bluuebunny/crossref_metadata_2025 huggingface dataset:
The effects of nitrogen, light and water availability on tropic leaf movements in soybean (Glycine max)
Authors: KAO W.‐Y. , FORSETH I. N.
Published: April 2006

Abstract. Rapid, tropic leaf movements and photo‐synthetic responses of the heliotropic plant, soybean, Glycine max cv. Cumberland, grown under two different nitrogen, three different light and two different water treatments were examined. Measurements of leaf orientation during midday periods outdoors, and tropic reorientation of leaflets in response to vertical illumination indoors, revealed a positive, linear relationship between leaf water potential and the cosine of the angle of incidence between the leaf and the direct beam of the excitation light. This relationship was altered by nitrogen availability, such that a lower cosine of incidence (lower leaf irradiance) for a given leaf water potential was measured for plants grown under low nitrogen compared to those grown under high nitrogen. Additionally, plants grown under low nitrogen and low water availability showed more rapid rates of leaf movement compared to plants receiving high levels of these resources. Light regime during growth had no effect on the relationship between the cosine of incidence and leaf water potential. Reduced water and nitrogen availabilities during growth resulted in lower photosaturated rates of photosynthesis and stomatal conductance, as well as alterations in the relationship between these parameters. Thus, higher values for the ratio of intercellular CO2/ambient CO2 were measured for low‐N grown plants (higher nitrogen use efficiencies) and lower values of this ratio for water stressed plants (higher water use efficiencies). The results show that environmental growth conditions other than water availability have the potential to modify leaf orientation responses to vectorial light in heliotropic legumes such as soybean. This has implications for the potential of heliotropic movements to minimize environmental stress‐induced damage to the photosynthetic apparatus, and to modulate leaf‐level resource use efficiencies.
Induction of extreme light sensitivity in buried weed seeds and its role in the perception of soil cultivations
Authors: SCOPEL A. L. , BALLARÉ C. L. , SÁNCHEZ R. A.
Published: April 2006

Abstract. Light, probably acting through the photo‐receptor phytochrome, promotes germination of weed seeds when the soil is disturbed by tillage operations. A short period of burial is shown to induce an enormous ∼10000‐fold increase in light sensitivity in the seeds of the arable weed Datura ferox which is interpreted as a natural transition to the ‘very‐low‐fluence’ mode of phytochrome action. Field experiments indicated that germination of buried seeds may be triggered by millisecond‐exposures to sunlight and suggested a key role for the process of sensitization in the mechanisms whereby light requiring seeds detect the occurrence of soil cultivation events in arable lands.
Epidermal conductance in different parts of durum wheat grown under Mediterranean conditions: the role of epicuticular waxes and stomata
Authors: ARAUS J. L. , FEBRERO A. , VENDRELL P.
Published: April 2006

Abstract. Epidermal (non‐stomatally‐controlled) conductance from the fourth leaf, first node leaf, flag leaf and ear of durum wheat (Triticum turgidum var durum L.) grown under Mediterranean field conditions has been measured, along with leaf stomatal frequency and the amount and distribution of epicuticular waxes. Measurements were carried out on varieties and land‐races from the Middle East, North Africa, ‘Institut National de la Recherche Agricole’ (INRA) and ‘Centra Internacional de Mejora de Maiz y Trigo’ (CIMMYT). Significant differences were observed among genotypes in the epidermal conductances (ge) of the four organs. For each of the four organs tested, genotypes from the Middle East and CIMMYT showed higher ge. values than those from North Africa and INRA. Ears showed epidermal conductances that were more than four times higher than those of leaves when ge. values were expressed per unit dry weight. The amount of epicuticular waxes was higher in the fourth leaves, intermediate in the first node and flag leaves and lower in the ears. For each organ, ge differences among genotypes were unrelated with the amount of epicuticular waxes. Removal of epicuticular waxes by dipping the organs into chloroform significantly increased the epidermal conductance for the fourth and first node leaves and the ear. However, this did not occur for the flag leaf. For the fourth leaf, ge of intact leaves and ge of leaves in which epicuticular waxes were removed were unrelated (r = ‐0.265). The regression coefficient of this relation for the first node and flag leaves showed values of 0.666 and 0.650 (P > 0.05), respectively, and values were even higher in the ear (r > m 0.892, P > 0.01). Scanning electron microscope analysis showed that wax bloom decreased from the fourth leaf to the flag leaf, whereas the extent of amorphous wax increased. Wax bloom in leaves consisted mainly of deposits of thin wax plates. In the ears and the adaxial surface of flag leaves, fibrillar waxes predominated. In the first node and flag leaves, the wax deposits on the adaxial side cover the surface of the leaf more densely and uniformly than those on the abaxial side. There was no significant correlation between ge and total stomatal density, or between ge and either adaxial or abaxial stomatal density for any sample of the three different leaves. The contribution of epicuticular waxes plus total stomatal frequency only explained 42.4, 11.8, 28.3 and 16% of ge (per unit leaf area) variations for the fourth leaf, first node leaf, flag leaf and the combined variation of the three leaves together, respectively. From these results, it is concluded that complex interrelationship between different morphophysiological characteristics probably control ge differences among genotypes and that these interrelationships differ for each different plant part.
Low temperature acclimation of guard cell chloroplasts by the arctic plant Saxifraga cernua L.
Authors: MAWSON B. T. , CUMMINS W. R.
Published: April 2006

