Suberin lamellae in the hypodermis of maize (Zea mays) roots; development and factors affecting the permeability of hypodermal layers

Abstract The development of suberin lamellae in the hypodermis of Zea mays cv. LG 11 was observed by electron microscopy and the presence of suberin inferred from autoliuorescence and by Sudan black B staining in nodal (adventitious) and primary (seminal) root axes. Suberin lamellae were evident at a distance of 30–50 mm from the tip of roots growing at 20°C and became more prominent with distance from the tip. Both oxygen deficiency and growth at 13°C produced shorter roots in which the hypodermis was suberized closer to the root tip. There were no suberin lamellae in epidermal cells or cortical collenchyma adjacent to the hypodermis. Plasmodesmata were not occluded by the suberin lamellae: there were twice as many of them in the inner tangential hypodermal wall (1,14 μn^?2) as in the junction between the epidermis and hypodermis (0.54 μm^?2). Water uptake by seminal axes (measured by micropotometry) was greater at distances more than 100 mm from the root lip than in the apical zone where the hypodermis was unsuberized. In the more mature zones of roots grown at 13°C rates of water uptake were greater than in roots grown at 20°C even though hypodermal suberization was more marked. Sleeves of epidermal/hypodermal cells (plus some accessory collenchyma) were isolated from the basal 60 mm of nodal axes by enzymatic digestion (drisclase). The roots were either kept totally immersed in culture solution or had the basal 50 mm exposed to moist air above the solution surface. In both treatments the permeabilities to tritiated water and ₈₆Rb were low (circa 10^?5mms^?1) in sleeves isolated from the extreme base. In roots grown totally immersed, however, the permeability of sleeves increased 10 to 50-fold over a distance of 40 mm. In roots exposed to moist air the permeability remained at a low level until the point where the root entered the culture solution and then increased rapidly (> 50-fold in a distance of 8 mm). Growth of roots in oxygen depleted (5% O₂) solutions promoted the development of extensive cortical aerenchymas. These developments were not associated with any reduction in permeability of sleeves isolated from the basal 40 mm of the axis. It was concluded that the presence of suberin lamellae in hypodermal walls does not necessarily indicate low permeability of cells or tissues to water or solutes. The properties of the walls (lamellae?) can be greatly changed by exposure to moist air, perhaps due to increased oxygen availability.     

Calcium bridges are not load-bearing cell-wall bonds in Avena coleoptiles

I examined the ability of frozen-thawed Avena sativa L. coleoptile sections under applied load to extend in response to the calcium chelators ethyleneglycol-bis-(-aminoethylether)-N,N,N,N-tetraacetic acid (EGTA) and 2-[(20bis-[carboxymethyl] amino-5-methylphenoxy)methyl]-6-methoxy-8-bis [carboxymethyl]aminoquinoline (Quin II). Addition of 5 mM EGTA to weakly buffered (0.1 mM, pH 6.2) solutions of 2(N-morpholino) ethanesulfonic acid (Mes) initiated rapid extension and wall acidification. When the buffer strength was increased (e.g. from 20 to 100 mM Mes, pH 6.2) EGTA did not initiate extension nor did it cause wall acidification. At 5 mM Quin II failed to stimulate cell extension or wall acidification at all buffer molarities tested (0.1 to 100 mM Mes). Both chelators rapidly and effectively removed Ca²⁺ from Avena sections. These data indicate that Ca²⁺ chelation per se does not result in loosening of Avena cells walls. Rather, EGTA promotes wall extension indirectly via wall acidification.Abbreviations EGTA ethyleneglycol-bis-(-aminoethylether)-N,N,N,N-tetraacetic acid - Quin II 2-[(2-bis-[carboxymethyl]amino-5-methylphenoxy)methyl]-6-methoxy-8-bis(carboxymethyl)aminoquinoline - Mes 2(N-morpholino)ethanesulfonic acid     

Calcium ion transport across discs of the cortical flesh of apple fruit in relation to fruit development

Transport of Ca²⁺ through discs of apple fruit tissue was examined in tissue taken at different stages of fruit development. Transport rates decreased with fruit development when cation exchange was the predominant influence on transport (with 10⁻⁶ M ⁴⁵CaCl₂ as the source solution). This decrease was associated with a reduction in relative cell wall surface area, cation exchange capacity and cell wall yield that occurred during fruit growth. When diffusion was the major transport force, and when transport was influenced by solution infiltration of the tissue disc (10⁻² M ⁴⁵CaCl₂ in the source solution), transport rates increased during fruit growth. This increment was related to increases in air space of the tissue. Ca²⁺ transport through apple fruit tissue is influenced by the extent and nature of the cell wall, changing proportions of air space and Ca²⁺ concentration in the extracellular solution.     

