Understanding the interaction of jasmonates and kinases in arsenic stress responses in Brassica juncea L.
Arsenic (As) contamination of the environment is a widespread problem with the situation at its worst in the South Asian region of West Bengal, India and Bangladesh. In order to cope up the problem and to be able to engineer plants as per the requirement in coming future, there is a need to thoroughly understand the mechanisms of As stress perception and tolerance. In this work, Brassica juncea L. was used to identify the active components involved in the perception of As stress. Brassica juncea L. seedlings were exposed to 500 μM arsenate [As(V)] for 4 and 24 h in absence or presence of different inhibitors. As(V) exposure induced thiol metabolism including the activity of ATP sulfurylase, cysteine synthase and γ-glutamylcysteine synthetase enzymes and the level of cysteine, and GSH/GSSG ratio. However, in presence of inhibitors of GSH biosynthe- sis; buthionine-L-sulfoximine (BSO), jasmonic acid (JA) biosynthesis, ibuprofen (IB) and propyl gallate (PG) and protein kinase inhibitor, stauropsorine (St), along with As(V), desirable induction of thiol metabolism was not seen. This in turn resulted in reduction of GSH/GSSG ratio. BSO negatively affected redox state, and induced a higher response of jasmonate biosynthesis gene (OPR1) and increased methyl jasmonate (MJ) levels. This sug- gested us that redox state mediates perception of As stress through jasmonate. Further, in presence of IB,the level of MJ declined and also resulted in down regulation of sulfur transporter (SULTR4;1) as well as in a mitogen activated protein kinase gene (MAPK-3). The integration of MAPKs in As(V) stress responses was confirmed through the employment of St inhibitor. In contrast, in presence of external supply of MJ, the GSH biosynthetic pathway was positively stimulated. These results emphasized the inter-relationship of sulfur metabolism, jasmonate and MAPKs in As stress perception and responses in plants.