The mitochondrial Rieske iron-sulfur protein is an obligatory component of the respiratory electron transport chain that is encoded by a single-copy gene in mammals and fungi. In contrast, this protein is encoded by a small gene family in dicotyledonous tobacco and monocotyledonous maize. We cloned four cDNAs from tobacco that encode the mitochondrial Rieske iron-sulfur protein. These clones, along with a previously isolated cDNA, represent five independent members of the gene family that can be divided into three subfamilies. All of these genes were derived from the two progenitor species and were expressed in amphidiploid tobacco. The proteins encoded by these five genes are probably functional because they all contain the universally conserved hexyl peptides necessary for the 2Fe-2S cluster formation. The expression of the Rieske protein gene family is differentially regulated; a 6- to 11-fold higher level of steady state transcripts was found in flowers than in leaves, stems, and roots. Members of at least two subfamilies were preferentially expressed in flowers, indicating that they share a common cis-regulatory element(s), which can respond to a flower-specific signal(s). Although approximately 10 times more transcripts occurred in flowers than in leaves, flower and leaf mitochondria contained a similar amount of the Rieske protein. Flowers, however, contained seven times more Rieske proteins than leaves. These results indicated an increase in mitochondrion number in flowers. High-energy demands during anther development might bring about an increase in mitochondrion numbers in flowers and the flower-enhanced expression of the Rieske protein gene family. Our results suggested that nuclear genes encoding mitochondrial respiratory proteins could sense and respond to changes in energy metabolism and/or changes in mitochondrion numbers.

cDNA clones coding for the nuclear-encoded mitochondrial Rieske iron-sulfur protein (RISP) have been isolated from maize and tobacco. Complementation analysis of hybrid proteins consisting of different domains of plant and yeast RISPs showed that the carboxyl two-thirds of the plant protein is functionally equivalent to that of the yeast protein. The amino terminus of the RISP, however, seems to be species specific because this region is not interchangeable between plant and yeast proteins. Complementation analysis of hybrid proteins also identified a structurally conserved domain probably essential for the function of bc1 complex RISPs. A specific domain from the plant RISP was found to cause temperature-sensitive respiratory growth in yeast. We have demonstrated that yeast can serve as a model system to study the structural and functional relationships of plant gene products that are enzymatic components of the mitochondrial respiratory chain.

Indirect selection may be a viable technique in certain situations for improving correlated traits. This study was designed to evaluate the efficacy of seedling selection as a means of improving mature plant performance. Field evaluations were conducted on nine generations of a Black Shank Resistant Synthetic tobacco (Nicotiana tabacum L.) population that had been selected 10 generations for 19‐d seedling weight on regular or stress nutrient agar. Linear increases in mean yield cycle−1 were 1.43 g plant−1 for the population selected on stress nutrient agar and 0.99 g plant−1 when selection was on regular nutrient agar. The only other significant change detected was a decrease in total alkaloids of 0.65 mg g−1 cycle−1 for the regular nutrient agar selections. The lack of a decrease in total alkaloids accompanying the increase in yield of the stress agar selections suggests indirect selection of root modifications that increased the efficiency of total alkaloid synthesis. The increase in yield from 10 cycles of indirect seedling recurrent mass selection on stress agar was equivalent to about 1.5 cycles of direct recurrent mass selection for yield in other field experiments.

A negative genetic correlation between yield and total alkaloids (TA) in tobacco, Nicotiana tabacum L., populations causes decreases in yield when selecting for increased TA. A restricted selection index was employed in an ‘NC13’ ✕ ‘McNair 135’ population to increase TA and hold yield at the mean of the population. The genetic correlation in the base population was −0.67. After three cycles of full‐sib family selection, TA had increased 2.5% of the mean per cycle and there had been no significant change in yield. The increase in TA was about 58% of that expected from direct selection for increased TA, where there would be an expected decrease in yield of 1.9% per cycle. Selection for increased TA also led to a correlated decrease in the ratio of particulate matter in smoke to TA in spite of a positive genetic correlation between particulate matter and TA.

Cultivar development by doubled haploid (DH) methods employing in vitro anther culture has not been highly successful in tobacco, Nicotiana tabacum L., because of the low yielding ability of DH lines. The objective of this study was to compare DH lines developed from androgenetic and gynogenetic haploid sporophytes from the same parental plants. Single plants from ‘Ky10’, ‘Ky15’, and ‘Kyl7’ were self‐pollinated, crossed with pollen of N. africana Merx. and Buttler, and immature buds were anther cultured. Haploid sporophytes arising from embryo sac nuclei and vegetative nuclei of pollen were chromosome doubled and self‐pollinated. Ten random androgenetic DH lines (ADHs), 10 random gynogenetic DH lines (MDHs), and selfed progenies of the parental plant were assigned to a set, or cultivar family, and grown in three replications in each set in two environments. Data were collected for eight characters. Sixteen second cycle MDH lines were produced from one random first cycle line, Ky 10 MDH 1, and compared with the original Ky 10 parent, a first cycle MDH line composite, and Ky 10 MDH 1. The ADH and MDH lines were significantly different for all characters measured. The MDH lines were agronomically superior to ADH lines and more closely resembled the cultivars. The ADHs and MDHs yielded 79.9% and 91.5%, respectively, of the cultivars. A second cycle of MDH line production resulted in no further yield reduction. A model of heterozygosity and inbreeding depression in the parental cultivars could explain the results for yield of the MDH lines; it would not account for differences between ADH and MDH lines.

