bluuebunny/crossref_metadata_2025 huggingface dataset:
Increasing Salt Tolerance of Plants Through Cell Culture Requires Greater
Understanding of Tolerance Mechanisms
Authors: Dracup M
Published: January 2006

Despite numerous attempts, increasing the salt tolerance of cultured cells has rarely led to increased salt tolerance in regenerated plants. Clearly the role of cultured cells in selecting for salt tolerance needs reappraisal. Although the relationship between salt tolerance of cultured cells and whole plants is crucial to the use of cultured cells in selecting for increased salt tolerance, it is not understood, and neither are the mechanisms of salt tolerance in cultured cells understood.
Our understanding of salt tolerance in cultured cells has been limited mainly by poor methodology, particularly failure to consider the large free space volume and the effect of high NaCl on the various phases of culture growth. Further, there has been a reluctance to search for mechanisms and test hypotheses. The relationship of salt tolerance in cultured cells and whole plants needs to be studied since much of the tolerance of whole plants is associated with their integrated functioning. Furthermore, cultured cells grow slowly and have different hormonal, osmotic and nutritional environments from cells in whole plants. Selection of cultured cells may be more productive if focused on specific cell-based physiological traits (such as Na+ accumulation, turgor regulation or tolerance to high Na+ : Ca2+) rather than on tolerance to high NaCl only. Expression in whole plants of traits in cultured cells also needs to be studied.
Abscisic Acid Levels in Nacl-Treated Barley, Cotton and Saltbush
Authors: Kefu Z , Munns R , King RW
Published: January 2006

Exposing barley and cotton plants to 75 mol m-3 NaCl reduced transpiration and increased abscisic acid (ABA) levels in leaves, roots and xylem sap. Exposing saltbush (Atriplex spongiosa) plants to 75 mol m-3 NaCI, at which concentration they grow best, did not affect transpiration or ABA levels but when the NaCl was increased to 150 mol m-3 transpiration fell and ABA levels rose.
ABA levels in leaves were high in salt-treated barley and saltbush even when the leaf water status was raised by pressurising the roots. These responses indicate that an increased leaf ABA level was not triggered by leaf water deficit, but by the root's response to the salinity. The flux of ABA in the xylem sap of the three species was more than enough to account for the amount of ABA in leaves, in the presence and absence of salinity. This suggests that the roots may be the source of at least part of the ABA found in leaves.
Influence of Chilling and Drought on Water Relations and Abscisic Acid Accumulation in Bean
Authors: Vernieri P , Pardossi A , Tognoni F
Published: January 2006

Intact bean seedlings were subjected to either chilling (4°C) or drought stress. Leaf water relations and abscisic acid (ABA) content were monitored throughout a stress-recovery cycle. Chilling at low relative humidity (RH) and drought caused similar water deficits, as indicated by the decline in relative water content and water potentials, but they had different effects on ABA accumulation. There was a rapid increase in ABA levels in the leaves of water-deprived plants while only slight ABA accumulation was observed after 48 h of chilling (4°C). After 24 h cold treatment there were large changes in turgor but no change in ABA content. Plants chilled for 24 h accumulated ABA only when transferred to recovery conditions (20°C, 90-95% RH, in the dark) to an extent that was related to the rate of leaf rehydration. When the chilling treatment was performed in a water-saturated atmosphere, plants did not suffer any water stress and ABA levels did not increase over a period of 48 h. However, when the chilling treatment lasted for a longer period (72 h), a significant increase in ABA levels was found also in the absence of water deficit. Experiments performed with leaf discs incubated in a mannitol solution (osmotic potential - 1.6 MPa) at different temperatures indicated that low temperature markedly inhibits ABA synthesis and that water stress induces increases in ABA content only at non-limiting warm temperatures.
Nitrogen Nutrition, Growth and Gas Exchange in Eucalyptus globulus Labill. Seedling
Authors: Sheriff DW , Nambiar EKS
Published: January 2006

Potted Eucalyptus globulus Labill. seedlings were grown in sand with added inorganic nutrients. Three treatments were applied: (1) inorganic nitrogen was added regulary (N2), (2) in a small initial quantity only (N1) and (3) after a period of N deficiency (N3); other nutrients were supplied regularly. Biomass increment, foliar nutrient concentrations and gas exchange of leaves were measured. Carbon assimilation, N uptake, growth, and leaf production and expansion were all greater at higher N. Partitioning of dry matter to roots and tops of seedlings was unaffected by treatment.
Carbon assimilation and diffusive conductance were linearly related at saturating light and were positively associated with foliar N concentrations; intercellular CO2 partial pressures were constant at c. 246 μbar. The relationship between carbon assimilation and foliar N concentration was better when calculated per leaf weight than per leaf area. Dark respiration was positively associated with foliar N concentration. Following refertilisation of N-deficient seedlings, foliar N and carbon assimilation increased rapidly; about 20 days later N uptake declined and seedling biomass started to increase.
Instantaneous transpiration efficiency [c. 5 mmol (CO2) mol-1 (H2O)] was not significantly affected by foliar N concentration or treatment. Instantaneous nitrogen use efficiency of leaves: (rate of carbon assimilation)/(leaf N content) was greater at higher N. In contrast to the literature, there was no simple relationship between nitrogen use efficiency of whole seedlings (biomass gain)/(nitrogen concentration) and seedling N. Instantaneous transpiration and nitrogen use efficiencies were generally high compared with values published for many woody plants.
A simple model predicted that, with no environmental constraints, exposed mature leaves with high N (1.5 mmol g-1) assimilate 5.4 times more carbon than similar leaves with low N (0.5 mmol g-1). Night respiration of foliage is a greater proportion of daily carbon balance for leaves with low N. When environmental factors constrain carbon assimilation foliage with high N is most affected.
Shoot Apex Sugars in Relation to Long-Day Induction of Flowering in Lolium temulentum L
Authors: King RW , Evans LT
Published: January 2006

