bluuebunny/crossref_metadata_2025 huggingface dataset:
In vitro Plantlet Formation in Linum marginale From Cotyledons, Hypocotyls, Leaves, Roots and Protoplasts
Authors: Zhan XC , Jones DA , Kerr A
Published: January 2006

Regeneration of shoots from cotyledons, hypocotyls, roots, leaf explants and callus derived from pro- toplasts of Linum marginale was achieved in vitro on Murashige and Skoog's (MS) medium with various combinations of growth substances. The regeneration capacity of explants from the various sources and their responses to the various media differed considerably. Hypocotyls seemed to be the best explant source for bud regeneration, followed by roots. The optimal combination of growth substances for bud regeneration on hypocotyl explants was 0.02 mg L-1 NAA, 1 mg L-1 6-BA and 20 mg L-1 adenine and on root explants, 1 mg L -1 zeatin. Protoplasts were readily isolated and cultured from shoots, and buds were regenerated from the resulting callus on media with various combinations of growth substances. The best medium was MS medium with 5 mg L-1 zeatin. About 10% of shoots from the various sources formed roots after transfer to MS medium. These regeneration results are assessed with respect to the possible use of various plant genetic engineering techniques to generate genetically transformed plants of L. marginale.
Chlorophyll a/b Ratios and Photosystem Activity of Mesophyll and Bundle Sheath Fractions From Sodium-Deficient C4 Plants
Authors: Johnston M , Grof CPL , Brownell PF
Published: January 2006

Significantly lower chlorophyll a/b ratios were observed in mesophyll thylakoids extracted from sodium-deficient than normal C4 plants of Amaranthus tricolor, Chloris gayana and Kochia childsii. The chlorophyll a/b ratio of bundle sheath thylakoids was not generally as significantly affected by sodium nutrition as the mesophyll thylakoids.
The lower chlorophyll a/b ratio in mesophyll thylakoids of sodium-deficient plants was associated with a lower photosystem II activity. The effect of sodium nutrition on photosystem I activity in the mesophyll thylakoids was dependent upon the species. Although no effect of sodium nutrition on photosystem I was observed in mesophyll thylakoids of K. childsii, photosystem I activity was greater in sodium-deficient than normal plants in A. tricolor. The photosystem II and I activities of the bundle sheath thylakoids were not affected by sodium nutrition in either K. childsii or A. tricolor.
Turgor-Volume Regulation and Cellular Water Relations of Nicotiana tabacum Roots Grown in High Salinities
Authors: Tyerman SD , Oats P , Gibbs J , Dracup M , Greenway H
Published: January 2006

Nicotiana tabacum plants were grown in solution culture with salinity treatments of 1, 100 and 200 mol m-3 [NaCl], in Hoagland solution. After several weeks, solute concentrations and osmotic pressure of cell sap from the roots were measured. Increases in cellular [Na+] and [Cl-] and a smaller reduction in [K+] accounted for the difference in sap osmotic pressure between the 200 mol m-3 and 1 mol m-3 treatments. Turgor pressure (P) of fully expanded cortex cells measured with the pressure probe were 0.48 MPa in 1 mol m-3, 0.24 MPa in 100 mol m-3, 0.20 MPa in 200 mol m-3, and these values agreed with those calculated by difference between internal and external osmotic pressure. Low values of volumetric elastic modulus (ε), ranging from 1.2 MPa to
3.0 MPa at P = 0.42 MPa were obtained, which accounted for long equilibration times to changes in water potential. There was no effect of high salinities on ε after accounting for the fact that ε was a function of P and neither was there an effect on hydraulic conductivity (Lp), which ranged between 1.9 × 10-8 and 24.1 × 10-8 m s-1 Mpa-1. At 200 mol m-3 [NaCl]o, and to a lesser degree at 100 mol m-3 [NaCl]o, root hairs became deformed to resemble spherical bladders (mean diameter = 88 �m) which displayed similar P and water relations to other epidermal cells and cortex cells.
In other experiments the response to a sudden reduction in [NaCl], from 200 to 1 mol m-3 was studied. P of cortex cells first rapidly increased from about 0.15 MPa to 0.53 MPa and then slowly declined with a half time of about 35 min to a new steady state of 0.3 MPa. This level was maintained in intact roots for at least 48 h. The rate of the initial increase in P is limited by water flow into the cells while the slow decline is limited by solute efflux from the cells with water following osmotically. The efflux was mainly in response to reduced external osmotic pressure rather than [NaCl]o. Efflux of Na+, K+ and Cl- accounted for the decrease in internal osmotic pressure but it is possible that the membrane also became more permeable to sugars. With the exception of bladder hairs, the overall integrity of the cell membrane was maintained since Lp did not increase and P declined smoothly to the new level with no evidence of rupture and resealing of the membrane. It is argued that the loss of solutes after the step down in external osmotic pressure consists of turgor or volume regulation in which solute permeability increases steeply as turgor or volume goes above a threshold.
Genotypic Variation in Carbon Isotope Discrimination and Transpiration Efficiency in Wheat. Leaf Gas Exchange and Whole Plant Studies
Authors: Condon AG , Farquhar GD , Richards RA
Published: January 2006

