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.     

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.     

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     

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     

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...     

What the Distribution of Cell Lengths in the Root Meristem Does and Does Not Reveal About Cell Division

Roots have long been realized to be useful material for studies of cell division. Despite this long history of use, the behavior of cells in the meristem is often misinterpreted. A common error is to argue that differences in cell length reflect differences in cell division rate. In this article we explain the fallacy behind this argument and show how the analysis of cell length distribution can lead to insight about the root meristem. These observations support a model for the root meristem where cells of various tissues grow at the same relative growth rate and divide at the same frequency, indicating that these growth parameters are built into the cells at a fundamental level. The differences in cell length between various tissues appear to arise at their formation, first at the tissue initials and ultimately in the seed. Length differences among mature cells may be enhanced by differences in the location within the meristem where division ceases. Discovering mechanisms regulating the length of initial cells and the position where cells cease division requires a realistic understanding of how growth constrains the division behavior of dividing cells.     

LDL Cholesterol Modulates Human CD34+ HSPCs through Effects on Proliferation and the IL-17 G-CSF Axis

Background

Hypercholesterolemia plays a critical role in atherosclerosis. CD34+ CD45dim Lineage- hematopoietic stem/progenitor cells (HSPCs) give rise to the inflammatory cells linked to atherosclerosis. In mice, high cholesterol levels mobilize HSPCs into the bloodstream, and promote their differentiation to granulocytes and monocytes. The objective of our study was to determine how cholesterol levels affect HSPC quantity in humans.

Methods

We performed a blinded, randomized hypothesis generating study in human subjects (n=12) treated sequentially with statins of differing potencies to vary lipid levels. CD34+ HSPC levels in blood were measured by flow cytometry. Hematopoietic colony forming assays confirmed the CD34+ population studied as HSPCs with multlineage differentiation potential. Mobilizing cytokine levels were measured by ELISA.

Results

The quantity of HSPCs was 0.15 ± 0.1% of buffy coat leukocytes. We found a weak, positive correlation between CD34+ HSPCs and both total and LDL cholesterol levels (r²=0.096, p < 0.025). Additionally, we tested whether cholesterol modulates CD34+ HSPCs through direct effects or on the levels of mobilizing cytokines. LDL cholesterol increased cell surface expression of CXCR4, G-CSFR affecting HSPC migration, and CD47 mediating protection from phagocytosis by immune cells. LDL cholesterol also increased proliferation of CD34+ HSPCs (28 ± 5.7%, n=6, p < 0.03). Finally, the HSPC mobilizing cytokine G-CSF (r²=0.0683, p < 0.05), and its upstream regulator IL-17 (r²=0.0891, p < 0.05) both correlated positively with LDL cholesterol, while SDF-1 levels were not significantly affected.

Conclusions

Our findings support a model where LDL cholesterol levels positively correlate with CD34+ HSPC levels in humans through effects on the levels of G-CSF via IL-17 promoting mobilization of HSPCs, and by direct effects of LDL cholesterol on HSPC proliferation. The findings are provocative of further study to determine if HSPCs, like cholesterol levels, are linked to CVD events.     

Effects of Zinc on Meristem Size and Proximity of Root Hairs and Xylem Elements to the Root Tip in a Zinc-tolerant and a Non-tolerant Cultivar of Festuca rubra L.

A 4 d exposure to zinc (0.1 and 02 µg Zn cm^–3) reducedthe length of the root apical meristem in a Zn-sensitive cultivar(S59) of Festuca rubra L. to a much greater extent than in aZn-tolerant cultivar (Merlin). In S59, Zn treatment also inducedroot hair and xylem formation much closer to the root cap boundarythan in control roots, whereas Merlin was only marginally affectedby Zn treatment. The data are discussed in relation to previouslyestablished effects of Zn on the cell cycle and other cellularcharacters of the two cultivars. zinc, meristem size, root hair, xylem, Festuca rubra     

