plants of both spinach (Spinacia oleracea) and sugarbeet (Beta vulgaris) was decreased with low levels of K+ in nutrient solutions. Addition of Na+ at low levels of K+ resulted in growth rates at least as great as those observed with adequate K+. By comparison, bean plants (Phaseolus vulgaris) had only low growth rates when part of the K+ was replaced with Na+. The concentration of starch in spinach leaves was not affected by the K+/Na+ supply, whereas sugarbeet leaves from plants grown on adequate levels of K+ contained nine times more starch than leaves grown on high Na+/low K+ culture solutions. K+, but not Na+, stimulated by about 100% the activity of starch-granule-bound ADPglucose starch synthase from sugarbeet, bean and Atriplex nummularia leaves but not from spinach leaves. Neither ion caused a marked stimulation of the activity of soluble ADPglucose starch synthase, phosphorylase or other enzymes likely to be associated with carbohydrate metabolism. Slices of bean or sugarbeet leaves incubated in 12.5 mM K2SO4, solutions in the light for 8 h contained higher amounts of starch, and slices of bean leaves contained lower amounts of soluble sugars, than similar slices in Na2SO4. There was a considerable efflux of sucrose but not of reducing sugars in the presence of K+ or Na+ ; this efflux was several times higher than in the presence of Ca2+.
The results suggest that K+ is essential for the conversion of sugars to starch in some plant species and that ADPglucose starch synthase is the enzyme involved in starch synthesis in the leaves of these species.
Effects of Low Water Potentials on Transpiration and Photosynthesis in Mitchell Grass (Astrebla lappacea)
Authors: Doley D , Trivett NBA
Published: January 2006

Gas-exchange studies were carried out on potted Mitchell grass plants raised in the glasshouse and in growth cabinets. Provided that nutrition was adequate, the low irradiance of the growth cabinets did not impair the photosynthetic capacity at levels approaching full sunlight. The optimum temperature for net photosynthesis was in excess of 40�C. Close linear relationships were established between leaf water potential and both transpiration and net photosynthesis. Most of the variation in gas exchange could be attributed to changes in stomatal diffusive resistance. Although there was an increase in mesophyll resistance as leaf water potential decreased, the proportion of the total resistance attributable to the mesophyll became substantially smaller. Gas exchange exhibited a remarkable recovery after brief but severe drought, during which leaf water potentials fell to about -48 bars. There was some inhibition of both transpiration and photosynthesis for about one week following rewatering. It is concluded that A. lappacea demonstrates a high degree of true drought tolerance.
Flowering in Pisum: Effect of 2-Chloroethylphosphonic Acid and Indole-3-Acetic Acid
Authors: Reid JB , Murfet IC
Published: January 2006

The flowering node of an early line of peas (genotype lf e sn hr) was delayed by Ethrel (active agent 2-chloroethylphosphonic acid) in concentrations as low as 1 p.p.m. The delay of 3.7 nodes obtained with 40 p.p.m. is one of the largest reported for any chemical treatment of peas. Indole-3-acetic acid also caused a significant delay when applied at the high rate of 1 mg per plant. We suggest that the delay in both cases may be mediated by ethylene.
Isolation, Purification and Characterization of the Seed Globulins of Lupinus angustifolius
Authors: Blagrove RJ , Gillespie JM
Published: January 2006

The three globulins of the seeds of L. angustifolius cv. Uniwhite may be satisfactorily resolved in 10 min by electrophoresis on cellulose acetate strips. These globulins, conglutins α, β and γ, vary markedly in their amino acid compositions, with conglutin Ω differing from conglutins α and β and most other legume storage proteins in its relatively high content of cystine and methionine and lower content of arginine and glutamic acid.
When examined on sodium dodecyl sulphate-polyacrylamide gels, both in the absence and presence of β-mercaptoethanol, the three globulins were found to differ completely in the type of subunit proteins they contain and in the significance of intrachain disulphide bonding. Conglutin α was found to contain three or four types of non-covalently linked subunits with apparent molecular weights in the range 55 000-80 000, each of which may contain a disulphide-bonded moiety with a molecular weight near 20 000. Conglutin γ was found to contain disulphide-bonded chains of molecular weights 17 000 and 30 000, whereas the four major subunits of conglutin β, whose molecular weights lie in the range 20 000-60 000, were not covalently linked together. The latter globulin does not appear to be homogeneous, for it can be separated by fractional precipitation with ammonium sulphate into a series of fractions which differ markedly in the proportion of subunit types they contain.
Subdivision of C4-Pathway Species Based on Differing C4 Acid Decarboxylating Systems and Ultrastructural Features
Authors: Hatch MD , Kagawa T , Craig S
Published: January 2006

