Effective diffusion rates and cross-correlation analysis of "acid growth" data

Abstract

We investigated the growth-temperature relationship in plants using a quantitative perspective of a recently derived growth functional. We showed that auxin-induced growth is achieved by the diffusion rate, which is almost constant or slowly ascending in temperature while the diffusion rate of fusicoccin-induced growth increases monotonically with temperature for the entire temperature range, though for some concentrations of IAA "super-diffusion" takes place for unperturbed growth. Furthermore, three kind of experiments were compared: for abraded coleoptiles, coleoptile segments and intact growing seedlings. From cross-correlation analysis it was found that the timing of IAA and FC-induced proton secretion and growth matches well. Unambiguous results, concerning fundamental conditions of the acid growth hypothesis, were obtained by cross- and auto-correlation analysis: (1) For abraded coleoptiles, because of the lowering of the cuticule potential barrier, auxin-induced cell wall pH decreases simultaneously with the change in growth rate; no advancement or retardation of pH (proton efflux rate) or growth rate takes place (2) Exogenous protons are able to substitute for auxin causing wall loosening and growth (3) Although the underlying molecular mechanisms vastly differ, a potent stimulator of proton secretion, the fungal toxin FC, promotes growth similar to auxin, however of much elevated intensity; as for auxin - no advancement or retardation takes place.