bluuebunny/crossref_metadata_2025 huggingface dataset:
Genetic Control of Male Fertility in Higher Plants
Authors: Chaudhury AM , Craig S , Bloemer KC , Farrell L , Dennis ES
Published: January 2006

Male development in higher plants is a complex process which requires the correct spatial and temporal expression of a large number of male fertility genes. They include the genes required for the structure of the male organs, as well as genes required for male gamete development. Male-sterile mutants, impaired in male fertility functions, have helped to identify a number of these genes in various plant species including Arabidopsis thaliana, the model crucifer. In A. thaliana, once these genes are mapped, they can be cloned by chromosome walking. Alternative strategies of cloning will be facilitated by the isolation of similar mutants by tagging with transposable elements, T-DNA, or by mutagen-induced deletion. Once the genes required for male fertility are cloned and their wild type function identified, an understanding of the molecular basis of male fertility is likely to result. The combination of genetic dissection and the modern techniques of genome manipulation have made such a goal feasible.
Nodule-Like Structures Induced on the Roots of Wheat Seedlings by the Addition of the Synthetic Auxin 2,4-Dichlorophenoxyacetic Acid and the Effects of Microorganisms
Authors: Ridge RW , Bender GL , Rolfe BG
Published: January 2006

The addition of the synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) at a concentration range of between 5 × 10-5 M and 1 × 10-6M caused nodule-like outgrowths on wheat seedling roots. Concentrations of 2,4-D greater than this range caused stunting and death, while concentrations less than 1 × 10-7 M had no obvious effect on plant growth. At the lower end of the concentration range, 2,4-D had a small inhibiting effect on seedling growth. Time-course studies on the development of the nodule-like outgrowths showed that they developed at the same rate as control lateral roots; there was regionality within the structure, and at least three cell types were present: a cell division zone, amyloplast-containing cells, and highly vacuolated cells. There was no organised vascular system similar to Rhizobium/legume symbiotic nodules, although vascular tissue was found to enter the nodule-like outgrowths. Different strains of Rhizobium, Azospirillurn, Agrobacterium and Escherichia coli were added separately with 2,4-D to the seedling roots, showing different effects on seedling health and on the growth and internal structure of the nodule-like outgrowths. Generally, bacteria caused a less-organised internal structure to the growths and earlier 'senescence'. Some bacteria also caused stunting and death of seedlings at concentrations of 2,4-D that would have no such effect alone. We conclude that these induced nodule-like outgrowths are modified lateral roots with carbon reserves (as starch in amyloplasts) similar to those found in the cortex of roots, and that microorganisms are able to modulate or interfere with the development of these outgrowths.
Root Growth, Osmotic Adjustment and NO3- Uptake During and After a Period of Drought in Artemisia tridentata
Authors: Bassirirad H , Caldwell MM
Published: January 2006

Nitrate uptake in pot-grown, well watered and water-stressed Artemisia tridentata seedlings was determined both during drought and during recovery from drought using >15NO3-. Water deficit caused a 40% decrease in NO3- uptake compared to well watered plants and the restricted NO3- uptake persisted 4 days after rewatering. Between 4 and 14 days after rewatering, NO3- uptake in previously stressed plants was the same as that of the controls. Root relative growth rate (RGR) during the drying cycle was about one-fourth that of the control, but recovered to the control level within 4 days after rewatering. Between 4 and 14 days after rewatering, the previously droughted plant roots exhibited nearly three times greater RGR than the control plant roots. Estimates of root solute content indicated that at no time during the stress and recovery periods did the droughted roots exhibit osmotic adjustment. Changes in root growth properties were uncoupled from turgor. During the recovery period, drought-induced adjustments in cell wall yielding properties are thought to have increased root growth in previously stressed seedlings. Nevertheless, the greater root growth of previously droughted plants did not result in more NO3- acquisition than in control plants. The pattern of NO3- uptake upon rewatering was apparently more closely associated with root uptake capacity.
Blue Light Induction of in situ Nitrate Reductase Activity in the Marine Green Alga Ulva rigida
Authors: Corzo A , Niell X
Published: January 2006

The regulation by light (especially blue light) and NO3- of the nitrate reductase (NR) activity was studied in the marine green macroalga Ulva rigida C. Agardh. NR activity was measured in situ as no available in vitro method exists for Ulva rigida. The effectiveness spectrum of NR-enhancement by light was determined. Blue light was clearly the most effective wavelength, being more effective than white or red light. Blue light enhancement of NR was strictly dependent on photosynthesis since it was inhibited by 95% in presence of 5 × 10-5 M DCMU. The time course of NR enhancement by blue light was hyperbolic in shape, the semimaximal level of increase was reached in 24 min in N-sufficient algae. Blue light activation of NR is dependent upon photo flux density in a sigmoidal manner; 95% of the maximum increase was reached at 137 μmol m-2 s-1. Blue light enhancement of NR is linearly dependent on the amount of KNO3 available in the medium at the beginning of the experiment. Increase in NO3- by itself, in dark or without a concomitant increase in photon flux density, only increases NR activity by 12% (darkness) or 25% (white light, 4 μmol m-2 s-1) with respect to a blue light control. The blue light enhancement of NR was inhibited by actinomycin D (33%), rifampicin (32%) and cycloheximide (88%). Therefore, in Ulva rigida the blue light enhancement of NR occurs mainly by induction of de novo synthesis.
Waterlogging Modifies Growth, Water Use and Ion Concentrations in Seedlings of Salt-Treated Eucalyptus Camaldulensis, E. tereticornis, E. robusta and E. globulus
Authors: Marcar NE
Published: January 2006

