The Interaction between Cold and Light Controls the Expression of the Cold-Regulated Barley Gene cor14b and the Accumulation of the Corresponding Protein1

We report the expression of the barley (Hordeum vulgare L.) COR (cold-regulated) gene cor14b (formerly pt59) and the accumulation of its chloroplast-localized protein product. A polyclonal antibody raised against the cor14b-encoded protein detected two chloroplast COR proteins: COR14a and COR14b. N-terminal sequencing of COR14a and expression of cor14b in Arabidopsis plants showed that COR14a is not encoded by the cor14b sequence, but it shared homology with the wheat (Triticum aestivum L.) WCS19 COR protein. The expression of cor14b was strongly impaired in the barley albino mutant an, suggesting the involvement of a plastidial factor in the control of gene expression. Low-level accumulation of COR14b was induced by cold treatment in etiolated plants, although cor14b expression and protein accumulation were enhanced after a short light pulse. Light quality was a determining factor in regulating gene expression: red or blue but not far-red or green light pulses were able to promote COR14b accumulation in etiolated plants, suggesting that phytochrome and blue light photoreceptors may be involved in the control of cor14b gene expression. Maximum accumulation of COR14b was reached only when plants were grown and/or hardened under the standard photoperiod. The effect of light on the COR14b stability was demonstrated by using transgenic Arabidopsis. These plants constitutively expressed cor14b mRNAs regardless of temperature and light conditions; nevertheless, green plants accumulated about twice as much COR14b protein as etiolated plants.

Ecological intensification of cereal production systems: Yield potential, soil quality, and precision agriculture

Wheat (Triticum aestivum L.), rice (Oryza sativa L.), and maize (Zea mays L.) provide about two-thirds of all energy in human diets, and four major cropping systems in which these cereals are grown represent the foundation of human food supply. Yield per unit time and land has increased markedly during the past 30 years in these systems, a result of intensified crop management involving improved germplasm, greater inputs of fertilizer, production of two or more crops per year on the same piece of land, and irrigation. Meeting future food demand while minimizing expansion of cultivated area primarily will depend on continued intensification of these same four systems. The manner in which further intensification is achieved, however, will differ markedly from the past because the exploitable gap between average farm yields and genetic yield potential is closing. At present, the rate of increase in yield potential is much less than the expected increase in demand. Hence, average farm yields must reach 70–80% of the yield potential ceiling within 30 years in each of these major cereal systems. Achieving consistent production at these high levels without causing environmental damage requires improvements in soil quality and precise management of all production factors in time and space. The scope of the scientific challenge related to these objectives is discussed. It is concluded that major scientific breakthroughs must occur in basic plant physiology, ecophysiology, agroecology, and soil science to achieve the ecological intensification that is needed to meet the expected increase in food demand.

Characterization of a Granule-Bound Starch Synthase Isoform Found in the Pericarp of Wheat1

Waxy wheat (Triticum aestivum L.) lacks the waxy protein, which is also known as granule-bound starch synthase I (GBSSI). The starch granules of waxy wheat endosperm and pollen do not contain amylose and therefore stain red-brown with iodine. However, we observed that starch from pericarp tissue of waxy wheat stained blue-black and contained amylose. Significantly higher starch synthase activity was detected in pericarp starch granules than in endosperm starch granules. A granule-bound protein that differed from GBSSI in molecular mass and isoelectric point was detected in the pericarp starch granules but not in granules from endosperm. This protein was designated GBSSII. The N-terminal amino acid sequence of GBSSII, although not identical to wheat GBSSI, showed strong homology to waxy proteins or GBSSIs of cereals and potato, and contained the motif KTGGL, which is the putative substrate-binding site of GBSSI of plants and of glycogen synthase of Escherichia coli. GBSSII cross-reacted specifically with antisera raised against potato and maize GBSSI. This study indicates that GBSSI and GBSSII are expressed in a tissue-specific manner in different organs, with GBSSII having an important function in amylose synthesis in the pericarp.

