Immunological assay of phytochrome in small sections of roots and other organs of maize (Zea mays L.) seedlings

Phytochrome was determined in small sections of maize (Zea mays L.) seedlings by means of a highly specific double sandwich enzyme immunoassay which uses a monoclonal anti-phytochrome antibody for binding phytochrome and anti-phytochrome serum to detect the bound phytochrome. The distribution of phytochrome in maize seedlings was followed from germination to the 7th d after soaking the caryopses. Regions of high phytochrome accumulation were found in the coleoptile tip, the root cap and the shoot apex: the values for 5-d-old seedlings were 120, 80 and 70 g phytochrome per g fresh weight (or 0.91, 0.61 and 0.53 nmol·g^-1), respectively. The mesocotyl and the leaves contained relatively low amounts of phytochrome (less than 10 g·g^-1FW), which were almost uniformly distributed throughout these organs. As might be expected, regions of these organs adjacent to the shoot apex showed higher levels. The root, other than root tip, was almost devoid of phytochrome (0.2 to 0.5 g·g^-1). The general distribution of phytochrome in organs did not change during the development of seedlings. The amount of phytochrome, however, did fluctuate: up to the 5th or 6th d after soaking the caryopses, the levels increased in the regions of high phytochrome accumulation but thereafter decreased. After the 6th d the roots were 15 cm or longer and the coleoptiles became prone to penetration by primary leaves. The tips of adventitious roots, emerging after the 6th d, were also found to contain phytochrome. When the root cap was illuminated (4.3 W·m^-1), phytochrome was degraded as in illuminated shoots. Degradation of phytochrome in coleoptile, mesocotyl and shoot apex started with a lag phase but phytochrome degradation in the root cap and the leaves started without a lag. In contrast to shoot phytochrome, which was almost completely degraded under continuous illumination, about 3% of initial phytochrome was measured in root caps after 24 h continuous illumination. Some of the data, obtained by immunological measurements, may indicate differences between phytochrome, or its synthesis or degradation, in the root cap and shoots. The results are discussed with a view to different red-light-mediated responses of grass seedlings.Abbreviations ABTS 2,2-azino-bis(3-ethylbenz-thiazoline)-sulfonic acid - EIA enzyme immunoassay - PBS phosphatebuffered saline - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis     

Organic acid exudation as an aluminum-tolerance mechanism in maize (Zea mays L.)

In this study, the role of root organic acid synthesis and exudation in the mechanism of aluminum tolerance was examined in Al-tolerant (South American 3) and Al-sensitive (Tuxpeño and South American 5) maize genotypes. In a growth solution containing 6 M Al³⁺, Tuxpeño and South American 5 were found to be two- and threefold more sensitive to Al than South American 3. Root organic acid content and organic acid exudation from the entire root system into the bulk solution were investigated via high-performance liquid chromatographic analysis while exudates collected separately from the root apex or a mature root region (using a dividedroot-chamber technique) were analyzed with a more-sensitive ion chromatography system. In both the Al-tolerant and Al-sensitive lines, Al treatment significantly increased the total root content of organic acids, which was likely the result of Al stress and not the cause of the observed differential Al tolerance. In the absence of Al, small amounts of citrate were exuded into the solution bathing the roots. Aluminum exposure triggered a stimulation of citrate release in the Al-tolerant but not in the Al-sensitive genotypes; this response was localized to the root apex of the Al-tolerant genotype. Additionally, Al exposure triggered the release of phosphate from the root apex of the Al-tolerant genotype. The same solution Al³⁺ activity that elicited the maximum difference in Al sensitivity between Al-tolerant and Al-sensitive genotypes also triggered maximal citrate release from the root apex of the Al-tolerant line. The significance of citrate as a potential detoxifier for aluminum is discussed. It is concluded that organic acid release by the root apex could be an important aspect of Al tolerance in maize.Abbreviations SA3 South American 3, an Al-tolerant maize cultivar - SA5 South American 5, an Al-sensitive maize cultivar The authors would like to express their appreciation to Drs. John Thompson, Ross Welch and Mr. Stephen Schaefer for their training and guidance in the use of the chromatography systems. This work was supported by a Swiss National Science Foundation Fellowship to Didier Pellet, and U.S. Department of Agriculture/National Research Initiative Competitive Grant 93-37100-8874 to Leon Kochian. We would also like to thank Drs. S. Pandey and E. Ceballos from the CIMMYT Regional office at CIAT Cali, Colombia for providing seed for the maize varieties and inbred line.     

