bluuebunny/crossref_metadata_2025 huggingface dataset:
Endogenous biosynthetic precursors of (+)-abscisic acid. VII. The 1′,4′-trans-diol is formed from ABA, it is not a precursor
Authors: Milborrow B. V. , Lee H.-S.
Published: January 2006

[14C]ABA fed to avocado fruit is known to be
converted into the 1′,4′-trans-diol and
[14C]1′,4′-trans-diol
has been shown to be converted into ABA by several plant tissues. As a
‘cold trap’of trans-diol becomes labelled
with 14C when
[14C]mevalonate is converted into ABA, the
trans-diol has been suggested to be the immediate precursor of ABA. This
proposal has now been tested by feeding
[5-14C,5-3H2]mevalonolactone
to unripe avocado fruit and measuring the 3H
:14C ratio in the ABA and in the
1′,4′-trans-diol isolated from the fruit
after 16 h. Little labelled diol was present unless a ‘cold trap’
of unlabelled 1,4-trans-diol was added with the
mevalonate. One 3H atom, derived from those at C-5 of
mevalonate, would be expected at C-4′ of the diol, adjacent to the
hydroxyl group, and another at C-5 of the side chain of the diol if the diol
were a precursor of ABA (3H:14C
ratio of 2:3). However, if the 4′-hydroxyl group had been oxidised to a
ketone to form ABA, then the 3H atom at C-4′ of
the diol would have been lost and the
3H:14C ratio would be expected to
be 1:3. The normalised 3H : 14C
ratios of ABA and 1′,4′-trans-diol
biosynthesised from
[14C,5-3H2]mevalonate
were 0.915:3 and 0.844:3 respectively and after oxidation of the diol to ABA
with MnO2 the ratio was 0.869:3 i.e. there was no
3H at C-4′ of the diol. These ratios are as
expected for the trans-diol if it had been formed by
reduction of ABA. This, and the absence of labelled diol in the fruit unless a
‘cold trap’was added, establishes that the
1′,4′-trans-diol is formed from ABA and it
is not a precursor. The formation of the diols from newly synthesised labelled
ABA in cell-free systems can be attributed to the addition to the homogenate
of compounds with strong reducing potential.
NADPH2+ (8.4 nmol) added to a mung
bean seedling homogenate caused the reduction of
(±)-[14C]ABA (0.37 nmol, 22.5
µCi/mol) to trans-diol (1189 dpm) whereas with
NADP+ only 338 dpm were present in
trans-diol. Glutathione (46 nmol) caused the formation
of 1214 dpm while oxidised glutathione produced 638 dpm. Less
1′,4′-cis-diol was formed.
Evaluation of the aluminium-induced root growth inhibition in isolation from low pH effects in Glycine max, Pisum sativum and Phaseolus vulgaris
Authors: Lazof Dennis B. , Holland Michael J.
Published: January 2006

The interaction between proton and aluminium toxicities was examined in
soybean (Glycine max L.), pea
(Pisum sativum L.) and bean
(Phaseolus vulgaris L.). Accurate characterization of
genotype Al-sensitivity in solution culture experiments, employing a
continuous Al-exposure, required response definition at both growth-enhancing
and growth inhibiting activities. Essentially, this involved multiple controls
to account for the interactive effects. Experiments measuring growth during a
recovery period in Al-free solution were more successful in distinguishing
genotypic response to Al, especially in species demonstrating high
H+ -sensitivity. The time, concentration and basal
solution dependencies of the characteristic genotype response for the three
species examined were consistent with the hypothesis that responses of
genotypes may be predicated upon conditions emphasizing irreversible (cell
division) effects. Cell extension effects, however, appear to be rapid,
largely-reversible and often not different between differentially Al-sensitive
genotypes growing in a complete nutrient solution.
Light use in relation to carbon gain in the mangrove, Avicennia marina, under hypersaline conditions
Authors: Sobrado M. A. , Ball M. C.
Published: January 2006

Photosynthesis was studied in relation to light use in the mangrove,
Avicennia marina (Forsk.) Vierh. var.
australasica (Walp.) Moldenke, growing under soil
salinities equivalent to one and two times seawater (i.e. 35 and 60‰).
Midday CO2 assimilation rates averaged 7.6 0.7 and 4.3
0.3 µmol m–2 s–1
at the seawater and hypersaline sites, respectively. Despite this difference,
xanthophyll pool sizes per Chl and epoxidation states were similar at both
sites. Non-photochemical quenching also indicated comparable energy
dissipation from pigment beds. Electron transport rates calculated from
fluorescence characteristics were also similar and exceeded the requirements
to sustain measured assimilation rates. However, cell wall conductance was low
in seawater plants (75 mmol m2
s–1 ) and declined to 40 mmol
m–2 s–1 in hypersaline
plants. This would cause CO2 concentrations in
chloroplasts (Cc ) to be lower
than expected from measurements of intercellular CO2
concentrations (Ci ). In seawater
plants, Cc was estimated to be 144
µmol mol–1 when
Ci was 245 mmol
mol–1, while values for
Cc and
Ci in hypersaline plants were 78
and 212 mmol mol–1, respectively. Reductions in
Cc would enhance rates of
photorespiration relative to assimilation, with the higher photorespiratory
rates being sufficient to account for apparent excess electron transport
rates.
Response to oxygen deficiency in primary maize roots. II. Development of oxygen deficiency in the stele has limited short-term impact on radial hydraulic conductivity
Authors: Gibbs J. , Turner D. W. , Armstrong W. , Sivasithamparam K. , Greenway H.
Published: January 2006

