Time series analysis of uptake and translocation of Cd and expression of transporter genes in nine Andrographis paniculata accessions

Abstract

Cadmium is a non-essential and toxic metal. Its presence in plants can have hazardous effects not only on the plants themselves but also on human health after consumption. A time-dependent experiment was conducted on nine accessions of A. paniculata (AP1, AP2, AP3, AP8, AP11, AP12, AP21, AP25, and CIM) in Cd-contaminated soil to understand the variability of Cd accumulation. The study examined the Cd uptake, translocation, antioxidant stress enzymes, ionic composition of root exudates, Cd bioavailability, and expression of transporter genes PCR, NRAMP, ABCC, HMA, and HIPP. Results demonstrated the lowest bio-concentration factor for Cd in AP1 and CIM (0.34-1.04). A significant increase in bio-concentration (6-37%), bioaccumulation (25-80%), and translocation (6-52%) of Cd was observed in nine accessions with time. However, AP1, AP8, AP11, and CIM demonstrated a significant decrease in bio-concentration (7-38%), bioaccumulation (14-50%), and translocation (8-45%) of Cd with time. The differential Cd uptake among the accessions was major associated with antioxidant enzyme activities, root exudates, Cd bioavailability, and biomass. The differential expression of Cd influx (ApNRAMP3 and ApNRAMP5) and efflux (ApPCR2, ApPCR6, ApPCR8, and ApPCR11) transporter genes was observed with time. According to the results, low accumulating accessions AP1, AP8, AP11, and CIM had higher biomass (10-46%) and lower Cd uptake (7-38%) than high accumulating accessions. These accessions also had minimal stress enzyme activities and a prevalence of cations in root exudates, which impeded Cd bioavailability (8-26%) and increased microbial biomass carbon (7-31%). The upregulation of ApPCR2, ApPCR6, ApPCR8, ApPCR11, ApHMA3, ApABCC3, ApABCC5, ApHIPP3.1, and ApHIPP3.2 while downregulation of ApNRAMP3, ApNRAMP5, and ApHMA1 genes further modulated Cd uptake and tolerance in low accumulating accessions.

Keywords: Andrographis paniculata; Cadmium bioavailability; Cadmium uptake; Root exudates; Transporter genes.