Abstract. The potential for thermal acclimation of photosynthetic electron transport by guard cell chloropiasts (GC ch) was assessed in epidermal peels taken from the abaxial side of Saxifraga cernua leaves grown at 20°C and 10°C. Chlorophyll a fluorescence induction kinetics measured in pairs of guard cells in individual stomata from tissue grown at 10 °C demonstrated a rise in the fluorescence to a maximum and a larger amplitude in variable fluorescence when measured at temperatures below 18°C than was seen in GC ch from tissue grown at 20°C. The rates of fluorescence quenching in 10°C‐grown tissue were also faster than in 20°C‐grown tissue when measured at temperatures below 18°C. State 1‐State 2 transitions by GC ch were measured at selected temperatures between 5 and 25 °C as changes in the magnitude of the fluorescence emission maxima at 685, 695 and 730nm (F685, F695 and F730) measured at 77K. At measuring temperatures of 5 and 10°C, GC ch in tissue grown at 10 °C showed a greater transition to State 2 (a larger F730/F695 ratio) than did GC ch in tissue grown at 20 °C. At measuring temperatures of 20 and 25 °C, there was no difference in either the kinetics or the magnitude of the State 1 to State 2 transition in the two tissues. The ultrastructure of GC ch from tissues grown at 10 and 20 °C was also examined using transmission electron microscopy. Less than half (48%) of the grana from the higher temperature grown tissue had more than nine thylakoids/grana. Grana in GC ch which had developed at 10 °C showed a dramatic reduction in stacking, such that 85% of the grana contained no more than two thylakoids. The reduction in grana stacking was also accompanied by a decrease in the degree of appression of thylakoid membranes. The results demonstrate a capacity for thermal acclimation of GC ch function to low temperatures. This acclimation is associated with alterations in the chloroplast ultrastructure.
PATCHY: simulating and visualizing the effects of stomatal patchiness on photosynthetic CO2 exchange studies
Authors: CHEESEMAN J. M.
Published: April 2006

Abstract. In this study, computer modelling has been used to simulate and analyse the effects which non‐homogeneous stomatal conductance (patchiness) might have on the appearance of the macroscopic relationship between photosynthetic CO2 assimilation (A) and intercellular CO2 (Q) in leaves. The problem was formalized using the assumptions that (1) the biochemical model of Farquhar, von Caemmerer & Berry applies [Planta, 149, 78–90 (1980)]; (2) that the parameters for the model are fixed for the period required to determine the relationship; (3) that the distribution of conductances in any leaf area is normal (but restricted to positive values); and (4) that the leaf is perfectly heterobaric. The model is interactive, allowing the user to explore–well beyond the conditions for which data are presented here–the effects of carboxylation capacity, photosynthetic electron transport rate and photorespiration over a range of possible conductances and degrees of patchiness. Regardless of the parameters used in the model, the results fail to predict the change in appearance of the A‐C1 curve which has been attributed to patchiness in other reports: even when conductance varies with a standard deviation of twice its mean value, the effects on the curve are minor. The need for reconsideration of the methods currently used to interpret gas exchange studies is indicated.
Glutamate dehydrogenase regulation in callus cultures of Nicotiana plumbaginifolia: effect of glucose feeding and carbon source starvation on the isoenzymatic pattern
Authors: MAESTRI E. , RESTIVO F. M. , GULLI M. , TASSI F.
Published: April 2006

