The role of strigolactones in counteracting the toxic effects of inorganic arsenic in two rice genotypes: Carnaroli and Zhonghua 11

Strigolactones (SLs), terpenoid lactones derived from carotenoids, are active biomolecules synthesized in low amounts mainly in plant root systems. These molecules affect various plant development processes (Saeed et al, 2017; Zhang et al, 2018). Moreover, SLs enhance the plant's ability to cope with abiotic stresses by interacting with other phytohormones (Kaniganti et al, 2022; Altamura et al, 2023), regulating ion balance, enhancing nutrient absorption, mitigating reactive oxygen species, and promoting nitric oxide production (Saeed et al, 2017, Tariq et al, 2023). Rice (Oryza sativa L.) has spread across the globe and forms the backbone of diets on all continents. Italy is among the main producers, cultivating approximately 1.4 billion kilograms of paddy rice per year. Nevertheless, its cultivation faces significant environmental challenges, such as the presence of arsenic (As) in rice paddies. Rice plants readily accumulate As from contaminated soil or irrigation water, posing a significant threat to food security. The most toxic As forms, arsenite and arsenate, once absorbed by the root system, induce a variety of harmful effects at morphological, physiological, and molecular levels (Piacentini et al, 2023). This research aims to deepen knowledge on the possible role of SLs in improving rice response to inorganic As (iAs) damage. Seedlings of the rice genotypes Carnaroli and Zhonghua 11 were grown in vitro from germination with or without iAs, added at toxic but sublethal concentrations to the culture media (25 μM NaAsO2 or 100 μM Na2HAsO4.7H2O), combined or not with GR24, a widely used synthetic SL, and analyzed at the morphological level. Four different GR24 concentrations (1.25, 2.5, 5, and 10 μM) were tested to determine whether, and at which concentration, SLs could alleviate iAs toxicity. Data show that Carnaroli is less sensitive to iAs than Zhonghua. When GR24 was added alone, it did not negatively affect seedling development in either genotype; instead, it showed a stimulatory effect on shoot, primary root (PR) and adventitious root (AR) elongation in Carnaroli. Moreover, the negative effects of iAs were recovered in both genotypes by GR24 when combined with the metalloid at specific concentrations, as shown by fresh weight, shoot growth, and lateral root density. Further analyses are needed to better understand the potential role of SLs in counteracting iAs effects in rice and may pave the way for the use of these molecules to sustainably reduce As contamination in edible plant organs.