Morphogenesis of Anthers Isolated From Cabbage (Brassica Oleracea L.) In Vitro

This study aimed to optimize the steps of obtaining regenerated cabbage plants by direct embryogenesis from isolated anthers and ovaries. Stepwise pretreatment of inflorescences was usedfor the studied hybrids and inbred lines. First, the inflorescences were placed in water and kept at a temperature of +4-6∘C for one day without the use of biologically active substances. Then the inflorescences were placed in a solution of the drug Dropp (10 mg/l) and cultivated for two days. After that, the anthers and ovaries were isolated from the flower buds and cultured on the MS culture medium at a temperature of + 32∘C for one day. The cultivation of the isolated explants on a nutrient medium (containing 0.01 mg/lof Dropp, 1.0 mg/lof NAA, 500 mg/lof asparagine, 100 mg/l of tyrosine, and 10 g/l of sucrose)led to an increase in their morphogenetic potential in the culture of anthers and ovaries (by 3.42% and 5.54%, respectively).A cytological method was usedto demonstrate the haploid nature of the regenerating plants. The number of chromosomes in the root meristem andleaves, and the chloroplasts in the closing cells of the stomatawere calculated. Keywords: cabbage, culture in vitro, regenerated plants, anthers, ovaries, reproductive organs

Distinct mechanisms orchestrate the contra-polarity of IRK and KOIN, two LRR-receptor-kinases controlling root cell division

In plants, cell polarity plays key roles in coordinating developmental processes. Despite the characterization of several polarly localized plasma membrane proteins, the mechanisms connecting protein dynamics with cellular functions often remain unclear. Here, we introduce a polarized receptor, KOIN, that restricts cell divisions in the Arabidopsis root meristem. In the endodermis, KOIN polarity is opposite to IRK, a receptor that represses endodermal cell divisions. Their contra-polar localization facilitates dissection of polarity mechanisms and the links between polarity and function. We find that IRK and KOIN are recognized, sorted, and secreted through distinct pathways. IRK extracellular domains determine its polarity and partially rescue the mutant phenotype, whereas KOIN’s extracellular domains are insufficient for polar sorting and function. Endodermal expression of an IRK/KOIN chimera generates non-cell-autonomous misregulation of root cell divisions that impacts patterning. Altogether, we reveal two contrasting mechanisms determining these receptors’ polarity and link their polarity to cell divisions in root tissue patterning.

Cellular and gene expression patterns associated with root bifurcation in Selaginella

The roots of lycophytes branch through dichotomy or bifurcation, which means that the root apex splits into two daughter roots. This is morphologically distinct from lateral root (LR) branching in the extant euphyllophytes, where LRs develop along the root axis at different distances from the apex. The process of root bifurcation is poorly understood, while such knowledge can be important, as it may represent an evolutionarily ancient strategy that roots recruited to form new stem cells or meristems. In this study, we examined root bifurcation in the lycophyte Selaginella moellendorffii. We characterized an in vitro developmental time-frame based on repetitive apex bifurcations, allowing us to sample different stages of dichotomous root branching and analyze the root meristem and root branching in S. moellendorffii at the microscopical and transcriptional level. Our results show that, in contrast to previous assumptions, initial cells in the root meristem are mostly not tetrahedral but rather show an irregular shape. Tracking down the early stages during root branching argues for the occurrence of a symmetric division of the single initial cell resulting in two apical stem cells allowing for root meristem bifurcation. Moreover, we generated a S. moellendorffii root branching transcriptome, which resulted in the delineation of a subset of core meristem genes. The occurrence of multiple meristem-related orthologues in this dataset, including inversely correlated expression profiles of a SCARECROW (SCR) versus a RETINOBLASTOMA-RELATED1 (RBR1) homologue suggests the presence of conserved pathways in the control of meristem and root stem cell establishment or maintenance.

The cytogenetic parameters of Pinus sylvestris L. under conditions of the Far North of Russia (Karelia)

The cytogenetic analysis of the Pinus sylvestris L. seed progeny in the forests of the northern taiga in the Far North of Russia conditions was carried out. Two Pinus sylvestris populations growing in Ambarnskoy and Pyaozerskoy forest divisions of Loukhsky district of Karelia Republic were studied. The number of chromosomes, the frequency and types of mitosis disturbances at the metaphase, anaphase and telophase (as a percentage of the total number of dividing cells at the same stages), and the frequency of micronuclei occurrence, as well as the laboratory seed germination, were studied. As a result of the study, it was found that 50–56% of the studied sprouts were mixoploid. Analysis of mitosis showed that the root meristem of the studied samples contained cells with various pathologies; simultaneously, the frequency of mitosis pathologies in the Ambarnskoy population was significantly higher than in the Pyaozerskoy one. It amounted to 6.8 ± 0.4 and 4.9 ± 0.4%, respectively. Nine types of abnormalities were identified; chromosome overrun and bridges prevailed. Micronuclei were registered in 35–38% of the studied Pinus sylvestris sprouts. At the same time, the proportion of cells with micronuclei in the Ambarnskoy population was 2-fold higher than in the Pyaozerskoy one and averaged 0.12 ± 0.03% and 0.07 ± 0.02%, respectively.

