Determinate Growth of Allium Sativum Peduncles: Evidence of Determinate Growth as a Design Factor for Biomechanical Safety

Abstract

Determinate growth in an organ can reduce the mechanical liability of dynamic wind loadings. This hypothesis was examined for the peduncles of Allium sativum grown under protected and unprotected field conditions and in the glasshouse. The extent to which the lengths of peduncles approach their critical buckling lengths lcr was correlated with the extent to which peduncles were perturbed mechanically. Glasshouse‐grown plants that were protected from dynamic loadings (wind or handling) produced peduncles with low ratios of critical to actual peduncle lengths (lcr/1 = 1.11 ± 0.07); field‐grown, unprotected plants had lcr/1 = 1.85 ± 0.29; while plants grown in the field but protected from the wind had lcr/1 = 1.29 ± 0.15. Statistical analyses indicated that peduncle length was the only morphometric parameter examined to significantly differ among plants grown under the three conditions. The frequency distributions of critical (buckling) stress for each of the three populations of peduncles differed; that of the unprotected population conformed to a three‐parameter Weibull distribution. Allium sativum exhibits thigmomorphogenesis, i.e., mechanical forces influence the extent and nature of organogenesis. Unlike other thigmomophogenetic species, however, the determinate growth of peduncles did not influence peduncle girth or the elastic (Young's) modulus of tissues. Thus, the extent to which vertical growth proceeded determined the design factor for dynamic loading in these reproductive organs. The design (“margin of safety”) factors of A. sativum peduncles grown under the three different conditions and calculated from lcr/1 were remarkably similar to those specified for engineered columns of wood subjected to stress durations differing in magnitude.

Effect of mechanical perturbation on the biomechanics, primary growth and secondary tissue development of inflorescence stems of Arabidopsis thaliana

“…Apart from the notable reduction in petiole diameter, these results are similar to those found in Arabidopsis and consistent with several woody herbs (Biddington and Dearman, 1985). A study on the response of determinate peduncles of Allium sativum to mechanical stress (Niklas, 1990) also showed a significant shortening of the axis, but differed from the results of the Arabidopsis stem by showing no change in values of flexural rigidity or Young's modulus. Determinate axial organs such as fertile shoots and leaf petioles may not respond to mechanical perturbation in the same way as indeterminate woody stems.…”

Effects of Wind on the Allometry of Two Species of Plants in an Elfin Cloud Forest

“…As plants grow, the shape and the material properties of organs and tissues change during their development such that they can support themselves and support external loadings such as wind (Niklas 1990). In addition to supporting this argument, this paper also suggests that alteration of the allometric relationships of plant parts, organs, or plant modules (leaves of P. acuminata and branches of C. erosum) and alteration of the number of parts (leaves and branches of C. erosum) could be viable strategies to compensate for the effects of wind or other mechanical stresses.…”

Wind, Size, and Tree Safety

“…Much of biology is explicable in terms of the operation of simple physical laws and processes (Wainwright et al 1976;Vogel 1981;Niklas 1992). The effects of these laws and processes on plants as well as animals are size-dependent (Huxley 1932;Niklas 1994). This is nowhere better seen than in the case of trees.…”

“…This is nowhere better seen than in the case of trees. To survive and grow, these long-lived and sedentary organisms must constantly adapt to their changing physical surroundings in which gravity and wind play persistent and important roles (Metzger 1893;King and Loucks 1978;Vogel 1981;Niklas 1998a).…”

“…For example, simple physics shows that gravity compresses tree trunks and causes cantilevered branches to bend under their own weight (Wainwright et al 1976;Niklas 1992). The same simple physics shows that the self-loading stems experience increases in proportion to growth in girth, length, or number such that older portions of stems support increasingly more weight (Niklas 1992(Niklas , 1994(Niklas , 1999a.…”