PubMed · 13542623
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
S F JACKSON, J T RANDALL. 1958-03-18. Cytoplasmic fine-structure.. https://doi.org/10.1098/rspb.1958.0021
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Cytoplasmic line 2 (CL2) has been previously reported as a cytoplasmically inherited chlorophyll-deficient mutant selected from a chloroplast-mutator genotype of barley. It was characterized by a localized effect on the upper part of the first-leaf blade. At emergence the CL2 seedlings-phenotype varied from a grainy light green to an albino color. They gradually greened during the following days, starting from the base of the blade and extending to cover most of its surface when it was fully grown. The present results, from both light microscopy and transmission electron microscopy (TEM), confirmed the previously described positional and time-dependent expression of the CL2 syndrome along the first-leaf blade. During the first days after emergence, light microscopy showed a normally developed chloroplast at the middle part of the CL2 first-leaf blade, meanwhile at the tip only small plastids were observed. TEM showed that the shapes and the internal structure of the small plastids were abnormal, presenting features of proplastids, amyloplasts and/or senescent gerontoplasts. Besides, they lack plastid ribosomes, contrasting with what was observed inside chloroplasts from normal tips, which presented abundant ribosomes. Phenotypic observations and spectrophotometric analysis of seedlings produced by mother plants that had been grown under different temperatures indicated that higher temperatures during seed formation were negatively associated with pigment content in CL2 seedlings. In contrast, higher temperatures during the growth of CL2 seedlings have been associated with increased pigment content. Aqueous solution with kanamycin and streptomycin, which are antibiotics known to interfere with plastid gene translation, were used for imbibition of wild-type and CL2 seeds. Antibiotic treatments differentially reduced the chlorophyll content in the upper part of the first-leaf blade in CL2, but not in wild-type seedlings. These results suggest that in the wild-type, plastid-gene proteins which are necessary for chloroplast development and chlorophyll synthesis in the upper part of the first-leaf blade are usually synthesized during embryogenesis. However, under certain circumstances, in CL2 seedlings, they would be synthesized after germination. In addition, a shortening of the sheath has been observed in association with pigment decrease suggesting the existence of plastid factors affecting the expression of some nuclear genes. We consider the CL2 mutant a unique experimental material useful to study biological phenomena and external factors regulating plastid, and nuclear gene expression during embryogenesis and early seedling development.
Morphological characteristics were studied in cytoplasmic male sterile (CMS) cybrids possessing the tobacco nuclear genome, Hyoscyamus niger plastome and recombinant mitochondria. After backcrosses with tobacco, new flower modifications were found, including: conversions of stamens into branched filamentous structures; alterations in the shape of petals and the corolla limb; and high degrees of reduction in most flower organs. Vegetative alterations (leaf elongation and stem branching) occurred in some cybrids. Results confirmed that a protoplast fusion-based alloplasmic cytoplasm transfer, followed by conventional backcrosses, is a useful tool for generating alternative CMS sources with novel nucleo-cytoplasmic compositions. These alterations in the genetic status were accompanied by modified floral and vegetative phenotypes.
Cytoplasmic male sterility alleles (CMS) and corresponding nuclear restorer alleles (R) determine gender expression in gynodioecious populations. In this article, we combine cytonuclear epistasis theory, multilevel selection theory, and resource allocation theory to partition the many selective forces acting in gynodioecious species. This description of selective forces reveals that the notion that genomic conflict leads to the spread of restorers is erroneous. By elucidating the effect of each selective force alone and in combination with the others, our approach shows why change in a single parameter, such as the degree of restorer dominance or the cost of restoration, can result in a myriad of opposing selective effects, making it difficult to test theoretical predictions in experimental systems. In particular, our approach allows us to identify the harmonic mean resource allocation between pollen and ovules and the attendant Fisherian selection as playing a critical role in the evolution of the restorer allele and gender polymorphism. We use this conceptual framework to propose empirical methods that emphasize the role of Fisherian selection acting in gynodioecious populations. Because our approach increases the number and specificity of theoretical predictions, we argue that it provides a better framework for empirical testing.