bluuebunny/crossref_metadata_2025_split huggingface dataset:
Freezing tolerance and avoidance in high‐elevation Hawaiian plants
Authors: LIPP C. C. , GOLDSTEIN G. , MEINZER F. C. , NIEMCZURA W. 
Published: April 2006

ABSTRACTFreezing resistance mechanisms were studied in five endemic Hawaiian species growing at high elevations on Haleakala volcano, Hawaii, where nocturnal subzero (°C) air temperatures frequently occur. Extracellular freezing occurred at around ‐5°C in leaves of Argyroxiphium sandwicense and Sophora chrysophylla, but these leaves can tolerate extracellular ice accumulation to ‐15°C and ‐12°C, respectively. Mucilage, which apparently acted as an ice nucleator, comprised 9 to 11% of the dry weight of leaf tissue in these two species. Leaves of Vaccinium reticulatum and Styphelia tameiameiae were also found to tolerate substantial extracellular freezing. Dubautia menziesii, on the other hand, exhibited the characteristics of permanent supercooling; a very rapid decline in liquid water content associated with simultaneous intracellular and extracellular freezing. However, in those species that tolerate extracellular freezing, the decline in liquid water content during freezing is relatively slow. Osmotic potential was lower at pre‐dawn than at midday in four of the species studied. Nocturnal production of osmotically active solutes may have helped to prevent intracellular freeze dehydration as well as to provide non‐colligative protection of cell membranes. Styphelia tameiameiae supercooled to ‐9·3°C and tolerated tissue freezing to below ‐15°C, a unique combination of physiological characteristics related to freezing. Tolerance of extracellular ice formation after considerable supercooling may have resulted from low tissue water content and a high degree of intracellular water binding in this species, as determined by nuclear magnetic resonance studies. The climate at high elevations in Hawaii is relatively unpredictable in terms of the duration of subzero temperatures and the lowest subzero temperature reached during the night. It appears that plants growing in this tropical alpine habitat have been under selective pressures for the evolution of freezing tolerance mechanisms.
A theoretical explanation of the Piper‐Steenbjerg effect
Authors: WIKSTRÖM F. 
Published: April 2006

ABSTRACTThe relation between plant yield and plant nutrient concentration is sometimes found to be negative, a phenomenon called the Piper‐Steenbjerg (PS) effect. A model was used to examine the underlying causes of the PS effect, and the conditions under which it is most likely to occur. The model uses the nutrient productivity concept for plant growth and a nutrient uptake equation in which root growth rate and external nutrient concentration determine the uptake rate. The study suggests that the PS effect occurs when the fast growth of plants grown in an initially higher nutrient medium eventually leads to a more rapid depletion of external nutrients than the slow growth of plants grown in an initially lower nutrient medium. The fast growth of plants combined with a rapid decrease of nutrient uptake leads to a fall in plant nutrient concentration. When these large plants with very low nutrient concentrations are compared with the smaller, slow‐growing plants, a PS effect may be found depending on the time at which the plants are harvested, and on the range of initial values of the external nutrient content. When it occurs, the effect is greatest when the depletion volume per unit new root (Vd) is lowest, and when the mobility of nutrients in the medium is highest (α=1). The results are sufficiently general to apply to a variety of nutrients, plant species and growth media.
Integrated tolerance mechanisms: constitutive and adaptive plant responses to elevated metal concentrations in the environment
Authors: MEHARG A. A. 
Published: April 2006

