bluuebunny/crossref_metadata_2025 huggingface dataset:
Further Studies of Proton Translocations in Chloroplasts After Single-Turnover Flashes. I. Proton Uptake
Authors: Hope AB , Matthews DB
Published: January 2006

Damped, binary oscillations were observed in proton uptake by class C pea chloroplasts given a train of light flashes. The oscillation at pH 7.8 is predictable if the species accepting protons is either the doubly reduced secondary acceptor B�- or a plastoquinone PQ- from the pool, if 0.29 of the secondary acceptor is B- in dark-adapted chloroplasts and if a miss factor α = 0.12 governs the amval of electrons at B or B- after a flash.
The rate of proton uptake was measured with varied pH, ionic strength and temperature. The half-time was 95 ms at pH 7.8 and 21°C. Using double flashes separated by variable intervals showed that the species able to accept protons was generated (t½) about 0.8 ms after a flash. The results are consistent with protons from the external solution reacting relatively slowly with univalent anions, which have earlier promptly supplied protons to B2- or PQ2-.
Under conditions of cyclic and of non-cyclic electron flow, H+/e- stoichiometries were 1.1 and 1.0 respectively, and so the results do not support a Q-cycle model for pea chloroplasts.
Responses of Vigna unguiculata (L.) Walp. To Atmospheric and Soil Drought
Authors: Nagarajah S , Schulze E
Published: January 2006

Growth responses, water relations, leaf conductance, and gas exchange of V.unguiculata were studied under conditions of drought in both the aerial and the soil environment. Dry air caused a significant reduction in whole plant biomass and all its components despite a plant water status which was not different from plants in humid air. Stomata closed in dry air and water loss per plant was lower in dry than in humid air because of both lower leaf conductances and a smaller total leaf area.
Dry soil also caused decreases in biomass growth, but leaf growth continued at the soil water status at which stomata began to close (45% depletion of plant available water). Relative leaf expansion rate started to decline below the rate of control plants when 60% (humid air) or 65% (dry air) of plant available water was depleted. Therefore, in V. unguiculata, stomata appear to be more sensitive to soil drought than growth of leaves. Leaf relative water content and osmotic potential remained at the level of control plants when stomata started to close and decreased only slightly below the level of control plants even under severe water stress. A trend of decreasing osmotic potentials at 55-60% depletion of plant available water was observed, but leaf growth ceased only when 90% of plant available water was depleted. Leaf conductance decreased more rapidly than CO2 assimilation during development of soil drought.
Comparison of Water Relations and Osmotic Adjustment in Sorghum and Cowpea Under Field Conditions
Authors: Shackel KA , Hall AE
Published: January 2006

Seasonal and diurnal patterns of xylem pressure potential, Ψx, and osmotic potential, Ψs, were compared using contrasting genotypes of sorghum [Sorghum bicolor (L.) Moench] and cowpea [Vigna unguiculata (L.) Walp.] under frequently imgated 'wet' and water-limited 'dry' field conditions. Generally, differences in Ψx and Ψs among genotypes within each species were small compared with differences between the two species. Sorghum exhibited a larger diurnal range and larger differences between wet and dry treatments for Ψx, Ψs, and estimates of bulk leaf turgor than did cowpea. Seasonal and drought- induced osmotic adjustment occurred in sorghum, but not in cowpea. Diurnal patterns of leaf conductance indicated that, under the dry treatment, cowpea avoided the occurrence of large plant water deficits by substantial reductions in leaf conductance, especially at midday, whereas sorghum maintained moderate values of leaf conductance throughout the day. Cowpea exhibited a larger diurnal range of leaf conductance and larger differences between wet and dry treatments than did sorghum. Differences were not observed between the species in overall soil water depletion or in root activity as estimated from profiles of soil water depletion until senescence occurred in cowpea. Sorghum genotypes that had been selected on the basis of differences in Ψs did exhibit significant differences in average values of leaf conductance and total soil water depletion, but the genotype that had the lowest Ψs (M35-1) also had the lowest leaf conductance and the least soil water depletion.
Temperature Regulation of the Development of Frost Hardiness in Pinus radiata D. Don
Authors: Greer DH
Published: January 2006

The development of frost hardiness in seedlings of P. radiata was followed using a photoperiod of 9 h and a constant day temperature of 12°C. The seedlings were preconditioned to a night temperature of 6.5°C for 35 days and 4°C for 7 days. The temperature was then reduced to -4°C for 66 days in one hardening treatment (designated 12/-4°C) and to 3°C for 136 days in another (designated 12/3°C). At the end of those periods, the night temperature was increased back to 6.5°C for a further 15 days. Frost hardiness was determined at regular intervals by exposing the seedlings to a series of artificial frosts.
During the low temperature regime, frost hardiness developed continuously in seedlings from both treatments, from -5 to -9.5°C in the 12/3°C treatment and to -16.5°C in the 12/-4°C treatment. The rate of development of frost hardiness was constant at constant temperatures. Using a temperature response model, specific rates of hardening were estimated for both this and an earlier experiment, and found to be approximately linear against temperature. The analysis establishes that temperature controls the hardening process of P. radiata by regulating the rate of development of frost hardiness.
Frost hardiness was also shown to be related to thermal time. Before this relationship could be useful in predicting frost hardiness of field-grown seedlings, the relative contribution of the photoperiod-induced and temperature-induced hardening in natural environments needs to be more clearly defined.
Frost Injury in Wheat Ears After Ear Emergence
Authors: Marcellos H , Single WV
Published: January 2006

