bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduction of ferric chelates by leaf plasma membrane preparations from Fe-deficient and Fe-sufficient sugar beet
Authors: González-Vallejo Elena B. , Abadía Anunciación , González-Reyes Jose Antonio , Abadía Javier , López-Millán Ana Flor , Yunta Felipe , Lucena Juan José
Published: January 2006

The ferric chelate reductase activities of leaf plasma membranes isolated from
the leaves of Fe-deficient and Fe-sufficient sugar beet have been
characterized. Substrates used were the complexes of ferric iron with ethylene
diamine tetraacetic acid, citric acid and malic acid. Iron deficiency was
associated with 1.5- to 2-fold increases in leaf plasma membrane ferric
chelate reductase activity when rates were calculated on a protein basis. The
natural complexes of ferric iron with citrate and especially with malate were
good substrates for the ferric chelate reductase enzyme present in leaf plasma
membrane preparations. The apparent affinities were higher for the ferric
malate complex. The optimal pH for the activity of the ferric chelate
reductase in sugar beet leaf plasma membranes was in the range 6.5–7.0.
The ferric chelate reductase activity decreased by approximately 30%
when the assay pH was decreased to 5.8 or increased to 7.5. Therefore, our
data provide evidence against the hypothesis that changes in apoplastic pH
could decrease markedly the activity of the ferric chelate reductase enzyme in
plasma membrane preparations from the leaves of Fe-deficient plants.
Influence of NaCl Salinity on the Behaviour of Protease, Aminopeptidase and Carboxypeptidase in Rice Seedlings in Relation to Salt Tolerance
Authors: Dubey RS , Rani M
Published: January 2006

Activities of the enzymes protease, aminopeptidase and carboxypeptidase were determined in seedlings of rice cultivars with different salt tolerances raised under increasing levels of NaCl salinity. Salinity caused a marked increase in protease activity in roots as well as shoots, though activity was higher in roots than in shoots. Salt-tolerant cultivars possessed higher levels of protease activity in control as well as salt-stressed seedlings compared with salt-susceptible cultivars. During a growth period of 5-20 days, leucine aminopeptidase (LAP) activity increased up to days 10-15 and decreased thereafter. Salt treatment caused a sharp increase in LAP activity in roots of both sets of cultivars. The increase was larger in tolerant than in susceptible cultivars. In shoots, unlike roots, higher salinity suppressed LAP activity, and suppression was more marked in susceptible cultivars than in tolerant ones. Carboxypeptidase activity was higher in susceptible cultivars than in tolerant ones under both control as well as salt treatments. Roots maintained higher levels of carboxypeptidase activity than shoots. Results suggest an increased rate of proteolysis in salt-stressed rice seedlings and an association of salt-tolerance ability with higher protease and aminopeptidase activities and lower carboxypeptidase activity under salinisation.
Manipulation of Chromosomal Segments From Wild Wheat for the Improvement of Bread Wheat
Authors: Appels R , Lagudah ES
Published: January 2006

Specific alien chromatin segments have been used for many years to introduce novel disease resistance genes into bread wheat. The 1RS chromosome segment being used in Australian wheats will be discussed in detail to present the molecular biological studies carried out on this chromosome segment as well as its agronomic contributions to wheat. Studies are also being carried out on the manipulation of the D genome of wheat. Within Australia we have initiated the screening of a collection of 420 accessions of Triticum tauschii (the donor of the D genome) involving groups in the Departments of Agriculture in New South Wales, Victoria, Western Australia and the University of Sydney as well in the Division of Plant Industry. Disease resistance has been sought and found for cereal cyst nematode, Septoria nodorum, Septoria tritici, Puccinia striiformis, P. recondita and P. graminis. At the DNA level the collection has been screened for variation at the 5Sdna and Nor loci, as well as generating Pst (a restriction endonuclease) genomic clones, in preparation for providing RFLP markers for a genetic linkage map. Lines of T. tauschii showing high levels of disease resistance have been crossed directly to Australian wheat cultivars or are being used to form synthetic hexaploids by crossing to tetraploid wheats.
Arabidopsis thaliana: a Model Plant for Studying the Molecular Basis of Morphogenesis
Authors: Smyth DR
Published: January 2006

Morphogenesis in higher plants is likely to be controlled by the serial activation of genes. These genes could be identified if the structure which they normally control is specifically disrupted when they are in mutant form. By cloning and characterising the products of such genes we could gain an understanding of the genetic control of morphogenesis. This report makes a case for following this strategy using Arabidopsis thaliana as a model species. This species is easily grown, has a short, 6-week life cycle and convenient genetics. Mutations affecting embryogenesis, trichome structure, the inflorescence and floral organs are already known. Because Arabidopsis has a tiny genome (70 000 kbp), cloning of genes known only by mutant phenotype is practicable by chromosome walking and DNA tagging. The role of their products in cellular and developmental decisions could then be investigated. Genes controlling morphogenesis are likely to be conserved across higher plants. Once they have been cloned from a model species their isolation from other species by DNA hybridisation is relatively simple. Generalisations about the origin, action and evolution of such genes would then be possible. Also artificial manipulation of morphogenesis may be achievable.
Cereal Dehydrins: Serology, Gene Mapping and Potential Functional Roles
Authors: Close TJ , Chandler PM
Published: January 2006

