Comparison of the Outer and Inner Epidermis

Hoson, Takayuki; Nevins, Donald J.

doi:10.1104/pp.98.4.1298

Cited by 30 publications

(6 citation statements)

References 22 publications

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“…A long-held idea is that the ␤-glucans, thought to have a role in cross-linking the cellulose microfibrils, are cleaved by an endo-␤-dglucanase, loosening the wall and allowing turgordriven cell expansion (Huber and Nevins, 1981). Two observations support this hypothesis: exo-and endo-␤-d-glucanase polypeptides and activities appear in cell walls during growth (Inouhe and Nevins, 1998), and polyclonal antisera that bind to these enzymes inhibit growth (Hoson et al, 1992). However, the mechanism by which the antisera inhibit growth has never been established satisfactorily, and the discoveries in growing grass tissues of xyloglucan endo-transglycosylase (Pritchard et al, 1993) and ␤-expansins (Cosgrove et al, 1997) have reopened the question of the necessity of ␤-glucan hydrolysis for Maize Cell Wall Architecture…”

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confidence: 48%

“…Kutschera (1989) reviewed evidence that the epidermis controls the rate of elongation, whereas the underlying mesophyll cells expand coordinately in a passive manner. Hoson et al (1992) demonstrate a slight lowering of elongation rate in the presence of polyclonal antibodies against ␤-glucan but only if they are permitted to infiltrate the outer epidermis. Our immunocytochemical detection of ␤-glucan shows that the polymer is largely confined to the inner portions of the outward facing epidermal wall (Fig.…”

Section: Architecture Of the Epidermal Walls Of Maize Coleoptilesmentioning

confidence: 99%

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Cell Wall Architecture of the Elongating Maize Coleoptile

et al. 2001

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The primary walls of grasses are composed of cellulose microfibrils, glucuronoarabinoxylans (GAXs), and mixed-linkage ␤-glucans, together with smaller amounts of xyloglucans, glucomannans, pectins, and a network of polyphenolic substances. Chemical imaging by Fourier transform infrared microspectroscopy revealed large differences in the distributions of many chemical species between different tissues of the maize (Zea mays) coleoptile. This was confirmed by chemical analyses of isolated outer epidermal tissues compared with mesophyll-enriched preparations. Glucomannans and esterified uronic acids were more abundant in the epidermis, whereas ␤-glucans were more abundant in the mesophyll cells. The localization of ␤-glucan was confirmed by immunocytochemistry in the electron microscope and quantitative biochemical assays. We used field emission scanning electron microscopy, infrared microspectroscopy, and biochemical characterization of sequentially extracted polymers to further characterize the cell wall architecture of the epidermis. Oxidation of the phenolic network followed by dilute NaOH extraction widened the pores of the wall substantially and permitted observation by scanning electron microscopy of up to six distinct microfibrillar lamellae. Sequential chemical extraction of specific polysaccharides together with enzymic digestion of ␤-glucans allowed us to distinguish two distinct domains in the grass primary wall. First, a ␤-glucan-enriched domain, coextensive with GAXs of low degrees of arabinosyl substitution and glucomannans, is tightly associated around microfibrils. Second, a GAX that is more highly substituted with arabinosyl residues and additional glucomannan provides an interstitial domain that interconnects the ␤-glucan-coated microfibrils. Implications for current models that attempt to explain the biochemical and biophysical mechanism of wall loosening during cell growth are discussed.Biochemical studies have provided a reasonably complete catalog of the major polysaccharides and phenolic substances that constitute the primary cell walls of angiosperms (McCann and Roberts, 1991;Carpita and Gibeaut, 1993). The walls of grasses and related monocots (commelinoids) have quite different compositions compared with those of all dicots and of the non-commelinoid monocot species (Carpita, 1996). The "type II" cell walls of commelinoid monocots are characterized by cellulose microfibrils cross-linked by glucuronoarabinoxylans (GAXs) and a network of polyphenolic substances (Carpita and Gibeaut, 1993;Carpita, 1996). Maize (Zea mays) and other members of the Poales also contain developmentally regulated polymers, the mixed-linkage (133),(134)-␤-dglucans (hereafter, called ␤-glucans). The ␤-glucans are initially absent from meristematic cells but accumulate up to about 20% dry mass of the cell wall coincident with the most rapid rates of coleoptile elongation (Kim et al., 2000). As the elongation rate slows, the ␤-glucan is hydrolyzed by exo-and endo-␤-d-glucanases located in the wall. Concomitant with th...

