Dealing with extremes: insights into development and operation of salt bladders and glands

Salt bladders and salt glands of recretohalophytes are specific salt-secreting structures evolving from trichomes that allow plants to adapt to extreme environmental conditions (such as salinity or drought) by precise regulation of the salt load in metabolically active leaf tissues. The knowledge of the process by which these structures are formed and operate may provide a blueprint for introducing them into cultivated crops thus creating climate-resilient genotypes. This review summarizes the recent progress in understanding mechanisms involved in the development and operation of salt bladders and glands, at physiological, molecular, and genetic levels. We show that these processes differ depending on the anatomical structure of glands (unicellular vs bi-cellular vs multicellular), as well as between salt glands and bladders. We also show that recretohalophytes with different types of salt glands may have different trichome development. We discuss new evidence for the role of vesicular transport in salt secretion and highlight the importance of multi-omics in understanding mechanisms of salt secretion and sequestration in epidermal bladder cells, and their contribution to salinity stress tolerance in plants.