Androgenic response is characterized by a multinucleate or multicellular stage of pollen development. Histological sections stained with toluidine blue and squashes in propionic-carmine and in 4¢-6-diamidino-2-phenylindole (DAPI) were used for serial observations (0, 14 and 28 days) in soybean pollen grains from cultured anthers and floral buds submitted to cold treatment at 4°C. In a total of 62,536 pollen grains, it were observed general averages of 2.06& of pollen grains with two symmetrical nuclei and of 1.41& pollen grains with typical extra nuclei (i.e. additional nuclei with typical morphology). Symmetrical and extra nuclei frequencies increased in both treatments but only the number of pollen grains with typical extra nuclei increased significantly with time of exposure to treatments. In addition, 8.59& of multinucleate pollen grains were recorded with atypical nuclei, smaller than vegetative or generative-types and with a fragmented shape. The frequency of these grains increased significantly with time of exposure to treatments. Thus, soybean multinucleate grains occurrence was not an exclusive response to culture. These preliminary results point to the need of further studies to clarify the relationship between typical and fragmented extra nuclei with both androgenesis and programmed cell death.Abbreviations: DAPI -4¢-6-diamidino-2-phenylindole; G -generative; V -vegetative In plants androgenesis implies a deviation from gametophytic to sporophytic development, characterized by multinucleate and multicellular stages of pollen grains. Cold pretreatment is a stress factor predisposing microspores to androgenesis in some plant species but, despite the assumptions of Horner and Street (1978) and Heberle-Bors (1985), studies have shown no evidence of pollen embryogenesis prior to culture.In soybean (Glycine max L. Merrill, 2n ¼ 2x ¼ 40) anther culture, Yin et al. (1982) recorded that the content of the multinucleate pollen grains disintegrated after a 25-day incubation and only multicellular grains were associated with androgenic response. Kaltchuk-Santos et al. (1997) recorded no multinucleate grains before culture, but the frequencies of such pollen grains increased in vitro after a 4°C pretreatment in cv. IAS 5 and RS 7. The authors suggested that some of these grains might be the precursors of embryos obtained from anther culture.In our recent cytological studies using carmine staining we have found multinucleate pollen grains of the soybean cv. IAS 5 in anthers submitted to low temperatures without having been placed in culture. In a subsequent histological analysis, a multinucleate pollen grain of cv. MG/BR 46 Conquista was also found, on the 18th day of culture, but the toluidine blue staining pattern indicated that it had already become non-viable.
In order to clarify the embryogenic responses in soybean anther culture, anthers of four cultivars were cultured under known conditions to trigger androgenic response. A histological study was performed with anthers in vivo and with approximately 100 explants sampled after 9, 12, 15, 18, 21, 30 and 45 days of culture. In vitro culture triggered the frequent accumulation of phenolic compounds on the locular and anther surfaces, and also caused the destruction of cells and tissues in complex structure such as the tapetum, microspores and pollen grains. Somatic embryogenesis of unicellular origin was observed from the epidermis and the middle layer, and of multicellular origin from connective calluses. No androgenic response could be observed in the anthers of these four soybean genotypes, in the medium and conditions indicated. We point out to the need of changing the approach to the study of androgenesis in soybean, either by using culture conditions unfavourable to the proliferation of diploid tissues, or by culturing isolated microspores.
The morphogenic response of anther walls and connective tissue is the greatest obstacle to androgenesis in soybean anther culture. Whereas induction to microspore embryogenesis occurs in the dark in almost all plant species, soybean anthers have been cultured under light. In an attempt to establish culture conditions that simultaneously stimulate microspore embryogenesis and inhibit epidermal and connective cell proliferation, the effect of light and two 2,4-dichlorophenoxyacetic acid (2,4-D) concentrations (2 and 10 mg l À1 ) on the induction process was investigated. Higher 2,4-D concentration speeded up microspore plasmolysis and did not improve androgenesis. Callogenesis and embryogenesis induction from sporophytic cells were significantly lower in the dark, and some microspores showed major alterations in the sporoderm. Auxin 2,4-D and induction under light contributed to the morphogenic response of the anther walls and connective tissue under the conditions previously recommended to trigger microspore embryogenesis.
Th is study presents a morphoanatomical analysis of Dyckia ibicuiensis, D. polyclada and D. racinae stamens. Flowers at anthesis were desiccated and their stamens were processed using common microtechniques for light microscopic analysis. Morphologically, the androecium in these species is diff erentiated by the disposition of the stamens around the gynoecium and by general anther characteristics. Included stamens, with antesepalous fi laments diff erent from those of the antepetalous, anthers in a radial disposition, always curved, and sporangia facing the gynoecium characterize D. ibicuiensis and D. racinae. Th is confi guration results from the fi lament connation, as well as special anatomical characteristics of the anthers, such as the connective with thickenings. In addition, these species are diff erentiated by the U-shaped thickening in the endothecium. D. polyclada is characterized by its small, free and exserted stamens, with a very short common tube, its anthers, that are not curved or organized around the gynoecium, and its divergent sporangia. Th e anatomical and morphological characteristics identifi ed here are important for characterization of these species. Considering that the androecium is important in the delimitation of Dyckia, the increased use of these data should be equally important for other species and infrageneric groupings.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.