The reaction of ears of wheat (Triticum aestivum L.) to frost after their emergence from the flag leaf sheath was studied for a number of cultivars under controlled conditions of radiative and convective energy exchange. Frost injury was measured in terms of the fertility of the ear, viz. number of grains set per spikelet. Despite being covered with frost crystals, the ear was unaffected by freezing temperature until a threshold level, below which there was a steep reduction in grain set, approximating 100% per 1°C. A threshold of about -4°C and T50 of -4.7°C were observed for the hardiest cultivar, Florence. Crystallization can be initiated within a supercooled floret by spread of freezing from either the peduncle or the vegetative structures of the spikelet. Neither of these pathways was critical and it was concluded that any nucleation in the rachis was sufficient to result in the patterns of injury described. A mechanism of injury was discussed, based on the proposal that nodal regions within the rachis and rachilla provided a distributed system of bamers to the spread of crystallization. These could be effective in allowing supercooled reproductive organs to remain so and avoid lethal injury.
Effects of Limb Girdling on Growth and Development of Competing Fruit and Vegetative Tissues of Peach Trees
Authors: Dann IR , Wildes RA , Chalmers DJ
Published: January 2006

The distribution of current assimilates between competing zones of potential growth in the peach tree (Prunus persica (L.) Batsch) was studied using limb girdling, which altered the balance between reproductive growth and vegetative growth in a similar manner to the aging process. Fruit matured earlier, and leaf senescence and abscission were advanced in girdled limbs. which supported normal fruit loads but had only half the leaf area. Lateral growth and secondary thickening were reduced by 50% but vegetative growth approached normal rates at times when fruit growth was minimal, indicating that girdling reduced the ability of vegetative growth to compete with reproductive growth for assimilates. Starch and soluble sugars did not accumulate above the girdles. The data are consistent with the hypothesis that girdling alters the balance between endogenous growth regulators which favour either vegetative or reproductive development. We suggest that the initial effects on the girdled limb are attributable to accumulation of growth regulators produced above the girdle. The reduced flow of growth regulators to the roots eventually results in lowered levels of root-produced hormones which subsequently causes effects throughout the tree.
Factors Controlling Endosperm Cell Number and Grain Dry Weight in Wheat: Effects of Shading on Intact Plants and of Variation in Nutritional Supply to Detached, Cultured Ears
Authors: Singh BK , Jenner CF
Published: January 2006

The association between endosperm cell number and grain dry weight, and the dependence of endosperm cell division on the availability of organic nutrients, have been investigated in wheat. Two different procedures were used to vary the supply of nutrients to the grains during the phase of cell division. Detached ears were cultured in solutions of sucrose (0-60 g 1-1) and glutamine (0.125-0.75 g N 1-1), or intact plants were exposed to high (560 �mol m-2 s-1) or low (55 �mol m-2 s-1) photon irradiance. Cell number per endosperm, and grain dry weight, were both responsive to the concentration of nutrients in the external medium, and to the level of photon exposure. Average dry weight per cell was relatively independent of the level of nutrition or of photon exposure until cell division had ceased but, in the later stages of grain-filling, dry weight per cell in the cultured ears displayed a dependence upon the concentration of nutrients in the external medium.
Amounts of sucrose, other soluble carbohydrates and soluble amino nitrogen were extracted from the grains and, on a per grain basis, the amounts of all fractions varied in response to variation in the level of nutrients supplied to the ears, and to photon exposure. However, concentrations of these nutrients in the developing grains, calculated on a dry weight or water basis, were not associated with the rate of cell division in the grains.
While the evidence gathered supports the notion that growth (in cell number, and dry weight) of the developing endosperm is controlled inter alia by the provision of organic nutrients, the nature of the controlling mechanism is obscure. It seems that cellular division is not affected directly by nutritional supply through a mechanism involving the concentration of substrates for energy and protein synthesis within the developing grain.
Lectins as Cytochemical Probes of the Developing Wheat Grain. V. Demonstration of Separate Polysaccharides Containing N-Acetyl-D-Glucosamine and D-Galactose in Nuclear Epidermal Cell Walls
Authors: Baldo BA , Barnett D , Lee JW
Published: January 2006