The short-term impact of oxygen deficiency on root hydraulic conductivity
(Lpr), was evaluated in excised
maize roots using hydrostatic and osmotic driving forces, after exposing the
roots to a flowing medium containing 0.05 mol m-3
dissolved O2. Hypoxia reduced hydrostatically-determined
Lpr of roots in a pressure probe,
but this reduction was transient, usually recovering to values for aerated
roots after 4–6 h of exposure to 0.05 mol m-3
O2. The Lpr
of exuding maize roots, calculated using the rate of exudation and osmotic
pressure of exuding sap, was depressed after 24 h exposure to 0.05 mol
m-3 dissolved O2, but only
marginally so. The data suggested that a reduction in
Lpr is not a principal effect of
exposure of these roots to hypoxia, and that long term changes in water fluxes
in O2 deficient roots, reported in the literature, may
be an indirect, rather than direct effect of O2
deficiency on roots. Despite a similar response to O2
deficiency, Lpr calculated for
exuding roots was 1/30th of that for roots attached to the pressure probe.
The reduction in hydrostatically determined
Lpr in response to
O2 deficiency, although transient, suggests that under a
hydrostatic driving force, there is a substantial flow of water via the
protoplastic pathway, in addition to the generally accepted apoplastic
component.
Interactions of rice seedlings with bacteria isolated from rice roots
Authors: Prayitno J. , Stefaniak J. , McIver J. , Weinman J. J. , Dazzo F. B. , Ladha J. K. , Barraquio W. , Yanni Y. G. , Rolfe B. G.
Published: January 2006

The interactions between two groups of rice endophytic bacterial strains and
several rice cultivars were investigated. Various strains of
Rhizobium leguminosarum bv.
trifolii, originally isolated from rice plants grown in
Egypt, comprise one group. The second group of bacterial strains was isolated
from rice cultivars grown in the Philippines. Inoculation experiments with
rice seedlings showed that specific isolates of these rice-associating
bacteria could either promote, inhibit, or have no influence on rice plant
growth. Furthermore, these growth effects were greatly influenced by the
environmental growth conditions used. Studies to examine root colonisation
patterns, using Rhizobium strains into which a plasmid
expressing the green fluorescent protein has been placed, showed that the
bacteria preferentially colonise rice seedling surfaces mainly in clumps. This
occurs along grooves on the rice root surface, or at the emerging lateral root
zones and at the root tips. However, rhizobia could also colonise
intercellularly in lateral roots formed on the main roots near the culm region
of the seedling. Under the growth conditions used, this occurred most
frequently with strain R4 which multiplied and migrated to form long lines of
individual bacterial cells along the inside of growing lateral roots. A
bioassay to measure bacterial multiplication in rice leaves showed that the
rice-associating strains can multiply and survive at different rates within
these tissues. They were not, however, detected migrating into other parts of
the leaf from the original site of pressure-infiltration, indicating that the
bacterial ability to migrate within the lateral roots is not matched by a
similar capacity in rice leaves. We suggest that some of these
rice-associating bacteria possess important genes that enhance their ability
to intimately colonise niches on and within rice tissues, and promote rice
plant growth.
Long-term effects of temperature shifts on xanthophyll cycle and photoinhibition in spinach (Spinacia oleracea)
Authors: Krause G. H. , Carouge N. , Garden H.
Published: January 2006

The present study tested with spinach (Spinacia oleracea
L.), whether leaves are capable of long-term acclimative responses of
carotenoids when warm-grown (20°C) plants were subjected to a regime of
low temperature (1–6°C) and excess light (250 mol
m–2 s–1). About 17
days after the temperature shift, leaves of the third leaf pair were compared
with the respective leaves of warm-grown control plants. The cold-treated
leaves exhibited reduced susceptibility to photoinhibition (at 4°C) and
considerably faster kinetics of ‘recovery’ (at 20°C), as
determined by changes in the ratio of dark-adapted variable to maximum
chlorophyll fluorescence,
FV/FM.
The temperature shift induced marked changes in the composition of
photosynthetic pigments. In particular, the pool of xanthophyll cycle
pigments, viola-, anthera- and zeaxanthin, based on chlorophyll
a+b, was enlarged by about
50%. The proportion of xanthophyll cycle pigments referred to the sum
of carotenoids increased by about 25% and, in excessive light, a larger
fraction of violaxanthin became deepoxidized. Overall, in respect of
carotenoid composition and xanthophyll cycle activity, leaves that had been
acclimated by temperature shift were very similar to leaves acclimated by
growth in the field during autumn and winter. The data show that in spinach
leaves, photoprotective mechanisms can be induced by temperature shift without
requirement for development and growth at low temperature.
Sequential expression of adaptive mechanisms is responsible for drought resistance in tobacco
Authors: Riga P. , Vartanian N.
Published: January 2006

Despite increasing interest in tobacco as a plant model for analysing stress
responses of transgenic lines, the drought behaviour of tobacco, in terms of
avoidance or tolerance, has not been investigated. In an attempt to elucidate
what strategy tobacco may express in response to a gradual and prolonged soil
drying and to analyse underlying physiological mechanisms, young plants were
subjected to progressive drought stress under controlled conditions. The
specific drought procedure we used aimed to mimic the physiological conditions
plants may experience in the field and allowed detection of any adaptive
potential of the species. Tobacco was shown to be highly drought resistant as
compared with other species previously studied under the same conditions. In a
first phase of decreasing soil moisture, osmotic adjustment helped maintain
plant turgor with a relative water content (RWC) above 90% and,
associated with a steep increase in stomatal resistance from a threshold water
deficit (<2%), characterizes a drought avoidance stategy. In a
second drought period, despite abrupt falls in leaf water potential and RWC,
enhancement of cell membrane stability (90% decrease in cell membrane
relative injury) initiated a drought tolerance strategy, resulting in
prolonged plant survival until severe soil desiccation. This is shown in the
capacity for plant recovery upon rehydration after 2 months of drought. Such
sequential expression of adaptive mechanisms, detected under progressive
drought stress, provides a new tool that should increase understanding of
changes in drought phenotypes of genetically engineered tobacco plants.
Variation in transpiration efficiency and carbon isotope discrimination in cowpea
Authors: Ashok  , Hussain I. S. Aftab , Prasad T. G. , Wright G. C. , Kumar M. Udaya , Rao R. C. Nageswara
Published: January 2006

