bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature effects on endogenous indole‐3‐acetic acid levels in leaves and stamens of the normal and male sterile ‘stamenless‐2′ mutant of tomato (Lycopersicon esculentum Mill.)
Authors: SINGH S. , SAWHNEY V. K. , PEARCE D. W. 
Published: April 2006

ABSTRACTThe indole‐3‐acetic acid (IAA) concentration in leaves and stamens of the normal and a temperature‐sensitive male sterile ‘stamenless‐2′ (sl‐2/sl‐2) mutant of tomato (Lycopersicon esculentum Mill.), grown under three temperature conditions, was measured by gas chromatography — mass spectrometry — selected ion monitoring (GC‐MS‐SIM) and by enzyme‐linked immunosorbant assay (ELISA). At low (LTR, 18°C day/15°C night), intermediate (ITR, 23°C day/18°C night), and high temperatures (HTR, 28°C day/23°C night), the mutant leaves had approximately 10 to 20 times higher IAA concentrations, respectively, than the normal leaves under these temperature regimes. Similarly, the stamens of mutant flowers had approximately five and eight times higher IAA concentration at ITR and HTR, respectively, than the normal flowers. In the low temperature reverted mutant stamens, however, the level of IAA was similar to that in normal stamens. Also, with an increase in temperature, there was an increase in the level of IAA in the leaves and stamens of mutant plants. However, different temperatures had no appreciable effect on the IAA content of leaves and stamens of normal plants. It is suggested that the high IAA content in leaves and stamens of the stamenless‐2 mutant is one of the factors associated with male sterility and carpellization of stamens in this mutant.
Changes in leaf Δ13C of herbarium plant species during the last 3 centuries of CO2 increase
Authors: PEÑUELAS J. , AZCÓN‐BIETO J. 
Published: April 2006

ABSTRACTΔ13C were determined for herbarium specimens of 12 C3 plants (trees, shrubs and herbs) collected during the last 240 years in Catalonia, an area with a Mediterranean climate. Values were 19.91 (S.E. = 0.32, n= 21) for 1750–1760, 19–86 (S.E. = 0.21, n= 49) for 1850–1890 and 19.95 (S.E. = 0.29, n= 25) for 1925–1950, and decreased significantly to 18.87 (S.E. = 0.31, n= 29) for 1982–1988. More irregular temporal changes were found in Δ13C of two C4 species, but they also suggest a decrease in discrimination in recent decades. These results suggest that either carbon assimilation rates have increased or stomatal conductance has decreased, and therefore, that there has been an increase in water use efficiency over the last few decades.
Electrotaxis of zoospores of Phytophthora palmivora at physiologically relevant field strengths
Authors: MORRIS B. M. , REID B. , GOW N. A. R. 
Published: April 2006

ABSTRACTPlant roots generate electrical fields in the rhizosphere as a consequence of their ion transport activities. We show here that zoospores of the plant pathogen Phytophthora palmivora exhibit anodal electrotaxis in electrical fields ≥0.5 V m−1 comparable in size to the physiological fields around roots. An experimental protocol for applying weak electrical fields and quantifying electrotaxis is described. In this system, zoospore suspensions are isolated from the electrodes and their products using agarose bridges. Therefore, electrotaxis was not due to movement or trapping of zoospores in chemical, oxygen, pH or inhibitor gradients established by electrolysis. The electrophoretic and electroosmotic mobilities of encysted zoospores were measured. These forces did not influence the distribution of zoospores in electrotactic experiments at physiological field strengths. The electrotactic response saturated at fields above 10 V m−1 was inhibited in media of osmotic strength below 400 Osmol m−3, was maximal at pH 7.5 and increased at high zoospore densities. These data suggest that electrotaxis may be a useful adjunct to chemotaxis in root targeting by zoospores.
Growth and gravitropism of corn roots in solution
Authors: NANTAWISARAKUL T. , NEWMAN I. A. 
Published: April 2006