Computation of Surface Electrical Potentials of Plant Cell Membranes : Correspondence to Published Zeta Potentials from Diverse Plant Sources

A Gouy-Chapman-Stern model has been developed for the computation of surface electrical potential (ψ0) of plant cell membranes in response to ionic solutes. The present model is a modification of an earlier version developed to compute the sorption of ions by wheat (Triticum aestivum L. cv Scout 66) root plasma membranes. A single set of model parameters generates values for ψ0 that correlate highly with published ζ potentials of protoplasts and plasma membrane vesicles from diverse plant sources. The model assumes ion binding to a negatively charged site (R− = 0.3074 μmol m−2) and to a neutral site (P0 = 2.4 μmol m−2) according to the reactions R− + IΖ ⇌ RIΖ−1 and P0 + IΖ ⇌ PIΖ, where IΖ represents an ion of charge Ζ. Binding constants for the negative site are 21,500 m−1 for H+, 20,000 m−1 for Al3+, 2,200 m−1 for La3+, 30 m−1 for Ca2+ and Mg2+, and 1 m−1 for Na+ and K+. Binding constants for the neutral site are 1/180 the value for binding to the negative site. Ion activities at the membrane surface, computed on the basis of ψ0, appear to determine many aspects of plant-mineral interactions, including mineral nutrition and the induction and alleviation of mineral toxicities, according to previous and ongoing studies. A computer program with instructions for the computation of ψ0, ion binding, ion concentrations, and ion activities at membrane surfaces may be requested from the authors.

Three Mechanisms for the Calcium Alleviation of Mineral Toxicities

Ca2+ in rooting medium is essential for root elongation, even in the absence of added toxicants. In the presence of rhizotoxic levels of Al3+, H+, or Na+ (or other cationic toxicants), supplementation of the medium with higher levels of Ca2+ alleviates growth inhibition. Experiments to determine the mechanisms of alleviation entailed measurements of root elongation in wheat (Triticum aestivum L. cv Scout 66) seedlings in controlled medium. A Gouy-Chapman-Stern model was used to compute the electrical potentials and the activities of ions at the root-cell plasma membrane surfaces. Analysis of root elongation relative to the computed surface activities of ions revealed three separate mechanisms of Ca2+ alleviation. Mechanism I is the displacement of cell-surface toxicant by the Ca2+-induced reduction in cell-surface negativity. Mechanism II is the restoration of Ca2+ at the cell surface if the surface Ca2+ has been reduced by the toxicant to growth-limiting levels. Mechanism III is the collective ameliorative effect of Ca2+ beyond mechanisms I and II, and may involve Ca2+-toxicant interactions at the cell surface other than the displacement interactions of mechanisms I and II. Mechanism I operated in the alleviation of all of the tested toxicities; mechanism II was generally a minor component of alleviation; and mechanism III was toxicant specific and operated strongly in the alleviation of Na+ toxicity, moderately in the alleviation of H+ toxicity, and not at all in the alleviation of Al3+ toxicity.

Does a Low Nitrogen Supply Necessarily Lead to Acclimation of Photosynthesis to Elevated CO2?1

Long-term exposure of plants to elevated partial pressures of CO2 (pCO2) often depresses photosynthetic capacity. The mechanistic basis for this photosynthetic acclimation may involve accumulation of carbohydrate and may be promoted by nutrient limitation. However, our current knowledge is inadequate for making reliable predictions concerning the onset and extent of acclimation. Many studies have sought to investigate the effects of N supply but the methodologies used generally do not allow separation of the direct effects of limited N availability from those caused by a N dilution effect due to accelerated growth at elevated pCO2. To dissociate these interactions, wheat (Triticum aestivum L.) was grown hydroponically and N was added in direct proportion to plant growth. Photosynthesis did not acclimate to elevated pCO2 even when growth was restricted by a low-N relative addition rate. Ribulose-1, 5-bisphosphate carboxylase/oxygenase activity and quantity were maintained, there was no evidence for triose phosphate limitation of photosynthesis, and tissue N content remained within the range recorded for healthy wheat plants. In contrast, wheat grown in sand culture with N supplied at a fixed concentration suffered photosynthetic acclimation at elevated pCO2 in a low-N treatment. This was accompanied by a significant reduction in the quantity of active ribulose-1, 5-bisphosphate carboxylase/oxygenase and leaf N content.

