Michael Marcotrigiano

Breakdown of self-incompatibility in tetraploid Lycopersicon peruvianum: inheritance and expression of S-related proteins

Abstract Lycopersicon peruvianum displays gametophytic self-incompatibility (GSI). We have isolated self-compatible (SC) tetraploids of L. peruvianum from tissue-cultured leaves and have explored the expression and inheritance of their S-related proteins. The Srelated protein profiles of styles of SC tetraploids were indistinguishable from the diploid self-incompatible (SI) explant source based on SDS-PAGE. All progeny obtained from self-fertilization of two tetraploids were SC. Cloned cDNA sequences of the S-related proteins were used to determine the inheritance of this locus in these progeny through Southern hybridization. The allelic ratio, as determined from the intensity of DNA restriction fragments, was consistent with the predicted ratio if only pollen bearing two different alleles was successful in achieving fertilization. All progeny obtained had at least one copy of each allele, and individuals fully homozygous for either allele were not found, indicating that pollen grains bearing two identical alleles were inhibited. In addition, the level of expression of the S-related proteins in the progeny correlated with the allelic dosage at the DNA level. We demonstrate that the observed self-compatibility in the tetraploids was not caused by an alteration in the expression of S-related proteins.

Shoot regeneration from tissue-cultured leaves of the American cranberry (Vaccinium macrocarpon)

A method for shoot regeneration from leaf explants in two cultivars of cranberry (Vaccinium macrocarpon Ait.) is described. Modified Andersons medium supplemented with combinations of thidiazuron (TDZ) with or without 1 μM NAA (α-naphthaleneacetic acid) was used to optimize shoot regeneration. The effect of light or dark incubation was also determined. Maximum regeneration was obtained in the light in the presence of 10 μM TDZ and 1 μM NAA. While this medium was suitable for leaf explants obtained from shoot cultures, regeneration did not occur from leaves collected from greenhouse-grown plants. Elongation of the regenerated shoot tips did not occur until explants were transferred to growth regulator-free medium at which time only a minority of shoots elongated. Elongated shoots could be dissected away from leaf tissue, rooted easily, and acclimitized to ambient conditions.

A role for leaf epidermis in the control of leaf size and the rate and extent of mesophyll cell division

Little is known about the control of leaf size in plants, yet there must be mechanisms by which organ size is measured. Because the control of leaf size extends beyond the action of individual genes or cells, an understanding of the role of leaf cell layers in the determination of leaf size is warranted. Following the construction of graft chimeras composed of small- and large-leaf genotypes of Nicotiana, bilateral leaf blade asymmetry was observed on leaves possessing either a genetically larger or smaller epidermis on one side of the midrib. Although cell size was unaffected by the genotype of the epidermis, the rate and extent of cell division in leaf epidermis altered the rate and extent of cell division in mesophyll and affected leaf size. The data presented neither prove nor disprove whether the mesophyll impacts epidermal cell division but provide the first unequivocal evidence that the extent of cell division in the leaf epidermis alters the extent of cell division in the mesophyll and is a factor regulating blade expansion and ultimate leaf size.

GENETIC MOSAICS AND THE ANALYSIS OF LEAF DEVELOPMENT

Genetic mosaics with phenotypic markers can be used to study the development of normal leaves. Mosaics synthesized between normal cells and cells possessing developmental mutations can be used to determine whether or not a mutation acts cell autonomously or if cell‐to‐cell interactions occur. This article reviews the use of cytochimeras, plastid chimeras, radiation‐induced chimeras, and graft chimeras to analyze leaf development in angiosperms and to gain insight into the cell lineage, cell‐to‐cell communication, and the control of morphology. New data are also presented. Leaves of plastid chimeras and graft chimeras were analyzed to determine the level of cell autonomy in different regions of the leaf blade. Evidence that small populations of leaf cells can act out developmental programs is presented. The relationship of these leaves to concepts such as developmental compartments, organismal theory, and pattern formation is discussed.

Herbivory could unlock mutations sequestered in stratified shoot apices of genetic mosaics.

Many higher plants have shoot apical meristems that possess discrete cell layers, only one of which normally gives rise to gametes following the transition from vegetative meristem to floral meristem. Consequently, when mutations occur in the meristems of sexually reproducing plants, they may or may not have an evolutionary impact, depending on the apical layer in which they reside. In order to determine whether developmentally sequestered mutations could be released by herbivory (i.e., meristem destruction), a characterized genetic mosaic was subjected to simulated herbivory. Many plants develop two shoot meristems in the leaf axils of some nodes, here referred to as the primary and secondary axillary meristems. Destruction of the terminal and primary axillary meristems led to the outgrowth of secondary axillary meristems. Seed derived from secondary axillary meristems was not always descended from the second apical cell layer of the terminal shoot meristem as is expected for terminal and primary shoot meristems. Vegetative and reproductive analysis indicated that secondary meristems did not maintain the same order of cell layers present in the terminal shoot meristem. In secondary meristems reproductively sequestered cell layers possessing mutant cells can be repositioned into gamete-forming cell layers, thereby adding mutant genes into the gene pool. Herbivores feeding on shoot tips may influence plant evolution by causing the outgrowth of secondary axillary meristems.

Phenotypic and ploidy status of Paulownia tomentosa trees regenerated from cultured hypocotyls

Shoots of Paulownia tomentosa Steud., the Empress tree, were regenerated from cultured hypocotyl segments. The phenotypic and ploidy status of a population of regenerated trees was investigated and compared with a control population of trees grown from seed. Five of the six measured phenotypic characteristics were not significantly different between both populations of plants. Twenty of twenty-one shoots had the normal diploid chromosome number and one was apparently mixoploid. Five phenotypic variants were recovered, including a variegated variant that appearsr to be a plastid chimera undergoing a segregation of normal and mutant plastids. The variegated variant was the only stable variant. All other variants displayed typical morphology in their second year of growth. Precocious flowering of five regenerated plantlets occurred in their first year of growth. These plants were derived from different hypocotyls and did not flower the subsequent year.

In vitro organogenesis and shoot proliferation of Paulownia tomentosa steud. (empress tree)

Abstract In Paulownia, organs such as hypocotyls, cotyledons and shoot tips regenerated roots and/or shoots on defined media in vitro. Hypocotyls had the ability in both light and dark to form roots and shoots, while cotyledons formed only roots in the dark. Shoot production from hypocotyls was greatest in the light and on media containing equal concentrations (mg/l) of indole-3-acetic acid (IAA) and 6-furfurylaminopurine (kinetin). In addition, shoot tips placed on medium containing 1.0 mg/l 6-benzylaminopurine (BA) and 0.1 mg/l indole-3-butyric acid (IBA) multiplied 11-fold in 21 days. On some treatments large amounts of callus formed at the base of shoots and if the callus was subcultured shoots occasionally appeared. It is apparent from these results that Paulownia has potential for sophisticated manipulations in vitro.

Genetic Mosaics and Chimeras: Implications in Biotechnology

Genetic mosaics are plants which are composed of tissues of two or more genotypes. They should not be confused with plant hybrids, which possess only one genotype; a genotype which is the product of recombination following fertilization. Mosaics can arise spontaneously or can be induced with chemical or physical mutagens. In mutagenized plants most of the mutant sectors arise outside the shoot apex (i.e., “extra-apical mosaicism”, described by Bergann 1967).