A MORPHOGENETIC STUDY OF LANCEOLATE,A LEAF-SHAPE MUTANT IN THE TOMATO

Mathan , D. S., and J. A. Jenkins . (U. California, Berkeley.) A morphogenetic study of lanceolate, a leaf-shape mutant in the tomato . Amer. Jour. Bot. 49(5): 504–514. Illus. 1962.—The single-gene mutant, lanceolate (La/La⁺), which has simple, entire leaves rather than the oddpinnately compound leaves of the normal tomato (Lycopersicon esculentum), differs from normal (La⁺/La⁺) in many characters which can be related to fewer and larger cells in meristematic regions. The homozygous lanceolate (La/La) is sometimes lethal, but is usually expressed as reduced, which consists of a hypocotyl without cotyledons, or occasionally either by modified, in which there is a single fused cotyledon and a bud, or by narrow, in which the bud produces a shoot with simple leaves even smaller than those of lanceolate and a tendril-like inflorescence without flowers. In an attempt to overcome the effect produced by the lanceolate gene, the mutant was treated with a number of substances. Embryos without cotyledons cultured in White's medium plus adenine or tyrosine or both gave a higher frequency of narrow plants. With added gibberellic acid, no narrow plants developed from embryos without cotyledons. When tyrosine was sprayed on young narrow plants, they developed larger leaves and morphologically normal but sterile flowers. On the other hand, gibberellic acid sprayed on young lanceolate plants altered their development in the direction of narrow.     

Morphogenetic effect of phenylboric acid on various leaf-shape mutants in the tomato, duplicating the effect of thelanceolate gene

Summary Treatment of germinating tomato seeds ofnormal (La ⁺/La ⁺),lanceolate (La ⁺/La) and several other leaf-shape mutants with phenylboric acid (PBA) duplicates the action of theLa gene with respect to the following: 1) Causes an increase in the level of activity of the four oxidative enzymes tyrosinase, laccase, peroxidase and catalase; 2) causes a corresponding change in leaf form; 3) shows a concentration effect similar to the dosage effect exhibited by theLa gene with respect to both the increase in the activity of oxidative enzymes and a change in leaf form; 4) causes changes, when applied to plants carrying any of several leaf-shape mutants, similar to those caused by theLa gene when the latter is in combination with these leaf shape mutant genes. Based on previous evidence and the current evidence, it is suggested that the primary action of PBA as well as of theLa gene, is to cause the increase in the level of activity of the four oxidative enzymes and the latter in turn, among other factors, determine the shape and size of the leaf in the tomato.     

PHENYLBORIC ACID,A CHEMICAL AGENT SIMULATING THE EFFECT OF THE LANCEOLATE GENE IN THE TOMATO

Lanceolate, a spontaneously occurring mutant in the tomato, which has 1 dosage of the mutant gene, causes a change in the shape of the leaf from the odd-pinnately compound leaf characteristic of the normal tomato plant to a simple, much-reduced in size lanceolate leaf. Homozygous mutant plants, which have 2 dosages of the mutant gene, exhibit extreme lanceolate features, producing a simple narrow leaf, similar in shape to the lanceolate leaf but much smaller in size. The mutant allele of the lanceolate gene causes, in addition to the change in leaf form, the increase in activities of the following oxidative enzymes: tyrosinase, laccase, peroxidase and catalase. The lanceolate gene exhibits a dosage effect with respect to these enzymes, homozygous lanceolate showing the highest activity; heterozygous lanceolate, an intermediate; and normal, the lowest activity. Treatment of germinating normal tomato seeds with phenylboric acid simulated the effect of the mutant allele of the lanceolate gene with regard to both the induction of a lanceolate leaf and the increase in the activity of the above 4 oxidative enzymes; phenylboric acid treatment resulted in relatively higher increase in the activities of the oxidative enzymes in normal and heterozygous lanceolate than in homozygous lanceolate. A direct and close relationship existed between the shape of the leaf and the activity of the enzymes during leaf development. It is suggested that the mutant allele of the lanceolate gene, as well as phenylboric acid, induces an increase in activity of the oxidative enzymes and that this increase in enzyme activities brings about the orderly change in form.     

