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Adsorption and desorption of phosphorus (P) and nitrogen (N) by stalk residues may influence the concentrations of P and N in runoff A laboratory study was conducted to measure the effects of P and N constituents in solution on adsorption and desorption of P and N by corn, soybean, and wheat stalk residues. Experimental variables included type of stalk material (corn, soybean, and wheat), inorganic nutrients in solution (PO4-P and NO3-N; PO4-P and NH4-N, NO3-N and NH4-N, and PO4-P, NO3-N, and NH4-N), solution concentration (0, 6, 12, and 24 µg g-1 residue), and stalk immersion period (25, 250, 2500, 25000, and 86400 s). The initial concentration of each of the P and N constituents in a particular test solution was the same (0, 6, 12 or 24 µg mL-1). Corn-stalk residues released PO4-P, NO3-N, and NH4-N. The quantity of PO4-P released generally increased as the length of time the corn stalks were immersed became greater. The presence of P and N constituents in solution in general did not affect the quantity of NO3-N released by corn-stalk residues. Soybean-stalk residues released PO4-P and adsorbed relatively small amounts of NH4-N. Wheat-stalk residues released PO4-P, and adsorbed NO3-N and NH4-N. The presence of stalk residues, P or N solution concentration, and residue immersion period may influence P and N concentrations of overland flow. The amount of P and N adsorbed or desorbed by residue materials can be significantly different if more than one nutrient constituent is present in solution. [ABSTRACT FROM AUTHOR]

Improved understanding of the impact of leafing phenology and soil water supplies on the gas exchange and water use efficiency (WUE) of trees in agroforestry systems in the semi-arid tropics is essential to optimise tree/crop interactions and the use of scarce natural resources, particularly in view of recent initiatives to use carbon credits to reward subsistence farmers who plant and manage trees effectively. Understanding of the relationships between photosynthetic and transpiration rates and chlorophyll content may help to explain variation in growth rate, productivity and WUE between species and growth environments. Such information is lacking for the species examined here, the evergreen Grevillea robusta (A. Cunn), semi-deciduous Alnus acuminata (HBK) and deciduous Paulownia fortunei (Hemsl.). Although differences in leafing phenology influence the extent of competition or complementarity between trees and crops in agroforestry systems, and hence crop yield, farmers may deliberately plant fast-growing, competitive tree species if they provide attractive economic returns or carbon credit subsidies. The objectives were to characterise: (1) the extent of variation in foliar gas exchange and instantaneous water use efficiency (WUE i ) between trees with contrasting leafing phenologies; (2) the influence of leaf age and available soil moisture on gas exchange and WUE i of trees; and (3) chlorophyll and foliar nitrogen (N) concentrations and gas exchange parameters for maize in agroforestry and sole crop systems. Foliar chlorophyll and N concentrations, assimilation (A) and transpiration rate (E) were much greater in P. fortunei than in A. acuminata or G. robusta. A, E and WUE i were greatest in young mature leaves of all three species but declined as they senesced. WUE i increased as soil moisture content declined and was similar in all species, suggesting their differing leafing phenologies were responsible... [Copyright &y& Elsevier]

In plants, cell wall placement during cytokinesis is determined by the position of the preprophase band (PPB) and the subsequent expansion of the phragmoplast, which deposits the new cell wall, to the cortical division site delineated by the PPB. New cell walls are often incorrectly oriented during asymmetric cell divisions in the leaf epidermis of maize (Zea mays) discordial (dcd1) mutants, and this defect is associated with aberrant PPB formation in asymmetrically dividing cells, dcd1 was cloned and encodes a putative B" regulatory subunit of the PP2A phosphatase complex highly similar to Arabidopsis thaliana FASS/TONNEAU2, which is required for PPB formation. We also identified alternative discordial (add1), a second gene in maize nearly identical to dcd1. While loss of add1 function does not produce a noticeable phenotype, knock down of both genes in add1(RNAi) dcd1(RNAi) plants prevents PPB formation and causes misorientation of symmetric and asymmetric cell divisions. Immunolocalization studies with an antibody that recognizes both DCD1 and ADD1 showed that these proteins colocalize with PPBs and remain at the cortical division site through metaphase. Our results indicate that DCD1 and ADD1 function in PPB formation, that this function is more critical in asymmetrically dividing cells than in symmetrically dividing cells, and that DCD1/ADD1 may have other roles in addition to promoting PPB formation at the cortical division site. [ABSTRACT FROM AUTHOR]

This study investigated the potential of support vector machine (SVM) methodology to extract information on crop growth and various biophysical parameters from airborne hyperspectral remote sensing data. The study was carried out in a corn field, consisting of a main plot with four weed control strategies (no weed control, broadleaf control, grass control, and full weed control) and a sub-plot with three nitrogen (N) fertilization rates (60, 120, 250 N kg/ha), all replicated four times. Hyperspectral data were taken in 72 narrow wavebands (409 to 947 nm) using a compact airborne spectrographic imager (CASI) sensor. Various crop physiological parameters were measured concurrently including: leaf greenness (SPAD readings), plant height, leaf nitrogen content, and leaf chlorophyll content. The objective of the study was to evaluate the ability of SVM regression models to extract continuous vegetation variables using aerial hyperspectral observations. Several SVM models were developed to estimate the crop biophysical parameters and the grain yield. The study showed that by using reflectance data collected at the tasseling stage, crop parameters can be estimated with reasonable accuracy. Generally speaking, the coefficients of determination (r2) were greater than 0.9 for biomass, yield, plant height, and SPAD with the training data set. The r2 was slightly lower for the test data set (0.51, 0.82, 0.91, and 0.86, respectively), which is acceptable given the small size of the data set used in the study. The results of the five fold cross validation procedure indicated that the SVM results were consistent. The results were also compared with those obtained with a stepwise approach, and the SVM results were found to be superior. [ABSTRACT FROM AUTHOR]

In addition to the exclusively granule-bound starch synthase GBSSI, starch granules also bind significant proportions of other starch biosynthetic enzymes, particularly starch synthases (SS) SSI and SSIIa, and starch branching enzyme (BE) BEIIb. Whether this association is a functional aspect of starch biosynthesis, or results from non-specific entrapment during amylopectin crystallization, is not known. This study utilized genetic, immunological, and proteomic approaches to investigate comprehensively the proteome and phosphoproteome of Zea mays endosperm starch granules. SSIII, BEI, BEIIa, and starch phosphorylase were identified as internal granule-associated proteins in maize endosperm, along with the previously identified proteins GBSS, SSI, SSIIa, and BEIIb. Genetic analyses revealed three instances in which granule association of one protein is affected by the absence of another biosynthetic enzyme. First, eliminating SSIIa caused reduced granule association of SSI and BEIIb, without affecting GBSS abundance. Second, eliminating SSIII caused the appearance of two distinct electrophoretic mobility forms of BEIIb, whereas only a single migration form of BEIIb was observed in wild type or any other mutant granules examined. Third, eliminating BEIIb caused significant increases in the abundance of BEI, BEIIa, SSIII, and starch phosphorylase in the granule, without affecting SSI or SSIIa. Analysis of the granule phosphoproteome with a phosphorylation-specific dye indicated that GBSS, BEIIb, and starch phosphorylase are all phosphorylated as they occur in the granule. These results suggest the possibility that starch metabolic enzymes located in granules are regulated by post-translational modification and/or protein–protein interactions. [ABSTRACT FROM PUBLISHER]

