Mechanism of action of carbon nanoparticle verified in rice: Improved water use efficiency is the key

Abstract Mechanism 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 CO₂ concentration. 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 in Arabidopsis and rice. Elevated endogenous ABA in rice seedlings and flag leaves along with increased expression of ABA biosynthetic genes in Arabidopsis and rice AtNCED3, AtNCED6, OsNCED1 confirmed increased ABA synthesis. Negative regulators of ABA pathway, OsSNRK2 down-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.