Brassinosteroids positively modulate growth: Physiological, biochemical and anatomical evidences using two tomato genotypes contrasting to dwarfism

Abstract

Our hypothesis considered that the utilization of genotypes with different levels of biosynthesis to BR can explain the roles of this steroid in relation to growth and metabolic behavior. The aim of this research was to investigate the possible interferences occasioned by the exogenous application of BR on growth and metabolism, using two genotypes contrasting to the DWARF gene (MT-d and MT-D), that are BR-deficient and BR-efficient, respectively. The experiment had four treatments, being two genotypes (BR-efficient and BR-deficient) and two levels of brassinosteroids (0 and 100 nM BR, here after described as – BR and + BR, respectively). This research revealed that the exogenous application of BR promoted improvement on growth, inducing increases in BR-deficient plants of 120%, 469%, 219%, and 203% in LDM, RDM, SDM and TDM, respectively. The positive effects on gas exchange and chlorophyll fluorescence confirm the benefits of this steroid on photosynthetic apparatus. The changes in the anatomical characteristics of the leaf are related to contribution of the BR on influx and consequent fixation of CO2. In addition, modifications related to root anatomy occurred by the BR action with objective to increase the barrier against biotic and abiotic stresses and the efficiency in the absorption of water and nutrients. The improvements in photosynthetic pigments, observed in the increases of 16%, 35%, 20% and 67% in Chl a, Chl b, Total Chl and Car, respectively, to BR-deficient plants, suggested that the role of BR must be linked to the chlorophyll biosynthesis route and maintenance of chloroplast integrity, this result being intrinsically associated with the increments found in the activities of antioxidant enzymes that modulate the accumulation of ROS.