Corn Mutant Research Articles

Performance of Physiological Characteristics and Content of Sweet Corn Mutant Some Lines of Sugar (Zea mays L. saccharate Sturt.) Sied of Gamma Ray Irradiation in M1 Generation.

ABSTRACT Sweet corn has a multipurpose function. The need for this commodity continues to increase every year, while the sied of production produced by farmers have not been able to meet the needs. One effort to increase sweet corn production is by mutation techniques to assemble the genetic traits of varieties. This study aims to obtain the best interaction between sweet corn lines and gamma ray irradiation doses on physiological characteristics and sugar content in maniss corn plants (Zea mays L saccharata Sturt). This research was carried out in PT. Pertani, Sirnabaya Village, East Telukjambe sub District, Karawang start in May 2019 until September 2019. The method used is an experimental method using a factorial randomized block design. There are two factors consisting of 20 treatments. The first factor was the sweet corn with replications consisting of 5 lines, the second factor is the dose of gamma ray irradiation consisting of 4 levels. The effect of the treatment was analyzed by analysis of variance, to find out the best treatment continued with the DMRT (Duncan Multiple Range Test) test at 5% level. There was the best interaction between sweet corn lines and gamma ray irradiation dose, the best effect was on G1M1 treatment in almost all parameters of observation (plant height, number of leaves, weight of cobs with hurt, weight of cobs without hurt, long of cobs with hurt, long of cobs without hurt, diameter of cobs with hurt, diameter of cobs without hurt, sugar content, leaf area, leaf area index, crop yields). Keywords : lines, sweet corn, gamma ray irradiation, sugar content

Wet milling characteristics of corn mutants using modified processes and improving starch yields from high amylose corn

Yellow dent, high amylose and waxy corn were evaluated using lab-scale conventional, enzymatic (E-milling) and intermittent milling and dynamic steeping (IMDS) processes. The application of proteolytic enzyme (E-milling) and sulfur dioxide (Conventional milling and IMDS process) during kernel hydration and their effects on overall starch yields from three corn types were studied. Despite using lower amount of SO2 (600 ppm) and shorter steeping duration (66.8%), E-milling yielded the highest amount of starch for yellow dent, high amylose and waxy corn (71.4%, 60.1% and 66.9% (db), respectively). The use of proteolytic enzyme during steeping resulted in 26.1% points higher starch yield for high amylose corn. In conventional wet milling process, the highest starch yields were obtained from yellow dent corn and the lowest from high amylose corn, the values being 70.1% and 46.2% (db), respectively. Similarly, highest starch yield (69.5%, db) was obtained from yellow dent corn from the IMDS process. Steepwater absorption for high amylose corn was on average 37.7% greater than the other two corn types for conventional process and 34.6% greater for the modified processes. Modified wet milling protocols with shorter steeping durations and requiring lesser amounts of SO2 can be used to efficiently process different corn mutants.

Fluorescence Characterization of Standard, Mutant and Sweet Corn.

This work resulted in the development of a method based on fluorescence spectroscopy to differentiate between three corn varieties, standard, mutant and sweet, and to characterize the corn variety present in finished products. This was achieved by recording fluorescence emission spectra as a function of excitation wavelength. For a standard, non-transgenic and non-sweet corn, the maximum of the first peak is around 412-414nm at the excitation wavelength equal to 280nm and shifts to the longer emission wavelengths as the excitation wavelength increases. Also, the second peak is located at 535nm or is slightly higher (537 to 540nm) and does not vary for excitation wavelengths from 280 to 360nm. For mutant corn, the position of the first peak is located at 420nm and above for λex = 280nm, while the second peak starts at 525-530nm (depending on the mutant) and never reaches 535nm. Finally, for a sweet corn, the position of the first fluorescence emission peak is around 430nm. If the sweet corn is non-hybrid, the position of the second emission peak is at 535nm. A hybrid sweet corn has its second peak around 530nm. Thus, fluorescence emission at 530 is characteristic of corn that has undergone natural or artificial genetic transformation. Finally, we found simple mathematical equations to calculate the percentage of amylopectin and amylose in a given corn.

