Characterization of a Virescent Chloroplast Mutant of Tobacco

Abstract

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 suaveoekns 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.Virescent mutants are a curious group of higher plants in which young leaves show much reduced Chl content, but recover more levels of Chl as they age. In contrast with many photosynthetic mutations, the virescent mutation is not lethal, and virescent plants survive to flower and produce seed.Virescent mutations occur in a wide range of flowering plants, including tomato (22), maize (6), cotton (5), and peanut (1). Despite the number of virescent mutants that have been described, the primary effect of the mutation is unknown. The phenotype suggests a temporal aberration in some factor governing Chl content, such as the ability to synthesize, protect, or accumulate Chl.The variety of ways Chl content can be influenced may explain why the virescent phenotype is produced by a number of distinct mutant loci within a given species. In maize, for example, 10 mutant loci on 8 different nuclear chromosomes each produce the virescent phenotype. In a few rare instances, virescent mutations have been reported which were maternally inherited. Presumably these were associated with the chloroplast genome (20,26). The existence of both nuclear and cytoplasmic mutations producing the same phenotype supports the view that virescent mutants comprise a diverse group, in which each distinct mutant locus disturbs a specific factor regulating Chl content.

Disruption of a Rice Pentatricopeptide Repeat Protein Causes a Seedling-Specific Albino Phenotype and Its Utilization to Enhance Seed Purity in Hybrid Rice Production

“…5E). This phenotype, in essence, is very similar to a previously described virescent (v) phenotype, which is defined as presenting young leaves with reduced chlorophyll but can accumulate almost normal amounts of chlorophyll as they mature (Archer and Bonnett, 1987). Due to the unique features of their chloroplast biogenesis and potential value in agriculture, v mutants have been studied for more than half a century in various plant species, including maize, rice, cotton (Gossypium hirsutum), tobacco (Nicotiana tabacum), peanut (Arachis hypogaea), and Arabidopsis (Zhou et al, 2009).…”

Rice Virescent3 and Stripe1 Encoding the Large and Small Subunits of Ribonucleotide Reductase Are Required for Chloroplast Biogenesis during Early Leaf Development

“…Among these mutants, v plants suffer from Chl deficiency in the leaves that develop during the early growth stages and produce mostly green leaves during the late growth stages (Archer and Bonnett, 1987). This developmental phenotype suggests that some of the key factors required for Chl synthesis and/or chloroplast development are absent or insufficient at the earlier developmental stages but are present at adequate levels as the mutant plants mature.…”

Spontaneous Chloroplast Mutants Mostly Occur by Replication Slippage and Show a Biased Pattern in the Plastome of Oenothera

“…Importantly, phenotypes of plastome mutants go beyond simple bleaching. Some plastome mutants display mild chlorotic effects, are developmentally impaired or sensitive to environmental factors, and show mottled phenotypes and/or bleach reversibly (Kirk and Tilney-Bassett, 1978;Stubbe and Herrmann, 1982;Chia et al, 1986;Archer and Bonnett, 1987;Colombo et al, 2008;Hirao et al, 2009;Landau et al, 2009;Greiner, 2012;Figures 1B to 1D, Table 1). A number of mutant lines have been described that display unexpected phenotypes, such as mutant plastids having a phenotypic effect on wild-type plastids in the same cell (Michaelis, 1957) or mutations that confer drought and temperature tolerance (Usatov et al, 2004;Mashkina et al, 2010).…”