赤霉素对拟南芥主根分生区和伸长区的调控

赤霉素是一类重要的植物激素,在植物整个生长发育的调控过程中起重要作用。近年来,人们发现赤霉素对拟南芥主根生长存在促进作用。本文从根系的解剖结构、赤霉素的源靶部位、促进作用的机理、赤霉素信号转导途径以及与其他激素的关系等方面,综述了赤霉素对拟南芥主根分生区和伸长区的影响。     

Epidermal Patterning Genes Impose Non-cell Autonomous Cell Size Determination and have Additional Roles in Root Meristem Size Control

The regulation of cellular growth is of vital importance for embryonic and postembryonic patterning. Growth regulation in the epidermis has importance for organ growth rates in roots and shoots, proposing epidermal cells as an interesting model for cellular growth regulation. Here we assessed whether the root epidermis is a suitable model system to address cell size determination. In Arabidopsis thaliana L., root epidermal cells are regularly spaced in neighbouring tricho- (root hair) and atrichoblast (non-hair) cells, showing already distinct cell size regulation in the root meristem. We determined cell sizes in the root meristem and at the onset of cellular elongation, revealing that not only division rates but also cellular shape is distinct in tricho- and atrichoblasts. Intriguingly, epidermal-patterning mutants, failing to define differential vacuolization in neighbouring epidermal cell files, also display non-differential growth. Using these epidermal-patterning mutants, we show that polarized growth behaviour of epidermal tricho- and atrichoblast is interdependent, suggesting non-cell autonomous signals to integrate tissue expansion. Besides the interweaved cell-type-dependent growth mechanism, we reveal an additional role for epidermal patterning genes in root meristem size and organ growth regulation. We conclude that epidermal cells represent a suitable model system to study cell size determination and interdependent tissue growth.     

钙调素参与拟南芥根细胞增殖及幼苗对外源脱落酸的敏感性反应过程

钙调素作为真核细胞的重要信号蛋白,在真核生物正常及逆境条件下的生长发育中发挥着重要作用.研究报道钙调素可促进离体培养的高等动植物细胞的增殖,但有关钙调素蛋白在植物体内的细胞增殖功能尚未见报道.特别是拟南芥基因组中存在7个编码经典钙调素亚型的基因,多数编码基因的功能有待进一步探究.首先借助常用的钙调素拮抗剂W7进行药理学实验,结果表明,野生型拟南芥幼苗根的生长受到了明显的抑制,根尖分生区的面积变小、细胞数目明显减少,根尖分生区中细胞分裂标记基因CYCB1;1的表达受到了明显抑制,这表明在根尖分生区W7可能通过对活性钙调素的抑制作用影响了根尖分生区域的细胞增殖,而根尖分生区正常的细胞增殖需要一定量活性钙调素蛋白的存在.脱落酸(ABA)是植物逆境下的重要激素,在植物种子萌发及幼苗生长发育中发挥着重要作用,W7存在下的拟南芥幼苗对ABA的敏感性下降.借助反向遗传学手段获得了拟南芥中三个编码典型钙调素蛋白基因的三重缺失突变体cam234,蛋白质印迹结果表明三重缺失突变体中钙调素蛋白的含量明显降低.相同培养条件下与野生型相比,三重突变体幼苗根长变短,并且幼苗对ABA敏感性也表现下降趋势,暗示着这三个基因编码的钙调素蛋白可能参与了根分生区域细胞增殖过程及幼苗对脱落酸的敏感性反应,讨论了钙调素的细胞增殖功能及与幼苗对脱落酸的敏感性反应间的关系.     