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supporting

confidence: 48%

Section: Architecture Of the Epidermal Walls Of Maize Coleoptilesmentioning

confidence: 99%

Cell Wall Architecture of the Elongating Maize Coleoptile

et al. 2001

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“…An alternative hypothesis is that the breakdown of mixed-linked /?-glucan by cell wall glucanases causes wall loosening in coleoptile segments (Masuda, 1990;Hoson, Masuda & Nevins, 1992). However, Hohl et al (1991) were not able to measure an effect of IAA on solubilization of y^-glucan in maize coleoptile segments.…”

Section: How Does Iaa Loosen the Outer Epidermal Wall?mentioning

confidence: 78%

The current status of the acid‐growth hypothesis

Kutschera

1994

New Phytologist

125

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SUMMARY Excised coleoptile segments that were depleted of endogenous auxin after pre‐incubation in water respond to the phytotoxin fusicoccin (FC) and the plant hormone auxin (indole‐3‐acetic acid, IAA) with an enhancement of growth. This promotion of organ elongation is caused by an increase in the extensibility of the thick, growth‐limiting outer epidermal wall. The acid‐growth hypothesis postulates that both FC and IAA cause wall‐loosening and the concomitant induction of growth by rapid acidification of the extension‐limiting cell wall. At saturating concentrations FC and IAA cause very similar growth responses. However, the equilibrium‐pH in the incubation medium (∼ pH of the peripheral cell wall) of abraded FC‐treated segments is 3.5–4.0, whereas in the presence of IAA a pH of 4.8–5.0 is established. The FC‐ and IAA‐mediated induction of growth can be stimulated by an external buffer of pH 3.5–4.0. Acid buffers of pH 5, however, cause almost no enhancement of growth compared WJth the water‐control. FC‐mediated growth can be inhibited by neutral buffers infiltrated into the outer epidermal wall, but a substantial growth response occurs after addition of IAA under identical conditions. A sub‐optimal concentration of FC was used to mimic the effect of IAA on acid secretion. When a pH of 4.8–5.0 was established by FC in the peripheral wall no promotion of growth occurred. Hence, IAA‐induced proton excretion is insufficient to cause cell‐wall loosening in the coleoptile. Abraded segments that rapidly elongate in acid buffers (pH 3.5–4.0) respond to IAA with an additional enhancement of growth, but under identical conditions FC is without effect. The growth‐promoting effects of acid and IAA are additive, i.e. IAA and acid act via separate mechanisms. These results are consistent with the acid‐growth hypothesis of FC action. However, they indicate that IAA induces growth by a mechanism independent of cell‐wall acidification. Alternative hypotheses of IAA‐mediated cell‐wall loosening are discussed.

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“…Shoots were excised from 3-dayold seedlings. In the case of whole-shoot detection, the cuticle of excised shoot was abraded with carborundum slurry by rubbing their surfaces between the thumb and forefinger (Hoson et al, 1992). Then, abraded shoots were suspended in the test solution (approximately pH 4) composed of 25 mM succinic acid, 3.5 mM EDTA, 4-chloro-1-naphthol (0.15 mg/mL), and presence or absence of 5 mM sodium oxalate and incubated for 15 min at 25 • C in the dark.…”

Section: Histochemical Staining Of Oxo Activitymentioning

confidence: 99%