bluuebunny/crossref_metadata_2025_split huggingface dataset:
mRNA levels of four tomato (Lycopersicon esculentum Mill. L.) genes related to fluctuating plant and soil water status
Authors: THOMPSON A. J. , CORLETT J. E. 
Published: April 2006

ABSTRACTExpression of the genes le20, ni3212, le25 and lcyp2 was quantified in relation to soil and plant water status for pot‐grown tomato (Lycopersicon esculentum Mill. cv. Ailsa Craig) in a replicated trial in a partially environmentally controlled glasshouse. Leaf water potential, relative water content, stomatal conductance and gravimetric soil water content were measured at 0800,1200 and 1600 h on three days during the imposition of three different watering regimes. Paired leaf samples were analysed for mRNA. Plant‐to‐plant variability was quantified and partitioned. le20 mRNA was found in all leaves and responded both to short‐term diurnal fluctuations in water status and to more severe stress, though with reduced sensitivity to the greatest stresses. An overnight decline in le20 mRNA was independent of soil or plant water status. The pattern of expression for ni3212 was similar though ni3212 mRNA was much more abundant and the overnight drop in expression was not significant. le25 mRNA was only detected where leaf water potential was below −0.9 MPa and increased linearly with further decline in leaf water potential. lcyp2 was constitutively expressed with a diurnal pattern characterized by a sharp depression at 1600 h but with expression being enhanced by increasing water deficit at all times. The control and significance of the four genes are discussed in relation to the proposed function of their respective gene products.
Enhancement of seed germination in high salinity by engineering mannitol expression in Arabidopsis thaliana
Authors: THOMAS J. C. , SEPAHI M. , ARENDALL B. , BOHNERT H. J. 
Published: April 2006

ABSTRACTThe bacterial gene mtlD, which encodes mannitol 1‐phosphate dehydrogenase (E. C. 1. 1. 1. 17), was transformed into Arabidopsis thaliana and expressed under control of the CaMV 35S promoter. MtlD‐transformants accumulated mannitol, a sugar alcohol that is not normally found in Arabidopsis. Amounts of soluble carbohydrates, sucrose, glucose, fructose, myo‐inositol and mannitol were determined in different tissues of wild‐type and transgenic plants. We estimated that less than 1& of the carbon assimilated was converted into mannitol by the transgenic plants. The establishment of individual transformed lines (after self‐crossing three times) resulted in high and low mannitol‐producing lines which were stably maintained. The presence of mannitol did not alter plant appearance or growth habit. When MtlD‐expressing seeds and control seeds (T3 generation) were imbibed with solutions containing NaCl (range 0 to 400 mol m−3), transgenic seeds containing mannitol germinated in medium supplemented with up to 400 mol m−3 NaCl, while control seeds ceased germination at 100 mol m−3 NaCl. It is doubtful whether the ability to germinate in high salt was a result of an osmotic effect exerted by elevated levels of mannitol, considering that mannitol concentrations were in the mol m−3 range in seeds. A specific effect of polyols, for example on the integrity of subcellular membranes or enzymes, cannot be excluded.
Guard cell zeaxanthin tracks photosynthetically active radiation and stomatal apertures in Vicia faba leaves*
Authors: SRIVASTAVA A. , ZEIGER E. 
Published: April 2006

ABSTRACTZeaxanthin, antheraxanthin and violaxanthin concentrations in guard cells from sonicated abaxial epidermal peels of Vicia faba were measured from dawn to dusk, and compared with concentrations in mesophyll tissue of the same leaves. Measured changes in guard cell zeaxanthin and violaxanthin concentrations indicate that guard cells operate the xanthophyll cycle throughout the day. Mesophyll tissue had no detectable zeaxanthin at dawn, whereas guard cells had 30–50 mmol mol−1 chlorophyll a+b. On a chlorophyll basis, maximal zeaxanthin levels were 3–4 fold higher in guard cells than in mesophyll cells. Zeaxanthin concentrations tracked levels of photosynthetically active radiation (PAR) in both mesophyll and guard cells. In the mesophyll, most of the zeaxanthin changes occurred in mid‐morning and mid‐afternoon. In guard cells, zeaxanthin concentrations changed nearly linearly with PAR in the early morning and late afternoon, and closely tracked PAR levels throughout the day. Guard cell zeaxanthin concentrations were also closely correlated with stomatal apertures. The close relationship between zeaxanthin concentrations and PAR levels in guard cells indicates that zeaxanthin is well suited to function as a molecular photosensor in stomatal movements.
Nastic curvatures of wheat coleoptiles that develop in true microgravity
Authors: HEATHCOTE D. G. , CHAPMAN D. K. , BROWN A. H. 
Published: April 2006