Fluorescein isothiocyanate-labelled lectin from wheat-gem, which binds N-acetyl-D-glucosamine, and Griffonia simplicifolia, Arachis hypogaea and Glycine max lectins, each of which binds D-galactose, react with nucellar epidermal cell walls in thin sections of plastic-embedded developing wheat grain. Reactivity of these cell walls with periodic acid-Schiff reagent, the absence of staining with protein stains and the failure of a number of proteases and the endoglycosidases D and H to prevent the binding suggested that the lectin-reactive wall components are neither proteins nor N-glycosidically linked glycoproteins. Morphological differences in lectin staining patterns and treatment of sections with chitinase and α-galactosidase, prior to the reaction with the lectins, indicated that two separate polysaccharides are probably involved in the binding. Chitinase removed the reactivity of the nucellar epidermal cell walls for wheat-germ lectin but the binding of D-galactose-specific lectins was unimpaired. Conversely, α-galactosidase did not affect the binding of wheat-germ lectin but reactivity with the galactose-specific lectins was abolished. From the available evidence we conclude that one polysaccharide in the nucellar epidermal cell wall reacts with wheat-germ lectin and contains N-acetyl-D-glucosamine in a chitin-like structure. The other polysaccharide reacts with D-galactose- specific lectins by virtue of terminal α-D-galactose residues. Hydrolysis and subsequent chromatographic analysis of nucellar epidermal cell walls peeled from immature grains revealed the presence of D-glucosamine, D-glucose, D-galactose, D-xylose, L-arabinose and a trace of D-mannose.
An Empirical Model of Stomatal Conductance
Authors: Farquhar GD , Wong SC
Published: January 2006

An empirical model of stomatal conductance is presented. The predictions of conductance correlate with experimental determinations of the responses to several kinds of short-term and long-term perturbations, including irradiance, temperature, CO2 and O2 partial pressures, and leaf age and nitrogen nutrition. The model is not mechanistic and cannot account for the observed functioning of stomata independent of mesophyll. Nevertheless its success in predicting responses in intact leaves means that the mathematical expressions used must be analogous to those describing actual functioning.
Canopy Development, Light Interception and Seed Production in Sunflower as Influenced by Temperature and Radiation
Authors: Rawson HM , Dunstone RL , Long MJ , Begg JE
Published: January 2006

Well watered mini-crops of sunflower were grown either in summer or winter in glasshouses maintained under five temperature regimes and a 16 h photoperiod. A field crop was grown concurrently with the summer glasshouse study.
Summer radiation (25.5 MJ day-1) increased the size and/or number of many of the variables measured compared with winter radiation (9.5 MJ day-1). However, there was interaction between light and temperature upon phenological development, plant height, leaf number and harvest index. Seed production declined at temperatures above 18/13°C in summer and above 24/19°C in winter radiation, but fatty acid composition of the seed oil changed progressively with increasing temperature and was unaffected by radiation.
Leaf area per plant increased faster under summer than winter radiation and in almost all temperature regimes reached considerably higher final values which resulted in a greater percentage of the incident radiation being intercepted. Temperature, though affecting the growth patterns and final areas of individual leaves in the canopies, did not alter the relationship between leaf area index and radiation interception. The light extinction coefficient changed with leaf area index and differed between summer and winter.
Biomass per plant at maturity (B, g) was best related to radiation interception up to anthesis (I, MJ m-2), such that B = -234 + 541ogl, r2 = 0.91, but seed number (S) was correlated similarly with radiation interception and with the number of degree days (D) accumulated between floral initiation and anthesis
(S = 1137+ 0.0051-0.762D, R2 = 0.90). Yield (Y, g per plant) was dependent on seed number, mean temperature (T) and radiation intercepted between anthesis and maturity, and the leaf area present at anthesis. However, over 97% of the variation in yield could be accounted for by the temperature and radiation factors in the manner Y = 39.07+0.047I- 1.26T. Harvest index and yield were not correlated for the cultivar examined.
A Model of the Effect of Interspecies Competition for Light on Dry-Matter Production
Authors: Rimmington GM
Published: January 2006

A model of the effect of interspecies competition for light on the daily dry-matter production of competing species is developed. It describes the absorption of light by the component species, accounting for their different optical properties. Absorption equations are formulated from the principle of conservation of light energy within a unit-leaf-area-index of canopy, and the integral of absorbed light energy is then used to calculate the rate of dry-matter production of each component species. This model proved useful for the analysis of data from experiments in which New Zealand white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.) were grown in mixtures. Application of the model enabled the proportion of incident light energy absorbed by each component to be estimated and unambiguous differentiation between the amount of light energy absorbed and the efficiency of use of the absorbed light energy.
Salt Resistance and Adaptation to Root-Zone Hypoxia in Sunflower
Authors: Kriedemann PE , Sands R
Published: January 2006

Sunflower plants (Helianthus annuus L.) were grown in temperature controlled (20-21°C) nutrient solutions under greenhouse conditions for up to 50 days. Root-zone oxygen status was varied by either continuous aeration or periodic gassing with nitrogen to simulate root response to anaerobiosis under flood irrigation. Salt treatments (up to 200 mM final concentration in culture solution) were imposed either during sustained aeration v. hypoxia, or else initiated at the time of reciprocal transfer between those two levels of oxygenation. Continuously aerated v. hypoxic cultures served for comparison.
Salt tolerance threshold, and especially Na+ ion exclusion, was lowered by hypoxia, while selectivity for K+ over Na+ ions also diminished. Such plants showed partially reversible decline in laminar expansion with reduction in aeration status and, due to a much reduced root : shoot ratio, were prone to wilting.
Adaptive responses to hypoxic culture solution, viz. minor osmotic adjustment within laminar tissues plus formation of root aerenchyma tissue external to an endodermal layer, appeared to confer improved salt tolerance when salinization coincided with lowered oxygenation. Time lag, between decline in root-zone O2 status, and onset of plant response, would limit relevance of this adaptation for improved salt resistance in cropping situations to periods of low transpirational demand.
Hydraulic Resistance of Plants. I. Constant or Variable?
Authors: Passioura JB
Published: January 2006