Selectively Desirable Rapeseed and Corn Stalks Distinctive for Low-Cost Bioethanol Production and High-Active Biosorbents

Crop straws provide large amounts of biomass resource for biofuels, but it remains to explore cost-effective lignocellulose process technology with additional valuable bioproducts. Using total eight rapeseed and corn stalks with distinct lignocellulose composition, this study initially performed mild alkali pretreatment (1% NaOH, 50 °C) for enzymatic hydrolysis and yeast fermentation to release bioethanol yields varied from 5 to 12% (% dry matter). By comparison, four corn stalks consistently showed more ethanol yields than those of the rapeseeds, but relatively higher sugar-ethanol conversion rates were examined in the rapeseed samples. Of all stalk samples, both genetic corn mutant (CY04) and classic rapeseed cultivar (Bn18) were respectively assessed as the desired lignocellulose residues for relatively high bioethanol production. Then, all remained solid residues of yeast fermentation were employed as biosorbents for Cd adsorption under various incubation conditions (pH, temperature, time, Cd concentration, biosorbent dose). In general, the solid residues exhibited much higher Cd adsorption capacities and removal rates than those of the raw stalks. In particular, two desirable rapeseed residues were of the highest Cd adsorption capacities, compared to the corn residues examined in this study or other major agricultural crop straws as previously reported. Furthermore, the solid residues were characterized as typical biosorbents via a classic chemical binding manner with much large surface areas accountable for their high Cd adsorption capacity. Therefore, this study has demonstrated a green-like strategy for low-cost cellulosic ethanol production and high-active biosorbents by selecting desired corn and rapeseed stalks.

Nutritional evaluation of 3 types of novel ethanol coproducts

Five 48-h precision-fed rooster assays were conducted with the objective to determine true metabolizable energy (TMEn) using conventional roosters and/or standardized amino acid digestibility using cecectomized roosters for distillers dried grains with solubles (DDGS) produced from human food waste at high solids content (FWDDGS), DDGS produced from 4 corn hybrids with increases in grain protein concentration or the concentrations of several dietary indispensable amino acids, and a coproduct that is produced by a process which separates a high protein and yeast fraction from ethanol stillage (Still Pro, Fluid Quip Process Technologies, Cedar Rapids, IA). These results from the first cecectomized rooster assay indicated that the standardized digestibility values for Lys, Met, Cys, Thr, and Val were 61, 75, 70, 70, and 72%, respectively. Using conventional roosters, the TMEn for the FWDDGS was 3,890kcal/kg DM. The DDGS produced from the high protein mutant corn hybrid had a higher protein content of 34% compared with 28% protein for DDGS from the control corn hybrid. Using Lys as an example, there was a large difference between the 2 samples; the high protein mutant DDGS contained 1.60% Lys vs 1.05% for the control DDGS. Standardized digestibility of amino acids was generally not different for the mutant DDGS and the control DDGS. Similar results were observed for Lys, Arg, and Trp for the DDGS produced from the second mutant corn hybrid. The Still Pro sample was analyzed to contain 53% protein (DM basis) with 2.22% Lys, 1.05% Met, 0.90% Cys, 2.06% Thr, and 3.08% Val. The standardized digestibility values for these amino acids were 84, 92, 87, 86, and 87%, respectively. The TMEn of the Still Pro sample was determined to be 3,372kcal/kg DM. In conclusion, the results of this study indicate that the nutritional value of the 3 types of novel ethanol coproducts is equal to or superior to the nutritional values generally reported for conventional DDGS.

