bluuebunny/crossref_metadata_2025 huggingface dataset:
Photosynthetic Acclimation and Nitrogen Partitioning Within a Lucerne Canopy. II. Stability Through Time and Comparison With a Theoretical Optimum
Authors: Evans JR
Published: January 2006

Nitrogen redistribution between and within leaves was examined in a plot of lucerne (Medicago sativa L. cv. Aurora) in relation to potential canopy photosynthesis. The canopy was sampled during regrowth after cutting and just prior to flowering. As leaves were progressively shaded by the newly produced leaves, nitrogen content fell and photosynthetic acclimation occurred. The rate of acclimation in the canopy was the same as occurred following a step change to 23 or 6% sunlight. The profile of leaf nitrogen content was stable with respect to leaf area index and independent of time of sampling. Optimal profiles of nitrogen distribution between leaves, photosynthetic rate per unit chlorophyll and nitrogen partitioning within leaves were calculated from the relationships between photosynthesis and nitrogen in conjunction with the light environment of the preceding 3 days. The optimal nitrogen content of the leaves should vary in proportion to the relative daily irradiance at each leaf. The observed distribution achieved 88% of the potential daily photosynthesis, while a uniform nitrogen distribution yielded only 80%. Photosynthetic acclimation and nitrogen partitioning within each leaf both responded to daily irradiance similarly to the calculated optimum except at the two extremes. At the top of the canopy, photosynthetic rate per unit of chlorophyll did not increase as much as the calculated optimum, while at the base of the canopy, nitrogen partitioning failed to fall as much as the calculated optimum. This may reflect the constraints on the flexibility of the photosynthetic system. Nitrogen redistribution between leaves made a dramatic contribution to increasing the potential photosynthesis by the canopy. Although acclimation to low irradiance reduced the photosynthetic capacity per unit nitrogen by 12%, the considerable reorganisation of proteins within the thylakoids increased potential daily photosynthesis by 20% over that which would have been gained by a 'sun' leaf. However, in terms of canopy photosynthesis, which is dominated by leaves intercepting most of the light, acclimation contributed only a few per cent to the potential daily canopy photosynthesis.
Effect of Nitrogen Content on the Photosynthetic Characteristics of Sunflower Leaves
Authors: Connor DJ , Hall AJ , Sadras VO
Published: January 2006

Photosynthesis-irradiance response curves and leaf nitrogen contents were measured weekly by destructive sampling over the life cycles of leaves 10, 15, 20 and 25 of sunflower plants (cv. Prosol 35) grown in large pots in the open under optimum conditions of temperature and high irradiance. Individual leaf responses were adequately described by a hyperbola of three parameters, viz. Pmax, the rate of photosynthesis in saturating irradiance; R, the rate of dark respiration adjusted for temperature (30�C); and ε, the apparent quantum efficiency of photosynthesis at low irradiance. Pmax (range 0-40 μmol CO2 m-2 s-1) and R (0-4 μmol CO2 m-2 s-1) were non-linearly related to nitrogen content per unit leaf area (NL) (range 0.3-2.9 g N m-2) across all leaf positions and for all leaf ages. ε (mean value 0.050 mol mol-1, s.e. 0.001) was independent of NL. The equations for net photosynthesis derived from pot studies were shown to explain (r2 =0.80) leaf photosynthesis in a crop of the same cultivar over a wide range of NL and irradiance.
Changes Induced by Ultraviolet-B Radiation in Vegetative Growth, Foliar Characteristics and Photosynthetic Activities in Vigna unguiculata
Authors: Lingakumar K , Kulandaivelu G
Published: January 2006

The effect of short-term ultraviolet-B (UV-B) radiation on growth and foliar characteristics was studied in Vigna unguiculata (L.) Walp. Daily UV-B exposure was varied from 0.9 to 4.5 kJ m-2 d-1 (15-75 min at 1 J m-2 s-1). Low doses of UV-B irradiation (1.8 kJ m-2 s-1) produced varying responses on growth and leaf morphology. Inhibition of growth and shoot length is attributed to the destruction of endogenous auxin levels by UV-B. Chl b content decreased more than Chl a. Room temperature absorption spectra of carotenes and xanthophyll extracts of treated chloroplasts showed an increased synthesis of carotene. Xanthophylls of UV-B treated seedlings exhibited marked spectral changes which confirm that the light harvesting chlorophyll protein assembly is affected under short term UV-B treatment. Inhibition by 50% of photosynthetic CO2 uptake was observed in seedlings after 3 days of treatment at 1.8 kJ m-2 s-1, which was accounted for by changes in primary carboxylase as well as at the primary photochemical reactions. Low temperature fluorescence emission spectra of chloroplasts reveal that strong UV-B radiation, besides acting directly at the photosystem level, induces a change in the stoichiometry of PS I to PS II.
Auxin-Regulated Transcription
Authors: Guilfoyle TJ , Hagen G , Li Y , Ulmasov T , Liu ZB , Strabala T , Gee M
Published: January 2006