ABSTRACTGrowth and early gravitropic responses of corn roots in solution have been studied using time‐lapse photography. Aeration was required for both root growth and gravitropism. The optimum pH for gravitropism was in the range 5 to 6. The bending response seemed to be greater for roots in non‐buffered solution than in buffered solution. Fastest growth and maximum curvature occurred with about 0.2 mol m−3 Ca2+. Under some conditions, the gravitropic response started with apparently negligible time delay after the start of the gravitropic stimulus. This may denote graviperception in or near the elongation zone itself. This mechanism for early but relatively weak gravitropism may help to explain a variety of gravitropic responses such as the ‘early wrong way’ curvature, and the behaviour of roots whose columella cells lack amyloplasts. More rapid bending appears to start at about 20 min, which is consistent with observations on roots in humid air and with the accepted statolith model of perception in the root cap.
Seasonal patterns of cell‐to‐cell communication in Chara corallina Klein ex Willd. I. Cell‐to‐cell communication in vegetative lateral branches during winter and spring
Authors: SHEPHERD V. A. , GOODWIN P. B. 
Published: April 2006

ABSTRACTCell‐to‐cell communication in lateral branches of limited growth in male Chara corallina plants has been studied using fluorescent plasmalemma‐impermeable probes. The extent of cell‐to‐cell communication was found to be seasonal. In winter, branch internodes were characterized by relatively low plasmalemma potential differences (–121·2±23·2 mV; [K+]o 0·5 mol m−3; pH 7·6), quiescent dactyls isolated from the symplast (conic tips) and by restricted cell‐cell communication (frequency of intercellular transport of six carboxyfluorescein = 42·9%). Cell‐to‐cell communication was inhibited during action‐potentials, and was more extensive between cells which did not give an action potential in response to a current pulse. An inhibitor of the action potential, La3+, promoted cell‐to‐cell communication. These may be characteristic features of winter dormancy in lateral branches of Chara. In spring, morphological and electrophysiological changes occurred immediately prior to the onset of fertility. Characteristic changes in morphology included increased abundance of spherosomes and glycosomes, elongation of stipulodes and development of active branch dactyls. Spring branch inter‐nodes were characterized by high plasmalemma PDs (–210·5±30·8mV; [K+]o 0·5 mol m−3; pH 7·6), predominantly active, non‐isolated dactyls (spinaceous tips), and extensive intercellular communication (frequency of intercellular transport of 6 carboxyfluorescein = 89·2%). Artificial elevation of the intracellular calcium ion concentration by application of ionophore A23187 or Ca2+ microinjection significantly restricted intercellular communication to a level similar to that found in winter. The depression of intercellular communication in winter tissues is suggested to be due to high sensitivity to action potentials and/or to Ca2+ fluxes. Changes in intracellular Ca2+ distribution may be involved in the transition between the morphologically distinct states of dormancy and incipient fertility.
Chemical composition of 24 wild species differing in relative growth rate
Authors: POORTER H. , BERGKOTTE M. 
Published: April 2006

ABSTRACTThe chemical composition of 24 plant species which showed a three‐fold range in potential growth rate was investigated. The carbon content of whole plants was lower for fast‐growing species than for slow‐growing ones. Fast‐growing species accumulated more organic N‐compounds, organic acids and minerals, whereas slow‐growing species accumulated more (hemi)cellulose, insoluble sugars and lignin. No correlations with relative growth rate were found for soluble phenolics, soluble sugars and lipids. The costs to construct 1 g of plant biomass were rather similar for fast‐ and slow‐growing species, both when expressed as C needed for C‐skeletons, as glucose to provide ATP and NAD(P)H, and as total glucose costs. Therefore, we conclude that, despite the differences in chemical composition between fast‐ and slow‐growing species, variation in the costs of synthesis of whole plant biomass cannot explain interspecific variation in relative growth rate of herbaceous species.
Shoot apex removal does not alter autoregulation of Modulation in soybean
Authors: DELVES A. C. , HIGGINS A. , GRESSHOFF P. 
Published: April 2006