Brassinosteroid Regulates Cell Elongation by Modulating Gibberellin Metabolism in Rice

Brassinosteroid (BR) and gibberellin (GA) are two predominant hormones regulating plant cell elongation. A defect in either of these leads to reduced plant growth and dwarfism. However, their relationship remains unknown in rice (Oryza sativa). Here, we demonstrated that BR regulates cell elongation by modulating GA metabolism in rice. Under physiological conditions, BR promotes GA accumulation by regulating the expression of GA metabolic genes to stimulate cell elongation. BR greatly induces the expression of D18/GA3ox-2, one of the GA biosynthetic genes, leading to increased GA₁ levels, the bioactive GA in rice seedlings. Consequently, both d18 and loss-of-function GA-signaling mutants have decreased BR sensitivity. When excessive active BR is applied, the hormone mostly induces GA inactivation through upregulation of the GA inactivation gene GA2ox-3 and also represses BR biosynthesis, resulting in decreased hormone levels and growth inhibition. As a feedback mechanism, GA extensively inhibits BR biosynthesis and the BR response. GA treatment decreases the enlarged leaf angles in plants with enhanced BR biosynthesis or signaling. Our results revealed a previously unknown mechanism underlying BR and GA crosstalk depending on tissues and hormone levels, which greatly advances our understanding of hormone actions in crop plants and appears much different from that in Arabidopsis thaliana.     

Salt Stress Reduces Root Meristem Size by Nitric Oxide-Mediated Modulation of Auxin Accumulation and Signaling in Arabidopsis