A selection of C4 species was surveyed to determine the relationship between their content of C4 acid decarboxylating enzymes, the activities of several other enzymes implicated in the C4 pathway, and their anatomical and ultrastructural features. The species examined clearly fell into three groups according to whether they contained high levels of either NADP malic enzyme (EC 1.1.1.40), phosphoenolpyruvate carboxykinase (EC 4.1.1.49) or NAD malic enzyme (EC 1.1 .1.39). The occurrence of high NADP malic enzyme activity was always associated with higher NADP malate dehydrogenase activity, while those species distinguished by high activities of either of the other two decarboxylases invariably contained high aspartate aminotransferase and alanine amino- transferase activities. Each of these decarboxylating enzymes was located in bundle sheath cells. NAD malic enzyme, but not phosphoenolpyruvate carboxykinase, was associated with mitochondria.
Light and electron micrographs revealed differences between these groups with respect to the intracellular location of chloroplasts and mitochondria in bundle sheath cells, and the content and ultrastructure of mitochondria. The trend was for species with high NAD malic enzyme to contain the most mitochondria in the bundle sheath cells with apparently the most extensively developed cristae membrane systems. However, mitochondrial respiratory enzyme activities were similar for the three groups of species.
The basic similarities and differences between the three groups of C4 plants distinguished by their differing C4 acid decarboxylating systems are discussed, and schemes for the probable photosynthetic reactions in bundle sheath cells are presented. A nomenclature to distinguish between these groups is proposed.
Mitochondria and Chloroplast Peripheral Reticulum in the C4 Plants Amaranthus edulis and Atriplex spongiosa
Authors: Chapman EA , Bain JM , Gove DW
Published: January 2006

Cytochemical techniques were used to show that all the many large mitochondrion-like bodies present in bundle sheath cells of the aspartate-donor C4 plants, Amaranthus edulis and Atriplex spongiosa, possessed mitochondrial characteristics. The techniques involved the location of cytochrome c oxidase activity with 3,3'-diaminobenzidine and examination of configurational changes in mitochondria after incubation in the inhibitors of oxidative phosphorylation, rotenone and oligomycin, and of substrate phosphorylation, iodoacetate, or the uncouplers of oxidative phosphorylation 2,4-dinitrophenol and carbonyl cyanide p-trifluoromethoxyphenylhydrazone. The peripheral reticulum, which is a prominent feature of C4 mesophyll and bundle sheath chloroplasts and whose internal structure closely resembles that of the bundle sheath mitochondria, was also examined cytochemically. Frequent protrusions or buds from the peripheral reticulum in the bundle sheath chloroplasts strongly suggested that it could give rise to all or some of the mitochondria. Cytochemical investigation with diaminobenzidine, however, demonstrated that the peripheral reticulum does not possess cytochrome c oxidase activity and that the mitochondrial population is homogeneous. Studies of developing leaves of Amaranthus edulis showed that the mitochondria were a prominent feature in the bundle sheath cells before the appearance of the peripheral reticulum. The close proximity of the peripheral reticulum to mitochondria or to peroxisomes and sometimes also to the cell wall plasmodesmata indicates that it may play a role in metabolite transport.
Characteristics of Phytochrome in Glutaraldehyde-Treated Maize Coleoptiles
Authors: Yu R
Published: January 2006