Inflorescence initiation in Lolium temulentum is induced by a single long day with a photoperiod extension of 16 h under low photon flux density (12 μmol PAR m-2 s-1) from incandescent lamps. Under these conditions the content of sucrose, the predominant free sugar in the shoot apex, fluctuates diurnally in the same way as in short day apices. There was no evidence of a greater apical sucrose content at any time during the long day or in the following period of high irradiance when floral evocation occurs. Thereafter, however, the diurnal fluctuation in apical sucrose content became more pronounced. Increasing the sugar supply to the apex by raising the photon flux density during the daily light period did not lead to flowering of non-induced plants; nor did the high contents of apical sugars reached in apices cultured in vitro on 5% sucrose medium. By contrast, when apices were excised after receipt of the floral stimulus from long day leaves, increase in the sugar content enhanced inflorescence development in vitro, this response being most pronounced after the inflorescences were initiated. Thus, floral evocation in L. temulentum does not require an increase in the content of sucrose at the apex although inflorescence development is highly responsive to it.
When photoperiodic extensions with incandescent or fluorescent lamps were compared for their effects on apical sugars and flowering response, there was no interaction between light quality and photon flux density. Thus the shoot apex response to the low irradiance, photoperiodic time-measurement processes of leaves is distinct from the apical response to sugar supply. In Lolium temulentum floral evocation is controlled by the photoperiodic processes, the response to which is amplified by high sugar supplies but not replaced as it is in Sinapis alba.
Effects of Abscisic Acid on Morphological and Physiological Responses to Water Stress in Eucalyptus camaldulensis Seedlings
Authors: Gibson A , Hubick KT , Bachelard EP
Published: January 2006

The effects of abscisic acid (ABA) and a subsequent water stress on the physiological and morphological characteristics of seedlings of three provenances of Eucalyptus camaldulensis Dehnh. grown in pots in a glasshouse were compared 56 days after application of ABA. Seedlings from a high rainfall monsoon provenance in the dry tropics (Katherine, Northern Territory, Australia) were largely unaffected by ABA or by water strees in either physiological or morphological characteristics. Seedlings from a lower rainfall monsoon provenance in the humid tropics (Petford, Queensland) responded to water stress by reducing gas exhange while increasing photosynthetic capacity, indicated by increased leaf nitrogen and chlorophyll concentrations, and both short- and long-term leaf transpiration efficiency, indicated by changes in carbon-isotope discrimination. The changes were largest when ABA was also applied. Seedlings from semi-arid Tennant Creek (Northern Territory), which had the highest assimilation rates overall, responded to both ABA and water stress primarily by morphological changes including suppression of apical growth and increase in specific leaf weight. The results are discussed in terms of specific adaptations for establishment in increasingly dry environments and the possible role of ABA in mediating stress responses.
Effects of Photon Flux Density on Nutrient Productivity in Eucalyptus grandis Seedlings
Authors: Kirschbaum MUF
Published: January 2006

In plants in which growth is limited by the availability of phosphorus, phosphorus productivity is defined as the plants' relative growth rate divided by their internal phosphorus concentration. An experiment was conducted to assess whether phosphorus productivity was dependent on photon flux density, or whether photon flux density only set an upper maximum relative growth rate below which phosphorus productivity remained constant with changing photon flux density.
Eucalyptus grandis seedlings were grown in growth units in which plants were suspended in air while continuously being sprayed with nutrient solution (aeroponic system). Plants were grown at five different relative phosphorus addition rates, and under natural lighting over the period from late summer to mid-winter when daily photon flux density decreased from about 30 to 10 mol quanta m-2 d-1. Relative growth rate was then plotted as a function of internal phosphorus concentration for a series of harvests. For the three highest relative phosphorus addition rates, there was a negative relationship between relative growth rate and internal phosphorus concentration. For the two lowest phosphorus addition rates, the internal phosphorus concentration increased throughout the experiment, while relative growth rate remained almost constant. This meant that phosphorus productivity changed throughout the experiment. When phosphorus productivity was expressed as a function of daily photon flux density, a linear relationship between phosphorus productivity and photon flux density was obtained. That relationship had a positive intercept on the axis of photon flux density which was interpreted as the plants' light compensation point. This finding has important implications for applications of the concept of nutrient productivity to the modelling of ecosystems in which growth is limited by nutrient availability.
Root Signals Mediate Coordination of Stomatal and Hydraulic Conductance in Growing Sugarcane
Authors: Meinzer FC , Grantz DA , Smit B
Published: January 2006

