ANNOUNCEMENTS
Brassinosteroids (BRs) are a group of plant steroidal hormones which are essential for proper growth and productivity. BRs induce tolerance to cell stress responses, mostly abiotic stress by balancing the expression of diverse genes (exact mechanism broadly unclear). The plant’s response to stress is coupled with the generation of Reactive Oxygen Species (ROS), the most reactive chemicals known to be formed from oxygen. On the other hand, the Cyanide (CN)-resistant respiratory pathway or Salicylhydroxamic acid (SHAM)-sensitive pathway (AOX) plays a role in the optimization of photosynthesis under environmental stresses (e.g., highlight, osmotic, and temperature) through dissipation of excess ROS and redox (Niyogi, KK., 1999). The present study focuses on the involvement of AOX pathway in the optimization of Brassinolide (BL) mediated photosynthesis, respiration, ROS (O2- and H2O2) in leaf discs of P. sativum pre-incubated under different conditions i.e., Darkness, Normal light (NL) and High light (HL). External application of BL showed an enhancement in bicarbonate-dependent photosynthetic O2 evolution and total respiration O2 uptake under all these conditions. However, BL application stimulated these rates more under NL when compared to pre-incubation under dark or HL. Further, the application of SHAM along with BL decreased the photosynthetic O2 evolution rates under all these conditions. However, the decline in rates is more pronounced under HL when compared to dark or NL. Like photosynthesis, total respiratory O2 uptake decreased under all conditions when leaf discs are treated with SHAM in presence of BL. Furthermore, a positive modulation in total cellular ROS levels has been observed under these conditions in the presence of BL or SHAM or both. Therefore, the present finding suggests that AOX and ROS play an important role in BR mediated photosynthesis under NL or HL.
Keywords: Brassinosteroids, Alternative oxidase, Photosynthesis, Respiration, Reactive Oxygen Species, leaf discs, BL, SHAM.