Two experiments were carried out in a glasshouse in Canberra during autumn 1987 to determine the extent to which waterlogging would modify the response to salinity of E. camaldulensis Dehnh., E. tereticornis Smith, E. robusta Smith and E. globulus Labill. Seedlings, 4-5 months old, established in free-draining sand-filled pots, were treated with either 150 (experiment 1) or 100 (experiment 2) mol m-3 NaCl with and without waterlogging for approximately 4 weeks; a waterlogging pretreatment of 3 weeks was included in experiment 2.
Salt × waterlogging (SW) significantly reduced seedling growth for all species whereas growth under NaCl (S) or waterlogging (W) treatment alone was not significantly affected, except for E. robusta. In addition SW significantly reduced leaf stomatal conductance and whole-plant water use and increased leaf and stem Na+ and Cl- concentrations. Pretreatment with waterlogging (experiment 2) significantly improved growth (particularly for E. globulus) and reduced the concentrations of Na+ and Cl- in leaves under SW treatment. E. camaldulensis showed least growth reduction and symptom development with addition of S, W and SW in these experiments.
Carbon Acquisition and Metabolism in a Root Hemiparasitic Angiosperm, Thesium humile (Santalaceae) Growing on Wheat (Triticum vulgare)
Authors: Fer A , Simier P , Arnaud MC , Rey L , Renaudin S
Published: January 2006

Thesium humile Vahl (Santalaceae) is a root-hemiparasite which causes economic losses in cereal crops in the Mediterranean countries. O2 exchange measurements showed that photosynthesis does occur in Thesium. Experiments using 14CO2 gave additional evidence of the photosynthetic capacity of T. humile at both preparasitic and parasitic stages; roots of T. humile, unlike those of non-parasitic plants, exhibited a low sink strength for photosynthates. The end product of photosynthesis in T. humile is mannitol which is also the main carbohydrate translocated in the phloem. Nevertheless, feeding host leaf with [3H]glucose clearly demonstrated that the parasite, in spite of its photosynthetic capacity, remained dependent upon its host for an additional supply of reduced carbon. Moreover, in isolated T. humile shoots supplied with [14C]sucrose via the transpiration stream, the absorbed sucrose was rapidly converted into mannitol. Thus the parasite would be able to convert sucrose derived from the host plant into mannitol.
The present work gives clear evidence that mannitol can be regarded as the major soluble carbohydrate in the carbon metabolism and in the translocation of reduced carbon in T. humile. The mannitol synthesis pathway might be a metabolic target for the chemical control of this parasite in cereals, in which this polyol has never been detected.
Photosynthetic Acclimation and Nitrogen Partitioning Within a Lucerne Canopy. I. Canopy Characteristics
Authors: Evans JR
Published: January 2006

Acclimation by the photosynthetic system to the gradient in irradiance through a leaf canopy was investigated with a plot of lucerne (Medicago sativa L. cv. Aurora). The aims were to determine the extent to which acclimation occurred in a natural canopy and to quantify the changes in the partitioning of nitrogen within the leaf that are associated with acclimation. The canopy grew up around light sensors placed at 10 cm height increments which logged the irradiance at 1 min intervals for the 4 days that preceded sampling. Photosynthetic capacity was measured with leaf disc oxygen electrodes and the chlorophyll, soluble protein and nitrogen contents of the leaves were determined. Daily irradiance declined exponentially down through the canopy. Nitrogen content and photosynthetic capacity both declined down through the canopy. Photosynthetic acclimation by the lower leaves was evident from the lower chlorophyll a/b ratios and reduced photosynthetic capacity per unit chlorophyll. The lower photosynthetic capacity per unit of chlorophyll was offset by an increased proportion of leaf nitrogen present in the thylakoids. Consequently, the photosynthetic capacity per unit leaf nitrogen was nearly independent of irradiance.
Based on a comparison of the response of many species to different irradiances during growth, it is generally the case that the proportion of thylakoid nitrogen increases for leaves grown under lower irradiance so as to maintain a constant ratio of photosynthetic capacity to total leaf nitrogen. However, the ratio of photosynthetic capacity to total leaf nitrogen varies widely between species.
Polyphenol Oxidase Enzymes in the Sap and Skin of Mango Fruit
Authors: Robinson SP , Loveys BR , Chacko EK
Published: January 2006

Severe sapburn occurs in mango fruit of the cultivar Kensington when sap contacts the fruit, resulting in browning and then blackening of the skin. Both the sap and skin of mango fruit contained considerable polyphenol oxidase (PPO) activity. The sap enzyme was not activated by SDS, was inhibited by hexadecyltrimethylammonium bromide, and was active with both para- and ortho-diphenol substrates. The skin enzyme was activated by SDS, was inhibited by salicylhydroxamic acid and polyvinylpyrrolidone, and was active only with ortho-diphenol substrates. These properties suggest that the sap PPO is a laccase-type enzyme (EC 1.10.3.2) whereas the skin contains the more common catechol oxidase-type PPO (EC 1.10.3.1). The skin enzyme had a temperature optimum at 30�C but the sap enzyme had maximum PPO activity at 75�C. Both enzymes were relatively thermostable, requiring more than 15 min at 80�C for 50% loss of activity. It is concluded that browning of mango skin induced by the sap is predominantly catalysed by PPO in the skin and that this is unlikely to be prevented by heat treatment of the fruit.
Abscisic Acid and Cytokinins as Possible Root-to-Shoot Signals in Xylem Sap of Rice Plants in Drying Soil
Authors: Bano A , Dorffling K , Bettin D , Hahn H
Published: January 2006

