bluuebunny/crossref_metadata_2025 huggingface dataset:
The Sulfur Content of Wheat Endosperm Proteins and Its Relevance to Grain Quality
Authors: Wrigley CW , Cros DLD , Archer MJ , Downie PG , Roxburgh CM
Published: January 2006

A distinction between sulfur-rich and sulfur-poor endosperm proteins is proposed on the basis of analyses of sulfur-deficient grain, of grain proteins labelled with 35S, and of heat-denatured proteins. Grain proteins from five wheat varieties, grown in pots with excess, normal or minimal supplies of sulfur, were examined by gradient gel and sodium dodecyl sulfate electrophoresis. Restriction of sulfur altered the proportions of proteins within and between protein classes. In particular, the proportion of the low-mobility gliadins (proposed as low-S) increased at the expense of the high- mobility gliadins. In addition, the low-S grain was severely depleted in all essential amino acids, though arginine and aspartic acid increased considerably compared to normal grain. Autoradiography following electrophoresis showed that the low-mobility gliadins contained no 35S whereas the high-mobility gliadins were well labelled. A further distinction between the two groups of gliadins was provided by heating a slurry of wholemeal at 130°C for 30 min: the low-mobility gliadin components were still readily extractable with 6% urea solution but the remaining gliadins (proposed as sulfur-rich) were not.
Quantifying the effect of cumulative water stress on stomatal conductance of Eucalyptus globulus and Eucalyptus nitens: a phenomenological approach
Authors: White Don A. , Beadle Christopher L. , Sands Peter J. , Worledge Dale , Honeysett John L.
Published: January 2006

This paper incorporates the cumulative effect of water stress, in a
phenomenological model of stomatal conductance of upper canopy foliage
(gsu) for
Eucalyptus globulus and
Eucalyptus nitens. Maximum observed stomatal conductance
of irrigated trees was moderated by three functions describing the response of
gsu to light, air temperature and
vapour pressure deficit. This model explained 70% of the variation in
gsu of irrigated trees using the
same parameter values for both species. Daily total conductance was calculated
for rainfed (Gsu,R) and irrigated
(Gsu,I) trees. Linear
relationships between the ratio of
Gsu,R/G
su,I (f(W))
and pre-dawn water potential explained only 46 and 30%, respectively,
of variation in f(W) for
E. globulus and E. nitens. The
average value of pre-dawn water potential for the preceding
x days
(Sψx) was calculated for a
range of values of x. When x was 8
for E. globulus and 20 for
E. nitens a single exponential decay function accounted
for 70% of variation in
f(W) for both species. This result
and the number of days over which it was necessary to calculate
(Sψx) were consistent with
previous studies of the leaf water relations, canopy and sapwood development,
and stomatal behaviour of the two species.
Effect of foliar applications of glycinebetaine on stomatal conductance, abscisic acid and solute concentrations in leaves of salt- or drought-stressed tomato
Authors: Mäkelä P. , Munns R. , Colmer T.D. , Condon A.G. , Peltonen-Sainio P.
Published: January 2006

Tomato (Lycopersicon esculentum Mill.) was used as a
model system for investigating the effects of glycinebetaine applications on
plants, as this species is unable to synthesise glycinebetaine, but is
sensitive to exogenous supply. Glycinebetaine application significantly
increased stomatal conductance of tomato plants grown in well-watered,
water-deficient or saline conditions; however, glycinebetaine did not affect
the leaf ABA concentration, relative water content, sap osmotic potential, or
shoot water potential. Glycinebetaine applied to the foliage was readily
absorbed, but the concentrations in the leaves made a negligible contribution
to the total leaf sap osmotic potential. Our results indicate that applied
glycinebetaine was involved in regulation of stomatal conductance but not via
ABA metabolism or water relations. Glycinebetaine may have been accumulated in
specific cells or cellular compartments, with consequences for stomatal
functions. Further work is required to elucidate the cellular and subcellular
localisation of applied glycinebetaine.
Recovery of tree photosynthetic capacity from seasonal drought in the wet - dry tropics: the role of phyllode and canopy processes in Acacia auriculiformis
Authors: Montagu K. D. , Woo K. C.
Published: January 2006

Trees in the wet–dry tropics experience droughts of 4–5 months
duration each year. We examined the phyllode and canopy responses to such
drought and the subsequent recovery following rains, in 2-year-old field-grown
Acacia auriculiformis A. Cunn. ex Benth., grown in
Darwin, Australia. During the dry season, photosynthesis declined from 24 to 5
µmol m–2 s–1.
Initially, decreases in phyllode chlorophyll and soluble protein content were
paralleled by a decrease in stomatal conductance and the ratio of
intercellular to ambient carbon dioxide concentrations
(Ci:Ca)
remained above 0.65. Only at the end of the dry season, when phyllode
chlorophyll and soluble protein content had declined 73 and 52%
respectively, did stomatal limitations predominated and the
Ci:Ca
ratio dropped to below 0.5. The first rains of the wet season, despite being
small, removed stomatal limitations after 1–8 days. Within 4 weeks,
photosynthetic rates in the phyllodes subjected to 5 months of drought,
recovered to 70–95% of wet season values. Photosynthetic recovery
appeared to be related to restoration of chlorophyll content and variations in
the extent of recovery could be explained by the differing final chlorophyll
contents. Both phyllode soluble protein content and stomatal conductance rates
recovered to more than 90% of wet season values. These results indicate
that during prolonged drought and recovery after rain, mesophyll limitations
to photosynthesis predominated in this tree species. Shoot growth, to replace
the 35–45% of foliage lost during the dry season, did not
commence until more than 11 weeks after the first rains. Thus, the recovery of
tree photosynthetic capacity in the early wet season was dependent on the
recovery of foliage retained during the dry season, rather than the production
of new foliage. Such a response may represent an important adaptive strategy
that permits a rapid response to the first rains with a minimum outlay of new
resource.
Viewpoint: New light on the importance of peristomatal transpiration
Authors: Maier-Maercker Uta
Published: January 2006