ABSTRACTDark‐grown wheat coleoptiles developed strong curvatures within 5 h of being transferred in orbit from a 1 g centrifuge to microgravity during an experiment flown on the IML‐1 shuttle mission. The curving tendency was strongest in seedlings that were immature, with coleoptiles shorter than 10 mm at the time of transfer. The curvature direction was non‐random, and directed away from the caryopsis (the coleoptile face adjacent to the caryopsis becoming convex). The curvatures were most marked in the basal third of the coleoptiles, contrasting with pho‐totropic responses, which occur in the apical third. We interpret these curvatures as being nastic, and related to the curvatures commonly reported to occur during clinostat rotation treatments.
Estimation of growth parameters in salt‐stressed maize: comparison of the pressure‐block and applied‐tension techniques
Authors: CRAMER G. R. , SCHMIDT C. 
Published: April 2006

ABSTRACTA custom‐built pressure block was used to estimate the effective turgor (turgor pressure minus the yield threshold) and the cell wall extensibility of the growing zone of the third leaves of 8‐d‐old maize (Zea mays L.) seedlings. In response to cell wall loosening, pressure in the chamber increased rapidly and reached a maximum after approximately 60 min. Plants treated with 80 mol m−3 NaCl for 4 h were compared to control plants. Pressure‐block analysis revealed that salinity reduced effective turgor, but had no effect on cell wall extensibility. These results are qualitatively and quantitatively similar to those obtained with an applied‐tension technique used previously in our laboratory. This study indicates that the pressure‐block and applied‐tension techniques, which use very different methodologies, estimate similar growth parameters.
Differential effects of elevated ultraviolet‐B radiation on the photochemical and reproductive performances of dicotyledonous and monocotyledonous arid‐environment ephemerals
Authors: MUSIL C. F. 
Published: April 2006

ABSTRACTFour dicotyledonous Astcraceac and four monocotyledonous Iridaceac species were grown from seed under three different effective ultraviolet‐B (UV‐B, 280–320 nm) fluenccs, which approximated those received daily over the natural growing periods of these species at their southerly and northerly distribution limits under ambient stratospheric ozone, and at the northerly limit assuming a 20% ozone depletion. Diminished photochemical efficiencies, delayed flowering, decreased flower production, pollen germination and tube growth, and reduced numbers of seeds set, accompanied by corresponding increases in mass per seed, were observed mainly in dicotyledons under elevated UV‐B radiation, despite their higher foliar and pollen polyphenolic contents, their possession of trinucleatc pollen and their natural occurrence at lower latitudes than monocotyledons with binucleate pollen. The results demonstrate the difficulties in determining plant sensitivity to UV‐B radiation from polyphenolic content, pollen type and natural geographic distribution, and suggest that monocotyledons possess other attributes that confer greater resilience to UV‐B radiation.
Effects of free‐air CO2 enrichment on the development of the photosynthetic apparatus in wheat, as indicated by changes in leaf proteins
Authors: NIE G. Y , LONG S. P. , GARCIA R. L. , KIMBALL B. A. , LAMORTE R. L. , PINTER P. J. , WALL G. W. , WEBBER A. N. 
Published: April 2006

