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.