Barley and maize seedlings exposed to a non-lethal dehydration treatment were previously shown to synthesise dehydration-induced protein (dehydrins). Antibodies against maize dehydrin react immunologically with polypeptides in dehydrating barley and wheat seedlings. Barley dehydrin cDNA hydridises to RNA present in dehydrating wheat, and other grass seedlings. These results indicate similarity of dehydrin epitopes, mRNA sequences, and gene regulation amongst dehydrins of several grasses, including wheat and barley. Two barley dehydrin genes were assigned to barley chromosome 6 (dhn3 and dhn4) and two to chromosome 7 (dhn1 and dhn2) using barley dehydrin cDNA clones and DNA from wheat-barley addition lines. Genes on the same chromosome have greater similarity in sequence than between chromosomes. Analysis of several different barley cultivars with one of the dehydrin cDNA clones revealed restriction fragment length polymorphism.
Substrate Gradients and Regional Patterns of Dry Matter Deposition Within Developing Wheat Endosperm. II. Amino Acids and Protein
Authors: Ugalde TD , Jenner CF
Published: January 2006

Microsectioning and HPLC techniques were used to determine the gradient of protein deposition in developing wheat endosperm along the radial axis from the endosperm cavity to the endosperm periphery on the dorsal side. Soluble amino acids were measured also along this axis to test whether the pattern of protein deposition could be due to amino acid supply.
Glutamine, serine, glycine and alanine accounted for 80% of the soluble amino acids in both the vascular bundle of the grain and the fluid of the endosperm cavity. Alanine, asparagine, glutamate, serine and glycine accounted for 70% of the soluble amino acids in the endosperm. There was little change in amino acid composition across the endosperm both in the pool of soluble amino acids and in protein. An exception was soluble aspartate which increased in the outward direction.
The outer region of developing endosperm contained nearly twice as much protein, per unit fresh volume, as the region adjacent to the endosperm cavity. The pattern of protein percentage (w/w) was due to the pattern of protein deposition, and not to regional variation in starch deposition.
There were two main features in the distribution of total soluble amino acids across the endosperm. First, the concentration (w/v) decreased along the axis from the endosperm cavity to the mid-point of the endosperm, due to the influence of higher concentrations in the fluid of the endosperm cavity. Second, there was an increase in the concentration of amino acids from the mid-point of the endosperm towards the endosperm periphery. We conclude that the regional pattern of protein deposition cannot be attributed to the pattern of substrate supply, and that transport of amino acids across the endosperm imposes no limits to the pattern of protein deposition.
The endosperm contained sufficient amino acid substrate for 1.4 days of protein accumulation. The turnover of amino acids as a whole within the endosperm was slow compared with the rapid turnover of substrate for starch deposition. There was large variation in turnover time for individual amino acids. We discuss the apparent anomaly that while there seems to be ample amino acid substrate to sustain protein deposition, additional amino acid supply in the form of glutamine enhances the rate of protein deposition.
Internal Phosphorus Flows During Development of Phosphorus Stress in Stylosanthes hamata
Authors: Smith FW , Jackson WA , Berg PJV
Published: January 2006

Partitioning and net transfer of phosphorus between shoots and roots in the tropical forage legume Stylosanthes hamata cv. Verano during the development of phosphorus deficiency has been studied. Plants were stressed by either growing them in dilute flowing culture on continuously maintained external phosphorus concentrations that were inadequate for maximal growth, or by transferring plants of varying phosphorus status to phosphorus-free media.
An external phosphorus concentration of 1 �M P was found to be just adequate for maximal growth of S. hamata. Phosphorus stress caused rapid and substantial increases in root weight percentage. It is proposed that this represents an important adaptive mechanism for maximising phosphorus uptake by S. hamata growing in phosphorus-deficient soils.
Roots contained the minimum proportion of the plant's phosphorus content when root phosphorus concentrations were 8-10 �mol P g-1 root, and shoot phosphorus concentrations were 16-20 �mol P g-1 shoot. When tissue concentrations were less than these values, plants suffered from phosphorus stress and phosphorus was either preferentially retained by the roots or rapidly transferred from shoots to roots, reducing the growth rates of shoots, but permitting root growth to continue. Upon reducing the external phosphorus supply to plants whose root phosphorus concentrations exceeded 8 to 10 �mol P g-1 root, excess phosphorus was rapidly transferred from the root to the shoot to maintain shoot growth rates.
The mobility of phospborus within the plant, and the apparent lack of any delay in transferring phosphorus from shoots to roots as phosphorus stress developed, represent another adaptive feature that is likely to be important to the successful growth of S. hamata in low phosphorus soils. When the phosphorus supply was limited, the plant's resources were directed toward maintaining root growth. Even extremely phosphorus deficient plants, in which shoot growth had ceased, maintained linear rates of root growth. These linear rates were related to the total phosphorus content of the plant. In the latter stages of phosphorus deprivation, linear rates of root growth were maintained by remobilisation of phosphorus from the older parts of the root system to sustain the phosphorus supply to the root meristems.
Growth and Carbon Economy of Wheat Seedlings as Affected by Soil Resistance to Penetration and Ambient Partial Pressure of CO2
Authors: Masle J , Farquhar GD , Gifford RM
Published: January 2006

