Virescent Mutant Research Articles

Inheritance of Cytoplasmic‐Virescent cyt‐V and Dense‐Glanding dg Mutants in American Pima Cotton

Morphological mutants of cotton (Gossypium spp.) have been used extensively in genetic mapping studies and in several instances have proven useful in agronomic improvement efforts. This investigation was conducted to determine the inheritance, allelism, and linkage associations of two spontaneous mutants found in plants of American Pima (G. barbadense L.) cotton. The two mutants were crossed to the normal phenotype cultivar PS‐6 and to several genetic marker stocks. Appropriate F1, F2, and BC populations were created for analyses of inheritance and linkage studies. Analyses of F1 and F2 populations of a virescent mutant indicated that it is inherited as an extranuclear factor. Expression of the mutant is transient, being strongest in the first true leaf after germination and fading by the fourth or fifth true leaf. It is proposed that the mutant be designated cytoplasmicvirescent and be assigned the gene symbol cyt‐V. Analyses of F1, F2, and BC populations of a second, juvenilely expressed, densely glanded mutant indicated that it is inherited as a single, recessively expressed gene. Tests for association of the dense glanding trait with 13 other mutant markers produced no evidence of linkage. Linkage tests with two markers, T1 and ms13, were inconclusive. Expression of the dense glanding mutant is confined to expanding leaves and internodes, and to bracteoles. Expression is strongest in the first and second apical leaves, and fades by the fourth or fifth leaf. The designation denseglanding and gene symbol dg are assigned to the mutant.

New Arabidopsis cue mutants suggest a close connection between plastid- and phytochrome regulation of nuclear gene expression.

We searched for new components that are involved in the positive regulation of nuclear gene expression by light by extending a screen for Arabidopsis cue (chlorophyll a/b-binding [CAB] protein-underexpressed) mutants (H.-M. Li, K. Culligan, R.A. Dixon, J. Chory [1995] Plant Cell 7: 1599-1610). cue mutants display reduced expression of the CAB3 gene, which encodes light-harvesting chlorophyll protein, the main chloroplast antenna. The new mutants can be divided into (a) phytochrome-deficient mutants (hy1 and phyB), (b) virescent or delayed-greening mutants (cue3, cue6, and cue8), and (c) uniformly pale mutants (cue4 and cue9). For each of the mutants, the reduction in CAB expression correlates with the visible phenotype, defective chloroplast development, and reduced abundance of the light-harvesting chlorophyll protein. Levels of protochlorophyllide oxidoreductase (POR) were reduced to varying degrees in etiolated mutant seedlings. In the dark, whereas the virescent mutants displayed reduced CAB expression and the lowest levels of POR protein, the other mutants expressed CAB and accumulated POR at near wild-type levels. All of the mutants, with the exception of cue6, were compromised in their ability to derepress CAB expression in response to phytochrome activation. Based on these results, we propose that the previously postulated plastid-derived signal is closely involved in the pathway through which phytochrome regulates the expression of nuclear genes encoding plastid proteins.

Phenotype, Inheritance, and Regulation of Expression of a New Virescent Mutant in Watermelon: Juvenile Albino

Juvenile albino, gene symbol ja, is a spontaneous virescent mutant, first observed in `Dixielee' and an F2 population of `G17AB' (msms) × `Dixielee' in 1992. Hypocotyls, new young leaves, shoot tips, tendrils and flowers on the main shoot of the ja mutant are all albino during early spring. The interior portions of albino leaves gradually become green, while the margins remain albino. Fruit rind color of the mutant is variegated. Growth of the ja mutant is severely impaired in the early spring. However, the mutant grows at a rate comparable to wild-type in the summer, and produces fruit of almost normal size. Genetic analysis of F1, F2, and BC1 populations derived from the ja mutant showed that the gene for the ja mutant is inherited as a single, recessive, nuclear gene. Segregation ratios in the F2 and BC1 progenies derived from the cross between the previously reported delayed green virescent mutant and the ja mutant indicate independent inheritance of the genes dg and ja. Temperature and red/far-red light had no differential effect on mutant and the wild-type plants. An increase of daylength from 8 to 15 hours increased fresh weight and chlorophyll content more in the ja mutant than in the wild-type. The mutant had a higher chlorophyll a: b ratio than the wild-type under long days. Chlorophyll synthesis or accumulation in the mutant is severely impaired under short days. This is the only virescent mutant in the family Cucurbitaceae whose expression is regulated by daylength.