ABSTRACTThe suppression of new nodule development in soybean (Glycine max (L.) Merr.) has been previously demonstrated to involve the shoot through reciprocal grafts between the wild‐type cultivar Bragg and its supernodulating mutant nts382. Using the same grafting technique, but modified through the excision of the shoot apex region and emerging lateral shoots, we show here that autoregulation of nodule number still existed despite apex removal. This radical treatment lowered total nodule number per plant as well as root, shoot and nodule dry weight. Bragg shoots grafted onto nts382 roots gave wild‐type nodulation (26 nodules, 15mg total nodule mass) as compared to nts382 shoots grafted onto Bragg roots (340 nodules, 277 mg total nodule mass). Specific nodule mass differed between supernodulating (about 0·5‐1·0mg per nodule) and wild‐type nodulating (2·3 mg per nodule) plants. In contrast to other growth characteristics, apex removal did not affect specific nodule size, except in plants with wild‐type shoots and nts382 (supernodulation) roots. Apex removal only slightly affected the percentage of nodule weight per total root weight in nts382, but had a severe effect in wild type. Growth reductions varied between the normal and supernodulating plants. The fact that autoregulation of nodulation still functions in plants devoid of functional shoot apices suggests that the autoregulation signal may not be derived from the apex regions and that the leaf may be a likely source.
Mode of action of paraquat in leaves of paraquat‐resistant Conyza canadensis (L.) Cronq
Authors: LEHOCZKI E. , LASKAY G. , GAAL I. , SZIGETI Z. 
Published: April 2006

ABSTRACTThe mode of action of paraquat (1,1‐dimethyl‐4,4‐bipyridinium) and the mechanism of resistance to it were studied in leaves of atrazine/paraquat co‐resistant (R) and susceptible (S) biotypes of horseweed (Conyza canadensis) collected from Hungarian vineyards. The application of 0·5 mol m−3 paraquat by spraying onto the surface of the leaves of intact plants in the light rapidly led to typical symptoms of paraquat action in the initial period in both biotypes, i.e. inhibition of CO2 fixation, suppression of variable chlorophyll fluorescence (Fv), decrease of oxygen evolution and stimulation of ethane production. The inhibitory effect of paraquat in the S plants was irreversible, whereas it was transient in the R plants and those plants recovered gradually afterwards. The R plants recovered from the inhibitory effect of paraquat only in the light, and an increase in light intensity was found to have a pronounced effect on the recovery of Fv. The mechanism of resistance to paraquat in C. canadensis is discussed.
Photosynthesis of oak trees [Quercus petraea (Matt.) Liebl.] during drought under field conditions: diurnal course of net CO2 assimilation and photochemical efficiency of photosystem II
Authors: EPRON D. , DREYER E. , BRÉDA N. 
Published: April 2006

ABSTRACTAdult trees of Quercus petraea were submitted to controlled water shortage in a natural stand near Nancy, France. Diurnal course of net CO2 assimilation rate (A) was measured in situ together with chlorophyll a fluorescence determined on dark adapted leaves. In 1990, trees experienced a strong water stress, with predawn and midday leaf water potentials below –2·0 and –3·0 MPa, respectively. Diurnal course of A of well‐watered trees exhibited sometimes important midday decreases in A related to high temperature and vapour pressure deficit. Decreases in initial (Fo) and maximal (Fm) fluorescence and sometimes in photochemical efficiency of photosystem II (Fv/Fm) were observed and probably revealed the onset of mechanisms for thermal de‐excitation. These mechanisms were shown to be sensitive to dithiothreitol. All these effects were reversible and vanished almost completely overnight. Therefore, they may be considered as protective mechanisms adjusting activity of photosystem II to the electron requirement for photosynthesis. Water stress amplified these reactions: A was strongly decreased, showing important midday depression; diurnal reductions in Fm and Fv/Fm were enhanced. The same trends were observed during summer 1991, despite a less marked drought. These protective mechanisms seemed very effective, as no photoinhibitory damage to PS II could be detected in either water stressed or control trees.
Electrical impedance of white spruce shoots in relation to pressure‐volume analysis and free sugar content
Authors: COLOMBO S. J. , BLUMWALD E. 
Published: April 2006