The purpose of this paper is to discuss in detail once again some
controversial views on the stomatal control mechanism, because it is essential
that a consistent, universally valid concept of plant water relations provides
a basis for an understanding of the impact of air pollutants on plants. The
reader is reminded of the original concept of peristomatal transpiration, and
its central role in the stomatal control system is reinforced, i.e. its
function as a sensory mechanism in the negative feedback loop of stomatal
conductance. The described stomatal dysfunction subsequent to the exposure of
ozone to Picea abies (L.) Karst. needles can be traced
to a specific impairment of this sensory mechanism, and this demonstrates once
again the paramount importance of peristomatal transpiration.
A lack of aerenchyma and high rates of radial oxygen loss from the root base contribute to the waterlogging intolerance of Brassica napus
Authors: Voesenek L.A.C.J. , Armstrong W. , Bögemann G.M. , Colmer T.D. , McDonald M.P.
Published: January 2006

The morphology and physiology of the response of two cultivars of
Brassica napus to an anaerobic root medium was
investigated. The cultivars Chikuzen and Topas showed a large reduction in
growth rate when their roots were exposed to a de-oxygenated stagnant nutrient
solution containing 0.1% w/v agar. Older seedlings (11 d old) were
more sensitive to stagnant agar, expressed as biomass accumulation, than
younger ones (5 d old). Brassica napus was characterized
by a constitutively low root porosity (3–5%), typical for plant
species with a low tolerance to waterlogging. A hypoxia pre- treatment (16 h;
2.25% O2) before exposure to de-oxygenated
stagnant agar had no effect on the final number or length of lateral roots and
adventitious roots. Brassica napus cv. Chikuzen is
characterized by radial oxygen loss being most at the basal portion of the
root, when a strong oxygen sink surrounds the root. Oxygen profiles through
laterals of Brassica napus cv. Chikuzen show a typical
pattern with low oxygen concentrations in the stele and somewhat higher levels
in the cortex. Despite the continuum of intercellular air spaces in the root
cortical tissue the lack of aerenchyma and therefore low rates of internal
oxygen diffusion restricts root growth in anaerobic media and presumably
contributes to the sensitivity of Brassica napus to
waterlogging.
Coniferyl alcohol oxidase activity of a cell-wall-located class III peroxidase
Authors: Barceló A. Ros , Aznar-Asensio G. J.
Published: January 2006

Coniferyl alcohol oxidase activity was determined in cell walls from
hypocotyls of the following species belonging to the family Asteraceae:
Calendula officinalis,
Callistephus sinensis,
Cosmos bipinnanthus,
Helianthus annuus,
Helianthus debilis and
Zinnia elegans. In all the cases studied, coniferyl
alcohol oxidase activity was partially located ionically-bound to cell walls
and resided in a basic peroxidase, the activity of which was stimulated by H
2 O 2 . This enzymatic activity
was insensitive to freezing and was inactivated by high H
2 O 2 concentrations, as tested
both in vitro and in situ by using
purified cell wall fractions. The peroxidase with coniferyl alcohol oxidase
activity was purified from Z. elegans hypocotyls until
apparent homogeneity, as checked by SDS-PAGE. It showed a visible spectrum
typical of a haem-containing high-spin ferric secretory (class III) plant
peroxidase. Coniferyl alcohol oxidase activity of this basic peroxidase
constitutes about 0.25% of the activity shown in the presence of H
2 O 2 . The significance of the
coniferyl alcohol oxidase activity in vivo was studied
in Z. elegans hypocotyls by means of histochemical
tests, which revealed that it was located in the H 2 O
2 -producing lignifying xylem cells. The results
obtained from the histochemical probes suggest that the coniferyl alcohol
oxidase activity of this basic peroxidase is physiologically irrelevant in
tissues that accumulate H 2 O 2 ,
as is the case of the lignifying xylem, where the peroxidase activity of the
enzyme favorably competes with the oxidase activity of the enzyme.
Gibberellins and flowering in long day plants, with special reference to Lolium temulentum
Authors: Evans L. T.
Published: January 2006

The relation between gibberellins (GAs) and flowering in some long day (LD)
plants is reviewed, with particular emphasis on
Lolium temulentum. Lang’s early experiments with
rosette plants established the effectiveness of several GAs in replacing the
need for LD. Subsequent work with mutants, especially of
Arabidopsis, has clarified genetic and environmental
control points in GA synthesis, various feedback effects and some of the
factors affecting responsiveness to, as well as synthesis of, GAs in the
flowering process. Further complexities are revealed in the experiments with
Lolium temulentum, which have clearly shown that the
structural requirements for effectiveness of GAs in the flowering process are
quite different from those for elongation growth. The precise role of GAs in
the long day induction of flowering remains unclear.
Hydraulic and electrical transmission of wound-induced signals in Vitis vinifera
Authors: Mancuso Stefano
Published: January 2006