Interaction of gravi- and phototropic stimulation in the response of maize (Zea mays L.) coleoptiles

The influence of gravitropic stimulation upon blue-light-induced first positive phototropism for stimulations in the same (light source and center of gravity opposite to each other) and in opposing directions was investigated in maize cole-optiles by measuring fluence-response patterns. As a result of gravitropic counterstimulation, phototropic bending was transient with maximum curvature occurring 100 min after stimulation. On a horizontal clinostat, however, the seedlings curved for 20 h. Gravistimulation in the opposite direction acted additively upon blue-light curvature. Gravistimulation in the same direction as phototropic stimulation produced a complex behaviour deviating from simple additivity. This pattern can be explained by a gravitropically mediated sensitization of the phototropic reaction, an optimal dependence of differential growth on the sum of photo-and gravistimulation, and blue-light-induced inhibition of gravitropic curvature at high fluences. These findings indicate that several steps of photo-and gravitransduction are separate. Preirradiation with red light desensitized the system independently of applied gravity-treatment, indicating that the site of red-light interaction is common to both transduction chains.Abbreviations BL blue light - G⁺ stimulation by light and gravity in the same direction (i.e. light source and center of gravity opposite to each other) - G^- stimulation by light and gravity in opposing directions     

Nastic response of maize (Zea mays L.) coleoptiles during clinostat rotation

Rotation of unstimulated maize (Zea mays L.) seedlings on a horizontal clinostat is accompanied by a strong bending response of the coleoptiles towards the caryopsis, yielding curvatures exceding 100°. The corresponding azimuthal distribution shows two peaks, each of which is displayed by 30° from the symmetry axis connecting the shortest coleoptile and caryopsis cross sections. It is argued that this spatial pattern is not the result of two independent bending preferences, but caused by a one-peaked distribution encountering an obstacle in its central part and thus being split into the two subpeaks. The existence of one preferential direction justifies considering this response to be a nastic movement. Its time course consists of an early negative phase (coleoptiles bend away from the caryopsis) followed 2 h later by a longlasting positive bending towards the caryopsis. In light-interaction experiments, fluence-response curves for different angles between blue light and the direction of the nastic response were measured. These experiments indicate that blue light interacts with the nastic response at two levels: (i) phototonic inhibition, and (ii) addition of nastic and phototropic curvatures. It is concluded that phototropic and phototonic transduction bifurcate before the formation of phototropic transverse polarity. The additivity of nastic and phototropic responses was followed at the population level. At the level of the individual seedling, one observes, in the case of phototropic induction opposing nastic movement, three distinct responses: either strong phototropism, or nastic bending, or an avoidance response which involves strong curvature perpendicular to the stimulation plane. With time the nastic bending becomes increasingly stable against opposing phototropic stimulation. This can be seen from a growing proportion of seedlings exhibiting nastic bending when light is applied at variable intervals after the onset of clinostat rotation. At the transition from instability to stability, this type of experiment produces a high percentage of seedlings displaying the avoidance response. However, no cancelling resulting in zero curvature can be observed. It is concluded that the endogenous polarity underlying the nastic response is different in its very nature from the blue-light-elicited stable transverse polarity described earlier (Nick and Schäfer 1988 b).Abbreviation BL blue light (449 nm)     

Some relationships between contents of photosynthetic intermediates and the rate of photosynthetic carbon assimilation in leaves of Zea mays L.