An assessment of cytotoxic potentiality of Aloe barbadensis on the root meristem cells of Trigonella foenum-graecum L.

The leaves of Aloe barbadensis are used in traditional and modern systems of medicine. The aim of this study was to evaluate the cytotoxic potentialities of aqueous solution of Aloe barbadensis leaves on Trigonella foenum-graecum root tip meristem cells using a cytogenetic approach. Treatments with various concentrations of Aloe barbadensis leaf extract to Trigonella foenum-graecum root meristem cells showed mito-inhibition and induced several chromosomal aberrations as chromsomal breakage, fragmentation, scattering, stickiness etc.

ABA represses TOR and root meristem activity through nuclear exit of the SnRK1 kinase

The phytohormone abscisic acid (ABA) promotes plant tolerance to major stresses like drought, partly by modulating plant growth and development. However, the underlying mechanisms are poorly understood. Here, we show that cell proliferation in the Arabidopsis thaliana root meristem is controlled by the interplay between three kinases, SNF1-RELATED KINASE 2 (SnRK2), the main driver of ABA signaling, the SnRK1 energy sensor, and the growth-promoting TARGET OF RAPAMYCIN (TOR) kinase. Under favorable conditions, the SnRK1α1 catalytic subunit is enriched in the nuclei of root meristematic cells and this is accompanied by normal cell proliferation and meristem size. Depletion of SnRK2s in a snrk2.2 snrk2.3 double mutant causes constitutive cytoplasmic localization of SnRK1α1 and a reduction in meristem size, suggesting that, under non-stress conditions, SnRK2s enable growth by retaining SnRK1α1 in the nucleus. In response to elevated ABA levels, SnRK1α1 translocates to the cytoplasm and this is accompanied by inhibition of TOR, decreased cell proliferation and meristem size. Blocking nuclear export with leptomycin B abrogates ABA-driven SnRK1α1 relocalization to the cytoplasm and the inhibition of TOR. Fusion of SnRK1α1 to an SV40 nuclear localization signal leads to defective TOR repression in response to ABA, demonstrating that SnRK1α1 nuclear exit is a premise for this repression. Finally, the SnRK2-dependent changes in SnRK1α1 subcellular localization are specific to the proliferation zone of the meristem, underscoring the relevance of this mechanism for growth regulation.

Changes in Epigenetic Patterns Related to DNA Replication in Vicia faba Root Meristem Cells under Cadmium-Induced Stress Conditions

Experiments on Vicia faba root meristem cells exposed to 150 µM cadmium chloride (CdCl2) were undertaken to analyse epigenetic changes, mainly with respect to DNA replication stress. Histone modifications examined by means of immunofluorescence labeling included: (1) acetylation of histone H3 on lysine 56 (H3K56Ac), involved in transcription, S phase, and response to DNA damage during DNA biosynthesis; (2) dimethylation of histone H3 on lysine 79 (H3K79Me2), correlated with the replication initiation; (3) phosphorylation of histone H3 on threonine 45 (H3T45Ph), engaged in DNA synthesis and apoptosis. Moreover, immunostaining using specific antibodies against 5-MetC-modified DNA was used to determine the level of DNA methylation. A significant decrease in the level of H3K79Me2, noted in all phases of the CdCl2-treated interphase cell nuclei, was found to correspond with: (1) an increase in the mean number of intranuclear foci of H3K56Ac histones (observed mainly in S-phase), (2) a plethora of nuclear and nucleolar labeling patterns (combined with a general decrease in H3T45Ph), and (3) a decrease in DNA methylation. All these changes correlate well with a general viewpoint that DNA modifications and post-translational histone modifications play an important role in gene expression and plant development under cadmium-induced stress conditions.

The root meristem is shaped by brassinosteroid control of cell geometry

Growth extent and direction determine cell and whole-organ architecture. How they are spatio-temporally modulated to control size and shape is not well known. Here we tackled this question by studying the effect of brassinosteroid (BR) signalling on the structure of the root meristem. Quantification of the three-dimensional geometry of thousands of individual meristematic cells across different tissue types showed that the modulation of BR signalling yields distinct changes in growth rate and anisotropy, which affects the time that cells spend in the meristem and has a strong impact on the final root form. By contrast, the hormone effect on cell volume was minor, establishing cell volume as invariant to the effect of BR. Thus, BR has the highest effect on cell shape and growth anisotropy, regulating the overall longitudinal and radial growth of the meristem, while maintaining a coherent distribution of cell sizes. Moving from single-cell quantification to the whole organ, we developed a computational model of radial growth. The simulation demonstrates how differential BR-regulated growth between the inner and outer tissues shapes the meristem and thus explains the non-intuitive outcomes of tissue-specific perturbation of BR signalling. The combined experimental data and simulation suggest that the inner and outer tissues have distinct but coordinated roles in growth regulation.