The nature and characteristics of the electrical response to wounding in the
woody plant Vitis vinifera L. were examined. Following
burning of a small area of a leaf, bioelectrical events spread throughout the
shoot. The heat wound triggered stem deformations
(widening–contraction), which preceded changes in biopotentials and that
are interpreted as reflecting wound-induced hydraulic signals. It also caused
marked decrease of extracellular resistance in stem tissues, starting about 15
s after stimulation, while intracellular resistance did not show any
modification. Under an N2 atmosphere (hypoxic
conditions), action potentials disappeared and the amplitude of variation
potentials decreased approximately 50%. At saturating humidity
variation potentials were completely eliminated, while action potentials were
evident. Taken together, the results demonstrate that action and variation
potentials differ both in their mechanism of propagation and electrogenic
nature. Action potentials are ‘genuine’ self-propagating
electrical signals travelling at a velocity of about 10 cm
s-1, with a metabolic nature involving active components
(electrogenic pumps). Variation potentials are a ‘local’ response
to the passage of an hydraulic wave. Results support the hypothesis that both
ion channels and pumps are involved in variation potential depolarisation.
Changes in Levels of Solutes During Osmotic Adjustment to Water Stress in Leaves of Four Tropical Pasture Species
Authors: Ford CW , Wilson JR
Published: January 2006

Three tropical grasses, green panic (Panicum maximum var. trichoglume), buffel grass (Cenchrus ciliaris), and spear grass (Heteropogon contortus), and a tropical legume, siratro (Macroptilium atropurpureum), were field-grown in a semi-arid environment. One set of plants was well watered, while another set was subjected to a continuous 35-day drying cycle. Samples of specific leaves were taken at the beginning, middle and end of the drying cycle, and 1, 5 and 14 days after rewatering.
The major low-molecular-weight solutes which accumulated in the grasses during water stress were the inorganic ions sodium (green panic), potassium (buffel and spear grass) and chloride (all grasses). Accumulation of these ions largely accounted for the osmotic adjustments determined from a previous study of water relations of the leaves. Concentrations of the minor constituents glucose and fructose increased only slightly in the stressed grasses, whereas levels of sucrose, the major carbohydrate component, increased substantially, particularly in spear grass. Inositol accumulated to a small extent in spear grass. Differences between the grasses were evident in the organic acid spectrum and also in changes in concentration of organic acids due to water stress. In water-stressed tissue, malate levels increased in green panic and spear grass but were reasonably constant in buffel grass. Aconitate concentrations (not detected in buffel grass) decreased in stressed green panic, but increased in spear grass. Oxalate (only trace quantities in spear grass) was a major component in green panic and buffel grass, but did not appear to vary with increase in water stress. Succinate accumulated only in stressed spear grass. The contribution of carbohydrates and organic acids to the osmotic adjustment was relatively small. Proline accumulated to varying degrees in all stressed grasses. Betaine occurred only in trace amounts in spear grass, but accumulated substantially in green panic and buffel grass.
Water-stressed leaves of siratro did not accumulate inorganic ions, sugars, organic acids, proline or betaine, but pinitol levels increased.
Implications of the results relating osmotic adjustment to changes in chemical composition are discussed.
Effect of Salinity on Growth and on Mineral and Organic Constituents of the Halophyte Disphyma australe (Soland.) J.M. Black
Authors: Neales TF , Sharkey PJ
Published: January 2006

The growth of the succulent halophyte Disphyma australe was stimulated by increments of salinity to a level of 200 mol m-3 NaCl. This was due to increases in leaf number per plant and in leaf water and total inorganic content, but not in leaf organic content. At high (500 mol m-3) salinity, leaf growth per plant was c. 30% less than the optimum and was attributable to decreases in leaf number per plant. Individual leaf fresh weight, water content and total inorganic content increased throughout the salinity range. At 500 mol m-3 NaCl, the inorganic component was 55 % of total leaf dry matter.
Leaf sap osmotic potential decreased from - 0.84 to - 2.24 MPa as salinity increased, and the uptake of Na+ and Cl- accounted for > 90 % of this osmotic adjustment. Leaf proline content also increased, from 0.7 to 8.3 mol m-3 (tissue water basis), over the salinity range of 0-500 mol m-3 NaCl, but was insufficient to account for osmotic equilibrium between cytoplasm and vacuole if it was assumed that all the proline was confined to a cytoplasmic relative volume of 5%. In the absence of external salinity, K+, NO3- and soluble sugars were the predominant contributors to osmotic potential of leaf cell sap.
Nitrogen Stress of Winter Wheat Changed the Determinants of Yield and the Distribution of Nitrogen and Total Dry Matter During Grain Filling
Authors: Blacklow WM , Incoll LD
Published: January 2006

The yields of grain dry matter (DM) and nitrogen (N) of winter wheat (cv. Maris Huntsman) were decreased by 26% and 45% when no fertilizer-N was applied in the spring. Fewer ears per m� and less mass of N per grain were the major reasons for the decreased yields. The low-N treatment decreased the rate and duration of grain filling for N but not for DM. Net assimilation of DM and N by the shoots of the low-N crop ceased at 35 and 28 days after anthesis but both continued, at a declining rate, through to maturity for the high-N crop; rates of grain-filling of DM and N were sustained at a constant rate for 2 weeks more as vegetative DM and N were redistributed. From 28 days to maturity the potential contribution to grain yield of DM and N from mobilized sources was estimated at 65% for both for the high-N crop, and 96% and 87%, respectively, for the low-N crop.
Effect of Temperature on Total Nitrogen Distribution in Pennisetum Americanum
Authors: Theodorides TN , Pearson CJ
Published: January 2006