The relationship between the gas-exchange characteristics of attached leaves of Zea mays L. and the contents of photosynthetic intermediates was examined at different intercellular partial pressure of CO₂ and at different irradiances at a constant intercellular partial pressure of CO₂. (i) The behaviour of the pools of the C₄-cycle intermediates, phosphoenolpyruvate and pyruvate, provides evidence for light regulation of their consumption. However, light regulation of phosphoenolpyruvate carboxylase does not influence the assimilation rate at limiting intercellular partial pressures of CO₂. (ii) A close correlation between the pools of phosphoenolpyruvate and glycerate-3-phosphate exists under many different flux conditions, consistent with the notion that the pools of C₄ and C₃ cycles are connected via the interconversion of glycerate-3-phosphate and phosphoenolpyruvate. (iii) The ratio of triose-phosphate to glycerate-3-phosphate is used as an indicator of the availability of ATP and NADPH. Changes of this ratio with CO₂ and with irradiance are compared with results obtained in C₃ leaves and indicate that the mechanism of regulation of carbon assimilation by light in leaves of C₄ plants may differ from that in C₃ plants. (iv) The behaviour of the ribulose-1,5-bisphosphate pool with CO₂ and irradiance is contrasted with the behaviour of these pools measured in leaves of C₃ plants.Abbreviations P _i intercellular CO₂ pressure - RuBP ribulose-1,5-bisphosphate - PEP phosphoenolpyruvate - triose-P triose phosphates - PGA glycerate-3-phosphate     

Spatial memory during the tropism of maize (Zea mays L.) coleoptiles

Photo- or gravitropic stimulation of graminean coleoptiles involves the formation of putative tropistic transverse polarities. It had been postulated that these polarities can be extended by stabilization to developmentally active polarities. Such polarities are known from unicellular spores and zygotes of lower plants and regeneration experiments in dicotyledonous plants. In coleoptiles, photo- or gravitropic stimulation results in stability to counterstimulation of equal strength (with only transient bending in the direction of the second stimulus), as a result of a directional memory, if the time interval between both stimuli exceeds 90 min. This directional memory develops from a labile precursor, which is present from at least 20 min after induction. Once it is stable, spatial memory is conserved for many hours. The formation of spatial memory involves at least one step not present in the common tropistic transduction chain. The spatial expression of memory as curvature is restricted to three distinct responses: (i) curving in the direction of the first stimulus (for time intervals exceeding 90 min); (ii) curving in the direction of the second stimulus (for time intervals shorter than 65 min); and (iii) zero-curvature (for time intervals between 65 and 90 min). This can be interpreted in terms of a stable transverse polarity, which is not identical with the putative tropistic transverse polarity, but might be an extension of it.     

Distribution of growth and proton efflux in gravireactive roots of maize (Zea mays L.)

Roots of Zea mays were maintained in a vertical orhorizontal position and the local elongation rate and H⁺ fluxes were measured using Sephadex beads containing a pH indicator. When the roots were kept horizontally, the growth of the lower side was strongly inhibited and that of the upper side slightly stimulated as compared with vertical roots. The H⁺ extrusion, which was greatest in the elongation zone, was strongly inhibited on the lower side and slightly stimulated on the upper side as compared with vertical roots.     

Separating the contribution of the upper and lower mesophyll to photosynthesis in Zea mays L. leaves