Two popular equations for describing the flow of water through plants are discussed and criticized. They are the Ohm's Law analogue, in which the flow rate is assumed to be proportional to the difference in water potential across the plant, between leaf and soil; and an equation, used widely to describe transmembrane fluxes of single cells, in which the flow rate is assumed to be the sum of two components, one proportional to the difference in hydrostatic pressure, the other proportional to the difference in osmotic pressure, between specified points in the plant. The well-established theoretical inadequacies of the Ohm's Law analogue are reviewed, especially the poorly recognized fact that it is of little use if substantial amounts of solutes are flowing with the water. The other, composite, equation does not have the same grave theoretical inadequacies, but its failure to agree with published data is highlighted.
Growth and Salt Balance of the Mangroves Avicennia marina (Forsk.) Vierh. And Rhizophora stylosa Griff. In Relation to Salinity
Authors: Clough BF
Published: January 2006

Seedlings of A. marina and R. stylosa were grown for 12 months in nutrient solutions containing 0, 25, 50, 75 and 100% seawater. Plants of both species grew poorly without sodium chloride in the culture medium. Growth was greatly stimulated in 25% seawater which, within the range of treatments used, was the optimum salinity for growth by both species. Dry matter production by R. stylosa fell sharply between 25 and 50% seawater, whereas A. marina displayed an extended growth response in up to 75% seawater. Plants of A. marina grown on solutions of increasing salinity accumulated increasing amounts of sodium and chloride in all tissues. As a result, all tissues had osmotic potentials that were considerably more negative than that of the solution on which they were grown. This implied that the reduction in growth displayed by plants of A. marina grown at high salinity was due to inhibition of growth by high concentrations of sodium and/or chloride, rather than to an effect of water stress. By contrast, the leaves and stem of R. stylosa contained relatively low concentrations of sodium and chloride, with the result that the osmotic potentials of these tissues were close to, or more positive than, that of the solution on which the plants were grown. This suggests that the poor shoot growth of this species at high salinities was due to water stress. The results of this study support the view that A. marina, which has salt-secreting glands in its leaves, is more salt-tolerant than R. stylosa, which does not possess salt-secreting glands.
Ashby's Law and the Pursuit of Plant Hormones: a Critique of Accepted Dogmas, Using the Concept of Variety
Authors: Canny MJ
Published: January 2006

A rule from the theory of the control of systems, Ashby's Law of Requisite Variety, is outlined and applied to the requirements of a message system that could specify the control of plant development. It is concluded that the recognized plant hormones have insufficient variety to function in this control. Some alternative systems are suggested where signalling messages with adequate variety might be found.
Occurrence of Globoid Crystals in Cotyledonary Protein Bodies of Pisum sativum as Influenced by Experimentally Induced Changes in Mg, Ca and K Contents of Seeds
Authors: Lott JNA , Randall PJ , Goodchild DJ , Craig S
Published: January 2006

In many species globoid crystals in protein bodies of seeds are very common while in other species they are rarely observed. A review of literature suggested that the balance between divalent (Mg2+ and Ca2+) and monovalent (K+) cations may be important in determining whether or not globoid crystals will form. To test this hypothesis, experiments were carried out to add Mg and Ca, or Ca alone, to pods developing on K-deficient pea plants. While it was possible to cause a reduction in K concentration and increases in Mg and Ca concentrations, any changes to the normal mineral storage pattern in pea cotyledons were remarkably small. In some treatments, statistically significant increases in the ratio (Mg + Ca)/K were obtained and the sample with the greatest increase was examined in detail by electron microscopy and energy dispersive X-ray analysis. In this sample globoid crystals were common, in
contrast to their normally rare occurrence in pea cotyledonary tissue.
Differential Responses to High Temperatures of Starch and Nitrogen Accumulation in the Grain of Four Cultivars of Wheat
Authors: Bhullar SS , Jenner CF
Published: January 2006

Plants of four cultivars of wheat were exposed during the grain-filling stage in two different experiments to brief episodes (10 or 20 days) of high temperature. About the same number of degree-days above a standard temperature were accumulated in both experiments. While the cultivars differed in detail in their responses, final single grain weight in all cases was reduced by elevating the temperature, and to about the same extent (14%) in both experiments. The numbers of B-type starch granules (but not of A-type) were substantially reduced by warming, but this reduction did not appear to account wholly for the smaller weight of starch per grain resulting from elevated temperature. Nitrogen content per grain was not affected by the warm conditions and, in the experiment with the short duration at the high temperature differential (33/25°C day/night as compared to 21/16°C), percentage nitrogen was significantly increased by warming from 2.61 to 3.05%. It is concluded that starch and nitrogen accumulation in the grain have differing susceptibilities to brief episodes of high temperature during grain-filling.
Short-Term Changes in Cambial Growth and Endogenous IAA Concentrations in Relation to Phloem Girdling of Peach, Prunus persica (L.) Batsch
Authors: Dann IR , Jerie PH , Chalmers DJ
Published: January 2006