Juvenile albino, a Virescent Mutant in Watermelon: Inheritance and Expression

juvenile albino (ja) is a spontaneous mutant, first observed in 1992. Hypocotyls, new young leaves, shoot tips, tendrils, and flowers on the main shoot of the ja mutant are all albino during early spring and late fall. The interior of the albino leaves gradually become green, while the margins remain albino. Fruit rind color of the mutant is variegated. Growth of the ja mutant is severely impaired in the early spring and late fall. However, the mutant grows almost normal in the summer, and produces fruits of almost normal size. Genetic analysis of F1, F2, and BC1 populations derived from the ja mutant showed that ja mutant is inherited as a single, recessive, nuclear gene. The segregation ratios in the F2 and BC1 progenies derived from the cross between the previously reported dg virescent mutant and the ja mutant indicated that both are inherited independently. Experiments with temperature (3–5C vs. 20–22C at night), day length (8 vs. 15 h), and red and/or far-red light (15 vs. 0 min) at the end of an 8-h day were performed to investigate the regulation of ja trait expression. Temperature and red/far-red light had no differential effect on mutant and wild-type plants. However, significantly increased fresh weight and chlorophyll content were observed in the ja mutant over the wild-type when grown under long-day conditions. In addition, chlorophyll synthesis or accumulation in the mutant is severely impaired under short-day conditions. To our knowledge, this is the only virescent mutant in Cucurbitaceae whose expression is regulated by day length.

Isolation and initial characterization of virescent mutants of Arabidopsis thaliana

In higher plants, development of the chloroplasts must be coordinated with development of the leaf. In order to study the signals that synchronize these two developmental processes, we have isolated virescent (delayed in greening) mutants of Arabidopsis thaliana. Two such mutants that have pale-green young leaves which gradually green more fully during leaf maturation have been partially characterized. The two, vir1 and vir2, are due to separate nuclear recessive mutations. The pale leaves of vir1 and vir2 both had reduced 77°K fluorescence emission at 730-734 nm relative to that at 686-687 nm, indicating a reduction in the relative amount of LHC I compared to WT. As leaves greened, the amount of LHC I increased to near wildtype levels. The shift in the fluorescence emission peak from 730 nm to 734 nm, characteristic of maturing LHC I, was seen for vir1, but not vir2, suggesting that vir1 is a regulatory mutant while vir2 may be defective in a specific aspect(s) of LHC I function.

Chlorophyll Deficiency Caused by a Specific Blockage of the C<sub>5</sub>-Pathway in Seedlings of Virescent Mutant Rice

Chlorophyll Deficiency Caused by a Specific Blockage of the C<sub>5</sub>-Pathway in Seedlings of Virescent Mutant Rice

Formation of functionally active chloroplasts is determined at a limited stage of leaf development in virescent mutants of rice

AbstractThe ability to form functionally active chloroplasts is determined at a certain early stage of leaf development in three non‐allelic temperature‐sensitive virescent mutants of rice. Temperature‐shift analysis, together with anatomical observations, indicates that the intrinsic developmental signals of the virescent genes are expressed at the stage immediately following the formation of basic leaf structure, but just before the onset of leaf elongation. These signals control the expression of chloroplast‐encoded genes but do not affect the subsequent morphological development of the leaf or the photo‐regulation of the expression of nuclear genes encoding chloroplast proteins.

Photosynthetic properties of leaves of a yellow green mutant of wheat compared to its wild type

We investigated several photosynthetic parameters of a virescent mutant of durum wheat and of its wild-type. Electron transport rate to ferricyanide was the same in the two genotypes when expressed on leaf area basis while O2 evolution of the leaf tissue in saturating light and CO2 was slightly higher in the yellow genotype. RuBPCase was also slightly higher. Quantum yield per absorbed light was similar in the two genotypes. P700 and Cyt f were less concentrated in the mutant while PS II was only marginally lower. The light response curve of CO2 assimilation indicated higher level of photosynthesis of the mutant in high light, which corresponded to a lower non-photochemical quenching compared to the wild-type. It is concluded that the reaction centres, cyt f and chlorophyll are not limiting factors of electron transport in wheat seedlings and that electron transport capacity is in excess with respect to that needed for driving photosynthesis. Since the differences in photosynthesis reflect differences in RuBPCase activity, it is suggested that this enzyme limits photosynthesis in wheat seedlings also at high light intensities.