The rhizotoxicity of aluminium at low-pH with Al3+ and at high pH with $${\hbox{ Al(OH) }}_{4}^{-}$$ as the main Al species was studied. Aluminium reduced root growth to similar levels at pH 8.0 and pH 4.3, although the mononuclear Al concentration at pH 8.0 was three times lower than at pH 4.3. Al contents of root apices were much higher at pH 8 than at pH 4.3. Callose was induced only marginally at pH 8 and the formation was confined to the epidermis, whereas it proceeded through the cortex with time at pH 4.3. Well-documented genotypical differences in callose formation and Al accumulation could not be found at pH 8. The largest fraction of the root-tip Al was recovered in the cell-wall fraction independent of the solution pH. A sequential extraction of isolated cell walls suggests that most of the cell-wall Al was precipitated Al(OH)3 at pH 8.0. This can be explained by a drastic pH reduction in the root apoplastic sap to 6.2, whereas at bulk solution pH 4.3 it rose to 5.6. Al precipitation was also confirmed by the microscopic localization of Al. At pH 8, Al could mostly be found in the epidermis, but in the apoplast of the outer cortex at pH 4.3. It is proposed here that at pH 4.3, Al3+ inhibits root growth through binding to sensitive binding sites in the apoplast of the epidermis and the outer cortex. At pH 8, Al(OH)3 precipitation in the epidermis causes a mechanical barrier thus impairing the root-growth control of the epidermis. [ABSTRACT FROM PUBLISHER]

Acquisition of cell identity requires communication among neighboring cells. To dissect the genetic pathways regulating cell signalling in later leaf development, a screen was performed to identify mutants with chloroplast pigmentation sectors that violate cell lineage boundaries in maize (Zea mays) leaves. We have characterized a recessive mutant, tie-dyed1 (tdy1), which develops stable, nonclonal variegated yellow and green leaf sectors. Sector formation requires high light, occurs during a limited developmental time, and is restricted to leaf blade tissue. Yellow tdy1 sectors accumulate excessive soluble sugars and starch, whereas green sectors appear unaffected. Significantly, starch accumulation precedes chlorosis in cells that will become a yellow sector. Retention of carbohydrates in tdy1 leaves is associated with a delay in reproductive maturity, decreased stature, and reduced yield. To explain the tdy1 sectoring pattern, we propose a threshold model that incorporates the light requirement and the hyperaccumulation of photoassimilates. A possible function consistent with this model is that TDY1 acts as a sugar sensor to regulate an inducible sugar export pathway as leaves develop under high light conditions. [ABSTRACT FROM AUTHOR]

Separation of the life cycle of flowering plants into two distinct growth phases, vegetative and reproductive, is marked by the floral transition. The initial floral inductive signals are perceived in the leaves and transmitted to the shoot apex, where the vegetative shoot apical meristem is restructured into a reproductive meristem. In this study, we report cloning and characterization of the maize (Zea mays) flowering time gene delayed floweringi (dlf1). Loss of dlf1 function results in late flowering, indicating dlf1 is required for timely promotion of the floral transition. dlf1 encodes a protein with a basic leucine zipper domain belonging to an evolutionarily conserved family. Three-dimensional protein modeling of a missense mutation within the basic domain suggests DLF1 protein functions through DNA binding. The spatial and temporal expression pattern of dlf1 indicates a threshold level of dlf1 is required in the shoot apex for proper timing of the floral transition. Double mutant analysis of dIf1 and indeterminate1 (id1), another late flowering mutation, places dlf1 downstream of id1 function and suggests dIf1 mediates floral inductive signals transmitted from leaves to the shoot apex. This study establishes an emergent framework for the genetic control of floral induction in maize and highlights the conserved topology of the floral transition network in flowering plants. [ABSTRACT FROM AUTHOR]

Most plant oxylipins, a large class of diverse oxygenated polyunsaturated fatty acids and their derivatives, are produced through the lipoxygenase (LOX) pathway. Recent progress in dicots has highlighted the biological roles of oxylipins in plant defence responses to pathogens and pests. By contrast, the physiological function of LOXs and their metabolites in monocots is poorly understood. Two maize LOXs, ZmLOX10 and ZmLOX11 that share >90% amino acid sequence identity but are localized on different chromosomes, were cloned and characterized. Phylogenetic analysis revealed that ZmLOX10 and ZmLOX11 cluster together with well-characterized plastidic type 2 linoleate 13-LOXs from diverse plant species. Regio-specificity analysis of recombinant ZmLOX10 protein overexpressed in Escherichia coli proved it to be a linoleate 13-LOX with a pH optimum at ∼pH 8.0. Both predicted proteins contain putative transit peptides for chloroplast import. ZmLOX10 was preferentially expressed in leaves and was induced in response to wounding, cold stress, defence-related hormones jasmonic acid (JA), salicylic acid (SA), and abscisic acid (ABA), and inoculation with an avirulent strain of Cochliobolus carbonum. These data suggested a role for this gene in maize adaptation to abiotic stresses and defence responses against pathogens and pests. ZmLOX11 was preferentially expressed in silks and was induced in leaves only by ABA, indicating its possible involvement in responses to osmotic stress. In leaves, mRNA accumulation of ZmLOX10 is strictly regulated by a circadian rhythm, with maximal expression coinciding temporally with the highest photosynthetic activity. This study reveals the evolutionary divergence of physiological roles for relatively recently duplicated genes. Possible physiological functions of these 13-LOXs are suggested. [ABSTRACT FROM PUBLISHER]

Fusarium verticillioides (Sacc.) Nirenberg (synonym F. moniliforme Sheldon) (teleomorph: Gibberella moniliformis) and F. proliferatum (Matsushima) Nirenberg (teleomorph: G. intermedia) are fungal pathogens of maize (Zea mays L.) that cause ear rot and contaminate grain with fumonisins, mycotoxins that can harm animals and humans. The objective of this study was to identify quantitative trait loci (QTL) for resistance to Fusarium ear rot and fumonisin contamination in two maize populations, comprised of 213 BC1F1:2 families from the first backcross of GE440 to FR1064 (GEFR) and 143 recombinant inbred lines from the cross of NC300 to B104 (NCB). QTL mapping was used to study the genetic relationships between resistances to ear rot and fumonisin contamination and to investigate consistency of QTL across populations. In the GEFR population, seven QTL explained 47% of the phenotypic variation for mean ear rot resistance and nine QTL with one epistatic interaction explained 67% of the variation for mean fumonisin concentration. In the NCB population, five QTL explained 31% of the phenotypic variation for mean ear rot resistance and six QTL and three epistatic interactions explained 81% of the phenotypic variation for mean fumonisin concentration. Eight QTL in the GEFR population and five QTL in the NCB population affected both disease traits. At least three ear rot and two fumonisin contamination resistance QTL mapped to similar positions in the two populations. Two QTL, localized to chromosomes four and five, appeared to be consistent for both traits across both populations. [ABSTRACT FROM AUTHOR]

We studied the effects of changes in the mitochondrial redox state, induced by respiration inhibitors, on the expression of mitochondrial genes in Zea mays. The highest levels of cox1, cox3, and cob transcripts were observed in 4 h and atp9 transcripts in 6 h after treatment with antimycin A (antA). Treatment with salicyl hydroxamic acid (SHAM) resulted in a decrease in the transcripts during the first 10 h of incubation with subsequent recovering of this gene transcript level by 24 h. Treatment with SHAM did not essentially affect the level of cox1 transcripts, whereas the levels of cox3 and cob transcripts somewhat increased during the first 4 h and remained stable thereafter. After combined treatment with antA and SHAM, the level of cox1 and cox3 transcripts dropped below the control level during the first 4 h and then increased by the end of the treatment. The content of cob transcripts increased markedly after 24 h of treatment. The rps13 transcript changed irregularly, and its changes did not coincide with changes of other transcripts studied. Thus, we demonstrated differential expression of mitochondrial genes at changes in the redox state of the mitochondrial electron transport chain (ETC). The cox1, cox3, and cob gene expression responded to these changes rather coordinately. The results obtained indicate the involvement of the ETC redox state and/or the level of reactive oxygen species in the control of mitochondrial gene expression. [ABSTRACT FROM AUTHOR]