For 2-3 days after all except one of the secondary limbs of a peach tree were girdled, all limbs (including the non-girdled limb) shrank. Shrinkage and subsequent growth was greatest in the zone immediately above the girdle whereas growth was least immediately below. After initial shrinkage the growth rate of the cambium, at specific positions in relation to the girdle, was more-or-less constant and consistent with the long-term effect of the girdle at each position.
The concentration of indole-3-ylacetic acid (IAA) extracted from the bark immediately above the girdle first increased sharply but then decreased to the level in the non-girdled limb. On the other hand, beneath the girdle the IAA concentration decreased by 75% and remained low.
Thus, immediately above the girdle IAA concentration in the bark increased while the limb shrank, and declined before the cambial growth rate increased. Beneath the girdle, however, the concentration of IAA was severely depleted while growth of the limb was inhibited. The possible implications of these observations in relation to control mechanisms of cambial growth are discussed.
The Electrical Properties of Plant Cell Membranes. III. The Effects of Insulated Regions upon the Cable Properties and Measured Membrane Conductance of Charophytes
Authors: Smith JR
Published: January 2006

A theoretical treatment of the electrical 'cable' properties of cylindrical, radially symmetric, plant cells with two concentric membranes is presented, in which the longitudinal conductivities of the cell wall and cytoplasm are explicitly included in conjunction with the separate admittances of the plasmalemma and tonoplast. The effects of electrically isolating different longitudinal regions of the cell by means of insulating external barriers are examined, and it is shown that the presence of the cell wall will ensure that any such insulation is imperfect. Using parameters that should be appropriate for charophytes such as Chara and Nitella, it is demonstrated that an appreciable fraction of the injected current can flow through the cell membranes within such 'insulated' regions, and consequently increase the effective membrane area. If not allowed for, this will produce an overestimation of the electrical current density and the area-specific conductances of the plasmalemma and tonoplast. Indeed, under some experimental conditions, the consequent error in the 'membrane' (plasmalemma and tonoplast in series) parameters can be several hundred percent. Thus reducing the fraction of the cell surface area bathed in electrolyte by means of insulating external barriers will not necessarily remove problems associated with the cable properties but will, in effect, transfer them to the insulated regions as the membrane conductance decreases. It is discussed how experimental configurations can be optimized for minimum error.
Photosynthesis and Dry Matter Production in C3 and C4 Pasture Plants, With Special Emphasis on Tropical C3 Legumes and C4 Grasses
Authors: Ludlow MM
Published: January 2006

The nature of C3 and C4 pasture plants is described, and the potential biomass productivity is discussed. Then differences in net annual production and crop growth rates of C3 and C4 pasture plants are analysed in terms of the interception of solar radiation and the efficiency of its conversion to dry matter. Finally, the components of photosynthetic production of tropical C4 grasses and tropical C3 legumes are compared with their growth rates and dry matter yields in the subtropics.
The higher crop growth rates of tropical C4 grasses compared with C3 pasture plants, whether they are of temperate or tropical origin, seem to be due mainly to higher leaf net photosynthetic rates and to the absence of photorespiration associated with possession of the C4 pathway. However, light utilization efficiencies are probably also higher in C4 grasses. In addition to these two characteristics, the longer growing season of C4 grasses in the warm conditions of the tropics contributes to their higher net annual production of dry matter.
There is a close association between possession of the C4 pathway, higher rates of photosynthesis and growth, and higher dry matter yields when tropical C4 pasture grasses are compared with tropical C3 legumes in a subtropical climate.
Transport of Tritiated Water and 14C-Labelled Assimilate Into Grains of Wheat. I. Entry of Tho Through and in Association With the Stalk of the Grain
Authors: Jenner CF
Published: January 2006

Dry matter is transported through the stalk of the wheat grain, and during grain filling is accumulated within it with no change in the quantity of water in the grain, and with little or no net transfer of water through the stalk. Accumulation of dry matter is also independent of the magnitude and the direction of a water potential gradient imposed between the plant and the atmosphere surrounding the grain. A procedure is described, based on sealing the grain (minus its bracts) within an impermeable capsule, for measuring the total net influx of radioactive water into the grain (FT). Tritiated water, THO, is used as a tracer for water. FT is assumed to comprise transport in the liquid phase and transport in the vapour phase, by mass flow and by diffusion. Apoplastic flow makes a negligible contribution in the system described because the water potential gradient is minimized.
FT was obtained by adding to the quantity of THO accumulating in the encapsulated assemblies an estimate of the amount of THO lost from the assemblies by leakage. Two types of ears were compared: ears on intact plants assimilating 14CO2 and growing in small pots watered with THO, and detached ears cultured on [14C]sucrose in a solution of THO. Both types gave similar results but the detached ear system probably furnished the most reasonable estimate, a rate of 10.1 �l of THO per assembly per day.
Biology of Fire Ephemerals of the Sandplains of the Kwongan of South-Western Australia
Authors: Pate JS , Casson NE , Rullo J , Kuo J
Published: January 2006

