An improved method of genome size estimation by flow cytometry in five mucilaginous species of Hyacinthaceae

Direct somatic embryogenesis and flow cytometric assessment of ploidy stability in regenerants of Caladium × hortulanum 'Fancy'

Caladium × hortulanum 'Fancy' is an important ornamental plant grown in pots and landscapes and known for its colorful leaves often used for interior decorations. In this work, we present a method of in vitro regeneration from three explants source through direct somatic embryogenesis (DSE) wherein the regenerated plants were screened for ploidy changes through flow cytometry analysis. Tuber, leaf and petiole explants were cultured on MS basal medium supplemented with 1-napthalene acetic acid (NAA), 6-benzyl amino purine (BAP) and N-phenyl-N'-1, 2,3-thiadiazol-5-ylurea (TDZ) concentrations. Tuber explants induced highest direct somatic embryos on NAA (1 mg L^- 1) + BAP (0.5 mg L^- 1) with 55.6 mean number of embryos per explant while as leaf and petiole explants amended with 1 mg L^- 1 TDZ developed 18.7 and 12.27 mean number of embryos per explant respectively. The highest embryo conversion frequency was achieved on BAP (2 mg L^- 1) + NAA (0.2 mg L^- 1) with 44.2, 18.7 and 7.5 mean number of plantlets produced per tuber, leaf and petiole explant respectively after 4 weeks of culture. Plantlets were later rooted and maximum number of roots (6.33) per shoot was achieved on 2 mg L^- 1 indolebutyric acid amended medium. Description of the process of DSE is presented through the histological and SEM evidences. The 2C DNA content of field grown plants and the DSE regenerants evaluated under flow cytometric analysis were 8.06 pg and 8.28 pg respectively showing no ploidy changes. Hence, a successful protocol of inducing direct somatic embryos from three explant types with efficient embryo conversion frequency was obtained with regenerants showing similar DNA ploidy as that of their parent plants.

Alterations in Mycelial Morphology and Flow Cytometry Assessment of Membrane Integrity of Ganoderma boninense Stressed by Phenolic Compounds

Global increase in demand for palm oil has caused an intensification in oil palm plantation; however, production is greatly hindered by Basal Stem Rot (BSR) disease caused by Ganoderma boninense. There are many approaches to controlling BSR, although, there is no accurate, sustainable and effective method to suppress G. boninense completely. Hence, four phenolic compounds [Gallic acid (GA), Thymol (THY), Propolis (PRO) and Carvacrol (CARV)] were selected to evaluate their antifungal effect, ability to alter the mycelium morphology, and fungal cell integrity against G. boninense. Significant differences (p < 0.05) were observed and 94% of inhibition was exerted by GA on G. boninense growth. Scanning Electron Microscopy and High-Resolution Transmission Electron Microscopy observations revealed that GA and THY treatment caused severe damage to the mycelium and recorded the highest amount of sugar and electrolyte leakage. The study of cell integrity and morphological disruption has elucidated the reduction of G. boninense cell viability. Generally, our findings confirm the fungistatic effects of GA and THY. The evolution of phenolic compounds during the phytopathology studies indicated their coherence in eradicating the G. boninense. It is proposed that GA and THY had the potential to be developed further as a natural antifungal treatment to suppress G. boninense.

New chromosome number and cyto-molecular characterization of the African Baobab (Adansonia digitata L.) - "The Tree of Life"

The African baobab (Adansonia digitata L.), also referred to as the "Tree of Life", is a majestic, long-lived and multipurpose tree of sub-Saharan Africa. Internationally, a growing demand for baobab products in the food, pharmaceutical and cosmetics industries has been observed. Considering this, there is a need for scientific information on the genetics and breeding of A. digitata, including cytogenetics, genetic diversity and reproductive biology. The objectives of our cytogenetic research were to determine the genome size, chromosome number, and organization of ribosomal DNA (45S and 5SrDNA) of A. digitata. Flow cytometry analysis revealed a 2C-DNA value of 3.8 ± 0.6 pg (1Cx monoploid genome size 919.1 ± 62.9 Mbp). Using our improved chromosome preparation technique, we were able to unequivocally count the chromosomes resulting in 2n = 4x = 168, a revised chromosome number for A. digitata. Fluorescent in situ hybridization (FISH) analysis revealed two massively large variants of 45S rDNA and their corresponding nucleolus organizer regions (NOR). The NOR variants were about two to four times larger than the main body of their respective chromosomes. To our knowledge, this is the first report of this phenomenon in a plant species. Furthermore, we found that FISH analysis using the Arabidopsis-type telomere repeat sequence probe clarified and confirmed the new chromosome number and characterized the 45S rDNA structural organization.