We have cloned and sequenced a number of auxin-responsive cDNAs and their corresponding genes from soybean and Arabidopsis. Each of these genes, with the exception of GH2/4, is transcriptionally regulated specifically by auxins within minutes after hormone application. The auxin-responsive mRNAs are induced some 3-60-fold depending on the type of mRNA analysed, the tissue examined, the dose and duration of auxin application, and the manipulation of the organ tested. Some of the mRNAs show rapid turnover kinetics. The mRNAs show distinct patterns of organ-specific, tissue-specific, and developmental-specific expression. The promoters of the auxin-responsive genes have been fused to the E. coli uidA gene which encodes β-glucuronidase (GUS) and transferred into tobacco and/or Arabidopsis via Agrobacterium T-DNA. These promoters and parts of these promoters have been used to follow the expression patterns and auxin-inducibility of the reporter genes in transgenic plants. We are attempting to identify minimal auxin-responsive elements and gravity-responsive elements within these promoters. We have also fused the auxin-inducible promoters to bacterial genes that encode cytokinin and auxin biosynthetic or conjugating enzymes to study the effects of organ, tissue, and developmental-specific expression of cytokinins and auxins on plant growth, development, and physiology.
Cytokinin Metabolism and Signalling in the Soybean Plant.
Authors: Nooden LD , Letham DS
Published: January 2006

Substantial evidence has indicated that cytokinins (CKs) inhibit senescence of a variety of plant organs, especially leaves, but how, or even whether, CK operates as an antisenescence signal in the intact plant needed to be determined. Because soybean has a number of advantageous features, we chose to analyse CK regulation of leaf senescence in that species. Toward the end of podfill, the leaves become visibly yellow and drop off (monocarpic senescence) leading to the death of the plant. This process appears to be mainly under the control of the pods, specifically the seeds, and therefore also needs to be correlated with pod development. Supplying CK solutions in lieu of the roots in explants (a leaf with the associated pod[s] and subtending stem segment) indicates that the roots are the main source of CKs for the leaves. The main conduit from the roots to the leaves is the xylem, and the dominant CKs of the xylem sap are zeatin riboside and dihydrozeatin riboside. These are also the most active in preventing leaf senescence. Early in pod development, before seed fill, the CK flux through xylem drops markedly and this decline is reflected in a decrease in foliar CK activity. This decrease in xylem flux is necessary but not sufficient to cause leaf senescence; however, if the CK flux is maintained in explants, it will largely override the senescence-inducing influence of the pods. Depodding of soybean plants at an early stage prevents the leaf yellowing and abscission and also causes a large resurgence of CK flux in the xylem, while depodding in late podfill does neither. 3H-labelled CKs fed through the xylem flow primarily to the leaves where they are rapidly metabolised, mainly to adenine and its riboside. Thus, a continuous supply of CK is required and modulation of CK flux into the leaf appears to be a sensitive signalling mechanism controlling the senescence of leaves and other parts. The possible roles of the various forms of CK are discussed. In addition to the root-leaf signal (CKs) and seed-leaf signal, a pod-root signal is considered.
Nodule-Like Structures Induced on the Roots of Rice Seedlings by Addition of the Synthetic Auxin 2,4-Dichlorophenoxyacetic Acid
Authors: Ridge RW , Ride KM , Rolfe BG
Published: January 2006

Nodule-like structures were induced on rice varieties Calrose and Pelde using 2,4-dichlorophenoxyacetic acid (2,4-D) in a concentration range of 2.5 × 10-6 M to 1 × 10-5M. The nodule-like structures appeared to result from the fusion of multiple meristems induced in very close proximity to each other. The internal tissue differentiation of some of the nodule-like structures was found to be similar to that of both Parasponia nodules and some kinds of determinate legume nodules. These spheroid nodule-like structures, similar in external morphology to determinate legume nodules, showed no internal infection or colonisation by Rhizobium strain NGR 234 or the Azorhizobium strain ORS 571. However, on the rice variety Calrose, the strain ORS 571 sometimes colonised extensively the surface of the nodule- like structures, in comparison to levels found on emerging lateral roots and to the root surface of the same plants. The strain NGR 234 did not colonise the surface of the nodule-like structures. The synthetic phytohormone 2,4-D also induced a range of other phenomena, including various levels of fusion of primordia and structures with a callus-like surface instead of an epidermis, but with a differentiated internal anatomy. These experiments indicate that tissue development in some types of nodule is the result of a number of meristems fusing together at a single site, and at a very early stage in development.
Ecophysiological Studies on Six Species of the Mangrove Red Algal Genus Caloglossa
Authors: Karsten U , West JA
Published: January 2006

Several aspects of the ecophysiology were compared in six eulittoral species of the mangrove red algal genus Caloglossa. The growth pattern in relation to different salt and light treatments, photosynthesis-irradiance curves, as well as the influence of salinity on the intracellular D-mannitol concentrations were studied. All Caloglossa isolates can be characterised as halotolerant due to a broad growth response under a range of salinities (5.3-70‰). The D-mannitol content of all isolates increased significantly with hypersaline treatments and decreased significantly with hyposaline treatments. These data indicate the strong involvement of this hexitol in the osmotic acclimation of Caloglossa. The growth-irradiance pattern and the photosynthesis-light response curves demonstrate an adaptation to shaded habitats for all species. All these physiological capabilities allow the successful colonisation of Caloglossa on various intertidal substrates.
The Global Carbon Cycle: a Viewpoint on the Missing Sink
Authors: Gifford RM
Published: January 2006