Glutaraldehyde treatment was used to stabilize the in situ distribution of phytochrome at intervals during the course of phytochrome dark reactions. Total cellular phytochrome decreased in maize coleoptiles when they were returned to darkness and incubated after red irradiation. Photoreversibility was lost in both the soluble and particulate fractions, being faster in the particulate fraction. Glutaraldehyde treatment of coleoptiles immediately after irradiation inhibited loss of particulate phytochrome in the dark. When coleoptiles were irradiated with R/FR, i.e, red light (R, 660 nm) followed by far-red light (FR, 737 nm), and then incubated in the dark, the loss of particulate phytochrome was compensated for by an increase of phytochrome in the soluble fraction, resulting in negligible loss of total phytochrome.
The phytochrome dark reactions in subcellular fractions of coleoptiles irradiated in vivo with R and R/FR and extracted in Mg2+-containing buffer were similar to those in corresponding subcellular fractions of coleoptiles treated with glutaraldehyde before cell fractionation. If the pattern of phytochrome dark reactions in subcellular fractions of R- and R/FR-irradiated coleoptiles treated with glutaraldehyde before cell fractionation truly reffects the in situ situation, this similarity suggests that the phytochrome distribution in subcellular fractions obtained by extraction in Mg2+-containing buffer of coleoptiles irradiated in vivo (without ghtaraldehyde treatment) also represents the intracellular distribution. This conclusion however cannot be extended to the distribution obtained following irradiation of Mg2+-containing non-cellular extracts.
Relationships Between Chloride Transport and Electrical Potential Differences in Carrot Root Cells
Authors: Cram WJ
Published: January 2006

The Cl- influx across the tonoplast increases at about 3 days after excision, and is inhibited by carbonyl cyanide m-chlorophenylhydrazone in well-washed tissue, while the influx of Cl- across the plasmalemma and the cellular electrical potential difference both remain constant under these conditions. The transport of Cl- within the cell therefore appears not to be electrogenic.
When SO42- is substituted for Cl-, keeping the external K+ concentration constant, the cell potential difference (p.d.) increases from - 54 mV in 10 mol m-3 KCl to -65 mV in 5 mol m-� KSO42- if the p.d. were solely a diffusion potential, then substituting SO42- for Cl- would be expected to reduce it. This prediction is based on the Goldman equation with a term for SO42- introduced, and various estimates of the parameters involved. It is therefore suggested that a small part of the p.d. in carrot may be due to the activity of a Cl- pump inwards across the plasmalemma, which is linked either to a larger cation influx or to a larger anion (e.g. OH-) efflux.
During accumulation of KCl, the cell p.d. increases slightly, from - 54 mV in the non-loaded cell in 10 mol m-3 KCl to -59 mV in the KCl-loaded cell in 10 mol m-3 KCl. This small change is not inconsistent with the response of the p.d. to changes in external salt concentration.
From these results, the electrochemical potential of Cl- in the vacuole is calculated to be greater than in an external solution of 1 mol m-3 KCl by 17 kJ mol-1 in non-loaded tissue and by 23 kJ mol-1 in KCl-loaded tissue. This increase in the gradient opposing Cl- entry is probably not sufficient to account for the fall in the active influx of Cl- during accumulation of KCl.
Factors Regulating the Accumulation of Starch in Ripening Wheat Grain
Authors: Jenner CF , Rathjen AJ
Published: January 2006

Estimates of the faculty of wheat endosperm to convert sucrose to starch were obtained by incubating dissected endosperm in solutions of [14C]sucrose and then measuring the absorption of [14C]sucrose and the amounts of 14C accumulating as insoluble material. Samples of grain were taken from plants growing in the field at each of four stages of maturity: at 17 days after anthesis, just after the synthesis of starch had begun; at 28 days when the grains were about half-grown; at 38 days when the accumulation of starch had slowed down and almost ceased; and at 49 days when the grains were fully grown. More [14C]sugar entered the free space of the endosperm of 49- than of 28-day-old grain, and more sucrose was absorbed by the endosperm cells of the older grain. Endosperm taken from grains sampled at 28 days produced more insoluble radioactive material (mostly starch) than grains sampled at any other stage, and compared to 28-day grain, grain sampled at 38 days produced less than one-third of the quantity of [14C]starch.
At each stage, the amounts of sucrose in the free space and in the cells of the endosperm were determined on comparable samples of grain developing normally in the field. There was significantly more sucrose on day 38 than on day 28, both in the free space and in the cells of the endosperm. It is concluded that the onset of the declining phase of accumulation of starch, as the grains begin to ripen, is due to a fall in the capacity of the grains to synthesize starch, and is not attributable to postulated reductions in the supply of assimilate to ripening grain.
Effect of Water Deficit on Photosynthesis and Tuber Metabolism in Potatoes
Authors: Moorby J , Munns R , Walcott J
Published: January 2006