Calcium and the mechanical properties of soybean hypocotyl cell walls: Possible role of calcium and protons in cell-wall loosening

The role of calcium in the mechanical strength of isolated cell walls of soybean (Glycine max (L.) Merr. cv. Wayne) hypocotyls has been investigated, using the Instron technique to measure the plastic extensibility (PEx) of methanol-boiled, bisected hypocotyl sections and epidermal strips, and atomic absorption spectroscopy to measure wall calcium. Plastic extensibility was closely correlated with the growth rate of intact soybean hypocotyls. Removal of calcium from isolated cell walls by ethylene glycol-bis(2-aminoethyl ether)-N,N,N,N-tetraacetic acid (EGTA) or low pH increased PEx, while addition of calcium decreased PEx; both effects were reversible. The amount of calcium removed and the increase in PEx at pH 4.5 were strongly dependent upon the chelating ability of the buffer anion. There was a direct correlation between the amount of calcium removed from the wall by EGTA or acid and the increase in PEx. Removal of up to 60% of the calcium increased PEx of half-section up to two fold, but further loss of calcium caused a much greater increase in PEx. With epidermal strips, PEx increased only when calcium was reduced below a threshold. At pH 3.5, there was an additional increase in PEx after a lag of about 2 h; this additional increase may be the result of acid-induced cleavage of a different set of load-bearing bonds. We conclude that calcium bridges are part of the load-bearing bonds in soybean hypocotyl cell walls, and that breakage of these crosslinks by apoplastic acid participates in wall loosening. Acid-induced solubilization of wall calcium may be one mechanism involved in wall loosening of dicotyledonous stems.Abbreviations EGTA ethylene glycol-bis(2-aminoethyl ether)-N,N,N,N-tetraacetic acid - PEx Instron plastic extensibility     

Mechanics of circadian pulvini movements in Phaseolus coccineus L.

The circadian movement of the lamina of primary leaves of Phaseolus coccineus L. is mediated by antagonistic changes in the length of the extensor and flexor cells of the laminar pulvinus. The cortex of the pulvinus is a concentric structure composed of hexagonal disc-like cells, arranged in longitudinal rows around the central stele. Observations with polarization optics indicate that the cellulose microfibrils are oriented in a hoop-like fashion in the longitudinal walls of the motor cells. This micellation is the structural basis of the anisotropic properties of the cells: tangential sections of the extensor and flexor placed in hypotonic mannitol solutions showed changes only in length. As a consequence a linear correlation between length and volume was found in these sections. Based on the relationship between the water potential (which is changed by different concentrations of mannitol) and the relative volume of the sections and on the osmotic pressure at 50% incipient plasmolysis, osmotic diagrams were constructed for extensor and flexor tissues (cut during night position of the pulvinus). The bulk moduli of extensibility, , were estimated from these diagrams. Under physiological conditions the values were rather low (in extensor tissue below 10 bar, in flexor tissue between 10 to 15 bar), indicating a high extensibility of the longitudinal walls of the motor cells. They are strongly dependent on the turgor pressure at the limits of the physiological pressure range.In well-watered plants, the water potentials of the extensor and flexor tissues were surprisingly low,-12 bar and-8 bar, respectively. This means that the cells in situ are by no means fully turgid. On the contrary, the cell volume in situ is similar to the volume at the point of incipient plasmolysis: the cell volumes of extensor and flexor cells in situ were only 1.01 times and 1.1 times larger, respectively, than at the point of incipient plasmolysis, whereas at full turgidity (cells in water) the corresponding factors were 1.8 and 1.5. It is suggested that the high elasticity of the longitudinal walls, the anisotropy of the cell walls, and the low water potential of the sections which is correlated with slightly stretched cell walls in situ, are favourable and effective for converting osmotic work in changes in length of the pulvinus cells, and thus for the up and down movement of the leaf.Symbols volumetric elastic modulus - _i instantaneous volumetric elastic modulus - _i stationary volumetric elastic modulus - weight-averaged stationary bulk modulus of extensibility - ₀ osmotic pressure of the vacuole of a cell at the point of incipient plasmolysis - weight-averaged osmotic pressure of the vacuoles of the tissue at 50% incipient plasmolysis - water potential     

Differentiation of cotton fibers from single cells in suspension culture

Summary A cotton cell suspension culture has been developed that provides unique opportunities for plant biologists to investigate early developmental events regulating cotton fiber properties, plant cell elongation, and cell wall biogenesis. The suspension culture was derived from cells of cotton (Gossypium hirsutum L.) ovule callus. These cells undergo the stages of fiber development previously described for in vivo fiber development. Fibers range in length up to 11 mm and have secondary walls. Supported by the U.S. Department of Agriculture, Agricultural Research Service, Southern Regional Research Laboratory, New Orleans, Louisiana, and Cotton Incorporated, Raleigh, North Carolina.     