Genotypic variation in transpiration efficiency (TE) was investigated in a set
of cowpea (Vigna unguiculata (L.) Walp.) genotypes grown
as isolated plants in pots and under canopy conditions in the field. In the
field, plants were grown in mini-lysimeters embedded in the ground around
which a crop was grown, to simulate crop canopy condition. Two moisture
regimes (100 and 60% of field capacity) were imposed from 30 to 60 days
after sowing in both pot and field experiments. TE was determined by measuring
transpiration and dry matter (DM) produced by the genotypes during the
treatment period. Genotypes differed significantly in DM although the
variation in the amount of water transpired (T) was relatively small. The TE
ranged from 2.2 to 3.7 g kg–1, representing a
significant genotypic and environmental effect on the variation. There was a
significant negative correlation (r =
–0.77, P<0.01) between TE adjusted for
prevailing vapour pressure deficit and carbon isotope discrimination ratio
(Δ) across all the experiments and treatments. A significantly positive
correlation of TE measured in pot and field experiments suggested a low G x E
interaction. There was a negative correlation (r
= –0.62, P < 0.01) between T and TE
while the correlation of TE with net assimilation rate was non-significant,
suggesting that the major cause for variation of TE in cowpea was in general
associated with stomatal rather than mesophyll factors. Because of the
positive relationship between T and DM, and negative relationship between TE
and T, selection for high TE might therefore be associated with reduced T and
hence lower DM. However, the present investigation showed a possibility of
identifying specific genotypes with a combination of high TE and high net
assimilation rate. The genotypes with high TE and high net assimilation rates
were able to produce high DM under moisture deficit conditions.
Endosperm Morphology and Protein Body Formation in Developing Wheat Grain
Authors: Campbell WP , Lee JW , O'brien TP , Smart MG
Published: January 2006

The development of wheat grain from intact plants and from detached ears growing in culture has been studied by light and electron microscopy. Provided the sucrose concentration was at a level sufficient to maintain a normal rate of starch synthesis, the endosperm morphology of grain from cultured ears was essentially identical to that of endosperm from intact plants. If, however, sucrose concentration in the culture medium was very low (0.25%), some morphological abnormalities occurred in the endosperm near the crease and adjacent to the seed coat.
The synthesis of storage protein in the endosperm is believed to occur largely on polyribosomes attached to endoplasmic reticulum even at the earliest stages of development. Protein bodies are always surrounded by a single membrane, the origin of which may vary. Some protein bodies arise by distention of the endoplasmic reticulum and clearly the membrane here represents the sac into which the protein is discharged after synthesis. In other cases the bounding membrane may be that of a true vacuole or it may be dictyosomal in origin.
The methods by which it is suggested that protein bodies are formed in wheat endosperm have parallels in other seeds, although there are some significant differences.
The Gluconeogenic Metabolism of Pyruvate During Deacidification in Plants With Crassulacean Acid Metabolism
Authors: Holtum JAM , Osmond CB
Published: January 2006

Pyruvate, PI dikinase (EC 2.7.9.1) was present in crassulacean acid metabolism (CAM) plants that lack phosphoenolpyruvate (PEP) carboxykinase (EC 4.1.1.32) but was not detected in plants that contain PEP carboxykinase or in C3 plants. It is suggested that, during deacidification in CAM plants that contain NAD and NADP malic enzymes (EC 1.1.1.38 and EC 1.1.1.40) but not PEP carboxykinase, pyruvate, P*i dikinase reverses the glycolytic reaction catalysed by pyruvate kinase (EC 2.7.1.40) and converts pyruvate to PEP as the first step in the gluconeogenic conservation of pyruvate as storage carbohydrate. The enzyme is not required by CAM plants that contain PEP carboxykinase and produce mainly PEP during decarboxylation.
Leaf slices from Kalanchoe daigremontiana and CAM Mesembryanthemum crystallinum, two species that possess pyruvate, PI dikinase, transfer label from exogenous [3-14C]pyruvate to carbohydrates more rapidly than either Stapelia gigantea, a PEP carboxykinase CAM plant, or C3 Mesembryanthemum crystallinum, which lack the dikinase. Label from [2-14C]- and [3-14C]pyruvate is converted to carbohydrate at the same rate in K. daigremontiana while in S. gigantea label from [2-14C]pyruvate accumulates in carbohydrates twice as rapidly as label from [3-14C]pyruvate. The patterns observed for K. daigremontiana and for CAM M. crystallinum are consistent with the gluconeogenic anabolism of pyruvate whereas the patterns observed for S. gigantea and for C.3 M. crystallinum suggest pyruvate is oxidized possibly via the tricarboxylic acid cycle in these species.
Deacidification in Aloe arborescens, a PEP carboxykinase CAM plant that also possesses NAD and NADP malic enzyme activity, was inhibited 80% by 0.1 mM 3-mercaptopicolinic acid (3-MPA), an inhibitor of PEP carboxykinase. It is thus likely that, in this species and probably also in other CAM plants with high PEP carboxykinase activities, a small proportion of the malic acid may be decarboxylated by malic enzymes. However, as 0.5 mM 3-MPA inhibited deacidification in K. daigremontiana by 40%, the inhibitor is probably only specific at low concentrations.
14CO2 fixation in the light by mesophyll cells isolated from K. daigremontiana was stimulated by 20-50% in the presence of 10 mM pyruvate, but there was no increase in 14CO2 fixation by mesophyll cells isolated from S. gigantea.
Change in Properties of Phosphoenolpyruvate Carboxylase From the Crassulacean Acid Metabolism Plant Mesembryanthemum crystallinum After Isolation
Authors: Winter K
Published: January 2006

