**1. Introduction**

Melon (*Cucumis melo* L.) is one of the major Cucurbit species, playing an important role in irrigated farmlands of the Mediterranean area [1]. In these regions, the water intended for irrigation could be contaminated with heavy metals as result of weathering of soil minerals and human activities [2]. Irrigation with contaminated water can affect food quality and safety for the presence of metalloids and/or heavy metals harmful for human health [3,4]. Among these, arsenic (As) is a persistent, non-degradable metalloid widely present in the environment both for geogenic or anthropogenic reasons [5]. Most As compounds are odorless, tasteless, and water-soluble, creating a serious health risk because of their carcinogenic potential [6]. This metalloid exists in plant organs both as inorganic and organometallic species, whose concentration and oxidation states are dependent on the type and amounts of sorbents in the substrate, pH, redox potential (Eh), and soil microbial activity [7,8].

Arsenic is non-essential and generally toxic to plants. At high concentrations (depending on the species) it interferes with multiple metabolic processes, leading to growth and yield disturbance,

and even plant death [9,10]. The As(III) root uptake (i.e., the dominating form in anaerobic root environments) occurs by passive transmembrane transport involving members of the nodulin 26-like intrinsic protein family of plant aquaporins [11]. As(V), which dominates in aerobic root environments, enters plant roots via phosphate (Pi) transporters, as the oxyanion chemical structure of As(V) is analogous to Pi [12]. As a consequence, As(V) compete with Pi absorption and P-dependent metabolic processes during ATP synthesis, with subsequent disturbance of major biological functions [13,14].

The efficiency of As translocation from roots to shoots via xylem loading affects the plants' As tolerance and their proneness to accumulate this metalloid into the edible fraction, so posing potential risks to human health [14].

In horticultural systems, vegetable grafting is a multipurpose technique improving crops performances and product quality under both optimal and suboptimal growth conditions [15–17]. It has been proposed as a means to reduce the heavy metals uptake and translocation to the shoots and the edible parts [18,19], although the mechanisms underlying such impediment are still unclear [20]. Thus, investigating the use of melon rootstocks could be useful for understanding the behavior of different grafting combinations, with the view to improve crop performances and product safety in As-polluted areas.

Considering the above, the objective of this research was to study the effects of different rootstock genotypes on As uptake, accumulation, and partitioning, as well as on agronomical and physiological response of melon plants subjected to a high concentration of the metalloid in the root environment. To this end, the present experiment was performed to investigate: (i) If As concentration in the nutrient solution influences its uptake and translocation in melon plants; (ii) if and how the different rootstocks can mitigate the As accumulation within plant organs; (iii) the possible role of different rootstock genotypes in modulating the bio-agronomical response of melon plants to the elevated As concentration in the root zone.
