Endogenous IAA affected fluoranthene accumulation by regulating H+-ATPase and SOD activity in ryegrass.

This study explores the role of endogenous indole-3-acetic acid (IAA) in modulating plant responses to pollution stress and its effect on pollutant accumulation, with a focus on fluoranthene (Flu) in ryegrass. To elucidate the mechanism, we employed an IAA promoter (α-aminobutyric acid [α-AB]) and an IAA inhibitor (naphthylphthalamic acid [NPA]) to regulate IAA levels and analyze Flu uptake characteristics. The experimental setup included a Flu treatment group (ryegrass with Flu addition) and a control group (ryegrass without Flu). Our findings demonstrate that Flu treatment enhanced IAA content and plant growth in ryegrass compared to the control. The Flu+AB treatment further enhanced these effects, while the Flu+NPA treatment exhibited a contrasting trend. Moreover, Flu+AB treatment led to increased Flu accumulation, in contrast to the inhibitory effect observed with Flu+NPA treatment. Flu treatment also enhanced the activities of key antioxidant enzymes (SOD, POD, CAT) and increased soluble sugar and protein levels, indicative of enzymatic and nonenzymatic defense responses, respectively. The Flu+AB treatment amplified these responses, whereas the Flu+NPA treatment attenuated them. Significantly, Flu treatment raised H+-ATPase activity compared to the control, an effect further elevated by Flu+AB treatment and diminished by Flu+NPA treatment. A random forest analysis suggested that Flu accumulation dependency varied under different treatments: it relied more on H+-ATPase activity under Flu+AB treatment and more on SOD activity under Flu+NPA treatment. Additionally, Flu+AB treatment boosted the transpiration rate in ryegrass, thereby increasing the Flu translocation factor, a trend reversed by Flu+NPA treatment. This research highlights crucial factors influencing Flu accumulation in ryegrass, offering potential new avenues for controlling the gathering of contaminants within plant systems.

Metaphire guillelmi exhibited predominant capacity of arsenic efflux.

Earthworm could regulate their body concentration of arsenic via storage or excretion, and the ability of As efflux among different earthworms is not consistent. Here, whole and semi As exposure patterns with 0-10-30-60-100 mg kg-1 exposure concentrations were set to characterize the As efflux in geophagous earthworm, Metaphire guillelmi. Cast As (As-C) and earthworms' antioxidative responses were monitored to explore the efflux mechanisms under 30 mg kg-1 As-spiked soil (As30), besides, As concentration in earthworm tissue after egestion and dissection depurations were compared. In the whole exposure pattern, As concentration in gut content (As-G, 19.2-120.3 mg kg-1) surpassed that in the tissue (As-T, 17.2-53.2 mg kg-1), and they both increased with exposure concentrations. With the prolong time, they firstly increased and kept stable between day 10-15, then As-G increased while As-T decreased between day 15-20. In the semi-exposure pattern, both As-G and As-T decreased when M. guillelmi was transferred to clean soil for 5 days. During the 42-day incubation in As30, the antioxidative responses including reactive oxygen species (ROS), glutathione (GSH) and glutathione-S-transferase (GST) were firstly increased and then decreased, and As-C (13.9-43.9 mg kg-1) kept higher than As-G (14.2-35.1 mg kg-1). Significantly positive correlations were found between As-T and GSH, As-C and GST. Moreover, tissue As after dissection (11.6-22.9 mg kg-1) was obviously lower than that after egestion (11.4-26.4 mg kg-1), but significantly related to ROS and GSH. Taken together, M. guillelmi exhibited excellent capacity of As efflux, and GSH explained tissue As accumulation while GST facilitated the As elimination via cast. Besides, dissection instead of egestion revealed the As efflux in M. guillelmi more accurately. These findings contributed to a better understanding of how geophagous earthworm M. guillelmi regulated tissue As accumulation for As stress tolerance, and recommended an optimal depuration mode to characterize As accumulation.