Phosphoenolpyruvate carboxylase (EC 4.1.1.31) in desalted extracts from the inducible crassulacean acid metabolism plant M. crystallinum exists in a highly malate-sensitive state when isolated from plants in the light, and after isolation rapidly changes into a less sensitive state typical of the dark period. Loss of sensitivity to malate inhibition after isolation is largely prevented when the enzyme is extracted and stored at acid pH and in the presence of malate. This demonstrates that, in addition to its effect as a strong inhibitor of enzyme catalysis during the light, malate may also maintain the highly malate-sensitive state of phosphoenolpyruvate carboxylase during the light, particularly in combination with a lowered cytoplasmic pH. These experiments also establish conditions necessary for the study of the molecular basis for the change in properties of phosphoenolpyruvate carboxylase.
Leaf Chlorophyll Fluorescence as an Indicator of High Light Stress (Photoinhibition) in Cucumis sativus L
Authors: Critchley C , Smillie RM
Published: January 2006

Chlorophyll fluorescence induction kinetics were measured in detached leaves of cucumber plants (Cucumis sativus L.) grown at low quantum flux density (120 �E m-2 s-1) and then irradiated with high quantum flux density (650 �E m-2 s-1). Short-term irradiations (e.g. 1 min) resulted in loss of the variable component of chlorophyll fluorescence which could be fully recovered over a period of 60-80 min of dark adaptation. Longer irradiations wlth high intensity light (up to 5 h), however, caused an irreversible reduction in fluorescence yield indicative of irreversible photoinhibition. Irradiations as short as 4.5 min produced significant photoinhibition. Similar treatments did not cause irreversible changes in the fluorescence induction kinetics of cucumber leaves grown in sunlight.
The capacity of low light grown leaves to photooxidize cytochrome f was not affected by photoinhibitory treatments for as long as 5 h, whereas the slow component of the 518 nm change was almost completely lost.
These results support previous findings and provide direct evidence that the sensitive site for photoinhibition in vivo is located on the oxidizing side of photosystem II and that photosystem I mediated reactions do not become inhibited.
It is suggested that measurements of chlorophyll fluorescence provide a rapid means of estimating photoinhibitory damage to plants.
Photoregulation and photodamage in Schefflera arboricola leaves adapted to different light environments
Authors: Schiefthaler U. , Russell A. W. , Bolhàr-Nordenkampf H. R. , Critchley C.
Published: January 2006

Leaves of the subtropical understorey shrub
Schefflera arboricola Hayata growing in full sunlight
had higher specific leaf weight, higher chlorophyll
a/b ratios, lower total
chlorophyll content and a threefold higher xanthophyll cycle pigment content
than leaves growing in a naturally shaded, but sunfleck-punctuated,
environment. A number of measurements, all made in situ
and during natural day/night cycles, were taken as follows: current
photochemical capacity (F√F
m after 10 min dark-adaptation), size and epoxidation
state of the xanthophyll cycle, CO 2 gas exchange and
determination of the D1 synthesis rate. In sun leaves the lowest daily
F√F m
was found to be approximately 0.6, the change from maximum correlating with an
increase in zeaxanthin. Daily changes in zeaxanthin were partly due to
de novo synthesis and turnover. We suggest that sun
leaves can dissipate most of the excess light energy absorbed safely via the
photoprotective xanthophyll cycle. D1 synthesis rates did not correlate with
photosynthetic photon flux density or
F√F m
. The shade leaves had high
F√F m
values and constant photosynthetic rates throughout the day except during
sunflecks, when photosynthetic rates increased and D1 synthesis accelerated,
all without a substantial decrease in
F√F m
. It seems that leaves of S. arboricola adapted to
natural shade conditions can use sunflecks to contribute significantly to
their pro-ductivity. The third leaf type investigated was from
greenhouse-grown plants of S. arboricola after exposure
to full sunlight. These leaves showed a rapid and large reduction in
F√F m
(to 0.3), which neither correlated with zeaxanthin formation nor recovered
within the same day. From long-term effects following full sunlight exposure
of greenhouse-grown plants we suggest that this
F√F m
reduction actually reflects photodestruction.
Aspartate Decarboxylation in Bundle Sheath Cells of Zea mays and Its Possible Contribution to C3 Photosynthesis
Authors: Chapman KSR , Hatch MD
Published: January 2006