The relationship between carbon isotope discrimination, Δ, measured in plant dry matter and the ratio of intercellular to atmospheric partial pressures of CO2, pi/pa, in leaves was examined in two glasshouse experiments using 14 wheat genotypes selected on the basis of variation in Δ of dry matter. Genotypic variation in Δ was similar in both experiments, with an average range of 1.8 x 10-3. Variation in pi/pa was significant but the range in pi/pa was relatively small, averaging 0.075. In both experiments, Δ measured in dry matter and pi/pa measured in flag leaves were positively correlated. Variation among genotypes in pi/pa was attributed, approximately equally, to variation in leaf conductance and in photosynthetic capacity.
The relationship between plant transpiration efficiency, W* (the amount of above-ground dry matter produced per unit water transpired) and � was also examined. There was a negative correlation between W * and Δ; under well watered conditions and under gradually increasing terminal water stress. The relationship between W* of stressed plants and Δ measured in well watered plants was also negative.
These results indicate that genotypic variation in Δ measured in dry matter should provide a reasonable measure of genotypic variation in long-term mean leaf pi/pa in wheat. Further, selection for improved plant transpiration efficiency in wheat under both well watered and terminally water- stressed conditions should be possible based on Δ measured in well watered plants. The extent to which such selection will be effective in improving transpiration efficiency at the field canopy level may depend on the influence of boundary layer resistance on transpirationsal water loss. Under well watered conditions and at full canopy closure, the influence of boundary layer resistance on canopy water loss may be relatively large and stomatal control of water loss may be limited. Under water stress, stomatal control of canopy water loss will be greater.
Flowering genes and the photothermal flowering responses of pea (Pisum sativum): a re-analysis
Authors: Alcalde J. A. , Wheeler T. R. , Summerfield R. J.
Published: January 2006

Attempts to quantify the effects of the flowering genes
Lf, Sn andHr
in Pisum sativum L. on durations from sowing to
flowering (f) have been hindered by the often strongly
interactive effects of temperature and photoperiod. The original data of Berry
and Aitken (Australian Journal of Plant Physiology
6, 573–587, 1979) for six cultivars have been
re-analysed as rates of progress from sowing to flowering
(1/f) and expressed as functions of mean
pre-flowering values of temperature (T) and photo-period
(P). The photothermal responses of rates of progress
from sowing to flowering were clearly divided into two planes, with the
boundary defined by the critical photoperiod
(Pc). Variations in the response
to temperature when
P<Pc were
associated with differences in alleles at the Lf locus,
whereas variations when P>Pc
were associated with differences at the Hr locus in the
presence of Sn. Allele sn
determined a single-plane response to temperature alone (i.e. a day-neutral
response). The base temperature for 1/f when
P>Pc was
1˚C for all six cultivars. The linear photothermal model used provided a
robust quantitative basis for analysing the effect of flowering genes in pea.
Recovery of the photosynthetic apparatus from photoinhibition during dark incubation of the green alga Dunaliella salina
Authors: Polle Jürgen E. W. , Melis Anastasios
Published: January 2006

The light-independent recovery of the photosynthetic apparatus from
photoinhibition was monitored upon a transition of irradiance-stressed
Dunaliella salina Teod. to darkness. Upon dark
incubation, the chlorophyll (Chl) a /Chl
b ratio of the cells decreased promptly with a half-time
of 2.5 h from about 12:1 to about 5:1. In contrast, dark incubation of control
cells resulted in only a negligible change of the Chl a
/Chl b ratio. During dark incubation of
irradiance-stressed cells, the level of the Chl a and
b light-harvesting proteins of photosystem II (PSII)
increased, a change accompanied by alterations in the composition of these
light-harvesting proteins. The amount of photodamaged PSII, measured from the
relative amount of a 160 kDa protein complex which contains the photodamaged
D1 reaction center protein, decreased during dark incubation after an initial
lag period. Concomitantly, the amount of functional PSII, measured from the 32
kDa form of D1, increased slightly in the dark. The results show that, in the
dark, photodamaged D1 is slowly removed upon degradation from the thylakoid
membrane and replaced by a de novo synthesized D1
protein. The amount of reaction center proteins and number of photochemically
active PSI centers increased in the dark. These results suggest that thylakoid
membranes of irradiance-stressed D. salina exist in a
state of dynamic flux. We conclude that several aspects of the
D. salina recovery from photoinhibition are light
independent.
Effects of Elevated Temperature and Reduced Water Uptake on Enzymes of Starch Synthesis in Developing Wheat Grains
Authors: Caley CY , Duffus CM , Jeffcoat B
Published: January 2006

The mechanism of temperature regulation of endosperm development has been investigated by studying the effects of two temperature regimes on starch deposition and starch synthase activity during grain development in two cultivars of wheat. Most of the starch synthase activity was present throughout development as the granule-bound form using ADPglucose as the principal substrate.
That starch synthase may be a rate-limiting enzyme for accumulation of starch, and hence dry weight, is suggested by: (1) rates are proportionately less in the cultivar with the lower final endosperm dry weight; (2) at elevated temperatures when starch content and dry weight are reduced, starch synthase activity falls; (3) the rate of starch deposition calculated to be possible from measured rates of starch synthase activity is close to the observed rate of starch deposition.
On the other hand, it was concluded that it is not lack of starch synthase activity that causes termination of starch deposition, since activity is maintained well after starch deposition has ceased.
Using the same two wheat cultivars, grown as detached ears in liquid culture, the effects of reduced endosperm water content, induced by the presence of polyethylene glycol in the culture medium, were investigated. Endosperm starch synthase activity was unaffected but ADPglucose pyrophosphorylase activity was greatly reduced, suggesting a possible role in the termination of starch synthesis.
Mechanism of Action of Ethylene in Promoting the Germination of Cocklebur Seeds I. Osmoregulation
Authors: Esashi Y , Matsuyama S , Hoshina M , Ashino H , Ishizawa K
Published: January 2006