Evidence for a revertant at the La locus in regenerating hypocotyl segments in tomato

Summary Leafy and leafless phenotypes were regenerated in vitro from hypocotyl segments of leafless forms (reduced and modified) of the homozygous lanceolate (La) mutant in tomato. Segregation of progeny of leafy regenerates into homozygous. mutant (La La), heterozygote (La La ⁺) and normal (La ⁺ La ⁺) indicates that cells forming the shoot apical meristems undergo a genetic reversion, and that the nutrient medium might be selecting for the heterozygote. Among the progeny of the regenerates is a true breeding, unlobed variant. Leaves of the variant are pinnately compound and the margins are entire. Opposite cotyledons followed in development by two simple leaves before the appearance of a pinnately compound leaf with an occasional lanceolate-shaped leaflet suggests that the unlobed variant is morphologically intermediate between La La ⁺ and La ⁺ La ⁺.     

MORPHOGENETIC ASPECTS OF A LEAFLESS MUTANT IN TOMATO I. GENERAL PATTERNS IN DEVELOPMENT

The embryo of the reduced form of the lanceolate mutant in tomato fails to undergo the heart-shaped stage of development. Cells in the shoot apical region of this leafless mutant lose their meristematic character and develop into mature parenchyma during embryogenesis. This early loss of meristem tissue leads to the determinate growth which is evident in the seedling. In contrast to normal, starch grains are visible with the light microscope in cells of the shoot tip of the mutant hypocotyl from early embryogeny up to and including the seedling stage, and protein bodies are abundant in the same tissue of fully developed mutant embryos. The shoot apical region in homozygous mutant embryos with cotyledons or cotyledon-like structures exhibits some cytochemical and morphological similarity with the normal shoot apex. Morphological variation in these forms appears to be in a continuous pattern. The extent of their development and consequent longevity is related to possible differences in rates of cell expansion and variation in environmental factors during the early stages of embryogenesis.     

DOSAGE EFFECTS OF THE LANCEOLATE GENE IN TOMATO

In contrast to the odd-pinnately compound leaf of the normal (+/+) tomato plant (Lycopersicon esculentum), the single-gene mutant lanceolate (La/+) generally has a simple leaf. Lanceolate plants, also, have small fruits and flowers, weak apical dominance, and exhibit variation in the position and fusion of cotyledons. Homozygous mutants (La/La) appear in 3 different phenotypes, 1 of which, narrow, has narrow simple leaves, sterile inflorescences, and extremely weak apical dominance. The other 2, modified, and reduced, lack an organized shoot. After selfing La/ + plants for 9 generations, autotetraploids were produced with the aid of colchicine. In addition, several triploid plants arose spontaneously. The study of diploid, triploid, and tetraploid material with various proportions of the La allele revealed in many characters a graded series as a function of the La dosage. With increasing La dose, there was a gradual reduction in: (1) total leaf length; (2) the number and size of primary and secondary lateral leaflets; (3) the number and size of marginal lobes of the terminal leaflet, associated with an increase in the proportional length of the terminal leaflet. Many leaves were found with the basal lobes of the terminal leaflet resembling incompletely separated lateral leaflets. The differences in leaf shape between different genotypes came about before the leaf primordium was 3 mm long. There was a progressive delay in the initiation of lateral primordia with increasing La dosage. It is proposed that the gradual changes from compound to simple leaves with increasing La dosage are produced by successively greater restrictions of meristematic activity after the terminal leaflet is formed. With increasing proportion of La alleles, the reproductive structures showed: (1) a decrease in the number of flowers per inflorescence; (2) a decrease in the length of the sepals; (3) an increase in the proportion of flowers with dialytic anthers. Dialytic anthers had narrow adaxial lobes and were frequently twisted along their main axes. The common denominator for most trends affected by the La allele seems to be a general reduction of growth, but more so in lateral than in longitudinal growth. Histological data suggest that the reduction in lateral growth is mainly brought about by a reduction of cell division in lateral meristems.     