Total N uptake and distribution and relative accumulation of N and dry matter were studied from 26 days after sowing until 50% anthesis in two genotypes of Pennisetum americanum growing at day/night temperatures ranging from 18/13 to 30/25°C. Nitrogen was taken up throughout growth and there was no indication of a net loss of N from the whole plant or from individual organs. Rate of N uptake was closely correlated with dry weight increments until stem elongation: there was a single relationship between uptake and dry weight increment over the three temperatures and two genotypes (41 mg N per g whole-plant dry weight increment). Relative rates of N accumulation and dry weight increment were higher at high temperature and again a single equation related relative accumulation of N to dry weight over all treatments. However, in contrast to the constancy of N uptake per unit dry weight, N distribution within the plant was affected by temperature. Low temperatures resulted in high root N concentrations and relatively high NO3 concentrations in root and stem apices. Temperature did not affect the proportional distribution of N between organs of the top.
The results are interpreted as showing that activity of components of the nitrogen pathway are adjusted to maintain a constant rate of N uptake per unit dry weight increment in vegetative growth, but that N distribution within pearl millet is sensitive to temperature.
Effects of Flower Bud Removal and Nitrogen Supply on Growth and Development of Cotton (Gossypium hirsutum L.)
Authors: Malik MNA , Edwards DG , Evenson JP
Published: January 2006

Effects of flower bud removal for various durations (20 or 90 days following first flower bud appearance or 35 days following first flower opening) and nitrogen supply (non-limiting and 33 % of the nitrogen uptake of non-limited plants) on growth characteristics of glasshouse-grown cotton plants are reported. Removal of flower buds and high nitrogen supply stimulated elongation of the main stem and the number of fruiting positions per plant. Nitrogen supply increased both main stem node number and mean internode length whereas flower bud removal increased only the number of nodes on the main stem. Flower bud removal did not reduce total dry matter yields, number of flowers produced or number of bolls. Vegetative organs provided efficient storage for excess assimilates resulting from the complete suppression of fruiting activity. Plants subjected to nitrogen stress had lower dry matter yield, number of flowers and number of bolls. Compensation following flower bud removal was greater at higher than at lower nitrogen supply. Relative fruitfulness, the partition of biomass between vegetative and reproductive organs, was not affected by either flower bud removal or nitrogen supply.
Effect of the Angle of Incidence of Light on the Net Photosynthesis Rates of Sorghum almum Leaves
Authors: Yates DJ
Published: January 2006

Modellers of plant canopy photosynthetic production make the assumption that there is no influence upon a leaf of the angle of incidence of parallel light it receives other than that arising from the geometrically reduced surface irradiance. This assumption was tested using attached leaves of Sorghum almum. Gas exchange measurements indicated that at oblique angles of incidence there was a marked reduction (up to 50% at 70�) in net photosynthesis rate below that expected on the basis of the reduced leaf surface irradiance. This 'angle effect' was shown to be at least partially the result of increased leaf reflectivity at oblique angles of incidence of light. The inclusion of this effect in a canopy model indicated that the common assumption tested could lead to a maximum overestimation of daily canopy production by about 7%.
Use of Callus Cultures to Detect NaCl Tolerance in Cultivars of Three Species of Pasture Legumes
Authors: Smith MK , Mccomb JA
Published: January 2006

The effect was examined of NaCl on the growth of callus from Medicago sativa L. cvv. Hunter River, Cuf 101, and Hasawi and line W75RS, and Trifolium repens L. cv. Ladino, all of which are regarded as salt-sensitive pasture legumes, and T. fragiferum L. cv. Palestine which is considered a moderately salt-tolerant pasture legume. Only M. sativa line W75RS showed some tolerance to NaCI, as callus growth was comparable at 0.1 and 62.5 mM NaCI. Whole plants in nutrient solution culture were grown from the same seed stocks and exposed to the same levels of NaCl as the callus. The responses were very similar to those shown by the callus cultures, with line W75RS showing some tolerance at 62.5 mM NaCI, which indicates the validity of using callus cultures to screen for tolerance to NaCl. However, on a yield basis, W75RS grew less than the other cultivars of M. sativa.
Abscisic Acid Content and Osmotic Relations of Salt-Stressed Grapevine Leaves
Authors: Downton WJS , Loveys BR
Published: January 2006

Changes in abscisic acid, phaseic acid, stomatal resistance, water potential, osmotic potential, turgor potential, proline, reducing sugars and ion content (Na+, K+, Cl-) in leaves from grapevines (Vitis vinifera L.) subjected to 0, 25, 50 or 100 mM NaCl (osmotic potentials of 0, - 0.1, - 0.2 and - 0.4 MPa, respectively) were monitored over a 3-week period. Abscisic acid concentration increased within 6 h for the 50 and 100 mM NaCl-treated vines. Proline did not accumulate until the next day for the 100 mM NaCl-treated plants and continued to accumulate for the duration of the experiment. Phaseic acid showed kinetics consistent with its being derived from abscisic acid. Stomatal resistance to water vapour exchange increased in the salt-treated plants over the course of the experiment despite a decline in abscisic acid concentration after the initial upsurge. Reducing sugar concentration showed an early upsurge, its contribution to osmotic readjustment being at least equal to that of accumulated Na+, K+ and Cl- the day after stress began. Potassium was preferentially accumulated over sodium into leaves during the first 8 days of the experiment and the sum of these two cations generally balanced accumulating chloride. Except for an initial loss of turgor in vines given 100 mM NaCl, turgor potential was maintained within 0.1 MPa of control plants for all of the treatments throughout the experiment.
Ethylene, Water Relations and Tolerance to Waterlogging of Three Eucalyptus Species
Authors: Blake TJ , Reid DM
Published: January 2006