Wheat seedlings were grown on soils with different resistances to root penetration and at various ambient partial pressures of CO2, pa. The partial pressure pa was varied either (a) as soon as seedlings emerged and until the end of the experiment (i.e. until c. 2 weeks after sowing, until the three leaf stage) or (b) only after the effects of high soil resistance were well established, and then for two days. In the first week after emergence, a higher soil resistance induced slower growth of both roots and shoot. This effect was independent of pa. We conclude that at this stage, with much of the plant's carbon being supplied from hydrolysis of seed reserves, growth at high soil resistance was not C-source limited. There was, however, a positive relationship between shoot growth rate and the carbohydrate concentration in that tissue, the degree of which varied with soil resistance. A given carbohydrate concentration was associated with a lower growth rate at high, compared with low, soil resistance. We deduced that this reduced sensitivity of growth to internal availability of substrate carbohydrate may be one manifestation of a sink limitation.
Subsequent to the first week following emergence, roots grew faster on soil with higher resistance, while the shoot continued to grow more slowly. As seed reserves were becoming exhausted, growth became sensitive to pa, i.e. somewhat source-limited. This response to partial pressure of CO2 was mainly seen in the roots. The correlation between growth rate and carbohydrate levels was maintained. We conclude that increased soil resistance induces a factor which retards shoot growth, partly by decreasing its sensitivity to carbohydrate levels, making more carbon available for root growth. It is unclear whether or not this factor also directly affects the physiology of the roots.
A higher soil resistance resulted in greater respiratory losses as a proportion, Φ, of carbon fixation. Reduced pa also induced greater Φ. Theory is developed relating Φ to carbon assimilation, allocation and maintenance. It leads to the prediction that respiratory losses, as a proportion, Φ, should be increased under most environmental conditions which reduce relative growth rate.
Photosynthetic Responses to Phosphorus Nutrition in Eucalyptus grandis Seedlings
Authors: Kirschbaum MUF , Tompkins D
Published: January 2006

Eucalyptus grandis seedlings were grown in growth units in which plant roots were suspended in air while continuously being sprayed with nutrient solution (aeroponic system). Phosphorus was added to nutrient solutions in exponentially increasing amounts which determined plant growth rates. Plants were grown at five relative phosphorus addition rates, and photosynthetic performance of leaves was compared across treatments. Carbon assimilation rates ranged from 11.7 μmol m-2 s-1 for plants with lowest phosphorus status to 23.1 μmol m-2 s-1 for plants with highest phosphorus status. Intercellular partial pressures of CO2 concomitantly decreased from 260 pbar for plants with lowest to 220 μbar for plants with highest phosphorus status. Leaves in all treatments showed a decrease in assimilation rate at intercellular partial pressures of CO2 above c. 600 μbar. There was no consistent correlation between the extent of that decrease and the phosphorus status of leaves.
Assimilation rates were correlated with leaf phosphorus content. This relationship was apparent on either a unit leaf area or unit leaf weight basis. Assimilation rates and leaf nitrogen content per unit leaf weight were also correlated. In contrast, there was no correlation between leaf assimilation rate per unit leaf area and nitrogen content per unit leaf area, as nitrogen content per unit area was similar for all phosphorus treatments. The differences between correlations on a weight and area basis were due to differences in specific leaf area in different treatments, with plants with lower phosphorus status having less leaf area per unit leaf weight. The photosynthetic measurements showed that CO2 assimilation rate, together with relative leaf growth rate, was one of the processes most sensitive to phosphorus nutrition.
Disruption by Temperature of Floral Evocation and Cell-Cycling in the Shoot Apical Meristem of Helipterum roseum
Authors: Sharman KV , Sedgley M , Aspinall D
Published: January 2006

Flowering is inhibited in plants of Helipterum roseum grown under constant 25°C temperature conditions with a 12 h photoperiod and irradiance of 250 W m-2, but not at a constant temperature of 20°C. Floral inhibition was investigated by transferring plants between the two temperature con- ditions at different times to determine the morphological stage of inhibition, and by investigating cell-cycling at the shoot apex at the two temperatures.
Floral initiation in Helipterum roseum was inhibited if the temperature increase from 20 to 25°C occurred at the doming of the apical meristem, and was delayed when the increase occurred at the initiation of involucral bracts. Steady-state cell-cycling was observed in the shoot meristem at 20°C and the cell-cycle duration was estimated at the morphological stages of large vegetative meristem, doming of the meristem and initiation of the involucral bracts. The length of the cell-cycle at these stages was 64 h, 41 h and 47 h respectively. Steady-state cell-cycling was not observed in shoot apical meristems at 25°C, and the meristem did not undergo the floral transition. It is concluded that the stage of commitment to flower is the initiation of involucral bracts, and that floral initiation is inhibited at 25°C by the loss of steady-state cell-cycling at the shoot apex.
The Influence of Salinity on Growth, Water Relations and Photosynthesis in Diplachne fusca (L.) P. Beauv. Ex Roemer & Schultes
Authors: Myers BA , Neales TF , Jones MB
Published: January 2006