OsCBL1 Modulates Lateral Root Elongation in Rice via Affecting Endogenous Indole-3-Acetic Acid Biosynthesis

<正>Root growth is important for plants to efficiently acquire water and mineral nutrients from soil.Root system architecture(RSA),which is determined mainly by root branching through lateral root formation and root angles,has a significant influence on root growth.Generally,the growth and development of roots are regulated by numerous plant hormones,which respond to external environmental stimulation through com-     

Variations in the Size of Mitotic Cells in the Root Meristem

Variations in the length of mitotic and interphase cells were analyzed in various tissues of wheat roots and in the cortex of maize roots. Reliable differences were shown in the length of mitotic cells in individual file clones of cells of the same tissue. The mean lengths of dividing cells in different roots differed to a lesser extent than those of different files in the same tissue of one root. Within the file, the length of the sister simultaneously dividing cells differed the least, while the difference of lengths of the neighbor simultaneously dividing nonsister cells was bigger. The mean length of interphase cells in any file was always less than that of mitotic cells by a factor of 1.45. This ratio was almost invariable for files and tissues in both the plants we studied and corresponded to that of an exponentially growing cell population. In addition, a very small number of cells were found (less than 1%) in meristems, which are longer than the mitotic cells. The length of these cells exceeded those of mitotic cells by less than twice. The origin of such cells is discussed. The length of mitotic cells near the quiescent center is more variable than in the middle of the meristem in the cortex of both plants. In the meristem basal part, the mitotic cells were no longer than those in the middle of the meristem but there were no small dividing cells. In the wheat epidermis, the cells are differentiated into trichoblasts and atrichoblasts and, therefore, the length of the dividing cells is highly variable. The cell length is essential for their transition to mitosis for all studied proliferating meristem cells.     

Strigolactone Positively Controls Crown Root Elongation in Rice

Strigolactones are recently identified plant hormones that inhibit shoot branching. Pleiotropic defects in strigolactone-deficient or -insensitive mutants indicate that strigolactones control various aspects of plant growth and development. However, our understanding of the hormonal function of strigolactones in plants is very limited. In this study we demonstrate that rice dwarf mutants that are strigolactone-deficient or -insensitive exhibit a short crown root phenotype. Exogenous application of GR24, a synthetic strigolactone analog, complemented the crown root defect in strigolactone-deficient mutants but not in strigolactone-insensitive mutants. These observations imply that strigolactones positively regulate the length of crown roots. Histological observations revealed that the meristematic zone is shorter in dwarf mutants than in wild type, suggesting that strigolactones may exert their effect on roots via the control of cell division. We also show that crown roots of wild type, but not dwarf mutants, become longer under phosphate starvation.     

Simvastatin Modulates Mesenchymal Stromal Cell Proliferation and Gene Expression

Statins are widely used hypocholesterolemic drugs that block the mevalonate pathway, responsible for the biosysnthesis of cholesterol. However, statins also have pleiotropic effects that interfere with several signaling pathways. Mesenchymal stromal cells (MSC) are a heterogeneous mixture of cells that can be isolated from a variety of tissues and are identified by the expression of a panel of surface markers and by their ability to differentiate in vitro into osteocytes, adipocytes and chondrocytes. MSC were isolated from amniotic membranes and bone marrows and characterized based on ISCT (International Society for Cell Therapy) minimal criteria. Simvastatin-treated cells and controls were directly assayed by CFSE (Carboxyfluorescein diacetate succinimidyl ester) staining to assess their cell proliferation and their RNA was used for microarray analyses and quantitative PCR (qPCR). These MSC were also evaluated for their ability to inhibit PBMC (peripheral blood mononuclear cells) proliferation. We show here that simvastatin negatively modulates MSC proliferation in a dose-dependent way and regulates the expression of proliferation-related genes. Importantly, we observed that simvastatin increased the percentage of a subset of smaller MSC, which also were actively proliferating. The association of MSC decreased size with increased pluripotency and the accumulating evidence that statins may prevent cellular senescence led us to hypothesize that simvastatin induces a smaller subpopulation that may have increased ability to maintain the entire pool of MSC and also to protect them from cellular senescence induced by long-term cultures/passages in vitro. These results may be important to better understand the pleiotropic effects of statins and its effects on the biology of cells with regenerative potential.     