ABSTRACTA spring wheat crop was grown at ambient and elevated (550 μmol mol−1) CO2 concentrations under free‐air CO2 enrichment (FACE) in the field. Four experimental blocks, each comprising 21‐m‐diameter FACE and control experimental areas, were used. CO2 elevation was maintained day and night from crop emergence to final grain harvest. This experiment provided a unique opportunity to examine the hypothesis that CO2 elevation in the field would lead to acclimatory changes within the photosynthetic apparatus under open field conditions and lo assess whether acclimation was affected by crop developmental stage, leaf ontogeny and leaf age. Change in the photosynthetic apparatus was assessed by measuring changes in the composition of total leaf and thylakoid polypeptides separated by SDS‐PAGE. For leaves at completion of emergence of the blade, growth at the elevated CO2 concentration had no apparent effect on the amount of any of the major proteins of the photosynthetic apparatus regardless of the leaf examined. Leaf 5 on the main stem was in full sunlight at emergence, but then became shaded progressively as 3–4 further leaves formed above with continued development of the crop. By 35 d following completion of blade emergence, leaf 5 was in shade. At this point, the chlorophyll alb ratio had declined by 26% both in plants grown at the control CO2 concentration and in those grown at the elevated CO2 concentration, which is indicative of shade acclimation. The ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) content declined by 45% in the control leaves, but by 60% in the leaves grown at the elevated CO2 concentration. The light‐ harvesting complex of photosystcm II (LHCII) and the chlorophyll content showed no decrease and no difference between treatments, indicating that the decrease in Rubisco was not an effect of earlier senescence in the leaves at the elevated CO2 concentration. Following completion of the emergence of the flag‐leaf blade, the elevated‐CO2 treatment inhibited the further accumulation of Rubisco which was apparent in control leaves over the subsequent 14 d. From this point onwards, the flag leaves from both treatments showed a loss of Rubisco, which was far more pronounced in the elevated‐CO2 treatment, so that by 36 d the Rubisco content of these leaves was just 70% of that of the controls and by 52 d it was only 20%. At 36 d, there was no decline in chlorophyll, LHCII or the chloroplast ATPase coupling factor (CFI) in the elevated CO2 concentration treatment relative to the control. By 52 d, all of these proteins showed a significant decline relative to the control. This indicates that the decreased concentration of Rubisco at this final stage probably reflected earlier senescence in the elevated‐CO2 treatment, but that this was preceded by a CO2‐concentration‐dependent decline in Rubisco.
Acclimation of photosynthesis in relation to Rubisco and non‐structural carbohydrate contents and in situ carboxylase activity in Scirpus olneyi grown at elevated CO2 in the field
Authors: JACOB J. , GREITNER C. , DRAKE B. G. 
Published: April 2006

ABSTRACTStands of Scirpus olneyi, a native saltmarsh sedge with C3 photosynthesis, had been exposed to normal ambient and elevated atmospheric CO2 concentrations (Ca) in their native habitat since 1987. The objective of this investigation was to characterize the acclimation of photosynthesis of Scirpus olneyi stems, the photosynthesizing organs of this species, to long‐term elevated Ca treatment in relation to the concentrations of Rubisco and non‐structural carbohydrates. Measurements were made on intact stems in the Held under existing natural conditions and in the laboratory under controlled conditions on stems excised in the field early in the morning. Plants grown at elevated Ca had a significantly higher (30–59%) net CO2 assimilation rate (A) than those grown at ambient Ca when measurements were performed on excised stems at the respective growth Ca. However, when measurements were made at normal ambient Ca, A was smaller (45–53%) in plants grown at elevated Ca than in those grown at ambient Ca. The reductions in A at normal ambient Ca, carboxylation efficiency and in situ carboxylase activity were caused by a decreased Rubisco concentration (30–58%) in plants grown at elevated Ca; these plants also contained less soluble protein (39–52%). The Rubisco content was 43 to 58% of soluble protein, and this relationship was not significantly altered by the growth CO2 concentrations. The Rubisco activation state increased slightly, but the in situ carboxylase activity decreased substantially in plants grown at elevated Ca. When measurements were made on intact stems in the field, the elevated Ca treatment caused a greater stimulation of,A (100%) and a smaller reduction in carboxylation efficiency (which was not statistically significant) than when measurements were made on excised stems in the laboratory. The possible reasons for this arc discussed.Plants grown at elevated Ca contained more non‐structural carbohydrates (25–53%) than those grown at ambient Ca. Plants grown at elevated Ca appear to have sufficient sink capacity to utilize the additional carbohydrates formed during photosynthesis.Overall, our results are in agreement with the hypothesis that elevated Ca leads to an increased carbohydrate concentration and the ensuing acclimation of the photo‐synthetic apparatus in C3 plants results in a reduction in the protein complement, especially Rubisco, which reduces the photosynthetic capacity in plants grown at elevated Ca, relative to plants grown at normal ambient Ca. Nevertheless, when compared at their respective growth Ca, Scirpus olneyi plants grown at elevated Ca in their native habitat maintained a substantially higher rate of photosynthesis than those grown at normal ambient Ca even after 8 years of growth at elevated Ca.
Interaction of ozone pollution and light effects on photosynthesis in a forest canopy experiment
Authors: TJOELKER M. G. , VOLIN J. C. , OLEKSYN J. , REICH P. B. 
Published: April 2006