Seedlings of rice cv. IR 36 were grown in soil in small pots with a horizontally divided root system: after 6-7 weeks, about 20% of the entire root system had protruded through the holes at the base of the pots and was kept in contact with nutrient solution. At this stage the plants were exposed to three different treatments: (a) the soil was kept watered and the protruding free roots were dried in air; (b) the free roots were kept moist and the soil left unwatered; (c) both soil and protruding roots were left unwatered for 30 h and then rewatered. During the first hours of treatment a and b, a decline in stomatal conductance was observed, whereas the stem water potential remained unchanged. The concentration of abscisic acid (ABA) in the xylem, however, increased. At later stages of treatment a and b, the stem water potential began to decrease with a parallel further increase of xylem ABA. Xylem sap contained considerable amounts of bound ABA, the level of which increased during total root drying and decreased again after rewatering. Level of cytokinins, zeatin (t-Z)+zeatin riboside (t-ZR) and isopentenyladenine (2iP) + isopentenyladenosine (2iPA), on the contrary, decreased during root drying and increased again after rewatering. The results are discussed with regard to a possible function of ABA and cytokinins as root-to-shoot signals.
Verification of Nitrogenase Activity (C2h2 Reduction) in Azospirillum Populated, 2,4-Dichlorophenoxyacetic Acid Induced, Root Structures of Wheat
Authors: Yu D , Kennedy IR , Tchan YT
Published: January 2006

The characteristics of C2H4 formation and H2 evolution associated with 2,4-D induced root structures on wheat seedlings inoculated with Azospirillum brasilense Sp7 have been investigated. C2H4 formation and H2 evolution with 2,4-D treatment is several times greater than that by wheat seedlings inoculated with Azospirillum alone, as the result of the formation of a niche for azospirilla protected from O2. This increased C2H4 production in 2,4-D treated seedlings was proportional to C2H2 concentration and it was strongly inhibited by nitrite and ammonia. The inhibition increased with greater ammonia and nitrite concentration, but was reversible. The increased rate of C2H2 reduction activity was correlated with 15N enrichment in 2,4-D treated seedlings. These results confirm that the C2H4 formation was C2H2 dependent and represented the nitrogenase activity of A. brasilense associated with the 2,4-D induced root structures of wheat seedlings rather than C2H2 produced by plant tissues.
High Temperature Affects the Activity of Enzymes in the Committed Pathway of Starch Synthesis in Developing Wheat Endosperm
Authors: Hawker JS , Jenner CF
Published: January 2006

Ears of wheat were exposed for up to 10 days during the grain-filling stage to high temperature (35�C) and activities of five enzymes in the sucrose to starch pathway were compared to those in ears maintained at lower temperature (21�C day/16�C night). Two cultivars of wheat known to differ in their post-anthesis tolerance of high temperature were compared. On a per grain basis, the activity of sucrose synthase and of ADPglucose pyrophosphorylase in ears maintained at 21/16�C throughout did not change greatly between days 16 and 32 after anthesis, whereas UDPglucose pyrophosphorylase and soluble starch synthase activities declined with advancing development.
Soluble starch synthase activity in grains of heated ears was decreased within 1 day to about one- half of the value in unheated grains, and 3 days' additional heating did not reduce the activity much further. Insoluble starch synthase activity was not significantly reduced by heating. Compared to soluble starch synthase, ADPglucose pyrophosphorylase activity was more slowly affected and decreased to a lesser extent by heat. Sucrose synthase and UDPglucose pyrophosphorylase activities were either not affected or only slightly reduced; part of this reduction could be due to advanced development at the higher temperature. In recovery experiments ears were heated for brief periods and then returned to 21/16�C for a few days. ADPglucose pyrophosphorylase and soluble starch synthase activities recovered in the cooler conditions but the other two enzymes generally only maintained or lost further activity. From a comparison of the activities of these enzymes with the rate of starch deposition, and by taking into account the effects of heating, it is proposed that the influence of heating on final grain dry weight is attributable to the observed reductions of soluble starch synthase activity.
Effects of Higher Temperatures, Photoperiod and Seed Vernalisation on Development in Two Spring Wheats
Authors: Rawson HM , Zajac M
Published: January 2006