ABSTRACTElectrical impedance measurements made on white spruce, Picea glauca (Moench) Voss, stems were related to shoot free sugar contents and to osmotic, turgor and water potential. During seasonal dormancy induction, there were commensurate increases in free sugar contents, osmotic potential at full turgor and impedance which resulted in linear relationships among these variables. When measured over the course of laboratory drying, impedance increased curvilinearly with decreasing relative water content. There was a linear increase in impedance with decreasing water potential, with a break point coincident with the turgor loss point, possibly attributed to disruption to current flow through broken plasmodesmatal connections between adjacent cells. This technique offers a non‐destructive method to measure tissue free sugar content, and therefore, short‐ and long‐term shifts in parameters historically derived from pressure‐volume analysis.
Effect of nitrogen and phosphorus availability on the growth response ofEucalyptus grandisto high CO2
Authors: CONROY J. P. , MILHAM P. J. , BARLOW E. W. R. 
Published: April 2006

ABSTRACTThe response ofEucalyptus grandisseedlings to elevated atmospheric CO2concentrations was examined by growing seedlings at either 340 or 660 n mol CO2mol‐1for 6 weeks. Graded increments of phosphorus and nitrogen fertilizers were added to a soil deficient in these nutrients to establish if the growth response to increasing nutrient availability was affected by CO2concentration. At 660 μmol CO2mol‐1, seedling dry weight was up to five times greater than at 340 μmol CO2mol‐1. The absolute response was largest when both nitrogen and phosphorus availability was high but the relative increase in dry weight was greatest at low phosphorus availability. At 340 μmol CO2mol‐1and high nitrogen availability, growth was stimulated by addition of phosphorus up to 76 mg kg 1 soil. Further additions of phosphorus had little effect. However, at 660 μmol CO2mol‐1, growth only began to plateau at a phosphorus addition rate of 920mg kg‐1soil. At 340 μmol CO2mol‐1and high phosphorus availability, increasing nitrogen from 40 to 160mg kg‐1soil had little effect on plant growth. At high CO2, growth reached a maximum at between 80 and 160mg nitrogen kg‐1soil. Total uptake of phosphorus was greater at high CO2concentration at all fertilizer addition rates, but nitrogen uptake was either lower or unchanged at high CO2concentration except at the highest nitrogen fertilizer rate. The shoot to root ratio was increased by CO2enrichment, primarily because the specific leaf weight was greater. The nitrogen and phosphorus concentration in the foliage was lower at elevated CO2concentration partly because of the higher specific leaf weight. These results indicate that critical foliar concentrations currently used to define nutritional status and fertilizer management may need to be reassessed as the atmospheric CO2concentration rises.
Diurnal variation in the temperature response of leaf extension of two bunchgrass species in the field
Authors: BUSSO C. A. , RICHARDS J. H. 
Published: April 2006

ABSTRACTThe effect of temperature on short‐term leaf extension rates was studied for two cool‐season tussok grasses, Agropyron desertorum and Pseudoroegneria spicata, growing in the field under a variety of water stress and defoliation conditions. Leaf extension rates and air temperatures were monitored every half hour during numerous 12‐ to 65‐h periods in three growing seasons using auxanometers constructed of precision resistors. For both species, a three‐phase relationship between leaf extension rate and temperature was observed during diurnal cycles. Leaf extension rate increased linearly with temperature from dawn until midday (phase 1). Leaf extension then increased rapidly, reaching maximum rates in the early evening (approximately 1900h), despite decreasing temperatures during this period (phase 2). Finally, leaf extension rate declined with temperature from evening until dawn (phase 3). This diurnal cycle was described by linear (phase 1) and quadratic (phases 2 and 3 combined) regression models. Although the rate of leaf extension and daily integrals were affected by the water stress and defoliation treatments, the diurnal pattern was consistently observed. Temperature was probably a major factor governing leaf extension rates at night (phase 3), but it appeared unimportant in controlling leaf extension between dawn and midday. The relative importance of physiological and environmental factors controlling leaf extension rate appears to shift during the day in these species under field conditions.
An abscisic‐acid‐responsive, low temperature barley gene has homology with a maize phospholipid transfer protein
Authors: HUGHES M. A. , DUNN M. A. , PEARCE R. S. , WHITE A. J. , ZHANG L. 
Published: April 2006