The germination potentials of upper and lower seeds of cocklebur (Xanthium pennsylvanicum Wallr.) were increased by pre-exposure to water stress imposed by mannitol or polyethylene glycol (PEG) solution. Both types of seeds were responsive to this 'seed priming' which was further enhanced by C2H4 applied exogenously for at least 1 day. The C2H4 effect that occurred during seed priming increased with increasing water stress. It was not influenced by respiratory inhibitors, such as cyanide, azide, benzohydroxymate or propyl gallate, but it was counteracted by CO2 and increased by O2 enrichment. Both C2H4 and O2 significantly increased osmolarity of the sap extracted from the whole seed, but CO2 reduced it. Similar events occurred in seed axial and especially in cotyledonary tissues, and in water extracts of these tissues. Increased osmotic pressure in response to C2H4 stimulated subsequent cotyledonary growth. These findings were applicable also to the action of C2H4 under anoxic conditions, in which the increased potential of seed germination caused by O2 shortage was further enhanced by C2H4 treatment. The higher osmolarities were linked to a stimulation of cotyledonary growth.
Phosphorylation State of the Light-Harvesting Chlorophyll-Protein Complex of Photosystem II and Chlorophyll Fluorescence Characteristics in Monstera deliciosa Liebm. And Glycine max (L.) Merrill in Response to Light
Authors: Cleland RE , Demmig-Adams B , Adams WW Iii , Winter K
Published: January 2006

Upon a transition from darkness to (low) light, leaves of the rainforest plant Monstera deliciosa which had developed in deep shade exhibited a decline in PS II chlorophyll fluorescence (FO and FM) and a net increase in PS I fluorescence (FO and FM) indicative of a state transition. Upon this transition, LHC-II became phosphorylated. Phosphorylation of LHC-II was maintained upon exposure of M. deliciosa leaves to photon flux densities (PFDs) representing an excess of light, independent of whether the excess of light was created by exposing the leaves to high PFDs in air (where photosynthesis and photorespiration can proceed) or by exposing them to intermediate PFDs in 2% O2 without CO2 (where photosynthesis and photorespiration are prevented). This was in contrast to the response of soybean leaves, in which LHC-II became dephosphorylated under both of these conditions representing an excess of light. These different response patterns may be associated with a heterogeneity of LHC-II populations and/or differences in the expression of energy dissipation in the chlorophyll pigment bed between the two types of leaves.
Survival of rice during complete submergence: effect of potassium bicarbonate application
Authors: Krishnan P. , Ramakrishnayya G.
Published: January 2006

The effect of potassium bicarbonate application to floodwater on the survival
and growth of submergence-tolerant (FR13A) and -intolerant (IR42) rice
cultivars during complete submergence was investigated. Potassium bicarbonate,
applied at different rates to enhance floodwater carbon dioxide
concentrations, increased the floodwater oxygen concentration. The treatment
that had CuSO4, added alone to reduce algal growth
showed the lowest O2 concentration at the time of
submergence and after 10 d of submergence. Potassium bicarbonate at higher
rates tended to maintain the floodwater pH near neutrality while copper
sulfate affected pH increase during a 10-day period of complete submergence.
Potassium bicarbonate addition led to 100% survival of tolerant FR13A.
Potassium bicarbonate, even at 0.01 mol m–3
enhanced the survival of intolerant IR42 to 69% and at 0.1, 0.5 and 1.0
mol m–3, the survival was above 85%. Dry
weights of submerged plants showed increases in both rice cultivars in
floodwater treated with potassium bicarbonate. The dry weight and leaf
chlorophyll concentration of both cultivars increased with increasing rates of
potassium bicarbonate. Algal chlorophyll concentration of floodwater treated
with potassium bicarbonate was comparable to that of the control without
copper sulfate. The findings suggest a possibility of environmental
manipulation of floodwater by potassium bicarbonate application to enhance the
survival and growth of rice cultivars during complete submergence.
Alignment of Cortical Microtubules by Anisotropic Wall Stresses
Authors: Williamson RE
Published: January 2006

Anisotropic mechanical forces exist in the walls of all turgid plant cells except those of spherical unicells. These forces potentially offer the cell important directional information regarding its major and minor axes, and the more complicated force patterns expected in multicellular organs could offer location-specific information. A mechanism is proposed to measure directional forces in the wall as deformations (strain) of molecules associated with cellulose microfibrils and transmit the information across the plasma membrane to orient cortical microtubules. Because microtubules in turn orient the synthesis of the cellulose microfibrils that determine the direction of future cell expansion, a feedback loop is established relating future cell shape to present cell shape and cell position. The loop can provide positive feedback to magnify a small asymmetry in shape, to reinforce an existing growth axis in a cylindrical cell or, by modification of the proteins postulated to convey directional information between wall and cytoplasm, the loop can be broken and the same directional information used to establish a new orientation for cortical microtubules. In this way, modification of a single protein replaces a transverse microtubule array with a helical one.
Rate of Imposition of Water Stress Alters the Accumulation of Nitrogen-Containing Solutes by Wheat Seedlings
Authors: Naidu BP , Paleg LG , Aspinall D , Jennings AC , Jones GP
Published: January 2006