Morphogenetic Aspects of a Leafless Mutant in Tomato: III. GROWTH AND PEROXIDASE ACTIVITY OF ROOTS

Using morphological and biochemical criteria, comparisons weremade between intact and excised roots of normal tomato (Lycopersiconesculentum Mill.) and the reduced form of the homozygous lanceolatemutant. Intact normal roots showed greater growth as reflectedin length of the main root axis, number of lateral roots, andprotodermal cell size. Excised normal roots grew more rapidlythan those of the mutant only during the first 24-h intervalof the first week in culture. Intact mutant roots revealed agreater activity of peroxidase, but excised mutant roots showedno increase in enzyme activity. It is concluded that the primarysite of action of the mutant allele is the shoot system, andin particular the leaf marginal meristem. The effects of thelanceolate gene on the root system in tomato are interpretedas being of secondary importance with regard to gene action.     

A null mutation of cytoplasmic malic enzyme in mice

In the course of conducting a biochemical screening program for mutant enzymes in mice, individuals with an apparent nonfunctional allele at the locus (Mod-1) responsible for cytoplasmic malic enzyme were observed. The variant, later attributed to a germinal mutation, was identified by starch gel electrophoresis and by enzyme activity measurements. A series of matings were made, and mice homozygous for the nonfunctional, null, allele (Mod-1) were produced. In liver, kidney, and testis homogenates, the homozygous mutant exhibited less than 10% of the enzyme activity of the control mice. By an enzyme immuno-inactivation study, the residual enzyme activity was shown to be mitochondrial malic enzyme in all of the tissues examined. By double immuno-diffusion experiments, the kidney homogenate of the mutant formed no precipitin lines with the antiserum to cytoplasmic malic enzyme. Thus, the null mutants express no proteins that crossreact with the antiserum to cytoplasmic malic enzyme (CRM negative). Tissue enzyme assays revealed no significant differences between the normal and the mutant mice in activities of other enzymes in the related metabolic pathways. Because malic acid and malic enzyme together are reported to serve as a pump for NADPH generation in cytoplasm, total cellular NADP⁺ and NADPH concentrations in liver were determined for the control and the mutant mice. In liver from two individual mutant mice, lower NADPH/NADP⁺ ratio was detected in comparison to the level in liver from control mice. In spite of the lower levels of NADPH in the mutant mice, their body weight and lipid content were not significantly altered. Mice without cytoplasmic malic enzyme exhibited no striking deficiencies in metabolism or viability.     

Theoretical study on the aromaticity from d-AOs in cationic X 3 + (X = Sc,Y, La) clusters

The stable structures and aromatic characters for three cationic X₃⁺ (X = Sc, Y, and La) and three relevant neutral X₃Cl (X = Sc, Y, La) clusters are investigated at the DFT and post HF level of theory. The calculated results show that the X₃⁺ cations each has two stable structures: the regular trigon (D_3h) and the line (D_￥h {{\hbox{D}}_{\infty {\rm{h}}}} ) with the regular trigon (D_3h) being the ground state, while for three neutral X₃Cl clusters, Sc₃Cl has three stable isomers: the trigon-pyramidal (C_3v), bidentate (C_2v-1), and C_2v-2 structures, Y₃Cl and La₃Cl each has only two stable isomers: the trigon-pyramidal (C_3v) and bidentate (C_2v-1) structures. The ground states for three X₃Cl species are all the bidentate (C_2v-1) isomers. The calculations of the resonance energy (RE) and NICS show that trigonal X₃⁺ isomers exhibit higher degree of aromaticity. The detailed molecular orbital analyzes reveal that the isolated trigonal Sc₃⁺ and Y₃⁺ cations each has one delocalized π-type MO and shows single π-aromaticity, while the isolated trigonal La₃⁺ cation has one delocalized σ-type MO and shows single σ-aromaticity. The single π- or σ-aromaticity for X₃⁺ are attributed to the contributions mainly from the d AOs of the corresponding transition metal X atoms. However, when a singly negatively charged counterion Cl^- is added to Sc₃⁺, Y₃⁺, and La₃⁺ cations respectively, the aromatic type for the two Sc₃⁺, Y₃⁺ units in the corresponding neutral Sc₃Cl, Y₃Cl complexes are changed from π-aromaticity into σ-aromaticity, whereas the σ-aromaticity of the La₃⁺ units in the La₃Cl complex keeps unchanged in this process. Thus three Sc₃⁺, Y₃⁺, La₃⁺ units in the corresponding X₃Cl complexes all have only one σ-type MO and exhibit single σ-aromaticity.     