Temperature-Stress-Induced Impairment of Chlorophyll Biosynthetic Reactions in Cucumber and Wheat1

Chlorophyll (Chl) biosynthesis in chill (7°C)- and heat (42°C)-stressed cucumber (Cucumis sativus L. cv poinsette) seedlings was affected by 90 and 60%, respectively. Inhibition of Chl biosynthesis was partly due to impairment of 5-aminolevulinic acid biosynthesis both in chill- (78%) and heat-stress (70%) conditions. Protochlorophyllide (Pchlide) synthesis in chill- and heat-stressed seedlings was inhibited by 90 and 70%, respectively. Severe inhibition of Pchlide biosynthesis in chill-stressed seedlings was caused by inactivations of all of the enzymes involved in protoporphyrin IX (Proto IX) synthesis, Mg-chelatase, and Mg-protoporphyrin IX monoester cyclase. In heat-stressed seedlings, although 5-aminolevulinic acid dehydratase and porphobilinogen deaminase were partially inhibited, one of the porphyrinogen-oxidizing enzymes, uroporphyrinogen decarboxylase, was stimulated and coproporphyrinogen oxidase and protoporphyrinogen oxidase were not substantially affected, which demonstrated that protoporphyrin IX synthesis was relatively more resistant to heat stress. Pchlide oxidoreductase, which is responsible for phototransformation of Pchlide to chlorophyllide, increased in heat-stress conditions by 46% over that of the control seedlings, whereas it was not affected in chill-stressed seedlings. In wheat (Triticum aestivum L. cv HD2329) seedlings porphobilinogen deaminase, Pchlide synthesis, and Pchlide oxidoreductase were affected in a manner similar to that of cucumber, suggesting that temperature stress has a broadly similar effect on Chl biosynthetic enzymes in both cucumber and wheat.

Development, Characterization, and Application of a Cadmium-Selective Microelectrode for the Measurement of Cadmium Fluxes in Roots of Thlaspi Species and Wheat1

A Cd2+-selective vibrating microelectrode was constructed using a neutral carrier-based Cd ionophore to investigate ion-transport processes along the roots of wheat (Triticum aestivum L.) and two species of Thlaspi, one a Zn/Cd hyperaccumulator and the other a related nonaccumulator. In simple Cd(NO3)2 solutions, the electrode exhibited a Nernstian response in solutions with Cd2+ activities as low as 50 nm. Addition of Ca2+ to the calibration solutions did not influence the slope of the calibration curve but reduced the detection limit to a solution activity of 1 μm Cd2+. Addition of high concentrations of K+ and Mg2+ to the calibration solution to mimic the ionic composition of the cytoplasm affected neither the slope nor the sensitivity of the electrode, demonstrating the pH-insensitive electrode's potential for intracellular investigations. The electrode was assayed for selectivity and was shown to be at least 1000 times more selective for Cd2+ than for any of those potentially interfering ions tested. Flux measurements along the roots of the two Thlaspi species showed no differences in the pattern or the magnitude of Cd2+ uptake within the time frame considered. The Cd2+-selective microelectrode will permit detailed investigations of heavy-metal ion transport in plant roots, especially in the area of phytoremediation.

Herbicide Safener-Binding Protein of Maize1 : Purification, Cloning, and Expression of an Encoding cDNA

Dichloroacetamide safeners protect maize (Zea mays L.) against injury from chloroacetanilide and thiocarbamate herbicides. Etiolated maize seedlings have a high-affinity cytosolic-binding site for the safener [3H](R,S)-3-dichloroacetyl-2,2,5-trimethyl-1,3-oxazol-idine ([3H]Saf), and this safener-binding activity (SafBA) is competitively inhibited by the herbicides. The safener-binding protein (SafBP), purified to homogeneity, has a relative molecular weight of 39,000, as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and an isoelectric point of 5.5. Antiserum raised against purified SafBP specifically recognizes a 39-kD protein in etiolated maize and sorghum (Sorghum bicolor L.), which have SafBA, but not in etiolated wheat (Triticum aestivum L.), oat (Avena sativa L.), barley (Hordeum vulgare L.), tobacco (Nicotiana tabacum L.), or Arabidopsis, which lack SafBA. SafBP is most abundant in the coleoptile and scarcest in the leaves, consistent with the distribution of SafBA. SBP1, a cDNA encoding SafBP, was cloned using polymerase chain reaction primers based on purified proteolytic peptides. Extracts of Escherichia coli cells expressing SBP1 have strong [3H]Saf binding, which, like binding to the native maize protein, is competitively inhibited by the safener dichlormid and the herbicides S-ethyl dipropylthiocarbamate, alachlor, and metolachlor. SBP1 is predicted to encode a phenolic O-methyltransferase, but SafBP does not O-methylate catechol or caffeic acid. The acquisition of its encoding gene opens experimental approaches for the evaluation of the role of SafBP in response to the relevant safeners and herbicides.