A rapid water stress, imposed by withholding water under a high transpirational demand or by the application of polyethylene glycol (PEG), resulted in the accumulation of glutamine, asparagine and valine in amounts equal to or greater than that of proline. However, progressive water stress imposition resulted in proline and glycinebetaine being the dominant accumulated compounds of those measured. PEG had an apparently specific effect on amino acid accumulation, particularly of the amide forms. With some exceptions, such as glycinebetaine, the stress-induced changes in the content of most solutes were reversible upon rewatering.
Accumulation and changes in molecular size distribution of polymeric proteins in developing grains of hexaploid wheats: role of the desiccation phase
Authors: Carceller J. L. , Aussenac T.
Published: January 2006

Two varieties of wheat differing in high molecular weight glutenin subunit
composition (Soissons, 5+10, Glu-D1a allele; Thésée,
2+12, Glu-D1a allele) were examined to follow the accumulation of
polymeric proteins and the changes in molecular size distribution of these
proteins during grain filling. The accumulation behaviour of polymeric
proteins was determined by size-exclusion-HPLC, multistacking SDS-PAGE and the
constituent polypeptides (high molecular weight and low molecular weight
glutenin subunits) by reversed-phase-HPLC. For both cultivars, the
accumulation of each class of protein was highly asynchronous, especially
between the early deposition of SDS-soluble polymers and the late deposition
of SDS-insoluble polymers, such that the average molecular size of polymeric
protein increased in the period from 30 to 45 days after anthesis in natural
conditions. By applying premature grain desiccations during the cell
enlargement phase, it was demonstrated that the SDS-insoluble polymers
formation was closely related with the process of water loss from the grain.
Moreover, the rapid accumulation of SDS-insoluble polymers coincided with a
rapid decrease in mass of both SDS-soluble polymers and monomers, suggesting
an aggregative mechanism. Over the same period, the molecular size
distribution of the polymers which can be used to differentiate the two
genotypes studied, is highly correlated with the percentage of high molecular
weight glutenin subunits in glutenins present in kernels when desiccation
occurred. The formation of SDS-insoluble fraction is discussed in connection
with the specific contribution of high molecular weight glutenin subunits to
the formation of polymers (subunits linked by disulfide bonds).
Lipids affect the charge stabilization in wild-type and mutant reaction centers of Rhodobacter sphaeroides R-26
Authors: Nagy László , Fodor Elfrida , Tandori Júlia , Rinyu László , Farkas Tibor
Published: January 2006

The effect of lipids on stabilization of electrons on the secondary quinone
was studied in reaction centers (RC) of herbicide-sensitive and -resistant
(L229Ile → Met)
Rhodobacter sphaeroides R-26. The lipid concentration
and the lipid/protein ratio of the intracytoplasmic membranes (ICM) were
larger in the mutant RCs than in the wild-type. The free energy changes of Q
A – Q
B → Q A Q
B – electron transfer were
ΔG 0 = –57 meV,
–69 meV, –85 meV for the wild-type and ΔG
0 = 0 meV, –15 meV, –46 meV for the
mutant at pH = 8.0, in detergent, liposome and ICM, respectively. The
differences in the stabilization energies of both strains decreased from the
detergent via proteoliposome to chromatophore. We conclude that the energetics
of the interquinone electron transfer depends on the environment of the
reaction center. The steric and/or electrostatic interactions of the
environment and Q B pocket can modulate the energetics
of the charge stabilization over large distances. The interaction may have
crucial importance on coupling the electron transport in the photosynthetic
membrane to the anabolic/catabolic processes taking place in the cells.
Antisense RNA inhibition of pyruvate, orthophosphate dikinase and NADP malate dehydrogenase in the C4 plant Flaveria bidentis: analysis of plants with a mosaic phenotype
Authors: Ashton Anthony R. , Furbank Robert T. , Trevanion Stephen J.
Published: January 2006

Antisense RNA suppression of either pyruvate, orthophosphate dikinase [EC
2.7.9.1] or NADP malate dehydrogenase [EC 1.1.1.82] gene
expression in the C4 dicot
Flaveria bidentis L. var. Kuntze produced several
independent transgenic lines with leaves showing heritable, mosaic phenotypes.
The appearance of these plants was highly variable, with leaves that were
either predominantly green, predominantly yellow, or a mixture of the two. The
yellow sectors appeared to be clonal in origin. For both sets of transgenic
plants, the green and yellow sectors showed a reduction in the activity of the
respective target enzyme compared to wild-type leaves. The mRNA of the target
enzyme was reduced in both green and yellow sectors of leaves of both types of
transformants compared to leaves from wild-type plants. The yellow sectors had
decreased amounts of other photosynthetic enzymes on an area basis, but most
enzyme activities and electron transport rates were similar to the green
sectors on a chlorophyll basis. The mosaic phenotype could not be attributed
simply to the degree of suppression of the target enzyme, because we have also
obtained uniformly green plants with similar or greater enzyme suppression.
The importance of this spatial variability in the effectiveness of the
antisense transgenes for the analysis of transgenic plants in general is
discussed.
Plant mitochondrial protein import: mechanisms and control
Authors: Whelan James
Published: January 2006

