Salt glands in exo‐recretohalophytes: Development, physiological functions, and prospects for improving crop salt tolerance

In exo-recretohalophytes, specialized structures known as salt glands secrete excess salt ions from plant tissues, thereby maintaining intracellular ion homeostasis and sustaining normal metabolism under salt stress. Based on their cellular composition, salt glands can be unicellular, bicellular, or multicellular, and they originate from undifferentiated precursor cells known as multipotent epidermal stem cells. A complex regulatory network drives the division and differentiation of these cells into functional salt-secreting structures. Three hypotheses have been proposed to explain the physiological mechanisms underlying salt secretion by salt glands, each supported by experimental evidence: The osmotic mechanism, the reverse pinocytosis mechanism, and the animal-like fluid transport mechanism. This review summarizes the structural characteristics, developmental processes, salt secretion mechanisms, and potential applications of salt glands in exo-recretohalophytes, providing a foundation for future studies on salt gland biology and their utilization in developing salt-tolerant crops.