Root hydraulic conductance and total stomatal conductance on a per plant basis changed in parallel during growth of sugarcane. Changes in root system water and solute transport properties were evaluated to determine the role of changes in root xylem sap composition in this coordination of vapour and liquid phase conductances. Stomatal conductance of excised leaf strips supplied with root exudate declined with increasing leaf area of the exudate donor plants. Leaf strips from plants of different sizes responded similarly to exudate from each donor plant, indicating that there were no inherent differences in leaf stomatal properties. The effect of xylem sap from plants of increasing size paralleled the decline in stomatal conductance of intact plants of similarly increasing plant size. Delivery rates per unit leaf area of K+, Ca2+, abscisic acid, and zeatin riboside (ZR) in xylem sap declined with increasing plant size. Patterns of delivery of ZR and K+ were consistent with a role in the plant size-dependent regulation of stomatal conductance, although additional xylem constituents are likely to be involved. Developmental patterns of stomatal conductance in intact sugarcane plants may be linked to plant hydraulic properties by the composition and flux of xylem sap arriving at the stomatal complexes in leaves.
Effects of CO2 Enrichment and Nitrogen Stress on Growth, and Partitioning of Dry Matter and Nitrogen in Wheat and Maize
Authors: Hocking PJ , Meyer CP
Published: January 2006

Atmospheric CO2 levels are increasing, but little is known about how this will affect tissue concentrations and the partitioning of agriculturally important nutrients such as nitrogen (N) within crop plants. To investigate this, a glasshouse experiment was conducted in which wheat, a C3 species, and maize, a C4 species, were grown for 8 weeks at high CO2 (1500 cm3 m-3) on N supplies ranging from deficient (0.5 mol m-3) to more than adequate for maximum growth (25 mol m-3).
Wheat responded to both CO2 enrichment and N supply; maize responded only to N supply. CO2-enriched wheat produced about twice the dry matter of control plants at all levels of N supply. Tiller and ear numbers were increased by CO2 enrichment irrespective of N supply. Enriched wheat plants had a lower Leaf Area Ratio but higher Net Assimilation Rate and Relative Growth Rate than control plants. There was no effect of CO2 enrichment on specific leaf weight. The enriched plants had lower shoot to root dry matter ratios than the controls at 6 mol m-3 N and higher. Shoot to root dry matter ratios of both wheat and maize increased with increasing N supply.
CO2-enriched wheat plants accumulated more N than the controls but the proportional increase in N content was not as great as that in dry matter, with the result that concentrations of total-N and nitrate-N were lower in all organs of enriched plants, including ears. Nitrate reductase activity was lower in enriched than in control wheat plants. N-use efficiency by wheat was increased by CO2 enrichment.
From a practical point of view, the study indicates that critical total-N and NO3-N concentrations used to diagnose the N status of wheat will need to be reassessed as global CO2 levels increase. Elevated CO2 may also reduce the protein content of grain and thus the baking quality of hard wheats.
Phase Change in Citrus: Immunologically Detectable Differences Between Juvenile and Mature Plants
Authors: Snowball AM , Zeman AM , Tchan YT , Mullins MG , Goodwin PB
Published: January 2006

Homogenates prepared from mature and juvenile grapefruit (Citrus paradisi Macf. cv. Marsh) were used to raise antibodies in rabbits. The resultant polyvalent antisera were subjected to immunoadsorption and selection techniques. A specific antiserum was obtained which reacted with an antigenic protein found in greater quantities in tissues of mature Citrus plants than in tissues of juvenile plants. This is referred to as the 'mature' protein. The 'mature' protein is resistant to temperatures of up to 80ºC, and has a molecular weight of approximately 59.7 kDa. The protein is found in Citrus species, but not in the closely related genera Poncirus, Microcitrus or Fortunella. It is not found in the other plant species studied. The mature protein content increases in the leaves towards the apex of single-stemmed seedlings, and in the floral shoots of precociously flowering Marsh grapefruit seedlings. There are few morphological or chemical characters which change concurrently with the achievement of maturity in citrus seedlings, and none is well suited as a predictor of phase change. The identification of a protein marker associated with phase change has important implications, both in the understanding of the processes of phase change, and in the practical field of plant breeding.
Further Studies on Quantifying Photosystem II in vivo by Flash-Induced Oxygen Yield From Leaf Discs
Authors: Chow WS , Hope AB , Anderson JM
Published: January 2006

It was shown briefly [W. S. Chow, A. B. Hope and J. M. Anderson (1989), Biochirnica et Biophysics Acta, 973, 105-8] that the oxygen evolved per flash from leaf discs, under steady-state flashing conditions and in the presence of background far-red light, gave a valid measure of the number of functional photosystem II (PS II) reaction centres. Further work on this direct and convenient method has been done to optimise conditions for making reliable measurements. It is found that, to obtain the higher estimates of [PS II], corresponding to functionality of practically all PS II reaction centres that bind herbicides, a form of 'light activation' is necessary after a prolonged dark pre-incubation. Without a sufficient number of flashes being given following a long dark incubation, the number of functional PS II reaction centres was underestimated. Provided light activation had occurred, the measured number of functional PS II reaction centres was independent of flash frequencies up to at least 40 Hz. The results strongly suggest that, in steady-state, light-limited photosynthesis, there does not exist any sub- stantial fraction of non-functional or 'slow' PS II reaction centres.
Establishment of Embryogenic Suspension Cultures of Wheat by Continuous Callus Selection
Authors: Yang YM , He DG , Scott KJ
Published: January 2006

