Increase In Cell Wall Extensibility Research Articles

Growth promotion and an increase in cell wall extensibility by silicon in rice and some other Poaceae seedlings.

The effect of silicon on organ growth and its mechanisms of action were studied in rice ( Oryza sativa L. cv. Koshihikari), oat ( Avena sativa L. cv. Victory), and wheat ( Triticum aestivum L. cv. Daichino-Minori) seedlings grown in the dark. Applying silicon in the form of silicic acid to these seedlings via culture solution resulted in growth promotion of third (rice) or second (oat and wheat) leaves. The optimal concentration of silicon was 5-10 mM. No growth promotion was observed in early organs, such as coleoptiles or first leaves. In silicon-treated rice third leaves, the epidermal cell length increased, especially in the basal regions, without any effect on the number of cells, showing that silicon promoted cell elongation but not cell division. Silicon also increased the cell wall extensibility significantly in the basal regions of rice third leaves. These results indicate that silicon stimulates growth of rice and some other Poaceae leaves by increasing cell wall extensibility.

Metabolic involvement in acid-mediated extension growth of maize coleoptiles

The acid-growth response (AGR) induced by acidic buffer (pH 4) in abraded maize (Zea mays L.) coleoptile segments can be completely inhibited within a few minutes by inhibitors of the haemoprotein function (KCN, Na-azide) or ionophores collapsing the proton gradients across membranes (carbonyl cyanide m-chlorophenyl hydrazone, monensin). These substances also interfere with the acid-mediated increase in cell-wall extensibility measured with a constant-load extensiometer in vivo in turgid or non-turgid segments, but have no effect on the extensibility of the cell walls measured in vitro with frozen/thawed segments. The inhibitors do not cause an alkalinization of the apoplastic solution or a decrease in the osmotic pressure of the cell sap of acid-treated segments. In contrast, inhibitors of ATP synthesis (N,N'-dicyclohexyl-carbodiimide, diethylstilbestrol), which arrest auxin-mediated growth in a similar way to KCN, have no effect on AGR. Removal of O 2 inhibits growth at pH 4 by about 25%; the anoxia-insensitive part of the AGR can be fully inhibited by azide. Diminishing the membrane potential with valinomycin has no effect on AGR. It is concluded that the AGR is controlled by protoplastic functions, possibly localized in the plasma membrane, which are lost when the cells are killed. The isolated cell wall may not represent a sufficient model system for the biochemical mechanism of AGR.

Cell Cycle Alteration and β-1,4 Endoglucanase in Heterotrophic Chlorella vulgaris UAM 101

Summary In Chlorella vulgaris UAM 101 synthesis of copies of the DNA occurs prior to the successive series of mitoses plus cytokinesis that give rise to the autospores. Glucose promotes a cell division delay leading to the appearance of giant cells both in mixotrophic conditions as well as in photoheterotrophic and chemoheterotrophic ones. This giantism phenomenon is closely related to the increase in cell wall extensibility mediated by s-1,4 endoglucanase activity. Glucose does not interfere either with DNA synthesis or with cytokinesis but rather with mitosis. The increase in cellular size is related to the increase in cellular content of DNA. Image analysis of nuclear size indicates the presence of seven size classes of nuclei in the population of mixotrophic vegetative cells. The synthesis of these multiple copies of DNA can be related to the decrease in the nuclear-cytoplasmic ratio promoted by glucose. The giant cells only undergo mitosis when accompanied by cytokinesis and lower s-1,4 endoglucanase activities. In this case they liberate a high number of autospores. We propose that the stimulation of s-1,4 endoglucanase activity recorded is most probably due to the acidification of periplasmic space generated by the glucose uptake system. The higher activity of this enzyme in the short term and glucose availability in the long term would contribute to the regulation of cell wall synthesis and subsequent nuclear and cell division initiation.

Osmotic relations during elongation growth in hypocotyls of Helianthus annum L.