Intrinsic Effects of Ruddlesden‐Popper‐Based Bifunctional Catalysts for High‐Temperature Oxygen Reduction and Evolution

Unveiling the intrinsic effects of Ruddlesden‐Popper (RP) series A_n+1B_nO_3n+1 (A = La, B = Ni, Co, Mn, Cu, n = 1, 2 and 3) catalysts is essential in order to optimize the activity of oxygen reduction reaction (ORR) and evolution reaction (OER). Here, it is demonstrated that the oxygen vacancy is not the key point for RP to realize high ORR and OER activity at high temperature. Instead, interstitial O^2? with high concentration and fast migration, and lattice oxygen with high activity are favorable for the high‐temperature catalytic activity. Aliovalent cation doping is an effective strategy to modify the catalytic activity. For the RP catalysts, low‐valence ion doping does not introduce oxygen vacancies, which suppresses the activity of lattice oxygen and decreases the interstitial O^2? concentration; whereas high‐valence ion doping enhances the interstitial O^2– concentration and the lattice oxygen activity. The evaluations of six RP series (La₂NiO₄, La₂CoO₄, La₃Co₂O₇, La₄Ni₃O₁₀, La₂MnO₄, and La₂CuO₄ based) and twenty samples as oxygen electrodes for solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs) demonstrate that this finding is applicable to all the selected RP series.     

Glucose phosphate isomerase enzyme-activity mutants inMus musculus: Genetical and biochemical characterization

Two glucose-6-phosphate isomerase (GPI) mutants with approximately 60% residual activity in blood compared to wild type have been independently detected in offspring derived from 1-ethyl-1-nitrosourea-treated male mice. Homozygous mutants with about 20% residual activity were recovered in progeny of inter se matings of heterozygotes. However, in both mutant lines the number of homozygous mutants was less than expected suggesting an increased lethality of these animals. Results of linkage studies and of investigations of physicochemical properties of the mutant enzymes indicate point mutations at theGpi-1s structural locus on chromosome 7. Based on these findings the two new alleles were designatedGpi-1s ^b-m1Neu andGpi-1s ^b-m2Neu, respectively. The b-m1Neu allele codes for an erythrocyte enzyme which, in the homodimeric form, exhibits a decreased stability toward heat and urea, an altered isoelectric point, normalpH dependence, an increasedK _m for fructose-6-phosphate, and increasedK _i's for 6-phosphogluconate and 2,3-diphosphoglycerate (2,3-DPG) compared to the wild-type enzyme. The GPI-1s^b-m2Neu homodimer, in contrast, is characterized by an even stronger instability, slightly alteredpH dependence, an increasedK _i for 2,3-DPG, normal other kinetics, and normal isoelectric point. The different degree of stability of the mutant homodimersin vitro seems to be reflected in a different degree of stabilityin vivo, since GPI deficiency in general is more strongly expressed in the tissues of the homozygousGpi-1s ^b-m2Neu mutant compared to the homozygousGpi-1s ^b-m1Neu mutant. The similarity of the mutant enzymes to the allozymes found in human GPI deficiencies indicates the GPI deficient mouse mutants to be excellent models for the human disease.This research was supported in part by Contract BI6-156-D from the Commission of the European Communities.     

Carbonic anhydrase II and H+-ATPase in osteoclasts of four osteopetrotic mutations in the rat