Embryogenic callus, derived from immature embryos of an Australian wheat (Triticum aestivum L. cv. Hartog) was used to establish liquid cultures which consisted of cell clumps (2-8 mm in diameter); these have been maintained for 20 months and still retain their embryogenic potential. This was achieved by continuous selection of embryogenic clumps at subculture. Incubation of callus in medium containing low concentrations of 2,4-D facilitated the selection of embryogenic cell clumps. After more than 1 year in liquid medium, 37% of the cell clumps formed embryoids and green plants on differentiation medium. The addition of silver nitrate to the subculture medium, which contained 5 μM 2,4-D, enhanced the differentiation frequency of the callus. A study of embryogenic calli from different wheat cultivars showed genotype was important for the retention of embryogenic potential in liquid medium. Fine suspension cultures, consisting of rapidly growing small aggregates of 2-200 cells, were derived from liquid cultures of cv. Hartog. Cytological examination showed that the cells of the fine suspension cultures had the normal wheat chromosome complement (2n = 42). Following transfer to differentiation medium, the fine suspension cultures formed soft as well as solid callus, from which embryoids and green plants have been obtained. Protoplasts isolated from the fine suspension cultures formed green plants with morphologically normal shoots and roots.
Transformation of an Australian Cotton Cultivar: Prospects for Cotton Improvement Through Genetic Engineering
Authors: Cousins YL , Lyon BR , Llewellyn DJ
Published: January 2006

Somatic embryogenesis and regeneration of whole plants is a highly genotype-dependent process in cotton. We have identified at least one highly regenerable Australian cultivar, Siokra 1-3, which is a sister line to the current major variety being grown in Australia. A number of plants have been regenerated and although some are showing abnormal pollen development, most can produce fertile seed when selfed or crossed with a normal pollen donor.
Agrobacterium tumefaciens has been used to efficiently produce fertile transgenic Siokra 1-3 plants expressing novel genes such as the bacterial neomycin phosphotransferase or the β-glucuronidase. This is the first example of the transformation of an elite commercial cultivar. Critical factors in the transformation are the use of a supervirulent disarmed Ti-plasmid with a binary transformation vector, and a highly regenerable genotype of cotton. Bacterial concentration at the time of infection, tissue age, kanamycin selection regime, and co-cultivation support and media composition all have an influence on transformation efficiency and were optimised in our protocol.
The ability to transform an elite Australian cultivar of cotton paves the way for agronomic improvements through genetic engineering. We have concentrated on increasing the tolerance of Australian cotton to the herbicide 2,4-D (to protect it from spray drift damage from adjacent cereal crops), and increasing its tolerance to insect pests, such as Helicoverpa armigera, using BT-toxin genes, protease inhibitors and other novel insect resistance genes.
Changes in Source-Sink Relationship for Nitrogen During Regrowth of Lucerne (Medicago sativa L.) Following Removal of Shoots
Authors: Kim TH , Ourry A , Boucaud J , Lemaire G
Published: January 2006

An experiment with lucerne plants (Medicago sativa L.) previously labelled with 15N and grown in hydroponic culture, was undertaken to define sink and source behaviour of different organs in defoliated and intact plants. Changes in 15N contents of plants during 24 days of regrowth on an unlabelled medium after defoliation were used to estimate flows of exogenous and endogenous nitrogen. The 15N content of regrowing stems and leaves increased as a result of remobilisation mainly from lateral and tap roots which, therefore, acted as source organs. Nitrogen remobilisation reached a plateau after 10 days of regrowth and, until this time, nearly all N for shoot regrowth came from endogenous N in roots and crown. Between 25 and 35% of N reserves were translocated to regrowing stems, the remainder to regrowing leaves. Amino acid-N was the most readily available form of N while protein-N was the largest storage pool. Nitrogen uptake from the medium and accumulation in source organs (roots and crown) was significant only between days 6 and 14, and almost all was subsequently translocated to regrowing tissues. Defoliation induced changes in source-sink relationships for N. Whereas stems and tap roots were the main sink organs in intact plants, regrowing shoots exerted a stronger sink behaviour in defoliated plants.
Effect of Low O2 Concentration and Azide on Hydraulic Conductivity and Osmotic Volume of the Cortical Cells of Wheat Roots
Authors: Zhang WH , Tyerman SD
Published: January 2006

The short-term effects of O2 deficiency and sodium azide (NaN3) on the hydraulic conductivity of cortical cells in wheat roots was studied using the pressure probe. Hydraulic conductivities were obtained by measuring either turgor relaxation, or volume relaxation under pressure clamp. Both low O2 concentration and NaN3 increased the half times of pressure and volume relaxations. The increases in T½ were found to be due to a decrease in the hydraulic conductivity (Lp) of the cells. The mean values of Lp from pressure relaxation experiments were 7.75 × 10-1m s-1 Mpa-1 in the fully aerated solution and 1.15 and 2.17 x 10-1m s-1 Mpa-1 in low O2 concentration and 1 mol m-3 NaN3 solutions respectively. The pressure clamp experiments yielded similar results to pressure relaxation experiments for both low O2 concentration and 1 mol m-3 NaN3 treatments. In addition to determination of Lp, pressure and volume relaxation experiments were also used to evaluate osmotic volume of the cells. In aerated solutions the osmotic volume of the cells was about twice that of their geometric volume, but in low O2 concentration and NaN3 solutions the osmotic cell volume was reduced and approximately equal to the geometric volume. The decrease in osmotic volume and part of the reduction in Lp may be explained by the occlusion of plasmodesmata induced by low O2 concentration and NaN3.
Acid Phosphatases Associated With Phosphorus Deficiency in Wheat: Partial Purification and Properties
Authors: Guthrie RE , Mclachlan KD , Marco DGD
Published: January 2006

