Plant sensitivity to inorganic arsenic exposure: a comparison between two rice (Oryza sativa L.) genotypes, Carnaroli and Zhonghua 11

The presence of arsenic (As) in the environment is still a critical issue worldwide. The highly toxic inorganic forms, arsenite (AsIII) and arsenate (AsV), negatively affect plant development and human health (IARC 2012) (1). Arsenic has been classified as one of the major public health concerns by the World Health Organization (WHO) (2) and many others authoritative organizations have established strict guidelines to mitigate human exposure to As. Particularly, the European Commission has recently set new limits (EU 2023/465) to reduce the presence of inorganic As (iAs) in rice-based foods, as a safeguard of public health. Indeed, rice (Oryza sativa L.) is among the main exposure sources of As for humans. Flooded rice cultivation facilitates iAs entrance through the roots, wherein the largest accumulation occurs, altering their development and hormonal homeostasis (3). Italy is the leading rice producer in Europe, whose production covers more than 50% of the total amount, thanks to the regions of Piedmont and Lombardy. In particular, Vercelli is the largest producer of Carnaroli variety (O. sativa subsp. japonica), which was obtained by crossing Vialone and Lencino varieties 80 years ago in Lombardy (4). Nowadays, this variety is still the most cultivated and exported all over the world thanks to its organoleptic qualities and good yield. However, Carnaroli is still poorly studied concerning the plant sensitivity to As. To date, due to the steady presence of As in paddy fields, it is essential to manage to select As-tolerant rice varieties capable of excluding or limiting this harmful semimetal in the grains. This research aims to investigate the iAs effects on the development of Carnaroli variety. Rice seedlings were grown in vitro in presence, or not, of AsIII and AsV, added at sublethal concentrations to the culture media, and analyzed at the morphological, cytohistological, and chemical levels. The responses of this variety were compared with those of the As-sensitive variety Zhonghua 11 (O. sativa subsp. japonica) (5). The first results show a lower sensitivity to iAs of Carnaroli rice plantlets, despite a higher root uptake compared to Zhonghua 11. The lateral root (LR) production was significantly reduced only with AsIII treatment compared to the Control in Carnaroli, whereas this decrease was more pronounced with both iAs forms in Zhonghua 11. The histological analysis of adventitious roots (AR), which are the main part of the rice root system, confirmed the results of morphological analysis and revealed anomalies in the development of LRs. Our results suggest deepening the knowledge of the mechanisms that allow different rice genotypes to cope with the presence of AsIII and AsV in the substrate and evaluating the involvement of the shoot. Hence, further analyses are currently underway.