 Osteopetrosis in laboratory animals is a metabolic bone disease characterized by increased skeletal mass. It is inherited as an autosomal recessive and results from a defect in the development and/or function of osteoclasts. We studied two enzymes essential for bone resorption, carbonic anhydrase II isoenzyme (CA II) and H⁺-ATPase, in osteoclasts from four osteopetrotic mutations in the rat; namely incisors-absent (ia), osteopetrosis (op), toothless (tl), and microphthalmia (mib), to test the hypothesis that reduced bone resorption in one or more of these mutations results from defects in the synthesis or activity of one of these enzymes. CA II was present in most osteoclasts from normal, tl, op, and mib littermates and was homogeneously distributed in cytoplasm. CA II staining in ia osteoclasts was more variable and less intense than in the other mutations. H⁺-ATPase was also present in osteoclasts from normal animals and mutants and immunostaining showed clear polarization to the ruffled border region in all normal rats and mutants except ia, which showed diffuse distribution of staining in the cytoplasm. H⁺-ATPase activity (proton transport) in a related tissue, kidney, was normal in tl and ia rats but increased in op and mib rats compared to their normal littermates. These results suggest that the osteoclasts in osteopetrotic rat mutations are not abnormal with respect to the distribution of CA II and H⁺-ATPase and that the function of these enzymes in the skeleton, while likely normal, needs to be tested directly in bone. Accepted: 25 September 1998     

Pleiotropic morphological and abiotic stress resistance phenotypes of the hyper-abscisic acid producing Abo™ mutant in the periwinkleCatharanthus roseus

The pleiotropic properties of aabo abo (Abo^™) γ-ray induced mutant ofCatharanthus roseuscv. Nirmal, selected among the M₂ generation seeds for ability to germinate at 45°C, are described. The mutant produced seeds possessing tricotyledonous embryos, unlike the typically dicotyledonous embryos present in the wild type Abo⁺ seeds. In comparison to Abo⁺ adults, the mutant plants had short stature and lanceolate leaves. The vascular bundles in the leaves and stem were poorly developed. Leaf surfaces were highly trichomatous, epidermal, cortex and mesophyll cells were small sized and a large majority of stomata were closed. Besides high temperature, the mutant was salinity and water-stress tolerant. The abscisic acid (ABA) content in the leaves was about 500-fold higher. The genetic lesionabo responsible for the above pleiotropy was recessive and inherited in Mendelian fashion. The seedlings and adult plants of the mutant accumulated higher proline than Abo⁺ plants. The phenotypes ofabo abo mutants permitted the conclusions that (i) the mutant synthesizes ABA constitutively, (ii) both ABA-dependent and ABA independent pathways for proline and betaine accumulation are functional in the mutant, and (iii) cell division, elongation and differentiation processes in embryo and adult plant stages are affected in the mutant.     

Lanthanum-induced alterations in cellular electrolytes and membrane potential in Ehrlich ascites tumor cells

We have investigated the effect of varying La⁺³ concentrations (0.01 mM to 2.0 mM) on membrane potential and electrolyte composition of Ehrlich ascites tumor cells. La⁺³ concentrations less than 0.02 mM had no effect. Above 0.02 mM, La⁺³ induced concentration-dependent loss of electrolytes and water from the cells. At 1.0 mM the effect was maximal and resulted in an 87% reduction in cellular K⁺, 79% in Cl^? and 21% in Na⁺ within 4.8 minutes. The Na⁺ loss occurred even in the face of an electrochemical potential gradient favoring Na⁺ entry. La⁺³ increased the recorded values of membrane potential; the magnitude of the effect was related to the external La⁺³ concentration, and was maximal at 1.0 mM. Studies using ¹⁴⁰La showed that La⁺³ binds rapidly to the cell surface and does not enter the cells. The amount of La⁺³ bound to the cells was related to the external La⁺³ concentration by a sigmoidal curve and was maximal at about 1.0 mM. The bound La⁺³ could not be displaced by either added La⁺³ or Ca⁺². Agents known to effect the integrity of the cell membrane, such as phospholipase C, neuraminidase, pronase and Hg⁺² were tested for their ability to displace bound La⁺³. Only pronase displaced bound La⁺³, indicating that La⁺³ associates with cell protein. It is hypothesized that La⁺³ rapidly interacts with membrane protein causing alterations in membrane permeability and capacity to actively transport ions.     