The relationship between growth, change in cell osmotic pressure and accumulation of osmotic solutes was investigated in hypocotyls of sunflower (Helianthus annum L.) seedlings. During growth in darkness the osmotic pressure decreased by 50% between days 2 and 6 after sowing. After irradiation of dark-grown seedlings with continuous white light (WL) an inhibition of hypocotyl growth was measured, but the osmotic pressure of the growing cells was not lower than in the dark-grown control. Growth in darkness and after WL irradiation was accompanied by an increase in the amount of osmotic substances (soluble sugars) which was proportional to the increase in length of the organ. During growth in continuous WL the cell osmotic pressure decreased by 45 % between days 2 and 6 after sowing. The transfer of WL-grown seedlings to darkness ("re-etiolation") resulted in a rapid acceleration of hypocotyl growth, but the cell osmotic pressure was the same as that of the WL grown control. Growth in continuous WL was accompanied by a corresponding accumulation of osmotic substances (soluble sugars). The transition from WL to darkness resulted in an enhanced accumulation of osmotica and an increase in cell-wall extensibility. The results indicate that the relative maintenance of cell osmotic pressure during rapid hypocotyl growth in darkness is caused by an enhanced accumulation of soluble sugars into the growing cells of the organ.

Avoidance and rheotropic responses in phycomyces. Evidence for an 'avoidance gas" mechanism.

If a mature sporangiophore is placed next to a barrier that is moving in a clockwise direction, it grows both away from the barrier and into the wind; the wind is generated by the moving barrier itself. When the barrier is moving in a counterclockwise direction, the sporangiophore grows towards both the barrier and the wind. The net direction of growth appears to be the vector sum of the rheotropic response and the avoidance aiming error and does not involve the classic stationary-barrier avoidance response. Our experiments all support the suggestion that the avoidance response, the rheotropic response and the variety of reported wind responses can be explained by the presence of a self-emitted, growth-simulating avoidance gas. We present data that suggest that it is the direction of the net flux (mass transfer) of this gas that determines both the direction and the magnitude of the sporangiophore growth. We further suggest that the region of the cell wall showing maximum mass transfer will show a minimum growth rate, i.e., the direction of growth will always be in the direction of maximum transfer. If water is the avoidance gas, then it would follow that the total hydration of the cell wall in an aqueous salt solution should result in cell wall softening; cell wall softening has been correlated directly to cell wall growth. Using the Instron technique, we now show that submerging the entire sporangiophore in an aqueous salt solution for 4 min causes an increase in cell wall extensibility.

The effect of ethylene and auxin on cell wall extensibility of the Semi-aquatic fern, Regnellidium diphyllum

Ethylene and auxin both enhance cell elongation growth in the rachis of the frond of Regnellidium diphyllum. Measurements of the stress relaxation modulus of the walls of methanol-killed rachis segments show that both auxin and ethylene cause an increase in cell wall extensibility, that the effects are additive, and that they occur in the presence of hypertonic solutions of mannitol that preclude cell elongation. The results are taken as evidence for the operation of two separate mechanisms for cell wall loosening.

Chapter 6 Control of Plant Cell Enlargement By Hydrogen Ions

This chapter discusses the evidence that in Avena coleoptiles and pea stem tissues the hormone auxin induces cell enlargement, by activating proton extrusion, and that the resulting acidification of the wall leads to enzymic cell wall loosening and thus cell enlargement. It emphasizes the point that auxin itself does not act directly on the wall but acts at the cell surface or within the cytoplasm. When a plant cell enlarges, most of the increase in volume is due to the uptake of water into an expanding–centrally located vacuole. The direction of the cell expansion depends on the molecular architecture of the wall and can be primarily in one direction or equally in all directions. Cell enlargement can be initiated in one of the two ways: by an increase in the osmotic concentration of the cell or by an increase in cell wall extensibility (cell wall loosening). In most systems, cell enlargement is initiated by wall loosening. If a section is removed from the elongation zone of a pea stem and placed in water, the cells enlarge, but only at a slow rate. Rapid enlargement can be induced by only four agents: the group of hormones called auxins, hydrogen ions, CO, and the phytotoxin fusicoccin. If hydrogen ions are excreted from auxin-treated Avena coleoptile cells, and if the pH of the wall region falls below 5.8, the walls would undergo cell wall loosening and growth would occur.

Requirement of RNA for the Auxin‐induced Elongation of Oat Coleoptile

AbstractUsing etiolated oat coleoptile segments the following results were obtained.Actinomycin D pretreatment for one hour produced about 50 per cent inhibition of RNA synthesis (labeled uracil incorporation), but the elongation caused by IAA was not inhibited in the following 5 hours at least. Actinomycin D pretreatment for three hours produced about 75 per cent inhibition of RNA synthesis and almost complete inhibition of subsequent IAA‐induced elongation, which is accompanied by the inhibition of IAA‐induced increase in cell wall extensibility. The inhibiting effect of actinomycin D seemed to be reduced when IAA was given within a certain period.