The growth, longevity, mineral relationships and reproductive biology of 18 species of fire ephemerals were examined in sclerophyllous shrubland, located mainly within the Jurien : Badgingarra region of the Northern Sandplains of the kwongan of SW. Australia. Ten of the species were monocarpic, completing their life cycle within the 6-8 month winter growing season after a summer or autumn fire. The remaining species were polycarpic, commencing reproduction in their second season and surviving and reproducing for a further two to eight seasons (depending on species). Detailed study was made of growth and dry matter allocation in the dioecious, sexually dimorphic, polycarpic species Tersonia brevipes (Gyrostemonaceae). Monocarpic species tended to produce smaller seeds, and exhibited greater seed output per unit biomass and higher harvest indices for dry matter and minerals than polycarpic species. Certain monocarpic species showed great plasticity in final dry weight, e.g. a 2700-fold difference between largest and smallest individuals in a sample of 250 plants of Stipa elegantissima (Poaceae), and a 180-fold range in a similarly sized sample of Macarthuria apetala (Aizoaceae). The fire ephemerals studied generally exhibited faster seedling growth rates, greater concentrations of P and N (but not of Ca, Mg and K) in seedling dry matter, but usually lesser concentrations of P and N (but not of Ca, Mg and K) in seed dry matter than in cohabiting obligate seeder or sprouter species with potential life spans exceeding 15 years. The above-mentioned features of fire ephemerals are suggested to be of special adaptive significance within the context of exploitation of transiently non-limiting habitat resources immediately following fire.
Sorbitol Versus Sucrose as Photosynthesis and Translocation Products in Developing Apricot Leaves
Authors: Bieleski RL , Redgwell RJ
Published: January 2006

Very young apricot leaves behave like the young leaves of most plants; that is, [14C]sucrose is formed as the main product of 14CO2 photosynthesis, and also when the leaves are supplied with [14C]glucose. [14C]sorbitol is not produced, and is poorly metabolized when fed to the leaf. Expanding leaves behave differently: [14C]sorbitol and [14C]sucrose are formed in similar amounts from both 14CO2 and [14C]glucose; and when [14C]sorbitol is supplied, it is readily metabolized and utilized for growth. Mature leaves are different again. They form [14C]sorbitol as the main product from 14CO2 and from [14C]glucose, and they do not metabolize [14C]sorbitol at all. Thus during development, apricot leaves gain but then lose the ability to utilize sorbitol. They also gain and keep the ability to synthesize sorbitol. This suggests that different biochemical paths exist for sorbitol formation and utilization, and that these paths are differently developed in the various stages of leaf development.
Although the very young leaves did not synthesize sorbitol from CO2 or glucose, they contained it as their major sugar. Translocation behaviour was therefore studied. Neither the very young leaves nor the expanding leaves export any photosynthate, but the mature leaf rapidly translocates carbohydrate, mainly in the form of sorbitol, to the younger leaves as well as the rest of the plant. [14C]sorbitol supplied to the mature leaf can be recovered in that form from the very young leaf on the same shoot. This further establishes the role of sorbitol in apricot as a specific transport carbohydrate.
Stomatal and Photosynthetic Limitations to Leaf Growth
Authors: Kriedemann PE
Published: January 2006

Leaf area derives from the product of cell number and cell size within lamina tissues. Cell division thus dictates potential size, while cell enlargement is responsible for expression of that potential. These two facets of leaf growth differ in their substrate requirements under well nourished conditions and also show dissimilar sensitivity to environmental stress.
Meristematic activity in terminal apices and subsequent emergence of successive leaves seem relatively insensitive to drought and salinity, but do appear limited by photoassimilate supply because CO2 input and radiation level exert strong effects. By contrast, lamina expansion depends more heavily on adequate supplies of water and nutrients, and is especially sensitive to environmental stresses.
Impact of adverse conditions on leaf growth can be alleviated by physiological adjustments such as alteration of viscoelastic properties of lamina tissues, regulation of ionic balance and accumulation of organic osmotica. Effective adjustment becomes manifest as turgor maintenance, continuity of leaf growth and sustained gas exchange. This necessitates finely tuned water relations and draws upon energy and substrate of recent photosynthetic origin. Alleviation of drought and salinity stress is thus subject to stomatal and photosynthetic limitations.
Ion Relations of Plants Under Drought and Salinity
Authors: Flowers TJ , Yeo AR
Published: January 2006

The review is primarily concerned with the ion relations of mature leaf cells of plants growing under saline conditions: during drought ions do not play such an important role in osmotic adjustment as in salinity. We conclude that, for succulent halophytes (Suaeda maritima), the demand for osmotic adjustment in the leaves matches closely (perhaps exceeds) the supply from the roots. Expanding leaves accumulate sodium at a greater rate than expanded leaves and apoplastic salt concentrations do not exceed those in the protoplast. For salt-sensitive species (Oryza sativa) supply exceeds demand, resulting in a sustained rate of xylem delivery of sodium to the expanded leaves. This in turn leads to either excessive apoplastic ion concentrations in the leaves and death through dehydration or excessive symplastic concentrations and death through ion toxicity.
Whole-Plant Responses to Salinity
Authors: Munns R , Termaat A
Published: January 2006

