Spinach (Spinacia oleracea) has epidermal bladder cells and exhibits characteristics of a facultative halophyte

While epidermal bladder cells (EBCs) have been well documented in quinoa, their presence in spinach has not been previously reported. Spinach is traditionally classified as a glycophyte but our previous and current results strongly suggest otherwise. In this study, we compared two quinoa with two spinach cultivars grown under low (2 dS m⁻¹) and high (25 dS m⁻¹) irrigation-water salinities. Using Scanning Electron Microscopy coupled with Energy-Dispersive X-ray Spectroscopy (SEM-EDS), we demonstrated that spinach has EBCs that accumulate mostly Cl, followed by K, and to a lesser extent Na, while quinoa EBCs showed no detectable Na signal. Morphologically, quinoa EBCs have single-celled stalks while spinach EBCs have multicellular stalks; both feature globular heads approximately 150 µm in diameter. Spinach displayed higher expression of Na- and Cl-transporter genes in EBCs than in EBC-free leaf tissue. Under identical salinity levels (2-24 dS m⁻¹), both spinach and quinoa exhibited comparable reductions in biomass and plant height. Despite higher Na and Cl accumulation, spinach exhibited no visible signs of salt toxicity. The presence of EBCs and apparent tissue-level salt tolerance provide new insights into spinach anatomy and ion partitioning under salinity stress, suggesting that spinach may be more accurately classified as a facultative halophyte.