Use-dependent block with tetrodotoxin and saxitoxin at frog Ranvier nodes II. Extrinsic influence of cations

Use-dependent declines of Na⁺ currents in myelinated frog nerve fibres were measured during a train of depolarizing pulses in solutions containing tetrodotoxin (TTX) or saxitoxin (STX). The following effects of external monovalent (Na⁺), divalent (Ca²⁺, Mg²⁺) and trivalent (La²⁺) cations on use dependence were found: Increasing the Ca²⁺ concentration from 2 to 8 mM shifts its voltage dependence by 20 mV whereas no significant use-dependent decline occurred at 0.2 mM Ca²⁺. Doubling the external Na⁺ concentration in 0.2 mM Ca²⁺ solutions did not initiate phasic block. External Mg²⁺ ions induced a smaller, and La²⁺ ions a larger, use dependence. The time constants of the current decline were 4-fold greater in 1.08 mM La²⁺. The static block of Na⁺ currents by La³⁺ could be directly demonstrated by the relief of block during a train of pulses. The results are qualitatively explained by a toxin binding site at the Na⁺ channel whose affinity for TTX or STX depends oni) the gating conformation of the channel, probably the inactivation andii) the occupancy of a blocking site by di- or trivalent external cations.     

The isolation and characterization of a mutant allele at a new X-linked locus,mex, affecting NADP+-dependent enzymes inDrosophila melanogaster

The isolation and characterization of mutant alleles in a regulatory gene affecting NADP⁺-dependent enzymes are described. The locus,mex, is at position 26.5 ± 0.74 on the X chromosome ofDrosophila melanogaster. The newly isolated mutant allele,mex ¹, is recessive to either themex allele found in Oregon-R wild-type individuals or that found in thecm v parental stock in which the new mutants were induced. Themex ¹ mutant allele is associated with statistically significant decreases in malic enzyme (ME) specific activity and ME specific immunologically cross-reacting material (ME-CRM) in newly emerged adult males. During this same developmental stage in males, the NADP⁺-dependent isocitrate dehydrogenase specific activity increases to statistically significant levels. Females of themex ¹ mutant strain show statistically significant elevated levels of the pentose phosphate shunt enzymes, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. Isoelectric focusing and thermolability comparisons of the active ME from mutant and control organisms indicate that the enzyme is the same. Developmental profiles ofmex ¹ and control strains indicate that this mutant allele differentially modulates the levels of ME enzymatic activity and ME-CRM during development. This work was supported by an Operating Grant from the Natural Sciences and Engineering Research Council of Canada to M.M.B.     

Induction of trehalase activity on a nitrogen-free medium: a sporulation-specific event in the fission yeast, Schizosaccharomyces pombe

Summary Kinetic experiments with synchronously sporulating cultures of a homothallic h⁹⁰ strain of Schizosaccharomyces pombe showed that trehalase activity abruptly increased in the late sporulation process, coinciding with the appearance of visible spores. Trehalase activity was absent in vegetative cells. A set of strains different in genetic constitution at the mating type loci was tested for induction of trehalase on nitrogen-free sporulation medium. The appearance of trehalase activity on the sporulation medium was observed only in sporulating cultures; cultures of homothallic strains (h⁹⁰) and diploid strains heterozygous for mating type (h⁺/h^–), and mixed cultures of heterothallic h⁺ and h^– strains. Trehalase activity was not induced in nonsporogenic strains: heterothallic haploid strains (h⁺ and h^–), diploid strains homozygous for mating type (h⁺/h⁺ and h^–/h^–) and the homothallic strain harboring the mutation in the mat2 gene, which was unable to undergo the first meiotic division. Trehalose accumulation on the sporulation medium was observed solely in the sporulating cultures. These results led us to conclude that the induction of trehalase activity as well as the accumulation of trehalose in the medium lacking nitrogen sources was a sporulation-specific event under the control of the mating type genes.     

Nitrate and nitrite reductase negative mutants of N2-fixingAzospirillum spp.

