Gasteria

Abstract: Genomic in situ hybridization (GISH) was used to study somatic chromosomes of parental and progeny plants (all 2n=2x=14) of the bigeneric hybrid between Gasteria lutzii and Aloe aristata (Aloaceae), which is partially fertile, a rare occurrence in plants. GISH successfully distinguished between the two parental genomes in the F1 hybrid and revealed numerous genomic recombinations in chromosomes transmitted by the F1 to the back-cross progeny. The results indicate high levels of meiotic compatibility between the parental genomes, even though they differ in size by 20%. Recombination occurred at a frequency that was higher than that expected from the analysis of orcein-stained meiosis in the F1. The discrepancy suggests that terminalization may occur prior to or during metaphase I, reducing the apparent chiasma frequency, or possibly reveals an under-estimation caused by difficulties in resolving closely grouped chiasmata by eye.

Abstract: Various leaf sections of Gasteria verrucosa Haw. and Haworthia fasciata Haw. were cultured on media to examine the effect of picloram (4-amino 3, 5, 6-trichloropicolinic acid) and 2, 4-D (2, 4-dichlorophenoxy acetic acid) on somatic embryogenesis. Picloram (0.5, 1.0, 2.0, 3.0 mgl-1) outperformed 2, 4-D (0, 1.0, 2.0, 3.0 mgl-1) as the auxin source of both earliness of callus and embryo induction and final yield of embryos produced at both kinetin levels examined (0.25, 1.0 mgl-1). Embryos arose initially as a yellow, compact globular masses from the area just beneath the epidermis in linear pattern parallel with the main axis of the leaf and then developed a heartshaped appearance. Embryo formation was preceded by growth of callus almost crystalline in appearance on the cut surface. Subsequent shoot formation developed from green pigmented loci in crystalline callus derived from embryos. Shoot and root development in Gasteria was induced on a defined medium containing quarter strength MS or B5 salts with no hormonal supplementation.

Abstract: The distribution of membrane calcium and calmodulin (CaM) has been fluorimetrically determined in the anther of Gasteria verrucosa with particular attention to sporogenous cells, meiocytes, microspores, pollen and stages of pollen germination and tube growth using chlortetracycline (CTC) and fluphenazine (FPZ). CTC and FPZ fluorescence in sporogenous cells is relatively higher than in the adjacent tapetal cells, indicating higher membrane calcium and CaM levels in the former cell type. However, during meiosis there is a significant increase in membrane calcium and CaM levels in the meiocytes compared to that found in the young microspores. CTC and FPZ fluorescence in the sporogenous cells, meiocytes and young microspores is punctate and slightly diffused throughout the cytoplasm. In the microspores of the tetrad and the young released microspores CTC fluorescence (CTCf) is polarized and mainly associated with the area opposite the future colporal region. FPZ fluorescence (FPZf) becomes polarized in the young microspore. Subsequently, there is a shift in the polarity, and most of the CTCf and FPZf in the old microspores and pollen is regionalized towards the colporal region, and the fluorescence is more diffused, indicating a change in the organellar-bound calcium and CaM. This final graded distribution of CTCf is maintained during pollen germination in that the growing pollen tubes invariably show a tip to base membrane-calcium gradient. In the tapetal cells a high level of Ca2+ is present during the microspore stage. During the preparation for anthesis the endothecium differentiation is marked by the presence of Ca2+. Post-treatment of labelled cells with a Ca2+ chelator such as EGTA resulted in a substantial decrease in diffuse and punctate CTCf. Alternatively, treatment of cells with non-ionic detergent Nonidet P-40 resulted in the total elimination of CTCf, suggesting that the observed CTC fluorescence was due to membrane-associated calcium. The cytological specification of CTC as a probe for calcium is discussed. From cytofluorometric measurements and atomic absorption, it became clear that the level of Ca2+ in the anther is high during the sporogenous and meiotic phases. An increase in CTCf and FPZf occurred after microspore mitosis. An interaction of Ca2+ transport from tapetum to the young pollen is postulated. These findings suggest that the level of Ca2+ in the anther during meiosis is generally relatively higher than at the sporogenous or young microspore stage. These findings are discussed in the light of available information on the role of Ca2+ and CaM-mediated processes such as cell division, callose synthesis and pollen-tube tip growth.

Abstract: While working on the form phases of the chromosomes of species of Gasteria (3), the question naturally arose as to the possible taxonomic bearing of the points observed In the microspore-development material, which came from many plants of various species, no distinguishing features were recognized The root-tip material for sporophytic mitoses was derived from a more limited assortment, and there also no distinctions were noted Consequently it did not appear that the cytological features would aid in establishing criteria of systematic value in this genus The natural problem along this line was then the examination of the related genera, of which Aloe and Haworthia were the most available These three genera offer very many points of similarity in morphology, and indeed Aloe formerly included the other two The writer has in previous notes outlined the pertinent literature dealing with chromosome shape (3, 4) as far as it had then become available Recently a paper by Nava'sin (i) has come to hand dealing with conditions in Leontodon autumnaiis Here he reports two pairs of heterochromosomes (satellites) His figures are not clear regarding fiber-attachment conditions Newton (2) has prepared a detailed study of chromosome conditions in Galtonia candicans and G princeps For the former he describes fiberattachment constrictions of the subterminal type and a single pair of satellites, the latter as reported by Navagin in I9I2 For the latter species he suggests three pairs of these elements An interesting feature of this paper is the consideration given to the constrictions in the vegetative prophases, which show conditions comparable to those described by the present writer for Gasteria and Velthemia maturation-division prophases The writer quite agrees with Newton in assigning to the constriction the determining r6le in orienting the attachment of the spindle fiber However, Newton's incidental statements of the size relations in Gasteria and Aloe (p 203) are not borne out by the present studies