Plant defense against fall armyworm in micro‐sympatric maize (Zea mays ssp. mays) and Balsas teosinte (Zea mays ssp. parviglumis)

Maize [Zea mays L. ssp. mays (Poaceae)] was domesticated from Balsas teosinte (Zea mays ssp. parviglumis Iltis & Doebley) in present‐day Mexico. Fall armyworm, Spodoptera frugiperda JE Smith (Lepidoptera: Noctuidae), is among the most important pests of maize in Mexico and Central America. We compared the strength of plant defenses against fall armyworm between micro‐sympatric landrace maize and Balsas teosinte in the field and laboratory. The field comparison, conducted in Mexico, consisted of comparing the frequency of fall armyworm infestation between young maize and Balsas teosinte plants in dryland agricultural fields in which Balsas teosinte grew as a weed. The laboratory comparison contrasted the performance of fall armyworm larvae provided a diet of leaf tissue excised from maize or Balsas teosinte plants that were intact or had been primed by larval feeding. In the field, maize plants were more frequently infested with fall armyworm than Balsas teosinte plants: over 3 years and three fields, maize was infested at a ca. 1.8‐fold greater rate than Balsas teosinte. In the laboratory, larval growth, but not survivorship, was differently affected by feeding on maize vs. Balsas teosinte, and on primed vs. intact plants. Specifically, survivorship was ca. 98%, and did not differ between maize and Balsas teosinte, nor between primed and intact plants. Larvae grew less on intact vs. primed maize, and similarly on intact vs. primed Balsas teosinte; overall, growth was 1.2‐fold greater on maize compared to Balsas teosinte, and on primed compared to intact plants. Parallel observations showed that the differences in growth could not be attributed to the amount of leaf tissue consumed by larvae. We discuss our results in relation to differences in the strength of plant defenses between crops and their ancestors, the relevance of unmanaged Balsas teosinte introgression in the context of fall armyworm defenses in maize, and whether greater growth of larvae on primed vs. intact plants signifies herbivore offense.     

Early responses to gibberellic acid in a dwarf maize mutant (Zea mays L. d 1)

Early effects of gibberellic acid (GA₃) (1–4 h treatment) on the ion ratios in a dwarf maize mutant (Zea mays L. d ₁) showing normal growth after hormone treatment, have been investigated by electron microprobe analysis. GA₃ exerts a different effect on the ion ratios in plastids, cytoplasm and vacuoles in short term experiments. The Cl content of chloroplasts and cytoplasm increases without a lag phase after GA₃ treatment. The K content of plastids increases after a lag phase of 2 h, whereas in the cytoplasm an increase can be observed immediately after GA₃ addition. The hormone has only little influence on the Ca content of the cell compartments investigated. Control experiments with water and the physiologically inactive GA₃ methylester confirm the specifity of the short-term actions of GA₃ on the ion ratios. The primary action of GA₃ at the membrane level is discussed.     

Interaction of maize (Zea mays) protein phosphatase 2A with tubulin

Immunological and biochemical evidence has been obtained for an interaction of maize protein phosphatase 2A (PP2A) holoenzyme with tubulin. Tubulin co-purifies with maize seedling PP2A. Affinity chromatography of the maize PP2A preparation on immobilized tubulin revealed two peaks of phosphorylase alpha phosphatase activity. In one of the peaks, the catalytic (C) and constant regulatory (A) subunits of PP2A were identified by Western blotting. The subunits (C and A) of PP2A were co-immunoprecipitated from maize seedlings homogenate by an anti-alpha-tubulin antibody. The interaction of plant PP2A with tubulin indicates a possible role of reversible protein phosphorylation in the dynamic structure of plant cytoskeleton.     