Histone modifications such as methylation and acetylation in the chromatin surrounding a gene are thought to regulate transcriptional activity. In this study, to determine whether dynamic changes occur in histone modification on the loci of stress-responsive genes in plants, we chose rice submergence-inducible ADH1 and PDC1 genes. When submerged, the rice ADH1 and PDC1 genes were activated in a biphasic manner: the first and second inductions occurred after approximately 2 and 12 h of submergence, respectively. Their expression was transcriptionally induced as shown by increased binding of RNA polymerase II to the ADH1 and PDC1 loci during submergence. The Lys4 residues of the histone H3 proteins (H3-K4s) at both the 5′- and 3′-coding regions of ADH1 and PDC1 were found to change from a di-methylated state to a tri-methylated state at the first induction period. On the other hand, acetylation of H3 increased throughout ADH1 and PDC1 genes at the later induction period. The methylation and acetylation levels recovered to the initial levels during re-aeration. Treatment of seedlings with a histone deacetylase (HDAC) inhibitor, trichostatin A, increased acetylation of histones H3 and association of RNA polymerase II on the ADH1 and PDC1 loci, thereby increasing transcript levels of ADH1 and PDC1. Together, these results showed dynamic and reversible changes of histone H3-K4 methylation and H3 acetylation in stress-responsive genes in a higher plant in response to the appearance or disappearance of an environmental stress. [ABSTRACT FROM AUTHOR]

Although sucrose synthase (SUS) is widely appreciated for its role in plant metabolism and growth, very little is known about the contribution of each of the SUS isoforms to these processes. Using isoform-specific antibodies, we evaluated the three known isoforms individually at the protein level. SUS1 and SUS-SH1 proteins have been studied previously; however, SUS2 (previously known as SUS3) has only been studied at the transcript level. Using SUS2 isoform-specific antibodies, we determined that this isoform is present in several maize tissues. The intracellular localization of all SUS isoforms was studied by cellular fractionation of leaves and developing kernels. Interestingly, SUS1 and SUS-SH1 were associated with membranes while SUS2 was not. The lack of membrane-associated SUS2 indicates that it might have a unique role in cytoplasmic sucrose metabolism. Using co-immunoprecipitation with kernel extracts, it was also established that SUS2 exists predominantly as a hetero-oligomer with SUS1, while SUS-SH1 forms only homo-oligomers. Using sequence-specific and phospho-specific antibodies, we have established for the first time that SUS-SH1 is phosphorylated in vivo at the Ser10 site in kernels, similar to the SUS1 Ser15 site. In midveins, additional evidence suggests that SUS can be phosphorylated at a novel C-terminal threonine site. Together, these results show that the isoforms of SUS are important in both cytosolic and membrane-associated sucrose degradation, but that their unique attributes most probably impart isoform-specific functional roles. [ABSTRACT FROM AUTHOR]

A better understanding of the physiological processes related to nitrogen (N) metabolism in maize (Zea mays L.) inbred lines is important for increasing the efficiency of breeding programs targeting low-N environments. This study analyzed the response to contrasting N availability of morphophysiological traits in a set of 12 maize inbred lines, from different origins (USA and Argentina) and breeding eras (from 1952 onward). Traits included in the analysis were related to canopy structure, light interception, shoot biomass production, and grain yield. Our results indicate that (i) the start of N effects on canopy size was more related to a threshold crop leaf area index (about 2) than to a given leaf stage (i.e., Vn), (ii) the light attenuation coefficient value was not affected by N availability, (iii) variations in kernel number per plant were explained by prolificacy (r² = 0.59), and (iv) differences in harvest index were related to kernel number per plant (r² = 0.77). The most important finding of our research was the detection in some inbreds of a particular response of kernel number to plant growth rate around silking, different from the general model established for hybrids. In these inbreds an additional effect of N availability was detected as reduced kernel set at a given plant growth rate under N deficient conditions (i.e., reduced reproductive efficiency). This result highlights the need of more research on reproductive sink development in this type of germplasm. [ABSTRACT FROM AUTHOR]

The cause of the strong non-photochemical fluorescence quenching was examined in maize ( Zea mays L.) plants that were treated with lincomycin during the 72 h period of greening. They were deficient in core complexes but seemed to contain the full complement of antennae. The following results were obtained: (1) High F o could not be attributed to the dark reduction of Q A but to the presence of a high amount of not properly organized antenna complexes due to the inhibited synthesis of reaction centres. (2) On illumination fluorescence intensity dropped considerably below F o within 20 s, and reached a steady state still below F o . (3) Slowly relaxing part of non-photochemical quenching was significantly higher than in control plants. (4) De-epoxidation state was constant, and corresponded to the maximal value of the control. (5) Free Lhca1/4 dimers could be detected in all submembrane fractions, including the grana, obtained by digitonin fractionation. (6) Increase in the 679 and 700 nm fluorescence emissions could be attributed to the monomerisation of part of LHCII and to the presence of free Lhca2 or LHCII aggregates, respectively. (7) LHCII or PSII+LHCII and Lhca1/4 interaction may contribute to the increase of long-wavelength fluorescence in the granal fraction. We assume that the elevated fluorescence quenching of monomeric LHCII as well as the interaction between LHCII or PSII+LHCII and Lhca1/4 can be considered as an explanation for the extensive non-photochemical fluorescence quenching in lincomycin treated plants. The permanent presence of zeaxanthin may have contributed to the fast formation of quenching. [ABSTRACT FROM AUTHOR]

An oxidative gating of water channels (aquaporins: AQPs) was observed in roots of corn seedlings as already found for the green alga Chara corallina. In the presence of 35 mm hydrogen peroxide (H2O2) – a precursor of hydroxyl radicals (*OH) – half times of water flow (as measured with the aid of pressure probes) increased at the level of both entire roots and individual cortical cells by factors of three and nine, respectively. This indicated decreases in the hydrostatic hydraulic conductivity of roots (Lphr) and of cells (Lph) by the same factors. Unlike other stresses, the plant hormone abscisic acid (ABA) had no ameliorative effect either on root Lphr or on cell Lph when AQPs were inhibited by oxidative stress. Closure of AQPs reduced the permeability of acetone by factors of two in roots and 1.5 in cells. This indicated that AQPs were not ideally selective for water but allowed the passage of the organic solute acetone. In the presence of H2O2, channel closure caused anomalous (negative) osmosis at both the root and the cell level. This was interpreted by the fact that in the case of the rapidly permeating solute acetone, channel closure caused the solute to move faster than the water and the reflection coefficient ( σs) reversed its sign. When H2O2 was removed from the medium, the effects were reversible, again at both the root and the cell level. The results provide evidence of oxidative gating of AQPs, which leads on to inhibition of water uptake by the roots. Possible mechanisms of the oxidative gating of AQPs induced by H2O2 (*OH) are discussed. [ABSTRACT FROM AUTHOR]