The appearance of transverse sections of maize leaves indicates the existence of two airspace systems serving the mesophyll, one connected to the stomata of the upper epidermis and the other to the stomata of the lower surface, with few or no connections between the two. This study tests the hypothesis that the air-space systems of the upper and lower mesophyll are separated by a defined barrier of measurable conductance. A mathematical procedure, based on this hypothesis, is developed for the quantitative separation of the contributions made by the upper and lower halves of the mesophyll to carbon assimilation using gasexchange data. Serial paradermal sections and three-dimensional scanning-electron-microscope images confirmed the hypothesis that there were few connections between the two air-systems. Simultaneous measurements of nitrous-oxide diffusion across the leaf and of transpiration from the two surfaces showed that the internal conductance was about 15% of the maximum observed stomatal conductance. This demonstrates that the poor air-space connections, indicated by microscopy, represent a substantial barrier to gas diffusion. By measuring the CO₂ and water-vapour fluxes from each surface independently, the intercellular CO₂ concentration (c _i) of each internal air-space system was determined and the flux between them calculated. This allowed correction of the apparent CO₂ uptake at each surface to derive the true CO₂ uptake by the mesophyll cells of the upper and lower halves of the leaf. This approach was used to analyse the contribution of the upper and lower mesophyll to CO₂ uptake by the leaf as a whole in response to varying light levels incident on the upper leaf surface. This showed that the upper mesophyll was light-saturated by a photon flux of approx. 1000 mol·m^-2·s^-1 (i.e. about one-half of full sunlight). The lower mesophyll was not fully saturated by photon fluxes of nearly double full sunlight. At low photon fluxes the c _i of the upper mesophyll was significantly less than that of the lower mesophyll, generating a significant upward flux of CO₂. At light levels equivalent to full sunlight, and above, c _i did not differ significantly between the two air space systems. The physiological importance of the separation of the air-space systems of the upper and lower mesophyll to gas exchange is discussed.Abbreviations and symbols A net leaf CO₂ uptake rate - A _upper ^app. and A _lower ^app. net rates of CO₂ uptake across the upper and lower surfaces - A _upper and A _lower derived net rates of CO₂ uptake by the upper and lower mesophyll - A _upward net flux of CO₂ from the lower to upper mesophyll - c _a, c _{a, upper} and c _{a, lower} the CO₂ concentrations in the air around the leaf above the upper surface and below the lower surface - c _N2O the concentration of N₂O in the air around the leaf - c _i, c _{i, upper} and c _{i, lower} the mesophyll intercellular CO₂ concentration of the whole leaf, the upper mesophyll and the lower mesophyll - g _i leaf internal conductance to CO₂ - g _s, g _{s, lower} and g _{s, upper} the stomatal conductance of the whole leaf, the lower surface and the upper surface - g the total conductance across the leaf - Q the photosynthetically active photon flux density     

Carbon metabolism and gas exchange in leaves of Zea mays L.

The aim of this work was to investigate the mechanism of formation of triose phosphates and 3-phosphoglycerate during photosynthetic induction in leaves of Zea mays. Simultaneous measurements of gas exchange, chlorophyll a fluorescence and metabolite contents of maize leaves were made. Leaves illuminated in the absence of CO₂ showed a build-up of triose phosphates during the first 2 min of illumination which was comparable to the build-up observed in the presence of CO₂. Isolated mesophyll protoplasts, which lack the Calvin cycle, also showed a build-up of triose phosphates upon illumination. Leaves contained amounts of phosphoglycerate mutase and enolase adequate to account for the formation of triose phosphates and 3-phosphoglycerate from intermediates of the C₄ cycle and their precursors.     

The intercellular compartmentation of metabolites in leaves of Zea mays L.

Sap extracted from attached leaves of two-to three-week-old maize plants witt the aid of a roller device was almost devoid of bundle-sheath contamination as judged by the distribution of mesophyll and bundle-sheath markers. The extraction could be done very rapidly (less than 1 s) and the extract immediately quenched in HClO₄ or reserved for enzyme assay. Comparison of the contents of metabolites in intact leaves and in the leaf extract allowed estimation of the distribution of metabolites between the bundle-sheath and the mesophyll compartments. Substantial amounts of metabolites such as malate and amino acids were present in the non-photosynthetic cells of the midrib. In the illuminated leaf, triose phosphate was predominantly located outside the bundle-sheath while the major part of the 3-phosphoglycerate was in the bundle sheath. The results indicate the existence of concentration gradients of triose phosphate and 3-phosphoglycerate in the leaf which are capable of maintaining carbon flow between the mesophyll and bundle-sheath cells during photosynthesis. There was no evidence for the existence of a gradient of pyruvate between the bundle-sheath and the mesophyll cells.     

Leaf vasculature in Zea mays L.

The vascular system of the Zea mays L. leaf consists of longitudinal strands interconnected by transverse bundles. In any given transverse section the longitudinal strands may be divided into three types of bundle according to size and structure: small, intermediate, large. Virtually all of the longitudinal strands intergrade structurally however, from one bundle type to another as they descend the leaf. For example, all of the strands having large-bundle anatomy appear distally as small bundles, which intergrade into intermediates and then large bundles as they descend the leaf. Only the large bundles and the intermediates that arise midway between them extend basipetally into the sheath and stem. Most of the remaining longitudinal strands of the blade do not enter the sheath but fuse with other strands above and in the region of the blade joint. Despite the marked decrease in number of longitudinal bundles at the base of the blade, both the total and mean cross-sectional areas of sieve tubes and tracheary elements increase as the bundles continuing into the sheath increase in size. Linear relationships exist between leaf width and total bundle number, and between cross-sectional area of vascular bundles and both total and mean cross-sectional areas of sieve tubes and tracheary elements.     

