Silver nitrate modulates organogenesis in Brassica juncea (L.) through differential antioxidant defense and hormonal gene expression

Abstract

Abstract Silver nitrate (AgNO3) is a known modulator of morphogenesis in plant cell and tissue culture but the underlying mechanism of its stimulatory effect on organogenesis is not clearly known. In Brassica juncea, we have studied AgNO3 induced high frequency shoot organogenesis and analyzed changes in antioxidant defense and, transcript profiling of hormone synthesis and signaling related genes. Hypocotyl explants cultured on medium with 2 mg/L BAP, 0.01 mg/L NAA and supplemented with 3 mg/L AgNO3 exhibited morphogenetic distinctness on 7 and 14th day and high frequency (95.89%) shoot organogenesis on 21st day of culture compared to medium without AgNO3 (14.6%). AgNO3 induced higher H2O2 content on 7th day (6.25 mM/g FW) compared to 14th (1.83 mM/g FW) and 21st day (0.65 mM/g FW) cultures whereas; both the SOD and CAT activities were induced and maintained during the entire culture period. Transcript profiling of ethylene and hormone synthesis-related genes suggested enhanced expression of ethylene signal transduction gene EIN2 in the absence of AgNO3 compared to that of AgNO3 treatment, indicating that AgNO3 could inhibit or nullify the ethylene response. The expression of cytokinin biosynthesis and negative regulator of auxin genes was also enhanced signifying that these may be involved in improved shoot regeneration. Taken together, it is suggested that AgNO3 application induces initial oxidative milieu followed by less-oxidized cellular environment and, upregulation of cytokinin receptor and negative regulator of auxin biosynthesis genes which may work in favour of improved shoot regeneration in Brassica juncea L.