Procedures for the partial purification of two phosphatase isozymes found in phosphorus deficient wheat plants are given. The method employs ammonium sulfate precipitation and hydroxylapatite, Con A-Sepharose, anion exchange and size exclusion chromatography. Measurements of their Km, Vmax, pI and molecular weight are reported. Evidence is provided that there are empirical differences in substrate utilisation between these phosphatase isozymes associated with phosphorus deficient plants.
Quantification of Active Vesicular-Arbuscular Mycorrhizal Infection Using Image Analysis and Other Techniques
Authors: Smith SE , Dickson S
Published: January 2006

Methods for the objective measurement of vesicular-arbuscular mycorrhizal infection in the roots of four species of host plant are described. The methods are based on vital staining of transverse sections of fresh roots, followed by evaluation of occurrence and/or numbers of living arbuscules and hyphae per section. The most useful method involved freeze-sectioning roots embedded in gelatin containing glycerol and DMSO, followed by staining the sections with nitroblue tetrazolium overnight to reveal succinate dehydrogenese activity.
Two systems of computer-aided image analysis were evaluated for measurement of the number, perimeter and cross-sectional areas of intercellular hyphae and arbuscules. This approach, which is clearly objective, is an advance on previous methods which were based on ranking sections or segments of root with respect to the intensity of development of arbuscules. The data were used to calculate the area of interface between plant and fungus in infected roots. Results are presented showing that the contribution of arbuscules to the total infection and area of interface declines markedly as plants and infections age. Differences in infection in different host/fungus combinations are also described.
Photoperiod and temperature effects on the rate of leaf appearance in quinoa (Chenopodium quinoa)
Authors: Bertero H. Daniel , King Roderick W. , Hall Antonio J.
Published: January 2006

Knowledge of factors controlling leaf
appearance is important for understanding climatic adaptation of a plant
species. For quinoa (Chenopodium quinoa Willd.) we show
that both temperature and photoperiod control the rate of leaf appearance.
Minimum phyllochron (thermal time between the appearance of two successive
leaves as observed under short days) and photoperiod sensitivity of the
phyllochron decreased as latitude of origin of a cultivar increased from
1˚13¢ N to 38˚46¢ S. Minimum phyllochron ranged from 21.8
˚Cd in the Colombian cv. Nariño, to 15.9 ˚Cd in the Chilean
cv. Baer (estimated for a common base temperature of 2˚C). Photoperiod
sensitivity ranged from 1.2 ˚Cd h –1 in
Nariño to insensitivity (0 ˚Cd h –1 )
in the Bolivian and Peruvian altiplano cvv. Kanckolla, Blanca de Juli and
Sajama. The phyllochron sensitivities to photoperiod and temperature were
linearly and positively associated with photoperiod and temperature
sensitivities of time to visible flower buds (R 2
= 0.70 and 0.55, respectively, P < 0.05), so that shorter
phyllochrons were associated with early flowering cultivars. Temperature
sensitivity was highest in cvv. originating in cold or dry climates, and
lowest for cvv. from more humid and warm climates. We suggest, therefore, that
in its domestication as a crop plant, photoperiod sensitivity of quinoa has
been selected for as a homeostatic mechanism to counteract the potentially
reduced leaf area associated with early flowering under short days and high
temperatures in the tropics.
Changes in free and conjugated IAA during dormancy and sprouting of potato tubers
Authors: Sorce Carlo , Lorenzi Roberto , Ceccarelli Nello , Ranalli Paolo
Published: January 2006

The time course of free and conjugated
indole-3-acetic acid (IAA) concentrations was investigated in three distinct
parts (eyes, subeye tissues and pith) of potato
(Solanum tuberosum L. cultivar Monalisa) tubers, from
the last period of tuber growth to sprouting under two different storage
temperatures (3 and 23˚C). The highest levels of both free and conjugated
IAA were detected in eyes, which showed a significant increase of the free
hormone concentration from harvest to the end of dormancy, regardless of
storage temperature. The concentration of conjugates was higher than free IAA
in eyes and subeye tissues at 23˚C, while at 3˚C conjugates
prevailed only in eyes. Present results suggest the involvement of IAA in the
control of potato tuber dormancy.
Characterisation of a Variegated Grapevine Mutant Showing Reduced Polyphenol Oxidase Activity
Authors: Rathjen H , Robinson SP
Published: January 2006