Internode length in Zea mays L.

[¹³C, ³H]Gibberellin A₂₀ (GA₂₀) has been fed to seedlings of normal (tall) and dwarf-5 and dwarf-1 mutants of maize (Zea mays L.). The metabolites from these feeds were identified by combined gas chromatography-mass spectrometry. [¹³C, ³H]Gibberellin A₂₀ was metabolized to [¹³C, ³H]GA₂₉-catabolite and [¹³C, ³H]GA₁ by the normal, and to [¹³C, ³H]GA₂₉ and [¹³C, ³H]GA₁ by the dwarf-5 mutant. In the dwarf-1 mutant, [¹³C, ³H]GA₂₀ was metabolized to [¹³C, ³H]GA₂₉ and [¹³C, ³H]GA₂₉-catabolite; no evidence was found for the metabolism of [¹³C, ³H]GA₂₀ to [¹³C, ³H]GA₁. [¹³C, ³H]Gibberellin A₈ was not found in any of the feeds. In all feeds no dilution of ¹³C in recovered [¹³C, ³H]GA₂₀ was observed. Also in the dwarf-5 mutant, the [¹³C]label in the metabolites was apparently undiluted by endogenous [¹³C]GAs. However, dilution of the [¹³C]label in metabolites from [¹³C, ³H]GA₂₀ was observed in normal and dwarf-1 seedlings. The results from the feeding studies provide evidence that the dwarf-1 mutation of maize blocks the conversion of GA₂₀ to GA₁.Abbreviations GA_n gibberellin A_n - GC-MS combined gas chromatography-mass spectrometry - HPLC high-performance liquid chromatography - RP reverse phase     

Effects of high temperature on the germination of maize (Zea mays L.)

Poor emergence of maize seedlings, due to high soil temperatures, is a major limitation of crop potential in the lowland tropics. Ability to germinate at high temperature (>c. 37° C) is related to the temperature sensitivity of the embryo, and there is considerable genotypic variation for this character.Respiration and mitochondrial phosphorylation proceed normally in seeds imbibing at 41° C, and ATP levels are adequate for germination. However, the specific activities of several important enzymes are lower, and the rate of protein synthesis is severely reduced compared with seeds imbibing at 28° C. The depression of the rate of protein synthesis in the embryos of several tropical hybrids imbibing at high temperature correlated with their known temperature sensitivity. It is concluded that protein synthesis is an especially temperature sensitive process in germinating maize embryos, and that this is the principal reason for the sensitivity of germinating maize seeds to high temperature.Abbreviations ADP adenosine-5-diphosphate - ATP adenosine-5-triphosphate - BSA bovine serum albumin - EDTA ethylenediaminetetra-acetic acid - HEPES N-2-hydroxyethylpiperazinc-N-2-ethanesulphonic acid - NADH nicotinamide-adenine dinucleotide, reduced form - PPO 2, 5-diphenyloxazole - PVP polyvinylpyrrolidone - SEM standard error of the mean - tris tris (hydroxymethyl)-methylamine     

Identical embryonal proteins in intact and isolated tissues of maize (Zea mays L.)

Minor antigens characteristic of developing and mature embryos were not found in the shoot and root meristems of the seedlings. Some of these embryonal antigens (EA) were present, however, in callus and cell-suspension cultures, irrespective of their tissue origin, and were maintained throughout repeated subcultures, in some cases for more than 2 years. These EA were distinct both from the meristematic antigens found in the intact seedlings and in callus cultures, and from organ-specific antigens found only in intact plants. The EA of callus tissues derived from several maize genotypes were serologically identical. We therefore assume that these EA are proliferation proteins or early proteins expressed by cells that have not undergone any determination and lack any tissue or organ specificity.     

