In plants, the shoot apical meristem (SAM), which is formed during embryogenesis, plays a crucial role in postembryonic development of the above-ground shoots. The SAM harbors pluripotent stem cells, which provide daughter cells to differentiate lateral organs and stems. As the plant grows, the primary shoot generates the axillary meristems, which are responsible for secondary shoot development. During the development of axillary meristem, stem cells must be established and maintained to build up the axillary meristems. While the mechanism underlying stem cell maintenance in the SAM, including the WUSCHEL-CLAVATA negative feedback loop, has been well elucidated, studies on the regulation of stem cell maintenance during axillary meristem development have only just begun. In this minireview, we describe the genetic mechanisms underlying stem cell maintenance in both the established SAM and the developing axillary meristem in two model plants, Arabidopsis thaliana and Oryza sativa (rice). We also discuss the function of genes that are specific or shared between the established and developing meristems or between Arabidopsis and rice.
Athyrium christensenianum has been considered a fern hybrid of diploid sexual A. crenulatoserrulatum and tetraploid sexual A. decurrentialatum. Based on plastid (rbcL) and nuclear (AK1) DNA phylogeny, this study solved relationships between A. crenulatoserrulatum (allele A), A. decurrentialatum (B) and A. opacum (C). Relationships of the complex suggested A. christensenianum had at least five allele constitution: α, AABB (tetraploid sexual); β, AAB (triploid sterile); γ, ABB (triploid sterile); δ, ABBB (tetraploid sterile); ε, ABC (triploid sterile). In addition, this study expected the existence of undetected tetraploid sexual species which is originated from hybrid between ancestral diploid sexual A. decurrentialatum and diploid sexual A. opacum.
Sandwich freezing (freezing the specimen rapidly with liquid propane by placing it between two copper disks) and freeze-substitution of living yeast cells has been used for observing exquisite close-to-native ultrastructure of cells. Glutaraldehyde fixation, sandwich freezing, and freeze substitution of bacteria and other microorganisms also yield close-to-native ultrastructure. Here, we have used glutaraldehyde fixation, sandwich freezing, and freeze substitution to observe human cells and tissues. We obtained clear and natural cell images of tissues sliced to 0.2 mm thickness. This is a remarkable result because, in the past, tissues as thick as 0.2 mm could only be frozen by high-pressure freezing. The present study has shown that it is possible to observe clear and natural cell structures in animal and human tissues anytime because glutaraldehyde-fixed tissues can be stored at 4°C for several months before freezing, and a sandwich-freezing device will soon become commercially available. Also, natural ultrastructure of cultured cells in suspension was found to be observed more clearly by glutaraldehyde-fixation, sandwich freezing, and freeze-substitution than sandwich freezing and freeze substitution of living cells. The present method should be used as a standard method to observe the close-to-native ultrastructure of animal and human tissues.
Techniques for protoplast isolation from various plants are widely applied. The purpose of this work is to develop an efficient system for isolating and purifying mesophyll protoplasts from a gymnosperm, Ginkgo biloba L. We tried to optimize main factors influencing the isolation of mesophyll protoplasts from G. biloba, including the enzyme type and concentration, incubation time, enzyme solution pH, osmotic pressure, nylon mesh size, and centrifugation speed. The suitable enzyme digestion system consisted of digestion by 2% (w/v) cellulase R-10, 0.2% (w/v) pectolyase Y-23 and 1.5% (w/v) macerozyme R-10 for 5 h in the dark at 25°C. After filtration through a 300-mesh nylon membrane and centrifugation at 50 G, the yield and viability of the obtained protoplasts reached approximately 5.39×106 protoplasts g−1 fresh weight (FW) and 80.23%, respectively, Then, the yield and viability of protoplasts isolated via the same method in two different years were compared under the optimal conditions. It proved that the protocol was repeatable and effective.