Genetics of resistance to the pink stem borer (Sesamia nonagrioides) in maize (Zea mays)

Our knowledge of the genetics of resistance to the pink stem borer ( Sesamia nonagrioides ) in maize ( Zea mays ) is restricted to a few crosses among maize inbreds. The objectives of this study were to enlarge our understanding of the genetics of traits related to damage by pink stem borer and yield under infestation and to use generation means analyses to compare per se and testcross performance for detecting epistatic effects. All generations, either per se or crossed to testers, were evaluated in a 10 × 10 triple lattice design under artificial infestation with S. nonagrioides in 2005 and 2006. Most traits fit an additive–dominance model; but evidence for epistasis for resistance and yield under infestation was shown. Epistasis, in general, did not appear to play an important role in the inheritance of yield under pink stem borer infestation. However, the epistasis contribution to maize yield performance could be important in some outstanding crosses such as EP42 × A637. Testcross generation means revealed epistatic effects undetected by the generation means analysis, but neither method was able to eliminate dominance effects that could prevail over epistatic effects.     

Bacterial communities associated with the rhizosphere of transgenic Bt 176 maize (Zea mays) and its non transgenic counterpart

The effect of transgenic Bt 176 maize on the rhizosphere bacterial community has been studied with a polyphasic approach by comparing the rhizosphere of Bt maize cultivated in greenhouse with that of its non transgenic counterpart grown in the same conditions. In the two plants the bacterial counts of the copiotrophic, oligotrophic and sporeforming bacteria, and the community level catabolic profiling, showed no significant differences; differences between the rhizosphere and bulk soil bacterial communities were evidenced. Automated ribosomal intergenic spacer analysis (ARISA) showed differences also in the rhizosphere communities at different plant ages, as well as between the two plant types. ARISA fingerprinting patterns of soil bacterial communities exposed to root growth solutions, collected from transgenic and non transgenic plants grown in hydroponic conditions, were grouped separately by principal component analysis suggesting that root exudates could determine the selection of different bacterial communities.     

Influence of phosphate status on phosphate uptake kinetics of maize (Zea mays) and soybean (Glycine max)

To obtain plants of different P status, maize and soybean seedlings were grown for several weeks in flowing nutrient solution culture with P concentrations ranging from 0.03–100 µmol P L^-1 kept constant within treatments. P uptake kinetics of the roots were then determined with intact plants in short-term experiments by monitoring P depletion of a 3.5 L volume of nutrient solution in contact with the roots. Results show maximum influx, I_max, 5-fold higher in plants which had been raised in solution of low compared with high P concentration. Because P concentrations in the plants were increased with increase in external P concentration, I_max was negatively related to % P in shoots. Michaelis constants, K_m, were also increased with increased pretreatment P concentration, only slightly with soybean, but by a factor of 3 with maize. The minimum P concentration, C_min, where net influx equals zero, was found between 0.06 and 0.3 µmol L^-1 with a tendency to increase with pretreatment P concentration. Filtration of solutions at the end of the depletion experiment showed that part of the external P was associated with solid particles.It was concluded that plants markedly adapt P uptake kinetics to their P status, essentially by the increase of I_max, when internal P concentration decreases. Changes of K_m and C_min were of minor importance.     

Modeling the tertiary structure of a maize (Zea mays ssp. mays) non-symbiotic hemoglobin.

The tertiary structure of a maize (Zea mays ssp. mays) non-symbiotic hemoglobin (Hbm) was modeled using computer tools and the known tertiary structure of rice Hb1 as a template. This method was tested by predicting the tertiary structure of soybean leghemoglobin a (Lba) using rice Hb1 as a template. The tertiary structures of the predicted and native Lba were similar, indicating that our computer methods could reliably predict the tertiary structures of plant Hbs. We next predicted the tertiary structure of Hbm. Hbm appears to have a long pre-helix A and a large CD-loop. The positions of the distal and proximal His are identical in Hbm and rice Hb1, which suggests that heme-Fe is hexacoordinate in Hbm and that the kinetic properties of Hbm and rice Hb1 are expected to be very similar, i.e. that Hbm has a high O2-affinity. Thermostability analysis showed that Hbm CD-loop is unstable and may provide mobility to amino acids located at the heme pocket for both ligand binding and stabilization and heme-Fe coordination. Analysis of the C-terminal half of Hbm showed the existence of a pocket-like region (the N/C cavity) where interactions with organic molecules or proteins could be possible. Lys K94 protrudes into the N/C cavity, suggesting that K94 may sense the binding of molecules to the N/C cavity. Thus, it is likely that the instability of the CD-loop and the possibility of binding molecules to the N/C cavity are essential for positioning amino acids in the heme pocket and in regulating Hbm activity and function.     