Type I callus as a bombardment target for generating fertile transgenic maize (Zea mays L.)

To develop a less genotype-dependent maize-transformation procedure, we used 10-month-old Type I callus as target tissue for microprojectile bombardment. Twelve transgenic callus lines were obtained from two of the three anther-culture-derived callus cultures representing different gentic backgrounds. Multiple fertile transgenic plants (T₀) were regenerated from each transgenic callus line. Transgenic leaves treated with the herbicide Basta showed no symptoms, indicating that one of the two introduced genes, bar, was functionally expressing. Data from DNA hybridization analysis confirmed that the introduced genes (bar and uidA) were integrated into the plant genome and that all lines derived from independent transformation events. Transmission of the introduced genes and the functional expression of bar in T₁ progeny was also confirmed. Germination of T₁ immature embryos in the presence of bialaphos was used as a screen for functional expression of bar; however, leaf painting of T₁ plants proved a more accurate predictor of bar expression in plants. This study suggests that maize Type I callus can be transformed efficiently through microprojectile bombardment and that fertile transgenic plants can be recovered. This system should facilitate the direct introduction of agronomically important genes in to commercial genotypes.     

Photosynthetic carbon metabolism during leaf ontogeny in Zea mays L.: Enzyme studies

The activities of several enzymes, including ribulose-1,5-diphosphate (RuDP) carboxylase (EC 4.1.1.39) and phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) were measured as a function of leaf age in Z. mays. Mature leaf tissue had a RuDP-carboxylase activity of 296.7 mol CO₂ g^-1 fresh weight h^-1 and a PEP-carboxylase activity of 660.6 mol CO₂ g^-1 fresh weight h^-1. In young corn leaves the activity of the two enzymes was 11 and 29%, respectively, of the mature leaves. In senescent leaf tissue, RuDP carboxylase activity declined more rapidly than that of any of the other enzymes assayed. On a relative basis the activities of NADP malic enzyme (EC 1.1.1.40), aspartate (EC 2.6.1.1) and alanine aminotransferase (EC 2.6.1.2), and NAD malate dehydrogenase (EC 1.1.1.37) exceeded those of both PEP and RuDP carboxylase in young and senescent leaf tissue. Pulse-chase labeling experiments with mature and senescent leaf tissue show that the predominant C₄ acid differs between the two leaf ages. Labeling of alanine in senescent tissue never exceeded 4% of the total ¹⁴C remaining during the chase period, while in mature leaf tissue alanine accounted for 20% of the total after 60 s in ¹²CO₂. The activity of RuDP carboxylase during leaf ontogeny in Z. mays parallels the development of the activity of this enzyme in C₃ plants.Abbreviations RuDP ribulose-1,5-diphosphate - PEP phosphoenol pyruvate - PGA 3-phosphoglycerate     

Production and diurnal utilization of assimilates in leaves of spinach (Spinacia oleracea L.) and barley (Hordeum vulgare L.)

Rates of CO₂ fixation during the light period and the rates of CO₂ release during the night period were measured using mature leaves from 39- to 49-d-old spinach (Spinacia oleracea L., US Hybrid 424; grown in 9 h light, 15 h darkness, daily) and mature leaves from 21-d-old barley (Hordeum vulgare L., cv. Apex; grown in 14 h light, 10 h darkness, daily). At certain times during the light and dark periods leaves were harvested for assay of their contents of soluble carbohydrates, starch, malate and the various amino acids. Evaluation of the results of these measurements shows that in spinach and barley leaves 46% and 26%, respectively, of the carbon assimilated during the light period is deposited in the leaves for export during the night period. Taking into account the carbon consumption in the source leaves by dark respiration, it is evaluated that rates of assimilate export during the light period from spinach and barley leaves [38 and 42 atom C · (mg Chl)^–1 · h^–1] are reduced in the dark period to 16 atom C · (mg Chl)^–1 · h^–1 in both species. The calculated C/N ratios of the photoassimilates exported during the dark period were 0.029 and 0.015 for spinach and barley leaves, respectively.This work was supported by the Deutsche Forschungsgemeinschaft. We thank Dr. Dieter Heineke for stimulating discussions and Mrs. Petra Hoferichter and Mrs. Marita Feldkämper for their technical assistance.     