Fruit of the variegated grapevine mutant Bruce's Sport is known to dry to a lighter colour than other seedless varieties. The biochemical basis for this decreased browning capacity was investigated. Bruce's Sport grapes had similar levels of phenolic compounds to Sultana H5. Activity of the enzyme polyphenol oxidase (PPO EC 1.10.3.1) in mature berries of Bruce's Sport was only 20-30% of that in Sultana H5. No evidence of inhibitors or activators of PPO was found when berry extracts were mixed. PPO activity on a fresh weight basis was highest in the grape seed traces, intermediate in the skin, and lowest in the pulp in both varieties. In each tissue type, however, PPO activity in Bruce's Sport was less than 25% of that in Sultana H5. On a fresh weight basis, PPO activity in Sultana H5 berries was high at fruit set then declined as the berry developed. PPO activity per berry increased from fruit set until veraison, then remained constant. PPO activity showed similar changes during development of Bruce's Sport berries but was lower than in Sultana H5 at all stages. The Bruce's Sport grapes were variegated and the green regions of skin had similar PPO activity to Sultana H5 skin while the white regions had very low activity. Only the green regions of skin of Bruce's Sport grapes stained for PPO activity with endogenous or exogenously applied phenolic substrates. The decreased browning in this grapevine mutant apparently results from decreased levels of PPO activity in the white regions of the berry, possibly arising from a disruption in chloroplast development.
Allocation and Retranslocation of 15N by Maize (Zea mays L.) Hybrids Under Field Conditions of Low and High N Fertility
Authors: Weiland RT , Ta TC
Published: January 2006

A field experiment was conducted with high and low N fertility regimes to evaluate root-absorbed 15N, and its subsequent remobilisation in four maize hybrids. In previous experiments, potential yield and patterns of senescence had varied among these hybrids. Individual plants were supplied with 15N at the 12-leaf stage and the uptake of the labelled N and its subsequent partitioning during successive harvests was followed. Grain yield and N accumulation at physiological maturity (PM) were reduced 20 and 40%, respectively, under low N compared with high N fertility. Neither hybrid type nor N fertility level initially affected the amount of lSN absorbed. Maximum 15N content was observed at mid grain-fill and a significant 10% loss of 15N from plants was found at PM. Compared with those under low N, plants cultured under high N maintained higher percentages of 15N in the lower stalk and roots over hybrids and across harvests.
Kernels were a sink for remobilised 15N from all vegetative and 'other' reproductive tissues. Patterns of N remobilisation varied among different vegetative tissues. N was remobilised from stalks earlier than from leaves, while N from roots was remobilised throughout the season. Stalk and leaves were the major sources of 15N for kernels (about 45% each) while roots contributed much less. Physiological differences between the hybrid with the highest yield at both fertility levels, and with other hybrids, are discussed.
Measurement of Aspartate Aminotransferase-P2 in Developing Lupin Nodules Using a Two Site ELISA Employing Monoclonal Antibodies
Authors: Jones WT , Jones SD , Liddane CP , Reynolds PHS
Published: January 2006

Leguminous root nodules contain two forms of aspartate aminotransferase (AAT). AAT-P1 is con- stitutively expressed in roots and nodules, whereas the second isoenzyme, AAT-P2, is induced in developing nodules. A two site ELISA system was developed to quantify AAT-P2 in nodule extracts. The assay comprised two affinity-purified monoclonal antibodies directed against different epitopes on the AAT-P2 molecule. The sensitivity was less than 200 pg mL-1, and AAT-P2 could be quantified in the range 1 to 15 ng mL-1. The assay was specific for AAT-P2, and did not measure AAT-P1. The assay was used to specifically measure AAT-P2 in the developing legume root nodule formed by the symbiotic liaison between Rhizobium lupini NZP2257 and the roots of Lupinus angustifolius L. The ELISA method, which measures AAT-P2 protein, was contrasted with an approach which relied on the heat lability of AAT-P2 at 60°C to measure individual isoenzyme catalytic activity.
Effects of NaCl and Na2SO4 on Growth and Solute Composition of Highbush Blueberry (Vaccinium corymbosum)
Authors: Muralitharan MS , Chandler S , Van Steveninck RFM
Published: January 2006

Hardwood cuttings from the field-grown blueberry cultivar Blue Crop were grown in nutrient solution with added NaCl(0-200 mol m-3) or Na2S04 (0-50 mol m-3). After 5 weeks' growth, leaf fresh weight was greater on either salt than on no salt, and was maximal at 20 mol m-3 NaCl or 25 mol m-3 Na2SO4. Leaf dry weight increased in proportion to external salinity for both salts. Leaf damage was severe at concentrations greater than 75 mol m-3 NaCl or 50 mol m-3 Na2SO4.
In the presence of NaCl, Na+ and Cl- concentrations in the leaves were 3-4 times greater than initial solution concentration. Growth in the presence of NaCl was accompanied by loss of K+ in leaves (from 94 to 36 μmol g FW-1), stems (from 48 to 20 μmol g FW-1) and roots (from 88 to 12 μmol g FW-1). In the presence of Na2SO4, leaf Na+ concentration increased to 2-3 times greater than initial solution concentration. Na+ uptake and loss of K+ were less in plants grown on Na2SO4 than on NaCl solutions containing equimolar concentrations of sodium. In Na2SO4 solutions, SO42- in stems and roots accumulated approximately to initial external concentration. SO42- concentration in leaves was 1.5-2.0 greater than initial external levels.
In plants grown in 20-50 mol m-3 NaCl, non-significant slight increases in the foliar concentrations of glycinebetaine, choline and proline were measured (maximum total of 8 μmol g FW-1 for all metabolites). However, sucrose (2-fold), glucose (3-fold), fructose (4-fold), sorbitol (4-fold) and malate (7-fold) concentrations were significantly enhanced. The total increase in concentration of all measured sugars was approximately 100 μmol g FW-1, while malate concentrations increased by approximately 15 μmol g FW-1.
Our data suggest that blueberries are poor Na+ and Cl- excluders and appear to accumulate these ions in leaves. Although growth is enhanced initially on the levels of salt tested, and accumulation of ions and sugars is presumably sufficient for osmotic adjustment, leaf damage eventually occurs. This is probably due to the toxic effects of accumulated Na+ and Cl- in leaves and/or to the severe reduction of K+ levels.
Effect of Hypocotyl Length on Morphogenesis of Explants of Cucumber (Cucumis sativus L.) in vitro
Authors: Gambley RL , Dodd W
Published: January 2006

