Cell Division In Higher Plants Research Articles

DNA replication arrest leads to enhanced homologous recombination and cell death in meristems of rice OsRecQl4 mutants

BackgroundMammalian BLM helicase is involved in DNA replication, DNA repair and homologous recombination (HR). These DNA transactions are associated tightly with cell division and are important for maintaining genome stability. However, unlike in mammals, cell division in higher plants is restricted mainly to the meristem, thus genome maintenance at the meristem is critical. The counterpart of BLM in Arabidopsis (AtRecQ4A) has been identified and its role in HR and in the response to DNA damage has been confirmed. However, the function of AtRecQ4A in the meristem during replication stress has not yet been well elucidated.ResultsWe isolated the BLM counterpart gene OsRecQl4 from rice and analyzed its function using a reverse genetics approach. Osrecql4 mutant plants showed hypersensitivity to DNA damaging agents and enhanced frequency of HR compared to wild-type (WT) plants. We further analyzed the effect of aphidicolin—an inhibitor of S-phase progression via its inhibitory effect on DNA polymerases—on genome stability in the root meristem in osrecql4 mutant plants and corresponding WT plants. The following effects were observed upon aphidicolin treatment: a) comet assay showed induction of DNA double-strand breaks (DSBs) in mutant plants, b) TUNEL assay showed enhanced DNA breaks at the root meristem in mutant plants, c) a recombination reporter showed enhanced HR frequency in mutant calli, d) propidium iodide (PI) staining of root tips revealed an increased incidence of cell death in the meristem of mutant plants.ConclusionsThese results demonstrate that the aphidicolin-sensitive phenotype of osrecql4 mutants was in part due to induced DSBs and cell death, and that OsRecQl4 plays an important role as a caretaker, maintaining genome stability during DNA replication stress in the rice meristem.

SSD1, which encodes a plant-specific novel protein, controls plant elongation by regulating cell division in rice

Plant height is one of the most important traits in crop improvement. Therefore revealing the mechanism of plant elongation and controlling plant height in accordance with breeding object is important. In this study we analyzed a novel dwarf mutant, ssd1, of which phenotype is different from typical GA- or BR-related dwarf phenotype. ssd1 exhibits pleiotropic defects in elongation of various organs such as stems, roots, leaves, and flowers. ssd1 also shows abnormal cell files and shapes, which suggests defects of normal cell division in the mutant. Map-based cloning and complementation test demonstrated that the dwarf phenotype in ssd1 mutant was caused by insertion of retrotransposon in a gene, which encodes plant-specific protein with unknown biochemical function. A BLAST search revealed that SSD1-like genes exist in diverse plant species, including monocots and dicots, but not fern and moss. Our results demonstrate that SSD1 controls plant elongation by controlling cell division in higher plants.

Roles of actin-depleted zone and preprophase band in determining the division site of higher-plant cells, a tobacco BY-2 cell line expressing GFP-tubulin.

The mode of cytokinesis, especially in determining the site of cell division, is not well understood in higher-plant cells. The division site appears to be predicted by the preprophase band of microtubules that develop with the phragmosome, an intracellular structure of the cytoplasm suspending the nucleus and the mitotic apparatus in the center. As the preprophase band disappears during mitosis, it is thought to leave some form of "memory" on the plasma membrane to guide the growth of the new cell plate at cytokinesis. However, the intrinsic nature of this "memory" remains to be clarified. In addition to microtubules, microfilaments also dynamically change forms during cell cycle transition from the late G2 to the early G1 phase. We have studied the relationships between microtubules and microfilaments in tobacco BY-2 cells and transgenic BY-2 cells expressing a fusion protein of green-fluorescent protein and tubulin. At the late G2 phase, microfilaments colocalize with the preprophase band of microtubules. However, an actin-depleted zone which appears at late prometaphase is observed around the chromosomes, especially at metaphase, but also throughout anaphase. To study the functions of the actin-depleted zone, we disrupted the microfilament structures with bistheonellide A, a novel macrolide that depolymerizes microfilaments very rapidly even at low concentrations. The division planes became disorganized when the drug was added to synchronized BY-2 cells before the appearance of the actin-depleted zone. In contrast, the division planes appeared smooth, as in control cells, when the drug was added after the appearance of the actin-depleted zone. These results suggest that the actin-depleted zone may participate in the demarcation of the division site at the final stage of cell division in higher plants.

Identification and role of adenylyl cyclase in auxin signalling in higher plants.

