Successful plant reproduction requires the precise control of the onset of flowering, which involves the transition from the vegetative growth phase to the reproductive growth phase. As a facultative long-day annual species, Arabidopsis thaliana flowers after an exposure to low temperatures under long-day conditions. This seasonal and diurnal control of flowering involves various epigenetic regulatory activities. We herein review the mechanism underlying the relevant epigenetic regulation, with a focus on the two key flowering regulatory genes, FLOWERING LOCUS C (FLC) and FLOWERING LOCUS T (FT). The expression of FLC, which encodes a flowering repressor, is controlled via a complex epigenetic mechanism involving histone modifications and long noncoding RNAs to establish the “winter memory” of plants annually exposed to winter conditions. In contrast, the expression of FT, which encodes a flowering activator, is temporally regulated through the diurnal binding of polycomb group proteins to the FT promoter to ensure day-length-dependent flowering. Thus, flowering is robustly and dynamically mediated via an epigenetic mechanism to ensure it occurs at the most appropriate time.
Meiotic studies were carried out on 26 accessions for the evaluation of genetic diversity of Cyanotis cristata and C. vaga from various geographical areas of Una, Hamirpur, Kangra, Palampur, Sirmaur (Himachal Pradesh), Dehradun and Mussoorie (Uttrakhand) in India. All accessions were diploids with n=12. The meiosis was found to be mostly normal in both species. In C. cristata, some meiotic cells showed abnormal figures such as early disjunction, bridges, laggards, interbivalent connections, vagrant or unoriented bivalents. All accessions of C. vaga showed normal meiotic course with low frequency of interbivalent connections. These species showed high pollen fertility in spite of presence of some meiotic abnormalities.
Mitochondria are some of the most highly dynamic organelles in eukaryotic cells. The spatial distribution and morphology of mitochondria undergo constant changes via division and fusion to adapt to cellular conditions and to maintain various biological processes. However, how mitochondrial division and fusion are coordinated within a cell is currently unclear. Here, we performed microscopic observation using single-molecule fluorescence in situ hybridization (smFISH) combined with immunostaining to simultaneously measure RNA molecules transcribed from mitochondrial division or fusion genes and the number of mitochondria in an individual cell. The RNA copy number in a single cell varied widely; with up to a 6–10 fold difference among cells. Notably, the expression levels of both types of genes seemed to be positively correlated with the number of fragmented mitochondria. Moreover, multiplexed smFISH imaging confirmed that the expression levels of eight species of mitochondrial division and fusion genes were significantly correlated in individual cells. These findings suggest that the increased expression of mitochondrial division/fusion genes is likely to trigger the homogenization of mitochondrial component molecules such as DNA, RNA, proteins, and lipids among mitochondria through structural remodeling via frequent division and fusion.
Meiotic analysis on 26 wild plants of Phacelurus speciosus collected from Kullu district, Himachal Pradesh recorded the existence of three intraspecific euploid cytotypes, the diploid (2n=20), tetraploid (2n=40) and hexaploid (2n=60). Besides chromosome number, cytotypes also differ in morphometric parameters such as plant height, number of internodes, length of uppermost internodes, length of leaf sheath, length and width of leaf lamina, length of spike/spikelet etc. The 4x and 6x plants grow much taller and robust compared to those of 2x. These cytotypes also differ in sizes of pollen grains and stomata. Plants of 2x, 4x and most of 6x showed normal meiotic course and high pollen fertility. On the other hand, three plants of 6x cytotype showed meiotic irregularities in the form of secondary chromosomal associations, non-synchronous disjunctions. Besides, one plant of 6x cytotype also showed the presence of 1-2 B chromosomes in PMCs.
Stromules are tubular structures that emerge from chloroplasts and other types of plastid. Although stromules have roles in plant immunity, little is known about other physiological functions of stromules or the significance of their formation, extent of protrusion and frequency of occurrence. In this study, we quantified the mean frequency of stromules occurrence in stomatal guard cells every hour during the diurnal cycle in developing and developed cotyledons in Arabidopsis seedlings. Stromule mean frequency was not constant during the diurnal cycle, but gradually increased and decreased, resulting in a local peak every 3–4 h. Observations in continuous light revealed that the variation in stromule mean frequency was independent of the lighting conditions. These results provide novel information about stromule formation, showing synchronized and periodic patterns of stromule frequency throughout the day-night cycle in guard cells of developing cotyledons.
Genome size determination by a flow cytometry (FCM) and chromosome characterization by fluorescent banding, including fluorescence in situ hybridization (FISH), were employed for cytogenetic analysis of two important marigold species, Tagetes erecta (African marigold) and T. patula (French marigold). The FCM data showed that T. erecta had a 2C value of 1.43 pg, while T. patula had a 2C value of 2.54 pg, showing 2-times difference in genome size. Somatic chromosome number was 2n=24 in T. erecta, while the number was 2n=48 in T. patula, indicating arise out of a chromosome doubling event. Chromomycin A3 (CMA) and 4′,6-diamidino-2-phenylindole (DAPI) bands were recognized at different positions on all chromosomes in Tagetes genome, making possible chromosome identification by fluorescent band pattern, especially in T. erecta. FISH results showed that clear telomere signals appeared at both ends of all chromosomes and eight weak 45 rDNA signals on the terminal and middle sites on certain chromosomes in diploid species T. erecta.