Cell wall composition of leaves of an inherently fast- and an inherently slow-growing grass species

Differences in the relative growth rules of the inherently slow-growing Deschampsia flexuosa L. and the inherently fast-growing Holcus lanatus L. were reflected in cell wall synthesis in the elongation zone of the leaves. Leaf elongation rates depended on the size of the plant and ranged from 6 to 14 mm d^?1 in Deschampsia and from 12 to 42 mm d^?1 in Holcus. Anatomical data showed that the epidermis and vascular tissue are the important tissues controlling leaf extension. The cell wall polysaccharides of fully expanded leaves of the two species were identical in sugar composition. Enzymatic hydrolysis of polymeric sugars in the cell walls of the sheath and the lamina gave glucose (85%), arabinose (3.5%), fucose (0.5%), xylose (5.0%), mannose (0.5%), galaclose (0.8%) and galacturonic acid (3–4%). This composition applied throughout the blade and the sheath and did not change with ageing. Polysaccharides in the meristems of the two species showed identical sugar compositions with 51–55% glucose, 13–15% galactoronic acid and 13–14% arabinose as the main components. The extension zone was marked by a gradual increase of driselase-digestable polymers (per mm tissue) and a concurrent shift in sugar composition. The massive increase of glucose in the cell wall polymers of the elongation zone is probably caused by cellulose synthesis. The rate of synthesis of cell wall polysaccharides in Holcus was twice as high as that in Deschampsia. The slower-growing Deschampsia has more ferulic acid esterified with cell walls, which might contribute to the slowing of leaf growth. Lignin is not significantly deposited until growth has essentially ceased and is not responsible for the difference in growth rate.     

Variations in the structure of neutral sugar chains in the pectic polysaccharides of morphologically different carrot calli and correlations with the size of cell clusters

Carrot (Daucus carota L.) embryogenic callus (EC) loses its embryogenic competence and becomes nonembryogenic callus (NC) during long-term culture. With the loss of embryogenic competence, the cell clusters become smaller and the extent of intercellular attachments is reduced. Pectic fractions prepared from EC and NC were separated into two subfractions by gel filtration. A difference in sugar composition between EC and NC was found only in the high-molecular-mass (ca. 1300 kDa) subfraction, and the ratio of the amount of arabinose to that of galactose (Ara/Gal) was strongly and positively correlated with the size of cell clusters in several different cultures. From the results of sugar-composition and methylation analyses, and the results of treatment with exo-arabinanase, models of the neutral sugar chains of pectins from EC and NC are proposed. Both neutral sugar chains are composed of three regions. The basal region is composed of linearly linked arabinan 5-Ara_f> moieties in both types of callus. The middle galactan region is composed of 6-linked galactose, some of which branches at the 3 and 4 positions, and this region is larger and more frequently branched in NC than in EC. Finally, the terminal arabinan region is composed of 5-linked arabinose, branched at the 3 position, and the size of the terminal arabinan is larger in EC than in NC. The significance of the neutral sugar chains of pectins in the interaction of cell wall components and intercellular attachment is discussed.Abbreviations Ara/Gal ratio (w/w) of the amount of arabinose to that of galactose - EC embryogenic callus - NC non-embryogenic callus - T-Ara_f terminal arabinose The authors are grateful to Dr. Naoto Shibuya of the National Institute of Agrobiological Resources for his gift of exo-arabinanase.     

Effect of the new fluorescent brightener Rylux BSU on morphology and biosynthesis of cell walls in Saccharomyces cerevisiae

Rylux BSU, a new fluorescent brightener from the family of 4,4-diaminostilbene-2,2disulfonic acid derivatives, inhibited growth and cytokinesis of the yeast Saccharomyces cerevisiae. In the presence of 0.1–1 mg/ml Rylux BSU the cells grew in clumps, had irregular shape and were larger than controls. They formed apparently normal primary septa but their secondary septa and lateral cell walls, especially those in older cells, were abnormally thick with large deposits of amorphous wall material in the periplasmic spaces all over the cell surface. Chitin content in the cell walls of cells grown in the presence of Rylux BSU was increased 2 to 5 times in comparison to that of the controls and glucan content was reduced by up to 30%. In the in vitro assays with particulate membrane fractions, Rylux BSU acted as a non-competitive inhibitor of -1,3-glucan synthase with inhibitory constant K _i=1.75 mg/ml whereas the chitin synthase was inhibited to a much lesser extent. From the difference of the effects of Rylux BSU on the synthesis of chitin in vivo and in vitro it is concluded that the brightener interacts with chitin synthase only indirectly, possibly by influencing the properties of integral plasma membrane.Abbreviations RBSU Rylux BSU, 1,4-benzenedisulfonic acid-2,2-[ethyleneidy]bis[(3-sulpho-4,1-phenylene)imino[6-bis(2-hydroxyethyl)amino]-1,3,5-triazine-4,2-diylamino]]bis-, hexasodium salt - FB fluorescent brightener