ABSTRACTOzone pollution may reduce net carbon gain in forests, yet data from mature trees are rare and the effects of irradiance on the response of photosynthesis to ozone remain untested. We used an open‐air system to expose 10 branches within the upper canopy of an 18‐m‐tall stand of sugar maple (Acer saccharumMarsh.) to twice‐ambient concentrations of ozone (95nmol mol−1, 0900 to 1700, 1 h mean) relative to 10 paired, untreated controls (45nmol mol−1) over 3 months. The branch pairs were selected along a gradient from relatively high irradiance (PPFD 14.5 mol m−2d−1) to deep shade (0.7mol m−2d−1). Ozone reduced light‐saturated rates of net photosynthesis (Asat) and increased dark respiration by as much as 56 and 40%, respectively. Compared to sun leaves, shade leaves exhibited greater proportional reductions in Asatand had lower chlorophyll concentrations, quantum efficiencies, and leaf absorptances when treated with ozone relative to controls. With increasing ozone dose over time, Asatbecame uncoupled from stomatal conductance as ratios of internal to external concentrations of carbon dioxide increased, reducing water‐use efficiency. Ozone reduced net photosynthesis and impaired stomatal function, with these effects depending on the irradiance environment of the canopy leaves. Increased ozone sensitivity of shade leaves compared to sun leaves has consequences for net carbon gain in canopies.
Rapid recycling of triose phosphates in oak stem tissue
Authors: HILL S. A. , WATERHOUSE J. S. , FIELD E. M. , SWITSUR V. R. , AP REES T. 
Published: April 2006

ABSTRACTWe report the carbon‐13 and oxygen‐18 isotope ratios in cellulose from the early and late wood of pedunculate oak (Quercus robur L.). The δ13 C value of the early wood correlates best with that of the late wood of the previous year. The δ18O value of the early wood correlates best with that of the late wood of the same year. We suggest that a biochemical explanation of these data is that there is a rapid cycle between hexose monophosphates and triose phosphates in oak stem tissue during cellulose synthesis. Evidence in support of this explanation is provided by the intramolecular distribution of 14C in labelled fructose extracted from cores of wood that had been supplied with [1−14C]‐ and [6‐14C]glucose.
Environmental and hormonal regulation of barley late‐embryogenesis‐abundant (Lea) mRNAs is via different signal transduction pathways
Authors: ESPELUND M. , DE BEDOUT J.A. , JR OUTLAW W.H. , JAKOBSEN K.S. 
Published: April 2006

ABSTRACTLate‐embryogenesis‐abundant (Lea) genes are induced in immature embryos by ABA and osmotic stress. Using the ABA‐biosynthesis inhibitor norflurazon in combination with ionic and non‐ionic stress, the expression of three distinct groups of Lea transcripts in immature barley embryos was investigated, these groups being embryoand aleurone‐specific B15C mRNAs, embryo‐specific B19 inRNAs, and rab/dehydrin mRNAs, which encode stress‐related proteins that are also expressed in vegetative tissues. The expression of B15C and rab/dehydrins in response to mannitol was not affected by the addition of norflurazon, which decreased the endogenous ABA levels by 89%; this observation is consistent with an ABA‐independent pathway. The expression of B19 was only slightly dependent on ABA. In contrast, induction of the Lea genes by salt (NaCI) required at least 25ümol m−3 endogenous ABA. Together, these results are evidence for different signal transduction pathways linking ionic and non‐ionic osmotic stress to Lea mRNA accumulation in barley embryos.
The effects of elevated temperature and atmospheric carbon dioxide concentration on the quality of grain lipids in wheat (Triticum aestivum L.) grown at two levels of nitrogen application
Authors: WILLIAMS M. , SHEWRY P. R. , LAWLOR D.W. , HARWOOD J. L. 
Published: April 2006