Strands of bundle sheath cells isolated from the NADP malic enzyme type C4 species, Zea mays, rapidly decarboxylate malate via NADP malic enzyme. The present studies show that these cells also decarboxylate aspartate, but at much lower rates. Aspartate decarboxylation is dependent upon added 2-oxoglutarate, is partially light dependent, and apparently proceeds via the following reaction sequence: aspartate ͛4 oxaloacetate ͛4 malate ͛4 pyruvate + CO2. Studies of the activity, properties, and location of enzymes indicated that these reactions are catalysed by a mitochondrial aspartate aminotransferase, mitochondrial or cytoplasmic NAD malate dehydrogenase, and chloroplast-located NADP malic enzyme, respectively. A mitochondria preparation isolated from Z. mays bundle sheath cells converted aspartate to oxaloacetate (with 2-oxoglutarate) and also pyruvate to alanine (with glutamate); the preparation did not reduce oxaloacetate to malate or decarboxylate malate at significant rates.
Bundle sheath strands of Z. mays have a relatively limited capacity for HCO3- plus ribose 5-phosphate dependent oxygen evolution and rates were almost as high with aspartate plus 2-oxoglutarate. We suggest that amongst NADP malic enzyme type C4 species there may be a direct relationsip between the capacity of bundle sheath cells to decarboxylate aspartate and their potential for the photosystem II-mediated oxygen evolution.
Ion Relations of Apple Fruit Tissue During Fruit Development and Ripening. II. Phosphate Uptake
Authors: Watkins CB , Ferguson IB
Published: January 2006

Phosphate uptake by discs of cortical tissue from apple fruit was followed during fruit development and ripening. Uptake from 10-3 M phosphate could be separated into a rapid, free-space uptake phase, followed by a plateau in the uptake rate, and then an increase in rate which was under metabolic control. During fruit development, the metabolic component of phosphate uptake underwent the greatest change. Apple fruit tissue exhibited an aging response in phosphate uptake. Accelerated uptake was found after 6 h aging and, after 20 h aging, the rate of phosphate uptake by the tissue was greatly enhanced. Aged tissue incorporated 32P into the ester fraction within 1 h, in contrast to fresh tissue where incorporation in 1 h was negligible.
Ion Relations of Apple Fruit Tissue During Fruit Development and Ripening. III. Calcium Uptake
Authors: Ferguson IB , Watkins CB
Published: January 2006

The ability of discs of apple cortical tissue to take up calcium from salt solutions declined during fruit development. This was true for both the cellular and free-space components of uptake. The extent of reduction was greatest in the slow, linear phase of uptake, which in young fruit had a metabolic component inhibited at 4°C. Free-space uptake contributed some 80% of the total uptake capacity and dominated calcium loss in wash-out experiments. The magnitude of calcium uptake was reduced in the presence of 10-3 M magnesium but not by equivalent concentrations of potassium.
Because of the low rate of calcium uptake into the cytoplasm and vacuole, we suggest that the greatest effect of calcium treatments used to control disorders such as bitter pit is to change the extracellular environment.
Effect of NaCl on the Growth of Whole Plants and Their Corresponding Callus Cultures
Authors: Smith MK , Mccomb JA
Published: January 2006

The effect of NaCl on growth was examined for whole plants and callus cultures of a salt-sensitive glycophyte (Phaseolus vulgaris L.), a salt-tolerant glycophyte (Beta vulgaris L.) and two halophytes (Atriplex undulata D. Dietr., which has salt glands, and Suaeda australis (R. Br.) Moq., a succulent). Whole plants were grown in nutrient solution culture at NaCl concentrations of 0.1-250 mM. Callus cultures were initiated from the same seed stock, and similar saline regimes were imposed. Whole plant responses were characteristic for the various types of plants: P. vulgaris showed a decrease in growth with increasing salinity; B. vulgaris showed a slight increase in growth at the intermediate salt level and a decrease at higher levels; A. undulata and S. australis showed well defined growth optima at 62.5 mM and 125 mM NaCl, respectively. Callus cultures of P. vulgaris and the two halophytes grew very poorly when salinity was increased. Callus of B. vulgaris showed the same tolerance to salt as did the whole plants. Thus salt tolerance of the halophytes depends on the anatomical and physiological complexity of the intact plant while callus from B. vulgaris appears to have a mechanism(s) of salt tolerance which operates at the cellular level.
Flowering in Pisum: Evidence That Vernalization Does Not Influence the Length of Evocation
Authors: Reid JB
Published: January 2006

Two further lines of peas with a high response to photoperiod are shown to possess long-lasting vernalization responses. However, the expression of these responses varies between lines and appears to be related to the sensitivity of the apex to the flowering hormones.
Vernalization is shown to reduce the number of days of continuous light required to induce flowering and the number of leaves expanded at induction. Unlike previous reports, this suggests that seed vernalization does influence the inductive processes. The length of evocation does not appear to be influenced by vernalization regardless of whether this period is measured in plastochronic or chronological terms. These results suggest that the vernalization and photoperiod responses in peas cannot be separated into effects on evocation and induction respectively. Further, this result does not allow the mechanism of the previously reported shoot response of vernalization to be determined.
Water Relations of Laticifers in Nerium oleander
Authors: Downton WJS
Published: January 2006

The water relations of laticifers in N. oleander were examined for plants growing in Death Valley, California, USA. Osmotic potential of laticifers in well watered plants paralleled the daily changes in leaf water potential. The turgor pressure of laticifers was usually less than bulk leaf turgor. Laticifer turgor was maintained in the absence of positive leaf turgor in severely water stressed plants (Ψw ͭ6 -7.0 MPa) and latex exuded when leaves were cut. The recovery in water status of leaves and laticifers following watering of the plants is described. Laboratory measurements confirmed that laticifer turgor differed from bulk leaf turgor and that it was maintained over a range of water potentials. These observations may have relevance for some of the latex-bearing plants currently being considered as future hydrocarbon sources.
An Analysis of Photosynthetic Response to Salt Treatment in Vitis vinifera
Authors: Walker RR , Torokfalvy E , Scott NS , Kriedemann PE
Published: January 2006

