Atmospheric-pressure air plasma promotes sorghum seed germination by nitrate accumulation causing suppression of ABA signaling

ABSTRACT Plants are often exposed to lightning, a natural form of plasma. We reveal that both rooting and shooting are promoted when dry sorghum seeds are irradiated with atmospheric-pressure plasma generated in air (air plasma). The expression of genes related to nitrogen metabolism, such as nitrate reductase, increased after air-plasma treatment compared with the negative control, and the treatment increased nitrate, but not nitrite, content in the seeds. Nitrate suppresses abscisic acid (ABA), which inhibits seed germination. Our analysis shows that ABA decreased 6 h after imbibition in air plasma-treated seeds and that transcripts of ABA 8’ hydroxylase , a key enzyme of ABA catabolism, increased 0 h after imbibition. ABA-signaling modulators, jasmonic acid (JA) and indole-3-acetic acid (IAA), were also altered by air plasma. These facts suggest that air plasma-induced nitrate, together with JA and IAA, drive the suppression of ABA signaling, and the induction of nitrogen metabolism, promoting seed germination.