This paper discusses whole-plant responses to salinity in order to answer the question of what process limits growth of non-halophytes in saline soils. Leaf growth is more sensitive to salinity than root growth, so we focus on the process or processes that might limit leaf expansion. Effects of short-term exposure (days) are considered separately from long-term exposure (weeks to years). The answer in the short term is probably the water status of the root and we suggest that a message from the root is regulating leaf expansion. The answer to what limits growth in the long term may be the maximum salt concentration tolerated by the fully expanded leaves of the shoot; if the rate of leaf death approaches the rate of new leaf expansion, the photosynthetic area will eventually become too low to support continued growth.
Production of α-Amylase Isozymes in Barley Caryopses in the Absence of Embryos and Exogenous Gibberellic Acid
Authors: Nicholls PB , MacGregor AW , Marchylo BA
Published: January 2006

The isozyme composition and kinetics of production of α-amylase were studied in three samples of barley. Acid-dehusked caryopses and endosperm halves from a sample of Klages and from two samples of Clipper that differed in their ability to produce α-amylase in the absence of added gibberellic acid were incubated on moist sand at two temperatures in the presence or absence of gibberellic acid. The isozyme composition of the extracts was analysed on isoelectric-focusing-polyacrylamide gels and chromatofocusing columns.
The endosperm halves of Klages and Clipper (type A) produced very low levels of enzyme in the absence of gibberellic acid while similar amounts of enzyme activity were found in both (+) and (-) gibberellic acid-treated incubates of Clipper (type B) endosperm halves. In these latter incubates, the initial kinetics of production, the proportion of α-amylase 1 to total enzyme activity and the effect of incubation temperature on the kinetics of production in both acid-dehusked caryopses and endosperm halves were similar, and were comparable to those observed in gibberellic acid-treated incubates of Klages and Clipper (type A). Since Clipper (type B) endosperm halves can produce α-amylase in the absence of added gibberellic acid, its role in this process should be reexamined.
Simple Relationships Describing the Responses of Leaf Growth to Temperature and Radiation in Sunflower
Authors: Rawson HM , Dunstone RL
Published: January 2006

In attempts to determine simple relationships describing the responses of leaf expansion to temperature and radiation, sunflower plants were grown in glasshouses under five temperature and two natural radiation regimes. Crops were also grown in the field at three radiation levels.
All leaves, regardless of their position on the plant, fitted a single relationship of relative leaf expansion rate versus leaf age for each regime. These relationships showed that, whilst increased temperature increased the rate of expansion of a leaf at day 1 on our growth scale (approximately unfolding), and reduced the period for which the leaf expanded, each leaf expanded for the same period in day-degree terms regardless of its temperature regime. However this expansion period was modified by radiation such that, for each 1 MJ m-2 day-1 increase, the day-degree sum was reduced by approximately 5°C. The strict inverse relationship between the initial rate of expansion and the expansion period, expressed in days, suggests that at least in some cases the final area of a leaf is largely determined by the stage of 'unfolding'.
Influence of Soil Water Supply on the Plant Water Balance of Four Tropical Grain Legumes
Authors: Sinclair TR , Ludlow MM
Published: January 2006

The water balance of soybean (Glycine max), cowpea (Vigna unguiculata), black gram (Vigna mungo), and pigeonpea (Cajanus cajan) grown in pots was studied during a soil drying cycle. The response of the plants was analysed for three distinct stages of dehydration. In stage I, the rate of transpiration remained constant and equal to that of well watered plants even though soil water status fell by more than 50%. Stage II began when the rate of soil water supply to the plant was less than potential transpiration and stomates closed resultingjn the maintenance of plant water balance. When soil water content was expressed as a fraction of transpirable soil water, all species showed a transition from stage I to stage II at a fraction of transpirable soil water of about 0.3 to 0.2. As the soil water declined further, all species had a similar decrease in relative transpiration rate. Consequently, the responses of the four species in stages I and II were essentially identical, except that pigeonpea extracted a slightly greater amount of soil water.
Stage III occurred once stomates had reached minimum conductance and water loss was then a function of the epidermal conductance and the environment around the leaf. Substantial differences were found among the four grain legumes in epidermal conductance. Soybean had the highest conductance, followed by black gram, cowpea and pigeonpea. Substantial variation in dehydration tolerance among the four grain legumes was also found: the ranking of dehydration tolerance based on the relative water content was pigeonpea > cowpea > mungbean > soybean. Differences among the four grain legume species in the duration of stage III which finished when plants died, were consistent with differences in epidermal conductance and in dehydration tolerance of leaves.
Free Amino Acid Concentrations in Leaves of Sodium-Deficient C4 Plants
Authors: Grof CPL , Johnston M , Brownell PF
Published: January 2006

Consistent changes in the free amino acid concentrations in response to sodium nutrition were observed in mature leaves of the C4 species Amaranthus tricolor and Chloris gayana. The amino acids alanine, γ-aminobutyric acid and glycine were present in greater and aspartate and arginine in lower concentrations in mature leaves of sodium-deficient than in normal plants of both species.
Stunting in 'Gigas' Wheat as Influenced by Temperature and Daylength
Authors: Atsmon D , Bush MG , Evans LT
Published: January 2006

