Effect of salicylic acid on nitrite reductase and glutamate dehydrogenase activities in maize roots

The effects of 0.01 to 5 m M salicyclic acid on the increase in nitrite reductase or glutamate dehydrogenase activities in maize roots by nitrate or ammonium respectively, were examined. Nitrite reductase activity was inhibited by the highest concentration of the acid. The activity of NADH-glutamate dehydrogenase was stimulated slightly (but consistently) by the lowest concentration and was inhibited by higher concentrations. Total protein content was also inhibited at high concentrations. When the crude enzyme extract was stored at 25°C in light, the glutamate dehydrogenase activity in the control decreased after 4 h of incubation. Low concentrations of the acid had no effect on this decrease but higher concentration accelerated the process. The divalent cations Caz²⁺, Mn²⁺, Mg²⁺ and Zn²⁺ protected against loss of enzyme activity during storage, both in the absence and presence of the acid. The inhibitory effect of 5 m M salicylic acid on glutamate dehydrogenase activity is apparent due to interference with the activity of the enzyme rather than with its synthesis.     

Influence of genotype and texture on zein content in endosperm of maize grains

The effect of genotypes and texture on the content of proteins in maize grains was examined by assessing absolute amounts of six protein fractions in the whole endosperms of four wild‐type lines with high protein content and four quality protein maize (QPM) varieties and for hand‐dissected hard and soft endosperm regions from eight other lines. As previously reported for six wild‐type lines and their opaque‐2(o2) versions, zeins were predominant for all genetic backgrounds and all types of endosperms. From these data and others the amounts of zeins and true proteins (crude proteins free of non‐protein nitrogen) in developing and mature endosperms of wild‐type lines were correlated. The data points for zeins from hard endosperms lay between the regression line and the upper limit of confidence area. Those for zeins from soft endosperms were located at the lower part of confidence area and on a level with the points corresponding to the most immature endosperms. Furthermore, some data points for zeins from o2 and QPM samples lay near the lower limit while the others were outside the confidence area. This suggested an initial zein accumulation dependent on the genotype at a low relative rate, followed by an accumulation at higher rate. The conditions used for isolating and quantitating zeins are discussed.     

Regulation of glutamate dehydrogenase activity by amino acids in maize seedlings

Root or secondary leaf segments from maize ( Zea mays L. cv. Ganga safed-2) seedlings were incubated with 9-amino acids and two amides separately, each at 5 m M for 24 h, to study their effects on glutamate dehydrogenase (GDH) activity. Most of the compounds tested inhibited the specific activity of NADH-GDH and increased that of NAD⁺-GDH in the roots in the presence as well as in the absence of ammonium. In the leaves, such effects were recorded only with a few amino acids. Total soluble protein in the root and leaf tissues increased with the supply of most of the amino compounds. The effect of glutamate on enzyme activity and protein was concentration dependent in both tissues. When the enzyme extracts from root or leaf tissues were incubated with some of the amino acids, NADH-GDH declined while NAD⁺-GDH increased in most cases. The inhibition of NADH-GDH increased with increasing concentration of cysteine from 1 to 5 m M . The experiments demonstrate that most of the amino acids regulated GDH activity, possibly through some physicochemical modulation of the enzyme molecule.     

Lax midrib1-O, a systemic, heterochronic mutant of maize

Lxm1-O, a dominant EMS (ethyl methanesulfonate) induced mutation in maize (Zea mays, Poaceae), was originally reported to affect the blade/sheath boundary over the midrib region of the leaf. Here we present a more extensive analysis of the Lxm phenotype in nine different inbred lines. Lxm leaves are longer and narrower, and can initiate ectopic leaves. Additionally, Lxm1-O affects all plant organs observed. Compared to wild-type siblings, Lxm plants have fewer nodes, basal displacement of reproductive structures, and advance more quickly to the reproductive phase. We address questions as to whether Lxm1-O abbreviates a specific developmental phase, using hair, wax, and ear node data. We found that each phase was affected, although to varying degrees, depending on the inbred line. We interpret Lxm1-O to be a heterochronic mutation, causing the developmental acceleration of each phase of the shoot. Lxm1-O is novel, since other systemic heterochronic maize mutants prolong the juvenile phase, thereby extending shoot development. We discuss the importance of heterochronic mutations in the context of morphological evolution.     

