Phosphorus deficiency decreases cell division and elongation in grass leaves

Leaf growth in monocotyledons results from the flux of newly born cells out of the division zone and into the adjacent elongation-only zone, where cells reach their final length. We used a kinematic method to analyze the effect of phosphorus nutrition status on cell division and elongation parameters in the epidermis of Lolium perenne. Phosphorus deficiency reduced the leaf elongation rate by 39% due to decreases in the cell production rate (-19%) and final cell length (-20%). The former was solely due to a lower average cell division rate (0.028 versus 0.046 cell cell(-1) h(-1)) and, thus, a lengthened average cell cycle duration (25 versus 15 h). The number of division cycles of the initial cell progeny (five to six) and, as a result, the number of meristematic cells (32-64) and division zone length were independent of phosphorus status. Accordingly, low-phosphorus cells maintained meristematic activity longer. Lack of effect of phosphorus deficiency on meristematic cell length implies that a lower division rate was matched to a lower elongation rate. Phosphorus deficiency did not affect the elongation-only zone length, thus leading to longer cell elongation duration (99 versus 75 h). However, the substantially reduced postmitotic average relative elongation rate (0.045 versus 0.064 mm mm(-1) h(-1)) resulted in shorter mature cells. In summary, phosphorus deficiency did not affect the general controls of cell morphogenesis, but, by slowing down the rates of cell division and expansion, it slowed down its pace.     

Determination of ploidy levels in Ipheion uniflorum (R. C. Graham) Rafin (Liliaceae)

In this study, chromosome number and ploidy levels of Ipheion uniflorum cv. "Wisley Blue" (spring starflower) were determined. In meristematic root tip cells, chromosome number was found as 2n = 12 and 4n = 24. The ratios of diploid and tetraploid cells were found as 80.74% and 19.26%, respectively. In differentiated root tissues and mature leaf tissues ploidy levels were analysed by flow cytometry and polysomaty were found in both organs. In differentiated root tissues, ploidy levels were found as 2C, 4C, 8C and 16C DNA. In root tissues percentages of 2C, 4C, 8C and 16C nuclear DNA content were observed as 57.2%, 33.1%, 2.47% and 7.23%, respectively. In mature leaf tissues, ploidy levels were determined 2C, 4C, 8C and 16C DNA. In this tissue the frequency of 4C DNA was found very higher (74.3%) and 2C DNA content was determined as 19.2%. In mature leaf tissue, 8C and 16C nuclear DNA contents were observed as 2.72% and 3.78%, respectively. When nuclear DNA contents in leaves and roots were compared, an apparent difference in 2C and 4C DNA contents was found.     

The mechanism of boron tolerance for maintenance of root growth in barley (Hordeum vulgare L.)

Cultivar differences in root elongation under B toxic conditions were observed in barley (Hordeum vulgare L.). A significant increase in the length and width of the root meristematic zone (RMZ) was observed in Sahara 3771 (B tolerant) when it was grown under excessive B concentration, compared to when grown at adequate B supply. This coincided with an increase in cell width and cell numbers in the meristematic zone (MZ), whereas a significant decrease in the length and no significant effect on the width of the MZ was observed in Clipper (B intolerant) when it was grown under excessive B supply. This was accompanied by a decrease in cell numbers, but an increase in the length and width of individual cells present along the MZ. Excessive B concentrations led to a significantly lower osmotic potential within the cell sap of the root tip in SloopVic (B tolerant) and Sahara 3771, while the opposite was observed in Clipper. Enhanced sugar levels in the root tips of SloopVic were observed between 48 and 96 h after excess B was applied. This coincided with an increase in the root elongation rate and with a 2.7-fold increase in sucrose level within mature leaf tissue. A significant decrease in reducing sugar levels was observed in the root tips of Clipper under excessive B concentrations. This coincided with significantly lower root elongation rates and lower sucrose levels in leaf tissues. Results indicate a B tolerance mechanism associated with a complex control of sucrose levels between leaf and root tip that assist in maintaining root growth under B toxicity.     