The responses to increasing salintiy (in the range 0-420 mol m-3 NaCl) of an Australian accession of the halophytic grass, Diplachne fusca, have been studied in two experiments; in terms of growth, water relations, ion uptake and leaf photosynthesis.
Twenty-one to 41 days after salinisation, plant dry weight, leaf area and relative growth rate were decreased at salinities at and above 300 mol m-3. Although salinity in the range 0-200 mol m-3 did not significantly affect growth rate, the highest value was at 200 mol m-3. Towards the end of the sampling period, a recovery of leaf growth rates was greater in plants at salinity levels of 90-200 mol m-3. The salt tolerance of this accession is similar to that reported for other populations of this species.
As salinity in the root environment was increased, the osmotic potential of the leaf sap (Ψs) and the difference between leaf water potential and Ψs increased progressively with each harvest. There was no evidence that a lack of a capacity to adjust osmotically was related to the observed inhibition of growth at high salinity levels.
It was confirmed that D. fusca possessed a C4 mode of leaf photosynthesis: the maximum assimilation rate (A) observed was high (>50 μmol m-2 s-1), the operating intercellular CO2 concentration (Ci) was approximately 140 μmol mol-1, the initial slope of the A v. CI curve ('carboxylation efficiency') was steep (1.24 μmol m-2 s-1) and the optimum leaf temperature for photosynthesis was approximately 45°C. At high salinities leaf conductance (g) was reduced by 78%. Using an analysis of A v. I and A v. CI relationships, the components of the 'photosynthetic capacity' of the mesophyll reduced by high salinity were Amax, carboxylation efficiency and photorespiration rate. There was no consistent relationship, at three salinity levels, between growth rates and Amax and carboxylation efficiency. It appears unlikely, therefore, that the primary inhibitory effects of salinity on growth are attributable to effects on leaf photosynthetic processes.
A UV-light activated cinnamic acid isomer regulates plant growth and gravitropism via an ethylene receptor-independent pathway
Authors: Yang Xiao Xian , Choi Hiu Wan , Yang Shang Fa , Li Ning
Published: January 2006

Naturally occurring cinnamic acids (CA) exist in both
trans- and cis-isoforms. UV-light
irradiation of trans-CA is able to produce
cis-CA. cis-CA was found to
possess auxin-like activity before. In contrast, the vapor of
cis-CA induced an epinastic response in tomato plants
just as ethylene does. Given the existence of a double bond in and the gaseous
nature of cis-CA, we suspected that
cis-CA might also function as an ethylene-like compound.
To distinguish between these possibilities, we selected an ethylene
perception-deficient tomato plant, Never-ripe
(Nr), and an ethylene biosynthesis-deficient tomato
plant, A11. Not only did the vapor of cis-CA fail to
trigger A11 tomato fruit ripening but it also delayed the ripening of banana
fruit. Moreover, the vapor of cis-CA induced epinasty
and the ‘triple response’ in both the wild type and
Nr tomato plants, indicating that the vapor of
cis-CA does not act via an ethylene receptor-dependent
pathway. Furthermore, the vapor of cis-CA inhibited the
negative gravitropic response of stems of both etiolated
Nr seedlings and young plants, whereas ethylene had
little effect on the negative gravitropism of the Nr
plants. These results support the conclusion that the action sites of the
vapor of cis-CA and ethylene are fundamentally
different.
Regulation of NaCl-induced proline accumulation by calmodulin via modification of proline dehydrogenase activity in Ulva fasciata (Chlorophyta)
Authors: Lee Tse-Min , Liu Chia-Hsiung
Published: January 2006

This paper examined the role of proline dehydrogenase (PDH; EC 1.4.3.1) in
salinity-induced (adjusted by increasing NaCl contents in seawater) proline
accumulation in the marine chlorophyte Ulva fasciata
Delile, and also determined whether calmodulin modulates proline accumulation
via a change in the activity and kinetic property of
PDH. Upon exposure to varying salinity (30–120‰, that is,
317.9–1858 mМ NaCl in seawater) for 9 h, proline levels increased
with increasing salinity, and were highly correlated with salinity
(r2 = 0.97). In contrast,
PDH-specific activity decreased with increasing salinity, and was inversely
related with external salinity (r2
= 0.95) and proline levels
(r2 = 0.80). When exposed
to 60‰ salinity (831.3 mМ NaCl), PDH-specific activity decreased at
hour 2, and proline levels increased at hour 3, as compared to the 35‰
(403.5 mМ NaCl) control. The addition of chlorpromazine (CP, 0.8
µМ) or trifluoperazine (TFP, 1 µМ), both calmodulin
binding inhibitors, in seawater enhanced the increase in the levels of
proline, but did not affect its Km
value. It also enhanced the decrease in the specific activity and
Vmax value of PDH in the
60‰-treated thallus discs. Overall, the reduction in catabolism via a
decrease in PDH activity is associated with the NaCl-induced proline
accumulation in U. fasciata, and the calmodulin-mediated
signal transduction might be negatively involved in the regulation of proline
accumulation via a modification in PDH properties.
Subcellular and tissue Mn compartmentation in bean leaves under Mn toxicity stress
Authors: González Alonso , Lynch Jonathan P.
Published: January 2006