Atmospheric carbon budgets that ignore the possibility of terrestrial ecosystem responses to global atmospheric change do not balance; there is a 'missing sink' of about 0.4 - 4 Gt C yr-1. This paper argues a case that mechanistically it is well within the bounds of possibility that increasing carbon storage in vegetation and soils in response to the globally increasing CO2 concentration, temperature and nitrogen deposition can account for the missing C sink. Global warming conditions considered alone would be unlikely to cause most ecosystems to emit CO2, because the N mineralised by any enhanced soil organic matter decomposition would be largely taken up by plants and reconverted into organic matter having a much higher C:N ratio than that in the soil. Models of the global terrestrial C cycle indicate that an extra 0.5 - 4 Gt C yr-1 could well be being stored in soils and vegetation today in response to the CO2 fertilising effect, having regard for the interactions with growth restricting water, light and nitrogen levels. To obtain direct proof as to whether that this is happening or not is a major challenge.
Changes in the Ultrastructure of the Root Tip of Wheat Following Exposure to Aluminium
Authors: Lima MLD , Copeland L
Published: January 2006

Investigations have been carried out on morphological changes induced by aluminium ions in roots of wheat seedlings (Triticum aestivum L. cv. Vulcan). Lesions were evident on the surface of the roots after 4-8 h of exposure, and within 24 h there was increased vacuolation, loss of turgor, and severe cytoplasmic disorganisation in epidermal and peripheral cap cells. The central cap and cortical layers were also severely damaged by aluminium, but changes in the meristematic cells became evident only after more prolonged exposure of roots to aluminium. Mobilisation of starch in amyloplasts of peripheral and central cap cells of aluminium-stressed roots was particularly noticeable, and this was accompanied by an increase in the amount of extractable activity of starch-degrading enzymes. The possibility that the mobilisation of starch is linked to a coincident increase in fermentative metabolism in Al-stressed wheat roots is considered.
Changes in the Photosynthetic Properties of Australian Wheat Cultivars Over the Last Century
Authors: Watanabe N , Evans JR , Chow WS
Published: January 2006

A selection of Australian wheat cultivars, representative of those widely cultivated over the last century, was grown in the glasshouse. Photosynthetic properties of the flag leaves were determined as well as the chlorophyll, soluble protein, nitrogen and photosystem II content of the leaves. The rate of electron transport was calculated from gas exchange measurements at high CO2 partial pressures or from chlorophyll fluorescence. We found a trend towards higher rates of CO2 assimilation, higher chlorophyll and nitrogen contents per unit leaf area over time. The increase in leaf nitrogen and photosynthetic rate is most probably due to the introduction of the Rht dwarfing genes. Counter to this we observed declines in rate of electron transport per unit chlorophyll, chlorophyll a/b ratio and photosystem II content per unit chlorophyll. Because the chlorophyll to nitrogen ratio was similar between cultivars, lowering of the rate of electron transport per unit chlorophyll in modern cultivars results in a fall in the rate of electron transport per unit of nitrogen. There was no variation in the ratio of intercellular to ambient CO2 partial pressures, or leaf mass per unit leaf area. The comparison of a near isogenic pair, with or without a portion of a rye chromosome that is associated with high yield, did not reveal any association with photosynthetic characteristics. It is suggested that selection for higher chlorophyll a/b ratios for a given leaf chlorophyll content may provide a feasible surrogate for selecting higher photosynthetic capacity.
Temperature Effects on the Activation and Inactivation of Pyruvate, Pi Dikinase in Two Populations of the C4 Weed Echinochloa crus-galli (Barnyard Grass) From Sites of Contrasting Climates
Authors: Simon JP , Hatch MD
Published: January 2006

Five-week-old plants of Echinochloa crus-galli (L.) Beauv. (barnyard grass) from Mississippi (MISS) and from Québec (QUE) grown under controlled conditions were subjected to cold temperature acclimatory treatments for periods of up to 3 days. After plants were transferred from a 26/20�C day/night regime to 14/8�C for 2-3 days the rate of activation of the C4 photosynthetic enzyme pyruvate, Pi dikinase (PPDK; EC 2.7.9.1), following illumination of plants at 26�C, was substantially reduced in both ecotypes. This effect was far more pronounced in MISS plants and the PPDK activity of these plants remained at less than half that of control plants (26/20�C) even after 2 h illumination. After 3 days at 14/8�C the half-time for PPDK activation was more than 120 min in MISS plants and 35 min in QUE plants compared with about 3 min for plants remaining in the 26/20�C regime. Lesser but qualitatively similar effects were observed when plants were exposed to only cooler nights (26/8�C) or cooler days (14/20�C). When plants at the 14/8�C regime were transferred back to 26/20�C for 2 days there was a substantial recovery of the capacity for rapid PPDK activation but recovery was slower in MISS plants. Predictably, the rate of activation of PPDK was reduced when activation in control plants (26/20�C) was carried out at 8�C instead of 26�C. However, a significant finding was that the rate of activation at 8�C was more strongly affected in MISS plants, with a reduction to about 15% of the rate of control plants and a final steady PPDK level after 60 min of only half that in control plants. PPDK extracted from MISS plants underwent more rapid in vitro cold inactivation (2�C) than the enzyme from QUE plants and only 80% of the initial activity was recovered upon rewarming at 25�C. The physiological significance of these results are discussed in relation to the cold sensitivity of C4 photosynthesis and the previously reported differences in the growth and physiological performance of MISS and QUE plants at lower temperatures.
Responses of Rice and Pea Plants to Hardening With Low Doses of Ultraviolet-B Radiation
Authors: He J , Huang LK , Chow WS , Whitecross MI , Anderson JM
Published: January 2006