A molecular phylogeny of the genus Drimia (Asparagaceae: Scilloideae: Urgineeae) in India inferred from non-coding chloroplast and nuclear ribosomal DNA sequences

The evolutionary history of the medicinally important bulbous geophyte Drimia (subfamily: Scilloideae) has long been considered as a matter of debate in the monocot systematics. In India the genus is represented by a species complex, however, the taxonomic delimitation among them is ill-defined till date. In the present study, a comprehensive phylogenetic relationship among Indian species of this genus has been inferred for the first time based on chloroplast DNA trnL intron, rps16-trnK intergenic spacer, atpB-rbcL intergenic spacer and ribosomal DNA ITS1-5.8S-ITS2 sequences, leaf morphology, anatomy, stomatal characteristics and pollen exine ornamentations. The present findings revealed the monophyletic origin of the Indian members of Drimia and grouped them into two possible lineages (clade- I and II). The phylogenetic tree based on cpDNA concatenated sequences further resolved the clade-I into two distinct subclades (I and II) and clarified the intraspecies relationship among the studied members. The present study suggested a strong relationship between the molecular phylogeny and the morphological characteristics of the species studied. A possible trend of evolution of two important traits: 'type of palisade cells' in leaf and 'pollen exine patterns' among the members of Drimia in India was also suggested.

Regeneration of plantlets through somatic embryogenesis from root derived calli of Hibiscus sabdariffa L. (Roselle) and assessment of genetic stability by flow cytometry and ISSR analysis

Induction of somatic embryogenesis and complete plantlet regeneration from callus culture of Hibiscus sabdariffa L. var. HS4288 has been made. Leaf and root explants were cultured on Murashige and Skoog (MS) and Driver–Kuniyuki Walnut (DKW) basal media supplemented with different concentrations of synthetic auxins and cytokinins. Root explants on DKW medium supplemented with 2.26μM 2, 4-Dichlorophenoxyacetic acid (2, 4-D) and 4.65μM kinetin (KIN) induced highest percentage (70%) of embryogenic calli. Average number of globular embryos per root derived callus produced within 6 weeks of culture initiation on MS media with different plant growth regulators (PGRs) ranged from 2.27±0.12 to 8.80±0.17 and that of cotyledonary embryos ranged from 0.00 to 2.53±0.20. On DKW medium comparatively more globular embryos (2.70±0.15 to 14.53±0.23) and cotyledonary embryos (0.00 to 8.90±0.17) were produced than that of MS medium. Regeneration of complete plantlets was highest (76.67%) when embryogenic calli with mature somatic embryos were grown on DKW medium containing 2.32μM KIN and 2.22μM 6-Benzyladenine (BA). Plants were primarily hardened in humidity, temperature and light controlled chamber and finally in a greenhouse showed 70% survival ability. Different stages of somatic embryogenesis process in the root derived embryogenic calli were elaborated in detail by morphological, histological and SEM study. The data were statistically analyzed by Duncan Multiple range test (p ≤ 0.05) and Principal component analysis (PCA). Flow cytometry and Inter-simple sequence repeats (ISSR) marker analysis confirmed that there was no genetic variation within the regenerated plants.

Novel nuclei isolation buffer for flow cytometric genome size estimation of Zingiberaceae: a comparison with common isolation buffers

BACKGROUND AND AIMS

Cytological parameters such as chromosome numbers and genome sizes of plants are used routinely for studying evolutionary aspects of polyploid plants. Members of Zingiberaceae show a wide range of inter- and intrageneric variation in their reproductive habits and ploidy levels. Conventional cytological study in this group of plants is severely hampered by the presence of diverse secondary metabolites, which also affect their genome size estimation using flow cytometry. None of the several nuclei isolation buffers used in flow cytometry could be used very successfully for members of Zingiberaceae to isolate good quality nuclei from both shoot and root tissues.

METHODS

The competency of eight nuclei isolation buffers was compared with a newly formulated buffer, MB01, in six different genera of Zingiberaceae based on the fluorescence intensity of propidium iodide-stained nuclei using flow cytometric parameters, namely coefficient of variation of the G0/G1 peak, debris factor and nuclei yield factor. Isolated nuclei were studied using fluorescence microscopy and bio-scanning electron microscopy to analyse stain-nuclei interaction and nuclei topology, respectively. Genome contents of 21 species belonging to these six genera were determined using MB01.

KEY RESULTS

Flow cytometric parameters showed significant differences among the analysed buffers. MB01 exhibited the best combination of analysed parameters; photomicrographs obtained from fluorescence and electron microscopy supported the superiority of MB01 buffer over other buffers. Among the 21 species studied, nuclear DNA contents of 14 species are reported for the first time.

CONCLUSIONS

Results of the present study substantiate the enhanced efficacy of MB01, compared to other buffers tested, in the generation of acceptable cytograms from all species of Zingiberaceae studied. Our study facilitates new ways of sample preparation for further flow cytometric analysis of genome size of other members belonging to this highly complex polyploid family.