Water deficit-induced abscisic acid (ABA) accumulation is one of the most important stress signaling pathways in plant cells. Redox regulation of cellular signaling has currently attracted particular attention, but much less is known about its roles and mechanisms in plant signaling. Herein, we report that water deficit-induced ABA accumulation could be regulated by ascorbic acid (AA)-controlled redox status in leave apoplast. The AA content in non-stressed leaves was approximately 3 μmol/g FW, corresponding to a mean concentration of 3 mmol/L in a whole cell. Because AA is mainly localized in the cytosol and chloroplasts, the volume of which is much smaller than that of the whole cell, AA content in cytosolic and chloroplast compartments should be much higher than 3 mmol/L. Water deficit-induced ABA accumulation in both leaf and root tissues of maize seedlings was significantly inhibited by AA and reduced glutathione (GSH) at concentrations of 500 μmol/L and was completely blocked by 50 mmol/L AA and GSH. These results suggest that the AA-induced inhibition of ABA accumulation should not occur at sites where AA exists in high concentrations. Although water deficit led to a small increase in the dehydroascorbic acid (DHA) content, no significant changes in AA content were observed in either leaf or root tissues. When compared with the whole leaf cell, the AA content in the apoplastic compartment was much lower (i.e. approximately 70 nmol/g FW, corresponding to 0.7 mmol/L). Water deficit induced a significant decrease (approximately 2.5-fold) in the AA content and an increase (approximately 3.4-fold) in the DHA content in the apoplastic compartment, thus leading to a considerably decreased redox status there, which may have contributed to the relief of AA-induced inhibition of ABA accumulation, alternatively, promoting water deficit-induced ABA accumulation. Reactive oxygen species (ROS) could not mimic water deficit in inducing ABA accumulation, suggesting that the inhibition of ABA accumulation by AA or GSH was not related to their ROS-scavenging ability. The results of the present study suggest that the redox status in the apoplastic compartment, as determined by AA and DHA, may play a vital role in the regulation of the signaling process for water deficit-induced ABA accumulation. (Managing editor: Ping HE) [ABSTRACT FROM AUTHOR]

The species composition of a Burkholderia cepacia complex population naturally occurring in the maize rhizosphere was investigated by using both culture-dependent and culture-independent methods. B. cepacia complex isolates were recovered from maize root slurry on the two selective media Pseudomonas cepacia azelaic acid tryptamine (PCAT) and trypan blue tetracycline (TB-T) and subjected to identification by a combination of restriction fragment length polymorphism (RFLP) analysis and species-specific polymerase chain reaction (PCR) tests of the recA gene. DNA extracted directly from root slurry was examined by means of nested PCR to amplify recA gene with species-specific B. cepacia complex primers and to obtain a library of PCR amplified recA genes. Using the culture-dependent method the species Burkholderia cepacia, Burkholderia cenocepacia, Burkholderia ambifaria and Burkholderia pyrrocinia were identified, whereas using the culture-independent method also the species Burkholderia vietnamiensis was detected. The latter method also allowed us to highlight a higher diversity within the B. cenocepacia species. In fact, by using the culture-independent method the species B. cenocepacia recA lineages IIIA and IIID besides B. cenocepacia recA lineage IIIB were detected. Moreover, higher heterogeneity of recA RFLP patterns was observed among clones assigned to the species B. cenocepacia than among B. cenocepacia isolates from selective media. [ABSTRACT FROM AUTHOR]

Corn drying is an energy-intensive process. Thus, the management of energy use is critical for economical corn drying. The Central Black Sea Region covering Amasya, Çorum, Ordu, Samsun and Tokat provinces has climatic and agronomic conditions suitable for corn production. However, the drying of newly harvested wet corn stays as a major problem lot farmers since it is traditionally dried by spreading it on the ground in open atmosphere. Low temperature drying was selected in this computational study to dry corn safely. Fan power, heating power, total electric energy need of fan and total heating energy needed and to dry 1 ton corn from 25% (wb) initial moisture content to 13% (wb) final moisture content were estimated in September, October and November for each province. The airflow requirements (i.e., 159.1 m³·ton-1·h-1 for Amasya) and overall electric energy needs of selected fans (i.e., 27245 kJ·ton-1 for Amasya) in September are more than in November (68.3 m³·ton-1·h-1 and 10221 kJ·ton-1, respectively) because of quick deterioration of wet corn associated with high air temperatures in September. On the other hand, heating power requirements showed a mixed trend while the total heating energy needs consistently increased for all provinces when the drying operation was moved from September to November. In conclusion, the estimated total heating need increased while the estimated total electric energy need of fan decreased since the heating process increased the adiabatic drying potential of air, which in turn reduced the amount of air volume having to he flown through corn in the drying bin. [ABSTRACT FROM AUTHOR]

Previous studies have shown that the invasive spread of Rhododendron ponticum in the British Isles is influenced by the more favourable environmental conditions in the new territory than in the species’ home range. In this study, we asked whether the species’ invasion success might also involve a genotypic background for higher growth and germination rates in invasive populations. We tested the hypotheses that invasive populations have higher absolute germination rates, germinate faster and exhibit higher growth rates. We present data from greenhouse and climate chamber experiments with seed material and Rhododendron cuttings from six populations each of native Georgian, native Spanish and invasive Irish populations subjected to different temperature environments. There were no differences in the maximum germination rate and optimum germination temperature between native and invasive origins. We found significant differences in germination velocity with the Irish seeds responding most rapidly to all germination treatments. Accordingly, in the growth experiment the invasive Irish origins had the highest relative growth rates in all environments tested. Our results provide evidence for a genetic shift in invasive populations towards an increased investment in growth and towards a faster germination rate. Both traits would contribute to explaining this species’ range expansion. The underlying evolutionary mechanisms for this shift are discussed, including the possibility of hybridisation or of an ecological release from hitherto experienced constraints in the native area. [ABSTRACT FROM AUTHOR]

The objectives of this research were to 1) verify the potential use of the secondary‐treated sewage effluent (STSE) as a source of water and nitrogen for maize and 2) evaluate nitrogen (N) and phosphorus (P) concentrations in soil, as well as their concentrations and contents in maize plants, treated with STSE. The treatments consisted of mineral fertilization and irrigation with the STSE, during 58 days. After this period, plants were harvested and processed for dry matter yield, and plant and soil analysis were realized. No variation in total carbon and P soil concentration was observed, but total nitrogen increased. Mineral fertilization plus STSE irrigation increased the plant's P content, but without any effect on dry matter yields. The STSE could completely substitute the water from irrigation, but it provided only part of the demanded nitrogen and other nutrients for the maize plants in the treatments with no mineral fertilizer added. [ABSTRACT FROM AUTHOR]

Maize (Zea mays L., line F2) plants were grown in the field under high or low fertilization input to monitor the metabolic, biochemical and molecular events occurring in young vegetative leaves and in the different leaf stages along the main axis in plants harvested 15 days after silking. This study shows that in maize which possess large sinks represented by the seeds, nitrogen (N) management is different compared with tobacco in which sink strength is much lower and mostly limited to young developing leaves. Although in young leaves nitrate assimilation predominates in both species, ammonium assimilation exhibits some species-specific differences with respect to inorganic and organic N metabolite accumulation during leaf ageing. These differences are likely to be related to the high sink strength of the ear in maize, which continuously imports carbon and N assimilates during grain filling. Consequently, a number of cytosolic glutamine synthetase isoenzymes are expressed during leaf ageing to maintain a constant flux of reduced N necessary for the synthesis of organic N molecules used either for leaf protein synthesis or directly translocated to the grain. This situation contrasts with that found in tobacco for which leaf ammonium assimilation in the plastids is shifted to the cytosol during the transition from sink leaves to source leaves. These species-specific differences for N assimilation and recycling are discussed in relation to the evolution of leaf photosynthetic activity and leaf senescence, which both seem to be largely dependent on the different sink strength in each species. [ABSTRACT FROM AUTHOR]

