Effects of brassinosteroids application on yield formation and root characteristics of direct-seed rice

Brassinosteroids (BR) is a plant growth regulator that could regulate the growth and development of crops. However, the effects of BR on the yield formation of rice and the related mechanism remain to be fully elucidated in direct-seeded rice. The present study conducted a field experiment using BR and a BR synthesis inhibitor (brassinazole, BZ) to explore the effects of BR on the yield formation in direct-seed rice. The results showed that BR increased grain yield by promoting grain numbers per panicle and seed-setting rate, while BZ treatments represented some inhibition on yield formation. The activities of sucrose synthetase-Ⅰ (SS-Ⅰ), sucrose synthetase-Ⅱ (SS-Ⅱ), sucrose phosphate synthase (SPS), and glutamine synthetase (GS) in leaves were enhanced by BR treatments and inhibited by BZ treatments. BR treatments also increased sucrose content in leaves and stem by 24.53-213.31% and 29.89-106.55%. Root morphology parameters, including length, surface area, volume, diameter, and tip number, increased under BR treatments. Root biomass and root-shoot ratio were also increased by BR treatments. Moreover, correlation analysis showed that root volume and root diameter both positively correlated with yield, while SS-II activity positively correlated with root tip number and grain yield. In conclusion, BR enhanced yield formation of direct-seed rice by promoting root growth and activities of carbon-nitrogen metabolism-related enzymes in leaves.