Rhizospheric nano-remediation salvages arsenic genotoxicity: Zinc-oxide nanoparticles articulate better oxidative stress management, reduce arsenic uptake, and increase yield in Pisum sativum (L.).

Pea (Pisum sativum L.), a legume, has a high nutritional content, but arsenic (As) in the agro-ecosystem poses a significant bottleneck to its yield, especially in South East Asia, by severely hampering ontogeny. The present study proposes a rhizospheric nano-remediation strategy to evade As-genotoxicity and improve crop yield using biogenic zinc-oxide nanoparticles (ZnONPs). Similar to any other source of environmental stress, As-toxicity caused rapid oxidative bursts with deterioration in morpho-physiological attributes (germination rate, shoot length, and root length decreased by 62 %, 16 %, and 14.9 % respectively in the negative control, over normal control). Reactive oxygen species (ROS) accumulation (12.8 and 9-fold increase in leaves and roots) overburdened antioxidative defense, and loss of cellular homeostasis resulted in membrane damage (82.75 % increase) and electrolyte-leakage (2.6-fold increase) in negative control. The study also reveals a significant increase in nuclear area, nuclear fragmentation, and micronuclei formation in root tip cells under As-stress, indicating severe genomic instability and increased programmed cell death (3.3-fold increase in early apoptotic cells) due to leaky plasma membrane and unrepaired DNA damage. Application of ZnONPs significantly reduced As-toxicity in peas due to its adsorption in the rhizosphere, causing diminished As-uptake and better antioxidant response. Improved phytochelatin synthesis enhanced vacuolar sequestration of arsenic, which reduced As-interference. Comparatively better flowering time (7.74-19.36 % reduction in flowering delay) with greater transcript abundance of GIGANTIA (GI), CONSTANS (CO), and FLOWERING LOCUS T (FT) genes; better photosynthetic activity (1.3-1.9-fold increased chlorophyll autofluorescence); increased pollen viability; lesser genotoxicity (decreased tail DNA in comet assay) was noticed. A maximum increase of 37.5 % in pod number and seed zinc content (1.67-fold) was observed while seed arsenic content decreased under ZnONPs treatment. However, the highest dose of ZnONPs (400 mg L) induced NP-toxicity in pea plants under our experimental conditions, while optimum stress-alleviation was observed up to 300 mg L.