To illustrate the development of the source-to-sink transition in maize leaves during the grain-filling period, an integrated physiological-agronomic approach is presented in this study. The evolution of physiological markers such as total leaf nitrogen (N), chlorophyll, soluble protein, amino acid and ammonium contents was monitored from silking to a period close to maturity in different leaf stages of three maize genotypes grown at high and low levels of N fertilization. In addition, the activities of glutamine synthetase (GS) and glutamate dehydrogenase (GDH), two enzymes known to play a direct or an indirect role during leaf N remobilization, were measured. In the three genotypes examined, we found that a general decrease of most metabolic and enzyme markers occurred during leaf ageing and that this decrease was enhanced when plants were N starved. In contrast, such variations were not observed between different sections of a single leaf even at an advanced stage of leaf senescence. We found that there is a strong correlation between total N, chlorophyll, soluble protein and GS activity, which is not dependent upon the N fertilization level, which indicates the N status of the plant, either in a single leaf or during ageing. In contrast, ammonium, amino acids and GDH activity were not subject to such variations, thus suggesting that they are indicators of the metabolic activity of the whole plant in response to the level of N fertilization. The use of these markers to predict the N status of maize as a function of both plant development and N availability is discussed. [ABSTRACT FROM AUTHOR]

Drought is a major abiotic stress affecting all levels of plant organization and, in particular, leaf elongation. Several experiments were designed to study the effect of water deficits on maize (Zea minis) leaves at the protein level by taking into account the reduction of leaf elongation. Proteomic analyses of growing maize leaves allowed us to show that two isoforms of caffeic acid/ 5-hydroxyferulic 3-O-methyltransferase (COMT) accumulated mostly at 10 to 20 cm from the leaf point of insertion and that drought resulted in a shift of this region of maximal accumulation toward basal regions. We showed that this shift was due to the combined effect of reductions in growth and in total amounts of COMT. Several other enzymes involved in lignin and/or flavonoid synthesis (caffeoyl-CoA 3-O-methyltransferase, phenylalanine ammonia lyase, methylenetetrahydrofolate reductase, and several isoforms of S-adenosyl-L-methionine synthase and methionine synthase) were highly correlated with COMT, reinforcing the hypothesis that the zone of maximal accumulation corresponds to a zone of lignification. According to the accumulation profiles of the enzymes, lignification increases in leaves of control plants when their growth decreases before reaching their final size. Lignin levels analyzed by thioacidolysis confirmed that lignin is synthesized in the region where we observed the maximal accumulation of these enzymes. Consistent with the levels of these enzymes, we found that the lignin level was lower in leaves of plants subjected to water deficit than in those of well-watered plants. [ABSTRACT FROM AUTHOR]

The regulation of anion loading to the shoot in maize (Zea mays) was investigated via an electrophysiological characterization of ion conductances in protoplasts isolated from the root stele. Two distinct anion conductances were identified. In protoplasts from well-watered plants, Z. mays xylem-parenchyma quickly-activating anion conductance (Zm-X-QUAC) was the most prevalent conductance and is likely to load the majority of NO3- and Cl- ions to the xylem in nonstressed conditions. Z. mays xylem-parenchyma inwardly-rectifying anion conductance was found at a lower frequency in protoplasts from well-watered plants than Zm-X-QUAC, was much smaller in magnitude in all observed conditions, and is unlikely to be such a major pathway for anion loading into the xylem. Activity of Z. mays xylem-parenchyma inwardly-rectifying anion conductance increased following a water stress prior to protoplast isolation, but the activity of the putative major anion-loading pathway, Zm-X-QUAC, decreased. Addition of abscisic acid (ABA) to protoplasts from well-watered plants also inhibited Zm-X-QUAC activity within minutes, as did a high free Ca2+ concentration in the pipette. ABA was also seen to activate' a Ca2+-permeable conductance (Z. mays xylem-parenchyma hyperpolarization activated cation conductance) in protoplasts from well-watered plants. It is postulated that the inhibition of anion loading into the xylem (an important response to a water stress) due to down-regulation of Zm-X-QUAC activity is mediated by an ABA-mediated rise in free cytosolic Ca2+. [ABSTRACT FROM AUTHOR]

The alleviating effect of silicon (Si) supply on aluminum (Al) toxicity was suggested to be based on ex or in planta mechanisms. In our experiments with the Al-sensitive maize (Zea mays) cultivar Lixis, Si treatment but not Si pretreatment ameliorated Al- induced root injury as revealed by less root-growth inhibition and callose formation. Si treatment did not affect monomeric Al concentrations in the nutrient solution, suggesting an in planta effect of Si on Al resistance. A fractionated analysis of Si and Al in the 1-cm root apices revealed that more than 85% of the root-tip Al was bound in the cell wall. Al contents in the apoplastic sap, the symplastic sap, and the cell wall did not differ between -Si and +Si plants. Si did not affect the Al-induced exudation of organic acid anions and phenols from the root apices. However, Al treatment greatly enhanced Si accumulation in the cell wall fraction, reducing the mobility of apoplastic Al. From our data we conclude that Si treatment leads to the formation of hydroxyaluminumsilicates in the apoplast of the root apex, thus detoxifying Al. [ABSTRACT FROM AUTHOR]

We present cellular- and ultracellular-level studies here to show developmental programmed cell death (PCD) of placentochalazal (P-C) cell layers in maternal pedicel tissue in developing caryopses of normal seed (Mn1) and in the invertase- deficient miniature (mn1) seed mutant in maize (Zea mays). PCD was evidenced by loss of nuclei and all subcellular membranous organizations in many P-C layers. The terminal deoxynucleotidyl transferase-mediated X-dUTP nick-end labeling (TUNEL) stain that is diagnostic of apoptotic-like PCD identified spatially and temporally two distinctive subdomains, which coincided with nucellar and integumental P-C layers based on their developmental origins. The early phase of PCD in the nucellar P-C was TUNEL negative and was specific to only the fertilized caryopses, indicating that the signaling for PCD in these maternal cells originated in the zygotic tissues. In fact, the initiation of PCD coincided with endosperm cellularization and was rapidly and coordinately completed prior to the beginning of the major storage phase in endosperm. Cell shape in these cell layers was also influenced by the genotype of filial endosperm. The later phase of PCD was restricted to the integumental P-C layers underneath the nucellar cells and was TUNEL positive in both genotypes. The two subdomains of the P-C layers were also distinguishable by unique cell wall-associated phenolic compounds. Based on collective evidence, we infer that the nucellar PCD may have osmolytic etiology and may lead to activation of the post-phloem transport function of the P-C layer, whereas the integumental PCD was senescent related, in particular, protecting the maturing seed against microbes that may be transported from the maternal tissue. [ABSTRACT FROM AUTHOR]

