Millimeter-Wave Seed Priming Alters the Rice Root Proteomic Response to Salt Stress

Salt stress is a major constraint on rice production because it inhibits plant growth and reduces yield. Although millimeter-wave (MMW) seed priming was reported to improve plant performance under environmental stress, the molecular mechanisms underlying its effects remain largely unknown. This study examined whether MMW seed priming improves early rice performance under salt stress and characterized associated changes in the root proteome. Rice seeds were irradiated with MMW, and morphological traits were evaluated under 150 mM NaCl as salt stress for 2 days. Based on morphological results, rice seeds were irradiated with 20 mW for 20 min. Root proteins were analyzed based on the growth responses. Among 6307 proteins analyzed with label-free proteomics, selected proteomic observations were further examined by immunoblotting, gene-expression analysis, and starch measurements. MMW irradiation improved seed germination and alleviated salt-induced inhibition of root growth. Proteomic analysis showed that proteins associated with carbohydrate metabolism and endoplasmic-reticulum function were markedly affected by MMW irradiation. Glutathione reductase and ascorbate peroxidase accumulated under salt stress and further increased following MMW irradiation. Calreticulin and calcium-dependent protein kinase were also increased in abundance by MMW irradiation under salt stress. In addition, soluble starch content, which declined under salt stress, was attenuated the salt-associated reduction by MMW irradiation. These findings extend molecular studies of MMW-mediated salt-stress responses to the rice root proteome and identify candidate proteins and biological processes associated with the improved salt-tolerant phenotype. The observed proteomic changes provide insight into potential mechanisms that may contribute to improved rice growth under saline conditions.