Responses of two rice cultivars (Oryza sativa L. cw. Er Bai Ai and Lemont) and a pea plant (Pisum sativum L. cv. Greenfeast) to low daily doses of ultraviolet-B (UV-B) radiation were measured to explore mechanisms underlying UV-B tolerance. On hardening of rice plants, cv. Er Bai Ai produced more UV-absorbing compounds than cv. Lemont; however, cv. Lemont produced more water-soluble proteins, which may be related to its greater UV-B tolerance. These responses occurred without apparent deleterious effects on the photosynthetic properties of rice leaves. In contrast, the same hardening doses caused damage to pea plants, as indicated by decreases in photosynthetic quantum yield, maximum photosynthetic capacity and chlorophyll content per unit leaf area, as well as water-soluble and total protein contents. The acquired tolerance of the two rice cultivars to a subsequent high UV-B dose increased with the duration of the hardening treatment. In contrast, the 'hardening' treatment exacerbated the damage to the photosynthetic apparatus of pea plants subsequently exposed to a high UV-B dose. It appears that for defence against UV-B radiation, cv. Er Bai Ai relies more upon the synthesis of UV-absorbing compounds, while cv. Lemont depends more upon the synthesis of protective, water-soluble enzymes; however, neither strategy seems to operate effectively in pea plants.
The Heat-Shock Response and Expression of Heat-Shock Proteins in Wheat Under Diurnal Heat Stress and Field Conditions
Authors: Nguyen HT , Joshi CP , Klueva N , Weng J , Hendershot KL , Blum A
Published: January 2006

The occurrence of heat-shock proteins (HSPs) in response to high temperature stress is a universal phenomenon in higher plants and has been well documented. However, in agriculturally important species, less is known about the expression of HSPs under natural environments. A review of the heat-shock response in wheat (Triticum aestivum L.) is presented and recent results on the expression of wheat HSPs under diurnal stress and field conditions are reported. In the field experiment, flag leaf blade temperatures were obtained and leaf blades collected for northern blot analysis using HSP 16.9 cDNA as a probe. Temperatures of leaf blades ranged from 32 to 35�C under the tested field conditions at New Deal near Lubbock, Texas. Messenger RNAs encoding a major class of low molecular weight HSPs, HSP 16.9, were detected in all wheat genotypes examined. The results suggested that HSPs are synthesised in response to heat stress under agricultural production, and furthermore, that HSPs are produced in wheats differing in geographic background. In the controlled growth chamber experiment, HSP expression in two wheat cultivars, Mustang (heat tolerant) and Sturdy (heat susceptible) were analysed to determine if wheat genotypes differing in heat tolerance differ in in vitro HSP synthesis (translatable HSP mRNAs) under a chronic, diurnal heat-stress regime. Leaf tissues were collected from seedlings over a time-course and poly (A)+RNAs were isolated for in vitro translation and 2-D gel electrophoresis. The protein profiles shown in the 2-D gel analysis revealed that there were not only quantitative differences of individual HSPs between these two wheat lines, but also some unique HSPs which were only found in the heat tolerant line. This data provides evidence of a correlation between HSP synthesis and heat tolerance in wheat under a simulated field environment and suggests that further genetic analysis of HSPs in a segregating population is worthy of investigation. In conclusion, the results of this study provide an impetus for the investigation of the roles of HSP genes in heat tolerance in wheat.
The Relationship Between Grain-Protein Content of Wheat and Barley and Temperatures During Grain Filling
Authors: Correll R , Butler J , Spouncer L , Wrigley C
Published: January 2006

This paper compares the relationship between temperatures at grain filling and grain-protein content for wheat and barley. Two similar statistical models have been developed using historical grain and climate data to reliably predict the protein content of wheat and barley at grain receival sites. Protein levels were predicted using multiple regressions with the same regression coefficients for all sites. The locality effect is absorbed in the regression intercept derived for each site. Australian Standard White (ASW) wheat data for 109 silos throughout South Australia for the years 1971-1991 were analysed in relation to rainfall and temperatures at the closest weather station. Rainfall from May to September was associated with a decrease in ASW wheat grain protein, and more importantly, the number of days in October above 30�C were positively associated with an increase in wheat grain-protein levels. Analysis of protein data from malting varieties of barley (1982-1991) from 160 South Australian hundreds (districts of about 260 km2) again showed that increased rainfall between July and September was associated with decreased grain protein. However, the dominating influence was the number of days in a row in November above 35�C, which was consistently associated with increased grain protein. This makes an interesting comparison with wheat where October temperatures were more important despite barley being harvested earlier than wheat.
Cytokinin and Carbohydrate Changes During Flowering of Boronia megastigma
Authors: Day JS , Loveys BR , Aspinall D
Published: January 2006