Effects of flooding of the roots on ethylene levels and water relations of flood-tolerant and flood-susceptible eucalypts were studied in an attempt to shed light on mechanisms of adaptation to waterlogging.
The order of most flood tolerant to least tolerant were Eucalyptus camaldulensis Dehnh., E. globulus Labill., and E. obliqua L'Hérit. Tolerance of flooding in E. camaldulensis was associated with an initial increase in ethylene production by the roots, a subsequent increase in ethylene evolution by the lower stem, and basal stem thickening and aerenchyma formation in response to flooding. In addition, exogenous ethylene gas (500 �ll-1) increased stem thickening in E. camaldulensis seedlings compared with untreated controls.
Although treatment of the flood-susceptible E. obliqua with ethylene gas resulted in stem hypertrophy, flooding did not induce either the stem thickening response nor did it stimulate ethylene production.
Eucalyptus globulus was intermediate as regards flood tolerance and basal stem thickening; ethylene production by the roots increased but it did not show marked hypertrophy of the unflooded lower stem and was unresponsive to exogenous ethylene gas.
Water stress was not associated with flooding damage in eucalypts. Early stomatal closure as shown by high leaf stomatal resistances occurred in both the flood-tolerant and the flood-susceptible species and leaf water potential did not decrease in any of the three species in response to flooding.
The results suggest that the high degree of flood-tolerance in E. camaldulensis may be due to (1) increased ethylene production which results in (2) tissue hypertrophy and basal stem thickening. Such tissue hypertrophy would permit the plant to eliminate the build-up of the potentially toxic gas ethylene and could also enhance the transport of oxygen to the roots.
The other species lacked one or other of these adaptive mechanisms and exhibited a lesser degree of flood tolerance.
A Coordinated Decline in the Synthesis of Subunits of Ribulosebisphosphate Carboxylase in Aging Wheat Leaves. II. Abundance of Messenger RNA
Authors: Speirs J , Brady CJ
Published: January 2006

RNA prepared from second leaves of wheat seedlings was used to prime in vitro synthesis of polypeptides in wheat germ and E. coli cell-free extracts. A major polypeptide synthesized in the wheat germ system had a molecular weight of c. 21 000 and was specifically precipitated with antibody to the small subunit of wheat ribulosebisphosphate carboxylase (EC 4.1.1.39). On these bases the polypeptide was identified as the precursor of the carboxylase small subunit. The major polypeptide synthesized in vitro in the E. coli system, primed either with total leaf RNA or with chloroplast RNA, had a molecular weight of c. 52 000 and was identified as the large subunit of the carboxylase enzyme by partial proteolytic digestion.
The products synthesized in vitro in wheat germ or E. coli systems primed with RNA from different ages of leaves were compared. Translatable messenger RNAs for the small and large subunits of the carboxylase enzyme decreased in abundance relative to most of the other messenger RNAs in preparations from leaves of increasing age. The decreasing abundances of the translatable messenger RNAs were coordinated and closely resembled the declines in synthesis of the subunits observed in vivo [Brady, C. J. (1981). Aust. J. Plant Physiol., 8, 591-602].
The messenger RNA for the small subunit was shown to have a 7-methylguanosine (cap) sequence at its 5' terminal; however, loss or modification of the cap sequence was not involved in regulating availability of translatable messenger RNA.
Regulation of ethylene and polyamine synthesis by elevated carbon dioxide in cherimoya fruit stored at ripening and chilling temperatures
Authors: Muñoz M. T. , Aguado P. , Ortega N. , Escribano M. I. , Merodio C.
Published: January 2006

In this study we focused on the effect of high CO2 level
(20%) on ethylene and polyamine biosynthesis in cherimoya
(Annona cherimola Mill.) fruits stored at ripening
(20˚C) and chilling (6˚C) temperatures. At ripening temperature,
CO2 inhibited ethylene production, but
1-aminocyclopropane-1- carboxylate (ACC) oxidase activity was similar to that
in ripe control fruits. CO2 treatment led to a decline
in putrescine (Put) and a major accumulation of spermidine (Spd) and spermine
(Spm) without any effect on arginine decarboxylase (ADC) activity. These
results confirm the preferential transformation of Put to Spd and Spm in
CO2 -treated fruits. At chilling temperature, the
increase in ACC oxidase activity was inhibited and the
Vmax of ADC increased. A
combination of chilling temperature storage and high CO2
level led to suppression of basal ethylene production while ACC oxidase
activity remained unchanged. In addition, fruits held at these conditions had
higher polyamine titres than the untreated control. We propose that, in
CO2 -treated fruits, the absence of autocatalytic or
basal ethylene production, depending on the temperature, may be due to
deviation of the S-adenosylmethionine (SAM) pool towards polyamine synthesis,
primarily Spd and Spm.
Purification and characterization of mannose 6-phosphate reductase, a potential target for the control of Striga hermonthica and Orobanche ramosa
Authors: Robert S. , Simier P. , Fer A.
Published: January 2006