Effects of microprojectile bombardment on embryogenic suspension cell cultures of maize (Zea mays L.) used for genetic transformation

We have investigated the interaction between tungsten and gold microprojectiles with suspension-culture cells of maize used for genetic transformation. Particle size measurements were evaluated before and after DNA precipitation to determine mean particle size and the effect of DNA precipitation on particle aggregation. Following particle bombardment, metal foils were examined by scanning electron microscopy to visualize dispersion of individual particles and aggregates. Particle penetration into suspension-culture cell clusters was examined in paraffin-embedded bombarded cells serially sectioned and viewed with light microscopy and by energy dispersive X-ray microanalysis. Acridine-orange-stained bombarded cells were examined to observe cellular response to particle penetration. Transient expression of reporter genes C1 and B and GUS, (-glucuronidase) were used to assess effects of particle bombardment on embryogenic cell types. Autoradiographic analysis of the transformable suspension cell culture SC82 (see Gordon-Kamm et al. 1990, Plant Cell 2, 603–618) was conducted to evaluate the S-phase and mitotic indices in embryogenic and nonembryogenic cells throughout a subculture passage and in response to DNA/particle delivery. The results of these investigations are discussed relative to cytodifferentiation of suspension cell clusters and recovery of transformed clonal sectors.Abbreviations GUS -glucuronidase - FAA formaldehyde-acetic acid-alcohol - SEM scanning electron microscopy     

Genotypic effects on the amino acid relationships in maize (Zea mays L.) pollen and style

Summary The free amino acid content of the pollen grains and the style from three single cross hybrids (Wf9 x H55, Ky49 x Ky27, K64 x K55) and two inbred lines (Oh43, H55) was determined. No tyrosine was detected in the pollen grains of any genotype. Significant differences between pollen genotypes were found for aspartic acid, threonine, serine, lysine and histidine with no effect resulting from the vigor of the pollen source. No proline was found in the style of any genotype. Significant differences between style genotypes were obtained for threonine, serine, glutamic acid, leucine, tyrosine, ethanolanine, aminobutyric acid and histidine with a relationship between vigor of the style genotype present for tyrosine, ethanolanine and aminobutyric acid. The relationship between the pollen and style level for each amino acid as influenced by genotype was analyzed. A significant negative correlation was found only for threonine. Apparently, a complementary relationship between the pollen and style exists for some amino acids. Proline and tyrosine are available only from the pollen and style respectively. Threonine levels are balanced with varying contributions from both pollen and style depending on the genotype.     

Epistasis in maize (Zea mays L.)

Summary Three flint and three dent maize (Zea mays L.) inbred lines, their possible F₁ crosses, F₂ and backcross progenies, and all possible three-way crosses were evaluated in a three-year experiment for yield, ear moisture, and plant height. The purpose was to estimate genetic parameters in European breeding materials from (i) generation means analysis, (ii) diallel analysis of generation means, and (iii) analysis of F₁ and three-way cross hybrids. Method (i) was based on the F-metric model and methods (ii) and (iii) on the Eberhart-Gardner (1966) genetic model; both models extended for heterotic maternal effects.Differences among generation means for yield and plant height were mainly attributable to dominance effects. Epistatic effects were significantly different from zero in a few crosses and considerably reduced heterosis in both traits. Additive x additive and domiance x dominance effects for yield were consistently positive and negative, respectively. Significant maternal effects were established to the advantage of generations with a heterozygous seed parent. In the diallel analysis, mean squares for dominance effects were greater than for additive effects for yield and plant height but smaller for ear moisture. Though significant for yield and plant height, epistatic variation was small compared to additive and dominance variation. Estimates of additive x additive epistasis for yield were significantly negative in 11 of 15 crosses, suggesting that advantageous gene combinations in the lines had been disrupted by recombination in the segregating generations. The analysis of hybrids supported the above findings regarding the analysis of variance. However, the estimates of additive x additive epistasis for yield were considerably smaller and only minimally correlated with those from the diallel analysis. Use of noninbred materials as opposed to materials with different levels of inbreeding is considered the main reason for the discrepancies in the results.