Physiological and molecular investigation of nanosilica mediated drought tolerance in cumin (Cuminum cyminum L.)

Cumin ( Cuminum cyminum L.) is widely recognized as an anticancer and antidiabetic agent. While the effects of drought stress on plants are well documented, there is a lack of comprehensive research on the use of nanosilica as a new strategy to mitigate them. In this study, two Iranian landraces (Isfahan and Semnan) were cultivated and treated with three concentrations of foliar nanosilica (0, 4, and 6 mM nSi) under three levels of drought stress (60, 40, and 20% of field capacity, FC). The treatment significantly improved plant physiological and biochemical responses, with the most pronounced benefits observed at 4 mM nSi under mild drought (60% FC). This optimal treatment increased total chlorophyll content up to 18.57 mg g − 1 FW and essential oil yield (EOY), reaching 8.22 kg ha − 1 with 2.81-fold compared to the mild drought stress without foliar nSi application (1.56 kg ha − 1 ). Expression of limonene synthase (LS) increased 3.6-fold, phenylalanine ammonia-lyase 1 (PAL1) increased 3.3-fold, and aldehyde dehydrogenase family 3 member H1 (ALDH3H1) peaked under moderate drought combined with 4 mM foliar nSi application. Concomitantly, nSi elevated osmoprotectants, with proline content rising to 5.20 µmol mg − 1 FW under severe drought. Our findings establish that nSi, particularly at a 4 mM concentration under mild water deficit, activates an integrated tolerance program in cumin, stabilizing photosynthesis and improving the allocation of resources toward enhancing essential oil yield.