Cell elongation ethylene

Ethylene as a stimulator of growth and development. The most observed actions of ethylene on growing plants involves growth inhibition, or acceleration of senescence. These actions are especially evident in the antagonism or opposition of ethylene to auxins, gibberellins and cytokinins (27), as already outlined above. Actually ethylene stimulates growth in many types of cells, especially in water plants (Table II). When ethylene acts to stimulate cell elongation, as in water plants, auxins and CC>2 enhance the ethylene effect (38,39). This interaction is the reverse of that observed on land plants wherein ethylene opposes the effects of auxin, GA3 and cytokinins. 

Plant hormones rarely act alone hormones interact to produce a final effect. According to Gaspar et al., Some responses of plants to auxins may be caused by increased ethylene synthesis in response to auxin treatment. At high ethylene concentrations, microtubule and microfibril orientation are altered, which results in decreased cell elongation and increased cell expansion. The role of ethylene is hard to understand because it effects vary with developmental stage and because low concentrations can promote (or sometimes inhibit) a process, whereas higher levels have the opposite effect [22]. 

In contrast to the auxins and gibberellins, abscisic acid (ABA) and ethylene usually retard cell elongation. With some exceptions (Takahashi 1972, Gaither et al. 1975, Malik and Mehan 1975 a, Van Staden and Bornman 1970) ABA is inhibitory to growth (Addicott and Lyon 1969, Milborrow 1974). ABA inhibits stem and root elongation and counteracts the promotive effects of other substances on these organs (Rehm and Cline 1973, Kaufman and Jones 1974,... 

In general, then, we may view the auxins and GA s as promoters of cell elongation and ABA and ethylene as inhibitors. The cytokinins act as promoters of leaf cell expansion and inhibitors of stem elongation. This is somewhat oversimplified in light of the aforementioned exceptions, and the evidence that effects of applied hormones are often modified by or mediated by other hormones. 

The most common effects of cytokinin, ethylene, and abscisic acid on stem and coleoptile cell elongation are inhibitory. They inhibit both auxin-enhanced... 

In light-grown hypocotyls of dwarf watermelon seedlings benzyladenine (BA) enhances ethylene production and promotes cell elongation (Loy and Pollard 1977). Prevention of BA-induced ethylene production prevents BA-induced elongation, an indication that ethylene is necessary for BA-induced growth promotion. 

In conclusion, ethylene can promote or inhibit growth depending on the cell type and plant species. Generally, it inhibits shoot elongation in most terrestrial plants, but stimulates underwater shoot extension in many amphibious, wetland, and aquatic species enabling them to keep foliage above the water and... 

Olefins or alkenes are defined as unsaturated aliphatic hydrocarbons. Ethylene and propylene are the main monomers for polyolefin foams, but dienes such as polyisoprene should also be included. The copolymers of ethylene and propylene (PP) will be included, but not polyvinyl chloride (PVC), which is usually treated as a separate polymer class. The majority of these foams have densities <100 kg m, and their microstructure consists of closed, polygonal cells with thin faces (Figure la). The review will not consider structural foam injection mouldings of PP, which have solid skins and cores of density in the range 400 to 700 kg m, and have distinct production methods and properties (456). The microstructure of these foams consists of isolated gas bubbles, often elongated by the flow of thermoplastic. However, elastomeric and microcellular foams of relative density in the range 0.3 to 0.5, which also have isolated spherical bubbles (Figure lb), will be included. The relative density of a foam is defined as the foam density divided by the polymer density. It is the inverse of the expansion ratio . 

The planar ethylene (C2H4) molecules form a different type of crystal structure than that for ethane. As shown in Figure 11.6, the structure is body-centered [3 2PTOT(o)l with two molecules in the orthorhombic unit cell, D j, Pnnm, a0 = 4.87, b0 = 6.46, c0 = 4.14 A. The cell is elongated along b0 because the C=C bonds are skewed in two orientations in this direction. The orientation of the C=C bond in the molecule in the center of the cell differs from those at the comers. The C=C bond length is 1.33 A. 

A second effect of ethylene is to alter the direction of cell enlargement in stems and roots [81]. By causing a change in orientation of cellulose microfibrils from transverse to random or longitudinal, it causes cells to swell up rather than elongate. As a result, stems and roots become shorter and thicker. The inhibition of stem and root growth induced by excess auxin is due in part to auxin-induced ethylene [82]. In a few tissues, such as... 

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