Early changes in root characteristics of maize (Zea mays) following seed inoculation with the PGPR Azospirillum lipoferum CRT1

The effect of direct inoculation of seeds with the plant growth promoting rhizobacteria (PGPR) Azospirillum lipoferum CRT1 was assessed on maize (Zea mays) grown for 35 days after sowing (d.a.s.) in controlled conditions (greenhouse) in a luvisol soil from south-eastern France. WhinRhizo^® software was used to describe the following changes in the root system morphology for each plant: distribution and average root diameter, root surface and the number of tips. The stress at breakage and stiffness of the roots in tension were also determined. Evaluation of biochemical components of roots was achieved by direct Attenuated Total Reflectance (or reflection) (ATR)-Fourier transform infrared (FTIR) on root section. Inoculated roots exhibited significantly larger numbers of tips and extending surface to rhizosphere when compared to controls. Measured mechanical parameters of inoculated roots showed a slight increase in rupture stress up to the largest diameter (1.2 mm) when compared to controls. Stiffness (Young’s modulus) values were nearly constant for inoculated plants with higher values than for non-inoculated plants at day 26 and day 35. Using Principal Components Analysis of ATR-FTIR profiles, the polysaccharide enrichment of inoculated roots compared to controls was found at day 35. Noticeable absorbance at wavenumber specific to aromatic ether (lignin) was observed in control plants. All these data had a pattern of immature root properties, when maize was inoculated with Azospirillum lipoferum CRT1. Observed modifications of root development are possibly conducive to unseen beneficial effects, like water retention, resistance to mechanical stress, or root litter quality. Studies on more mature plants are required to assess if the differences between inoculated and control plants would persist or become accentuated with time until harvest.     

Application of NMR-based metabolomics to the investigation of salt stress in maize (Zea mays)

Introduction – High salinity, caused by either natural (e.g. climatic changes) or anthropic factors (e.g. agriculture), is a widespread environmental stressor that can affect development and growth of salt‐sensitive plants, leading to water deficit, the inhibition of intake of essential ions and metabolic disorders. Objective – The application of an NMR‐based metabolic profiling approach to the investigation of saline‐induced stress in Maize plants is presented. Methodology – Zea Maize seedlings were grown in either 0, 50 or 150 mM saline solution. Plants were harvested after 2, 4 and 6 days (n = 5 per class and time point) and ¹H NMR spectroscopy was performed separately on shoot and root extracts. Spectral data were analysed and interpreted using multivariate statistical analyses. Results – A distinct effect of time/growth was observed for the control group with relatively higher concentrations of acetoacetate at day 2 and increased levels of alanine at days 4 and 6 in root extracts, whereas concentration of alanine was positively correlated with the shoot extracts harvested at day 2 and trans‐aconitic acid increased at days 4 and 6. A clear dose‐dependent effect, superimposed on the growth effect, was observed for saline treated shoot and root extracts. This was correlated with increased levels of alanine, glutamate, asparagine, glycine‐betaine and sucrose and decreased levels of malic acid, trans‐aconitic acid and glucose in shoots. Correlation with salt‐load shown in roots included elevated levels of alanine, γ‐amino‐N‐butyric acid, malic acid, succinate and sucrose and depleted levels of acetoacetate and glucose. Conclusions – The metabolic effect of high salinity was predominantly consistent with osmotic stress as reported for other plant species and was found to be stronger in the shoots than the roots. Using multivariate data analysis it is possible to investigate the effects of more than one environmental stressor simultaneously. Copyright © 2010 John Wiley & Sons, Ltd.     