Mannose 6-phosphate reductase (M6PR, EC 1.1.1.224), a potential target for the
chemical control of the parasitic angiosperms that produce mannitol, was
purified from the photosynthetic parasite
Striga hermonthica (Del.) Benth. and the achlorophyllous
parasite Orobanche ramosa L. Except for the
Km values for NADPH, most of the
characteristics of the enzymes are similar in these species, i.e. a monomeric
structure of 38–39 kDa molecular mass, a pH optimum of 7.0–7.5
suggesting a cytosolic location, a relatively high optimum temperature
(35–45˚C), a low Km
value for mannose 6-phosphate of 5.9–8.6 mM and, lastly, a significant
preference for NADPH as nucleotidic cofactor.
Consequences of intergeneric chloroplast transfers on photosynthesis and sensitivity to high light
Authors: Peter Stefan , Spang Otto , Medgyesy Péter , Schäfer Christian
Published: January 2006

Plants with alien chloroplasts (cybrids) were investigated to identify
species-specific nucleus-chloroplast interactions which affect the
organisation and the functionality of the photosynthetic apparatus. The
cybrids had nuclei of Nicotiana tabacum L. and
chloroplasts of Atropa belladonna L. (cybrid Nt(Ab)) or
Salpiglossis sinuata R. et P. (cybrid Nt(Ss)). Despite
the exchange of the chloroplast genome the morphology of the cybrids was
similar to their nuclear parent. Also the PSI/PSII ratio was comparable.
In Nt(Ab) modified LHCII proteins could be detected which were absent in the
parental plants. The trimerisation of LHCII, the chlorophyll contents and the
chlorophyll fluorescence parameters were not affected by this modification,
but the portion of trimeric LHCII was slightly reduced. In Nt(Ss) the
formation of the antenna system was disturbed, and impaired PSII centres could
be detected in older leaves. These cybrid-specific features suggest that
nucleus-chloroplast interactions are involved in the processing of LHCII and
in chloroplast development. High light sensitivity was considerably increased
in the cybrids and this risk should be considered when cybridisation is used
in crop breeding.
Mechanisms for drought tolerance in two Mediterranean seasonal dimorphic shrubs
Authors: Grammatikopoulos G.
Published: January 2006

Pressure-volume curves were constructed on a seasonal basis in two
malacophyllous, drought semi-deciduous Mediterranean species
(Phlomis fruticosa L. and
Cistus creticus L.). Summer reduction of water potential
at the turgor loss point in both species was less pronounced than
corresponding changes in relative water content (RWC) at the turgor loss
point, implying the existence of turgor maintenance mechanisms. However,
actual summer leaf water potentials and RWCs in the field indicate that plants
may experience zero or negative turgor pressure during the dry period. In both
species, gradual decreases in osmotic potential and apoplastic relative water
content, as well as increases in tissue elasticity, were observed during the
summer. In particular, P. fruticosa exhibited a
remarkable elasticity throughout the year. Indications for osmotic adjustment
processes were also recorded. Critical (sublethal) RWCs measured during the
winter and summer were lower not only from the corresponding RWCs at turgor
loss point but also from the actual midday RWCs usually observed in the field.
Both species seem to use a combination of elastic and osmotic adjustments in
order to maintain their turgidity during the dry period. However, even though
turgor may be lost during part of the summer, water deficits do not usually
surpass critical levels under field conditions. This is probably achieved
through the occurrence of two leaf populations (summer and winter leaves) with
differential physiological drought tolerance.
Aluminium induces an increase in cytoplasmic calcium in intact wheat root apical cells
Authors: Zhang W.-H. , Rengel Z.
Published: January 2006

Disturbance of cytoplasmic Ca 2+ homeostasis,
leading to breakdown in Ca 2+ -mediated signal
transduction processes, has been suggested as a primary mechanism of aluminium
(Al) rhizotoxicity in plants. To test this hypothesis, Al-related changes in
cytoplasmic free activity of Ca 2+ ions ([Ca
2+ ] c ) in root apical
cells of near-isogenic wheat (Triticum aestivum L.)
lines differing in Al tolerance at a single locus were examined by visualising
the Ca 2+ -sensitive probe Fluo-3 with confocal
laser scanning microscopy. Exposure of roots to 50 µM AlCl
3 (pH 4.2) led to an increase in [Ca
2+ ] c of root apical
cells in both Al-sensitive (ES8) and Al-tolerant (ET8) wheat lines. An
increase in [Ca 2+ ]
c was greater in ES8 than in ET8; after 1-h treatment
with 50 µM AlCl 3 an increase in [Ca
2+ ] c was 48 and 27
% in ET8 and ES8, respectively. An increase in [Ca
2+ ] c of ES8 roots, but
not ET8 roots, was observed upon treatment with 2.6 µM AlCl
3 (pH 4.5). Al-related increases in [Ca
2+ ] c were correlated
with inhibition of root growth. The Al-induced increase in the [Ca
2+ ] c was reversible
upon removing AlCl 3 . These findings provide direct
evidence to support the hypothesis that Al interactions with cytoplasmic Ca
2+ are involved in the Al toxicity syndrome in
plants.
Effect of Proline, Betaine and Some Other Solutes on the Heat Stability of Mitochondrial Enzymes
Authors: Nash D , Paleg LG , Wiskich JJ
Published: January 2006