Inheritance of a Second Virescent Mutant in American PIMA Cotton

Eighteen virescent mutants have been described in allotetraploid cotton (Gossypium sp.); however, only one originated in G. barbadense L. These mutants are useful as seedling and mature plant markers for studies of genetic systems and photosynthesis. A second virescent mutant was found in a G. barbdense (Pima) breeding nursery at Maricopa, AZ in 1984. Experiments indicated that it was under genetic control and was a new phenotype in Pima cotton. The objectives of the present study were to determine the inheritance of this new virescent trait and its linkage and allelic relationships with other Gossypium mutants. The genetic studies showed that the virescent trait is inherited as a monogenic recessive, and that it is not linked with 22 Gossypium mutant genes or allelic with v7 in G. barbdense of v1 and v2 in G. hirsutum L. The name virescent‐21 and the gene symbol v21, are assigned to the new Pima plant color trait.

C4 Photosynthesis: Activities of Photosynthetic Enzymes in a Virescent Mutant of Maize Having a Low-Temperature Induced Chloroplast Ribosome Deficiency

A virescent mutant of maize (v16/v16), which has a low temperature induced deficiency in 70S ribosomes, was used to examine whether the enzymes of the C4 pathway and other photosynthetic enzymes are synthesised on chloroplast ribosomes. The mutant and control plants were grown at 20°C and 30°C and the rates of photosynthesis and enzyme activities were compared. There was no photosynthesis in v16/v16 grown at 20°C (pale yellow), while plants grown at 30°C (normal green) had rates equivalent to the wild type and normal enzyme activities. On a leaf area basis, with v16/v16 grown at 20°C, the activity of ribulose 1,5-bisphosphate (RuP2) carboxylase was only 2% that of the wild type grown at this temperature, while the activities of enzymes of the C4 cycle were much higher (as a percentage of the wild type activity: pyruvate,PI dikinase, 22%; NADP-malate dehydrogenase, 35%; NADP-malic enzyme, 47%; and phosphoenolpyruvate (PEP) carboxylase, 68%). In another experiment v16/v16 plants were grown initially at 30°C, then transferred to 20°C. After transfer to 20°C leaves previously formed under 30°C remained green and had normal rates of photosynthesis and enzyme activities, but newly formed leaves were pale yellow (only 11% as much Chl) and had low photosynthesis rates (2% of normal) and RuP2 carboxylase activity (5% of control). However, there was high activity of eight enzymes of the C4 cycle. The low activity of RuP2 carboxylase in the mutant grown at 20°C is consistent with the requirement of 70S ribosomes for its synthesis, while the high activities of enzymes of the C4 cycle, including those which are chloroplastic, suggest their synthesis is nuclear-encoded.

Characterization of a Virescent Chloroplast Mutant of Tobacco

Virescent mutations produce plants in which young leaves have reduced chlorophyll levels but accumulate nearly normal amounts of chlorophyll as they age; they are predominantly nuclear mutations. We describe here a virescent mutation (designated Vir-c) found in a somatic hybrid line derived from Nicotiana tabacum L. and Nicotiana suaveolens Lehm. This mutation is inherited maternally. Young, half-expanded Vir-c leaves contained three to six times less chlorophyll than did control leaves, and reached maximum chlorophyll levels much later in development. Chlorophyll synthesis rates and chloroplast numbers per cell in Vir-c were similar to the control, and carotenoid content in Vir-c was sufficient to protect chlorophyll from photo-oxidation. Photosynthetic rates of Vir-c at low light intensities suggested a reduced ability to collect light. Electron micrographs of Vir-c chloroplasts from half-expanded leaves showed a significant reduction in thylakoids per granum. The decrease in granal thylakoids was strongly associated with low chlorophyll levels; mature Vir-c leaves with nearly normal chlorophyll content showed normal granal profiles. These results are discussed in relation to virescent mutants previously described.

Nuclear, Virescent Mutants of Zea mays L. with High Levels of Chlorophyll (a/b) Light-Harvesting Complex during Thylakoid Assembly

We have found nuclear, recessive mutants in Zea mays L. where assembly of the major chlorophyll (a/b) light-harvesting complex (LHC) was not delayed relative to most other thylakoid protein complexes during thylakoid biogenesis. This contrasts with the normal development of maize chloroplasts (NR Baker, R Leech 1977 Plant Physiol 60: 640-644). All four mutants examined were allelic and virescent, and displayed visibly higher yields of leaf Chl fluorescence during greening. Fully greened mutants had normal leaf Chl fluorescence yield and normal levels of LHC, and grew to maturity under field conditions. Therefore, delayed LHC assembly is not an obligate feature of thylakoid differentiation.Assigning the molecular basis for the mutation should provide information concerning reguation of LHC assembly. Several possibilities are discussed. The pleiotropic mutant phenotype is not attributable to defects in thylakoid glycerolipid synthesis. Thylakoids isolated from greening mutant leaf sections had elevated glycerolipid/Chl ratios. In addition, both the molar distribution and acyl composition of four major glycerolipids were normal for developing mutant thylakoids.