Explants of cucumber seedlings having different lengths of hypocotyl attached were grown axenically on Murashige and Skoog medium supplemented with kinetin (2 mg L-1). Multiple shoots developed from the apical regions of all explants. In this tissue shoots may also develop at the base of the hypocotyl, but this response is strongly dependent upon the length of the hypocotyl. As the length of the hypocotyl increased beyond 5 mm, there was a rapid reduction in basal shoot numbers and a concomitant increase in root production. We suggest that these responses are related not to the ratio or concentration of endogenous growth regulators but to different regions of sensitivity to growth regulators along the hypocotyl.
Metabolite Contents and Panicle Development in Indica Rice Varieties Belonging to Different Growth Duration Groups
Authors: Sahu SK , Mohapatra PK
Published: January 2006

Growth, spikelet number and assimilate contents of the panicle on the mainshoot of 20 indica rice varieties consisting of four duration groups were measured at intervals during the period between 2 weeks prior to anthesis and maturity. Panicle development was of longer duration in the late maturing varieties than in the early, and grain yield of the former was more than that of the latter due to difference in grain number. Shifting the cultivation of an early duration check variety to match the time of reproductive development in the medium duration group did not change its pattern of development. During development, the concentration of soluble carbohydrates, amino acids and phosphates changed significantly with time, and the pattern was the same in all varieties. Initially the concentration was low, but increased sharply a few days before anthesis to a peak level, then declined until anthesis. After anthesis it decreased to a minimum at maturity. Pre-anthesis metabolite concentration of the panicle was higher in the late varieties than in the early varieties, but not much difference was observed post-anthesis. Growth durations of the vegetative, reproductive and grain filling periods collectively influenced grain yield but, on the basis of partial correlation analysis, the vegetative duration was found most important for yield.
Synthesis of Spinach Phosphoribulokinase and Ribulose 1,5-Bisphosphate in Escherichia coli
Authors: Hudson GS , Morell MK , Arvidsson YBC , Andrews TJ
Published: January 2006

Phosphoribulokinase catalyses the reaction which supplies the CO2-acceptor of the photosynthetic carbon reduction cycle, D-ribulose 1,5-bisphosphate (RuBP). In plants, this enzyme is inactivated in the dark by oxidation of two cysteinyl residues, Cys16 and Cys55, on the same subunit. A cDNA for spinach phosphoribulokinase was isolated by amplification from leaf RNA and cloned into a bacterial expression plasmid to give plasmid pMMPRK. Escherichia coli carrying pMMPRK grown in rich medium accumulated both the enzyme phosphoribulokinase and its reaction product RuBP. This accumulation of RuBP severely retarded growth of the cells on minimal media. The enzyme was isolated from cell extracts and shown to be kinetically similar to authentic phosphoribulokinase isolated from spinach leaves. Cys55 was altered by site-directed mutagenesis to explore the role of this residue in catalysis and regulation. Alteration of Cys55 to Ser or Gly caused a 10-fold reduction in Vmax and altered Km(ATP). These results are consistent with Cys55 being located at the ATP-binding site but the side chain of this residue is clearly not essential for catalysis. Loss of the Cys55 thiol group accounts for most, but not all, of the loss of activity which occurs during dark inactivation of phosphoribulokinase.
Photoinhibition of Photosynthesis in situ in Six Species of Eucalyptus
Authors: Ogren E , Evans JR
Published: January 2006

Photoinhibition of photosynthesis was investigated in horizontally and vertically restrained leaves of Eucalyptus plants growing outdoors. This was done by measuring the quantum yield of PSII photochemistry, assayed by the ratio of variable to maximal fluorescence (FV/FM) after 15 min of dark adaptation, and the quantum yield of O2 evolution. On clear days, a time-dependent depression in both parameters was observed. Though horizontal leaves showed stronger photoinhibition (max. 40%) than did vertical leaves (max. 30%), this difference was smaller than the threefold difference in light interception. Since the inherent susceptibility to photoinhibition was the same in vertical and horizontal leaves, a non-linear light dependence of photoinhibition was assumed. The time course of recovery from photoinhibition under low light followed the kinetics of a first order reaction, with 50% recovery after 45 min. When watering was restricted on a hot and clear day a more severe photoinhibition developed in horizontal leaves, which took several days of low light to overcome. This photoinhibition state was triggered by high leaf temperatures, resulting from decreased stomatal conductance and transpiration, which sensitised the leaf to light.
Involvement of Membrane Damage in Stress-Induced Oxidative Deactivation of Ribulose Bisphosphate Carboxylase From Lemna minor
Authors: Franco E , Ferreira RB , Teixeira AN
Published: January 2006