Chlorate resistant spontaneous mutants ofAzospirillum spp. (syn.Spirillum lipoferum) were selected in oxygen limited, deep agar tubes with chlorate. Among 20 mutants fromA. brasilense and 13 fromA. lipoferum all retained their functional nitrogenase and 11 from each species were nitrate reductase negative (nr^–). Most of the mutants were also nitrite reductase negative (nir^–), only 3 remaining nir⁺. Two mutants from nr⁺ nir⁺ parent strains lost only nir and became like the nr⁺ nir^– parent strain ofA. brasilense. No parent strain or nr⁺ mutant showed any nitrogenase activity with 10 mM NO ₃ ^– . In all nr^– mutants, nitrogenase was unaffected by 10 mM NO ₃ ^– . Nitrite inhibited nitrogenase activity of all parent strains and mutants including those which were nir^–. It seems therefore, that inhibition of nitrogenase by nitrate is dependent on nitrate reduction. Under aerobic conditions, where nitrogenase activity is inhibited by oxygen, nitrate could be used as sole nitrogen source for growth of the parent strains and one mutant (nr^– nir^–) and nitritite of the parent strains and 10 mutants (all types). This indicates the loss of both assimilatory and dissimilatory nitrate reduction but only dissimilatory nitrite reduction in the mutants selected with chlorate.     

The gene fl(2)d is required for various Sxl-controlled processes in Drosophila females

Summary In Drosophila melanogaster, the gene Sex-lethal (Sxl) controls the processes of sex determination, dosage compensation, oogenesis and sexual behaviour. The control of Sxl is by alternative splicing of its primary RNA. We have identified a gene, female-lethal-2-d (fl(2)d), which is needed for the female-specific splicing of Sxl RNA and which also has a vital function independent of Sxl. Here we analyse other aspects of the gene fl(2)d. Specifically, we have analysed the effect of the temperature-sensitive mutation fl(2)d ¹ on the viability of adult flies homozygous for this mutation. We have found that the viability of the mutant females is reduced, while that of the mutant males is not affected. In addition, the capacity of the mutant females to be inseminated is considerably reduced, whilst all the mutant males are able to inseminate females. These effects on females are suppressed by Sxl ^M1. However, the fat body cells of fl(2)d ¹ homozygous females are able to synthesize yolk proteins at the restrictive temperature. We have also carried out, in males, a clonal analysis of fl(2)d ², a mutation lethal in both sexes. We have found that the clones are fully viable. We conclude that the gene fl(2)d seems to be necessary during the adult life of females for the processes that require Sxl ⁺ activity. Moreover, the Sxl-independent vital function of fl(2)d seems to be required in both sexes only during larval development. Offprint requests to: L. Sánchez     

The maternal and zygotic roles of the gene Polycomb in embryonic determination in Drosophila melanogaster

The mutation Polycomb (Pc) is known to cause a variety of intersegmental transformations in homozygous and heterozygous individuals of Drosophila melanogaster; Pc⁺ is thought to act as a negative regulator of genes of the bithorax complex. The function of this gene in the maternal germ line has been assessed by examining the variation in expression of these homoeotic phenotypes in individuals derived from a maternal germ line with a single or no dose of the Pc⁺ allele. Mosaic individuals with a homozygous or heterozygous Pc germ line were produced by transplantation of pole cells, the embryonic precursors of the germ line. By employing an X-linked dominant female-sterile mutation, the identification of mosaic females and the study of progeny derived from the exogenous germ line were greatly simplified; the advantages of this system for the transplantation of pole cells for such analyses are described. In general, all thoracic and abdominal segments of homozygous Pc embryos differentiate characteristics of the eighth, most posterior, abdominal segment. The extent and uniformity of this transformation as well as other manifestations of the homozygous Pc genotype are described and shown to be correlated with the maternal germ line genotype; homozygous Pc embryos derived from a homozygous Pc maternal germ line show greater expression of these phenotypes than do genetically identical embryos derived from a heterozygous Pc maternal germ line. The expression of some homoeotic phenotypes typical of heterozygous Pc adults shows only a slight correlation with the maternal genotype, while no homoeotic transformations are clearly evident in heterozygous larvae of either origin. Thus, the maternal effect of Pc is rescuable. The results suggest that the Pc⁺ gene is active in the maternal germ line but that the absence of the maternally derived Pc⁺ product can be largely compensated by the introduction of a wild-type allele upon fertilization; this rescue indicates that the maternal activity of Pc⁺ plays no major role in the normal process of embryonic segmental determination. The normal fertility of males and females with a homozygous Pc germ line and of their progeny suggests that Pc⁺ plays no role in the determination or development of the germ line in either the maternal or zygotic genome.