ABSTRACTIsolation and study of metal tolerant and hypersensitive strains of higher plant (and yeast) species has greatly increased our knowledge of the individual pathways that are involved in tolerance. Plants have both constitutive (present in most phenotypes) and adaptive (present only in tolerant phenotypes) mechanisms for coping with elevated metal concentrations. Where studies on the mechanisms of tolerance fall down is in their failure to integrate tolerance mechanisms within cell or whole‐plant function by not relating adaptive mechanisms to constitutive mechanisms. This failure often distorts the relative importance of a proposed tolerance mechanism, and indeed has confused the search for adaptive mechanisms. The fundamental goal of both constitutive and adaptive mechanisms is to limit the perturbation of cell homeostasis after exposure to metals so that normal or near‐normal physiological function may take place. Consideration of the response to metals at a cellular rather than a biochemical level will lead to a greater understanding of mechanisms to withstand elevated levels of metals in both contaminated and uncontaminated environments. Recent advances in the study of Al, As, Cd, and Cu tolerance and hypersensitivity are reported with respect to the cellular response to toxic metals. The role of genetics in unravelling tolerance mechanisms is also considered.
Effects of patchy stomatal closure on gas exchange measurements following abscisic acid treatment
Authors: MOTT K. A. 
Published: April 2006

ABSTRACTGas exchange data and images of leaf fluorescence were collected concurrently as stomata responded to abscisic acid (ABA) application. When 10−5kmolm−3 ABA was applied to the transpiration stream in a short pulse, stomatal conductance (gs), photosynthesis (A) and intercellular CO2 concentration (Ci) decreased rapidly after a short lag period and became approximately constant after 2h. There was an apparent reduction in the A versus c1 relationship as stomata closed, but the data returned to the A versus C1 curve while stomatal conductance was constant or slowly rising during the second hour after ABA treatment. Larger amounts of ABA administered during the pulse caused larger deviations from the A versus c1 relationship. When 10−7kmolm−3 ABA was applied continuously through the transpiration stream, gs, A and Ci decreased, but there was no substantial deviation from the A versus c{ curve. Fluorescence images were patchy as stomata closed for all experiments, but became slowly more uniform during the time that gas exchange was returning to the A versus Cj curve. The distribution of con‐ductance among patches was not bimodal, and larger devi‐ations from the A versus ct curve had greater ranges of pixel values and more pixel values representing low values of Cj during stomatal closure than did experiments show‐ing small or no deviation. Estimates of A and gs from fluo‐rescence images compared favourably with measured val‐ues in most cases, suggesting that the patchy distributions of fluorescence were caused by patchy distributions of stomatal conductance and that apparent reductions in the A versus ct relationship were the result of these patchy stomatai distributions and not direct effects of ABA on mesophyll functioning. The data show that stomatal patches can be temporary and that patchiness may not be reflected in gas exchange data if the range of stomatal con‐ductances is not large. These observations may explain some of the discrepancies among previous studies concerning the effect of ABA on the A versus Ci relationship.
A comparison of direct and indirect methods for measuring leaf and surface areas of individual bushes
Authors: BRENNER A. J. , CUETO ROMERO M. , GARCIA HARO J. , GILABERT M. A. , INCOLL L. D. , MARTINEZ FERNANDEZ J. , PORTER E. , PUGNAIRE F. I. , YOUNIS M. T. 
Published: April 2006

ABSTRACTIndirect estimates of leaf area from measurements with three commercially available instruments (DEMON, LAI‐2000 and Sunfleck Ceptometer) were compared with directly measured areas of individual Retama sphaerocarpa bushes. The three indirect methods gave good estimates of the total surface area of individual bushes. For the DEMON, the method of log‐linear averaging of transmitted radiation gave estimates closer to directly measured surface area than the method of averaging transmission linearly. For the LAI‐2000, estimated surface area index multiplied by canopy projected area gave the best agreement with directly measured values. For measurements with the Sunfleck Ceptometer, values of surface area estimated from the transmission of photosynthetic quantum flux density, without correcting for diffuse radiation, gave the best agreement with directly measured values. Surface areas estimated by the three instruments were not significantly different from directly measured total (leaf + branch + stem) surface areas. Leaf surface area could be calculated from estimated total surface area minus directly measured branch surface area. Measured branch surface area was linearly related to canopy projected area.
NaCI stress enhances proteolytic turnover of the tonoplast H+‐ATPase of Citrus sinensis: appearance of a 35 kDa fragment of subunit A still exhibiting ATP‐hydrolysis activity?
Authors: BAÑULS J. , RATAJCZAK R. , LÜTTGE U. 
Published: April 2006

