Favouring NO over HO production will increase Pb tolerance in Prosopis farcta via altered primary metabolism.

Reactive oxygen species (ROS) and nitric oxide (NO) are known in triggering defense functions to detoxify heavy metal stresses. To investigate the relevance of ROS production, Pb treatment (400µM) alone and in combination with 400µM sodium ascorbate (Asc: as HO scavenger) were given to hydroponically grown Prosopis farcta seedlings over a time course of 72h. Data presented here indicate that, the low extent of HO due to scavenging by ascorbate, together with high level of NO improved Pb+Asc- treated Prosopis growth. Following the evoked potential of both the signals, significant increases in phenolic acids; caffeic, ferulic and salicylic acid were observed with Pb treatment; which are consistent with observed increase in lignin content and consequently with growth inhibition. In contrast, Pb+Asc treatment induced more flavonoids (quercetin, kaempferol, luteolin), diminished phenolic acids contents and also lignin. Elicited expression rate of phenylalanine ammonia-lyase gene (PAL) and also its enzymatic activity verified the induced phenylpropanoid metabolism by Pb and Pb+Asc treatments. In comparison with Pb stress, Asc+Pb application induced the high expression of arginine decarboxylase gene (ADC), in polyamines biosynthesis pathway, and conducted the N flow towards polyamines and γ-amino butyric acid (GABA). Examining the impact on enzyme activities, catalase, and guaiacol peroxidase; Pb+Asc reduced activity but this increased ascorbate peroxidase, and aconitase activity. Our observations are consistent with conditions favouring NO production and reduced HO can improve Pb tolerance via wide-ranging effects on a primary metabolic network.