Linkage disequilibrium between fitness QTLs and the sugary1 allele of maize

Understanding how biological systems evolve across changing conditions has been a crucial focus of research. Mutations change the genetic context in which genes are expressed and yet the mechanisms underlying mutation fitness are still unclear. We use the sweet corn mutant sugary1 (su1) as a model for understanding the genetic regulation of mutant fitness, focusing on the mutant × genotype interaction across diverse environments. In a previous work, we identified quantitative trait loci (QTLs) affecting fitness in a mapping population of recombinant inbred lines (RILs) derived from a cross between field corn (B73) × sweet corn (P39 or IL14h) parents; however, the epistatic effects of these QTLs on su1 fitness were not investigated. In the present study, we estimated fitness for two seed production environments. Viability of su1 is under genetic and environmental controls, regulated by multiple genes with minor contributions, and these genes depend on the genotype into which the mutation is introduced and on the environment. Some QTLs were in linkage disequilibrium with the maize gene Su1 and had epistatic effects on su1 fitness. These QTLs could be used by sweet corn breeders by combining the most favorable alleles associated with su1 viability in breeding new genotypes from field × sweet corn crosses. These results also have implications for mutagenesis breeding or genome editing because the epistatic effects of the target genome on the new alleles generated by these techniques could affect the success of the breeding program.

Genetic diversity of sweet corn inbreds using agro-morphological traits and microsatellite markers.

Assessment of genetic diversity is a pre-requisite to broaden the genetic background of cultivated base of sweet corn, an endosperm mutant of field corn that alters starch biosynthesis pathway in endosperm. In the current investigation, genetic divergence among 39 inbred lines was assessed on the basis of 14 agro-morphological traits, two quality parameters and 63 microsatellite markers, selected on the basis of their association with QTLs affecting kernel quality. The cluster analysis based on unweighted pair-group method using arithmetic averages for agro-morphological and quality traits grouped the 39 inbreds into three clusters with 5, 14 and 20 genotypes, respectively. The unweighted neighbor-joining method for microsatellite markers also categorized the inbred lines into three major clusters grouping 10, 9 and 20 genotypes in cluster I, II and III, respectively. The two cluster distribution patterns showed approximately 36 percent similarity. The assay of 30 microsatellite repeats identified 82 alleles with allele size ranging from 80 to 400bp. The major allele frequency and PIC value of the markers ranged from 0.42 to 0.79 and 0.27 to 0.63, respectively, which suggested the presence of high amount of polymorphism among the inbreds. The average heterozygosity was recorded to be 0.19 which signifies proper maintenance of inbred population. Principle co-ordinate analysis also depicted diverse nature of inbred lines and agreed well with the previously determined clustering pattern. This study has identified several inbreds, having good yield and high sugar content which will not only enhance the genetic background of sweet corn germplasm but will also lead to development of high-yielding hybrids with improved quality.

Ethanol yields and elevated amino acids in distillers dried grains with solubles from maize grain with higher concentrations of essential amino acids

Concentrations of the essential amino acids, lysine and tryptophan, present in corn distillers dried grains with solubles (DDGS) are insufficient to fully meet the nutritional requirements in non-ruminant feeds. Mutations known to increase lysine and tryptophan concentrations were combined by breeding into two maize hybrid backgrounds that differ for grain protein concentration (FR1064×Mo17 normal protein, FR1064×IRHP1 high protein). These mutant hybrids were compared to their non-mutant control isolines for field performance and ethanol and DDGS processing using laboratory scale procedures: conventional dry grind process and modified dry grind process using granular starch hydrolyzing enzyme (GSHE).The mutant hybrid grain contained higher concentrations of a number of amino acids, with notable increases to at least 0.55% w/w lysine and 0.18% w/w tryptophan. Due to lower grain yield and starch concentrations, final ethanol yields of FR1064×Mo17: o2; asaC28 hybrid were reduced compared to control for both the conventional and modified dry grind processes. However, with the modified process, ethanol yield for FR1064×IRHP1: o2; asa2-C28 hybrid was similar to its control isoline. DDGS yields increased for both mutant hybrids compared to controls. Although amino acid profiles were similar for DDGS recovered from both the conventional and modified processes, DDGS from the mutant hybrids contained higher concentrations of lysine (1.48–1.70% w/w) and tryptophan (0.32–0.39% w/w) compared to controls (1.09% w/w lysine, 0.22% w/w tryptophan). Using these mutant corn hybrids at an ethanol plant resulted in lower ethanol yields; however, this loss can be recovered with the higher DDGS yield and increased nutritional value of the DDGS.