Boronia megastigma, a native Australian shrub, requires 10-12 weeks of low temperatures to initiate flowers and commit them to develop through to anthesis. Our understanding of the environmental control of flowering of B. megastigma has improved in recent years but less is known of the endogenous control. This paper reports qualitative and quantitative measurements of carbohydrates and cytokinins during flower initiation and development of B. megastigma. A transient increase in zeatin riboside and dihydrozeatin riboside concentrations occurred in root and stem tissue within days of transferring the plants to cool (17/9�C day/night) conditions. Starch concentrations increased throughout the plant within 2 days of transferring the plants to cool conditions and remained high for 10 weeks. A transient decrease in the starch concentration occurred during weeks 1-4 which correlated with early flower differentiation. Between weeks 10 and 12 in cool conditions, cytokinin concentrations increased, carbohydrate concentrations decreased, flower buds became committed to develop through to anthesis and a period of rapid bud expansion began. Evidence suggests that cytokinins may influence the rate of flower development by altering the mobilisation of carbohydrates.
Malate-Regulated Channels Permeable to Anions in Vacuoles of Arabidopsis thaliana
Authors: Cerana R , Giromini L , Colombo R
Published: January 2006

Anion channels in isolated vacuoles of Arabidopsis thaliana cultured cells were studied by means of the patch clamp technique in the whole-vacuole configuration. In symmetrical 100 mM KCl, a high resistance of the membrane at positive potentials inside the vacuole was observed. In symmetrical 100 mM K2-malate positive potentials inside the vacuole elicited slowly developing inward currents, due to the opening of channels, which, according to measurements of reversal potential, are selective for malate. The activation potential of the channels shifted as a function of the cytoplasmic malate concentration, but it was always such that the channels opened only to mediate malate influx into the vacuole. The channels were also permeable to succinate, fumarate and, to a lesser extent, oxaloacetate. In vacuoles preincubated with cytoplas- mic malate, inward currents were also elicited in the presence of KCl or KNO3 at the cytoplasmic side of the tonoplast. Malate channels were different from the cation slow vacuolar-type channels with regard to their sensitivity to changes in the cytoplasmic concentrations of Ca2+ and ATP, and in temperature between 10 and 20�C.
Influence of the Mesophyll on Stomatal Opening
Authors: Lee JS , Bowling DJF
Published: January 2006

Some studies have shown that stomata in detached epidennis behave differently, both quantitatively and qualitatively, from those in the intact leaf. Stomata in the intact leaf are very sensitive to environmental factors such as light, CO2 and osmotic stress, but stomata in detached epidermis are less sensitive to these factors than those in the intact leaf. Stomata in the intact leaf open in the light and close in the dark, whereas previously opened stomata in detached epidermis do not close on transfer to darkness and they are dependent on the KCl concentration in the incubation medium. Electrophysiological results also demonstrate different responses of guard cells in the intact leaf and detached epidennis. The electrical potential across the membrane of the guard cell in the intact leaf was hyperpolarised in response to light and CO2. However, there were no changes in the membrane potential difference in response to light and CO2 in detached epidermis. In CCCP-infiltrated leaf discs, the guard cell membrane was conversely depolarised by light, indicating that the guard cell membrane hyperpolarisation was related to the mesophyll cells. These results suggest the participation of the mesophyll in stomatal control. It is possible that stomatal opening in the intact leaf, to a greater or lesser extent. is dependent on an electrical signal or a chemical propagated from the mesophyll.
Malate Efflux From Root Apices and Tolerance to Aluminium Are Highly Correlated in Wheat
Authors: Ryan PR , Delhaize E , Randall PJ
Published: January 2006

Aluminium (Al) can stimulate the efflux of malate and other organic acids from root apices of wheat (Triticum aestivum L.) seedlings. This response has been implicated in a mechanism of Al tolerance since the amount of malate released from an Al-tolerant genotype was 5-10-fold greater than the amount released from a near-isogenic, but Al sensitive, genotype. In the present study, 36 wheat cultivars were screened for Al tolerance and for the amount of malate released from their root apices with a standard A1 treatment. Excised root apices (3.0 mm) were used to measure malate efflux, and the relative tolerance to Al was determined from root growth measurements in 3 and 10μM AlCl3 with 200 μM CaCl2, pH 4.3. There was a significant correlation between relative tolerance of the genotypes to Al and the amount of malate released from their root apices. Growth measurements were also used to investigate the amelioration of Al toxicity by exogenous malate. In the presence of 3 μM Al alone, relative root growth of an Al-sensitive genotype was reduced to 13% of the control. Addition of 10 μM malate to the solution increased relative root growth to 50%, and 20 �M malate completely alleviated the Al-induced inhibition of root growth. The results support the hypothesis that the Al-stimulated efflux of malate from root apices is involved in a general mechanism for Al tolerance in wheat.
Photosynthetic Responses of Thirteen Pasture Species to Elevated CO2 and Temperature
Authors: Greer DH , Laing WA , Campbell BD
Published: January 2006