Experimental Modification of Cell Division Patterns in the Root Meristem of Zea mays

In the meristem of the young primary root of maize seedlingsthe first transverse division in the cortex 250 µm fromthe root apex results in two daughter cells of distinctly unequalsize. This division could be rendered equal by raising the seedlingsin up to 7.5% methanol. The pattern of the subsequent two orthree transverse divisions in the cortex, as revealed by thearrangement of the newly divided cells in the resultant cellularpackets, was acropetal in the methanol-treated roots but basipetalin the control roots. The sequence of division within a cellularpacket tended to follow the distribution of cell sizes - largercells divided earlier than smaller cells. A temporary arrestof cell division by exposing roots to cold (5 °C) conditionshad no effect on the sequence of divisions that followed whenthe roots were allowed to recover at 20 °C. The resultssuggest that the normally asymmetric position of the cell wallformed at cytokinesis is subject to active regulation and thatmethanol interferes with this process. The cytoplasm of certaincells in the root meristem was also found to be unequally distributed,as judged by Azure B staining, between the two ends of the cell.Cytoplasmic asymmetry was not directly correlated with inequalityof division, although it too was affected by methanol. Cell polarity, root meristem, unequal division, Zea mays     

Glucose Regulates Rat Beta Cell Number through Age-Dependent Effects on Beta Cell Survival and Proliferation

Background

Glucose effects on beta cell survival and DNA-synthesis suggest a role as regulator of beta cell mass but data on beta cell numbers are lacking. We examined outcome of these influences on the number of beta cells isolated at different growth stages in their population.

Methods

Beta cells from neonatal, young-adult and old rats were cultured serum-free for 15 days. Their number was counted by automated whole-well imaging distinguishing influences on cell survival and on proliferative activity.

Results

Elevated glucose (10–20 versus 5 mmol/l) increased the number of living beta cells from 8-week rats to 30%, following a time- and concentration-dependent recruitment of quiescent cells into DNA-synthesis; a glucokinase-activator lowered the threshold but did not raise total numbers of glucose-recruitable cells. No glucose-induced increase occurred in beta cells from 40-week rats. Neonatal beta cells doubled in number at 5 mmol/l involving a larger activated fraction that did not increase at higher concentrations; however, their higher susceptibility to glucose toxicity at 20 mmol/l resulted in 20% lower living cell numbers than at start. None of the age groups exhibited a repetitively proliferating subpopulation.

Conclusions

Chronically elevated glucose levels increased the number of beta cells from young-adult but not from old rats; they interfered with expansion of neonatal beta cells and reduced their number. These effects are attributed to age-dependent differences in basal and glucose-induced proliferative activity and in cellular susceptibility to glucose toxicity. They also reflect age-dependent variations in the functional heterogeneity of the rat beta cell population.     

OsCKX5 Modulates Root System Morphology and Increases Nutrient Uptake in Rice

Journal of Plant Growth Regulation - Cytokinin is a plant hormone and an important regulator of root growth. Reduced cytokinin levels increase root systems, which can be beneficial for crops grown...     

The Effect of Coumarins on Root Elongation and Ultrastructure of Meristematic Cell Protoplast

The effect of coumarin, umbelliferone and xanthotoxin on rootelongation, as well as their influence on the cell structureof root meristem, was investigated in cucumber, maize and gardenpea. Umbelliferone retarded the growth of roots less stronglythan coumarin and xanthotoxin, which arrested elongation andmarkedly thickened cortical cells. Response to coumarin andxanthotoxin varied depending on the plant species. Cucumberseedlings were much more sensitive to coumarin than was maize,but garden pea was resistant. In sensitive plants coumarin andxanthotoxin affected the endomembrane system, mostly dictyosomesand the endoplasmic reticulum. They stimulated the fragmentationof endoplasmic reticulum cisternae and decreased the numberof dictyosomes, which became less active. The mitochondrialmatrix became condensed, indicating a possible energy shortagein the cell.Copyright 1994, 1999 Academic Press Allelopathic effect, coumarins, growth inhibition, roots