Genomic regions affecting fitness of the sweet corn mutantsugary1

SUMMARYMutants often reduce fitness when incorporated into some genotypes, as is the case of the mutant genesugary1(su1) in maize (Zea maysL.). Understanding the genetic factors affecting variation in the fitness of a mutant is of major interest from a theoretical point of view and also from a breeder's perspective. The genetic regulation ofsu1behaviour was examined in two independent materials. First, populations of two recombinant inbred lines (RIL) were used, belonging to the Nested Association Mapping (NAM) design produced from crosses between the maize inbred B73 and two sweet corn lines (P39 and Il14h) that were genotyped with 1106 single nucleotide polymorphisms (SNPs). These RILs had a group of lines with thesu1allele and another group with the wild allele. At each marker, the allele frequencies of both groups of RILs were compared. Second, an F2population derived from the cross between A619 (a field maize inbred line) and P39 (a sweet corn inbred line) was characterized with 295 simple sequence repeats (SSRs). In addition, the population was phenotyped for several traits related to viability. A large linkage block was detected aroundsu1in the RILs belonging to the NAM. Furthermore, significant genomic regions associated withsu1fitness were detected along the 10 maize chromosomes, although the detected effects were small. Quantitative trait loci (QTLs) with effects in multiple traits related tosu1fitness were detected in the F2population, for example at bin 5·04. Therefore, the present results suggest that thesu1fitness depends on many genes of small effect distributed along the genome, with pleiotropic effects on multiple traits.

Effect of reduced ferulate-mediated lignin/arabinoxylan cross-linking in corn silage on feed intake, digestibility, and milk production

Cross-linking of lignin to arabinoxylan by ferulates limits in vitro rumen digestibility of grass cell walls. The effect of ferulate cross-linking on dry matter intake (DMI), milk production, and in vivo digestibility was investigated in ad libitum and restricted-intake digestion trials with lambs, and in a dairy cow performance trial using the low-ferulate sfe corn mutant. Silages of 5 inbred corn lines were fed: W23, 2 W23sfe lines (M04-4 and M04-21), B73, and B73bm3. As expected, the W23sfe silages contained fewer ferulate ether cross-links and B73bm3 silage had a lower lignin concentration than the respective genetic controls. Silages were fed as the sole ingredient to 4 lambs per silage treatment. Lambs were confined to metabolism crates and fed ad libitum for a 12-d adaptation period followed by a 5-d collection period of feed refusals and feces. Immediately following the ad libitum feeding trial, silage offered was limited to 2% of body weight. After a 2-d adaptation to restricted feeding, feed refusals and feces were collected for 5 d. Seventy Holstein cows were blocked by lactation, days in milk, body weight, and milk production and assigned to total mixed ration diets based on the 5 corn silages. Diets were fed for 28 d and data were collected on weekly DMI and milk production and composition. Fecal grab samples were collected during the last week of the lactation trial for estimation of feed digestibility using acid-insoluble ash as a marker. Silage, total mixed ration, feed refusals, and fecal samples were analyzed for crude protein, starch, neutral detergent fiber (NDF), cell wall polysaccharides, and lignin. The W23sfe silages resulted in lower DMI in the ad libitum trial than the W23 silage, but DMI did not differ in the restricted trial. No differences were observed for NDF or cell wall polysaccharide digestibility by lambs with restricted feeding, but the amount of NDF digested daily increased for lambs fed the M04-21 W23sfe silage ad libitum. Lambs were less selective against NDF and lignin when offered W23sfe silages. The B73bm3 silage did not affect DMI or digestibility of cell walls at the restricted feeding level, but total daily NDF digested was greater at ad libitum intake. Intake, milk production, and cell wall digestibility were greater for cows fed diets containing W23sfe silages than for those fed W23 silage. Although milk production was greater for the B73bm3 diet, DMI and cell wall digestibility were not altered. Cows were less selective against cell wall material when fed both W23sfe and B73bm3 silages. Reduced ferulate cross-linking in sfe corn silage is a new genetic mechanism for improving milk production.