The development of the plant root system is highly plastic, which allows the plant to adapt to various environmental stresses. Salt stress inhibits root elongation by reducing the size of the root meristem. However, the mechanism underlying this process remains unclear. In this study, we explored whether and how auxin and nitric oxide (NO) are involved in salt-mediated inhibition of root meristem growth in Arabidopsis (Arabidopsis thaliana) using physiological, pharmacological, and genetic approaches. We found that salt stress significantly reduced root meristem size by down-regulating the expression of PINFORMED (PIN) genes, thereby reducing auxin levels. In addition, salt stress promoted AUXIN RESISTANT3 (AXR3)/INDOLE-3-ACETIC ACID17 (IAA17) stabilization, which repressed auxin signaling during this process. Furthermore, salt stress stimulated NO accumulation, whereas blocking NO production with the inhibitor N^ω-nitro-l-arginine-methylester compromised the salt-mediated reduction of root meristem size, PIN down-regulation, and stabilization of AXR3/IAA17, indicating that NO is involved in salt-mediated inhibition of root meristem growth. Taken together, these findings suggest that salt stress inhibits root meristem growth by repressing PIN expression (thereby reducing auxin levels) and stabilizing IAA17 (thereby repressing auxin signaling) via increasing NO levels.Due to agricultural practices and climate change, soil salinity has become a serious factor limiting the productivity and quality of agricultural crops (Zhu, 2007). Worldwide, high salinity in the soil damages approximately 20% of total irrigated lands and takes 1.5 million ha out of production each year (Munns and Tester, 2008). In general, high salinity affects plant growth and development by reducing plant water potential, altering nutrient uptake, and increasing the accumulation of toxic ions (Hasegawa et al., 2000; Munns, 2002; Zhang and Shi, 2013). Together, these effects severely reduce plant growth and survival.Because the root is the first organ to sense high salinity, salt stress plays a direct, important role in modulating root system architecture (Wang et al., 2009). For instance, salt stress negatively regulates root hair formation and gravitropism (Sun et al., 2008; Wang et al., 2008). The role of salt in lateral root formation depends on the NaCl concentration. While high NaCl levels inhibit lateral root formation, lower NaCl levels stimulate lateral root formation in an auxin-dependent manner (Zolla et al., 2010; Ji et al., 2013). The root meristem plays an essential role in sustaining root growth (Perilli et al., 2012). Salt stress inhibits primary root elongation by suppressing root meristem activity (West et al., 2004). However, how this inhibition occurs remains largely unclear.Plant hormones are important intermediary signaling compounds that function downstream of environmental stimuli. Among plant hormones, indole-3-acetic acid (IAA) is thought to play a fundamental role in root system architecture by regulating cell division, expansion, and differentiation. In Arabidopsis (Arabidopsis thaliana) root tips, a distal auxin maximum is formed and maintained by polar auxin transport (PAT), which determines the orientation and extent of cell division in the root meristem as well as root pattern formation (Sabatini et al., 1999). PINFORMED (PIN) proteins, which are components of the auxin efflux machinery, regulate primary root elongation and root meristem size (Blilou et al., 2005; Dello Ioio et al., 2008; Yuan et al., 2013, 2014). The auxin signal transduction pathway is activated by direct binding of auxin to its receptor protein, TRANSPORT INHIBITOR RESPONSE1 (TIR1)/AUXIN SIGNALING F-BOX (AFB), promoting the degradation of Aux/IAA proteins, releasing auxin response factors (ARFs), and activating the expression of auxin-responsive genes (Gray et al., 2001; Dharmasiri et al., 2005a; Kepinski and Leyser, 2005). Aux/IAA proteins are short-lived, nuclear-localized proteins that play key roles in auxin signal activation and root growth modulation (Rouse et al., 1998). Other hormones and stresses often regulate auxin signaling by affecting Aux/IAA protein stability (Lim and Kunkel, 2004; Nemhauser et al., 2004; Wang et al., 2007; Kushwah and Laxmi, 2014).Nitric oxide (NO) is a signaling molecule with diverse biological functions in plants (He et al., 2004; Fernández-Marcos et al., 2011; Shi et al., 2012), including important roles in the regulation of root growth and development. NO functions downstream of auxin during the adventitious rooting process in cucumber (Cucumis sativus; Pagnussat et al., 2002). Exogenous auxin-induced NO biosynthesis is associated with nitrate reductase activity during lateral root formation, and NO is necessary for auxin-induced lateral root and root hair development (Pagnussat et al., 2002; Lombardo et al., 2006). Pharmacological and genetic analyses in Arabidopsis indicate that NO suppresses primary root growth and root meristem activity (Fernández-Marcos et al., 2011). Additionally, both exogenous application of the NO donor sodium nitroprusside (SNP) and overaccumulation of NO in the mutant chlorophyll a/b binding protein underexpressed1 (cue1)/nitric oxide overproducer1 (nox1) result in reduced PIN1 expression and auxin accumulation in root tips. The auxin receptors protein TIR1 is S-nitrosylated by NO, suggesting that this protein is a direct target of NO in the regulation of root development (Terrile et al., 2012).Because NO is a free radical, NO levels are dynamically regulated by endogenous and environmental cues. Many phytohormones, including abscisic acid, auxin, cytokinin, salicylic acid, jasmonic acid, and ethylene, induce NO biosynthesis (Zottini et al., 2007; Kolbert et al., 2008; Tun et al., 2008; García et al., 2011). In addition, many abiotic and biotic stresses or stimuli, such as cold, heat, salt, drought, heavy metals, and pathogens/elicitors, also stimulate NO biosynthesis (Zhao et al., 2009; Mandal et al., 2012). Salt stress stimulates NO and ONOO^– accumulation in roots (Corpas et al., 2009), but the contribution of NO to root meristem growth under salinity stress has yet to be examined in detail.In this study, we found that salt stress significantly down-regulated the expression of PIN genes and promoted AUXIN RESISTANT3 (AXR3)/IAA17 stabilization. Furthermore, salt stress stimulated NO accumulation, and pharmacological inhibition of NO biosynthesis compromised the salt-mediated reduction in root meristem size. Our results support a model in which salt stress reduces root meristem size by increasing NO accumulation, which represses PIN expression and stabilizes IAA17, thereby reducing auxin levels and repressing auxin signaling.