Moderately High Temperatures Inhibit Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase (Rubisco) Activase-Mediated Activation of Rubisco1

We tested the hypothesis that light activation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is inhibited by moderately elevated temperature through an effect on Rubisco activase. When cotton (Gossypium hirsutum L.) or wheat (Triticum aestivum L.) leaf tissue was exposed to increasing temperatures in the light, activation of Rubisco was inhibited above 35 and 30°C, respectively, and the relative inhibition was greater for wheat than for cotton. The temperature-induced inhibition of Rubisco activation was fully reversible at temperatures below 40°C. In contrast to activation state, total Rubisco activity was not affected by temperatures as high as 45°C. Nonphotochemical fluorescence quenching increased at temperatures that inhibited Rubisco activation, consistent with inhibition of Calvin cycle activity. Initial and maximal chlorophyll fluorescence were not significantly altered until temperatures exceeded 40°C. Thus, electron transport, as measured by Chl fluorescence, appeared to be more stable to moderately elevated temperatures than Rubisco activation. Western-blot analysis revealed the formation of high-molecular-weight aggregates of activase at temperatures above 40°C for both wheat and cotton when inhibition of Rubisco activation was irreversible. Physical perturbation of other soluble stromal enzymes, including Rubisco, phosphoribulokinase, and glutamine synthetase, was not detected at the elevated temperatures. Our evidence indicates that moderately elevated temperatures inhibit light activation of Rubisco via a direct effect on Rubisco activase.

Moderately High Temperatures Inhibit Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase (Rubisco) Activase-Mediated Activation of Rubisco

We tested the hypothesis that light activation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is inhibited by moderately elevated temperature through an effect on Rubisco activase. When cotton (Gossypium hirsutum L.) or wheat (Triticum aestivum L.) leaf tissue was exposed to increasing temperatures in the light, activation of Rubisco was inhibited above 35 and 30°C, respectively, and the relative inhibition was greater for wheat than for cotton. The temperature-induced inhibition of Rubisco activation was fully reversible at temperatures below 40°C. In contrast to activation state, total Rubisco activity was not affected by temperatures as high as 45°C. Nonphotochemical fluorescence quenching increased at temperatures that inhibited Rubisco activation, consistent with inhibition of Calvin cycle activity. Initial and maximal chlorophyll fluorescence were not significantly altered until temperatures exceeded 40°C. Thus, electron transport, as measured by Chl fluorescence, appeared to be more stable to moderately elevated temperatures than Rubisco activation. Western-blot analysis revealed the formation of high-molecular-weight aggregates of activase at temperatures above 40°C for both wheat and cotton when inhibition of Rubisco activation was irreversible. Physical perturbation of other soluble stromal enzymes, including Rubisco, phosphoribulokinase, and glutamine synthetase, was not detected at the elevated temperatures. Our evidence indicates that moderately elevated temperatures inhibit light activation of Rubisco via a direct effect on Rubisco activase.

Structure repair of a compacted vertisol with wet-dry cycles and crops

We hypothesized that the four rotation crops: wheat (Triticum aestivum L.), sorghum [Sorghum bicolor (L.) Merr.], lablab [Lablab purpureus (L.) Sweet] and mung bean [ Vigna radiata (L.) R. Wilczek] differ in their ability to repair soil structure. The study was conducted on a Typic Haplustert, Queensland, Australia, locally termed a Black Earth and considered a prime cropping soil. Large (0.5-m depth by 0.3-m diam.) soil cores, collected from compacted wheel furrows in an irrigated cotton (Gossypium hirsutum L.) field, were subjected to three, six, or nine wet-dry cycles that simulated local flood irrigation practices. After each cycle, soil profiles were sampled for clod bulk density, image analysis of soil structure, and evapotranspiration. Generally, all crops improved soil structure over the initial field condition but lablab and mung bean gave improvements to greater depths and more rapidly than wheat and sorghum. Mung bean and lablab caused up to a threefold increase in clod porosity in the 0.1- to 0.4-m soil layer after only three wet-dry cycles, whereas sorghum required nine wet-dry cycles to increase clod porosity in only the 0.2- to 0.3-m layer, and wheat gave no improvement even after nine wet-dry cycles. Image analysis of soil structure showed that lablab and mung bean rapidly (by three wet-dry cycles) produced smaller peds with more interconnected pore space than wheat and sorghum. By nine wet-dry cycles, sorghum achieved deep cracking of the soil but the material between the cracks remained large and dense. Evapotranspiration was double under lablab and mung bean compared with wheat and sorghum. Our results indicate greater cycles of wetting and drying under lablab and mung bean than wheat and sorghum that have led to rapid repair of soil compaction.