We have isolated and characterized the F0-ATPase subunit 6 gene (atp6) from tobacco mitochondria. The tobacco sequence exists as a single copy, is transcribed and contains an open reading frame (ORF) capable of encoding a peptide of 395 amino acids. The first 130 amino acids of the tobacco putative polypeptide show limited homology with the N terminus predicted for the maize ATPase subunit 6. Although poorly conserved at the sequence level, the tobacco and maize amino termini are hydrophilic and have a high percentage of charged amino acids. This portion of the predicted peptide may represent a presequence that is common to the ATPase subunit 6 of plants. Significant homology between tobacco and maize begins with amino acid 131, in a region that is highly conserved among fungal ATPase 6 subunits. In the remainder of the predicted protein, tobacco and maize share approximately 81% homology. A 41 by sequence and a 175 by conserved region found upstream from the tobacco atp6 coding region are homologous with sequence elements found in the 5′ flanking regions of other plant mitochondrial genes and may be important for regulation and expression of the atp6 gene.

A transcribed segment of mitochondrial DNA (mtDNA) from Nicotiana tabacum contains the F0-ATPase subunit 9 gene, an open reading frame with homology to the E. coli small subunit ribosomal protein S13 and an open reading frame with homology to a portion of the mammalian “URF 1” protein, recently shown to be a component of the NADH:ubiquinone reductase complex (NADH:Q 1). The transcriptional patterns of the tobacco ATPase 9 gene and S13-like open reading frame share eight RNA species indicating the two sequences are part of the same transcriptional unit. A maize mtDNA fragment contains the S13 homologous sequence and the NADH:Q 1 homologous sequence in an orientation similar to tobacco. The S13-like sequence is present as a single copy in maize and tobacco, as two copies in wheat, and is absent in pea and bean. We discuss the distribution and orientation of the S13-like and “URF 1”-like sequences and the possibility that they are active genes.

Mitochondrial DNAs from Nicotiana tabacum, an amphiploid, and its putative progenitor species, N. sylvestris and N. tomentosiformis were compared in structure and organization. By using DNA transfer techniques and cloned fragments of known genes from maize and N. sylvestris as labeled probes, the positions of homologous sequences in restriction digests of the Nicotiana species were analyzed. Results indicate that the mitochondrial DNA of N. tabacum was inherited from N. sylvestris. Conservation in organization and sequence homology between mtDNAs of N. tabacum and the maternal progenitor, N. sylvestris, provide evidence that the mitochondrial genome in these species is evolutionarily stable. Approximately one-third of the probed restriction fragments of N. tomentosiformis mtDNA showed conservation of position with the other two species. Pattern variations indicate that extensive rearrangement of mtDNA has occurred in the evolution of these Nicotiana species.

A quantitative genetic modelf or arbitrary numbers of alleles and loci with additive, dominance, and additive by additive epistatle effects was employed. Utilizing descent measures and the genetic components, the selection response from selecting among self‐fertilized progenies in generation g, and measuredin selffertilized relatives in generation g', where the last common ancestor was in generation t, was formulated. Permanent response, g' = ∞, led to considerable simplifications. The effect of the number of generations, t, of selfing before testing on the permanent response relative to the response from selecting among homozygotes,t = ∞, was evaluated numerically for a model with two loci, two alleles each. The result varied within a narrow range depending on gene frequencies and effects with a mean relative response of 0.68, 0.83, 0.92, 0.96, 0.98 for t = 1,2,3,4,5, respectively. Selection response based on self‐progeny evaluation was also formulated for the outbred performance of the offspring of randomly mated g's. On a per generation basis, the numerical evaluations gave about the same overall picture for t = 1 and t = 2 and less response for t > 2. If time is of no importance, the response generally increased with t, but there are parameter combinations of gene frequencies and effects for which the response is slightly negative. These responses were compared to those from evaluating full‐sib progenies from crossing pairs of self progenies, which give exactly the same result for t = 1 and t = 2 on a per generation basis. Self‐progeny evaluations generally lead to more selection response than fullsib progenies except for those parameter combinations for which the response is slightly negative, and then it is very small for the full‐sib progeny evaluation. Permanent response is slightly less than immediate response for inbred performance, and varies more with gene frequencies and effects when t is small. Permanent response for outbred performancec an be muchl ess than immediate response depending on the additive by additive variance.

Selection for increased weight of Nicotiana tabacum L. seedlings was conducted for 10 generations of recurrent mass selection in optimal and stress nutrient environments. Following the last cycle of selection, all cycles were evaluated on the nutrient level on which they were selected as well as on the alternate level. Selection response for both nutrient levels was significant when evaluated on either level; however, the responses were less than those predicted from estimates of genetic parameters in the base population. Maximum gains were obtained from selection on the optimum nutrient level whether final evaluation was made on either the optimum or stress level. Selection for increased seedling weight led to a correlated response of earlier germination. Only slight changes were obtained for a correlated change in root length, reflecting the compensation of genetic and maternal correlations of opposite sign.

