Root meristems

Aluminium toxicity is a major stress factor in many acidic soils. At soil pH levels below 5.0, intense solubilization of mononuclear A1 species strongly limits root growth by multiple cytotoxic effects mainly on root meristems (240,241). There is increasing evidence that A1 complexation with carboxylates released in apical root zones in response to elevated external Al concentration is a widespread mechanism for Al exclusion in many plant species (Fig. 10). Formation of stable Al complexes occurs with citrate, oxalate, tartarate, and—to a lesser extent— also with malate (86,242,243). The Al carboxylate complexes are less toxic than free ionic Al species (244) and are not taken up by plant roots (240). This explains the well-documented alleviatory effects on root growth in many plant species by carboxylate applications (citric, oxalic, and tartaric acids) to the culture media in presence of toxic Al concentrations (8,244,245) Citrate, malate and oxalate are the carboxylate anions reported so far to be released from Al-stressed plant roots (Fig. 10), and Al resistance of species and cultivars seems to be related to the amount of exuded carboxylates (246,247) but also to the ability to maintain the release of carboxylates over extended periods (248). In contrast to P deficiency-induced carboxylate exudation, which usually increases after several days or weeks of the stress treatment (72,113), exudation of carboxylates in response to Al toxicity is a fast reaction occurring within minutes to several hours... 

W. J. Horst, A. Wagner, and H. Marschner, Mucilage protects root meristems from aluminium injury. Z. Pflanzenphys. 105 435 (1982). 

The others form an extra-embryonic suspensor (Fig. 32-8B).475 The apical part of the embryo develops the shoot meristem and the central part the radial pattern of tissue layers characteristic of plants. The root meristem develops from the basal portion of the embryo. Movements of proteins that provide positional cues are involved in the development of the embryo.476,477 Early embryonic and endosperm development is largely under maternal control. Most paternal genes may be initially silent.478... 

Figure 32-8 (A) The life cycle of a flowering plant with emphasis on egg-cell formation and seed development. (B) Some further details of embryo development. T, terminal cell B, basal cell C, cotyledon A, axis SC, seed coat En, endosperm EP, embryo proper S, suspensor SM, shoot meristem Pd, protoderm RM, root meristem. From Goldberg et al.i66 with modification.

Levi, M., Sparvoli, E, Sgorbati, S., and Chiantante, D. (1990) Biotin-streptavidin immunofluorescent detection of DNA replication m root meristems through Brd Urd incorporation- cytological and microfluorimetnc applications Physiol Plantarum 79, 231-235... 

Mucilage has protective functions for the root meristem and improves root-soil contact by inclusion and aggregation of soil particles. It may also contribute to P desorption and to the exclusion of toxic elements (Al, Cd, Pb) by complexation with galacturonates, mainly in exchange with Ca2+ (Neumann and Romheld, 2002). Secreted enzymes contribute to the extracellular enzyme pool it has been shown that the activity of extracellular enzymes, such as phophatases, proteases, and aryl-sulfatases, exhibit more activity in the rhizosphere relative to the bulk soil and may have a dramatic effect on the cycling of nutrients such as P, N, and S (Badalucco and Nannipieri, 2007). 

Once clear inhibitory effects were detected on germination and radicle growth of lettuce plants exposed to BOA,12,35 our group developed methodology to show whether there is a detectable BOA effect on the cell cycle progression in lettuce root meristems.13 This allows a more detailed characterization of the putative direct or indirect effect on the meristems of BOA-treated seedlings. 

When the HU synchronization period was finished, and the HU was removed, the seedlings were immediately incubated with 1 mM BOA or water (controls), and the cell cycle was analyzed at different times. Samples (nuclear suspensions) are prepared from root meristems and analyzed by flow cytometry every 2 h during a time period of 12-14 h.15 Comparison of the synchronized-cell cycle progression of BOA-treated plants with that of the corresponding controls allows for detection of partial or total inhibition of the cell cycle. 

Mitotic indices were counted in the root tip cells from lettuce root meristems treated with 1 mM BOA (treated-meristems) or with distilled water (control-meristems) after 6 h HU synchronization (Fig. 12.3).36... 

So, these results showed a double effect of BOA on lettuce meristems an increasing significant delay in the cell cycle progression and a decrease in the mitotic index. Flow cytometry analysis showed a weak effect of BOA at cell cycle level in the step from G2 to M. BOA effect appeared to retard the cell cycle progression of treated-root meristems, which was very clear after 10 h BOA exposition (Fig. 12.5), and as an inhibition of the number of cells undergoing cell division. 

Then, and every 2 h, samples of BOA-treated plants and the corresponding controls were simultaneously processed using flow cytometry analysis. The 1 mm-apical tips of root meristems from forty BOA-treated plants were chopped with a razor blade in Galbraith buffer, supplemented with 100% Tween 20 and 100% beta-mercaptoethanol. Once filtered, the suspension, 5 pL of 1% RNase solution and 30 pL of 10 mg/mL ethidium bromide (EtBr), were added to 500 pi of filtered nuclei suspension and incubated for 30 min at room temperature in the dark. 

HU-synchronized root meristems were fixed for 24 h with acetic acid/chloroform/ethanol (6 3 1) and trace iron, then stored before analysis at -20 °C for at least 3 days. After storage, samples were hydrolyzed with hot 1N HCI for 25... 

Dolezel, J., Cihalikova, J., Weiserova, J., and Lucretti, S. 1999. Cell cycle synchronization in plant root meristems. Meth. Cell Sci. 21, 95-107... 

The precise role of polyamines in the control of dormancy and the onset of cell division in Jerusalem artichoke tubers, and for that matter in plant development per se, remains in question. Evidence from arginine decarboxylase mutants of Arabidopsis does indicate a possible role in root meristem function (Watson et al., 1998). 

Inhibition of root meristem mitosis, rapid elongation of epidermis - short, pitted trachea with lesions, root hairs at root tip only, considerable vacuolation and lignification. 

Treatment of cherry-mazzard hybrid seeds with acenaphthene powder for 10 h inhibited the seed germination and seedling growth. Treatment of Allium cepa root meristem cells with acenaphthene vapor for 12-96 h caused anomalies leading to random development of cells. Acute toxicity value for bluegill fish was 1700 in freshwater and the toxicity... 

For thermal analysis, shoot and root meristems were analyzed using a differential scanning calorimeter (DSC) Mettler TA 4000. Samples were rapidly cooled to — 100°C and then warmed in the DSC from —100 to 100°C at 10°C min . The data were analyzed using TCII TA Processor and Graph Ware TA 72 software. The ratio of unfrozen water was calculated from the... 

Abdel-Azeem EA. 1996. Selenium cytotoxicity in root meristems of vicia faba 1. Al-Azhar Bull Sci 7(l) 401-409. 

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