Previous studies indicated that the deficiency of starch-branching enzyme (SBE) Ia in the single mutant sbe1a::Mu (sbe1a) has no impact on endosperm starch structure, whereas the deficiency of SBEIIb in the ae mutant is well known to reduce the branching of starch. We hypothesized that in maize (Zea mays) endosperm, the function of SBEIIb is predominant to that of SBEIa, and SBEIa would have an observable effect only on amylopectin structure in the absence of SBEIIb. To test this hypothesis, the mutant sbe1a was introgressed into lines containing either wx (lacking the granule-bound starch synthase GBSSI) or ae wx (lacking both SBEIIb and GBSSI) in the W64A background. Both western blotting and zymogram analysis confirmed the SBEIa deficiency in sbe1a wx and sbe1a ae wx, and the SBEIIb deficiency in ae wx and sbe1a ae wx. Using zymogram analysis, no pleiotropic effects of sbe1a genes on SBEIIa, starch synthase, or starch-debranching enzyme isoforms were observed. High- performance size exclusion chromatography analysis shows that the chain-length profiles of amylopec tin as well as β-limit dextrin were indistinguishable between wx and sbe1a wx, whereas significant differences for both were observed between ae wx and sbe1a ae wx, suggesting an effect of SBEIa on amylopectin biosynthesis that is observable only in the absence of SBEIIb. The amylopectin branch density and the average number of branches per cluster were both higher in endosperm starch from sbe1a ae wx than from ae wx. These results indicate possible functional interactions between SBE isoforms that may involve enzymatic inhibition. Both the cluster repeat distance and the distance between branch points on the short intracluster chains were similar for all genotypes however, suggesting a similar pattern of individual SBE isoforms in cluster initiation and the determination of branch point location. [ABSTRACT FROM AUTHOR]

The NB mitochondrial genome found in most fertile varieties of commercial maize (Zea mays subsp. mays) was sequenced. The 569,630-bp genome maps as a circle containing 58 identified genes encoding 33 known proteins, 3 ribosomal RNAs, and 21 tRNAs that recognize 14 amino acids. Among the 22 group II introns identified, 7 are trans-spliced. There are 121 open reading frames (ORFs) of at least 300 bp, only 3 of which exist in the mitochondrial genome of rice (Oryza sativa). In total, the identified mitochondrial genes, pseudogenes, ORFs, and cis-spliced introns extend over 127,555 bp (22.39%) of the genome. Integrated plastid DNA accounts for an additional 25,281 bp (4.44%) of the mitochondrial DNA, and phylogenetic analyses raise the possibility that copy correction with DNA from the plastid is an ongoing process. Although the genome contains six pairs of large repeats that cover 17.35% of the genome, small repeats (20-500 bp) account for only 5.59%, and transposable element sequences are extremely rare. MultiPip alignments show that maize mitochondrial DNA has little sequence similarity with other plant mitochondrial genomes, including that of rice, outside of the known functional genes. After eliminating genes, introns, ORFs, and plastid-derived DNA, nearly three-fourths of the maize NB mitochondrial genome is still of unknown origin and function. [ABSTRACT FROM AUTHOR]

Maize seedling water relations and abscisic acid (ABA) levels were measured over 24 h of root chilling (5.5 °C). At 2.5 h into chilling, leaf ABA levels increased by 40× and stomatal conductance (gs) decreased to 20% compared with prechill levels. Despite a rapid gs response to root chilling, leaf water potential (ΨL) of chilled seedlings decreased to −2.2 MPa resulting in a complete loss of turgor potential (ψp). Ineffective gs control early in chilling resulted from decreased root hydraulic conductance (Lr) due to increased water viscosity and factor(s) intrinsic to the roots. After 24 h chilling, ΨL and ψp of chilled seedlings recovered to control levels due to stomatal control of transpiration and increased Lr. The impact of the temporal changes in gs and Lr on maize seedling water relations during chilling was analysed using a simple, quantitative hydraulic model. It was determined that gs is critical to stabilizing ΨL at non-lethal levels in chilled seedlings at 2.5 h and 24 h chilling. However, there was also a significant contribution due to increased Lr at 24 h chilling so that ψp increased to control levels. As a first step in determining the factor(s) responsible for the increase in Lr, cDNA microarrays were used to quantify the transcript levels of eight aquaporins obtained from mature root tissue at 24 h chilling. None of these were significantly up-regulated, suggesting that the increase in Lr was not due to regulation of these aquaporins at the transcriptional level. [ABSTRACT FROM PUBLISHER]

Some native subsistence farmers in South Africa store maize (Zea mays L.) cobs over a fireplace and subject the seeds to smoke and heat. Taro (Colocasia esculenta L. Schott.) propagules are maintained in dry pits for one month, in layers separated by grass straw, and water is prevented from contacting them. These methods have been used together with others to maintain landraces for centuries, but they have largely been abandoned with no modern technology replacements. The objective of this study was to examine the effects of the maize and taro storage methods on the quality of planting material. Experiments were conducted on three subsistence farms located in KwaZulu-Natal, and at the University of KwaZulu-Natal, South Africa. Two maize landraces, yellow and white, were subjected to the smoke-over-firs storage method for five months during the normal off-season period for maize production in the location. Control maize seeds were stored in unsealed containers away from fire and smoke. Taro propagules of different sizes (80–100g corm-1, 40–60g corm-1 and 20–30g corm-1) were compared for storsbility in dry pits, in layers separated by grass straw, for one month. Subsequently, sprouted corns were stored in dry conditions to allow shoot development. During maize seed storage, water content was determined monthly. Maize seed quality was determined by viability, germination and seedling vigour. Sprouting and rooting during taro pit storage, and main shoot development during air storage were used to determine taro propagule performance in storage. Seeds that were stored over fire and smoke showed higher germination and vigour that non-smoked seed. Sprouting and shooting of taro propagules were better in large propagules and the optimum storage depth was 35cm to 40cm. α-amylase activity increased during pit storage and declined to almost the pre-storage levels during shoot growth period outside the pits, in all corm sizes. It is concluded that smoke and heat storage improve maize seed quality and pit storage enhances taro propagules by inducing sprouting. Data from this study can be used to investigate the physiological and biochemical basis of seed and propagule quality enhancement, and possibly contribute to technological inventions that are based on indigenous knowledge systems. [ABSTRACT FROM AUTHOR]

Eukaryotic elongation factor 1A (eEF1A) appears to be a multifunctional protein because several biochemical activities have been described for this protein, in addition to its role in protein synthesis. In maize (Zea mays) endosperm, the synthesis of eEF1A is increased in o2 (opaque2) mutants, and its concentration is highly correlated with the protein-bound lysine content. To understand the basis of this relationship, we purified eEF1A isoforms from developing endosperm and investigated their accumulation and their functional and structural properties. Formation of three isoforms appears to be developmentally regulated and independent of the o2 mutation, although one isoform predominated in one high lysine o2 inbred. The purified proteins differ in their ability to bind F-actin in vitro, suggesting that they are functionally distinct. However, they share similar aminoacyl-tRNA-binding activities. Tandem mass spectrometry revealed that each isoform is composed of the four same gene products, which are modified posttranslationally by methylation and phosphorylation. The chemical differences that account for their different actin-binding activities could not be determined. [ABSTRACT FROM AUTHOR]