ABSTRACTSalinity stress caused a decrease in the relative amount of the subunits of the hydrophilic head of the tonoplast H±ATPase from leaf cells of Valencia orange [Citrus sinensis (L.) Osbeck]. In parallel, a 35 kDa polypeptide appeared in the tonoplast, which could be separated from the tono‐plast H±ATPase and cross‐reacted with an antiserum against the catalytic subunit A of the tonoplast H±ATPase. This polypeptide seems to show ATP hydrolysis activity and is considered to be a product of proteolytic breakdown of subunit A. This indicates an increased turnover of the tonoplast H±ATPase of Valencia orange under salinity stress.
Stress‐dependent redistribution of abscisic acid (ABA) in Hordeum vulgare L leaves: the role of epidermal ABA metabolism, tonoplastic transport and the cuticle
Authors: DAETER W. , HARTUNG W. 
Published: April 2006

ABSTRACTWhen 14C‐labelled abscisic acid ([14C]ABA) was supplied to isolated protoplasts of the barley leaf at pH 6, initial rates of metabolism were about five times higher in epidermal cell protoplasts than in mesophyll cell protoplasts if equal cytosolic volumes were considered. In spite of the fact that epidermal cells make up only about 35% of the total water space in barley leaves, and despite the small cytosolic volume of these cells, in intact leaves all epidermal cells would thus metabolize half as much ABA per unit time as the mesophyll cells (0–27 and 0–51 mmol h−1 m−3 leaf water). Therefore, under these conditions epidermal cells seem to be a stronger sink than mesophyll cells for ABA that arrives via the transpiration stream. However, at an apoplastic pH of 7–25, which occurs in stressed leaves, the proportion of total metabolized ABA would be much smaller in epidermal than in mesophyll cells (0–029 and 0–204 mmolh−l m−3 leaf water). Our results indicate that under conditions of slightly alkaline apoplastic pH the epidermis may serve as the main source for fast stress‐dependent ABA redistribution into the guard cell apoplast. This is partly the result of ABA transport across the epidermal tonoplast, which is dependent on the apoplastic pH and possibly on the cytosolic calcium concentration. The cuticle seems to be of no particular importance in stress‐induced apoplastic ABA shifts and cannot be regarded as a significant sink for high ABA concentrations under stress.
Temporal and spatial variations in the oxygen‐18 content of leaf water in different plant species
Authors: WANG X.‐F. , YAKIR D. 
Published: April 2006

ABSTRACTTemporal variations in the δ18 oxygen (δ18O) content of water transpired by leaves during a simulated diurnal cycle fluctuated around the δ18O content of the source water. Reconstructed variations in the δ18O values of leaf water differed markedly from those predicted by conventional models. Even when transpiring leaves were maintained under constant conditions for at least 3 h, strict isotopic steady‐state conditions of leaf water (equality of the 18O/16O ratios in the input and transpired water) were rarely attained in a variety of plant species (Citrus reticu‐lata, Citrus paradisi, Gossypium hirsutum, Helianthus annuns, Musa musaceae and Nicotinia tabacum). Isotopic analysis of water transpired by leaves indicated that leaves approach the isotopic steady state in two stages. The first stage takes 10 to 35 min (with a rate of change of about 3–3%h−1), while in the second stage further approach to the isotopic steady state is asymptotic (with a rate of change of about 0–4% h−1), and under conditions of low transpiration leaves can last for many hours. Substantial spatial isotopic heterogeneity was maintained even when leaves were at or near isotopic steady state. An underlying pattern in this isotopic heterogeneity is often discerned with increasing 18O/16O ratios from base to tip, and from the centre to the edges of the leaves. It is also shown that tissue water along these spatial isotopic gradients, as well as the average leaf water, can have 18O/16O ratios both lower and higher than those predicted by the conventional Craig and Gordon model. We concluded, first, that at any given time during the diurnal cycle of relative humidity the attainment of an isotopic steady state in leaf water cannot be assumed a priori and, secondly, that the isotopic enrichment pattern of leaf water reflects gradual enrichment along the water‐flow pathway (e.g. as in a string of pools), rather than a single‐step enrichment from source water, as is normally assumed.
Photoinhibition in the Antarctic moss Grimmia antarctici Card when exposed to cycles of freezing and thawing
Authors: LOVELOCK C. E. , OSMOND C.B. , SEPPELT R. D. 
Published: April 2006