ABSTRACTWheat plants were cultivated under growth regimes combining two temperatures (ambient and 4°C above ambient temperature) with two concentrations or carbon dioxide (350 and 700 μmol mol) and two nitrogen fertilizer applications (high and low). The aim of this study was to define any changes in the acyl lipid composition of wheat grains which could result from alterations in the growth conditions. Qualitative and quantitative changes were observed in both non‐starch and starch lipid fractions. Temperature was by far the most influential growth factor, although interactions between all three growth conditions occurred, as confirmed by analysis of variance. Growth at elevated temperatures had the general effect of reducing the amounts of accumulated lipids, particularly non‐polar lipids (1322 nig fatty acids per 100 g fresh weight at ambient temperatures as opposed to 777 mg fatty acids per lOOg fresh weight at 4°C above ambient temperatures). There were changes in the proportions of the major non‐starch as well as the starch lipids. In the former category, non‐polar lipids (principally triacylglyc‐erols), the membrane glycosylglyccridcs and phos‐phatidylcholinc were the main constituents, whereas in the starch lipids, lysophosphatidylcholine and lysophos‐phatidylethanolamine represented over 70% of the total. Depending on the growth conditions, the percentages of lipids such as monogalactosyldiacylglycerol, digalactosyl‐diacylglycerol and phosphatidyleholine (non‐starch) or the starch lysophosphatidylethanolamine varied 2‐fold or more. Significant changes in the acyl composition of individual lipids were also observed, most often in the proportions of palmitate, oleate and linoleate. The observed alterations in wheat lipids arc likely to affect the properties of any flours derived from grain grown under climate change conditions.
Biosynthesis of halomethanes and methanethiol by higher plants via a novel methyltransferase reaction
Authors: SAINI H. S. , ATTIEH J. M. , HANSON A. D. 
Published: April 2006

ABSTRACTBiogenic emissions of halomethanes (CH3CI, CH3Br and CH3I) and methanethiol (CH3SH) are of major significance to atmospheric chemistry, but there is little information on such emissions from higher plants. We present evidence that plants can produce all these gases through an identical methyltransferase reaction. A survey of 118 herbaceous species, based on CH3I production by leaf discs supplied with Kl, detected the presence of in vivo halide methyltransferase activity in 87 species. The activities ranged over nearly 4 orders of magnitude. Plants generally considered salt tolerant had relatively low activities, and salinization of three such species did not increase the activity. The highest activities were found in the family Brassicaceae. Leaf extracts of Brassica oleracea catalysed the S‐adenosyl‐L‐methioninc‐dependenl niethylalion of the halides I−, Br− and CI− to the respective halomethanes. In addition, the extract similarly methylated HS− (bisulphide) to CH3SH. These two types of enzyme activity (halide and bisulphide methyltransferase) were also present in all of the 20 species comprising a subsample that represented the range of CH3I emissions observed in the initial survey of in vivo CH3I production ability, and in a marine red alga Endocladia muricata. Moreover, the two activities occurred in approximately the same ratio in all the higher plants tested. These findings highlight the potential of higher plants to contribute to the atmosphericbudget of halomethanes and melhanethiol. The halide and bisulphide methyltransferase activities may also provide a mechanism for the elimination of halide and HS− ions, both of which are known to be phytotoxic.
Salt tolerance of maize (Zea mays L.): the role of sodium exclusion
Authors: FORTMEIER R. , SCHUBERT S. 
Published: April 2006

ABSTRACTThe influence of NaCl and Na2SO4 on growth of two maize cultivars (Zea mays cv. Pioneer 3906 and cv. Across 8023) differing in Na+ uptake was investigated in two green‐house experiments. Na+ treatment with different accompanying anions (Cl−/SO42−) showed that ion toxicity was caused by Na+. While shoot growth of the two cultivars was markedly affected by salt in comparison to the control during the first 2–3 weeks, there were only slight differences between the cultivars. The shoot Ca2+ concentration was reduced in both cultivars, and the youngest leaves contained an even lower concentration compared with the rest of the shoot. During this first phase, Across 8023 tended to have higher concentrations of Ca2+ than Pioneer 3906. The Na+‐excluding cultivar Pioneer 3906 showed continuous, although reduced, growth compared with the control, while the Na+ concentration in the shoot decreased until flowering. Cultivar Across 8023 accumulated Na+ until flowering: the reduction in the growth of stressed plants was greater than that for Pioneer 3906. Leaves of cultivar Across 8023 showed clear toxic symptoms, while those of the more salt‐tolerant cultivar Pioneer 3906 did not. It is concluded that Na+ exclusion contributes to the salt tolerance of maize.