Chromosome number, morphology, and behavior in the mitotic cycle were examined for 334 individuals from 34 local populations of Chamaelirium japonicum, including two infraspecific taxa so far chromosomally uninvestigated, and for 20 individuals from three populations of C. koidzumianum, including one variety cytologically unexplored to date. All of the individuals proved to have holocentric chromosomes, and 351 out of the 354 individuals exhibited 2n=24=4L+20S (where L and S denote ‘long’ and ‘short,’ respectively) and were regarded as diploids (2x). Of the other three individuals of C. japonicum ssp. japonicum, two were triploids (3x) with 2n=36=6L+30S, and one was a hyperploid (2x+1) with 2n=25=4L+19S+2f, of which the two small chromosomes (f) presumably arose by fission in one short chromosome. The triploid and the hyperploid showed lower pollen stainability (16.3 and 71.7%, respectively) with cotton blue than normal diploids (98.0–99.5%). Factors leading to the high stability of chromosomal traits in the two species are suggested.
Chromosome numbers of four endemic Hesperis species (H. armena Boiss., H. kotschyi Boiss., H. pisidica Hub.-Mor. and H. thyrsoidea Boiss.) in Turkey have been reported for the first time. All species have 2n=14 chromosomes, except H. pisidica Hub.-Mor. (2n=12). This species is also different from the others because of having satellite. Determining of the basic chromosome numbers x=6 and 7 are consistent with previous reports on Hesperis taxa in Turkey.
The course of male meiosis was studied in six species of Abutilon collected from different localities in North-West India. Abutilon bidentatum, A. indicum, A. muticum, A. pannosum and A. theophrasti showed gametic chromosome number n=21 and were found to be hexaploid (6x). A. ramosum was found to be diploid (2x) with chromosome number n=8. A. muticum (n=21) has been worked out for the first time. The present study revealed that genus Abutilon is dibasic having basic chromosome numbers x=7 and 8. The genetic divergence among the selected accessions of six species of Abutilon was analyzed by using ITS of rDNA as a DNA marker. The sequences of ITS showed divergence at 126 nucleotide positions. Two major clades of Abutilon species were resolved in the phylogenetic tree with basic chromosome numbers x=7 and 8. A. ramosum (x=8) lies genetically between Abutilon species with x=7 and those species of Abutilon already shifted to genus Callianthe with x=8.
Lactuca sativa L. is one of the most important reference species for genome research in Compositae. In the present study, chromosome image analysis system IV (CHIAS IV) and fluorescence in situ hybridization (FISH) were applied to obtain detailed information of the characteristics of lettuce chromosomes. One lettuce cultivar of L. sativa and three wild species of L. serriola, L. saligna and L. virosa were used to analyze chromosome lengths, arm ratios and degrees of chromosomal condensation at prometaphase. Locations of 45S and 5S rRNA genes were determined by FISH technique. Our results showed that nine pairs of homologous chromosomes could be discriminated for all four species by their morphological characteristics, condensation patterns (CPs) and localization of rRNA loci. Statistical analysis showed that the total length of L. saligna chromosomes was significantly the shortest among the species tested. The present study is the first for the physical mapping of condensed regions and rDNAs using CPs and FISH of prometaphase chromosomes in lettuce. The information provided here would be valuable for practical breeding and genetics of lettuce.
Cytological studies of five genera, six species of Commelinaceae from Thailand revealed the following karyotypes: Amischotolype mollissima, 2n=36 (2m+16sm+18st); Callisia fragrans, 2n=12 (6m+6st); Commelina benghalensis, 2n=22 (12m+6sm+4st); Co. diffusa 2n=48 (26m+22sm); Murdannia loriformis 2n=20 (8m+12sm); and Tradescantia spathacea 2n=12 (4m+4sm+4st). The satellites appeared in the karyotype of Co. benghalensis and M. loriformis. The karyotype formula, fundamental number (NF), and total chromosome length of A. mollissima, M. loriformis, and T. spathacea were studied for the first time.