A diallel crossing scheme was used to estimate genetic parameters for seedling weight, root length, and day of germination in a random mating tobacco (Nicotiana tabacum L.) synthetic population. Estimates were obtained from plants grown under two nutrient levels in aseptic culture in controlled environmental growth chambers. Significant estimates of direct additive and dominance variances and, maternal additive variance for seedling weight were obtained in both stress and optimal nutrient levels. The heritability for seedling weight in the optimal environment, 0.178, was larger than that in the stress environment, 0.124. Predictions of selection response were greater for performance on either the stress or optimal nutrient level if selection would be conducted in the optimal environment. Correlations among characters varied between the two nutrient levels. The large correlations between seedling fresh weight and root length for direct additive and maternal additive effects were of opposite sign, leading to prediction of little change in root length when selecting for increased seedling weight.

AbstractDemand for flue−cured tobacco (Nicotiana tabacum L.) from basal leaf positions has decreased in recent years, and production systems which maximize higher quality, upstalk, leaf grades are needed.In this study we tested production regimes utilizing photoperiod−sensitive genotypes to prevent flowering and produce additional upstalk leaves as a substitute for discarded basal leaves.Normal and photoperiod−sensitive (mammoth) versions of four cultivars were grown in field experiments at two locations in 2 years. Apical meristems of mammoth genotypes were removed when plants had produced the same number of leaves as normal cultivars, four leaves more than normal in 1977, and two leaves more than noma1 in 1978.Mammoth genotypes allowed to produce the same leaf number as normal cultivars provided higher yields, with leaf quality equal or superior to the controls. Total alkaloids were lower than in normal cultivars in 1977, but equal in 1978. Reducing sugar contents were equal in both types in 1977, but significantly higher for mammoths in 1978.Permitting mammoth plants to produce four more leaves than normal, with the bottom four leaves removed from the plants and discarded, resulted in yield overcompensation with slight reductions in leaf alkaloids and increases in reducing sugars. Two additional top leaves on mammoth entries did not compensate adequately for yield reductions caused by discarding the bottom four leaves. Leaf alkaloids and sugar contents in the latter production regime did not differ from those of control cultivars.These regimes could reduce the production of downstalk tobaccos without significant yield reductions and would eliminate all premature flowering. The maintenance of apical dominance in mammoths would enhance axillary bud control.

Crop ScienceVolume 17, Issue 5 cropsci1977.0011183X001700050045x p. 825-825 Registration of Crop Cultivars Registration of NC 13 Tobacco1 (Reg. No. 87) D. F. Matzinger, D. F. MatzingerSearch for more papers by this authorE. A. Wernsman, E. A. WernsmanSearch for more papers by this authorT. J. Mann, T. J. Mann Professor of genetics, professor of crop science, and professor of genetics, North Carolina State Univ., Raleigh, N.C. 27607, respectively.Search for more papers by this author D. F. Matzinger, D. F. MatzingerSearch for more papers by this authorE. A. Wernsman, E. A. WernsmanSearch for more papers by this authorT. J. Mann, T. J. Mann Professor of genetics, professor of crop science, and professor of genetics, North Carolina State Univ., Raleigh, N.C. 27607, respectively.Search for more papers by this author First published: 01 September 1977 https://doi.org/10.2135/cropsci1977.0011183X001700050045x 1 Registered by the Crop Sci. Soc. Am. Contribution from the North Carolina Agric. Exp. Stn. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. Volume17, Issue5September–October 1977Pages 825-825 RelatedInformation

The suitability of progenitor species germplasm as a source of genetic variation for the improvement of quantitatively inherited genetic traits in a cultivated allotetraploid species was investigated. Tobacco, Nicotiana tabacum L. cv. SC 58 was doubled with colchicine to the octoploid state and crossed with the diploid progenitor species N. sylvestris Speg. and Comes. The partially fertile pentaploid hybrid was selfed, or backcrossed one generation to SC 58, to increase fertility. Two cycles of a recurrent selection scheme using SC 58 as a tester parent were then followed to concentrate desirable germplasm from N. sylvestris in the species‐derived synthetic populations.The two synthetic populations (Syn I and Syn II), 58, S1 families, and testcrosses to SC 58 of plants in Syn I which were used to produce Syn II were evaluated in three environments for 11 agronomic and chemical constituents. Significant differences were detected among genetic entries for all characters measured except percent nornicotine in cured leaf, indicating that germplasm from the diploid species, N. sylvestris, had been introgressed into the N. sylvestris genome of tobacco. The potential value of this genetic variation is demonstrated by the fact that Syn I and Syn II yielded 7.7 and 12.9%, respectively, more cured leaf than SC 58. Thus, the breeding technique may be useful in broadening the genetic base for the improve. merit of quantitatively inherited characters in this cultivated species.