Maturation of stamens and ovaries on cultured ear inflorescences of maize (Zea mays L.)

Observations were made on the maturation of stamens and ovaries from cultured maize (Zea mays L.) ear inflorescences. Immature ears (5.1–10.0 mm long) of maize were cultured in kinetin medium to study microsporogenesis and pollen maturation in developing stamens. Male spikelets developed on ears cultured in kinetin medium. Meiosis-I began by 7 days of culture in the developing anthers and the mature tri-nucleate pollen grains were developed by 20 days of culture. Further, kinetin was required in the culture medium for at least initial 5 days to obtain the microspores in differentiated stamens.To observe the embryosac formation in developed ovaries, ears were cultured in control, kinetin (10.1–15.0 mm long ears) medium, and kinetin + gibberellic acid (5.1–10.0 mm long ears) medium. Formation of embryosacs was noticed in the developed ovaries which were sampled after 20 days of culture. This differential flower development using two growth regulators provides an opportunity to uncover the biochemistry and physiology of micro- and mega-gametophyte development in maize.     

Tissue culture‐induced genomic alteration in maize (Zea mays) inbred lines and F1 hybrids

Genomic alteration is a common phenomenon associated with plant tissue culture, which often encompasses genetic changes and epigenetic modifications (e.g. cytosine methylation). Here, we studied genomic alteration in maize by assessing calli and regenerated plants derived from three inbred lines (M17, J7 and JC) and two pairs of reciprocal F1 hybrids (pair I: M17/J7 and J7/M17 and pair II: M17/JC and JC/M17). By employing two molecular markers, the amplified fragment length polymorphism and methylation‐sensitive amplified polymorphism, we found that both types of genomic alterations occurred in calli and regenerated plants of all the studied maize inbred lines and F1 hybrids, but the extent and pattern of changes varied substantially across the genotypes. Among the three inbred lines, M17 showed markedly higher frequencies of both genetic (from 2.1% to 3.8%) and methylation alterations (from 6.5% to 9.9%, by adding up the various patterns) than the other two lines which showed similar frequencies for both types of alterations (genetic: 0.5–1.8%, methylation: 2.1–3.7%). Of the two F1 hybrid pairs, while pair I showed genetic variation frequencies similar to that of the inbred parent with lower changing frequency and pair II was intermediate of those of the parents, both pairs showed frequencies of methylation alteration more or less intermediate of those of their inbred parental lines. Parent‐of‐origin effects in both genetic and methylation changes were detected in only one of the hybrid pairs (primarily pair II) for a given changing pattern. Statistical testing confirmed the genotypic difference in both genetic and methylation (hypomethylation) alterations among the regenerants. Taken together, it could be concluded that the frequency and pattern of both genetic and cytosine methylation alterations in maize tissue culture were largely genetic context‐dependent traits, but stochasticity also played an important part. F1 hybrids were not significantly more stable than their inbred parental lines under tissue culture conditions.     

Effect of pretreatment with hydrogen sulfide donor sodium hydrosulfide on heat tolerance in relation to antioxidant system in maize (Zea mays) seedlings