Prolamellar bodies (PLB) contain two photochemically active forms of the enzyme protochlorophyllide oxidoreductase POR-PChlide640 and POR-PChlide650 (the spectral forms of POR-Chlide complexes with absorption maxima at the indicated wavelengths). Resuspension of maize PLB in media with a pH below 6.8 leads to a rapid conversion of POR-PChlide650 to POR-PChlide640 and a dramatic re-organization of the PLB membrane system. In the absence of excess NADPH, the absorption maximum of the POR complex undergoes a further shift to about 635 nm. This latter shift is reversible on the re-addition of NADPH with a half-saturation value of about 0.25 mm NADPH for POR-PChlide640 reformation. The disappearance of POR-PChlide650 and the reorganization of the PLB, however, are irreversible. Restoration of low-pH treated PLB to pH 7.5 leads to a further breakdown down of the PLB membrane and no reformation of POR-PChlide650 . Related spectral changes are seen in PLB aged at room temperature at pH 7.5 in NADPH-free assay medium. The reformation of POR-PChlide650 in this system is readily reversible on re-addition of NADPH with a half-saturation value about 1.0 µm. Comparison of the two sets of changes suggest a close link between the stability of the POR-PChlide650 , membrane organization and NADPH binding. The low-pH driven spectral changes seen in maize PLB are shown to be accelerated by adenosine AMP, ADP and ATP. The significance of this is discussed in terms of current suggestions of the possible involvement of phosphorylation (or adenylation) in changes in the aggregational state of the POR complex. [ABSTRACT FROM AUTHOR]

Examines the underlying processes by which kernel set is regulated in maize by quantifying lead photosynthesis, sugars, starch, abscisic acid, and cytokinin in plants subjected to water deficit and shade. Nonstructural carbohydrate accumulation in the apical and basal florets at the pre-pollination stage; Alteration of zeatin-like cytokinin concentrations.

Inhibition of root growth and accumulation of putrescine caused by exogenous spermidine in roots of maize seedlings (Zea mays L., cv Samodek) were partially prevented by a concomitant treatment with dimethylthiourea (DMTU), that traps H[sub 2]O[sub 2] produced from spermidine by the activity of polyamine oxidase (PAO) in the apoplast. Treatment with spermidine caused a strong increase of ascorbate peroxidase (APX) gene expression, that was induced to a lesser extent by removing spermidine-generated H[sub 2]O[sub 2] by DMTU. Over-expression of APX was associated with increased APX activity in spermidine-treated seedlings whereas the addition of DMTU to spermidine completely prevented spermidine-induced increase of APX activity. Thus, DMTU permitted the demonstration that exogenous spermidine supplied to maize seedlings causes an oxidative stress and induces APX, a key enzyme of the antioxidant defence mechanism, through H[sub 2]O[sub 2], a spermidine catabolic product. [ABSTRACT FROM AUTHOR]

ABSTRACT Signalling process of water stress-induced abscisic acid (ABA) accumulation was investigated in maize (Zea mays L.) leaf and root tissues. Potent free-radical scavengers and reducing agents, N-acetyl cysteine (NAC) and cystein (Cys), significantly inhibited or nearly completely blocked dehydration-induced ABA accumulation. Dithiothreitol (DTT), a reducing agent but not a free-radical scavenger, also significantly inhibited such accumulation whereas solely free-radical scavengers, dimethyl sulphoxide (DMSO) and melatonin (Mela), had no effects. Moreover, water stress-induced ABA accumulation was not affected either by free radicals, such as superoxide anion and hydrogen peroxide, or by oxidants such as KIO4. These observations suggest that the blocking of water stress-induced ABA accumulation resulted from the reducing effect, rather than from anything associated with free radicals. The disulphide bond might be crucial to the reactivity of some signal element(s) in the signalling process of water stress-induced ABA accumulation. To test the hypothesis, we used a sulfhydryl modifier, iodoacetamide (IOA), and found that it nearly totally blocked the water stress-induced ABA accumulation. Furthermore, an impermeable sulfhydryl modifier, p-chloromercuriphenylsulphonic acid (PCMBS), could also inhibit the water stress-induced ABA accumulation in the leaf tissues. These results indicate that water stress-perception protein(s) or receptor(s) may be located on the plasmalemma and a sulfhydryl group in the extracellular domain is critical to the reactivity of the speculated water stress receptors. Cys, DTT and IOA did not lead to a decrease of the baseline ABA level, i.e. in non-stressed roots. Result indicates that their blocking of water stress-induced ABA accumulation occurred upstream of the ABA biosynthesis pathway, i.e. in the signalling process that initiates such accumulation. [ABSTRACT FROM AUTHOR]

Studies the effect of increased manganese-superoxide (SOD) dismutase on antioxidant enzymes and metabolites in maize. Progeny of the backcross of the primary transformants; Effects of elevated SOD on cold tolerance and antioxidant defenses.

This study investigated several independent variables affecting the expansion volume of microwave popcorn; (a) different hybrids were used, (b) hybrids were popped at different moisture contents, (c) microwave ovens with various wattages were employed, and (d) kernels were separated by size. The greatest expansion volume was achieved with Hunt-Wesson 214 at 11% moisture. Overall, the large-capacity bag and the 1000-watt microwave oven produced the greatest expansion volume. Medium-sized kernels produced the greatest expansion volume. [ABSTRACT FROM AUTHOR]

Deals with a study which examined the distribution of aquaporin in the plasma membrane of maize root protoplasts. Function of aquaporins; Materials and methods; Presentation of results; Conclusion.

Summary A family of homeo box genes with cell layer-specific expression patterns defining subdomains of the embryo and certain meristems has been isolated from maize. These genes encode proteins from the class of plant specific homeo domain-leucine zipper (HD-Zip) transcription factors containing the previously described ZmOCL1 protein, and have been designated ZmOCL2 , ZmOCL3 , ZmOCL4 and ZmOCL5 . ZmOCL3 , ZmOCL4 and ZmOCL5 , like ZmOCL1 , showed essentially L1 or epidermis-specific expression. However, each gene was expressed in a distinct region of the embryonic protoderm during early development, with ZmOCL3 showing suspensor-specific expression, ZmOCL4 transcripts being localized to the adaxial face of the embryo proper and ZmOCL5 showing a more abaxial expression pattern. All three genes were also expressed in vegetative, inflorescence and floral apices, although ZmOCL3 transcripts were excluded from meristems and very young organ primordia. In contrast, ZmOCL2 expression was entirely meristem-specific and was excluded from the L1 layer, appearing instead to be largely restricted to a cell layer directly beneath the L1, especially in floral meristems. This expression pattern is unprecedented and may indicate that cell-layer organization in maize meristems is more complex than that suggested by the classical L1/L2 (outer cell layer/inner cell mass) model. These differing expression patterns indicate that the members of the HD-ZipIV family of maize may not only play roles in defining different regions of the epidermis during embryonic development, but could also be responsible for maintaining cell-layer identity in meristematic regions. [ABSTRACT FROM AUTHOR]

Analyzes cell wall adaptations to multiple environmental stresses in maize roots. Characterization of the soil substrates; Thickening of the cell wall; Chemical composition of the cell walls from the endodermis to the hypodermis; Root morphology and structure; High amount of lignin and suberin in the cell walls.