Genetic effects on fitness of the mutant sugary1 in wild-type maize

SUMMARYKnowing the genetic regulation of fitness is crucial for using mutants in breeding programmes, particularly when the mutant is deleterious in some genetic backgrounds, as it happens with the sweet corn mutant sugary1 (su1) in maize (Zea mays L.). The fitness and genetic effects of maize mutant su1 were monitored through five successive selfing generations in two separated mean-generation designs. The first involved two inbreds with similar genetic backgrounds, while unrelated inbreds were used for the second design. Parents, F1s, F2s, and backcrosses were crossed to P39 as the donor of su1 and the 12 crosses were successively self-pollinated for 5 years. The su1 frequency decreased linearly across selfing generations in both designs. Additive effects were significant for su1 seed viability. However, dominance effects were of higher magnitude than additive effects, even though the dominance effects were not significant. Genetic effects depended on genotypes and environments. Therefore, the fitness of su1 is under genetic control, with significant additive effects due to minor contributions of multiple genes. The fitness of su1 is strongly affected by maize genotypic background and environment. It is hypothesized that genotypes could have evolutionary potential for modulating the fitness of single mutations.

Effects of Low Dose Radiation on Plant-Pathogen Interactions in Chernobyl Zone

Low dose chronic radiation may represent some threats to agriculture because it could induce mutations or speed up a pace of race formation in pathogen population [Dmitriev et al., 2002]. The aim of this study was to investigate the effects of radionuclide contamination in Chernobyl zone (CZ) on plant-pathogen interactions. Puccinia graminis, the causal agent of cereal stem rust, is most damaging disease of these crops. We found the fungus in CZ on cultural plants (wheat, rye and oat) and susceptible grasses. Incidence and pathotypes of P. graminis were determined. The data obtained suggest that population structure of P. graminis has been changed in CZ by appearance of a new population with high frequency of more virulent clones. Low dose radiation has also affected plant disease resistance. Radionuclide contaminated wheat seeds (M3) collected in CZ were sowed in uncontaminated soil. Plants grown from the seeds were 2 – 2.5-fold more susceptible to powdery mildew than control ones. The data were confirmed in a set of experiments with artificial inoculation of wheat plants by other pathogens in greenhouse. Incidence and brown rust development were 2.6-fold higher in radionuclide contaminated seedlings than in control ones. To elucidate alterations in plant disease resistance field trials were carried out in CZ on three plots with matched soil parameters but differed in dose exposure rates. Wheat plants of three cultivars were artificially inoculated with brown rust spores. Incidence and extent of wheat rust was more severe on heavy contaminated plots. We analyzed biochemical mechanisms underlying the decrease in plant disease resistance. Activity of proteinase inhibitors in grains of wheat and rye under low dose radiation was decreased to 30-55 % as compared to control. The inhibitors form stable complexes with proteolytic enzymes of pathogens and restrict the disease extent. Decrease of proteinase inhibitor activities could diminish plant disease resistance. This assumption was confirmed by experiments with high lysine opaque-mutation of corn, which characterized by increased sensitivity to stress factors. In the mutant corn grains the proteinase inhibitor activity was 2-fold less than in irradiated plants of the original corn line and 4-fold less than in control unirradiated plants. Thus results obtained both in greenhouse and in field trials demonstrate the influence of low dose chronic radiation on plant-pathogen interactions. We believe that monitoring of evolution processes in plant pathogen populations in radionuclide contaminated areas should provide better understanding on how serious the threats to agriculture are.

Functional properties of starch from normal and mutant corn genotypes

The thermal and functional properties of starches from a wild-type corn, and amylose extender25, dull39, sugary2 ( su2), and sugary1( su1) corn mutants, all in the same (ExSeed68) genetic background were evaluated and related to their structural features obtained in a previous study. The onset temperature of gelatinization values of starches from all mutant lines ranged from 52.0 to 62.9 °C, temperatures that were all lower than that of the wild-type starch. The viscosity of the su2 starch was relatively stable over the cooking process, showing only a small breakdown of the peak viscosity, suggesting high stability of starch granules against mechanical shear. The su1 mutant starch formed the strongest gel among all starch-gel samples during measurements of both fresh and stored gel. Correlations were established between amylose percentage, chain-length distributions and pasting properties; Rapid Visco Analyser (RVA) and Differential Scanning Calorimeter (DSC) parameters; and DSC and texture analysis data.