Thirteen common pasture species, (eleven C3 and two C4), were grown in controlled environments at 12/7, 18/13 and 28/23�C and at 350 and 700 ppm CO2 to evaluate the effects of elevated CO2 on their photosynthetic responses. Photosynthesis was measured at the growth temperatures and at both 350 and 700 ppm CO2. In C3 species, short-term (within minutes) increases in CO2 had the greatest effect on photosynthesis, with an average of 50-60% higher rates in plants exposed to 700 ppm CO2 at each temperature. However, there was a continuum of response between the C3 species whereas C4 species were unaffected by short-term changes in CO2. There was also a long-term (4-8 weeks) response to high CO2, with an average of about 40-50% higher rates of photosynthesis, with some response by C4 species. Both short- and long-term responses were negatively correlated with the photosynthetic rate of each species at 350 ppm CO2 and all species were less efficient at converting photosynthate to dry matter at elevated CO2. These data show clearly that photosynthesis of these cool temperate pasture species can respond to elevated CO2, especially at low temperatures. This will have consequences for predicting the potential effects of climate change, accompanied by rising CO2, on pasture ecosystems.
Floral Induction in Growing Buds of Lychee (Litchi chinensis) and Mango (Mangifera indica)
Authors: Batten DJ , Mcconchie CA
Published: January 2006

Buds of potted plants of the terminal flowering tree species lychee (Litchi chinensis) and mango (Mangifera indica) forced to begin growth at high temperatures (florally non-inductive) and then transferred to low temperatures produced inflorescences, so the whole process of floral induction can occur in growing buds. Floral initials were visible in lychee within 39 days of transfer to low temperature and 30 days in mango, indicating that floral induction occurs relatively quickly in both species. In most cases where plants were transferred to winter ambient temperatures for floral induction, pre-activated (growing) buds flowered more consistently than buds that were dormant at the time of transfer. If the buds were small when plants were transferred from high temperature to low temperature, leafless inflorescences formed. If buds were a little larger, leafy inflorescences formed, with leaves basally and flowers terminally. If the buds were larger again, the shoots were purely vegetative. All these observations are consistent with floral induction occuning while the bud is growing and provide for much improved experimental systems for studying the physiology of floral induction in species such as lychee and mango.
Measuring and Modelling Whole-Tree Gas Exchange
Authors: Lloyd J , Wong SC , Styles JM , Batten D , Priddle R , Turnbull C , Mcconchie CA
Published: January 2006

Diurnal patterns of CO2 and water vapour exchange were determined for Macadamia integrifolia and Litchi chinensis trees enclosed in whole-tree gas exchange chambers at Alstonville, New South Wales (28.5�S) during October and November 1991. Whole-tree gas exchange responses to photon irradiance (I), ambient partial pressure of CO2 (Ca) and vapour pressure deficit (D) were similar to those normally observed for individual leaves. Nevertheless, at a given I (above approximately 500 μmol quanta m-2, s-1) stomatal conductances (gs) and CO2 assimilation rates (A) were higher under overcast, as opposed to clear sky conditions. This difference was maintained even when A and gs were examined as a function of sun angle. Combined with a simple light interception model, nested quadratic equations combining stomatal responses and biochemical characteristics of individual leaves were found to provide excellent descriptions of the gas exchange responses of the isolated trees. This indicates a close to optimal partitioning of photosynthetic machinery throughout the canopy. From the whole-tree gas exchange model it was found that higher A and gs under overcast conditions are attributable to both lower T1 and D as well as to a more uniform distribution of irradiance across the canopy surface.
The Composition of Apoplast Fluid Recovered From Intact Developing Tomato Fruit
Authors: Ruan YL , Patrick JW , Brady CJ
Published: January 2006

A pressure dehydration technique for recovering sap from the apoplast of the pericarp tissue of developing tomato fruit has recently been developed. Samples of this sap from two cultivars have now been analysed for sugars, amino acids, organic acids, ammonia and inorganic ions. The measured solutes accounted for 92 and 97% of the osmolality of the apoplast sap from the two cultivars. The osmotic potential of the apoplast samples was similar in the two cultivars, and the apoplast samples were distinctly different in osmolality and in composition from samples of the bulk sap obtained after thawing frozen tissue. Hexoses and inorganic compounds, principally potassium and chloride, accounted for 75% of the osmotic potential of the apoplast samples. There is little prior information on the composition of the apoplast in fruit. The impact of this new knowledge is discussed in relation to the uptake of solutes into fruit cells, the partitioning of solutes between apoplast and symplast, and the ionic environment of the cell wall and wall-bound enzymes.
Comparison of Vibrio and Firefly Luciferases as Reporter Gene Systems for Use in Bacteria and Plants
Authors: Mudge SR , Lewis-Henderson WR , Birch RG
Published: January 2006

Luciferase genes from Vibrio harveyi (luxAB) and firefly (luc) were introduced into E. coli, Agrobacteriurn, Arabidopsis and tobacco. Transformed bacteria and plants were quantitatively assayed for luciferase activity using a range of in vitro and in vivo assay conditions. Both lux and luc proved efficient reporter genes in bacteria, although it is important to be aware that the sensitive assays may detect expression due to readthrough from distant promoters. LUX activity was undetectable by liquid nitrogen-cooled CCD camera assays on intact tissues of plants which showed strong luxAB expression by in vitro assays. The decanal substrate for the lux assay was toxic to many plant tissues, and caused chemiluminescence in untransformed Arabidopsis leaves. These are serious limitations to application of the lux system for sensitive, non-toxic assays of reporter gene expression in plants. In contrast, LUC activity was readily detectable in intact tissues of all plants with luc expression detectable by luminometer assays on cell extracts. Image intensities of luc-expressing leaves were commonly two to four orders of magnitude above controls under the CCD camera. Provided adequate penetration of the substrate luciferin is obtained, luc is suitable for applications requiring sensitive, non-toxic assays of reporter gene expression in plants.
Leaf Temperature Kinetics Measure Plant Adaptation to Extreme High Temperatures
Authors: Shabala SN
Published: January 2006