Meiotic studies carried out in Brassica rapa L. (Brassicaceae), which exists at diploid level (2n=20) revealed the presence of 0-3 B chromosomes in the collections from Ladakh division of Jammu & Kashmir in India. The chromosome number of n=10 from northwest Himalayas agrees with most previous reports. The presence of B chromosomes is the first record for the species. The paper documented the presence of B chromosomes, meiotic course and pollen fertility in a plant carrying B chromosomes.
Three cultivars of tuberose (Polianthes tuberosa L.), one having spikes with single type of flowers (‘Single’), another with double type of flowers (‘Double’) and the third with single flowers and variegated leaves (‘Variegated’) had somatic chromosome number of 2n=60 and karyotypes comprising 10 long and 50 short chromosomes. The three cultivars, and hybrids of ‘Single’×‘Double' and ‘Variegated’×‘Single’ showed regular meiosis with the chromosomes paired into 30 bivalents at metaphase I (M I). These observations suggest that flower doubling and leaf variegation in tuberose have arisen due to gene mutations and do not necessarily involve changes in chromosome number or structure. Self- and cross-pollination studies revealed that ‘Single’ was self-incompatible, whereas ‘Variegated’ was self-compatible and ‘Single’×‘Variegated’ and ‘Single’×‘Double’ crosses were also compatible. However, fruit and seed set and percent seed germination varied among compatible combinations. Self-incompatibility in ‘Single’ was gametophytic in nature with the pollen tubes getting inhibited in the style. Intervarietal hybrids showed useful variation in inflorescence and floral characters, some hybrids having larger spikes and more flowers/spike than either of the parents.
When hydroponically cultured lettuce seedlings are transferred from a medium at pH 6.0 to another one at pH 4.0, the formation of root hairs takes place. Previous studies have revealed that this low-pH-induced root hair formation requires a phytochrome-mediated light signal and randomization of the existing transverse cortical microtubule (CMT) arrays in the future hair-forming cells, which occurs before the bulge formation. Here, we investigated the relationship between these two requisites, i.e., whether phytochrome is involved in CMT randomization. To test this, seedlings were cultured throughout in the dark except the various periods and timings of red (R) or far-red (FR) light irradiation. In seedlings that had already been transferred to pH 4.0 medium, R light irradiation induced CMT randomization, whereas neither FR light irradiation nor continuous dark culturing instead of R light irradiation did. R light irradiation during the pre-culture at pH 6.0 also caused CMT randomization later when the seedlings were transferred to pH 4.0 medium. Irradiation of FR light immediately after the R light irradiation suppressed the R light-induced CMT randomization, regardless of whether R/FR irradiation was carried out before or after the transfer of seedlings to pH 4.0 medium. The efficacy of R light and R/FR photo-reversibility in the induction of CMT randomization proves that the light signal needed for CMT randomization was indeed mediated by phytochrome, during lettuce root hair formation.
Karyotypes of three Piper species viz. P. betle L., P. longum L., and P. retrofractum Vahl were studied with a conventional staining and a fluorescent banding. P. betle, P. longum, and P. retrofractum possessed 2n=68, 2n=48 and 2n=72 chromosomes in root tip cells, respectively. Chromosome number of P. retrofractum (2n=6x=72) is the first report. The three species of Piper showed distinct chromomycin A3 (CMA)- and 4′,6-diamidino-2-phenylindole (DAPI)-band patterns based on the number, location, and size of CMA- and DAPI-bands. The several chromosomes fluoresced overall by CMA or DAPI and these fluorescent bands will be a good marker for chromosome study. The three species were different in respect of conventional karyotype and fluorescent banding pattern. In three Piper species, the comparative karyotype analysis of fluorescent banded chromosomes might suggest that chromosome diversity occurs in aneuploidy and polyploidy.
Somatic chromosomes of two Scorzonera species from subgenus Scorzonera, section Intricatae collected from four localities in southeast Iran were observed. In S. tortuosissima, 2n=28 was observed. S. intricata revealed two chromosome numbers of 2n=20 and 21. The chromosome numbers of 2n=21 had one B chromosome then the basic number is x=10 which is a new basic chromosome number for Scorzonera. Both species showed a predominance of metacentric chromosomes in each karyotype. The karyotype was formulated as 12m+2sm for S. tortuosissima and 8m+2sm for S. intricata.