ABSTRACT bltA is a barley gene which, as measured by steady state mRNA levels, is induced by a low positive temperature treatment of shoot meristems. The gene is also induced in shoot meristems by drought stress. We now report the response of this gene to foliar applications of abscisic acid. The striking similarity between the predicted amino acid sequence of bltA and two maize phospholipid transfer proteins indicates a biochemical function for the bltA gene product. This homology also demonstrates the hitherto unreported environmental regulation of expression of a phospholipid transfer protein which may involve abscisic acid in the signal transduction pathway.
Effects of nitrogen supply and high temperature on the growth and physiology of the chickpea
Authors: LAURIE S. , STEWART G. R. 
Published: April 2006

ABSTRACTChickpeas were grown with or without nitrate nitrogen feeding, or nodulated with Rhizobium leguminosarum. High [40°C day, 25°C night (HT)] and moderate [25°C day, 177°C night (LT)] temperature regimes were employed during growth. Growth rates, photosynthetic capacity and enzymes of carbon and nitrogen metabolism were monitored to assess the acclimatory capacity of the chickpea. Initial growth rates were stimulated by high temperatures, particularly in nitrate‐fed and nodulated plants. Older HT plants had fewer laterals, smaller leaves, and fewer flowers were produced than in LT plants. There was some indication of an acclimation of photosynthesis to high temperatures and this was independent of nitrogen supply. Rubisco activity was increased by high growth temperatures. However, HT plants also had higher transpiration rates and lower water use efficiency than LT plants both in respective growth conditions and when compared in a common condition. High temperatures reduced shoot nitrate reductase activity but had little effect on root activity, which was the same if not greater than activity in LT roots. The amino acid, asparagine, was found at high concentrations in all treatments. Concentrations were maintained throughout growth in HT plants but declined with age in LT plants.
Effects of flooding on carbohydrate and ABA levels in roots and shoots of alfalfa
Authors: CASTONGUAY Y. , NADEAU P. , SIMARD R. R. 
Published: April 2006

ABSTRACTAlfalfa is sensitive to waterlogging, and its yields are significantly reduced under this condition. We investigated the effects of soil flooding on free abscisic acid (ABA) accumulation in shoots and roots of alfalfa in relation to plant growth and stomatal conductance responses. The production of dry matter in alfalfa was significantly affected by flooding mainly as a result of a rapid reduction in root growth. Shoot dry matter accumulation was maintained during the first 10 d of treatment and started to decline thereafter. Foliar concentration of the major mineral elements (N, P, K) was reduced by flooding, whereas only K concentration decreased in roots of flooded plants. Regrowth declined with duration of flooding and was less than 50% of controls after 2 weeks. While no changes in ABA concentration could be detected in flooded roots, an increase was noted within a few days in leaves when compared to unflooded controls. This increase in free ABA coincided with the accumulation of large quantities of starch in leaves and a rapid decline in leaf stomatal conductance. Our results support the suggestion that leaf ABA originates from the leaf itself and may be accumulating along with starch as a result of reduced translocation to the roots. Our observation of large accumulations of sucrose in flooded roots agrees with previous reports that supply of carbohydrates is not a limiting factor to root anaerobic metabolism in flooded alfalfa.
Photosynthetic acclimation to low temperature by western red cedar seedlings
Authors: WEGER H. G. , SILIM S. N. , GUY R. D. 
Published: April 2006

ABSTRACTImposition of low, but above freezing, temperatures resulted in a gradual increase in the cold hardiness of western red cedar seedlings. This was associated with a decrease in the maximum rates of photosynthetic CO2 fixation and O2 evolution, and changes in chlorophyll a fluorescence transients which indicated that photoinhibition had occurred. Maximum photosynthetic rates declined approximately 40% during cold hardening. The leaves changed colour from green to red‐brown during the hardening process. The colour change was due to the synthesis of large amounts of the carotenoid rhodoxanthin. Lutein levels doubled, while chlorophyll declined slightly. Dehardening resulted in the rapid recovery of photosynthesis to control levels, the rapid disappearance of rhodoxanthin, and the return of lutein levels to control. It is suggested that rhodoxanthin accumulation at low temperature functions to decrease the light intensity reaching the photosynthetic apparatus. The combination of photoinhibition and rhodoxanthin synthesis probably serves to protect the photosynthetic capacity of the seedlings at low temperature.