Leaf temperature kinetics were studied as a function of the rate of change of ambient temperature (Vt), light conditions, plant age, and genotypic and species diversity for Zea mays, Cucumis sativus, Lycopersicon esculentum, Phaseolus vulgaris, Beta vulgaris, Cucurbita pepo and Raphanus sativus. Ambient temperature was varied from 26 to 60�C at rates from 0.5 to 8�C/min. Leaf-air temperature differences (LATD) were registered with differential copper-constantan thermocouples. As the ambient temperature rose LATD increased because stomata had been closed in darkness. Still in the darkness, at some critical ambient temperature stomata opened and the leaf temperature reduced dramatically as result of stomatal transpiration. The critical temperature is strongly dependent upon Vt. Simple equations for the calculation of a threshold of plant temperature sensitivity and of a time constant for stomatal signal transduction have been obtained. These parameters show a high correlation with plant heat tolerance both in genotypic and species aspects. This is consistent with the idea that temporal organisation of plant regulatory systems plays a leading role in evolution and in adaptation to extreme environmental conditions. Both characteristics measured tend to change with plant age. It is concluded that the measurement of leaf temperature kinetics is a very convenient procedure for estimating plant adaptive ability to high temperatures.
Morphological and Physiological Comparisons of Clonal Lines of Eucalyptus camaldulensis. I. Responses to Drought and Waterlogging
Authors: Farrell RCC , Bell DT , Akilan K , Marshall JK
Published: January 2006

Morphological and physiological responses to drought and waterlogging of six clonal lines of Eucalyptus camaldulensis Dehnh., originally from five geographically separated locations, were compared under controlled glasshouse conditions. The clones differed significantly in their ability to produce leaf and root tissue during stress periods. Clones which produced the greatest numbers of leaves (Dongara, WA clone M76 and Silverton, NSW clone M79) had leaves of low specific weight, while clones which produced fewer leaves (Erudina, SA clone M66 and Murray Bridge, SA clone M86) had leaves of relatively high specific weight. Clonal lines that produced the greatest leaf area also produced the greatest root weight. Comparisons of water use produced fewer differences, although clone M76, which produced the greatest number of leaves and the greatest total leaf area, also used the most water in both the drought and waterlogging trials. Stomatal conductance, net gas exchange and leaf nutrient allocation did not differ greatly among the clonal lines. An ability to produce and maintain transpiration surface appears the most valuable physiological attribute of plants selected to dewater damaged agricultural catchments currently being subjected to increasing periods of waterlogging due to excessive clearing of native woodlands.
Mechanism of Action of C2H4 in Promoting the Germination of Cocklebur Seeds. III. A Further Enhancement of Priming Effect With Nitrogenous Compounds and C2H4 Responsiveness of Seeds
Authors: Yoshiyama M , Maruyama A , Atsumi T , Esashi Y
Published: January 2006

Efficiency of organic or inorganic osmotica for seed priming of cocklebur (Xanthium pennsylvanicum Wallr.) revealed that KNO3 was the most promising, and was more effective than mannitol or other salts at the same concentration (200 mM) and was independent of the C2H4 action. However, KNO3 applied as a priming reagent enhanced the effect of C2H4 or that of the water stress imposed with mannitol. Unlike the action of mannitol, both KNO3M and C2H4 augmented the pool size of amino acids in seed cells. However, below 50 mM KNO3 imposing no stress only slightly, though insignificantly, affected the germinability as well as the levels of total cyanogen. On the other hand, at a high concentration which imposed water stress on the seeds, 200 mM KNO3 remarkably elevated the contents of both cyanogenic glycosides and lipids in the excised cotyledons. When C2H4 was added with KNO3, the level of cyanogenic compounds significantly increased but when added without KNO3, the contrary effect was shown. Hence the enhancement of the mannitol-induced priming effect by nitrogenous reagents in cocklebur seeds could be implicated in the accumulation of cyanogenic compounds. Unlike cocklebur, both common chickweed and barnyard grass seeds are very responsive to 30 mM KNO3 on germination, and such species abundantly contain cyanogen. The amount of cyanogen was further augmented by contact with KNO3 at only 30 mM. The role of NO-3 -dependent cyanogenesis is highlighted in relation to germination response of seeds.
Seasonal Variations of Antioxidants in Wheat (Triticum aestivum) Leaves Grown Under Field Conditions
Authors: Badiani M , Paolacci AR , Miglietta F , Kimball BA , Pinter PJ , Garcia RL , Hunsaker DJ , Lamorte RL , Wall GW
Published: January 2006