Rooted cuttings of grapevines (Vitis vinifera L. cv. Sultana; syn. Thompson Seedless) were grown under glasshouse conditions and supplied with dilute nutrient solution containing either 0 or 90 mM of added NaCl. Growth and photosynthetic response to salt treatment and subsequent recovery were followed over 80 days.
Shoot growth and photosynthesis were reduced by salt treatment. At relatively low concentrations of leaf chloride (< c. 150 mM, on a tissue water basis), photosynthetic reduction was largely due to increased stomatal resistance. Internal disturbances were involved at higher leaf Cl- concentrations (> c. 150 mM) and included an apparent reduction in photochemical efficiency and a faster rate of photorespiration. Levels of fraction I protein, and specific activity of ribulose-1,5-bisphosphate carboxylase measured in vitro, were not reduced by salt treatment.
Vines showed remarkable adaptation to salinity insofar as leaves maintained positive turgor despite leaf Cl- concentrations exceeding 300 mM, implying osmotic adjustment.
Cessation of salt treatment led to an immediate decrease in leaf Cl-, a promotion of shoot growth and a progressive recovery in photosynthesis accompanied by a marked but not necessarily concurrent reduction in both stomatal and internal resistances. Leaves tolerated Cl- levels up to 200 mM (under glasshouse conditions) without sustaining permanent reduction in photosynthetic activity.
New shoots formed subsequent to stress relief are not a prerequisite for Cl- retranslocation from mature leaves as decapitation at the time of stress relief did not prevent attenuation of leaf Cl- or recovery in photosynthesis.
Effect of Auxin, Fusicoccin and Tris Buffer on Ion Uptake, Organic Acid Synthesis and Cell Elongation in Barley Coleoptile Segments
Authors: Kholdebarin B
Published: January 2006

The effects of auxin, fusicoccin and tris buffer on K+ and Cl- uptake, total organic acids synthesis and cell elongation in barley coleoptile segments were tested. Some differences between the effects of fusicoccin and auxin on cell elongation and ion uptake were observed which support the idea that the two hormones may not be acting through a common mechanism. Tris buffer in the presence and absence of hormones stimulated K+ uptake and inhibited both Cl- absorption and to some extent cell elongation. Tris buffer treatments, which resulted in excess K+ uptake over Cl-, also caused a net synthesis of organic acids in the tissues. In some experiments, the relation between auxin-induced cell elongation and total organic acid synthesis was also examined.
Involvement of Phosphorus in Nitrogen Fixation by Subterranean Clover (Trifolium subterraneum L.)
Authors: Robson AD , O'hara GW , Abbott LK
Published: January 2006

Effects of phosphorus supply on nodulation and nitrogen fixation in subterranean clover paralleled those on growth and occurred only after, or at the same time as, growth responses. However, correcting phosphorus deficiency increased nitrogen concentrations in tops as well as weight of tops.
Effects of vesicular-arbuscular (VA) mycorrhizas on growth, nodulation and nitrogen fixation operated through effects on phosphorus nutrition of the host. Inoculation with a VA mycorrhizal fungus only stimulated nodulation and nitrogen fixation when insufficient phosphorus was applied for maximum growth of the non-mycorrhizal plant.
Phosphorus concentrations in nodules greatly exceeded those in either tops or roots in both mycorrhizal and non-mycorrhizal plants and with phosphorus levels ranging from severely deficient to luxury supply for plant growth.
Nitrogen applied after nitrogen fixation had commenced increased fresh weight of tops to a greater extent where phosphorus was non-limiting to growth. This positive interaction between nitrogen and phosphorus on the growth of nodulated nitrogen-fixing subterranean clover suggests that phosphorus deficiency does not limit growth in legumes by decreasing nitrogen fixation.
It is concluded that increasing phosphorus supply increases nitrogen fixation in subterranean clover by stimulating host plant growth rather than by effects on either rhizobial growth and survival or on nodule formation and function.
Isolation and Ultrastructure of Aleurone Cell Walls From Wheat and Barley
Authors: Bacic A , Stone BA
Published: January 2006

Aleurone layers and cell walls from both wheat (Triticum aestivum L. cv. Insignia) and barley (Hordeum vulgare L. cv. Clipper) have been isoIated by differential centrifugation in benzene-carbon tetrachloride mixtures and by air classification. The isolated walls were obtained in sufficient quantities and purity for comprehensive chemical analysis. Morphological characteristics of the isolated aleurone layers and walls were examined by bright field, fluorescence and scanning electron microscopy and compared with their appearance in whole grains. Transmission electron microscopy of wall sections clearly showed their characteristic bilayered structure. Aniline blue-positive deposits were observed at the aleurone-starchy endosperm interfaces of both wheat and barley.
A Coordinated Decline in the Synthesis of Subunits of Ribulosebisphosphate Carboxylase in Aging Wheat Leaves. I. Analysis of Isolated Protein, Subunits and Ribosomes
Authors: Brady CJ
Published: January 2006

In wheat plants, the rate of synthesis of ribulosebisphosphate carboxylase (EC 4.1.1.39) protein, in the second leaf approaching full expansion, is at about the average rate for all proteins. In the days following full expansion of the leaf, the rate of synthesis of the carboxylase falls sharply relative to the average rate for all protein. According to analyses of the subunits in the carboxylase holoprotein, there was little difference in the rates of decline of synthesis between the large subunit, made on plastid ribosomes, and the small subunit which is made on cytoplasmic ribosomes. Fractions smaller than the carboxylase holoprotein and reactive to antibodies to the carboxylase proteins were identified in leaf extracts. This fraction was present in greatest amount in young, expanding leaves. Carboxylase subunits in the low-molecular-weight fractions were not labelled rapidly after pulse-labelling of expanded leaves, and there was no evidence of a continuing high rate of synthesis of non-assembled carboxylase subunits in expanded leaves.
The cumulative evidence is of a coordinated decline with leaf age in the synthesis of each of the subunits of the enzyme.
Accumulation and Conversion of Sugars by Developing Wheat Grains. I. Liquid Culture of Kernels Over Several Days
Authors: Gifford RM , Bremner PM
Published: January 2006