Abstract. In callus cultures of Nicotiana plumbaginifolia, the activity of glutamate dehydrogenase was repressed by glucose, whereas, on the contrary, carbon and energy source deprivation induced a remarkable increase in specific activity. Definition of these two opposite types of response was made possible by the use of glycerol as a non‐repressing carbon source: in this condition, glutamate dehydrogenase activity reached an intermediate level, which was similar to the derepressed values of activity obtainable when cultures were allowed to exhaust the glucose supply in the medium. Isoelectric focusing analysis revealed the existence of three different isoenzymatic patterns which could be correlated to the three different levels of specific activity: repressed (glucose), induced (carbon starvation) and intermediate (glycerol). Repression affected mainly the four more cathodic bands which were predominant in non‐repressed conditions. The possible catabolic role of these isoenzymes is discussed.
Stomatal response to blue light: water use efficiency in sugarcane and soybean*
Authors: GRANTZ D. A. , ASSMANN S. M.
Published: April 2006

Abstract. The significance of blue light‐stimulated stomatal conductance for carbon assimilation (A), stomatal conductance (g), intercellular CO2 (Ci), stomatal limitation of A (L), transpiration (E) and water use efficiency (W = A/E), was determined in a C4 and a C3 species. W and L were evaluated for steady‐state gas exchange with constant, saturating red light (As, gs, Es), and for the integrated gas exchange above the steady state baseline induced by a single, brief pulse of blue light (Ap, gp, Ep). Sugarcane (Saccharum spp. hybrid), a C4 grass, and soybean (Glycine max) a C3 dicot, were compared. Sugarcane exhibited typical C4 behaviour, with A saturing at Ci of ca. 200 μmol mol−1, compared to >500 μmol mol−1 in soybean. Steady‐state W was also considerably higher in sugarcane. The extent of stomatal opening in response to a blue light pulse, from baseline (gs) to the maximum value of conductance during the opening response (gm), was similar in the two species. More rapid opening and closing of stomata in sugarcane resulted in a smaller integrated magnitude of the conductance response (gp) than in soybean. At the peak of the blue light response, both species exhibited similar levels of L. During the response to the pulse of blue light, A and Ci increased and L decreased to a greater extent in sugarcane than in soybean. As a result, the gas exchange attributed to the stomatal response to blue light exhibited a higher ratio of Ap to Ep (Wp) in sugarcane than in soybean. This Wp was lower in both species than was the Ws associated with the steady state gas exchange. The two species did not differ in the rate of induction of photosynthetic utilization of elevated Ci. The greater stimulation of A in sugarcane was attributed to its C4 attributes of greater carboxylation efficiency (slope of the A versus Ci relationship), lower gs and prevailing Ci,s, and greater Ls under steady‐state red illumination. Despite saturation of A at low levels of Ci in C4 species, the gas exchange attributed to the stomatal response to blue light decreased L and contributed considerably to carbon acquisition, while maintaining the high level of W associated with C4 metabolism.
The carbon canopy economy of the association between cowpea and the parasitic angiosperm Striga gesnerioides
Authors: GRAVES J. D. , PRESS M. C. , SMITH S. , STEWART G. R.
Published: April 2006

The association between the parasite Striga gesnerioides and cowpea (Vigna unguiculata) was investigated using measurements of growth and gas exchange together with calculations of the carbon budget of the association. Striga gesnerioides has a very low photosynthetic capacity coupled with high rates of respiration. Even at photosynthetic light saturation shoots exhibit no net carbon gain. Thus S. gesnerioides is highly dependent on its host for carbon as well as for water and inorganic solutes. It is estimated that 70% of the carbon transferred from host to parasite is used in parasite respiration. Infected cowpea had a lower photosynthetic capacity, at times less than half that of uninfected plants. Infection with S. gesnerioides reduced the growth of cowpea by 75%. Calculations indicate that the loss of carbon from the host by export to the parasite is more important than reduced photosynthetic capacity of the host in accounting for the observed growth reductions.
β‐oxidation enzymes and the carnitine‐dependent oxidation of palmitate and palmitoyl CoA in mitochondria from avocado
Authors: MASTERSON C. , WOOD C. , THOMAS D. R.
Published: April 2006