The intention of this work was to examine to what degree development in wheat is modified by increased temperature when other environmental factors are also varied. The genotypes used were an early season wheat, Hartog, and a closely related mid-season line, Late Hartog. Plants were grown throughout in temperature regimes of 25/15�C or 17/7�C and photoperiods of 9, 11, 13 or 15 h with 9 h of natural summer radiation. Seeds were vernalised for 0, 2 or 4 weeks.
Increased temperature extended the thermal time to ear emergence, particularly in Late Hartog, and particularly under short days after plants had been vernalised for 4 weeks. Phyllochron intervals on the main shoot were increased by higher temperature, as were spikelet numbers in Late Hartog under long photoperiod. However, in Hartog and in Late Hartog exposed to short days, spikelet numbers were reduced by increased temperature. Long seed vernalisation significantly reduced leaf and spikelet number in Late Hartog but only at the higher temperature. Fewer spikelets were produced per leaf at short photoperiod.
The apparently complex interactions between temperature, photoperiod, genotype, and seed vernalisation on development are explained in terms of their effects on the timing of floral initiation and the related numbers of primordia accumulated on the apex at that stage. We hypothesise that, in the absence of source limitation, delays in floral initiation such as occur through shortening of photoperiod can increase numbers of leaves and spikelets, though at a decreasing rate with increasing delay. When source is limiting, as under higher temperature and unchanged or reduced radiation, long delays result in a greater reduction in the rate of production of organs and their final number. We further propose that much of the change may be associated with the interplay between the plastochron and phyllochron intervals. Published data are examined to show that high temperatures delay ear emergence in other genotypes both in controlled environments and in the field.
Time of Flowering Affects Grain Quality and Spikelet Partitioning Within the Rice Panicle
Authors: Mohapatra PK , Patel R , Sahu SK
Published: January 2006

Anthesis of spikelets in the panicle of a tall indica rice cultivar, Kajalghara, was completed within a period of 7 days. Development progressed in basipetal fashion from the spikelets of the uppermost primary branch of the panicle to the lowermost. According to the timing of onset of anthesis, spikelets of the panicle were segregated into seven groups. Dry mass accumulation and starch and assimilate (soluble carbohydrates and amino acids) contents of each group were studied from anthesis to grain maturity. Spikelets that anthesed earlier produced better quality grains and also had higher sink efficiency in converting soluble assimilates into reserve structural matter than those which anthesed later. These results rule out deficiency in supply of assimilates as a cause of partial filling of grains in the rice panicle. The study also emphasises the need for improving the percentage of high density grains in the rice panicle to maximise the use of available assimilates and enhance the grain yield potential of the plant.
Effect of the Radicle, and Hormones on the Subunit Composition and Molecular Form of Pyrophosphate-Dependent Phosphofructokinase in the Cotyledons of Citrullus lanatus
Authors: Botha AM , Botha FC
Published: January 2006

After initiation of radicle elongation, the pyrophosphate dependent phosphofructokinase (PFP) activity increases in the cotyledons of Citrullus lanatus. A selective increase of the β-subunit and a constant level of the α-subunit is apparent in the cotyledons during early seedling establishment. The radicle plays an important role in the control of the level of PFP activity and β-subunit content in the cotyledons, as removal during the incubation prevented the increase in PFP activity. Radicle removal also largely restricted the increase in specific β-subunit content, observed in the intact embryos. Application of kinetin (0.5 μM) or 2-chlorophosphonic acid (0.1 μM ethrel) to isolated embryos replaces the effect of the radicle. Application of ethrel to isolated embryos increased the specific β-subunit, while the α-subunit content remained constant. Exogenous kinetin resulted in a substantial increase in the specific β-subunit content, while the α-subunit content declined. The PFP isoenzyme ratio differs between the hormonal treatments and the control tissue, probably as a result of their differential effect on the level of the PFP subunits.
The Behaviour of Shoot Apices of Lolium temulentum in vitro as the Basis of an Assay System for Florigenic Extracts
Authors: King RW , Blundell C , Evans LT
Published: January 2006

Previous experiments have shown that shoot apices excised from plants of L. temulentum that had been exposed to one long day (LD) could form inflorescence primordia in vitro if gibberellic acid (GA3) was present in the medium whereas apices from plants in short days (SD) could not. We show here that apices from older plants grown under high irradiance can undergo inflorescence differentiation in vitro after one LD even in the absence of GA3, as can apices from plants in SD if GA3 is present in the medium.
For apices excised from both SD and one LD plants, the order of effectiveness of gibberellins for inflorescence induction was 2,2-dimethyl GA4 > GA5 > GA3 > GA1, in agreement with their ranking for effectiveness on intact plants. Application of GA3 to leaves before apex excision can substitute for GA3 in the growth medium. The presence of GA3 in the medium is not required until 4-6 days after excision from plants given one LD, and appears to be necessary for differentiation beyond the spikelet primordia stage.
Three hypotheses concerning the relation between GAs and the LD stimulus to flowering, as affected by plant age, are considered.
Rhizobial Lipo-oligosaccharide Signals and Their Role in Plant Morphogenesis; Are Analogous Lipophilic ChitinDerivatives Produced by the Plant?
Authors: Spaink HP , Wijfjes AHM , van Vliet TB , Kijne JW , Lugtenberg BJJ
Published: January 2006

Rhizobia, bacterial symbionts of leguminous plants, produce lipo-oligosaccharide signal molecules after induction of their nod genes by the plant host. The effects of these signals on plant developmental processes are discussed. Considering the similarity of the lipo-oligosaccharides with chitin, we discuss the possible basis of these effects and show some preliminary results which indicate that analogous molecules could occur in uninfected plants.
Alterations in Auxin and Cytokinin Metabolism of Higher Plants Due to Expression of Specific Genes From Pathogenic Bacteria: a Review
Authors: Hamill JD
Published: January 2006