ABSTRACTFreezing and thawing of the endemic moss species Grimmia antarctici Card, caused photoinhibition. When snow cover was removed from moss in the field, resulting in exposure to fluctuating temperatures and light conditions, photoinhibition, measured as a reduction in the ratio of variable to maximum chlorophyll a fluorescence (Fv/Fm), was observed. The extent of photoinhibition was highly variable and appeared to be reversible during periods of warmer temperatures. A series of controlled laboratory studies found that the light conditions that prevail between freezing and thawing events influenced the recovery from photoinhibition observed during freezing and thawing, with low light conditions facilitating the greatest rates of recovery. After four cycles of freezing and thawing, recovery from photoinhibition in hydrated moss was achieved within 12 h of transfer to 5°C and 15 μmol quanta m−2 s−1. These results favour the hypothesis that photoinhibition observed during freezing represents a protective process involving the down‐regulation of photo‐system II when photosynthetic carbon assimilation is limited by low temperatures.
Xylem cavitation in two mature Scots pine forests growing in a wet and a dry area of Britain
Authors: JACKSON G. E. , IRVINE J. , GRACE J. 
Published: April 2006

ABSTRACTThe xylem cavitation rate, stem water content, stomatal conductance and leaf water potential of mature Scots pine (Pinus sylvestris L.) were compared over a period of 18 months at two sites in Britain where trees were planted from the same seed source. The sites were at Thetford in south‐east England, where the climate is relatively warm and dry (average rainfall of 600mm per year), and Aberfoyle in central Scotland, where it is relatively cool and wet (average rainfall of 1500 mm year−1). In the first year of study (1992) the natural difference between the sites was amplified by a severe drought affecting south‐east England. Acoustic emissions (as a result of cavitation) were detected at both sites, but were not an everyday occurrence, and rates depended on short‐term meteorological variation. The relative water content (RWC) of the trunk at breast height at Thetford was significantly lower than at Aberfoyle, and declined in parallel with increasing severity of drought. Following the release from drought a gradual increase in RWC was found, but the pre‐drought RWC was not attained. The same xylem water potential gradient and stomatal conductance was found at the two sites; but on a diurnal basis, as water potential declined, cavitation rates increased. There was no difference in vulnerability to cavitation or in hydraulic conductance between the sites.
UV‐B increases the harvest index of bean (Phaseolus vulgaris L.)
Authors: DECKMYN G. , IMPENS I. 
Published: April 2006

ABSTRACTThe effects of small changes in natural UV‐B on the photosynthesis, pigmentation, flowering and yield of bean plants (Phaseolus vulgaris L. var. Label) were studied. To obtain a relatively natural growth environment, the plants were grown in small, half‐open greenhouses of UV‐transmitting Plexiglas of different thickness (3 and 5 mm), resulting in an 8% difference in the weighted UV‐B reaching the plants. Although the UV‐B doses used did not significantly influence photosynthesis on a leaf area basis during vegetative growth, important changes in biomass allocation were noted. A UV‐B‐O induced reduction in leaf area during the period of vegetative growth resulted in decreased dry weight after 57 d. During the flowering and pod‐filling stages (57–79.d after planting), however, plants grown at high UV‐B retained their photosynthetic capacity longer: maximal photosynthesis, chlorophyll and N content of the leaves were higher under the higher UV‐B dose at a plant age of 79 d. Combined with an increased allocation under the higher UV‐B dose of both N and biomass to the pods, this resulted in a small increase in yield and an important increase in harvest index with increased UV‐B.
The gravitropic set‐point angle (GSA): the identification of an important developmentally controlled variable governing plant architecture*
Authors: DIGBY J. , FIRN R. D. 
Published: April 2006