European and African maize cultivars differ in their physiological and molecular responses to mycorrhizal infection

Physiological and molecular responses to phosphorus (P) supply and mycorrhizal infection by Glomus intraradices were compared in European (River) and African (H511) maize (Zea mays) cultivars to examine the extent to which these responses differed between plants developed for use in high- and low-nutrient-input agricultural systems. Biomass, photosynthetic rates, nutrient and carbohydrate contents, mycorrhizal colonization and nutrient-responsive phosphate transporter gene expression were measured in nonmycorrhizal and mycorrhizal plants grown at different inorganic phosphorus (P(i)) supply rates. Nonmycorrhizal River plants grew poorly at low P(i) but were highly responsive to mycorrhizal infection; there were large increases in biomass, tissue P content and the rate of photosynthesis and a decline in the expression of phosphate transporter genes. Nonmycorrhizal H511 plants grew better than River plants at low P(i), and had a higher root : shoot ratio. However, the responses of H511 plants to higher P(i) supplies and mycorrhizal infection were much more limited than those of River plants. The adaptations that allowed nonmycorrhizal H511 plants to perform well in low-P soils limited their ability to respond to higher nutrient supply rates and mycorrhizal infection. The European variety had not lost the ability to respond to mycorrhizas and may have traits useful for low-nutrient agriculture where mycorrhizal symbioses are established.     

Tissue distribution and developmental patterns of NADH-dependent and ferredoxin-dependent glutamate synthase activities in maize (Zea mays) kernels

Both NADH-dependent glutamate synthase (NADH-GOGAT, EC 1.4.1.14) and ferredoxin-dependent glutamate synthase (Fd-GOGAT, EC 1.4.7.1) activities were present in the endosperm, embryo, pedicel and pericarp of maize ( Zea mays L. var. W64A × A619) kernels. The endosperm contained the highest proportions of each activity on a per tissue basis. In the endosperm, NADH-GOGAT and Fd-GOGAT activities increased 12- and 2.5-fold, respectively, during early zein accumulation. NADH-GOGAT and Fd-GOGAT activities were expressed in the upper, middle and lower portions of the endosperm in a manner that paralleled but preceded zein accumulation. Maize endosperm NADH-GOGAT was purified 159-fold using ammonium sulfate fractionation, anion exchange chromatography and dye-ligand chromatography. Apparent K_m values for glutamine, α-ketoglutarate and NADH were 850, 19 and 1 μM, respectively. The results are consistent with endosperm GOGAT functioning to redistribute nitrogen from glutamine, the predominant nitrogenous compound delivered to the endosperm, into other amino acids needed for storage protein synthesis.     

The effect of abscisic acid on cell growth, cell division and DNA synthesis in the maize root meristem

Cis -abscisic acid (ABA), when applied to maize ( Zea mays L. cv. LG 11) roots, decreases the rates of cell growth and cell division in the meristem. It also decreases the rate at which nuclei become labelled with [³H]-thymidine and enter mitosis. Removing the root cap accelerates the entry of nuclei into the DNA synthetic phase of the mitotic cycle and enhances the rate of cell proliferation in the quescent centre. ABA diminishes these effects, but does not suppress them. Thus, ABA cannot wholely substitute for the presence of a cap. One of the primary effects of applied ABA is to retard cell enlargement which may in turn affect the rate of cell division; natural endogenous ABA may act similarly. ABA might in this way assist in maintaining the quiescent centre in intact roots, but cannot be the sole agent involved.     