This review deals with the physiological and morphological effects of altering the auxin/cytokinin balance in transgenic plants by expressing specific genes from pathogenic bacteria. Genes which have been used to alter auxin levels or sensitivity in transgenic plants include the iaaM/iaaH genes from Agrobacterium tumefaciens and A. rhizogenes; gene 5 and possibly gene 6b from A. tumefaciens; the rol B and possibly the rol A gene from A. rhizogenes and the iaaL gene from Pseudomonas syringae subsp. savastanoi (P. savastanoi). Genes which have been used to alter cytokinin levels in transgenic plants include the ipt gene from A. tumefaciens and the rol C gene from A. rhizogenes. A variety of biochemical mechanisms have been identified which result in alterations to phytohormone levels following expression of these genes in transgenic plants. Many of the effects on plant development are consistent with observations made following exogenous auxin and/or cytokinin application to plant tissues, and the availability of these genes offers a new approach to the study of plant physiology using transformation methodology.
The Mechanosensory Calcium-Selective Ion Channel: Key Component of a Plasmalemmal Control Centre?
Authors: Pickard BG , Ding JP
Published: January 2006

Mechanosensory calcium-selective ion channels probably serve to detect not only mechanical stress but also electrical, thermal, and diverse chemical stimuli. Because all stimuli result in a common output, most notably a shift in second messenger calcium concentration, the channels are presumed to serve as signal integrators. Further, insofar as second messenger calcium in turn gives rise to mechanical, electrical, and diverse chemical changes, the channels are postulated to initiate regulatory feedbacks. It is proposed that the channels and the feedback loops play a wide range of roles in regulating normal plant function, as well as in mediating disturbance of normal function by environmental stressors and various pathogens. In developing evidence for the physiological performance of the channel, a model for a cluster of regulatory plasmalemmal proteins and cytoskeletal elements grouped around a set of wall-to-membrane and transmembrane linkers has proved useful. An illustration of how the model might operate is presented. It is founded on the demonstration that several xenobiotics interfere both with normal channel behaviour and with gravitropic reception. Accordingly, the first part of the illustration deals with how the channels and the control system within which they putatively operate might initiate gravitropism. Assuming that gravitropism is an asymmetric expression of growth, the activities of the channels and the plasmalemmal control system are extrapolated to account for regulation of both rate and allometry of cell expansion. Finally, it is discussed how light, hormones, redox agents and herbicides could in principle affect growth via the putative plasmalemmal control cluster or centre.
The Touch-induced Action Potential in Chara: Inquiry into the Ionic Basis and the Mechanoreceptor
Authors: Staves MP , Wayne R
Published: January 2006

We developed an assay to characterize the mechanoreceptor for the touch-induced action potential of Chara internodal cells in order to compare it with the mechanoreceptor involved in sensing the gravitational pressure that induces a polarity of cytoplasmic streaming in the same cells. We show that there are at least two classes of mechanoreceptors in characean internodal cells. One class contains a RGD-binding, integrin-like protein that is localized at the end of the cells. This class of mechanoreceptors requires a turgid plasma membrane for sensing-competence and does not exhibit adaptation. We propose that this type of mechanoreceptor senses gravitational and hydrostatic pressure by sensing the magnitude and sign of its displacement relative to the extracellular matrix.
The second class of mechanoreceptors most likely does not contain RGD-binding, integrin-like proteins and does not require a turgid plasma membrane. This class is uniformly localized throughout the length of the cell and displays adaptation. We propose that this class of mechanoreceptors senses touch by sensing changes in tension which is a result of the magnitude but not the sign of the displacement of the membrane.
Control of Stem Elongation by Gibberellin A1: Evidence From Genetic Studies Including the Slender Mutant sln
Authors: Ross JJ , Reid JB , Swain SM
Published: January 2006

Information from well-known stem length mutants, both short and elongated, is discussed in the context of criteria necessary to demonstrate that the level of GA1 controls stem elongation in wild- type plants of the garden pea. Whilst this evidence is compelling, a mutant which over-produces GA1 would afford further insight, particularly into whether GA1 levels are saturating for growth in the wild-type. In this paper we further characterise the first reported garden pea mutant (sln) which possesses elevated levels of GA1. Evidence is presented from studies using this mutant that GA1 is normally limiting for growth over the early internodes in wild-type plants.
In the developing seed, the mutant sin is shown to block the metabolism of [13C, 3H]GA29 to [13C, 3H]GA29-catabolite, particularly in the testa. Associated with this there were dramatically elevated GAGA29 levels in the dry seed from sln plants (400 times) compared with seeds from Sln plants. Upon germination, it appears that some of this GAGA20 is converted to GAGA1, which leads to substantial elongation of the early internodes. This hypothesis is supported by the observation that the inhibitor of an early step in GA biosynthesis, paclobutrazol, reduces elongation of sln plants when applied to developing seeds but not when applied at the start of germination. By contrast, prohexadione-calcium (BX-112), which inhibits the step GA20 to GA1, dramatically reduces internode length of sln plants when applied to seeds at the start of germination. Finally, application of GA20 to the dry seed of a wild-type (Sln) line (before sowing) resulted in a phenocopy of the sln mutant.
Stomatal Response to Humidity in Common Bean (Phaseolus vulgaris): Implications for Maximum Transpiration Rate, Water-Use Efficiency and Productivity
Authors: Comstock J , Ehleringer J
Published: January 2006