Hydrogen sulfide (H₂S) is a signal molecule that is involved in plant growth, development and the acquisition of stress tolerance including heat tolerance, but the mechanism of H₂S-induced heat tolerance is not completely clear. In present study, the effect of sodium hydrosulfide (NaHS), a H₂S donor, treatment on heat tolerance of maize seedlings in relation to antioxidant system was investigated. The results showed that NaHS treatment improved survival percentage of maize seedlings under heat stress in a concentration-dependent manner, indicating that H₂S treatment could improve heat tolerance of maize seedlings. To further study mechanism of NaHS-induced heat tolerance, catalase (CAT), guaiacol peroxidase (GPX), superoxide dismutase (SOD), glutathione reductase (GR) and ascorbate peroxidase (APX) activities, and glutathione (GSH) and ascorbic acid (AsA) contents in maize seedlings were determined. The results showed that NaHS treatment increased the activities of CAT, GPX, SOD and GR, and GSH and AsA contents as well as the ratio of reduced antioxidants to total antioxidants [AsA/(AsA+DHA) and GSH/(GSH +GSSG)] in maize seedlings under normal culture conditions compared with the control. Under heat stress, antioxidant enzymes activities, antioxidants contents and the ratio of the reduced antioxidants to total antioxidants in control and treated seedlings all decreased, but NaHS-treated seedlings maintained higher antioxidant enzymes activities and antioxidants levels as well as the ratio of reduced antioxidants to total antioxidants. All of above-mentioned results suggested that NaHS treatment could improve heat tolerance of maize seedlings, and the acquisition of this heat tolerance may be relation to enhanced antioxidant system activity.     

Distribution of the glutamine synthetase isozyme GSp1 in maize (Zea mays)

In maize (Zea mays L.), GSp1, the predominant GS isozyme of the developing kernel, is abundant in the pedicel and pericarp, but absent from the endosperm and embryo. Determinations of GSp1 tissue distribution in vegetative tissues have been limited thus far to root and leaves, where the isozyme is absent. However, the promoter from the gene encoding GSp1 has been shown to drive reporter gene expression not only in the maternal seed-associated tissues in transgenic maize plants, but also in the anthers, husks and pollen (Muhitch et al. 2002, Plant Sci 163: 865-872). Here we report chromatographic evidence that GSp1 resides in immature tassels, dehiscing anthers, kernel glumes, ear husks, cobs and stalks of maize plants, but not in mature, shedding pollen grains. RNA blot analysis confirmed these biochemical data. In stalks, GSp1 increased in the later stages of ear development, suggesting that it plays a role in nitrogen remobilization during grain fill.     

Acid phosphatase changes associated with development of male sterile and fertile maize (Zea mays L.)

Free and bound acid phosphatase were investigated biochemically and electrophoretically in male sterile and fertile plants. Scutella at the 72-hr seedling stage and anthers with enclosed reproductive tissue at the premeiosis, meiosis, and mature developmental stages were tested. Biochemical data show that while the total amount of free acid phosphatase behaved similarly in fertile and sterile plants, specific activities decreased in fertile plants and remained unchanged or increased in sterile plants. Total amounts of bound acid phosphatase increased significantly in fertile plants while specific activities decreased. In sterile anthers both specific activity and amount of bound acid phosphatase decreased significantly (except cms-S). Electrophoretic results indicated that the basic form of the enzyme was very similar in each location.Published with the approval of the Director of the West Virginia Agricultural Experiment Station as Scientific Paper No. 1573. Based in part on a dissertation by C. V. W. submitted to the Division of Plant Science, West Virginia University, Morgantown, West Virginia.     

Pyridine nucleotide-dependent ferricyanide reduction associated with isolated plasma membranes of maize (Zea mays L.) roots