Non-aqueous fractionation was used to characterize subcellular and tissue Mn
compartmentation of mature and immature leaves of two common bean
(Phaseolus vulgaris L.) cultivars contrasting in their
response to Mn toxicity. Excess Mn decreases leaf CO2
assimilation through a reduction of chlorophyll content in immature leaves
with no effect detected on mature leaves. We hypothesized that differential
accumulation of Mn in chloroplasts occurs at different leaf developmental
stages. Chloroplasts of immature leaves accumulated at least three times as
much Mn as those of mature leaves at equivalent total foliar Mn. Chlorosis was
positively correlated with Mn concentration in chloroplasts from high-Mn
plants (r2 = 0.96;
P = 0.003) but was not correlated with Mn in
unfractionated tissue (r2 =
0.026; P = 0.793) nor with Mn in the
epidermis-enriched fraction (r2
= 0.33; P = 0.314). Both cultivars showed
high accumulation of Mn in the vacuoles as determined by the co-localization
of α-mannosidase and Mn content on a continuous density gradient.
Cultivars differed significantly in Mn concentration in an epidermis-enriched
fraction, with the tolerant cultivar Calima accumulating more Mn in this
fraction than the sensitive cultivar ZPV-292. In both cultivars, Mn was
accumulated up to 2400 µg g–1 dry weight in
crystal-type structures whereas the unfractionated leaf tissue contained about
500 µg g–1 dry weight. The results
demonstrate that Mn compartmentation occurs at both the tissue and the
organelle level and that Mn accumulation in the epidermis-enriched fraction
could contribute to Mn tolerance in common bean. The role of Mn accumulation
in structures resembling oxalate crystals is discussed.
Drought-induced increase in wheat germ agglutinin (WGA) accumulation in developing wheat embryos appears to be independent of ABA
Authors: Bhaglal Priya , Singh Prabhjeet , Bhullar S. S.
Published: January 2006

Accumulation of wheat germ agglutinin (WGA) in the developing embryos of three
different wheat (Triticum aestivum L.) cultivars,
PBW-138, PBW-299 and C-306, was studied in relation to abscisic acid (ABA)
accumulation under water stress conditions at 18, 24 and 30 days post anthesis
(DPA) under natural conditions. Imposition of water stress in all three
cultivars resulted in enhanced ABA levels in the embryos at all stages of
grain development. On the contrary, the increase in WGA accumulation in the
embryos in response to drought was stage- and cultivar-dependent. Our results
suggest that apart from ABA, other factors that are temporally expressed may
be involved in drought-induced regulation of the WGA gene.
Effect of salinity on salt accumulation and reproductive development in the apical meristem of wheat and barley
Authors: Munns Rana , Rawson H. M.
Published: January 2006

Two cultivars of wheat and two of barley differing in salt tolerance were
grown at 0, 100 and 175 mМ NaCl, and the development of the apex was
followed as it turned from vegetative to reproductive. Apices were taken for
ion analysis when most of the spikelet primordia had been produced and the
process of differentiation into floral organs was starting. K
+ concentrations in apices were unaffected by the
salinity treatment, Na + concentrations were
generally low in all treatments, below 50 mМ, while Cl
− levels were very low, below 30 mМ. These
levels of Na + and Cl −
are too low to affect metabolism. In spite of these negligible effects on ion
levels in the apex, salinity affected reproductive development: fewer spikelet
primordia formed, and final spikelet numbers at ear emergence were reduced.
Salinity greatly advanced the time of floral initiation in the wheat
cultivars. This indicates that modification of apical development by salinity
was not determined by salt in the apex itself, but mediated by signals or
substrates derived from elsewhere in the plant.
Ethylene inhibitors improve dry matter partitioning and development of late flowering spikelets on rice panicles
Authors: Mohapatra Pravat Kumar , Naik Pradeep Kumar , Patel Rajesh
Published: January 2006

Primary branch development of the rice panicle
was in the order of a basipetal sequence from the top to the bottom at the
time of anthesis. Delayed development of spikelets on the proximal branches of
the panicle resulted in reduced grain filling. Two experiments were carried
out to manipulate growth and development of the proximal spikelets with
exogenous application of chemicals regulating formation or action of ethylene.
In the first experiment, inhibitors of ethylene synthesis (cobalt) and action
(silver) improved grain biomass and specific gravity of the basal spikelets,
while 2-chloroethylphosphonic acid (CEPA) depressed these parameters
significantly. In the second experiment, the ethylene synthesis inhibitor
1-aminoethoxyvinylglycine (AVG) promoted spikelet development on the basal
primary branches and improved their survival and grain biomass. On the
contrary, the ethylene precursor 1-aminocyclopropane-1- carboxylic acid (ACC)
inhibited growth and development of these spikelets. The action of AVG was
reversed when ACC was applied in combination with AVG. In both experiments,
the chemicals did not influence growth and development of the superior
spikelets on the apical primary branches of the panicle. Depression of growth
and development by CEPA or ACC coincided with a concomitant rise in soluble
carbohydrate concentration of the spikelets, whereas treatments with ethylene
inhibitors decreased the concentration of the materials. The role of ethylene
in metabolic dominance of the apical spikelets and its impact on grain yield
of rice panicles is discussed.
Influence of plant age and growth conditions on nitrate assimilation in roots of Lotus japonicus plants
Authors: Pajuelo Purificación , Pajuelo Eloísa , Orea Alicia , Romero José M. , Márquez Antonio J.
Published: January 2006