The characterisation of components of the plant mitochondrial import apparatus
along with the availability of over one hundred nuclear-encoded mitochondrial
proteins allows the study of plant mitochondrial protein import in homologous
systems. From these studies it has emerged that although similarities in the
import process exist with other organisms, significance differences exist,
such as receptor structure, location of processing peptidase and targeting
signals. These differences mean that previous studies carried out in
heterologous systems must be re-evaluated. Further studies into protein import
in plants need to be directed at understanding the mechanism of import and how
this process may be controlled. In this review the latter points will be dealt
with in terms of summarising our current knowledge and possible future
directions.
Thylakoid membrane architecture
Authors: Mehta Monaz , Sarafis Vassilios , Critchley Christa
Published: January 2006

Confocal scanning laser microscopic observations were made on live
chloroplasts in intact cells and on mechanically isolated, intact
chloroplasts. Chlorophyll fluorescence was imaged to observe thylakoid
membrane architecture. C3 plant species studied included
Spinacia oleracea L.,
Spathiphyllum sp. Schott, cv. ‘Mauna Loa’,
and Pisum sativum L. C4 plants
were also investigated: Saccharum officinarum L.,
Sorghum bicolor L. Moench,
Zea mays L. and Panicum miliaceum
L. Some Spinacia chloroplasts were treated with
3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) to enhance or sodium dithionite
(SD) to reduce the photosystem II fluorescence signal. Confocal microscopy
images of C3 chloroplasts differed from electron
microscopy pictures because they showed discrete spots of bright fluorescence
with black regions between them. There was no evidence of fluorescence from
stroma thylakoids. The thylakoid membrane system at times appeared to be
string-like, with brightly fluorescing grana lined up like beads.
C4 bundle sheath chloroplasts were imaged from three
different types of C4 plants.
Saccharum and Sorghum bundle
sheath chloroplasts showed homogeneous fluorescence and were much dimmer than
mesophyll chloroplasts. Zea had rudimentary grana, and
dim, homogeneous intergrana fluorescence was visualised.
Panicum contained thylakoids similar in appearance and
stringlike arrangement to mesophyll chloroplasts. Isolated
Pisum chloroplasts, treated with a drop of 5 mM
MgCl2 showed a thylakoid membrane system which appeared
to be unravelling. Spongy mesophyll chloroplasts of
Spinacia treated with 5 mM sodium dithionite showed a
granal thylakoid system with distinct regions of no fluorescence. A
time-series experiment provided evidence of dynamic membrane rearrangements
over a period of half an hour.
Insights into the consequences of grana stacking of thylakoid membranes in vascular plants: a personal perspective
Authors: Anderson Jan M.
Published: January 2006

The striking structural architecture of thylakoid membranes of higher plant
and some green algal chloroplasts that house the light harvesting and energy
transducing functions of chloroplasts have evoked many hypotheses concerning
the significance of grana. The differentiation of the thylakoids into grana
and stroma membrane regions is a morphological reflection of the non-random
distribution of the photosystems II and I between appressed and non-appressed
membrane domains, which became known as lateral heterogeneity. In this
overview, the first section deals with changing concepts regarding the
distribution of the photosystems between stacked and unstacked thylakoid
domains from a personal historical perspective. The remaining section
describes some functional implications of the lateral separation of most PSII
complexes in appressed membrane regions of grana stacks from PSI complexes,
ATP synthase and auxiliary proteins located in non-appressed membrane domains.
Effects of sulfate-starvation and re-supply on growth, NH4+ uptake and starch metabolism in Chlorella sorokiniana
Authors: Di Martino Rigano Vittoria , Vona Vincenza , Carfagna Simona , Esposito Sergio , Carillo Petronia , Rigano Carmelo
Published: January 2006

Chlorella sorokinianaShihira & Krauss, strain 211/8K resuspended in a illuminated mediumshowed continuous growth, and concomitantly NH4 +in the medium depleted at a constant rate. Upon sulfate removal, i) growthdeclined, ceasing within 5 h; ii) NH4 + depletionbecame almost undetectable over 2 h; and iii) photosynthetic capacity (Pc) wasreduced over 24 h by 80% in the light, but was reduced by only30% in darkness. Over 24 h of S starvation the chlorophyll content ofilluminated cells decreased by 50%, whereas that of darkened cellsdecreased by only 10%. Sulfate-deprivation over 24 h resulted in anoticeable increase in the starch content of the cell and a net increase inthe pools of glutamate, glutamine, serine and asparagine. Cysteine content, incontrast, was decreased. Sulfate addition to cells starved of S for 24 hprovoked a sudden time-dependent increase in Pc and in an immediate renewal ofgrowth in light but not in darkness. Sulphate supply also caused a suddenenhancement of respiratory oxygen consumption and a prompt degradation ofstarch. Starch was degraded at a higher rate in illuminated than in darkenedcells. After the S addition, depletion of NH4 + inthe medium occurred at slowly increasing rates; amino acids decreasednoticeably over 4 h, where in contrast, cysteine increased noticeably.
Inhibition of carnation petal inrolling by growth retardants and cytokinins
Authors: Taverner Elizabeth A. , Letham David S. , Wang Jian , Cornish Edwina
Published: January 2006

