Differential physiology and expression of phenylalanine ammonia lyase (PAL) and universal stress protein (USP) in the endangered species Astragalus fridae following seed priming with cold plasma and manipulation of culture medium with silica nanoparticles.

KEY MESSAGE: Seed priming with cold plasma in combination with manipulation of culture medium with silica nanoparticle provokes anatomical, physiological and molecular changes, thereby reinforcing the plant growth and protection. ABSTRACT: This study addressed responses of Astragalus fridae to seed priming with cold plasma (0.84 W/cm2; 0, 30, 60, and 90 s) and applications of SiO2 nanoparticle (nSi; 0, 5, 40, and 80 mgl-1) in culture medium (an in vitro study). FE-SEM confirmed nSi uptake and translocation. Bulk Si at high concentrations reduced biomass accumulation (mean = 45%), while nSi did not make significant differences. The growth-enhancing effects of plasma by 41.5% were promoted by the nSi supplementation and reached 71%. Plasma did not make significant changes in Chla, while led to the slightly higher (mean = 14%) Chlb. The presence of nSi at high doses caused slight reductions in Chlb (mean = 25%) which were mitigated by plasma. The plasma and/or nSi treatments modified activities of phenylalanine ammonia lyase (PAL) in both roots (mean = 32%) and leaves (mean = 44%). With a similar trend, both individual and combined treatments of plasma and nSi provoked inductions in peroxidase activities in roots and leaves. The simultaneous treatments of plasma and nSi had the highest expression rates of PAL gene. The individual treatments of plasma did not make a significant difference in the expression of universal stress protein (USP) gene, whereas the nSi-treated seedlings exhibited the higher expression rates of USP. Leaf thicknesses and development of the vascular system (xylem and phloem) were reinforced in response to plasma and nSi. The findings provide evidence on potential benefits and phytotoxicity of nSi and plasma which may be employed as a theoretical basis for possible exploitation.