When plants of the uniculm 'gigas' wheat line 492 were grown at 15/ 10°C, all plants were severely stunted in long days (LD) but normal in short days (SD). The results of reciprocal transfers between SD and LD indicate that line 492 plants pass through a stage which is very sensitive to LD at 15/ 10°C, between about 14 and 27 days after sowing, just before double ridge formation at the shoot apex. LD during that interval caused stunting in most plants whereas SD at that stage allowed all plants to develop normally.
Transfers between temperature regimes of 15/10°C and 24/19°C under LD also indicated that the period just prior to double ridge formation was critical for stunting. In the uniculm line 492 stunting in LD was caused by temperature regimes cooler than 21 /16°C;, whereas in the oligoculm line 380 the main shoots of most plants were normal even at 15/ 10°C.
Relationship of Pre-anthesis Fructan Metabolism to Grain Numbers in Winter Wheat (Triticum aestivum L.)
Authors: Hendrix JE , Linden JC , Smith DH , Ross CW , Park IK
Published: January 2006

Four cultivars of winter wheat were analysed for non-structural carbohydrates at four harvest dates starting at inflorescence initiation and ending at anthesis. Grain number was determined from comparable plants harvested at maturity. Fructose, glucose, sucrose, and fructans were quantified in extracts of stems and inflorescences. In stems the content of the four carbohydrates increased until about a week before anthesis. During the week before anthesis the trend for the sugars was variable, but fructan content continued to increase. In inflorescences, trends for sugars were similar to those in stems; however, fructan content peaked 7-10 days before anthesis. Peak quantities of fructans in inflorescences and the quantities degraded after the peak were both correlated with grain numbers. The average degree of polymerisation of fructans from stems was 5 with most being in the range from 3 to 7. The degree of polymerisation in inflorescences ranged from 3 to 56. All of these data indicate that inflorescences differ from stems in their control of fructan metabolism.
Gas Exchange and Growth in Wheat and Barley Grown in Salt
Authors: Rawson HM
Published: January 2006

By measuring a range of gas exchange and growth variables, attempts were made to select key indicators of response to salinity in a wheat (Q61) and a barley (Beecher). A second wheat (WW15, Anza) was included in the growth measurements.
Plants were grown to anthesis in gravel culture flushed with 0, 75 or 150 mol m-3 NaCl, and under the high radiation and evaporative conditions of summer. Salinity increased leaf chloride contents and reduced peak photosynthesis, the initial slope of the light response curves, and dark respiration of young leaves at ligule emergence, but dark respiration of slightly older leaves was increased by salinity as were the CO2 compensation points. Short-duration changes in salinity could modify photosynthesis rates by no more than 15% though dark respiration rates moved quickly towards those of plants held continuously at the new salinity level.
While Q61 wheat appeared superior to Beecher barley at moderate salinity using these gas exchange indicators, it died at 150 mol m-3 NaCl; Beecher and WW15 survived. Carbon and water budgets are used to propose that the demise of Q61 could have been partially due to its marginally poorer water-use efficiency and its higher specific leaf weight, i.e. its higher requirement for carbon and water to produce each unit area of leaf. It is suggested that measurements of relative leaf expansion rate, specific leaf weight, and water use efficiency would be basic requirements in a salinity screening program. Measurements of ion contents and gas exchange variables are of little benefit when used alone.
Purification and Properties of Phosphoenolpyruvate Carboxykinase from C4 Plants
Authors: Burnell JN
Published: January 2006

Phosphoenolpyruvate (PEP) carboxykinase (EC 4.1.1.49) from the leaves of Urochloa panicoides, Chloris gayana and Panicum maximum has been purified to homogeneity and its properties determined. The enzyme from all three PEP carboxykinase-type C4 plants have similar physical and kinetic properties. The native enzyme has a molecular weight of 380 000 and its monomeric molecular weight is about 64 000, suggesting the enzyme is hexameric. It is active over a wide pH range and has a pH optimum between 7.4 and 8.2, has a wide nucleotide specificity, has an absolute requirement for Mn2+ and is stimulated by C-. The enzyme is inhibited by 3-phosphoglyceric acid, fructose 6-phosphate and fructose 1,6-bisphosphate; the mechanism of inhibition is discussed. The purified PEP carboxykinase is unable to catalyse the conversion of oxaloacetate to pyruvate, nor does it possess pyruvate kinase activity. These findings are discussed in relation to the C4 photosynthetic pathway operating in PEP carboxykinase-type C4 plants.
In vivo Chlorophyll a Fluorescence in Sodium-Deficient C4 Plants
Authors: Grof CPL , Johnston M , Bronwell PF
Published: January 2006

The fluorescence ratio (Fp-FI)/FI gave a consistent value when leaf tissue weights greater than 0.1 g were used and was lower in sodium-deficient than normal C4 plants. Of the group I elements only sodium, irrespective of the salt supplied to deficient cultures, increased the fluorescence ratio to that observed in normal plants. The concentration of sodium required to increase the fluorescence ratio corresponded to the concentration of sodium required to bring about a growth response in Kochia childsii. The application of sodium, either directly onto the leaves or via the culture solution, brought about a rapid and parallel increase in the chlorophyll a/b ratio and the fluorescence ratio in K. childsii.