Cyclic AMP is an important signalling molecule in prokaryotes and eukaryotes1, but its significance in higher plants has been generally doubted2 because they have low adenylyl cyclase activity and barely detectable amounts of cAMP3. Here we used activation T-DNA tagging to create tobacco cell lines that can proliferate in the absence of the phytohormone auxin in the culture media4,5. The sequence tagged in one line, axi 141, was used to isolate a complementary DNA encoding adenylyl cyclase, the first from a higher plant. Sequence analysis reveals that the tobacco adenylyl cyclase is probably soluble, contains characteristic leucine-rich repeats, and bears similarity with adenylyl cyclase from the yeast Schizosaccharomyces pombe. Expression of the cDNA in Escherichia coli results in an increase in endogenous cAMP levels, and in yeast its expression functionally complements the cry1 mutation. Tobacco protoplasts treated with cAMP, or the adenylyl cyclase activator forskolin, no longer require auxin to divide. This finding, together with the observation that the adenylyl cyclase inhibitor dideoxyadenosine inhibits cell proliferation in the presence of auxin, suggests that cAMP is involved in auxin-triggered cell division in higher plants.

Chapter 21 Methods for Studying Cell Division in Higher Plants

Publisher Summary This chapter discusses the methods for studying cell division in higher plants. The study of mitosis and cytokinesis in cells of higher plants has a long and distinguished history. From the outset, the distinct parallels in mitotic processes between plant and animal cells have been apparent, leading to the conclusion that a similar substructure and mechanism underlies both. However, it was also recognized early that there are notable differences. Mitotic plant cells, for example, generally do not possess a centrosome or a highly focused spindle apparatus at the mitotic poles. During anaphase they also generally exhibit chromosome to pole motion (anaphase A) but with little pole separation (anaphase B) when compared to animal cells. Further, they accomplish cytokinesis by forming a phragmoplast and cell plate within the cell interior, which then grows outward, rather than by inward furrowing as occurs typically in animal cells. Indeed, the process of cytokinesis and cell plate formation determines the plane of division and thus plays a crucial role in defining cell shape and tissue morphogenesis for which a parallel event is not so evident in animal cells. It is for these and all the other obvious reasons that the study of cell division in plants is both interesting and important.

Identification and role of adenylyl cyclase in auxin signalling in higher plants.

Cyclic AMP is an important signalling molecule in prokaryotes and eukaryotes, but its significance in higher plants has been generally doubted because they have low adenylyl cyclase activity and barely detectable amounts of cAMP. Here we used activation T-DNA tagging to create tobacco cell lines that can proliferate in the absence of the phytohormone auxin in the culture media. The sequence tagged in one line, axi 141, was used to isolate a complementary DNA encoding adenylyl cyclase, the first from a higher plant. Sequence analysis reveals that the tobacco adenylyl cyclase is probably soluble, contains characteristic leucine-rich repeats, and bears similarity with adenylyl cyclase from the yeast Schizosaccharomyces pombe. Expression of the cDNA in Escherichia coli results in an increase in endogenous cAMP levels, and in yeast its expression functionally complements the cry1 mutation. Tobacco protoplasts treated with cAMP, or the adenylyl cyclase activator forskolin, no longer require auxin to divide. This finding, together with the observation that the adenylyl cyclase inhibitor dideoxyadenosine inhibits cell proliferation in the presence of auxin, suggests that cAMP is involved in auxin-triggered cell division in higher plants.

Effects of Spaceflight on Growth and Cell Division in Higher Plants

This chapter reviews the effects of spaceflight on growth and cell division in higher plants. The chapter focuses on the expression and modulation of the genetic information which is present in developing and growing systems. At the cellular level, the genetic information involves an understanding of the external and internal growth regulatory controls which operate in resting or quiescent cells as they are activated to grow again at rapid rates. Using an embryogenic system of an organism similar to carrot showed an increased biomass of embryonic structures generated in space in liquid cultures. Chromosomes and plant cell division is also discussed in the chapter. The CHROMEX experiment employed, for the first time in a space-based experiment, tissue culture-derived plantlets. For H. gracilis , comparably sized seed-derived plants, were included in the experimental protocol. In all cases, the experimental plants began as fully differentiated individuals, complete with leaves, shoots, and roots, which had been maintained under aseptic conditions from their initiation.