Wheat kernels, detached from the ear during the linear phase of grain growth and with their outer pericarps removed, took up sucrose from a liquid culture medium and sustained starch synthesis linearly for a week. Kernels cultured with their outer pericarps left on, but cut transversely in half, had more rapid starch synthesis initially but the rate was linear for only 3 days. The presence of the embryo was not necessary for the observed rates of starch synthesis. Rates of net uptake of sucrose into the kernels approximated rates of grain growth in vivo but only some was converted to starch, the rest remaining in an ethanol-soluble fraction. When the sucrose concentration in the medium was below about 300 mM, the concentration of 14C label (derived from [14C]sucrose), which had accumulated in the intracellular soluble pool after 3 days of culture, exceeded the concentration in the medium. Substrate response curves for starch synthesis showed an optimum at about 230 mM sucrose in the medium, declining at higher substrate concentrations. This optimum concentration approximated the sucrose concentration determined in the endosperm cavity directly after grain was taken from the plant.
Accumulation and Conversion of Sugars by Developing Wheat Grains. II. Light Requirement for Kernels Cultured in vitro
Authors: Gifford RM , Bremner PM
Published: January 2006

Light stimulated the incorporation of [14C]sucrose into the starch of developing wheat kernels cultured in liquid medium. The light response curve saturated at about one-tenth full sunlight. Surgical removal of the green-layer of the inner pericarp, or inhibition of its photosynthesis by 3-(3,4-dichlorophenyl)-1,1-dimethylurea, eliminated the light response. Experiments with different gases above the culture medium suggested that photosynthetic generation of oxygen by the green- layer was a possible cause of the response.
Accumulation of label from [14C]sucrose into the alcohol-soluble fraction of the grain was slightly light-sensitive. This effect also saturated at about one-tenth full sunlight but there was no evidence that it was related to the photosynthetic behaviour of the green-layer.
These observations are discussed in relation to in vitro culturing methodology, to the layered structure of wheat starch granules, and to the role of the green-layer of the inner pericarp of the wheat kernel.
Temperature Dependence of Dark CO2 Fixation and Acid Accumulation in Kalanchoe daigremontiana
Authors: Medina E , Osmond CB
Published: January 2006

Kalanchoe daigremontiana was grown at 25/15 and 34/24°C and net CO2 fixation and acid synthesis were measured at 8, 15 and 24°. The ratio of net dark CO2 fixation to acid accumulation was nearly 1 at all temperatures tested. Although the increased contribution of respiratory CO2 to total acid synthesis at high temperatures was demonstrated by incubating leaf discs in CO2-free air, it was not enough to account for the reduction of dark CO2 fixation. Plants grown at 25/15° temperature regime showed maximal rates of nocturnal acid accumulation at 15°, the rates decreasing markedly at 24°. Plants grown at 24/34° showed similar rates at 15 and 24°, but acid accumulation was significantly lower at 8°. Measurements of dark acid accumulation in CO2-free air indicated that 34/24° plants have reduced respiration rates in comparison with 25/15° plants. These observations are discussed in relation to hypotheses seeking to account for effects of temperature on crassulacean acid metabolism.
Distribution within the plant or compartmentation does not contribute substantially to the detoxification of excess boron in sunflower (Helianthus annuus)
Authors: Dannel Frank , Pfeffer Heidrun , Römheld Volker
Published: January 2006

Distribution and compartmentation of boron as possible mechanisms for the
notable tolerance of sunflower (Helianthus annuus L.) to
excess B supply have been studied. Following a short- term treatment (6 h)
with 1000 µМ B, the distribution of B between different shoot organs
was preferentially directed to the readily transpiring ones. Thus, B
distribution in sunflower plants seems to be mainly influenced by
transpiration and does not act as a B tolerance mechanism in sunflower. As a
second possible mechanism for B tolerance, the compartmentation of B between
water insoluble residue (i.e. cell wall) and cell sap (i.e. symplasm) was
determined. Additional binding of B in the cell wall in response to excess B
supply for 6 h was very low in leaves and negligible in roots. Thus, a
substantial contribution of the cell wall in detoxification of excess B can be
ruled out. In an additional experiment with a B supply of 1 µМ
(marginal) to 1000 µМ (moderately toxic), the compartmentation of B
between the apoplasmic fluid and the cell sap was investigated. The B
concentration in the apoplasmic fluid was always lower than that in the
symplasm. Thus, B was not excluded from the symplasm, but accumulated within
it. The apoplasmic fluid did not contribute substantially to the
detoxification of excess B in the leaf.
Accurate area determination of complex leaves using digital image analysis
Authors: Hunt Mark A. , Hodson Stephen L.
Published: January 2006

A recently described computer image analysis method was modified forquantification of leaf area. These areas were compared to those estimated by alower resolution method based on planimetry. Leaves ofEucalyptus nitens (Deane & Maiden) Maiden, pinnae ofDicksonia antarctica Labill. and leaves ofAcacia dealbata Link were used for analysis, offeringsurfaces of low, intermediate and high complexity, respectively.Low-resolution planimetry was found to be a suitable method for thecalculation of leaf area of simple broadleaves. However, for surfaces ofgreater complexity, the higher resolution of image analysis gave more accurateestimates of area. Overlapping of primary pinnae in the complexA. dealbata leaf proved to be a larger source of errorthan inadequacy of resolution.
An extensin peroxidase is associated with white-light inhibition of lupin (Lupinus albus) hypocotyl growth
Authors: Jackson P. , Paulo S. , Ricardo C. P. P. , Brownleader M. , Freire P. O.
Published: January 2006