The primary effect of a period of drought on potato plants was to reduce the rate of photosynthesis. Decreases in CO2 uptake could mainly be ascribed to an increase in the residual resistance to CO2 transport. Levels of sugars and of starch-synthesizing enzymes in extracts from tubers of droughted and control plants were similar, and it is likely therefore that the effect of drought on tuber growth is exerted mainly via a reduction in the supply of assimilate.
Photosynthesis in Developing Asparagus Plants
Authors: Downton WJS , Torokfalvy E
Published: January 2006

The gas exchange characteristics of asparagus shoots at various stages of development are described. Reassimilation in spears conserved 50-100% of the carbon dioxide produced in respiration. Refixation was influenced by light intensity and CO2 concentration in the surrounding air, but not by oxygen concentration. The absence of an inhibitory effect of oxygen on refixation is attributed to suppression by high levels of CO2 inside the spear. Assimilation of radioactive CO2 in both the spear and fern forms of asparagus was by the C3 pathway. Fern forms displayed more usual C3 properties, with photosynthesis and CO2 compensation points showing sensitivity to oxygen concentration.
Glycolysis in CAM Plants
Authors: Sutton BG
Published: January 2006

Enzymes involved in the movement of carbon from glucan to malic acid in the crassulacean acid metabolism (CAM) plant, Kalanchoe daigremontiana were assayed. The kinetic characteristics determined for the enzymes from this plant were similar to those already known for the same enzymes from non-CAM tissue. °-Amylase activity could not be demonstrated in the CAM leaf and glucokinase activity was low. These results, together with a high level of phosphorylase, suggested that the latter enzyme was involved in trasfer of glucan breakdown products to glycolysis. The activity of pyruvate kinase was only 1.7% of the activity of phosphoenolpyruvate (PEP) carboxylase, suggesting that pyruvate production from PEP at night posed little drain on PEP supply for malic acid synthesis. Starch losses and glycolytic enzyme activities of non-CAM plants were sufficient to allow dark acidification comparable to that of CAM plants.
Kinetic Properties of Phosphorylase and 6-Phosphofructokinase of Kalanchoe daigremontiana and Atriplex spongiosa
Authors: Sutton G
Published: January 2006

The kinetic properties of phosphorylase (EC 2.4.1.1) and 6-phosphofructokinase (EC 2.7.1.11) extracted from a crassulacean acid metabolism (CAM) plant, Kalanchoe daigremontiana Hamet et Perrier, and a C4 plant, Atriplex spongiosa F. Muell., were compared. The phosphorylase from the CAM plant was strongly inhibited by P1 (1 mM), phosphoenolpyruvate (PEP) (2 mM) and glucose (4 mM). The C4 phosphorylase was less strongly inhibited by P1, and not at all by PEP or glucose. The C4 6-phosphofructokinase was, at Km levels of substrate, about 100 times more sensitive to inhibition by PEP than the CAM enzyme. These results are discussed as the basis for a biochemical regulation of carbohydrate metabolism in CAM plants at night.
Quantitative Studies on Root Development. III. Further Observations on Growth in the Seedling Phase
Authors: Rahman L , Aspinall D , Paleg LG
Published: January 2006

The influences of light intensity, rooting medium, and the excision of various organs on the early phases of root growth in barley seedlings (cv. Piroline) were explored. The emergence of root axes was affected by light intensity and excision of roots, endosperm or shoot, but was not altered by the rooring medium. Elongation of the emerged axes was similarly responsive. The elongation rate of both the set of axes and individual axes fell wi4h time. The elongation rate of laterals was less than that of the axes and was sensitive to the excision of seedling organs. The data are discussed in relation to the hypothesis that the growth of the root system is determined by the availability of substrate.
The Free Space of Citrus Leaf Slices
Authors: Smith FA , Fox AL
Published: January 2006

