Silver form and aquaporin deficiency regulate transcriptional and protein responses in Solanum lycopersicum

Silver-based materials are widely used in medical, industrial, and consumer applications, increasing the likelihood of environmental release of both nanoparticulate and ionic forms of silver. Despite growing concern over plant exposure, the molecular mechanisms of how different silver forms affect membrane transport and stress-response pathways remain poorly understood. Here, we investigated how nanoparticulate silver (AgNPs) versus ionic silver (AgNO₃) differentially modulates transcriptional and post-transcriptional responses in tomato using wild-type and aquaporin-deficient genotypes. Plants were exposed for 30 days to 30 mg L⁻¹ AgNPs (2 nm) or AgNO₃, followed by integrated analyses of membrane transport, metal homeostasis, and oxidative stress responses using RT-qPCR, western blotting, and confocal immunofluorescence imaging. Ionic silver elicited stronger transcriptional activation of transport and stress-related genes, including H⁺-ATPase (2.16–4.32-fold), CAT2 (3.97–4.06-fold), and MET2 (up to 6.28-fold), while suppressing aquaporin transcripts (PIP2;1 reduced to 0.76–0.79-fold at Day 30). Under AgNP exposure, CAT2 increased to 3.87-fold in the aquaporin-deficient genotype, and MET2 increased to 6.28-fold at Day 30, indicating a stronger stress-response activation in this line. At the protein level, AgNO₃ caused pronounced loss of PIP2:1 abundance (∼3.5-fold lower in aquaporin-deficient plants), whereas AgNPs preserved higher aquaporin levels. Immunofluorescence analyses further showed retention of membrane-associated aquaporin signal under AgNPs exposure and enhanced vacuolar proton pump activity under AgNO₃. Collectively, these findings demonstrate that silver form influences plant response more strongly, rather than nanoparticle presence alone or aquaporin disruption per se, highlighting membrane transport networks and post-transcriptional regulation as potential determinants of resilience to silver exposure.