Excised carnation petals induced to senescence
by ethrel (an ethylene-releasing compound) exhibited morphological changes
that closely resembled those of senescing petalsin situ
in cut flowers. The sensitivity of the excised petals to ethylene was reduced
by exogenous cytokinin and this type of hormonal interaction in the control of
plant development is discussed. Using the excised petals, a number of known
and potential growth inhibitors were compared for ability to prevent petal
inrolling induced by ethrel. Cycloheximide and 6-methylpurine were the most
effective and inhibited inrolling almost completely, but purine, purine
riboside, lauric acid, L-azetidine-2-carboxylic acid and
n-decyl alcohol were also very effective. All these
compounds were considerably more effective than any cytokinin tested. When
supplied through the transpiration stream to short-stemmed carnations,
cycloheximide, 6-methylpurine and purine inhibited inrolling nearly completely
and the flowers finally senesced by water loss. 6-Methylpurine inhibited
ethylene production in cut flowers and RNA synthesis in excised petals very
markedly. Degradation of exogenous zeatin riboside by cytokinin oxidase, and
the level of activity of the enzyme in petals, were reduced by 6-methylpurine.
These biochemical changes probably account for the strong inhibition of
inrolling induced by this compound.
Hypothesis: Are grana necessary for regulation of light harvesting?
Authors: Horton Peter
Published: January 2006

The importance of the functional flexibility of the light-harvesting complexes
of photo-system II (LHCII) in accommodating the fluctuation in the balance
between light input and metabolic capacity in plants is emphasised. This
flexibility is provided for by a relatively complex assembly of protein
subunits, the interactions between them being controlled by protonation,
xanthophyll de-epoxidation and phosphorylation. It is suggested that the
3-dimensional order imposed upon this assembly of proteins by the grana is a
vital aspect of the modulation of LHCII function. Grana establish the LHCII
conformation needed for efficient light harvesting and help prevent the dense
array of proteins from collapsing into a highly dissipative state. The grana
then allow a controlled development of non-photochemical quenching under the
driving force of violaxanthin de-epoxidation and protonation. In plants grown
under different irradiances the different grana content and xanthophyll cycle
pool size together allow maximum quantum yield in limiting light and an
appropriate level of non-photochemical quenching in excess light.
Estimation of photorespiratory carbon dioxide recycling during photosynthesis
Authors: Delfine Sebastiano , Di Marco Giorgio , Loreto Francesco
Published: January 2006

Photorespiration rate can be estimated in vivo but the
actual amount of photorespiratory CO2 emitted or
recycled by the leaf is largely unknown. We exploited the insensitivity of
infrared gas analy-zers to 13CO2
to detect the photorespiratory CO2 emission of leaves
exposed to air containing only
13CO2. Photorespiratory
CO2 emission was calculated by subtracting the
12CO2 emitted under
non-photorespiratory (2% O2) conditions from that
emitted under photorespiratory (21% O2)
conditions. Illuminated leaves of herbaceous and tree species emitted a
constant amount of 12CO2 within
30–60 s after switching to
13CO2. Photorespiratory
CO2 emission was less than 20% of the
photorespiratory rate simultaneously calculated by combining fluorescence and
gas exchange. Thus, the leaves recycled more than 80% of
photorespiratory CO2. The highest recycling was
associated with high rates of photosynthesis in tomato and spinach. In the
dark, mitochondrial respiration measured by the emission of
12CO2 in air with
13CO2 was similar to that measured
by conventional gas exchange in ambient air, thus confirming the accuracy of
our method. In the light, mitochondrial respiration estimated from the
emission of 12CO2 after complete
labeling of photorespiration was lower than in the dark, suggesting either
light-inhibition or recycling of respiratory carbon.
Contribution of Stem Dry Matter to Grain Yield in Wheat Cultivars
Authors: Pheloung PC , Siddique KHM
Published: January 2006

Field experiments were conducted in the eastern wheat belt of Western Australia in a dry year with and without irrigation (1987) and in a wet year (1988), comparing three cultivars of wheat differing in height and yield potential. The aim of the study was to determine the contribution of remobilisable stem dry matter to grain dry matter under different water regimes in old and modern wheats.
Stem non-structural carbohydrate was labelled with 14C 1 day after anthesis and the activity and weight of this pool and the grain was measured at 2, 18 and 58 days after anthesis. Gutha and Kulin, modern tall and semi-dwarf cultivars respectively, yielded higher than Gamenya, a tall older cultivar in all conditions, but the percentage reduction in yield under water stress was greater for the modern cultivars (41, 34 and 23%). In the grain of Gamenya, the increase in 14C activity after the initial labelling was highest under water stress. Generally, loss of 14C activity from the non-structural stem dry matter was less than the increase in grain activity under water stress but similar to or greater than grain activity increase under well watered conditions. Averaged over environments and cultivars, non-structural dry matter stored in the stem contributed at least 20% of the grain dry matter.
Effects of Exposure of Wheat Ears to High Temperature on Dry Matter Accumulation and Carbohydrate Metabolism in the Grain of Two Cultivars. I. Immediate Responses
Authors: Jenner CF
Published: January 2006

