Physiological and proteomics analyses reveal the resistance response mechanism to alkali stress in the early seedlings (cotyledons vs. roots) of castor plant (Ricinus communis L.)

•Cotyledons and roots of castor have different adaptive mechanisms under alkali stress.•Roots could sequester a large amount of Na+, so that cotyledons can maintain physiological functions such as photosynthesis.•Cotyledons retain efficiency of photosynthetic electron transport and accumulation of osmolytes.•Roots enhance the transfer efficiency of the mitochondrial electron transport chain and promote PA biosynthesis