葱属植物棱叶薤的形态性状与核型特征

对新疆不同地理位置分布的葱属植物棱叶薤的形态性状以及核型特征进行了研究,结果表明:鳞茎、株型、叶形等43个形态性状在3个棱叶薤居群之间不存在差异,而株芽、叶色、叶长、单株叶片数、小花数目、花序高度、花葶长度等19个性状在3个棱叶薤居群之间存在显著或极显著差异。采集自乌鲁木齐红旗水库居群的棱叶薤的核型公式是2n=2x=16=12m+4sm;塔城阿西尔乡巴尔鲁克山居群的棱叶薤的核型公式是2n=3x=24=18m+3sm+3st;裕民巴旦杏保护区居群的棱叶薤的核型公式是2n=4x=32=28m(4SAT)﹢4sm。棱叶薤居群内形态性状和倍性稳定,居群间存在形态性状分化,同时还存在二倍体、三倍体、四倍体的倍性分化。居群间染色体结构组成和相对长度组成也存在差异。核型类型均为2A型。     

Effect of N deficiency on leaf growth and cell wall peroxidase activity in contrasting maize genotypes

Two maize genotypes differing in leaf elongation rate (high-LER and low-LER) were used for the investigation of the effects of nitrogen deficiency on leaf growth and development and activity of enzyme cell wall peroxidase in the leaf growth zone. Plants were grown in a growth cabinet in perlite as a substrate and watered with complete N-NO₃ solution (+N) and N-NO₃ deficient solution (–N). Comparison between the investigated genotypes showed that final leaf length in both N treatments was related with LER, but not with the duration of leaf elongation. Faster leaf elongation rate in high-LER compared with low-LER genotype, was associated with longer growth zone, a bigger number of cells in it, and higher cell flux rate, although cell elongation rate was similar in both genotypes. These lines of evidence indirectly indicated that leaves of the faster growing genotype were characterized by higher meristematic activity. Nitrogen deficiency reduced the flux of cells and cell elongation rate, length of cell division zone and the number of cells in whole zone, significantly for both genotypes, although duration of cell elongation was increased and final epidermal cell length was unchanged. These results showed that N deficiency reduced both cell division and cell elongation, which in turn resulted in decreased leaf length and prolonged time for leaf development. Nitrogen deficiency significantly increased both bulk and segmental cell wall peroxidase activity in the growth zone of both investigated genotypes, thus showing an interaction between leaf growth cessation and enzyme activity.     

Nitrogen deficiency inhibits leaf blade growth in Lolium perenne by increasing cell cycle duration and decreasing mitotic and post-mitotic growth rates

Nitrogen deficiency severely inhibits leaf growth. This response was analysed at the cellular level by growing Lolium perenne L. under 7.5 mM (high) or 1 mM (low) nitrate supply, and performing a kinematic analysis to assess the effect of nitrogen status on cell proliferation and cell growth in the leaf blade epidermis. Low nitrogen supply reduced leaf elongation rate (LER) by 43% through a similar decrease in the cell production rate and final cell length. The former was entirely because of a decreased average cell division rate (0.023 versus 0.032 h(-1)) and thus longer cell cycle duration (30 versus 22 h). Nitrogen status did not affect the number of division cycles of the initial cell's progeny (5.7), and accordingly the meristematic cell number (53). Meristematic cell length was unaffected by nitrogen deficiency, implying that the division and mitotic growth rates were equally impaired. The shorter mature cell length arose from a considerably reduced post-mitotic growth rate (0.033 versus 0.049 h(-1)). But, nitrogen stress did not affect the position where elongation stopped, and increased cell elongation duration. In conclusion, nitrogen deficiency limited leaf growth by increasing the cell cycle duration and decreasing mitotic and post-mitotic elongation rates, delaying cell maturation.     