Bananas provide a vital food source for growing populations in many countries that used as a staple food and played an important role in poverty alleviation in many of the underdeveloped countries. To increase the productivity of cultivated banana against growing pest and disease pressure under changing environmental conditions, wild banana needs to explore for their disease resistance and climate resilience gene pool. Musa laterita, a wild species of Gangtok of Indian occurrence was described for the first time morphologically, compared with the existing two accessions of Musa Germplasm Information System (MGIS) data and found different in 18 morphological characters against the recorded 117 morphological data as Simmonds (1962) morphological index suggesting its genome of AB. This species has upright inflorescence and very small 7.6–8.9 cm seeded fingers (yellow-skinned after ripening with sweet pulp) on 2–3 hands (4 to 5 finger each). The somatic chromosome number recorded was 2n=22 with total chromosome length and volume was 42.6 µm and 18.8 µm3 respectively in the karyotype. The flowcytometric analysis confirmed the 2C DNA content for the first time was 1.302 pg and calculated genome size of ∼637 Mbp. Detailed genomic characterization of diploid seeded wild banana could be used as a progenitor in the banana breeding program for crop improvement by introgressing the wild disease-resistant traits in cultivated banana for their conservation and sustainable utilization.
For the assessment of radiation-induced damage in human cells, the frequency of chromosomal aberrations, especially that of dicentric chromosomes in peripheral blood lymphocytes, has been used as the measure in biodosimetry. Considering mass-casualty radiological incidents, it is hoped to preserve part of the blood specimens to be examined at an appropriate time after the medical triage process. In this study, the potential usefulness of lymphocytes cryopreserved for longer than one year was assessed as a pilot study. Seven blood specimens from three healthy donors were experimentally irradiated and cryopreserved for approximately one to five years. All cryopreserved specimens examined were successfully cultured to obtain a sufficient number of mitotic cells for dosimetric analyses. Blood specimens from one donor were intensively examined for the precise comparative analysis of chromosomal aberrations between cultures of cryopreserved specimens and those of freshly prepared specimens. The frequencies of cells with chromosomal aberrations in 1.5-year-cryopreserved specimens after 2-Gy gamma irradiation were not significantly different from those examined using a fresh blood specimen. In this study, we showed the practical significance of the cryopreservation method of peripheral blood lymphocytes that can offer a new strategy of preparedness for triage in mass-casualty radiation incidents/accidents.
The chromosome numbers and karyotypes of 11 species the subgenus Leopoldia of the genus Muscari distributed in Turkey were analyzed. These taxa are M. comosum (L.) Miller, M. weissii Freyn, M. caucasicum (Griseb.) Baker, M. tenuiflorum Tausch, M. babachii Eker & Koyuncu, M. erdalii Özhatay & Demirci, M. longipes Boiss., M. massayanum Grunert, M. mirum Speta, M. elmasii Yıldırım, and M. haradjiani Briq. ex Rech., and six of them (M. babachii, M. erdalii, M. massayanum, M. mirum, M. elmasii, M. haradjiani) are endemic species in Turkey. The somatic chromosome number of all studied taxa were determeined as 2n=2x=18. Haploid chromosome lengths varied 44.06 (M. massayanum) to 67.50 µm (M. babachii) among species. Karyotype analysis indicated that Muscari taxa generally have median (m), submedian (sm) and subterminal (st) chromosomes. In addition, only M. comosum has one terminal (t) chromosome. Satellites were observed in five species, M. tenuiflorum, M. erdalii, M. longipes, M. mirum and M. haradjianii. This study is the first in terms of revealing the karyotypes of all taxa of subgenus Leopoldia on the genus Muscari.
Karyomorphology, distribution of constitutive heterochromatin, and intrapopulation polymorphism of C-bands in a cross-pollinated population of Nigella sativa L. were studied. Enzymatic digestion of the cell wall allows cytoplasm-free chromosome preparation and enhances the stain resolution, thereby promoting accurate chromosome measurements and identification of chromosomal landmarks. The diploid chromosome number is 2n=12, of which five pairs are moderately long and have median centromere, whereas one small pair has a subterminal centromere. Secondary constriction has been observed in two pairs of long chromosomes. Polymorphism of the C-band size in individuals of the same population and even between two homologous chromosomes of a single individual has been detected by the C-banding technique. Further, the absence of any DAPI-bands indicated that the DNA of C-band region is not AT-rich. The heterogeneity of C-bands in homologous pairs of a single individual is a consequence of cross-pollination where chromosomes come from two different parents. The pattern of heterochromatin distribution can serve as a unique marker that can enrich the karyosystematic database and prove useful in the breeding program of N. sativa.