ABSTRACTThe angle at which an organ is maintained by gravit‐ropism is characteristic of the organ, its developmental state and the prevailing environmental conditions. We propose that this angle be called the gravitropic set‐point angle (GSA), defined as the angle with respect to the gravity vector (with a vertically downward orientation being 0°) at which an organ is maintained as a consequence of gravitropism. Studies of the gravitropic behaviour of organs from trailing plants show that the GSA is subject to developmental regulation. Depending on the developmental age and prevailing environmental conditions, the GSA of an organ can he set at any value between 0° and 180° The previously reported reversal of the sign of the gravitropic response in such organs, whether this is brought about developmentally or induced by light, represents the change from one common extreme (GSA = 180°, conventionally referred to as negative orthogravitropism) to another (GSA = 0°, or positive orthogravitropism). The concept of a variable gravitropic set‐point offers a more unified view of all forms of gravitropic behaviour than has been advanced previously, and places a new constraint on models of gravitropism. Current models of gravitropism appear to be unable to explain either the ability of organs to change their orientation with respect to gravity as they develop, or the re‐orientation that can be observed when some organs are exposed to new environmental conditions.
Transpiration inhibition by stored xylem sap from well‐watered maize plants
Authors: SINCLAIR T. R. , VALLERANI C. , SHILLING D. G. 
Published: April 2006

ABSTRACTThere is increasing evidence that a chemical signal exists in xylem sap of plants subjected to water deficits which influences physiological responses in plant shoots. An important method of studying this signal is the transpiration response of excised leaves exposed to xylem sap collected from plants. However, Munns et al [Plant, Cell & Environment 16, 867–877] cautioned that transpiration inhibition is observed when xylem sap collected from wheat and barley is stored before determining physiological activity. The objective of the study reported here was to determine if transpiration inhibition develops in maize sap collected from well‐watered plants when the sap is stored under various conditions. It was found that storage of maize sap collected from well‐watered plants for only 1 d at ‐20°C resulted in the development of substantial transpiration inhibition in bioassay leaves. Storage of sap at 4°C resulted in the development of the effect after 2 weeks, while storage at −86°C showed only small transpiration inhibition after 3 weeks. The major source of the transpiration inhibition was the development of a substance in the stored sap that resulted in physical blockage of the transpiration stream in bioassay leaves. However, a small signal component may also have developed in the stored sap. Because of the possibility of ionic activity under freezing conditions at −20°C, calcium was studied for its potential involvement in the transpiration inhibition. However, the calcium concentrations found to inhibit transpiration were nearly an order of magnitude larger than the calcium concentrations observed in xylem sap.
The expression of a small heat shock gene is activated during induction of tobacco pollen embryogenesis by starvation*
Authors: ZARSKY V. , GARRIDO D. , ELLER N. , TUPY J. , VICENTE O. , SCHÖFFL F. , HEBERLE‐BORS E. 
Published: April 2006

ABSTRACTA tobacco (Nicotiana tabacum L.) cDNA clone, Nthsp 18P, encoding a class I low‐molecular‐weight heat shock protein (LMW HSP), has been isolated from a mid‐biccllular pollen cDNA library by hcterologous hybridization with a low‐molecular‐weight heat shock cDNA clone of alfalfa. Northern analysis showed that Nthsp 18P expression is activated at normal temperature during the dehydration phase of in situ pollen development, just before anthesis. Induction of pollen embryogenesis by an in vitro starvation treatment of mid‐bicellular tobacco pollen was accompanied by a dramatic increase in the levels of the Nthsp 18P transcript, which accumulated in embryogenic pollen grains at 25°C; lower levels of this transcript were also detected in early pollen‐derived embryos. A similar pattern of expression was observed in transgcnic tobacco plants containing the promoter of Gmhsp 17.3‐B, a soybean homologue of the Nthsp 18P gene, fused to the GUS reporter gene. This is the first characterized gene shown to be transcriptionally activated during the induction of pollen embryogenesis.