Structural Properties of Starch Fractions Isolated from Normal and Mutant Corn Genotypes Using Different Methods

ABSTRACTThe objectives of this research study were to isolate, evaluate, and compare the fine structures of starch fractions obtained from a wild‐type (normal) corn starch and amylose‐extender25, dull39, sugary2, and sugary1 corn mutants in the same genetic background using three different fractionation procedures based on gel‐permeation chromatography or alcohol‐precipitation methods. Starch fractions obtained from each of the three methods were enzymatically debranched and analyzed using high‐performance anion‐exchange chromatography with a postcolumn amyloglucosidase reactor and a pulsed amperometric detector. The separations were performed by fractionation on a GPC column, by precipitation with 1‐butanol, and by preferential precipitation with 1‐butanol and isoamyl alcohol. Using any of these methods, no apparent differences in the molecular weight distributions of amylopectin or of amylose among the different starches were observed. The proportions of branch chain lengths of the starch components obtained by the various fractionation methods were very similar among methods for each of the starch types analyzed, such as the predominance of long branch chains in ae25 corn and that of the short branch chains in su2 corn. Overall, the effect of the corn mutations was more important to the differences observed among the starch types than was the method of fractionation used.

Improving nutritional quality of maize proteins by expressing sense and antisense zein genes.

The predominant proteins in maize grain are a family of alcohol-soluble prolamin storage proteins called zeins. They account for >50% of total seed proteins but are deficient in several essential amino acids. As a result, the corn grain is considered to be nutritionally poor for monogastric animals with respect to key essential amino acids, most notably lysine, tryptophan, and methionine. Thus, corn mutants with reduced levels of zeins, such as opaque-2 (o2), have been demonstrated to possess grain with improved nutritional quality characteristics. The o2 mutant has a superior amino acid composition and has been used through conventional breeding to develop Quality Protein Maize (QPM) for human and animal consumption in developing countries. With the understanding of molecular genetics of zeins and progress in biotechnology, an alternative approach to zein reduction is explored here. Through the targeted reduction of the 19-kDa alpha-zeins, increased levels of lysine, tryptophan, and methionine have been engineered in grain of transgenic hybrids. Currently, the agronomic properties and nutritional values of these transgenic lines are being evaluated.

Enzyme Resistant Dextrins from High Amylose Corn Mutant Starches

This work was undertaken to investigate the effects of amylose content and chemical modification on enzyme resistant dextrin content of high amylose corn mutant dextrins. Dextrins made from high amylose corn mutant starches, including dull sugary 2 (du su2), amylomaize V, amylose extender dull (ae du), amylomaize VII, and chemically modified amylomaize V and VII, were characterized for moisture, solubility, reducing sugars, and enzyme resistant dextrin contents after dextrinization. Moisture content decreased, whereas soluble and reducing sugar contents rose rapidly in the first 60 min of conversion. Reducing sugar content began to decrease after 60 min of reaction, which corresponded to the onset of a rapid increase in enzyme resistant dextrin content. The enzyme resistant component in dextrin was not detected until fragments of low molecular-weight saccharides were produced by hydrolysis. These fragments recombined into randomly branched molecules that were resistant to enzymatic digestion. One proposed mechanism contributing to the lower enzyme resistant dextrin content of chemically modified high amylose corn dextrins is that the introduction of modifying groups to starch presented a steric hindrance for transglucosidation and repolymerization reactions during dextrinization, consequently resulting in lower enzyme resistant dextrin content.