Twelve common bean (Phaseolus vulgaris L.) cultivars were grown under greenhouse conditions to study the response of net photosynthesis (A) and transpiration (E) to variation in the leaf-to-air humidity gradient (v). Large differences were observed between cultivars in maximum rates of A and E. The variation in A correlated with both leaf nitrogen content and specific leaf area. Thin leaves had higher nitrogen contents per unit dry weight, but thick leaves had higher nitrogen content per unit surface area. Photosynthetic nitrogen-use efficiency did not correlate with nitrogen content on either a mass or a surface area basis. Very little variation was found between cultivars in the sensitivity of total leaf conductance (g) to increasing v, when sensitivity was defined as the slope of ln(g) versus v (δln(g)/δv). No significant correlation existed between δln(g)/δv and variation in maximum conductance values. Much steeper slopes (greater sensitivity) were found in the response of stomatal conductance alone (gs) to the leaf-leaf surface humidity gradient (vs). The sensitivity of stomatal response correlated positively with variation in maximum conductance among cultivars, and, since stomatal conductance was in series with a fixed boundary layer conductance, this positive correlation made possible the uniform sensitivity of g(total) with respect to v(leaf-air) despite the wide variation in gmax. All cultivm reached their maximum E at very similar v values, and all showed a relatively constant E over a wide range of high v. The implications of this relative homeostasis in E are discussed in the context of possible hydraulic limitations on E. Considerable recent interest has focussed on the use of carbon isotope discrimination (Δ) as a useful screening character in crop breeding programmes, and Δ has been found to correlate positively with yield in P. vulgaris. We found that Δ measured on bulk leaf tissue, positively correlated with both Amax and gmax between bean cultivars, but did not correlate with instantaneous measures of intercellular CO2 (cI) when v was held constant across all measurements. This apparent discrepancy may be due, at least in part, to variation in leaf temperatures among cultivars under normal growing conditions. Leaf-energy-budget simulations indicated that the observed range of maximum leaf conductance at low v would generate up to 3.0�C variation in leaf temperatures under field conditions of low to moderate windspeed. Given the strong stomatal response to v, this variation in leaf temperature could cause variation in carbon isotope discrimination, which reflects long-term cI values. Such a mechanism of producing variation in cI would not be apparent in cI measurements taken under cuvette conditions where leaf temperature was held constant.
Regulation of Glycinebetaine Accumulation in the Halotolerant Cyanobacterium Aphanothece halophytica
Authors: Ishitani M , Takabe T , Kojima K , Takabe T
Published: January 2006

When cells of the halotolerant cyanobacterium, Aphanothece halophytica were transferred from control culture medium that contained 0.5 M NaCl to a hypersaline medium with either 1.5 M or 2.0 M NaCl, the rate of photosynthetic CO2 fixation fell instantaneously. Subsequently, the photosynthetic activity returned to almost the original level within 1 day. Under salt stress, ultrastructural changes in the cells were observed by electron microscopy, these cells appeared to recover in parallel with the recovery of their photosynthetic activity. However, the intracellular level of glycinebetaine increased more slowly than the recovery of the photosynthetic CO2 fixation. The maximum rate of accumulation of betaine was estimated to be approximately 60 nmol (mg protein)-1 h-1. This rate is at least one order of magnitude greater than rates reported previously in leaves of salt-stressed higher plants. The accumulation of betaine did not take place in the dark. The intracellular level of betaine decreased as a result of the transfer of the cells to a hypo-osmotic NaCl-containing medium. The accumulation of betaine was also induced by an organic osmoticum, sorbitol. Nitrate enhances the accumulation of betaine under salt stress.
Anatomy of the Legume Nodule Cortex With Respect to Nodule Permeability
Authors: Brown SM , Walsh KB
Published: January 2006

We describe the anatomy of the cortex of a range of legume nodules (43 species of 31 genera of 13 tribes, principally of the Papilionoideae). To our knowledge, the nodule anatomy of 19 of the genera examined (30 species) was previously unreported. All nodules have a layer(s) in the inner cortex with distorted radial walls ('boundary layer') and occlusions of the intercellular spaces within the middle cortex. The 'nodule endodermis' as defined by Frazer (1942) was difficult to identify unless modified by sclerification or tannin deposition. In other species, the outer cortex contains a well developed periderm, often with several layers of tannin-containing cells. When present, sclereids contain a living cytoplasm, and are interspersed with parenchyma cells to form a water-filled barrier c. 50 μm in width about the nodule. Nodule sclereids are apparent within 5 days of inoculation in Glycine max. Sclerification of the common endodermis did not significantly increase following growth at 50 or 80% rhizosphere pO2. We suggest that the intercellular space deposition, the common endodermal layer and the periderm layer will act as a fixed resistance to gas diffusion into the nodule, allowing for a fine control of a variable resistance (boundary) layer within the inner cortex.
Causes of Growth Reduction in Elongating and Expanding Leaf Tissue of Sugarcane Under Saline Conditions
Authors: Kumar S , Naidu KM , Sehtiya HL
Published: January 2006