When isolated plant mitochondria are heated, isocitrate dehydrogenase, malate dehydrogenase and fumarase lose activity at different rates. The rate of loss of activity of each enzyme is reduced if the mitochondria are heated in the presence of proline, betaine or some other solutes; protection by proline or betaine against heat inactivation is also evident with these enzymes when they are solubilized. NAD-isocitrate dehydrogenase in pea mitochondria and NADP-dependent isocitrate dehydrogenase of pea chloroplasts are also protected by proline and betaine against inactivation when the isolated organelles are heated.
Breaking of Secondary Dormancy in Cocklebur Seeds by Cyanide and Azide in Combination With Ethylene and Oxygen, and Their Effects on Cytochrome and Alternative Respiratory Pathways
Authors: Esashi Y , Komatsu H , Ushizawa R , Sakai Y
Published: January 2006

The mechanism by which O2, C2H4, KCN and NaN3 stimulate germination was examined using completely after-ripened, non-dormant upper seeds of Xanthium pensylvanicum Wallr. in which secondary dormancy was induced by presoaking. Although the presoaked seeds had lost the ability to respond to these chemicals applied singly, they were highly responsive to C2H4 alone, but not to O2 alone, when pretreated with KCN or NaN3. Transfer of seeds exposed to KCN or NaN3 to C2H4 under O2 enrichment was the best practice for breaking secondary dormancy. Both O2 and C2H4 stimulated total respiration of untreated seeds by increasing the ratio of alternative path flux (Valt) to cytochrome path flux (Vcyt), which had been very low during the secondary dormancy stage. Maximal values of Valt and Vcyt were obtained when O2and C2H4 were applied together. The respiration surge induced by O2 or C2H4 was also produced when the seeds were pretreated with KCN or NaN3, but it did not occur until KCN or NaN3 treatment was continued beyond 32 h. This time corresponds to that required for complete restoration of C2H4 responsiveness. The respiration surge did not occur when the KCN solution was renewed, suggesting that the operation of the cytochrome system, even if restricted, was required to develop the alternative path. In order to observe the respiration-enhancing action of C2H4 in seeds pretreated with KCN or NaN3, C2H4 had to be applied in combination with O2. This combination led to maximal fluxes of both Vcyt and Valt, although it did not significantly increase the Valt/Vcyt ratio. O2 enrichment was ineffective in stimulating germination of these seeds and in increasing the Valt/Vcyt ratio, since it stimulated the flux via the cytochrome path rather than the alternative one. It is concluded that both the large increase of Valt and the high Valt/Vcyt ratio are required for seed germination and that KCN, NaN3, O2 and C2H4 exert their actions on the germination by increasing either or both.
Stem Xylem as a Possible Pathway for Mineral Retranslocation From Senescing Leaves to the Ear in Wheat
Authors: Martin P
Published: January 2006

Retranslocation of mineral nutrients in wheat (Triticum aestivum L. cv. Kolibri) during the development phase from 19-22 days post-anthesis to maturity was investigated in isolated culms (with three leaves attached). From the amounts present in leaves and stem at the time when the culms were detached, 75% nitrogen, 86% phosphorus, 22% potassium, and 37% magnesium were retranslocated from vegetative plant parts to the ear. No calcium was retranslocated from the leaves, but up to 27% calcium in the stem was relocated. Steam girdling of the stem between the flag leaf and the ear did not change the amounts of nitrogen, phosphorus and magnesium retranslocated and transported to the ear but reduced calcium movement slightly. Potassium transport to the ear was, however, almost completely inhibited by the phloem discontinuity induced by steam girdling. The results for nitrogen and potassium were confirmed in short-term experiments (24-48 h) using 15N and 86Rb. In a comparison between girdled culms, it was found that removal or shading of the ear decreased nitrogen retranslocation from the leaves and delayed the time course of leaf senescence. The results show that a continuous connection by sieve elements between leaves as source and grains as sink in wheat is not a prerequisite for retranslocation of nitrogen, phosphorus or magnesium.
Effects of Temperature on Leaf Expansion in Sunflower
Authors: Rawson HM , Hindmarsh JH
Published: January 2006

Five commercial cultivars of sunflower were grown in cabinets at three temperature regimes, 32/22, 27/17 and 22/12°C, and with 15-h and 11-h photoperiods, and expansion of leaves 5-15 was followed. Leaves appeared faster with increasing temperature (0.022 leaves day-1 °C-1) and with increasing daylength. Areas of individual leaves increased linearly up the plant profile and, although final area per leaf (Amax) decreased with increasing temperature, the relative change was similar for each leaf position. Cultivars maintained their ranking for Amax across temperatures, and these rankings agreed with those in previous field studies. Within each temperature regime, both the expansion rate of leaves and the duration of expansion increased with leaf position. As temperature increased, leaves grew for shorter periods with a change of 1.04 days °C-1, but under the photon flux density used (500 �mol m-2 s-1, or about 25% full sunlight) expansion rates were greatest at the lowest temperature. Expansion rates were only one-third of those in field studies at comparable temperatures, but durations were similar. Cultivars that achieved the largest Amax did so via faster rates of expansion and not via longer durations: only one cultivar differed from the mean (20 days) duration of leaf expansion. All cultivars reached floral initiation progressively earlier with extension of photoperiod from 10 to 15 h, with the change for the most sensitive cultivars being 8 days and for the least sensitive 5 days. Rates of leaf emergence were linked with this sensitivity.
Salt Tolerance of Trifolium alexandrinum L. I. Comparison of the Salt Response of T. alexandrinum and T. pratense
Authors: Winter E , Lauchli A
Published: January 2006