Measurements of 36Cl and 22Na efflux have been used to estimate water free space and Donnan free space in Citrus (orange) leaf slices. The water free space within the slices amounts to about 0.025 ml/g fresh weight, suggesting that there is little infiltration of bathing solution into intercellular air spaces. The exchangeable cations of the Donnan free space within the slices total 20-25 μ-equiv/g fresh weight, and these values appear to reflect the exchange properties of the cell walls. The role of the free space as a 'reservoir' for ions in the intact leaf is discussed.
Productivity of Vegetable Crops in a Region of High Solar Input. IV. Field Chamber Measurements on French Beans (Phaseolus vulgaris L.) And Cabbages (Brassica oleracea L.)
Authors: Sale PJM
Published: January 2006

Net CO2 uptakes have been measured for crop canopies of French beans and cabbages, sown at two plant densities, using a large field assimilation chamber and a semi-closed gas-analysis system.
For both species, the maximum rates of uptake were a little less than 40 mg CO2 dm-2 (ground area) h-1, and light saturation of the canopy occurred at 600-650 W m-2 (French beans) or about 800 W m-2 (cabbages). Net CO2 uptake decreased with leaf area index at values below about 5, but was relatively insensitive to temperature over the range used. Once this leaf area index was reached, the relationship between net uptake and solar radiation remained fairly constant throughout the growth period. For both species, dark respiration rates were markedly dependent on temperature, and also were lower at night than during the day when measured at the same temperature.
For both French beans and cabbages, growth analyses showed the maximum growth rates to be 18-19 g dry weight m-2 (ground area) day-1. The mean growth rate from emergence to harvest for an overwintered cabbage crop was 5.5 g m-2 day-1. It is suggested that the main advantage of the region in terms of plant productivity lies in the long frost-free growing season and the ability of frost-tolerant crops to maintain fairly high growth rates throughout a mild and comparatively sunny winter.
Chlorophyll Synthesis in a Yellow Mutant of Wheat
Authors: Newell E , Rienits KG
Published: January 2006

A spontaneous non-lethal chlorophyll mutant of hexaploid wheat was shown to have a greatly diminished rate of chlorophyll accumulation compared to the wild type when 8-day-old dark-grown plants were illuminated with white light. The rate of conversion of protochlorophyllide to chlorophyll was approximately the same in both types. When leaves from dark-grown plants were incubated in �-aminolaevulinate, protoporphyrin and protochlorophyll accumulated in the mutant whereas larger amounts of protochlorophyll accumulated in the wild type. It was concluded that the mutation brings about a restriction in the rate of conversion of protoporphyrin to magnesium protoporphyrin and its methyl ester. The effect of the mutation on protoporphyrin and protochlorophyll accumu- lation was intensified in crosses of the mutant with lines deficient in one of the No. 7 chromosomes, which control chlorophyll synthesis.
Ultrastructure and Lipid Composition of Zooxanthellae from Tridacna maxima
Authors: Bishop DG , Bain JM , Downton WJS
Published: January 2006

Isolation of zooxanthellae (Gymnodinium microadriaticum) from clam tissue does not result in any loss of the outer limiting layers and the ultrastructure of the cell is similar to that of zooxanthellae found in other clams and corals. The major lipid components of G. microadriaticum are galactosyldiacylglycerols which comprise about 50% of the extractable lipid. The major fatty acids present are palmitic, γ-linolenic and octadecatetraenoic acids, together with a component identified as octadecapentaenoic acid. The presence of γ-linolenic acid is more representative of animal lipids than of plant lipids and there is a possibility that growth of the zooxanthella in a host tissue can affect the fatty acid composition.
Glycine and Serine Production in Marine Plants as a Measure of Photorespiration
Authors: Burris JE , Holm-Hansen O , Black CC
Published: January 2006

The relative amounts of glycine and serine, intermediates in the glycollate pathway in plants, that were 14C labelled in the light in six marine plants under different oxygen concentrations were measured to give an estimation of photorespiration. Glycine and serine were labelled most under the highest concentration of oxygen and least labelling occurred in the lowest oxygen concentration. These results support the theory that an increase in oxygen concentration increases the flow of carbon through the glycollate pathway, thus increasing photorespiration.