Gibberellin deficiency uncouples shoot and root growth in tomato and alters morphology and carbon allocation

Gibberellins promote differentiated root and shoot responses in growth, morphology, and carbon allocation. Gibberellins (GAs) are plant hormones that are produced in young tissues and organs, acting locally in growing shoots and roots or being transported to other organs. The role of GAs in root development was first investigated decades ago using plants severely deficient in GA biosynthesis. However, only few studies have examined root metabolism in plants with reduced GA levels and evaluated its association with root growth and morphology. Furthermore, the signaling between the root and shoot systems plays a key role in coordinating plant growth and development. Therefore, this study aimed to assess the impact of endogenous alterations in GA levels on tomato mutants exhibiting mild (gibberellin deficient-3, gib3), intermediate (gib2), and high (gib1) GA deficiency on root and shoot growth, morphology, respiratory metabolism, and labeled carbon allocation. The low GA content exerted an effect on shoot growth and morphology, which, surprisingly, led to minor changes in the mutant roots. The gib2 and gib1 mutants exhibited higher proportions of thick roots than the wild-type and gib3, but the growth of roots with smaller diameters was most pronounced in these genotypes. The carbohydrate oxidation was influenced by a reduction in GA biosynthesis within mutant leaves and roots. In addition, the differential sensitivity to GA by each organ likely contributed to variations in sugar accumulation. Together, these results indicate that shoot tissues exhibit a distinct response compared to root tissues, suggesting a decoupling of root growth and carbon allocation from shoot growth and development in GA-deficient plants. This observation points to a key role for GA in orchestrating the growth of both shoots and roots.