Two sites for the β‐oxidation of fatty acids in avocado (Persea americana L.) mesocarp exist. One site is the microbody, the other the mitochondrion. It is apparent that the mitochondrial membrane barrier, which remains intact after sucrose density gradient centrifugation, prevents rapid access of acyl CoA substrates to matrix β‐oxidation sites. Thus, intact mitochondria showed little β‐oxidation enzyme activity. Rupturing of the mitochondrial membrane allowed rapid access of the acyl CoA substrates to matrix sites. Consequently, in ruptured mitochondria, high O2‐oxidation enzyme activities were measured. O2 uptake studies further distinguished the two organellar sites of β‐oxidation. During palmitoyl CoA oxidation, O2 uptake was reduced by catalase and increased by KCN in the microbodies, whilst mitochondrial O2 uptake was unaffected by catalase and reduced by KCN. This reflected the differing fates of FADH2, produced during the first β‐oxidation step, in the two organelles. In addition, only the mitochondrial β‐oxidation of fatty acids was carnitine‐dependent.
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

The 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

Δ13C 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

Plant 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

Growth 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.
The units of currency for plant water status
Authors: SCHULTE P. J.
Published: April 2006

Abstract. The appropriate measure for plant water status is of fundamental importance in plant water relations. One possible approach is to consider a hypothetical sensor for water status at the cell level. It is argued that such a sensor must respond to an intrinsic variable describing the quantity of water present in the cell. Uncertainty about the variable being sensed has affected our interpretion of plant responses to drought. In general, a more rigorous analysis of the effects of tissue hydraulic parameters and further understanding of the pertinent variable for water status are needed to assess such questions. For example, the significance of changes in the elasticity of cell walls in response to drought depends on the measure for water status. A simple model for water transport suggests that a decrease in the elastic modulus may act to maintain turgor for succulent plant species, but it is not clear how increases in the elastic modulus enhance water uptake for non‐succulent species.
Net efflux of Cl− during hypotonic turgor regulation in a brackish water alga Lamprothamnium*
Authors: OKAZAKI Y. , IWASAKI N.
Published: April 2006

Abstract. Net efflux of Cl− was measured potentiometrically (Ag/AgCl electrode) during turgor regulation which was induced by hypotonic treatment (hypotonic turgor regulation) in the alga Lamprothamnium succinctum. The efflux of Cl− reached the peak value (11 μmol m −2s−1) several minutes after the hypotonic treatment was started and then declined. The efflux of Cl− and inhibition of the cytoplasmic streaming [reflection of an increase in cytoplasmic concentration of free Ca2+([Ca2+]c)] were blocked under a low external concentration of Ca2+ ([Ca2+]e) (0·01 mol m−3) and resumed after raising [Ca2+]e to the normal value (3·9 mol m−3). The decrease in cell‐osmotic pressure upon hypotonic treatment was inhibited by lowering either turgor pressure or [Ca2h]e. The inhibition was reflected in decreases of both the efflux of Cl− and the membrane conductance. Recovery of the cytoplasmic streaming from the inhibition was also accelerated by the same treatments. It is concluded that an increase in turgor pressure is continuously sensed by the cells and that continuous presence of external Ca2+ is necessary for the hypotonic turgor regulation.
An evaluation of techniques for measuring yield turgor in excised Salix leaves
Authors: SANDS R. , McDONALD A. J. S. , STADENBERG I.
Published: April 2006

Abstract. The use of three techniques for determining yield turgor in excised Salix leaves was investigated. These were the osmotic‐solutions technique, the psychrometer technique, and the pressure‐chamber technique. The application of the osmotic‐solutions technique to a range of leaf types was discussed and the appropriate corrections for volume changes and the contribution of apoplastic water were detailed. It was concluded that the osmotic‐solutions technique is not satisfactory for use with slowly growing and/or very elastic leaves. The psychrometer and pressure‐chamber techniques were both simple compared with the osmotic‐solutions technique, and gave values for yield turgor in the range of 0·3–0·5 MPa. A disadvantage of the psychrometer technique for field applications is that it requires one psychrometer chamber per sample. The pressure‐chamber technique was modified for use as a field technique where multiple sampling could be easily and inexpensively achieved. Particular care was required with this technique to prevent water loss from the leaf during stress relaxation, but simple and effective procedures for doing so were found. The modified pressure‐chamber technique described here, is recommended as the preferred technique for measuring the yield turgor of leaves in experiments where many simultaneous estimates of yield turgor are to be made.
Effect of a salt‐osmotic upshock on the edaphic microalga Neochloris oleoabundans
Authors: BAND C. J. , ARREDONDO‐VEGA B. O. , VAZQUEZ‐DUHALT R. , GREPPIN H.
Published: April 2006

