Bioenergy sorghum stems respond to mechanical stimulation with tissue-specific modifications in hormone homeostasis...

Sorghum [Sorghum bicolor (L.) Moench] is a promising and highly productive bioenergy crop but remains susceptible to stem lodging, typically caused by severe weather-related mechanical forces like wind and rain. However, when exposed to less severe mechanical stimulation, plants may exhibit alterations in their growth and development through a process known as thigmomorphogenesis that may enhance their ability to withstand stronger forces. Accordingly, understanding mechanisms regulating thigmomorphogenesis may facilitate the development of lodging-resistant sorghum varieties. In this study, the hormonal responses of four stem tissues, including pulvinus, white band, zone of division, and zone of maturation, were investigated at multiple time points following moderate mechanical stimulation, revealing distinct hormonal profiles and tissue-specific response patterns across these tissues. JA level was reduced exclusively in the pulvinus, while GA₁ level declined specifically in the zone of division. In contrast, the levels of GA₂₀, IAA, and ABA decreased in all tissues following mechanical stimulation. Eight weeks of continuous mechanical stimulation reduced plant height and the length of most internodes, primarily by decreasing the number of internodes and reducing cell elongation. Microscopic analysis of internodes at different developmental stages further demonstrated that mechanical stimulation generally increased the density and radial length of pith vascular bundles, enhanced the lignification level in both the pith and rind, and increased the rind thickness. The findings from this study could provide new insights into tissue-specific responses of sorghum stems to mechanical stimulation and may offer new opportunities for improving lodging resistance in sorghum.