Clastogenicity of pentachlorophenol, 2,4-D and butachlor evaluated by Allium root tip test

The meristematic mitotic cells of Allium cepa is an efficient cytogenetic material for chromosome aberration assay on environmental pollutants. For assessing genotoxicity of pentachlorophenol (PCP), 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-chloro-2,6-diethyl-N-(butoxymethyl) acetanilide (butachlor), 50% effective concentration (EC(50)), c-mitosis, stickiness, chromosome breaks and mitotic index (MI) were used as endpoints of genotoxicity. EC(50) values for PCP and butachlor are 0.73 and 5.13 ppm, respectively. 2,4-D evidently induced morphological changes at higher concentrations. Some changes like crochet hooks, c-tumours and broken roots were unique to 2,4-D at 5-20 ppm. No such abnormalities were found in PCP and butachlor treated groups, however, root deteriorated and degenerated at higher concentrations (<3 ppm) in PCP. MI in 2,4-D showed a low average of 14.32% followed by PCP (19.53%), while in butachlor it was recorded 71.6%, which is near to the control value. All chemicals induced chromosome aberrations at statistically significant level. The highest chromosome aberration frequency (11.90%) was recorded in PCP at 3 ppm. Large number of c-mitotic anaphases indicated that butachlor acts as potent spindle inhibitor, whereas, breaks, bridges, stickiness and laggards were most frequently found in PCP showing that it is a potent clastogen.     

Desiccation tolerant ‘resurrection’ grasses from Kenya and West Africa

Summary Only a very small proportion of angiospermae have foliage which can recover (within 24 h) from full airdryness. The number of such plants was extended by five grass species, in the genera Eragrostis, Sporobolus and Tripagon, and by two sedges, Kyllinga spp. The basal leaf meristematic zones in most species survived equilibration to air of 0 to 5% RH, whereas mature leaf tissue in most survived 5 to 30% RH.     

The improved Allium/Vicia root tip micronucleus assay for clastogenicity of environmental pollutants

The meristematic mitotic cells of plant roots are appropriate and efficient cytogenetic materials for the detection of clastogenicity of environmental pollutants, especially for in situ monitoring of water contaminants. Among several cytological endpoints in these fast dividing cells, such as chromosome/chromatid aberrations, sister-chromatid exchanges and micronuclei, the most effective and simplest indicator of cytological damage is micronucleus formation. Although the Allium cepa and Vicia faba root meristem micronucleus assays (Allium/Vicia root MCN) have been used in clastogenicity studies about 12 times by various authors in the last 25 years, there is no report on the comparison of the efficiency of these two plant systems and in different cell populations (meristem and F₁) of the root tip as well as under adequate recovery duration. In order to maximize the efficiency of these bioassays, the current study was designed to compare the Allium and the Vicia root MCN assays on the basis if chromosome length, peak sensitivity of the mitotic cells, and the regions of the root tip where the MCN are formed. The total length of the 2n complement of Allium chromosomes is 14.4 μm and the total length of the 2n complement of Vicia is 9.32 μm. The peak sensitivity determined by serial fixation at 12-h intervals after 100 R of X-irradiation is 44 h. The slope of the X-ray dose-response curve of Allium roots derived from the meristematic regions was lower than that derived from cells in the F₁ region. Higher efficiency was also demonstrated when the MCN frequencies were scored from the F₁ cells in both Allium and Vicia treated with formaldehyde (FA), mitonycin C (MMC), and maleic hydrazide (MH). The results indicated that scoring of MCN frequencies from the F₁ cell region of the root tip was more efficient than scoring from the meristematic region. The X-ray linear regression dose-response curves were established in both Allium and Vicia cell systems and the coefficients of correlations, slope values were used to verify the reliability and efficiency of these two plant cell systems. Based on the dose-response slope value of 0.894 for Allium and 0.643 for Vicia, the Allium root MCN was a more efficient test system. The greater sensitivity of the Allium roots is probably due to the greater total length of the diploid complement and the higher number of metacentric chromosomes. The Allium/Vicia root MCN test system was applied to determine the clastogenicity of saccharin (SC) and wastewater from Rio Queretaro and the Arena canal in the city of Queretaro, Mexico. The minimum effective dose (MED) is 10 R for X-rays, 50 mM for FA, 2.2 mM for MMC, 0.01 mM for MH, and 40 ppm for SC.     