Aqueous and methanolic leaf extracts of two medicinal plants, Clerodendrum inerme (L.) Gaertn. and C. viscosum Vent. (Family: Lamiaceae) were evaluated on root tip mitotic cells of Allium cepa L. for assessment of cytotoxicity relevant to their potential applicability for therapeutic uses. Results revealed mitodepressive as well as cytotoxic effects in mitotic cells of Allium test system following treatments with the extracts; however, the manifestation of effects was differential in relation to extract types and concentrations. Aberration types encountered in dividing and resting cells of A. cepa highlight cytotoxic potentiality of the extracts. The present study is therefore significant for biomonitoring of the cytotoxic effects with studied leaf extracts.
The in situ detection of specific DNA sequences by fluorescence in situ hybridization (FISH) is a widely used tool for physical mapping, which is important to understand genome structure and organization. For species with small chromosomes, detection of the position of marker sequences is useful to aid chromosome identification and classification. Primed in situ labeling (PRINS) comprises an alternative to FISH, but its specificity and sensitivity may be influenced by species-specific factors, as chromosome length and chromatin structure. To overcome these obstacles, we designed a reproducible PRINS protocol for physical mapping of 5S rDNA in Eucalyptus dunnii Maiden and Zea mays L. Slides containing mitotic metaphases were submitted to one cycle of PRINS using 5S rDNA primers. Clear signals for 5S rDNA were observed in metaphase chromosomes of both species. In E. dunnii, 5S rDNA was mapped on the pericentromeric region of the short arm of chromosome 5. For Z. mays, the signal was detected in the terminal region of the long arm of chromosome 2. Although chromosome structure may influence the PRINS resolution, a high signal/background ratio was obtained for both species. In Z. mays, clear 5S rDNA signals were obtained by PRINS and FISH. Nonetheless, the former was superior regarding the time required for signal detection. Therefore, PRINS has the potential to aid plant genome studies by allowing fast detection of repetitive sequences, even in species with small chromosomes. Moreover, this is the first report of specific sequence mapping in Eucalyptus by PRINS, contributing to physical mapping progress in this genus.
The genus Curculigo is represented by 17 species and four varieties distributed in worldwide of which seven species and three varieties reported in India. The genus is well-known for its medicinal property. One Indian species C. janarthanamii Gore & Gaikwad was collected in Maharashtra and was investigated its chromosomes for the first time. The mitotic chromosome count was 2n=18. The karyotype was composed of one subterminal, seven submedian and one median chromosomes showing asymmetric feature.
Cytological investigations have been carried out in one wild accession of Anemone rupicola Cambess. collected from the cold deserts of Ladakh division of Jammu & Kashmir India. The chromosome count of 2n=16 was observed and is the first chromosome record for the species from India. Meiotic analysis showed structural heterozygosity for reciprocal translocations as indicated by the presence of multiple associations of four chromosomes. Detailed meiotic analysis showed Pollen Mother Cells (PMCs) with laggards (32.87%) and chromatin bridges (21.91%) at anaphases I, II (A I, II)/telophases I, II (T I, T II), leading to abnormal microsporogenesis. Consequently, abnormal sporads such as triads (37.14%) and polyads (28.57%) were formed. Structural heterozygosis and other associated abnormal meiotic irregularities in the species showed considerable pollen sterility (32.20%) which could be attributed to the presence of ring/chain shaped multivalent in PMCs.
Here we discuss the cytogeographical patterns of cytotypes and the chromosomal evolution of Lysimachia mauritiana in the Ryukyus and Taiwan based on fluorescence in situ hybridization (FISH) analyses of 18 cytotypes using probes consisting of 5S and 45S rDNAs and telomere sequences. In the Ryukyus, the expansion of cytotypes was likely to have been influenced by maritime dispersal via the Kuroshio Current. The representative three cytotypes in Taiwan were also found in Japan: 20 (4m) TS was in the Daito Group; 20 (4m) TN characteristic of the northern Tokara Group was found within the Japanese mainland and named 20 (4m) JM; 18 (6m) Taiwan of the Sakishima Group was distinguished as 18 (6m) Ryukyu by FISH. Decreasing chromosome number was postulated as the result of the centric fusion of two pairs of t-chromosomes to a pair of m-chromosomes; 18 (6m) TF was formed from 20 (4m) TN in Taiwan, 16 (8m) from 18 (6m) Taiwan, Ryukyu, Satsunan, and 16 (6m) Satsunan from 18 (4m) Satsunan, respectively. Increasing chromosome number also occurred, by the centric fission of a pair of m-chromosomes to two pairs of t-chromosomes. 20 (4m) HD was formed from 18 (6m) Ryukyu. By centric fission of a pair of m-chromosomes to two pairs of t-chromosomes, and subsequent pericentric inversion of a pair of them to a pair of st-chromosomes, 20 (4m) MR was formed from 18 (6m) Satsunan. Karyotypic polymorphism among cyotypes has occurred by centric fusion/fission, pericentric inversion, deletion and reciprocal translocation in the Ryukyus and Taiwan.