Effects of seismic stress on the vegetative growth of Glycine max (L.) Merr. cv. Wells II

Effects of mechanical stress and plant density on mechanical characteristics, growth, and lifetime reproduction of tobacco plants

Plastic increases in stem elongation in dense vegetation are generally believed to be induced by canopy shading, but because plants protect each other from wind, shielding (reduced mechanical stress) could also play a role. To address this issue, tobacco Nicotiana tabacum plants were subjected to two levels of mechanical stress, 0 (control) or 40 (flexed) daily flexures, and grown solitarily, in a dense monostand (with plants of only one mechanical treatment), or in a mixed stand (flexed and control plants grown together). Flexed plants produced shorter and thicker stems with a lower Young's modulus than control plants, while dense-stand plants had relatively taller and thinner stems than solitary ones. Flexing effects on stem characteristics were independent of stand density. Growth, reproduction, and survival of solitary plants were not affected by flexing, while in the monostand growth was slightly reduced. But in the mixed stand, flexed plants were readily shaded by controls and had considerably lower growth, survival, and reproduction rates. These results suggest that wind shielding indeed plays a role in the plastic increase in stem elongation of plants in dense vegetation and that this response can have important consequences for competitive ability and lifetime seed production.

Mechanical perturbation-induced ethylene releases apical dominance in Pharbitis nil by restricting shoot growth

Mechanical perturbation (MP, rubbing) or internodes of Pharbitis nil shoots initiates release of lateral buds (LB) from apical dominance within 48 h. Evidence is presented which suggests that MP promotion of LB outgrowth is mediated by ethylene-induced restriction of main shoot growth. Ethylene production in the internodes is stimulated by MP within 2 h. Effects of MP are mimicked by treatments with 1-aminocyclopropane-1-carboxylic acid (ACC) and are negated by the inhibitors of ethylene production or action, aminoethoxy vinylglycine (AVG) and AgNO3. The fact that effects of MP, ACC, and ethylene inhibitors are observed to occur on main shoot growth at least 24 h before they are observed to occur on LB growth suggests a possible cause and effect relationship. MP also causes an increase in internode diameter. MP stimulation of ethylene production appears to be mediated by ACC synthase. The results of this study and our previous studies suggest that apical dominance may be released by any mechanism which induces ethylene restriction of main shoot growth.