A Naturally Occurring Point Mutation Confers Broad Range Tolerance to Herbicides That Target Acetolactate Synthase

Acetolactate synthase (ALS) inhibitors are among the most commonly used herbicides. They fall into four distinct families of compounds: sulfonylureas, imidazolinones, triazolopyrimidine sulfonanilides, and pyrimidinyl oxybenzoates. We have investigated the molecular basis of imidazolinone tolerance of two field isolates of cocklebur (Xanthium sp.) from Mississippi and Missouri. In both cases, tolerance was conferred by a form of ALS that was less sensitive to inhibitors than the wild type. The insensitivity pattern of the Mississippi isolate was similar to that of a commercial mutant of corn generated in the laboratory: ICI 8532 IT. Sequencing revealed that the same residue (Ala57-->Thr) was mutated in both Mississippi cocklebur and ICI 8532 IT corn. ALS from the Missouri isolate was highly insensitive to all the ALS herbicide families, similar in this respect to another commercial corn mutant: Pioneer 3180 IR corn. Sequencing of ALS from both plants revealed a common mutation that changed Trp552 to Leu. The sensitive cocklebur ALS cDNA, fused with a glutathione S-transferase, was functionally expressed in Escherichia coli. The recombinant protein had enzymatic properties similar to those of the plant enzyme. All the possible point mutations affecting Trp552 were investigated by site-directed mutagenesis. Only the Trp-->Leu mutation yielded an active enzyme. This mutation conferred a dramatically reduced sensitivity toward representatives of all four chemical families, demonstrating its role in herbicide tolerance. This study indicates that mutations conferring herbicide tolerance, obtained in an artificial environment, also occur in nature, where the selection pressure is much lower. Thus, this study validates the use of laboratory models to predict mutations that may develop in natural populations.

Growth and physiological responses of normal, dwarf, and albino corn ( Zea mays) to clomazone treatments

The effects of the bleaching herbicide clomazone (2-[(2-chlorophenyl)methyl]-4,4-dimethyl-3-isoxazolidinone) on the growth of selected mutants of corn ( Zea mays L.) were evaluated. A normal hybrid (“Dekalb XL67”), a gibberellin-deficient dwarf-5 mutant, and a chlorophyll- and carotenoid-deficient albino ( lw 3 ) mutant of corn were exposed to clomazone applied preemergence at rates of 0.0, 0.3, 0.6, and 1.1 kg/ha under greenhouse conditions. Normal corn was very sensitive to clomazone treatments and was severely bleached. Shoot height, shoot dry weight, and chlorophyll content of normal corn were strongly inhibited by all application rates of clomazone. The effects of combined treatments of clomazone and the growth retardant CCC on the growth of normal corn were additive or synergistic. The clomazone induced retardation of the longitudinal growth of normal corn was reversed by exogenously applied gibberellin (GA 3). The dwarf-5 mutant exhibited a greater tolerance to clomazone than normal corn. Clomazone caused a slight chlorosis and reduced the longitudinal growth of this mutant only when applied at the highest rate of 1.1 kg/ha. The short-lived growth of the lethal albino mutant of corn was not affected significantly by clomazone. Normal and dwarf-5 corn responded quite differently when treated with the bleaching herbicide norflurazon. In contrast to the results obtained with clomazone, both normal and dwarf-5 corn were bleached severely by all rates of norflurazon but their shoot heights were not affected by this herbicide. Norflurazon reduced shoot dry weights of normal corn, but not of the dwarf-5 mutant. These results support previously published reports suggesting that clomazone acts by a new mechanism of bleaching action which is different than that of norflurazon. The lesser sensitivity of the gibberellin-deficient dwarf-5 mutant to clomazone and the reversal of clomazone-induced effects on normal corn by exogenous gibberellin suggest a secondary action of this herbicide on gibberellin biosynthesis.

Chloroplast biogenesis. Molecular structure of chlorophyll b (E489 F666).

Nuclear magnetic resonance analysis established the presence of two vinyl groups/macrocycle of chlorophyll b (E489 F666). The latter is the only chlorophyll b that accumulates in a corn mutant (ON 8147). On the other hand the presence of only one vinyl group/macrocycle of authentic monovinyl chlorophyll b (E475 F660) was confirmed.

Effects of Processing (Grinding versus Rolling) of Normal and Mutant Corn Hybrids on Performance of Growing Pigs

Effects of Processing (Grinding versus Rolling) of Normal and Mutant Corn Hybrids on Performance of Growing Pigs