Induced elongation

Certain polymers can be crystallized by mechanical stress. Namely, the stress induced elongation decreases the entropy of the chains. For this reason, an additional decrease in entropy, which is required for crystallization is comparatively small. Strain induced crystallization phenomena are of great practical importance since the elastomeric properties can be tailored in some way. In particular, PIB readily undergoes strain induced crystallization already close to room temperature. 

In turbulent flow, the macromolecules are also believed to experience burst-induced elongation. However, it has to date not been possible to formulate structure-property relationships which allow an ad hoc prediction of the onset of mechanical degradation and its influence on drag reduction. 

A long-chain dihydroxy compound, isolated from Avocado mesocarp, inhibited soybean callus growth and induced elongation of wheat coleoptiles. This compound was identified as 1-acetoxy-2,4-dihydroxy-n-heptadeca-16-ene, otherwise known as avocado inhibitor (14). 

BR-induced elongation also differs from that induced by IAA in that the former is not affected but rather enhanced in the presence of 50mM sucrose in the light, while the latter is inhibited. A similar sucrose-enhancement has been shown for gibberellin-induced elongation (24). In this case the mode of BR action is similar to that of gibberellin. 

N,N -Dicyclohexylcarbodiimide (DCCD), an inhibitor of membrane bound ATPase, has been shown to strongly inhibit IAA-induced elongation of cucumber hypocotyl sections, while it has no effect on GA-induced elongation (36). DCCD markedly inhibits BR-induced elongation (8), suggesting that BR acts differently from GA, but similarly to IAA in this particular case. 

Sequential Interaction. Synergism between two hormones is sometimes more clearly observed in sequential treatments of the two hormones. Thus, GA pretreatment always results in synergistic enhancement of IAA-induced elongation of hypocotyl sections (37). Sequential interaction between BR and IAA is very similar to that between GA and IAA (3). Sections pretreated with BR for 2 h respond to IAA synergistically. The reverse order treatment is rather inhibitory as is the case for GA. Therefore, both BR and GA seem to sensitize hypocotyl sections to a later response by IAA. These facts suggest that cells which have already been initiated to elongation by IAA are not the target cells of BR/GA. 

Figure 1. Effect of 0.01 pM IAA on the BR-induced elongation of pea stem segments. Lines are curves of best fit as calculated by PEST, and comparison gave a model where a change in lnlH] accounted for the difference between the data sets.

Figure 2. Effect of 1 and 10 pM colchicine on BR-induced elongation of pea stem segments, 14 segments per treatment, 29.5h growth. BR and colchicine effects significant at p<0.01, interaction NS, bar is LSD P=0.05.

As expected, the electrical conductivity of the doped blend is also a function of the polyacetylene composition of the material. (5) Furthermore, stretch induced elongation of the blends leads to a dramatic increase in conductivity subsequent to doping, further confirming that the electrical properties are also very sensitive to the arrangement of the respective phases. 

It may finally be noted that a geometrical constraint that induces elongational flow if Re < Recr (e.g., a sudden constriction in a tube) tends locally to depress turbulence if Re > Recr. Turbulence is also depressed by the presence of large-molar mass polymers or by a high concentration of dispersed particles in the liquid. 

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