Plants of sugarcane, cv. Co 1148, were subjected to salinisation with 200 milliequivalents L-1 of Cl- -type salts mixture (having Na+, Ca2+ and Mg2+ as 3 :1:1 and Cl- and SO42- as 4:1 on a milli- equivalent basis) for two weeks or more during the tillering phase. Soluble sugar concentrations increased by 55% in the blades of recently matured leaves (source tissues) and by nearly 225% in the elongating sheath bases (sink tissues) as a result of salinisation. Leaf elongation within 3 h of desalin- isation was much faster than for the non-saline controls. The accumulated sugars also dropped in the rapidly elongating sheath bases by 43% during this period after desalinisation. Further, the drop in sugar levels upon desalinisation was of greater magnitude in the more rapidly growing sheath bases. The present studies indicate that even though the supply of carbohydrates from the source tissues is reduced, the sink tissues are not able to make use of these sugars under saline conditions. As Na+ and Cl- concentrations did not change within 3 h of desalinisation, the ions themselves did not appear to affect metabolic activities of the sink tissues; this suggestion is further supported by the utilisation of accumulated sugars within 3 h of desalinisation.
The Use of the Emu Promoter With Antibiotic and Herbicide Resistance Genes for the Selection of Transgenic Wheat Callus and Rice Plants
Authors: Chamberlain DA , Brettell RIS , Last DI , Witrzens B , Mcelroy D , Dolferus R , Dennis ES
Published: January 2006

Coding sequences of selectable marker genes were introduced into a plasmid containing the Emu promoter sequence which drives high levels of expression in cereal cells. The selectable markers were those coding for the enzymes neomycin phosphotransferase (NPT*) for kanamycin resistance, hygromycin phosphotransferase (HPT) for hygromycin resistance, phosphinothricin N-acetyltransferase (PAT) for resistance to the herbicidal compound phosphinothricin, and a mutant acetolactate synthase (ALS) for resistance to sulfonylurea herbicides. Plasmid DNAs were introduced into wheat and rice protoplasts by electroporation. Wheat protoplast-derived callus lines producing NPT and PAT were selected with kanamycin and phosphinothricin respectively. Wheat callus transformed with the gene coding for the mutant ALS was selected with sulfometuron methyl following the bombardment of suspension cultures with DNA-coated microparticles. With rice, transformed plants were regenerated from protoplast-derived cultures selected with kanamycin and hygromycin. Integration of the introduced DNA in transformed rice plants was confirmed by gel blot hybridisation, and significant levels of the NPT enzyme were measured by ELISA in leaves of the primary transformants as well as in leaves, seeds and roots of progeny plants. The results confirm that efficient selection of transformed cereal cultures and plants can be achieved by using selectable genes linked to the Emu promoter.
Comparative Analysis of Two Indirect Methods of Measuring Leaf Area Index as Applied to Minimal and Spur Pruned Grape Vines
Authors: Sommer KJ , Lang ARG
Published: January 2006

Leaf area index of spur and minimal pruned vines was measured directly by destructive leaf sampling and indirectly from light transmission measurements using the LAI-2000 and the DEMON instruments. Both instruments provided good estimates of plant and leaf area index. The LAI-2000 had a tendency to underestimate leaf area index. The DEMON instrument provided the most accurate estimate of plant and leaf area index. With both instruments it is important to validate indirect with direct estimates of vine leaf area.
The Plant Toxin Victorin Binds to a Discrete Number of Proteins in All Organisms Tested
Authors: Loschke DC , Tomaska LD , Chen H , Gabriel DW , Rolfe BG
Published: January 2006

We have used the plant toxin victorin C, which is synthesised by the saprophytic fungus Cochliobolus victoria, as a biological probe. Victorin C, labelled with either 125I or 35S, bound to eight distinct proteins (victorin-binding proteins) in oat plants that were either resistant or sensitive to the toxin. Using a series of in vitro experiments, we observed a difference in the victorin-binding properties between resistant and susceptible plants. Furthermore, we found that other plant species contain a set of proteins of similar sizes which specifically bind victorin. Unexpectedly, we also found a low molecular weight victorin-binding protein present in all tested eukaryotic and prokaryotic cells.
Photosynthetic and Growth Responses of Variegated Ornamental Species to Elevated CO2
Authors: Downton WJS , Grant WJR
Published: January 2006

Variegated and completely green cultivars of oleander (Nerium oleander L.) and willow myrtle (Agonis flexuosa (Willd.) Sweet) were grown in controlled environment cabinets for 3 and 5 months, respectively, under either ambient levels of CO2 or with supplementary CO2 to a partial pressure of 800 μbar. Photosynthesis of entirely green leaves and the green portions of variegated leaves on both species was greatly stimulated by high CO2 and there was no evidence of downward adjustment (acclimation) of photosynthetic rates to high CO2 during the experiment. Dark respiration rates of these leaves were lowered by high CO2. The yellow portions of willow myrtle leaves showed a low level of photosynthetic activity which was stimulated by high CO2; however, dark respiration rates showed little response to elevated CO2. Green and yellow areas on variegated leaves of willow myrtle had much lower dark respiration rates than completely green leaves, but this difference was not evident for oleander. Yellow portions of oleander leaves showed little evidence of photosynthetic capacity. This was also confirmed by a low photochemical efficiency as determined by chlorophyll fluorescence. A major effect of variegation was to slow overall plant growth compared with completely green plants. The respective 3-fold and 6-7-fold differences in biomass between fully green and variegated cultivars of oleander and willow myrtle was closely related to estimated net carbon gain per day by the plant canopy. Variegation for both species averaged close to 50:50, green:yellow areas. Variegated plants developed about twice the leaf area ratio and specific leaf area compared with their completely green counterparts. The relative growth response to high CO2 was significantly greater for the variegated plants compared to the completely green plants.
The nodDABC Genes of Rhizobium leguminosarum biovar trifolii Confer Root-Hair Curling Ability to a Diverse Range of Soil Bacteria and the Ability to Induce Novel Root Swellings on Beans
Authors: Plazinski J , Ridge RW , Mckay IA , Djordjevic MA
Published: January 2006

