An intracellular glutathione (GSH) responsive phytochemical delivery system based on thiol gated mesoporous silica nanoparticles (MSNs) was developed and tested on the model plant Arabidopsis thaliana. In the present study, monodispersed MSNs with particle diameters of ~20 nm and pore sizes of ~2.87 nm were synthesized and modified. Abscisic acid (ABA), a key phytohormone, was entrapped in the mesopores of MSNs and then the pore entrances of MSNs were covered with decanethiol gatekeepers through GSH-cleavable disulfide linkages. An in vitro release test of ABA from decanethiol gated MSNs proved that there was efficient loading and entrapment of phytochemicals in the absence of a GSH redox trigger. Most importantly, in planta experiments demonstrated that GSH-mediated release of ABA from the pores of MSNs significantly reduced the leaf stomatal aperture and inhibited water loss of treated plants. Moreover, compared with the usage of free ABA, the controlled release of the encapsulated phytohormone from MSNs markedly prolonged the expression of the ABA inducible marker gene (AtGALK2) and finally, improved the drought resistance ability of Arabidopsis seedlings under drought stress. Therefore, the concept of using short-chain molecules as gatekeepers to encapsulate biomolecules in MSNs was demonstrated. The application of MSNs with redox-responsive gatekeepers has been shown in this study to be a potential and efficient technique to deliver phytochemicals into plants and release them in a controllable fashion.