Root exudation as a strategy for plants to deal with salt stress: An updated review

The release of plant metabolites from the root plays a vital role in the way plants react to and transform their surroundings, particularly when faced with stressful conditions such as salt stress. High soil salinity poses a significant challenge to the growth and viability of plants, as it has the potential to disturb the intricate equilibrium of ions and water essential for the proper functioning of plant tissues. In response, plants develop different mechanisms to cope with this stress. There is no clear evidence to suggest that plants have a specialized root exudation process explicitly aimed at defending against salt stress. However, numerous studies have shown that when a plant encounters salt stress, it releases root exudates with distinct compositions in response to this challenge. These specialized root exudates have a beneficial role in helping plants deal with soil salinity by attracting stress-reducing rhizobacteria. In this review, we compile recent evidence supporting the notion that plants exhibit a "cry for help" response when exposed to salt stress, which leads to the recruitment of stress-relieving rhizobacteria. Furthermore, we address important methodological considerations in choosing experimental approaches, such as sampling medium (soil, agar matrix, glass beads, hydroponics), and the impact of sterility on sampling accuracy in natural terrestrial environments. Additionally, we provide a summary of the main analytical techniques used to analyze components of root exudates.