Ears of wheat were exposed for up to 7 days during the grain-filling stage to high temperature (35�C day/25�C night) and metabolic responses in the grain were compared to those in ears maintained at lower temperatures (21�C day/16�C night). Two cultivars of wheat known to differ in their post-anthesis tolerance of high temperature were compared. Raising the temperature resulted in a small increase in the rate of dry matter accumulation: both cultivars responded similarly. Sucrose content of the endosperm was either not affected or increased by raising the temperature. Raising the temperature had differential effects on glucose and fructose content: fructose was substantially reduced while glucose was either unaffected or slightly increased. After raising the temperature the concentrations of all three hexose phosphates measured, glucose-6-phosphate (G-6-P), glucose-1-phosphate (G-1-P) and fructose-6-phosphate (F-6-P), were reduced similarly on a percentage basis and to about the same extent as fructose. The concentration of the sugar nucleotide (UDP-glucose) resulting from the breakdown of sucrose by sucrose synthase was also reduced at high temperature. Judging from calculated mass-action ratios, all three catalytic steps involved in the interconversion of the metabolites mentioned above were close to equilibrium, and only one mass action ratio (for sucrose synthase) was affected by heating: it was doubled. Although temperature clearly resulted in changes in the reaction catalysed by sucrose synthase, it was not clear how temperature had acted. Concentration of the precursor for starch synthesis (ADP-glucose) was slightly lower in both cultivars at the higher temperature. Taken together the responses could provide at least a partial explanation for the smallness of the increase in starch deposition with increase in temperature, but do not explain the different responses of these two cultivars to high temperature.
AC Impedance Measurements on Chava corallina.II. Can the Presence of Plasmalemmasomes be Detected?
Authors: Chilcott TC , Coster HGL
Published: January 2006

Impedance measurements on cells of Chara corallina at frequencies of 10-102 Hz were used to investigate dielectric and geometrical properties of the plasmalemma and tonoplast at different longitudinal positions along the cylindrical surface of the cells.
Large (100%) spatial variations occurred in the measured capacitance of some individual cells. Further, for spatially uniform cells, a 100% variation (from cell to cell) in capacitance was observed.
Variations in capacitance (at 10-102 Hz) could be partially attributed to variations in: (i) the conductance of the series conductance element, (ii) the dielectric/geometrical properties of the tonoplast and (iii) the conductance of the cell membranes. However, we attribute a substantial part of the variations in capacitance to variations in the area of the plasmalemma per unit area of cell surface arising from extensive folding of the plasmalemma such as that found in plasmalemmasomes (charasomes).
The Effect of High Temperature on the Accumulation of Dry Matter, Carbon and Nitrogen in the Kernel of Rice
Authors: Tashiro T , Wardlaw IF
Published: January 2006

Transferring rice plants (Oryza sativa L. cv. Calrose) growing at 27/22�C to a range of dayhight temperatures 7 days after heading resulted in little variation in kernel size with temperature in the range from 24/19�C (mean 21.7�C) to 30/25�C (mean 26.7�C). This is close to the mean monthly temperature recorded for the rice growing areas of southern Australia during the period of kernel development. There was a significant drop in kernel dry weight with a further increase in temperature to 33/28�C and 39/24�C.
When plants were transferred to a temperature of 36/31�C for periods of 8 days, commencing at regular intervals from heading, the greatest change in dry weight of the kernels occurred when the treatment commenced 12 days after heading and the kernels were in the linear phase of dry matter accumulation.
The flow of nitrogen into kernels was more stable than that of carbon as temperatures were increased, with little change in nitrogen (mg) per kernel until the temperature was greater than 33/28�C. Changes in temperature away from the optimum (27/22�C) always resulted in an increase in the concentration of kernel nitrogen. The greatest reduction in kernel nitrogen (mg kernel-1), like that of carbon, occurred in high temperature treatments commencing 12 days after heading.
In vitro Thermal and Salt Stability of Pyruvate Kinase Are Increased by Proline Analogues and Trigonelline
Authors: Shomer-Ilan a , Jones GP , Paleg LG
Published: January 2006

The nitrogenous compounds N-methyl-L-proline (MP), trans-4-hydroxy-N-methyl-L-proline (MHP) and trigonelline (T), which undergo stress-induced accumulation in some Australian plants, were analysed and compared with proline (P) and glycinebetaine (B) for possible protective roles. The activity of pyruvate kinase (PK), prepared from Zea mays leaves and rabbit muscle, was unaffected even in the presence of 750 mM of the proline analogues. Thus, MP and MHP, like P and B, have the properties to act in vivo as compatible osmotica. T was not as compatible, decreasing enzyme activity 20% at 0.5 M. Like P and B, however, MP, MHP and T all also exhibited protective properties. They increased, in vitro, the thermal stability of PK from both plant and animal sources, and they protected PK (Zea mays) from salt inhibition at two substrate levels. The effect of salt on PK (Zea mays) was substrate dependent; at low phosphoenolpyruvate (PEP) levels, salt inhibited the enzyme activity, while salt effects were less severe in the presence of higher substrate levels. In the presence of high NaCl concentrations, the protective effects of high substrate levels and the compatible solutes seem to be additive. The Km (PEP) value of the plant PK increased in the presence of salt but the effect was ameliorated by the compatible solute MHP.
Silicon Accumulation and 13C Composition as Indices of Water-Use Efficiency in Barley Cultivars
Authors: Walker CD , Lance RCM
Published: January 2006

Barley cultivars were examined for silicon accumulation in dry matter as a possible indicator of water-use efficiency (W), and for their organic 13C composition, whose discrimination from the 13C composition of atmospheric CO2 (Δ) is an accepted indicator of W. Silicon concentration was found to correlate with 13C discrimination more strongly in the field than in the glasshouse experiments. We suggest that, under mild glasshouse conditions, plants actively accumulate Si whereas, under higher evaporative demand in the field, Si accumulates passively on the transpiration stream. We find that Si may be used as a corroborative indicator of water-use efficiency in normal field circumstances.
Factors Determining Host Recognition in the Clover-Rhizobium Symbiosis
Authors: Djordjevic MA , Weinman JJ
Published: January 2006