Temperature-induced chloroplast ribosome deficiency in virescent maize

Seedlings of the virescent mutant v16/v16 of maize (Zea mays L.) exhibit extreme chlorosis when grown at temperatures below 25°C. Chlorotic leaves, grown at 20°C, contain plastids that appear to have been arrested at an early stage of development. Plastids are two-thirds the size of fully developed chloroplasts, contain aberrant thylakoids and appear deficient of plastid ribosomes. Chlorotic leaves contain only trace amounts of 70s ribosomes or 23s and 16s plastidic rRNA. Deficiency of chloroplast ribosomes in v16/v16 is not due to photodestruction. A survey of five virescent mutants establishes a strong correlation between expression of the virescent trait and temperature-induced chloroplast ribosome deficiency.

Genetics of a virescent foliage mutant in beans

Genetics of a virescent foliage mutant in beans

Genetic Analysis of Virescent Mutants and the Identification of Virescents υ12, υ13, υ14, υ15 and υ16 υ17 in Upland Cotton1

Nine virescent mutants of cotton (Gossypium hirsutum L.) were tested for allelism with known virescent mutants and with each other in both greenhouse and field plantings. One mutant was allelic to υ1, two were allelic to yg1yg2, and one was allelic to υ10. One mutant gave a positive F1 allelic test with υ2, but segregation in the F2 established that it was a homoeologue of υ2. Of the remaining mutants, three were identified as simply inherited recessive mutants, and one was a duplicate factor recessive residing on the same chromosomes as υ3 and υ6.

Formation of chloroplast pigments in a temperature-sensitive, virescent mutant of maize

Pigment levels and greening responses have been examined in a temperature-sensitive virescent 16 mutant of maize with a temperature threshold of 25 °C for greening. Expansion of tissue at 20 °C leads to a reduction of protochlorophyll level as well as carotenoids and chlorophyll. Seedlings will not green at 20 °C under low-intensity intermittent or continuous light. Chlorophyll is formed at 20 °C in the light following etiolation at 28 °C. These results suggest that absence of chlorophyll in the virescent seedling at temperatures below the threshold is not due to loss of the protective function of carotenoids and consequent photooxidation of chlorophyll.

POLLEN CONTAMINATION OF BROMEGRASS (Bromus inermis Leyss.) IN THE GREENHOUSE

Contamination of bromegrass (Bromus inermis Leyss.) by wind-blown pollen was measured in the greenhouse using a homozygous recessive virescent mutant as the female parent. Pollen distribution was enhanced by manual shaking of male parents and by use of a fan. In previous tests, the mutant produced less than 0.005% normal green seedlings upon selfing. In this trial, green seedlings averaged 81.1, 40.8, 13.1, 6.9 and 1.1% among the progenies of the mutant when it was grown at 0, 1.5, 3.0, 4.5 and 7.5 m, respectively, from normal green parents. We conclude that satisfactory spatial isolation of several groups of bromegrass clones for breeding can be readily obtained in a greenhouse.

INHERITANCE OF A VIRESCENT TRAIT IN BROMUS INERMIS

The genetics of a virescent mutant was investigated in Bromus inermis Leyss. The trait was inherited as a single, tetrasomic recessive. Selfing the original mutant resulted in 4755 virescent:21 green seedlings when grown at 15 °C. From the data it was concluded that the mutant was homozygous for the virescent gene and that the occasional green, selfed seedlings probably arose by outcrossing.

Genetics of self-compatibility in dihaploids of Solanum tuberosum L. 4. Linkage between an S-bearing translocation and a locus for virescens

Three dihaploids of Solanum tuberosum (two self-compatible, one self-incompatible) were found to be heterozygous for a monogenic recessive virescent mutant. Intercrossing resulted in the expected 3 : 1 ratio only in crosses involving one self-compatible and one self-incompatible parent. Self-compatible x self-compatible matings produced F1's in which 6:1 was found. The same ratio was observed in the self progeny of the two self-compatible dihaploids. This significant deviation could be explained by assuming linkage (25% crossing-over) between v and an S-bearing translocation. This translocation causes self-compatibility in the dihaploids used and early lethality when homozygous.

Temperature sensitivity of virescent mutants of maize

Temperature sensitivity of virescent mutants of maize