Preosteoblast production 55 hours after a 12.5-day spaceflight on Cosmos 1887

The influence of 12.5 days of spaceflight and a 55 h stressful recovery period (at 1 g) on fibroblastlike osteoblast precursor cells was assessed in the periodontal ligament (PDL) of rats that were 91 days old at launch. Nuclear morphometry was used as a marker for precursor cell differentiation in 3 microns sections cut in the midsagittal plane from the maxillary first molar. According to nuclear volume, cells were classified as preosteoblasts (C + D cells, greater than or equal to 120 microns 3) and less differentiated progenitor cells (A + A' cells, 40-79 microns 3). Compared with synchronous controls (simulated flight conditions), the 55 h postflight recovery period at 1 g resulted in a 40% decrease in the A + A' cell population, a 42% increase in the C + D cells, and a 39% increase in the number of PDL fibroblastlike cells near the bone surface. These results are consistent with a postflight osteogenic response in PDL. This recovery response occurred despite physiological stress in the flight animals that resulted in a highly significant (P less than or equal to 0.001) increase in adrenal weight. The data suggest that after spaceflight there is a strong and rapid recovery mechanism for osteoblast differentiation that is not suppressed by physiological stress.     

Comprehensive characterization of cultivated in vitro <Emphasis Type="Italic">Deschampsia antarctica</Emphasis> E. Desv. plants with different chromosome numbers

D. antarctica E. Desv. plants cultivated in vitro were analyzed for the chromosome number, leaf length, and efficiency of callus formation. Most of the studied plants had a typical diploid chromosome number. However, a hypotriploid and a plant with B chromosomes demonstrated mixoploidy caused by the presence of a significant proportion (up to 15–25%) of aneuploid cells. Jaccard genetic distances between the plants determined from the data of ISSR- and IRAP-PCR analyses were within the range of 0.0323 to 0.1803. Furthermore, genetic distances between the specimens with atypical karyotype and diploids did not exceed the paired distances within the group of diploid plants. Variations in the leaf length and growth parameters of the plants were characterized. Plants with different chromosome numbers differed in the leaf length and efficiency of callus formation. Obtained results may indicate relationships between the chromosome number, studied morphometric parameters, and efficiency of callus formation in the analyzed D. antarctica plants.     

Response of cassava leaf area expansion to water deficit: cell proliferation, cell expansion and delayed development

BACKGROUND AND AIMS: Cassava (Manihot esculenta) is an important food crop in the tropics that has a high growth rate in optimal conditions, but also performs well in drought-prone climates. The objectives of this work were to determine the effects of water deficit and rewatering on the rate of expansion of leaves at different developmental stages and to evaluate the extent to which decreases in cell proliferation, expansion, and delay in development are responsible for reduced growth. METHODS: Glasshouse-grown cassava plants were subjected to 8 d of water deficit followed by rewatering. Leaves at 15 developmental stages from nearly full size to meristematic were sampled, and epidermal cell size and number were measured on leaves at four developmental stages. KEY RESULTS: Leaf expansion and development were nearly halted during stress but resumed vigorously after rewatering. In advanced-stage leaves (Group 1) in which development was solely by cell expansion, expansion resumed after rewatering, but not sufficiently for cell size to equal that of controls at maturity. In Group 2 (cell proliferation), relative expansion rate and cell proliferation were delayed until rewatering, but then recovered partially, so that loss of leaf area was due to decreased cell numbers per leaf. In Group 3 (early meristematic development) final leaf area was not affected by stress, but development was delayed by 4-6 d. On a plant basis, the proportion of loss of leaf area over 26 d attributed to leaves at each developmental stage was 29, 50 and 21 % in Group 1, 2 and 3, respectively. CONCLUSIONS: Although cell growth processes were sensitive to mild water deficit, they recovered to a large extent, and much of the reduction in leaf area was caused by developmental delay and a reduction in cell division in the youngest, meristematic leaves.     