Trifolium alexandrinum and Trifolium pratense were grown in solution culture at salinity levels of 50, 100, 150 and 200 mM NaCl. Trifolium alexandrinum survived at all salt treatments. Salt-induced growth reductions of 30 and 47% occurred at 50 and 100 mM NaCl, respectively, mostly affecting stems. Plants still survived at 150 and 200 mM NaCl. This species can therefore be considered moderately salt tolerant. Trifolium pratense showed a low survival potential at salt treatments of 100 mM NaCl or higher, and the dry weight production of all plant parts was considerably affected at moderate salt levels. Thus T. alexandrinum is considered more salt tolerant than T. pratense. The distribution and contents of K+, Na+ and Cl- in both species indicate that T. pratense translocates Na+ and Cl- linearly with increasing salt treatment into stems and leaves, whereas low foliar Na+ and Cl- contents in T. alexandrinum suggest some mechanisms that control the ion distribution in the different plant parts. Salt-induced changes of the K+ and Ca2+ contents of the different plant parts of both species are discussed.
Salt Tolerance of Trifolium alexandrinum L. IV. Ion Measurements by X-Ray Microanalysis in Unfixed, Frozen Hydrated Leaf Cells at Various Stages of Salt Treatment
Authors: Winter E , Preston J
Published: January 2006

Bulk-frozen leaf tissue of salt-treated (50 mM NaCI) T. alexandrinum plants harvested at various stages of the salt treatment was fractured in a scanning electron microscope. By means of X-ray microanalysis, Na+ and Cl\- was measured in single cells of the veins and of the surrounding tissue. From the corrected peak values Na+ : K+ ratios were calculated for each cell. For each sampling interval the average percentage of cells falling into various categories of Na+ :K+ and CI- :K+ was determined in all tissues. In the phloem parenchyma the percentage of cells having a very high Na+ :K+ ratio (>4) rose between days 10 and 16 of the salt treatment, whereas the percentage of xylem parenchyma cells falling into this category declined. It is concluded that the increasing Na+ :K+ ratios in the phloem are the result of both an enhanced inflow of Na+ into the veins (measured in a previous experiment) and the retranslocation of Na+ from the xylem to the phloem. The results support the hypothesis of intraveinal recycling of Na+ in salt-stressed young leaves of T. alexandrinum and may explain the gradual damage to the phloem transfer cells observed with progressive salt treatment.
Distribution of Mineral Elements in Green and Chlorotic Leaf Tissue of Eucalyptus obliqua L'hérit., Determined With a Scanning Proton Microprobe
Authors: Mazzolini AP , Anderson CA , Ladiges PY , Legge GJF
Published: January 2006

A scanning proton microprobe was used to compare the relative concentrations and the localizations of various elements in green and chlorotic leaf tissue of E. obliqua. Proton Induced X-ray Emission (PIXE) has a high sensitivity for detecting trace elements. Chlorosis develops in those genotypes of E. obliqua which are native to acidic soils and which are transplanted to alkaline, calcareous soils. The chlorosis was correlated with high internal levels of P, S, K and Ca. Levels of the trace elements Mn, Fe, Cu and Zn were either higher than or similar to levels in those genotypes native to, and grown in, the calcareous soils, and it is suggested that chlorosis is related primarily to an imbalance of elements, particularly the ratio of P to Fe. There was no evidence of phosphate-induced precipitation of Fe in veins or other localized areas in leaves.
Effect of Temperature on Nitrate Uptake, Translocation and Metabolism in Pennisetum americanum
Authors: Theodorides TN , Pearson CJ
Published: January 2006

Daily cycles of net nitrate uptake, in vitro and in vivo nitrate reduction, and nitrogen transport from roots to tops were studied in two cultivars of Pennisetum americanum growing at day/night temperatures of 18/13°C and 30/25°C or 33/28°C. Rates of net nitrate uptake, xylem exudation and loading of amino acids into the xylem usually peaked once in the light period, whereas rates of in vitro nitrate reductase activity and in vivo reduction of NO3- to NO2- showed two peaks, one in the light and one in the dark period. Mean hourly rates per gram dry weight root of net nitrate uptake, xylem exudation and loading of amino acids into the xylem were 20, 44 and 40% respectively lower at 18/13°C than at 30/25°C. A whole-plant budget showed that both genotypes reduced the same amount of nitrate per day when they were grown at the same temperature. The proportion of nitrate which was reduced in roots was higher at 30/25°C (50%) than at 18/13°C (20%). At 30/25°C there was net export of reduced nitrogen from roots to tops whereas at 18/13°C there was import of reduced nitrogen into roots. Temperature-induced changes in daily cycles of nitrate uptake, rates of nitrate reduction and transport are interpreted as adaptations toward better carbon economy at low temperature.
Ecophysiology of Two Solar-Tracking Desert Winter Annuals. I. Photosynthetic Acclimation to Growth Temperature
Authors: Forseth IN , Ehleringer JR
Published: January 2006

The ability of two solar-tracking desert winter annuals, Lupinus arizonicus Watson and Malvastrum rotundifolium Gray, to acclimate their photosynthetic characteristics to different growth temperatures was examined. Plants were grown in growth chambers under 25/15°C and 40/30°C thermal regimes. The plants grown at 40/30°C were also subjected to a drying cycle in order to assess whether or not drought affected the photosynthetic acclimation to high temperatures. Both species exhibited shifts in their temperature optima and thermal death points for photosynthesis. The droughted plants showed no further acclimation than did the watered plants grown at 40/30°C. Using representative meteorological conditions measured in Death Valley, California, it was predicted that photosynthetic acclimation plays only a small role in enhancing daily carbon-gaining ability for late-season conditions. However, under conditions of drought stress and high temperatures, the acclimation may prevent thermal death and extend plant life.