Cloned DNA fragments coding for the nodDABC genes of Rhizobium leguminosarum biovar trifolii strain ANU843 were introduced into Rhizobium strains possessing Sym plasmid deletions. These strains were able to: (a) synthesise four butanol-soluble Nod metabolites; (b) affect the normal growth pattern of plant root hairs of a wide range of host and non-host legumes; and (c) induce many root outgrowths on Phaseolus plants. The four Nod metabolites produced by these strains were labelled by supplying cultures with 14C-acetate in the presence of a flavonoid inducer of nod gene expression. In contrast, more than ten Nod metabolites were synthesised by wild-type strains or constructed strains containing the full complement of R. leguminosarum biovar. trifolii nodulation and host specific nodulation genes. Strain ANU845 containing nodDABC did not induce infection threads or nodule initiation sites but distorted and curled cells in plant root hairs. However strain ANU845 induced root outgrowths on beans (Phaseolus vulgaris) that appeared to result from a proliferation of the epidermal tissue. Transfer of plasmids bearing nodDABC to various Gram-negative bacteria, Agrobacterium tumefaciens, Pseudomonas aeruginosa, Lignobacter sp., Azospirillum brasilense and Escherichia coli, and different non-nodulating mutant rhizobia conferred on these strains the ability to cause root-hair curling and distortions. Several strains induced root-hair curling on clover and a range of other non-host legumes. We suggest that the expression of nodDABC in a range of soil bacteria may extend or alter the effects of these soil bacteria on the roots of host plants.
Anatomical Changes of Grapevine (Vitis vinifera L. Cv. Shiraz) Roots Related to Radial Resistance to Water Movement
Authors: Mapfumo E , Aspinall D
Published: January 2006

The anatomical features of grapevine roots that are postulated to influence radial resistance to water movement through plants were studied using roots of pot-grown 212-day-old and young roots of 20-year-old field grown grapevines. The number and percentage of cells and the percentage of surface area of the endodermis suberised rose with distance from the root tip. There were no significant differences between the extent of suberisation of well-watered and stressed plants. There was a significant negative relationship between the proportion of the root occupied by the cortex and distance from the tip, but the regression coefficient for non-irrigated plants was more negative than that of irrigated plants suggesting greater cortical breakdown in non-irrigated than irrigated root segments at equal distance from the tip. Cortical resistance is likely to be the major component of radial resistance to water through apical regions of the root while endodermal resistance and resistance offered by the peripheral vascular parenchyma are likely to become the dominant components of radial resistance in basal regions of the root. In large and older roots of grapevine the cortex is completely destroyed and cortical resistance becomes negligible.
The Relationship Between CO2 Transfer Conductance and Leaf Anatomy in Transgenic Tobacco With a Reduced Content of Rubisco
Authors: Evans JR , Caemmerer SV , Setchell BA , Hudson GS
Published: January 2006

The CO2 transfer conductance in leaves quantifies the ease with which CO2 can diffuse from sub-stomatal cavities to sites of carboxylation within the chloroplast. The aim of this work was to test the hypothesis that the CO2 transfer conductance is proportional to the surface area of chloroplasts exposed to intercellular airspaces. We compared two genotypes, wild-type and transgenic tobacco, that had been transformed with an antisense gene directed at the mRNA of the Rubisco small subunit. Transgenic tobacco had lower rates of CO2 assimilation than wild-type but similar chlorophyll contents. Leaf anatomy was altered by growing plants in two different environments: a high daily irradiance in a growth cabinet (12 h photoperiod of 1 mmol quanta m-2 s-1) and a sunlit glasshouse. The growth cabinet gave at least twice the daily irradiance compared to the glasshouse. The CO2 transfer conductance was calculated from combined measurements of gas exchange and carbon isotope discrimination measured in 2% oxygen.
Following gas exchange measurement, leaves were sampled for biochemical and anatomical measure- ment. In transgenic tobacco plants, Rubisco content was 35% of that found in the wild-type tobacco, the CO2 assimilation rate was 50% of the wild-type rate and the chlorophyll content was unaltered. While leaf mass per unit leaf area of transgenic tobacco was 82% of that of the wild-type, differences in leaf thickness and surface area of mesophyll cells exposed to intercellular airspace per unit leaf area (Smes) were small (92 and 87% of wild-type, respectively). Leaves grown in the growth cabinet under high daily irradiance were thicker (63%), had a greater Smes (41%) due to the development of thicker palisade tissue, had higher photosynthetic capacity (27%) and contained more chlorophyll (58%) and Rubisco (77%), than leaves from plants grown in the glasshouse.
Irrespective of genotype or growth environment, CO2 transfer conductance varied in proportion to surface area of chloroplasts exposed to intercellular airspaces. While the method for calculating CO2 transfer conductance could not distinguish between limitations due to the gas or liquid phases, there was no reduction in CO2 transfer conductance associated with more closely packed cells, thicker leaves, nor with increasing chloroplast thickness in tobacco.