Previous studies have shown that Lemna minor L. responds to an osmotic shock by producing an enzyme system capable of oxidising ribulose bisphosphate carboxylase (RuBP carboxylase; EC 4.1.1.39) to an acidic and catalytically inactive form. The induction of the oxidase system which occurs when Lemna is subjected to osmotic shock in the light is delayed by darkness and inhibited in the presence of protein synthesis inhibitors. When Lemna fronds are deprived of calcium, the oxidase system is induced in a manner identical to that observed during osmotic shock. Furthermore, a similar phenomenon is observed when the plants are incubated in the presence of membrane-damaging compounds such as filipin, ethanol or Triton X-100. This effect is reversed by the addition of compounds that are known to stabilise cellular membranes, namely calcium, polyamines and sterols.
Our results suggest that osmotic shock, calcium starvation and other stress situations damage Lemna cellular membranes, releasing the oxidase system. The presumed membrane damage and the induction of the oxidase system may be somewhat related, as shown by the observation that, in the presence of certain membrane-damaging situations, membrane stabilisers not only protect Lemna membranes but also prevent the stress-induction of the oxidase system.
Photosynthetic Physiology of Spur Pruned and Minimal Pruned Grapevines
Authors: Downton WJS , Grant WJR
Published: January 2006

Canopy development, photosynthetic performance and yield characteristics of Riesling grapevines managed by either conventional spur pruning or minimal pruning were compared over a growing season. Leaf area development 4-5 weeks after budburst was 4-5-fold greater on the minimal pruned vines due to the 6-7-fold greater number of buds that burst to produce shoots. By time of flowering (8 weeks after budburst) there was less than a 2-fold difference between the pruning treatments in leaf area per vine. At time of harvest the leaf area of spur pruned vines on a Y-shaped trellis exceeded that of minimal pruned vines. Average photosynthetic rates of leaves on shoots on minimal pruned vines were 40% higher than on spur pruned vines at 4 weeks after budburst, but average rates were similar the following week and thereafter. Calculated instantaneous photosynthetic rates for entire vines were 3-6-fold higher for the minimal pruned vines at 4-5 weeks after budburst. However, by time of flowering, vines in both treatments had similar photosynthetic rates. At harvest, spur pruned vines showed somewhat greater instantaneous carbon gain than minimal pruned vines. Carbon gain per vine per day estimated from hourly measurements of irradiance over the canopy showed a similar trend to the instantaneous rates. Leaf conductances did not differ with pruning treatment. Calculated instantaneous water loss per vine was 2-5-fold higher for minimal pruned vines 4-5 weeks after budburst, but from flowering onwards spur pruned vines were likely to use more water than minimal pruned vines. Minimal pruned vines yielded twice the quantity of fruit of spur pruned vines, but only one-quarter the dry weight of new canes. Total carbon invested in fruit, new canes and leaves, however, was similar in both pruning treatments, accounting for 60-70% of the estimated carbon gain by the vines.
Sodium Accumulation in Leaves of Triticum Species That Differ in Salt Tolerance
Authors: Schachtman DP , Munns R
Published: January 2006

The ability to limit the accumulation of Na+ in leaves may be an important mechanism in salt tolerance because the excessive accumulation of Na+ causes the premature senescence of leaves. The objectives of this study were to test the importance of Na+ accumulation rates in determining salt tolerance and to determine whether observed genotypic differences in leaf Na+ accumulation are linked to rates of leaf expansion. Six salt-sensitive and salt-tolerant genotypes of Triticum tauschii (Coss.) Schmal., T. aestivum L. and T. turgidum L. were grown in 150 mol m-3 NaCl and harvested at regular intervals over approximately 3 weeks. Na+ concentrations and leaf growth were measured in individual leaf blades over this time. The salt-tolerant accessions all had lower rates of Na+ accumulation than the salt-sensitive. This was not due to genotypic differences in growth rates: it was independent of the overall growth rate (vigour) of the genotypes, and the growth phase of individual leaves. In the growing leaf, the rate of Na+ accumulation was lower in salt-tolerant genotypes both during and after the phase of expansion. Leaf longevity was greater in the salt-tolerant genotypes. In one salt-sensitive genotype, the maximum Na+ concentration was much lower than that of all the other genotypes. Two mechanisms of salt tolerance appear to be operating in Triticum genotypes. One is a lower rate of Na+ accumulation which is independent of the growth of individual leaves and therefore probably regulated by some root process. The second is ion compartmentation within leaves, which enhances the ability to tolerate high concentrations of Na+ in leaves.
A Tale of Two Genomes: Role of a Chloroplast Signal in Coordinating Nuclear and Plastid Genome Expression
Authors: Susek RE , Chory J
Published: January 2006

Plant cells coordinately regulate the expression of nuclear and plastid genes that encode components of the photosynthetic apparatus. Nuclear genes that regulate chloroplast development and chloroplast gene expression provide part of this coordinate control. However, there is compelling evidence that information also flows in the opposite direction, from chloroplasts to the nucleus. This hypothesised, second pathway functions to coordinate the expression of nuclear genes encoding components of the photosynthetic apparatus with the functional state of the chloroplast. Here we review the evidence for the signal transduction pathway from the chloroplasts to the nucleus and suggest possible signal molecules.