The relationship between respiration rate and peroxidase activities in maize root mitochondria

In the present study we provide the evidence of different respiration rates and peroxidase activities in maize (Zea mays L.) mitochondria isolated from germinated seeds and roots of 2-week-old seedlings. The negative relationships between mitochondrial respiration rate measured with NADH as substrate and activities of peroxidases that oxidized NADH in both oxidative and peroxidative cycles were found. The possible role of peroxidase in the regulation of reactive oxygen species metabolism in expense of NADH oxidation was hypothesized.     

Effects of water stress on growth, osmotic potential and abscisic acid content of maize roots

Under water stress conditions, induced by mannitol solutions (0 to 0.66 M ) applied to the apical 12 mm of intact roots of Zea mays L. (cv. LG 11), a growth inhibition, a decrease in the osmotic potential of the cell sap and a significant accumulation of abscisic acid (ABA) were observed. When the roots were placed in a humid atmosphere after the stress, the growth rate increased again, even if elongation had been totally inhibited. Under a stress corresponding to an osmotic potential of -1.09 MPa in the solution, growth was totally inhibited, which means that the root cell turgor pressure was reduced to the yield threshold. These conditions led to the largest accumulation of ABA. The effect of water stress on the level of ABA was studied for three parts of the root. The greatest increase in ABA (about 10 fold) was obtained in the growth zone and this increase was apparently independent of the hydrolysis of the conjugated form. With a mannitol treatment of 1 h equivalent to a stress level of -1.39 MPa, a 4-fold increase in ABA efflux into the medium was obtained. These results suggest that there are interactions between water stress, root growth, osmotic potential and the ABA level. The growth under conditions of stress and the role of endogenous ABA in the control of plant metabolism, specially in the growth zone, are discussed.     

Ethylamine in maize callus: isolation, identification and first approach to the physiological role of its hyper-production

A primary amine, ethylamine, was isolated, purified and identified by ¹H-NMR from perchloric acid-extracts of maize embryogenic callus, where it occurred in high amount (2 μmol/g fresh weight, an amount ten-fold higher than that of other well-known amines such as polyamines) while only a faint trace was found in maize plant organs. Ethylamine amount was measured in different phases of callus proliferation and differentiation (somatic embryogenesis). Results indicated that ethylamine mostly accumulates in the proliferation phase. It decreased to very low concentration in cells that have acquired a new competence for differentiation or are already differentiated, except for in the developing somatic embryo phase. Undifferentiated callus appears to be an ethylamine hyper-accumulator.     

玉米离体根尖的多层滤纸床液体静止培养方法

设计建立了适于玉米根尖离体培养的多层滤纸床液体静止培养方法,培养的适宜体系为：1／4MS大量元素改良＋1／2MS微量元素＋IBA0.1-0.3mg/L,黑暗培养。该方法避免了传统液体培养通气状况不良的问题,玉米根的生长速度可达到1－2cm/d,分支和生长正常。该方法在控制条件下快速繁殖根系,成本低廉,简便易行,是根系发育和生理研究的理想实验体系。     

Effects of moderate drought on ascorbate peroxidase and glutathione reductase activities in mesophyll and bundle sheath cells of maize

Mesophyll and bundle sheath cells of maize leaves ( Zea mays L.) both contain the enzymes ascorbate peroxidase (AP; EC 1.11.1.11) and glutathione reductase (GR; EC 1.6.4.2) which are involved in hydrogen peroxide detoxification. Since bundle sheath cells of maize are deficient in photosystem II and have high CO₂ levels, oxidative stress may be less severe in these cells than in mesophyll cells. The present study was conducted to determine if AP and GR activity levels preferentially increase in mesophyll cells relative to bundle sheath cells when plants are subjected to moderate drought. Although drought inhibited the growth of greenhouse-grown plants, it did not affect the levels of protein, chlorophyll or AP. GR was unaffected by drought in whole leaf tissue and mesophyll cells, but did increase slightly in bundle sheath cells. This slight increase is of questionable biological importance. AP and GR activity levels were similar in mesophyll cells, bundle sheath cells and in whole leaf tissue. The data suggest that moderate drought has little effect on enzymes of the hydrogen peroxide scavenging system and that mesophyll and bundle sheath cells may be exposed to similar levels of hydrogen peroxide.     