Effects of soil resistance to root penetration on leaf expansion in wheat (Triticum aestivum L.): kinematic analysis of leaf elongation

Wheat leaves (Triticum aestivum L.) elongated 50% more slowlywhen plants were grown in soils with high mechanical resistanceto penetration (R_s. The profiles of epidermal cell lengths alongthe growth zone of expanding leaves and the locations of newlyformed walls were recorded in order to compare the kineticsof elongation and partitioning of both meristematic and non-meristematiccells. In leaf 5, which completely developed under stress, highR_s, did not affect the flux of mature cells through the elongationzone; leaf elongation was reduced only because these cells wereshorter. This reduced size reflected a reduction in cell lengthat partitioning, associated with shorter cycling time. The relativerates of cell elongation before and after partitioning wereunchanged. Cell fluxes were similar because the population ofmeristematic cells was reduced, offsetting their increased partitioningrate. In contrast, in leaf 1, high R_s, had no effect on thenumber of dividing cells; elongation rate was reduced becauseof slower relative cell expansion rate and slower cell partitioningrate. These differences could reflect differences in the stageat which successive leaves perceived root stress and also time-dependentchanges in the responsiveness of leaf development to stress-inducedroot signals or in the nature of these signals. The data reveal that cell cycling time may in fact be decreasedby unfavourable growth conditions and is not directly relatedto cell expansion rates; they also show that the elongationrate of meristematic cells is partly independently controlledfrom that of non-meristematic cells. Key words: Wheat, kinematics of leaf expansion, cell partitioning, cell elongation, root impedance     

Tomato cybrids with mitochondrial DNA from Lycopersicon pennelli

Summary Cybrids have been regenerated following protoplast fusion of iodoacetamide-treated leaf mesophyll cells of Lycopersion esculentum cv UC82 and gamma-irradiated cell suspensions of L. pennellii, LA716. The cybrids were recovered in the regenerant population at a frequency of 19%, no selection pressure was applied for the persistence of the donor cytoplasm. The nuclear genotype of ten cybrids was characterized extensively using isozyme markers, cDNA-based restriction fragment length polymorphisms (RFLPs), and the morphology of the plants. No nuclear genetic information from L. pennellii was detected in the cybrids. The organellar genotype of the cybrids was determined using cloned probes and species-specific RFLPs. All the cybrids had inherited the tomato chloroplast genome and had varying amounts of L. pennellii mitochondrial DNA. The cybrids all had a diploid chromosome number of 24, produced pollen, and set seed.     

Dynamics of structural and functional association of nucleolar chromosomes in cells of the hexaploid wheat Triticum aestivum L. at different stages of the cell cycle and during genome polyploidization

Quantitative analysis of interphase association of the nucleolar chromosomes at different stages of the cell cycle and during genome polyploidization was carried out. Cells of various tissues of hexaploid wheat Triticum aestivum L. (Moskovskaya-35) were used, including diploid root meristematic cells, endopolyploid root cells, triploid endosperm cells and antipodal cells with polytene chromosomes. Interphase nucleoli impregnated with silver or stained with autoimmune antibodies to 53 kDa nucleolar protein served as markers of the nucleolar chromosome association. The following data were obtained: (1) silver-staining revealed two pairs of homologous chromosomes 1B and 6B with active nucleolus-organizing regions in the root meristematic cells; (2) maximal number of nucleoli in diploid meristematic cells reaches four, which corresponds to the number of chromosomes with active organizers; (3) analysis of cells at different stages of the cell cycle has shown that the tendency to the nucleoli association is observed as soon as cells pass individual stages of the cycle; (4) after DNA and chromosome reduplication, the nucleolus-organizing regions in sister chromatids function as a common structure-functional complex; (5) in endopolyploid root cells and antipodal cells with polytene chromosomes, the number of nucleoli does not correlate with ploidy level, and an additional nucleolus revealed in some cells is the result of activation of the latent organizer in one of the nucleolar chromosomes; (6) in the triploid endosperm nucleologenesis, the stage of prenucleolar bodies is missing. Our data suggest that "fusion" of nucleoli and reduction of their number due to the "satellite" association of the nucleolar chromosomes are two independent processes regulated by different mechanisms.     