In roots of Lotus japonicus (Regel) Larsen cv. Gifu, the
level of NADH-nitrate reductase (NR) activity and protein, as well as
ferredoxin-nitrite reductase activity and nitrate accumulation, were higher in
roots of young plants, and decreased in mature plants grown in seed trays.
When plants were grown in larger pots, the decrease in NR activity and nitrate
accumulation took place at a later stage of growth, suggesting that the
cessation of nitrate assimilation in mature plants could be related to both
ageing and a lower availability of space for roots. Low NR activity was
detected in leaves, whereas nitrate accumulation in this tissue could reach
relatively high levels. NR activity and protein, and nitrate accumulation,
also decreased in leaves of mature plants, indicating that the diminution in
nitrate accumulation and NR in roots from mature plants is not related to a
shift of the nitrate assimilation process from roots to leaves. Measurement of
the extent of total and active NR according to the
phosphorylation/dephosphorylation inactivating mechanism described for
spinach leaf NR, indicates that this mechanism is operative on NR from
L. japonicus roots, being responsible for a great
proportion of inactive NR protein. The amount of inactive NR protein in roots
due to the aforementioned phosphorylation mechanism also increased in mature
plants.
A model for the topology of the chloroplast thylakoid membrane
Authors: Arvidsson Per-Ola , Sundby Cecilia
Published: January 2006

A model for the topological organization of the chloroplast thylakoid membrane
is presented. A series of illustrations is provided, which outline a suggested
3-dimensional structure in cross-section and in full shape, which accounts
both for the folding of one continuous membrane into multiple grana stacks as
seen in cross-sectional electron micrographs and for the rapid reversible
unfolding (destacking) of the grana stacks into lamellar sheets.
Defensive strategies against high light stress in wild and D1 protein mutant biotypes of Erigeron canadensis
Authors: Darkó Éva , Váradi Gyula , Lemoine Yves , Lehoczki Endre
Published: January 2006

The Ser264ÆGly
substitution on the D1 protein is accompanied by a higher photosensitivity of
the mutant plant. This may be due to an increased D1 protein turnover
and/or to a lower xanthophyll cycle activity
in vivo. The relative importance of these two
photoprotective mechanisms in wild and D1 protein mutant biotypes of
Erigeron canadensis L. was established by using
dithiothreitol and streptomycin. Moreover, the interconversion of
violaxan-thin to zeaxanthin via antheraxanthin was studied in isolated
thylakoids and in intact leaves treated with paraquat. Streptomycin caused a
more severe decrease in the optimal quantum yield
(Fv/Fm)
of PS II and a large increase in the initial fluorescence yield
(Fo) in the mutant compared to the wild biotype. In the
fluorescence-quenching parameters of the wild-type leaves, dithiothreitol
caused alterations similar to those observed in the mutant plant without
dithiothreitol. A lowered activity of the xanthophyll cycle was detected in
the mutant biotype compared to the wild-type in vivo.
However, under in vitro, conditions which were optimal
for violaxanthin de-epoxidation, or when paraquat was used on intact leaves to
accelerate the electron transport, violaxanthin could readily be converted to
zeaxanthin even in the mutant plants. This demonstrates that neither the
decrease in the enzymatic activity of violaxanthin de-epoxidase nor the low
availability of violaxanthin is responsible for the low zeaxanthin formation
under in vivo conditions. It is presumed that,
in vivo, the D1 protein mutation results in slower
electron transport, a smaller DpH and lower zeaxanthin formation, and thereby
in alterations in the defensive strategies against high light illumination.
On the Occurrence and Structure of Subunits of Endopolygalacturonase Isoforms in Mature-Green and Ripening Tomato Fruits
Authors: Pogson BJ , Brady CJ , Orr GR
Published: January 2006

Endopolygalacturonase [poly(1,4-α-galacturonide) glycanohydrolase EC 3.2.1.151 occurs in tomato fruit in three molecular forms- PG1, PG2A, PG2B. Trace amounts of PG1, 1-10 pkat g-1 are shown to occur in mature-green fruit as compared to 17 nkat in ripe fruit. As polygalacturonase activity increases through ripening, the percentage of the activity due to PG1 decreases progressively from 100 to less than 20. On fully or partly demethylated substrates, PG1 is more active than PG2 when the ionic strength is that expected in the tissue apoplast. A method for purifying PGI from ripe fruit is described. PG1 preparations contain polypeptides of Mr 45, 43 and 38 thousand. The Mr 43 thousand and 45 thousand components correspond in size to PG2A and PG2B and are detected by antisera raised against PG2A. The M, 38 thousand polypeptide is immunologically distinct. From carbohydrate and amino acid analyses, this polypeptide appears to contain 2870 carbohydrate as glucosamine, mannose, xylose and fucose attached to a polypeptide of estimated Mr 28 342 that is rich in tyrosine and glycine. A method for purifying the subunits of PG1 by cation exchange chromatography in 6 M urea is described. PG2A and PG2B were separated by column chromatography and shown to have identical N-terminal sequences, and serine at the C-terminus. PG2A and PG2B are confirmed as two glycoforms of the one polypeptide. The possibility that PGl consists of populations of molecules containing either PG2A or PG2B coupled with the Mr 38 thousand polypeptide is discussed.
Distribution of Charasomes in Chara: Banding Pattern and Effect of Photosynthetic Inhibitors
Authors: Bisson MA , Siegel A , Chau R , Gelsomino A , Herdic SL
Published: January 2006

