Carbon nanoparticle exposure strengthens water-relation parameters by stimulating abscisic acid pathway and aquaporins genes in rice

Abstract

ABSTRACTMechanism of action and molecular basis of positive growth effects including yield increase due to carbon nanoparticle (CNP) treatment in rice plants is dissected here. CNP at 500 -750 µg/mL were found to be the optimum dosages showing best seedling growth. CNP treatment resulted increase in stomata size, gaseous exchange and water use efficiency along with decrease in stomata frequency, relative humidity, internal CO2concentration. CNP treatment exerted cold tolerance in seedlings and water stress tolerance in reproductive stage. CNP-coupled with water uptake was found to be endocytosis mediated, although CNP uptake was not affected by endocytosis inhibitor application in roots. Genomic analysis resulted major involvement of ABA pathway and stomata size and frequency genes inArabidopsisand rice. Elevated endogenous ABA in rice seedlings and flag leaves along with increased expression of ABA biosynthetic genes inArabidopsisand riceAtNCED3,AtNCED6,OsNCED1confirmed increased ABA synthesis. Negative regulators of ABA pathway,OsSNRK2down-regulation and up-regulation of stomagen (OsEPFL9) reconfirmed ABA’s involvement. CNP treatment resulted water stress tolerance by maintaining lower stomatal conductance, transpiration rate and higher relative water content. Increased ABA (OsSNRK1,OsSNRK2) and aquaporin (OsPIP2-5) genes’ expressions could explain the better water stress tolerance in rice plants treated with CNP. Altogether, due to thermomorphogenesis, down-regulation of Phytochrome B resulted altered the ABA pathway and stomatal distribution with size. These changes resulted improved water relation parameters and WUE showing improvement in yield. Detailed mechanism of action of CNP in abiotic stress tolerance can be exploited in in nano-agriculture.