Abstract. The edaphic microalga Neochloris oleoabundans (isolated from desert soil) was subjected to a salt‐osmotic shock from 0 to 0·6 kmol m−3 NaCl. The effect of the osmotic upshock on the cell composition was determined. The cell dry weight and the lipid, glycerol and soluble amino acids contents remained unchanged during 5d of osmotic upshock. The protein content increased after 2d of initial osmotic shock, and it appears to be a long‐term haloadaptation process of the cells. The most important short‐term effects of salt osmotic upshock were a decrease in polysaccharide content and an increase in the soluble carbohydrate content of Neochloris oleoabundans cells. Within the first 4h after the initial shock, there was a transfer of carbon units from polysaccharides to sucrose which was independent of photosynthesis. The increase of intracellular concentration of sucrose contributed to cell osmoregulation.
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

Cell‐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

The 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

The 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

The 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

Adult 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

Electrical 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

The 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

The 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

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

Chickpeas 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

Alfalfa 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

Imposition 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.
Spectral quality during pod development modulates soybean seed fatty acid desaturation
Authors: BRITZ S. J. , CAVINS J. F.
Published: April 2006

High‐density cropping of soybeans results in considerable mutual shading. Consequently, pods mature under a range of light conditions, with those lower in the canopy exposed to drastically altered spectral quality as well as lower irradiance. The influence of spectral quality on reproductive development and seed quality was investigated in soybeans raised to physiological maturity under either broad spectrum or blue‐deficient light sources. The absence of blue light had a large influence on vegetative morphology, but the timing of reproductive events was not affected. Total seed yield per plant, dry matter per seed, per cent protein and per cent oil were similar for all treatments. However, seeds harvested from plants matured under broad spectrum illumination contained high levels of oleic acid (18:1) and low linoleic acid (18:2) compared to seeds from plants grown under blue‐deficient conditions. In addition to the spectral quality effect, there was a smaller effect of pod position. Seeds from pods lower in the canopy contained less 18:1 and more 18:2 than seeds that matured closer to the top of the canopy. Considering both spectral quality and pod position, the ratio of 18:1 to 18:2 varied four‐fold between 0·35 and 1·43, indicative of a possible photoregulatory step in fatty acid desaturation. The spectral effects are consistent with the participation of a photomorphogenetic photoreceptor in the control of fatty acid metabolism during seed maturation and triglyceride accumulation.
Water relations of cotton flower petals and fruit
Authors: TROLINDER N. L. , McMICHAEL B. L. , UPCHURCH D. R.
Published: April 2006

Water needed for expansion is believed to enter plant tissue in response to a growth‐induced water potential gradient that occurs as turgor is reduced during relaxation of cell walls or in response to increased solutes. Under water stress, the cotton flower petal continues to expand when all leaves on the plant are wilted and new leaf expansion has ceased in the shoot tips. This study was undertaken to determine if water for expansion entered the petal in response to a gradient or to increased solutes. Water potentials of cotton petal, leaf, bract and fruit were determined pre‐dawn and midday in dryland and irrigated field plots. The mechanism by which petal expansion occurs appears not to be associated with a growth‐induced water potential gradient or to increased solutes because the gradient is reversed from that needed to drive expansion. The water potential of the petal tissues was consistently higher than that of the subtending leaves and bracts both during and after anthesis, and under different water stress conditions. How this reversal in water potential gradient is established and maintained should provide insight into mechanisms involved in growth during water stress.
Asymmetric patchy stomatal closure for the two surfaces of Xanthium strumarium L. leaves at low humidity
Authors: MOTT K. A. , CARDON Z. G. , BERRY J. A.
Published: April 2006

Images of chlorophyll fluorescence were used to demonstrate patchy stomatal closure at low humidities in leaves of well‐watered Xanthium strumarium plants. The pattern and extent of patchy stomatal closure were shown to be different for the two surfaces of amphistomatous leaves by taking images of leaves with CO2 available to only one leaf was exposed to low humidity, patchiness was more extensive on that surface. Gas‐exchange experiments were also conducted to determine the apparent photosynthetic capacity of the mesophyll (photosynthesis rate at constant ci when it was supplied with CO2 through both surfaces or through each surface alone. These experiments showed declines in the apparent photosynthetic capacity of the mesophyll at low humidities that were consistent with patchy stomatal closure on one or both surfaces. The results suggest that patchy stomatal closure can be a factor in the steady‐state reponses of stomata to humidity. In amphistomatous leaves this is further complicated by the fact that patches on one epidermis may not coincide with those of the other surface.