Charasomes are structured elaborations of plasmalemma of some Charophytes which may be involved in enhanced transport of ions or inorganic carbon across the plasmalemma. They show a highly non-uniform distribution. We report here a novel method of quantifying charasome population density, using scanning electron microscopy of cell fragments removed from the cell wall. Consistent differences in density can occur in neighbouring regions of the membrane. The distribution of densities is not normal, but is skewed toward lower densities, with large areas of membrane showing no charasomes. Contrary to previous published reports, we found no correlation with acid and alkaline banding patterns. Inhibition of photosynthesis by either dark or DCMU (dichlorophenyl dimethyl urea, an inhibitor of photosystem II) results in a complete loss of charasomes in 1-3 weeks.
Differences in Water Relations Parameters for the Chlorenchyma and the Parenchyma of Opuntia ficus-indica Under Wet Versus Dry Conditions
Authors: Goldstein G , Andrade JL , Nobel PS
Published: January 2006

Water relations of the photosynthetic tissue (chlorenchyma) and of the water-storage parenchyma were studied for well watered and droughted Opuntia ficus-indica, a crassulacean acid metabolism plant cultivated worldwide for its fruits and cladodes. For well watered plants, die1 changes in osmotic pressure were evident in the chlorenchyma. Droughting the plants for 4 months resulted in a massive loss of water from the cladodes, particularly from the water-storage parenchyma, which could lose up to 82% of the water present at full turgor without irreversible tissue damage. Pressure-volume curves indicated a decrease in the osmotic pressure at full turgor of about 0.1 MPa for the water-storage parenchyma cells during drought; such a decrease of osmotically active solutes was consistent with the appearance of large numbers of starch grains. The bulk modulus of elasticity was 0.36 MPa for the water-storage parenchyma cells and 2.5-fold higher for the chlorenchyma cells, which were smaller with thicker cell walls than the former cells. Mucilage, a polysaccharide occurring extracellularly, constituted about 14% of the cladode dry weight; it could hold more than 30% of the total water content of the water-storage parenchyma. Polymerisation of sugars, large elastic cells in the water-storage parenchyma and mucilage with its high water-holding capacity helped maintain a positive turgor in the photosynthetic tissue, even after 4 months of drought.
AC Impedance Measurements on Chara corallina.I. Characterisation of the Static Cytoplasm
Authors: Chilcott TC , Coster HGL
Published: January 2006

Measurements of impedance (or admittance) of Chara corallina at frequencies of 1-102 Hz have revealed conduction, dielectric, geometrical and phenomenological properties of the plasmalemma and tonoplast.
At much higher frequencies, 102-104 Hz, the impedance of these membranes is mainly capacitative and small. Thus, measurements of the overall impedance of these frequencies largely reflect the electrical properties of regions in series with the membranes. The data and arguments presented indicate impedance measurements at these frequencies derive substantially from the static cytoplasm.
Results indicated the conductance of the static cytoplasm ranged from 0.5 to 300 S m-2. Conductance was strongly dependent on temperature; a 10�C rise in temperature produced more than a 2-fold increase in conductance.
The Physiology of Starch and Protein Deposition in the Endosperm of Wheat
Authors: Jenner CF , Ugalde TD , Aspinall D
Published: January 2006

Yield and protein percentage are key issues in the production and marketing of wheat. Yield is a measure of the activity of processes contributing to deposition of starch in the grain, and protein percentage, while not independent of yield, reflects processes in nitrogen metabolism. This paper considers starch and protein deposition in the endosperm of wheat from a physiological point of view and, in particular, explores the extent to which deposition of starch or protein can be manipulated and increased independently of the other product.
Rate and duration of both starch and protein deposition in the endosperm of wheat are all independent events, controlled by separate mechanisms. Consideration of this independence can contribute to promoting specific responses within the plant that culminate in starch and protein deposition, whether attempts at improvement be genetic or agronomic in approach. The capacity, or potential, of the grain to accumulate dry matter is established during the grain enlargement phase, that is within the first 15-20 days after anthesis. Genetic, morphological and physiological factors influence development of this capacity, but a major determinant is a substrate effect on mitotic activity in the endosperm. Grain filling commences 10-15 days after anthesis and occupies the last 20-30 days until the grain ripens. Grain filling is the deposition of polymeric product in cells and organelles formed during the grain enlargement phase. Undoubtedly, stress curtails assimilate supply during grain filling but, under adequate growing conditions, both the rate and duration of starch deposition during grain filling are determined mainly by factors that operate within or close to the grain itself. On the other hand, the rate and duration of protein deposition are determined mainly by factors of supply external to the grain. This contrast can be considered in its simplest form as starch deposition lying on an asymptotic region of a rate-versus-supply relationship, while protein deposition lies on a linear region.
Strategies for improving starch and protein deposition in wheat are discussed. Starch yield and protein yield should be selected as independent traits in cultivar improvement, and crop management should reflect differences in source-sink relations for starch deposition and protein deposition during the grain filling stage.
Sugar Metabolism and Compartmentation
Authors: Hawker JS , Jenner CF , Niemietz CM
Published: January 2006

A brief general picture of areas of current interest in the field of sugar metabolism and compartmentation in higher plants is presented. The control of partitioning of carbohydrate between sucrose and starch in leaves (source), the breakdown and utilisation of sucrose in sinks, and the storage of sugars and starch in sinks is described. Pathways of sucrose transport (excluding plasmalemma transport), control of sugar metabolism by fructose 2,6-bisphosphate, the role and source of inorganic pyrophosphate in sugar metabolism and the transport of carbon across the amyloplast envelope receive special attention.
Drought Stress Induces Changes in the Non-Structural Carbohydrate Composition of Wheat Stems
Authors: Virgona JM , Barlow EWR
Published: January 2006