Water-soluble antioxidants, glycolate oxidase activity and net photosynthesis were measured from seedling establishment to physiological maturity, in healthy, expanded, uppermost leaves collected weekly from wheat (Triticum aestivum L. cv. Yecora Rojo) plants growing under near-optimum field conditions. Most of the antioxidants fluctuated in a cyclic, non-regular manner throughout the season, the strongest oscillations being shown by glutathione and by H2O2 -scavenging enzymes. Time series analysis revealed significant correlation among the seasonal profiles of those antioxidants participating in the 'ascorbate-glutathione cycle'. Their seasonal changes were also synchronised with those of both midday maximal net CO2 assimilation rate and of glycolate oxidase activity. This could confirm, over the whole of plant ontogeny and in field-grown plant material, the connections among photosynthetic activity and the plant cell antioxidant network and could suggest that similar mechanisms intervene in the integrated control of active oxygen generated during photorespiration. Peaks of antioxidant levels concentrated during certain periods of the plant growing season. Since no evidence of environmental stress was concurrently observed, it is suggested that a higher antioxidant capacity could be required in order to face endogenous and transient oxidative strain associated with definite plant developmental stages, namely juvenility, floral induction, stem elongation, anthesis and senescence.
Lack of correlation between conceptual karyotype and maternal response to placentation
Authors: Khong T. Y. , Ford Judith H.
Published: January 2006

The placental karyotype was correlated with the morphology of the placental
bed in miscarriages. Abnormal placentation was as likely to be seen in euploid
conceptions as in aneuploid conceptions, whereas normal placentation was seen
with both euploid and aneuploid pregnancies. No consistent chromosomal
abnormality was found with abnormal placentation. Since abnormal placentation
is implicated in the pathogenesis of preeclampsia and miscarriages, these
findings may be useful with respect to the localization of a candidate
‘preeclampsia gene’ by identifying a specific chromosome
associated with abnormal placentation.
Effects of active and passive gonadotrophin-releasing hormone immunization on recognition and establishment of pregnancy in pigs
Authors: Tast A. , Love R. J. , Clarke I. J. , Evans G.
Published: January 2006

This study investigated the effects of a reduction in gonadotrophins, by means
of differently timed active and passive gonadotrophin-releasing hormone (GnRH)
immunization at various stages, on the maintenance of early pregnancy in pigs.
In the first experiment crossbred sows (n = 11)
were immunized against GnRH using a commercial vaccine on the day of
farrowing, mated at the first oestrus, and a booster immunization was
administered 10 days (n = 7) or 20 days
(n = 4) after mating. Plasma samples were
collected every second day and assayed for GnRH antibodies and progesterone.
Pregnancy testing was carried out by real time ultrasound. None of the sows
receiving the booster immunization 10 days after mating were pregnant on Day
18 after mating. All sows receiving the booster on Day 20 after mating
aborted, with a mean vaccination-to-abortion interval of 10.0 1.5 days. In the
second experiment, crossbred gilts (n = 6) were
passively immunized by infusing (i.v.) GnRH immune pig serum on Day 12 after
mating. Luteinizing hormone profiles were determined on the day before
immunization and one day afterwards. Daily plasma samples were assayed for
GnRH antibodies and progesterone. None of the gilts were pregnant 18 days
after mating, compared with 5 of 6 non-immunized controls. Booster
immunization 10 days after mating resulted in failure of embryonic development
and establishment of pregnancy before the corpora lutea (CL) regressed,
according to progesterone profiles, whereas immunization 20 days after mating
resulted in regression of CL followed by abortion. Passive immunization 12
days after mating had a similar effect to the active immunization 10 days
after mating. These results demonstrate two different outcomes of active GnRH
immunization depending on the timing of immunization, and indicate that loss
of pregnancy between Days 12 and 18 may occur due a reduction in progesterone
rather than complete failure of the CL, as occurs at later stages. The
findings may provide an explanation for the reduced fertility of pigs in the
summer–autumn period.
Only low levels of spermadhesin AWN are detectable on the surface of live ejaculated boar spermatozoa
Authors: Petrunkina A. M. , Harrison R. A. P. , Töpfer-Petersen E.
Published: January 2006

The zona-binding protein family of spermadhesins are constituents of boar
seminal plasma that are generally believed to attach to the acrosomal region
of spermatozoa and thereby assist sperm interaction with the zona pellucida at
fertilization. However, previous studies have yielded conflicting results with
respect to amounts of adhesin bound to ejaculated cells, to the distribution
of bound adhesin within the sperm population, and the regionalization of
binding on the sperm surface. In the present study, spermadhesin AWN in
unfixed living suspensions of boar spermatozoa was assessed by means of flow
cytometry and immunocytochemistry, using a polyclonal antibody raised in
chicken. Direct probing with an Oregon Green conjugate of the antibody was
compared with indirect probing using Alexa Fluor-conjugated goat anti-chicken
IgG as second antibody. Regardless of staining procedure, the live
sub-population showed homogeneously low levels of staining, whereas the dead
sub-population showed high (more than 5-fold greater) levels of staining. The
live cells were stained about 2-fold more intensely by anti-AWN than by
preimmune immunoglobulin, indicating the presence of small amounts of AWN.
Immunocytochemistry showed the live cells to be faintly stained all over their
surface, whereas staining of the dead cells was largely localized to the
acrosomal region. This latter staining was non-specific, preimmune
immmunoglobulin resulting in as much bound fluorescence as anti-AWN. Attempts
to block non-specific staining with appropriate pretreatment with chicken or
goat serum (as compared with routine use of BSA) met with variable and
incomplete success, and did not increase staining by anti-AWN relative to
preimmune serum in either live or dead cells. It is concluded that limited
amounts of spermadhesin AWN bind tightly over the whole surface of live
ejaculated boar sperm. However, the acrosomal region of disrupted sperm has an
alarming tendency to bind fluoro-conjugates of immunoglobulins
non-specifically.