Rhizobia are microbes that exploit host plants as a nutritional source but cause little or no host damage. They may provide, through biological nitrogen fixation, a valuable source of nitrogen for plant growth. Different rhizobia nodulate a limited range of plants. In this review we will show that host range specificity is determined by the success or otherwise of communication events between the interacting partners. To infect different plant species, a distinct cocktail of phenolic compounds (flavonoids) is recognised. Flavonoids of the correct structure induce the expression of several bacterial nodulation (nod) and other genes required for plant infection. Flavonoids of the incorrect, but related, structure can antagonise nod gene induction. Some nod genes are responsible for the synthesis of a small family of lipo-oligosaccharides necessary for the triggering of a defined but complex series of morphological responses in the host plant including root hair curling and cortical cell division. Lipo-oligosaccharides are active at concentrations of between 10-8 and 10-12 M. The appropriate lipo-oligosaccharide required for infection of one plant host can have antagonistic effects on other non-host plants and this effect appears to be determined by minor chemical changes to the basic lipo-oligosaccharide structure. Apart from host specificity operating at the genus level, other interdependent nod gene functions determine host specificity at the cultivar level. A complex interplay between positively and negatively acting nod genes and a single host gene affects cultivar specificity in a manner analogous to, but more complex than, the gene-for-gene interactions common amongst plant-pathogen interactions.
Viroids in Australian Citrus: Relationship to Exocortis, Cachexia and Citrus Dwarfing
Authors: Gillings MR , Broadbent P , Gollnow BI
Published: January 2006

Viroids are the smallest infectious agents known, being unencapsidated RNAs of 240-380 bases. Citrus exocortis viroid (CEV) causes poor tree performance, especially when infected scions are grafted to trifoliate orange or citrange rootstocks. To eliminate infected budwood trees, various methods were used to detect CEV, including field inspections, bud inoculation of Etrog citron indicators (in which CEV causes severe epinasty) and hybridisation with CEV cDNA. A large number of trees with exocortis- like symptoms such as dwarfing and/or bud union abnormalities produced only mild epinasty when grafted on Etrog citron and did not hybridise to the CEV probe. Upon purification and electrophoretic analysis, the presence of viroids other than CEV was demonstrated.
Screening of over 1800 trees resulted in the detection of four groups of viroids as determined by RNA homology and length in nucleotides. CEV was the only member of the first group and was the largest viroid detected, with 371 bases. CEV almost invariably occurred with other viroids of lower molecular weight. The second group, CV I, contained two viroids, of 325 and 332 bases, which were not homologous to CEV or hop stunt viroid (HSVd). Group CV II contained three viroids, of 297, 299 and 302 bases, all of which were homologous to HSVd. The CV III group contained two viroids, of 290 and 295 bases, which were not homologous to CEV or HSVd. The CV II and CV III groups were strongly associated with various field symptoms, including the disease cachexia (CV IIb), and dwarfing of trees on trifoliate orange rootstock. To confirm any causal relationship between individual viroids and field symptoms, viroids representative of each group were purified and used to inoculate Etrog citron. Tissue from these citrons was used to inoculate young field trees with viroids, singly and in combination. Parson's Special mandarin inoculated with CV IIb showed symptoms of cachexia after 2 years, confirming CV IIb as a causal agent of this disease. It will probably be 5 years before the effect of other inoculations can be assessed.
The role of biomass allocation in the growth response of plants to different levels of light, CO2, nutrients and water: a quantitative review
Authors: Poorter Hendrik , Nagel Oscar
Published: January 2006

The allocation of biomass to different plant
organs depends on species, ontogeny and on the environment experienced by the
plant. In this paper we first discuss some methodological tools to describe
and analyse the allocation of biomass. Rather than the use of shoot:root
ratios, we plead strongly for a subdivision of biomass into at least three
compartments: leaves, stems and roots. Attention is drawn to some of the
disadvantages of allometry as a tool to correct for size differences between
plants. Second, we tested the extent to which biomass allocation of plants
follows the model of a ‘functional equilibrium’. According to this
model, plants respond to a decrease in above-ground resources with increased
allocation to shoots (leaves), whereas they respond to a decrease in
below-ground resources with increased allocation to roots. We carried out a
meta-analysis of the literature, analysing the effect of various environmental
variables on the fraction of total plant biomass allocated to leaves (leaf
mass fraction), stem (stem mass fraction) and roots (root mass fraction). The
responses to light, nutrients and water agreed with the (qualitative)
prediction of the ‘functional equilibrium’ theory. The notable
exception was atmospheric CO2, which did not affect
allocation when the concentration was doubled. Third, we analysed the
quantitative importance of the changes in allocation compared to changes in
other growth parameters, such as unit leaf rate (the net difference between
carbon gain and carbon losses per unit time and leaf area), and specific leaf
area (leaf area: leaf biomass). The effects of light,
CO2 and water on leaf mass fractions were small compared
to their effects on relative growth rate. The effects of nutrients, however,
were large, suggesting that only in the case of nutrients, biomass allocation
is a major factor in the response of plants to limiting resource supply.