Here we report the cloning of a sucrose transporter cDNA from maize (Zea mays L.) and an analysis of the expression of the gene. A cDNA clone (ZmSUT1) was identified as a sucrose transporter cDNA from its sequence homology at the amino acid level to sucrose transporters that have been cloned from other higher plant species. Based on the results of genomic Southern hybridization, ZmSUT1 appears to be a single copy gene. A Northern blot analysis of seedlings and leaf blades suggests that the sucrose transporter is involved in the export of accumulated carbohydrates from source leaf blades. From the measurements of transcript levels and carbohydrate contents in mature leaf blades, we propose that the expression of the gene for the maize sucrose transporter is positively regulated by the amounts of soluble sugars such as sucrose arid glucose in source leaves of maize. In addition, based on the tissue specificity of the expression of the gene in maize plants at the reproductive stage, it is possible that the sucrose transporter acts in sink tissues such as pedicels as well as in source tissues such as leaf blades. [ABSTRACT FROM AUTHOR]

The relationship between autolytic degradation of β(1–3),(1–4)-D-glucan and acid pH-induced extension of isolated Zea mays cell walls has been investigated using a constant-load extension technique. Acidic buffer (4.5) was able to induce an additional extension (Ea) on cell walls already extended at pH 6.8 buffer under a 20 g-mass load, indicating that the additional extension (Ea) was the parameter that better represented the effect of the different treatments on the mechanical properties of maize coleoptile cell walls. The additional extension in response to acidic pH was higher when cell walls had been previously autolysed for 24 h at pH 5.5. Furthermore, the acid-pH effect was dependent on the presence during the constant load extension of some thermo-labile factors, suggesting the participation of expansins. Acid pH increased Ea of native cell walls through an increase in the plastic extension (Ep) in agreement with a one step mechanism leading directly to irreversible (plastic) wall extension as suggested by Cosgrove (1977). The autolytic degradation of β(1–3), (1–4)-D-glucan was also able to modify the mechanical properties of maize coleoptile cell walls increasing its elastic extension (Ee) in response to pH 4.5 buffer but that modification only leads to an increase in wall extension when expansins are active, suggesting a cooperation between β-glucan turnover and expansin action. [ABSTRACT FROM AUTHOR]

Transgenic maize (Zea mays L.) plants have been generated by particle gun bombardment that overproduce an Arabidopsis thaliana iron superoxide dismutase (FeSOD). To target this enzyme into chloroplasts, the mature Fesod coding sequence was fused to a chloroplast transit peptide from a pea ribulose-1,5-bisphosphate carboxylase gene. Expression of the chimeric gene was driven by the CaMV 35S promoter. Growth characteristics and in vitro oxidative stress tolerance of transgenic lines grown in control and chilling temperatures were evaluated. The transgenic line with the highest transgenic FeSOD activities had enhanced tolerance toward methyl viologen and had increased growth rates. [ABSTRACT FROM AUTHOR]

Studies whole-plant gas exchange and stem water potential throughout the water deficit stress cycle and during the subsequent recovery period upon rehydration in maize hybrids. Gas exchange and stem water potential measurements; Canopy transpiration; Canopy phytosynthesis; Water use efficiency; Aboveground canopy respiration and gross canopy photosynthesis.

A field experiment was conducted to evaluate the effect of long-term exogenous sucrose supply on aspects of corn plant physiology and development during the grain filling period. Concentrated sucrose solution was supplied to corn (Zea mays L.) stems by an injection technique. This injection technique delivered pressurized solutions through syringe needles sealed to the stem with latex. The pressure was applied to the syringe plunger with ceramic construction bricks. Solutions containing sucrose at 0, 150, and 300 g L-1 were injected over a 32 day period encompassing the duration of the active grain filling period. The primary ears of plants injected with sucrose produced approximately 50 % more kernels and 30 % more grain weight than those injected with distilled water. The injected internode was also considerably heavier (56%) for plants receiving 300 g sucrose L-1 than plants receiving distilled water. For all measured variables, plants injected with distilled water were either not different from or had larger values than the non-injected controls. After one week sucrose injection caused photosynthetic inhibition (as measured by chlorophyll fluorescence) in the leaf just above the ear and the ear leaf, and this was more severe for plants receiving 300 g sucrose L-1 than for those receiving 150 g sucrose L-1. For sucrose injected plants, the increased size of the primary ear was concomitant with a large decrease in grain production by the secondary ear and an overall decrease in per plant grain production. These results suggest that the mechanisms for signalling between sinks (the primary and secondary ears) and the primary sink and the source (leaves) are different. [ABSTRACT FROM AUTHOR]

Chloroplast ATPase (CF1) was isolated from spinach, pea and maize thylakoids by EDTA extraction followed by anion-exchange chromatography. CF1 was purified and resolved by HPLC into integral CF1, and CF1 lacking the &delta ; & ε subunits: CF1(-&delta ;) and CF1(-&ε;). Washing Mono-Q-bound CF1 with alcohol-containing buffers followed by elution without alcohol produced the β subunit and in separate peaks CF1(-&delta ;) and CF1(-ε). Elution from Mono Q in the presence of tenside yielded a β &delta ; fragment, CF1(-&delta ;) and CF1(-&delta ; ε). Chloroplasts were CF1-depleted by EDTA extraction. Reconstitution of photophosphorylation in these 'EDTA vesicles' was obtained by addition of CF1 and its fragments. CF1, CF1(-&delta ;) and CF1(-&delta ; ε) were active with cross-reactivity between spinach, pea and maize. &delta ;-containing CF1 always reconstituted higher activities than &delta ;-deficient CF1. The β &delta ; fragment and dicyclohexylcarbodiimide (DCCD)-inhibited CF1 also were reconstitutively active while β and DCCD-inhibited CF1(-&delta ;) were not. These results support the notion that subunit &delta ; can function as a stopcock to the CF0 proton channel as proposed by Junge, W., Hong, Y. Q., Qian, L. P. and Viale, A. [(1984) Proc. Natl Acad. Sci. USA 81, 3078-3082]. [ABSTRACT FROM AUTHOR]

Shows the localization of sucrose synthase activity in developing maize kernels by in situ enzyme histochemistry. Correlation between sucrose synthase activity and starch synthesis during kernel development; Changes in sucrose synthase distribution patterns during kernel development.

The cell and subcellular localization of plasma membrane P-type H+-ATPase in root apices from Zea mays L. (maize) seedlings was investigated by immunofluorescence microscopy. H+-ATPase was highly abundant in cells of epidermal and endodermal tissues as well as in phloem companion cells. Strong immunodecoration was also observed in a subset of xylem parenchyma cells forming a connection between the endodermis and metaxylem. Evidence that these cells are equipped for active membrane transport raises the potential that they play a special role in xylem loading. Significant amounts of H+-ATPase were also observed in outer cortical cells. Progressively less H+-ATPase was seen in cortical cells further away from the root-soil interface. The H+-ATPase was asymmetrically localized within both epidermal and outer cortical cells, with higher levels detected on cell surfaces closest to the root-soil interface. This asymmetric localization of H+-ATPase is consistent with the hypothesis that transport systems for uptake of nutrients from the soil are selectively targeted to cell surfaces most exposed to nutrients. [ABSTRACT FROM AUTHOR]

The effects of abscisic acid (ABA) and high osmoticum on catalase (Cat) gene expression in maize have been examined. Each Cat gene responds differently to ABA and osmotic stress at different developmental stages and in different tissues. Cat1 transcript accumulates to high levels in developing and germinating embryos, and in leaves. In embryos, Cat2 and Cat3 transcripts are up-regulated only at very high ABA concentrations during late embryogenesis and in response to various concentrations of ABA in germinating embryos. Cat3 transcript is down-regulated by ABA and osmotic stress in leaves. Accumulation of Cat1 transcript in response to osmotic stress is a consequence of increased endogenous ABA levels. Our data suggest that two separate pathways might be involved in the ABA-mediated induction of Cat1. The Vp1 trans-acting factor is required for maximum induction of Cat1 transcript in wild-type (Vp1/—) and in W64A developing embryos; however, Vp1 is not required for inducing the Cat1 transcript in vp1 mutant developing embryos, nor in W64A germinating embryos or in leaves. Given the fact that the Cat genes have a known function, we hypothesize that the increase in Cat gene products in response to ABA is due, in part, to ABA-mediated metabolic changes leading to changes in oxygen free radical levels, which in turn, lead to the induction of the antioxidant defense system. [ABSTRACT FROM AUTHOR]