Turgor pressure growth

Table 4. Wheat root seedling elongation (30 replicates), tip turgor pressure (4 mm, >10 replicates) and tip tensiometric plasticity (2-7 mm, >10 replicates) following various growth altering treatments...

Subsequent tests with velvetleaf, Kodkia, Jerusalem artichoke, and cocklebur showed that their allelopathic action altered water balance (55,94,95). Growth reductions in sorghum and soybean seedlings in nutrient solution amended with extracts from these weeds correlated with high diffusive resistances and low leaf water potentials. Stomatal closure occurred in plants treated with the more concentrated extracts. Depressions in water potential were due to a reduction in both turgor pressure and osmotic potential. A lower relative water content was also found in velvetleaf-treated plants. These impacts on water balance were not from osmotic factors. Allelochemicals from these weeds have not been thoroughly ascertained, but the present evidence shows that some contain phenolic inhibitors. Lodhi (96) reported that Kodkia contains ferulic acid, chlorogenic acid, caffeic acid, myricetin, and quercetin. As noted earlier, an effect on plant-water relationships is one mechanism associated with the action of ferulic acid. 

These bundles are the primary component of cell walls in plants. Cellulose provides the cell wall with the strength to resist the turgor pressure in plant cells, maintain size and shape, and influence the direction of plant growth [57],... 

A mathematical description of steady-state growth is provided by recent restatements of the Lockhart equation [1]. This relates internal and external osmotic potentials, cell wall properties and hydraulic conductance to growth rate. Co-variations of growth rate and turgor pressure at various growth temperatures are detailed for wild-type and slender seedlings in Fig. 1. 

Fig. 1. Growth rate ( ) and turgor pressure ( ) changes with respect to meristem temperature for 3-leaf slender (sin/sin) and wild-type seedlings. Growth rates determined using high-resolution displacement transducers connected to emerging leaves and turgor pressures measured by pressure probe for individual meristem cells. Bars indicate SEM...

Turgor-driven cell expansion is a consequence of three superimposed but independent phenomena viscoelastic deformation, wall stress relaxation, and wall synthesis. Viscoelastic effects are reversible and occur whenever walls are placed under tension by turgor pressure. Viscoelasticity is a intrinsic mechanical property of the primary wall that is not mediated by enzymic or chemical reactions [76, 77]. In contrast, wall stress relaxation which is associated with expansive growth is believed to involve the chemical or enzymic irreversible loosening of load-bearing bonds in the wall. As a consequence, turgor pressure and water potential are reduced. Water is then taken up by the cell with the result that turgor is restored and there is a net increase in cell volume. 

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