Localization of the genes controlling B chromosome transmission rate in maize (Zea mays ssp. mays, Poaceae)

In previous papers we found that the frequency of B chromosomes in native races of maize varies considerably in different populations. Moreover, we found genotypes that control high and low transmission rates (TR) of B chromosomes in the Pisingallo race. In the present work crosses were made to determine whether the genes controlling B-TR are located on the normal chromosome set (As) or on the B chromosomes (Bs). We made female f.0B × male m.2B crosses between and within high (H) and low (L) B-TR groups. The Bs were transmitted on the male side in all cases. The mean B-TR from the progeny of f.0B (H) × m.2B (H) and f.0B (H) × m.2B (L) crosses was significantly higher than that from f.0B (L) × m.2B (L) and f.0B (L) × m.2B (H) crosses. The results show that the B-TR of the crosses corresponds to the H or L B-TR of the 0B female parents irrespective of the Bs of the male parent. This indicates that B-TR is genetically controlled by the 0B female parent and that these genes are located on the A chromosomes.     

Genome size and numerical polymorphism for the B chromosome in races of maize (Zea mays ssp. mays, Poaceae)

Twenty-one native populations (1120 individuals) of maize from Northern Argentina were studied. These populations, which belong to 13 native races, were cultivated at different altitudes (80-3620 m). Nineteen of the populations analyzed showed B chromosome (Bs) numerical polymorphism. The frequency of individuals with Bs varied from 0 to 94%. The number of Bs per plant varied from 0 to 8 Bs, with the predominant doses being 0, 1, 2, and 3. Those populations with varying number of Bs showed a positive and statistically significant correlation of mean number of Bs with altitude. The DNA content, in plants without Bs (A-DNA)(2n = 20), of 17 populations of the 21 studied was determined. A 36% variation (5.0-6.8 pg) in A-DNA content was found. A significant negative correlation between A-DNA content and altitude of cultivation and between A-DNA content and mean number of Bs was found. This indicates that there is a close interrelationship between the DNA content of A chromosomes and doses of Bs. These results suggest that there is a maximum limit to the mass of nuclear DNA so that Bs are tolerated as long as this maximum limit is not exceeded.     

Pattern of sulfate uptake during root elongation in maize: its correlation with productivity

The efficiency of sulfate uptake was evaluated in excised roots of 22 maize genotypes, 12 inbreds and 10 hybrids, in order to study the relationship between the kinetic characteristics of the uptake and the grain productivity. During root elongation, the uptake capacity showed a pulse which appeared when the root reached 1/3 to 1/2 of its final length. The size of the accumulated pool of sulfate was significantly correlated with the productivity. The kinetic parameters of the uptake, Vmax and Km, followed the same trend, showing pulses, whoxe maximum had the same position for Vmax and Km in each genotype. The variability with the genotype of the size and duration of the Vmax pulse was not strictly connected with that of Km. The main correlation between Vmax and Km patterns was the following; inbreds were generally characterized by low Vmax and low Km; hybrids by high Vmax and high Km. As a consequence, in most cases, the benefit of the heterotic stimulation of Vmax was contrasted by the loss of affinity of the transport system or the nutrients.     