Summary Plasma membranes (PM) from maize roots (Zea mays L.) were isolated by aqueous two-phase partitioning. The isolated membrane fraction showed a 4.6-fold enrichment in specific activity of the PM marker enzyme vanadate-sensitive, Mg²⁺-ATPase over a microsomal pellet collected at 50,000 × g. Activities of marker enzymes for mitochondria, endoplasmic reticulum, tonoplast, and Golgi apparatus were low or not detectable in the PM fraction. Quantitative morphometric analysis using the PM-specific silicotungstic acid stain showed the fraction to be > 92% PM vesicles. Using detergent stimulation of ATPase activity as a measure of structurally linked latency, greater than 90% of the PM vesicles were oriented with the cytoplasmic surface inside.An electron transport activity was investigated in the PM fraction. The rate of NADH oxidation in the absence of an artificial electron acceptor was < 167pkat·mg protein^–1; however, NADH catalysed the reduction of a variety of artificial electron acceptors including ferricyanide (2.6 nkat·mg protein^–1), cytochromec (0.8 nkat·mg protein^–1), a tetrazolium derivative (0.6 nkat·mg protein^–1) and dichlorophenol indophenol (0.4 nkat·mg protein^–1). While the NADH-dependent ferricyanide and dichlorophenol indophenol reductases were stimulated 6-fold by 0.025% (v/v) Triton X-100, the cytochromec and INT reductases were not greatly stimulated. Washing membranes with high salt significantly decreased the NADH-dependent, and eliminated the NADPH-dependent, ferricyanide reductase activity measured in the absence of detergent. These results suggest that NADH was oxidized on the extracytoplasmic surface of the membrane; however, a significant portion of this activity was extrinsic and may have originated from cytoplasmic contamination during isolation. The greater portion of the PM-associated NAD(P)H oxidation and/or ferricyanide reduction was catalyzed on sites not exposed to the outer surface of the membrane.Abbreviations BTP 1,3-bis[tris(hydroxymethyl)-methylamino]-propane - CHAPS 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate dihydrate - cytc cytochromec - DCIP 2,6-dichlorophenol indolphenol - INT 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyltetrazolium chloride - kat mole·s^–1 - Mes 2-(N-morpholino)ethanesulfonic acid - MF microsomal fraction - PM plasma membrane - STA silicotungstic acid - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol The mention of vendor or product does not imply that they are endorsed or recommended by U.S. Department of Agriculture over vendors of similar products not mentioned.     

Sloughing of root cap cells decreases the frictional resistance to maize (Zea mays L.) root growth

Root caps provide a protective layer in front of the meristemthat protects the meristem from abrasion by soil particles.The continuous production and sloughing of the root cap cellsmay be an adaptation to decrease the friction at the soil-rootinterface by acting as a low-friction lining to the channelformed by the root. Experiments were performed which providethe first direct evidence that such cell sloughing decreasesfrictional resistance to root penetration. The penetration resistance (force per unit crosssectional area)to maize roots, which were pushed mechanically into the soil,was compared with the penetration resistance to growing rootsand to 1 mm diameter metal probes (cone semi-angles of 7.5or 30). The pushed roots experienced only about 40% of thepenetration resistance experienced by the 7.5 metal probe thatwas pushed into the soil at the same rate. Thus, the frictionbetween the soil and the pushed root was much smaller than betweenthe soil and the metal probe. The penetration resistance tothe growing root was between 50% and 100% of that to the pushedroot, indicating that the relief of friction and slower rateof soil compression were more efficient around the growing root.SEM examination of the surface of roots pushed or grown intothe soil showed that numerous root cap cells had detached fromthe cap and slid for several millimetres relative to the root.The low friction properties of roots may be due largely to thelow coefficient of friction between sloughing root cap cells,and may be decreased further by intracellular mucilage secretions. Key words: Zea mays, root cap, frictional resistance, root penetration, cell sloughing     

Tribology of the root cap in maize (Zea mays) and peas (Pisum sativum)

Frictional resistance to a penetrating body can account for more than 80% of the total resistance to penetration of soil. We measured the frictional resistance between growing root caps of maize and pea and ground and smooth glass surfaces, which was linearly correlated to load, allowing calculation of the coefficient of kinetic friction and adhesion. Coefficients of kinetic friction between the root caps and the ground and smooth glass surfaces were approximately 0.04 and 0.02, respectively, the first measurements of the frictional properties of root tips at rates approaching those of root elongation, and an order of magnitude smaller than those previously reported. Results suggest that roots are well designed for penetrating soil, and encounter only small frictional resistance on the root cap. These data provide important parameters for modelling soil stresses and deformation around growing root tips.