Light perception by the root is essential for gibberellin-induced primary-root elongation in tomato

- The promoting effect of gibberellin (GA) on primary-root elongation wasdemonstrated in several species, including Arabidopsis (Arabidopsis thaliana).However, in some other species its effect is less clear.- We have used tomato (Solanum lycopersicum) GA-deficient mutants to study therole of GA in primary-root elongation and examined the involvement of light inthis response.- Application of GA to gib-1 immediately after germination, promoted primary-rootelongation, but when the roots were deeper in the growth medium, in the dark, ithad no effect. If the roots were lighted deep in the growth medium, the hormonepromoted their elongation. RNA-seq analysis revealed a normal GAtranscriptional response in dark-grown roots, but the output toward cell-expansion was blocked. Using Dark-root (D-root) and D-shoot systems, wedemonstrated that direct light perception by the root is essential for GA-inducedelongation. Similar light dependent GA-elongation response was found in wheat(Triticum aestivum) roots, but not in Arabidopsis.- We suggest that in tomato GA promotes root elongation right after germination,in the light and this contributes to seedling establishment. Later, in the dark theinsensitivity to GA may be important for continues root growth under fluctuatingwater availability, as water deficiency suppresses GA accumulation.