Ecological stoichiometry controls the transformation and retention of plant-derived organic matter to humus in response to nitrogen fertilisation

Carbon (C) sequestration in soils is a means for increasing soil organic carbon (SOC) stocks and is a potential tool for climate change mitigation. One recommended management practice to increase SOC stocks is nitrogen (N) fertilisation, however examples of positive, negative or null SOC effects in response to N addition exist. We evaluated the relative importance of plant molecular structure, soil physical properties and soil ecological stoichiometry in explaining the retention of SOC with and without N addition. We tracked the transformation of 13C pulse-labelled buffel grass (Cenchrus ciliaris L.), wheat (Triticum aestivum L.) and lucerne (Medicago sativa L.) material to the <53 μm silt + clay soil organic C fraction, hereafter named “humus”, over 365-days of incubation in four contrasting agricultural soils, with and without urea-N addition. We hypothesised that: a) humus retention would be soil and litter dependent; b) humus retention would be litter independent once litter C:N ratios were standardised with urea-N addition; and c) humus retention would be improved by urea-N addition. Two and three-way factorial analysis of variance indicated that 13C humus was consistently soil and litter dependent, even when litter C:N ratios were standardised, and that the effect of urea-N addition on 13C humus was also soil and litter dependent. A boosted regression analysis of the effect of 44 plant and soil explanatory variables demonstrated that soil biological and chemical properties had the greatest relative influence on 13C humus. Regression tree analyses demonstrated that the greatest gains in 13C humus occurred in soils of relatively low total organic C, dissolved organic C and microbial biomass C (MBC), or with a combination of relatively high MBC and low C:N ratio. The greatest losses in 13C humus occurred in soils with a combination of relatively high MBC and low total N or increasing C:N ratio. We conclude that soil variables involved in soil ecological stoichiometry exert a greater relative influence on incorporating organic matter as humus compared to plant molecular structure and soil physical properties. Furthermore, we conclude that the effect of N fertilisation on humus retention is dependent upon soil ecological stoichiometry.

The effect of environment on endosperm cell-wall development in Triticum aestivum during grain filling: an infrared spectroscopic imaging study

One of the major factors contributing to the failure of new wheat varieties is seasonal variability in end-use quality. Consequently, it is important to produce varieties which are robust and stable over a range of environmental conditions. Recently developed sample preparation methods have allowed the application of FT-IR spectroscopic imaging methods to the analysis of wheat endosperm cell wall composition, allowing the spatial distribution of structural components to be determined without the limitations of conventional chemical analysis. The advantages of the methods, described in this paper, are that they determine the composition of endosperm cell walls in situ and with minimal modification during preparation. Two bread-making wheat cultivars, Spark and Rialto, were selected to determine the impact of environmental conditions on the cell-wall composition of the starchy endosperm of the developing and mature grain, focusing on the period of grain filling (starting at about 14 days after anthesis). Studies carried out over two successive seasons show that the structure of the arabinoxylans in the endosperm cell walls changes from a highly branched form to a less branched form. Furthermore, during development the rate of restructuring was faster when the plants were grown at higher temperature with restricted water availability from 14 days after anthesis with differences in the rate of restructuring occurring between the two cultivars.

Influencia de gluteninas LMW en la fuerza del gluten de variedades locales españolas de trigo panadero (Triticum aestivum ssp. vulgare L.)

Las prolaminas son las principales proteínas del endospermo de los trigos panaderos que están relacionadas con la calidad panadera. El objetivo de este trabajo es caracterizar gluteninas LMW según la nomenclatura de Liu et al y relacionarlas con la fuerza panadera