The spatial distribution of the major basic (B2; pI 8.8) peroxidase of the
intercellular fluid has an inverse relation with extension rate in etiolated
hypocotyls of Lupinus albus L., suggesting its possible
role in the control of cell expansion. White-light irradiation of etiolated
hypocotyls resulted in growth inhibition and the induction of B2 and acidic
(A2, pI 4.7–5.2) isoperoxidases (EC 1.1.11.7) to higher physiological
activities. However, only the activities of the B2 isoperoxidases underwent
quantitative changes in both space and time which suggested their role in
growth-retardation.
We have purified the B2 and A2 (pI 5.2) peroxidases to apparent
electrophoretic homogeneity. To corroborate evidence obtained elsewhere that
growth cessation coincides with cell wall structural changes and cell wall
rigidification, we have shown that the B2 peroxidase, and not A2 peroxidase,
cross-links tomato extensin in vitro. The B2 peroxidase
may therefore catalyse the developmentally and light regulated formation of a
covalently cross-linked cell wall extensin matrix in lupin hypocotyls. The
cell wall would be more rigid or more recalcitrant to wall-loosening and
subsequently contribute to the control of cell expansion.
A basic peroxidase isoenzyme from the grape pedicel is induced by gibberellic acid
Authors: Pérez Francisco J. , Morales Verónica
Published: January 2006

Soluble peroxidase activity from pedicels of seedless table grape cv. Sultana
was highly stimulated by post-bloom applications of gibberellic acid
(GA3) to vines. The increase in peroxidase activity was
mainly due to the induction of a basic peroxidase isoenzyme (pI > 9;
BPrx-HpI). The activity of two other peroxidase isoenzymes of pI 6.5 and 3.2
was not altered by the hormone treatment. BPrx-HpI was induced by
GA3 in pedicels and rachis but not in berries, although
in berries peroxidase activity was also stimulated by post-bloom
GA3 applications. BPrx-HpI oxidised guaiacol and
ortho-phenylenediamine (o-PDA), while the others
peroxidases found in the pedicel and in the berry oxidised only
o-PDA. Hence, BPrx-HpI was characterised as a
guaiacol-peroxidase showing no activity towards ascorbic acid (ASC). The
possible role of BPrx-HpI in pedicel lignification and berry-drop caused by
GA3 applications to cv. Sultana vines is discussed.
HarpinPSS-induced peroxidase and lignin accumulation in tobacco during the hypersensitive response
Authors: Wang Wei-Chang , Liu Zin-Huang
Published: January 2006

Harpinpss, a pathogenic protein encoded by hrpZ in the
hrp gene cluster of Pseudomonas
syringae pv. syringae, induces the
hypersensitive response (HR) in tobacco
(Nicotiana tabacum L. cv. Xanthi). An increase in
peroxidase activity, lignin content and salicylic acid was observed during the
HR elicited by harpin. The increase in anionic, moderately anionic and
cationic peroxidase isozymes is positively correlated with the HR in tobacco.
In addition, the increase of the anionic peroxidase isozyme (pI 3.5) is
correlated with a rise of the transcript of the encoding gene.
Durum wheat and barley yields in antiquity estimated from 13C discrimination of archaeological grains: a case study from the Western Mediterranean Basin
Authors: Romagosa I. , Slafer G. A. , Araus J. L.
Published: January 2006

This study develops a novel approach by which to estimate cereal yields in
ancient times based on the 13C discrimination (Δ)
of ancient grains. First, a yield model based on Δ in grains from modern
durum wheat (Triticum durum Desf.) and barley
(Hordeum vulgare L.) crops was developed using a wide
range of genotypes and Mediterranean environments. For both crops, a strong
positive linear regression between yield on a logarithmic basis and the
Δ of grains (r2 =
0.72, 506 d.f. for durum wheat and
r2 = 0.50, 316 d.f. for
barley) was observed; the slope of the relationship was significantly higher
for durum wheat than for barley. Initial estimates of yield were subsequently
corrected from bibliographical data to take into consideration the two major
differences between ancient and modern crops unaccounted for by the Δ of
ancient samples: atmospheric CO2 levels and the harvest
index ratio. As a case study, this method was used to obtain estimates of
ancient yields of durum wheat and barley in two areas of the Western
Mediterranean Basin (NE and SE Iberian Peninsula) using Δ data of grain
samples from a number of archaeological sites. These sites dated from the
beginning of agriculture in these areas (Neolithic Age,
ca 7500 years before present (BP)) to the Middle Ages
(ca 800 years BP). Our results show the absence of a
marked trend in the yields of both durum wheat and barley, which seem to have
remained relatively high from the Neolithic to the Middle Ages. The average
values for the whole period (mean ± SD) were 1.61 ± 0.49 and
1.08 ± 0.25 Mg ha–1 for durum wheat and
barley, respectively in the NE Iberian Peninsula, and 1.18 ± 0.48 and
0.97 ± 0.30 Mg ha–1, respectively, in SE
Iberian Peninsula. These yield estimates are within the range indicated by the
limited data (mostly from contemporary written sources) available for the
Mediterranean Basin, and suggest relatively good growing conditions throughout
the period studied, particularly in the NE Iberian Peninsula.