高油、高淀粉玉米吸硫特性及施硫对其产量、品质的影响

研究了高油、高淀粉玉米硫素的吸收分配及施硫对籽粒产量、品质的作用。结果表明：在11250kg/hm^2的产量水平下,开花前硫素吸收量占总吸收量的百分比平均为57.53%,花后对硫的吸收较强;高油1号、长单26、掖单13每公顷吸硫量分别为：32.46kg、34.94kg,34.20kg。施硫能增加穗粒数和粒重（高油玉米粒重增加不显著）,并显著提高其产量,施硫22.5kg/hm^2（S1）能使籽粒含油率和蛋白质含量分别比对照提高9.05%和6.88%,蛋白质中清蛋白、球蛋白和谷蛋白含量提高,品质改善;施硫量增至90kg/hm^2(S2)时,籽粒含油率和蛋白质含量仍有提高,但蛋白质中醇溶蛋白含量增加,蛋白质品质降低。     

Light-dependent, chilling effects on phosphorylation of thylakoid proteins and consequences for associated photochemical activities in maize

When maize ( Zea mays L. cv. LG11) leaves are exposed to low temperatures and high light modifications to both photosystem 2 (PS2) and the light-harvesting chlorophyll a/b protein complex associated with photosystem 2 (LHC2) occur. This study examines the consequences of these modifications for phosphorylation of LHC2 and PS2 polypeptides and the associated changes in electron transport. Maize leaves were chilled at 5°C for 6 h under photon flux densities of 1 500 and 250 μmol m^-2 s^-1. Thylakoids were then isolated from the leaves and their abilities to phosphorylate LHC2 and PS2 polypeptides and modify electron transport activities were determined. Measurements of chlorophyll fluorescence induction in the thylakoids were also made. Thylakoids isolated from leaves chilled under high light and from leaves kept in the ambient growth environment had similar phosphoprotein profiles. However, polypeptide phosphorylation in thylakoids from the chilled leaves did not produce a decrease in PS2 electron transport. Chilling leaves under low light produced a decrease in the ability of isolated thylakoids to phosphorylate PS2, but not LHC2, polypeptides, which was not associated with any change in the phosphorylation-induced decrease in PS2 electron transport. Chilling under high, but not low, light appears to produce changes in membrane organisation that do not affect the ability of the thylakoids to phosphorylate PS2 and LHC2 polypeptides, but which do prevent the phosphorylation-induced decrease in excitation energy transfer from LHC2 to PS2.     

Efficiency of the first steps of sulfate utilization by maize hybrids in relation to their productivity

The genetic variability of the efficiency of the first steps of sulfate utilization and its correlation with productivity were evaluated in nine maize hybrids. ³⁵SO₄²⁻ uptake by excised roots, uptake by intact plant roots, translocation to leaves, and ATP sulfurylase in leaves were taken into account. Uptake rate by roots of intact plants did not show any pulse within 7 to 12 days from emergence, in contrast with the previously observed behaviour of excised roots during root elongation. The uptake rate of intact plants was positively correlated with that of excised roots, but the variability within the nine genotypes tested was less. Productivity was positively correlated with sulfate uptake by both intact plant and excised roots, the level of significance being higher in the first case. Translocation to leaves and ATP sulfurylase activity were not correlated to productivity. Therefore, in the case of sulfate, the grain yield of commonly cultivated maize hybrids appeared to be controlled more by the root uptake step than by the activation and translocation steps.     

The expansion of maize root-cap mucilage during hydration. 2. Observations on soil-grown roots by cryo-scanning electron microscopy

Expansion of root-cap mucilage during hydration was followed by cryo-scanning analytical microscopy of soil-grown roots of diploperennis and Zea mays. Roots examined directly from the soil have no expanded mucilage. Their condensed, unexpanded mucilage is in three domains, periplasmic, intercellular and peripheral to the cap tissue. Carbon concentration is the same in the three domains. During hydration there is no change in carbon concentration as the condensed mucilage moves through these three domains; however there is a sharp drop at the periphery where a gel phase transition occurs. The rate of expansion of the mucilage blob around the root tip is limited by the rate of this gel phase transition.