A role for preprophase bands of microtubules in maturation of new cell walls, and a general proposal on the function of preprophase band sites in cell division in higher plants

ABSTRACT Time-lapse video microscopy of dividing Tradescantia stamen hair cells that are undergoing cytokinesis has revealed that the maturation of the new cell wall is aided by factors at the site where the preprophase band of microtubules forms before mitosis. The wall changes from being fluid and wrinkled before it is inserted into the parental wall at the end of cytokinesis, to being stiff and flat by about 20 min after the time of attachment. This change occurs only if the new wall is inserted at the site formerly occupied by the preprophase band. The cell plate does not flatten when it is caused to insert elsewhere by drug treatments or by centrifugal displacement. If insertion at the correct site is delayed locally by centrifugation against the direction of expansion of the cell plate, then flattening is delayed at the same locality. In combination with a number of points from the literature of plant cell division, some of them very long-standing, our observations lead to a general proposal regarding the nature of the preprophase band site, its mode of action and timing of its operations, and how its role in spatial regulation of histogenesis is achieved.

Cell division in higher plants: a cdc2 gene, its 34-kDa product, and histone H1 kinase activity in pea.

The mitotic cell cycle of yeast and animal cells is regulated by the cdc2 gene and its product, the p34 protein kinase, and by other components of the MPF or histone H1 kinase complex. We present evidence that cdc2, p34, and a histone H1 kinase also exist in higher plants. Protein extracts from 10 plant species surveyed display a 34-kDa component recognized by a monoclonal antibody directed against an evolutionarily conserved epitope of fission yeast p34. Nondenatured protein extracts of mitotic Pisum sativum (garden pea) tissues were fractionated by gel filtration, electrophoretically separated under denaturing conditions, and immunoblotted. p34 crossreactive material was apparent in both low and high molecular mass fractions, indicating that pea p34 occurs as both a monomer and as part of a high molecular mass complex. Histone H1 kinase activity was found predominantly in the higher molecular mass fractions, those to which the least phosphorylated form of pea p34 was confined. We also report the cloning of the pea homologue of cdc2 by polymerase chain reaction. DNA sequence analysis reveals perfect conservation of the hallmark "PSTAIR" sequence motif found in all cdc2 gene products analyzed to date.

Karyological observations.

Root tips prepared for metaphase chromosome analysis from seedlings germinated under microgravity on the Space Shuttle (oats and mung bean) or which were exposed to space flight as very young seedlings (sunflower) have been examined. Experimental constraints did not permit pre-fixation in space with a cytostatic agent but arrest was achieved in the first division cycle on Earth after recovery. The number of cells in division was significantly depressed in all three species. Several chromosomal abnormalities were encountered in flight material. Bridge formation was seen in sunflower, as was aneuploidy. Breakage and fracture of chromosomes was prevalent in oats. No aberrant features could be detected in the chromosomes of mung bean. These results, although preliminary, should serve to alert investigators of the need to assess carefully as many aspects of cell division in higher plants exposed to space flight conditions as possible.

Reviews

Book Reviewed in this article: Botanical Microtechnique and Cytochemistry. By G. P. Berlyn and J. P. Miksche. Annual Review of Plant Physiology. Ed. by W. R. Briggs. Mechanical Design in Organisms. By S. A. Wainwright, W. D. Biggs, J. D. Currey & J. M. Gosline. Uptake of Ions by Plant Roots. By D. J. F. Bowling. Phytochrome and Photomorphogenesis. By Harry Smith. Water and Plants. By Hans Meidner and D. W. Sheriff. Physiological Aspects of Dryland Farming. Edited by U. S. Gupta. Pollen: Biology, Biochemistry, Management. By R. G. Stanley and H. F. Linskens. The Evolutionary Significance of the Exine. Ed. by I. K. Ferguson and J. Muller. Cell Division in Higher Plants. Ed. by M. M. Yeoman. Intercellular Communication in Plants: Studies on Plasmodesmata Ed. by B. E. S. Gunning & A. W. Robards. Methods in Plant Ecology. Ed. by S. B. Chapman Ökologie DER Pflazen By Walter Larcher. Progress in Botany. Vol. 37. Ed. by H. Ellenberg, K. Esser, H. Merxmüller, E. Schnepf & H. Ziegler. British Botanical and Horticultural Literature before 1800. By Blanche Henrey.

BOOK REVIEWS

M. M. Yeoman (ed.): Cell Division in Higher Plants. Academic Press, London, 1976. pp. 452. $41.—.

Lycorine as an inhibitor of ascorbic acid biosynthesis

LYCORINE, an alkaloid extracted from Amarillidaceae1,2, is a powerful inhibitor of growth in higher plants, algae and yeasts. At the very low concentration of 10−6 M, lycorine inhibits cell division in higher plants, red algae and yeasts, and the cell cycle is arrested in the interphase stage3. No inhibition of cell division was observed in Escherichia coli (O. A., unpublished).