Phenotypic Variation of Gelidocalamus stellatus Wen Complex (Bambusoideae)

Gelidocalamus stellatus Wen complex includes Gelidocalamus stellatus, Gauritus, Gmonophyllus, Gmultifolius and Gwugongshanensis, indicating the existence of some taxonomic disputes within this taxon. Based on 13 main phenotypic traits, in this paper, 13 populations of the complex are investigated and the results show that 1) All 13 characters have some changes between and within populations, of which the maximum is the height under branch with 276%, while the minimum is the ratio of length and width with 64%; 2) In the Jing Gang Mountain population (JGM), seven characters, such as the diameter at breast height, the node number, the height under branch, the leaf length, the leaf width, the ratio of leaf length and width, and numbers of each branch, are relatively stable among 4 different populations, and populations of Gstellatus Wen complex can be distinguished effectively by that seven characters, so it maybe have some worth for the clarification of the complex; 3) Besides that Jiu Yi Mountain population (JYM) and Xiao Long Gui population (XLG) share the same or similar traits with that of JGM, there have many remarkable differences between other populations, such the leaf in Lian Ping Country population (LPC) and Huang He Village population (HHV), the culm in Wu Gong Mountain population (WGM) and the numbers of each branch in Gan Zi Depression population (GZD) and Rong Jia Cavity population (RJC). With the observation of the culm sheath and the abaxial epidermis of leaves, the taxonomic position of some populations is discussed. Our results still indicate that Gmultifolius (Huang He Village population) and Gauritus may be null and void. Furthermore, we proposal Gwugongshanensis (Wu Gong Mountain population) and Gmonophyllus (Jiu Yi Mountain population) should be as a taxon under Gstellatus.     

Dynamics of microtubule depolymerization in monocytes

Human monocytes, which contain few interphase microtubules (35.+/- 7.7), were used to study the dynamics of microtubule depolymerization. Steady-state microtubule assembly was abruptly blocked with either high concentrations of nocodazole (10 micrograms/ml) or exposure to cold temperature (3 degrees C). At various times after inhibition of assembly, cells were processed for anti-tubulin immunofluorescence microscopy. Stained cells were observed with an intensified video camera attached to the fluorescence microscope. A tracing of the entire length of each individual microtubule was made from the image on the television monitor by focusing up and down through the cell. The tracings were then digitized into a computer. All microtubules were seen to originate from the centrosome, with an average length in control cells of 7.1 +/- 2.7 microns (n = 957 microtubules). During depolymerization, the total microtubule polymer and the number of microtubules per cell decreased rapidly. In contrast, there was a slow decrease in the average length of the persisting microtubules. The half-time for both the loss of total microtubule polymer and microtubule number per cell was approximately 40 s for nocodazole-treated cells. The rate-limiting step in the depolymerization process was the rate of initiation of disassembly. Once initiated, depolymerization appeared catastrophic. Further kinetic analysis revealed two classes of microtubules: 70% of the microtubule population was very labile and initiated depolymerization at a rate approximately 23 times faster than a minor population of persistent microtubules. Cold treatment yielded qualitatively similar characteristics of depolymerization, but the initiation rates were slower. In both cases there was a significant asynchrony and heterogeneity in the initiation of depolymerization among the population of microtubules.     

栓皮栎核型及体胚发生的细胞学特性研究

采用常规制片方法对栓皮栎核型、体胚发生过程中胚性愈伤组织细胞染色体进行了分析。结果表明,栓皮栎体细胞染色体数目2n＝24,核型公式K(2n)＝2x=24=20m十4sm,属于“2B”型,染色体组总长18.55 μm。继代8个月的胚性愈伤组织细胞的染色体数目和结构相对稳定,其中二倍体细胞占 97.20%,四倍体细胞占1.87%,单倍体细胞占0.93%。未发现有非整倍体细胞和染色体形态结构变异。子叶期体胚胚轴亚表层起源的分生组织团中有些细胞核呈片状或椭圆形。个别成熟体胚中偶见有3核细胞。