The effect of drought stress on the non-structural carbohydrate (NSC) composition and water relations of the wheat (Triticum aestivum L.) stem has been investigated. Five separate parts of the stem were sampled: the unsheathed portion of the peduncle (Stem 1a), the sheathed portion of the peduncle (Stem 1b), the penultimate internode (Stem 2), the lower internodes (Stem 3+4) and the flag-leaf-pulvinus (pulvinus). The NSC was analysed as two fractions, an ethanol-soluble carbohydrate (ESC) fraction containing mono- and di-saccharides and some low molecular weight oligosaccharides, and a water-soluble carbohydrate (WSC) fraction containing mostly fructans and some high molecular weight oligosaccharides.
In Stems 1b, 2 and 3 +4, the imposition of drought midway through grain filling resulted in a shift in soluble carbohydrate from the WSC to the ESC fraction indicating hydrolysis of fructans. In Stem 2 on day 29 of grain filling, the WSC/ESC ratio was 7.6 � 1.5 in well watered plants in contrast to 0.5 � 0.1 in droughted plants on day 30, even though NSC concentration did not differ. The NSC content of Stem la and the pulvinus increased threefold under drought, although levels were significantly lower than in the rest of the stem. The WSC/ESC ratio in these tissues was low com- pared to the rest of the stem but still declined noticeably under drought stress. Turgor (P) was fully maintained in Stem 2 and the pulvinus of droughted plants. Under drought, P in the pulvinus was maintained at higher levels (1.9-2.4 MPa) than in Stem 2 (0.8-1.2 MPa).
Determination of the Average Partial Pressure of CO2 in Chloroplasts From Leaves of Several C3 Plants
Authors: Caemmerer SV , Evans JR
Published: January 2006

Measurements of CO2 and water vapour exchange by leaves were combined with measurements of carbon isotope composition (13C/12C) of CO2 in the air passing over the leaf. Carbon isotope discrimination during CO2 uptake was determined from the difference in carbon isotope composition of the air leaving the leaf chamber with or without a leaf enclosed. Leaves of wheat plants grown with different nitrogen nutrition and leaves of several other species were examined.
The measurements, made at different irradiances for a given leaf, showed that carbon isotope discrimination was strongly correlated with the rate of CO2 assimilation as well as the ratio of intercellular to ambient partial pressure of CO2, pI/pa. A function relating carbon isotope discrimination to the rate of CO2 assimilation was used to estimate the CO2 transfer conductance, gw, from the substomatal cavities to the sites of carboxylation for individual leaves. The photosynthetic capacity correlated with the CO2 transfer conductance, gw, and the average ratio of chloroplastic to intercellular partial pressure of CO2, pI/pa, was 0.7. This means that in general under high irradiance, the ratio of chloroplastic to ambient partial pressure of CO2 is about 0.5. In wheat, variation in gw was correlated with the chloroplast surface area appressing intercellular airspaces.
Anther Culture of Australian Wheat Germplasm Using Modified C17 Medium and Membrane Rafts
Authors: Luckett DJ , Venkatanagappa S , Darvey NL , Smithard RA
Published: January 2006

Experiments with wheat anther culture were conducted with the aim of assembling a workable system for doubled-haploid production for Australian wheat breeding. One Australian cultivar, Grebe, carrying the 1BL/1RS translocation was particularly responsive. A modified C17 medium was developed which proved effective when solidified with agarose or when used as a liquid in conjunction with membrane support rafts. The membrane rafts have great potential to assist the development of the anther culture procedure since the medium can be rapidly replenished or replaced with minimal disturbance of the tissue.
Quantum Yield of Photosystem II and Efficiency of CO2 Fixation in Flaveria (Asteraceae) Species under Varying Light and CO2
Authors: Krall JP , Edwards GE , Ku MSB
Published: January 2006

The quantum yields of electron transport from photosystem II (PSII) (Φe, determined from chlorophyll a fluorescence), and CO2 assimilation (ΦCO2, photosynthetic rate/light intensity) were measured simultaneously in vivo with representative species of Flaveria which show a progression in development between C3 and C4 photosynthesis and in reduction of photorespiration. These were F. pringlei (C3), F. sonorensis (C3-C4, but lacking a C4 cycle), F. floridana (C3-C4, with partially functional C4 cycle), F. brownii (C4-like) and F. bidentis (C4). The level of PSII activity with varying CI under 210 mbar O2 was very similar in all species. However, the progressive development of C4 characteristics among the species produced an increased efficiency in utilisation of PSII derived energy for CO2 assimilation under 210 mbar O2, due to reduced photorespiratory losses at low CO2 levels. In all species, when photorespiration was limited by low O2 (20 mbar), there was a linear or near linear relationship between the quantum yield of PSII v. the quantum yield of CO2 fixation with varying intercellular levels of CO2 (Ci) indicating that CO2 fixation in this case is linked to PSII activity. When switching from 20 to 210 mbar O2 at atmosphere levels of CO2, there was a similar decrease in the efficiency in utilising PSII activity for CO2 assimilation at different light intensities, but the degree of sensitivity to O2 progressively decreased among the species concomitant with the development of C4 photosynthesis. These results may help explain why there is an advantage to evolution of C4 photosynthesis in environments where Ci becomes limiting.