Abscisic acid (ABA) priming is known to enhance plant growth and survival under salinity. However, the mechanisms mediating this long-term acclimatization to salt stress are still obscure. Specifically, the long-term transcriptional changes and their effects on ion relations were never investigated. This motivated us to study the longterm (8 days) effect of one-time 24 h root priming treatment with 10 μM ABA on transcription levels of relevant regulated key genes, osmotically relevant metabolites, and ionic concentrations in Vicia faba grown under 50 mM NaCl salinity. The novelty of this study is that we could demonstrate long-term effects of a one-time ABA application. ABA-priming was found to prevent the salt-induced decline in root and shoot dry matter, improved photosynthesis, and inhibited terminal wilting of plants. It substantially increased the mRNA level of AAPK and 14-3-3 ABA inducible kinases and ion transporters (PM H + -ATPase, VFK1, KUP7, SOS1, and CLC1). These ABA-induced transcriptional changes went along with altered tissue ion patterns. Primed plants accumulated less Na + and Cl − but more K + , Ca 2+ , Zn 2+ , Fe 2+ , Mn 2+ , NO 3 − , and SO 4 2− .Priming changed the composition pattern of organic osmolytes under salinity, with glucose and fructose being dominant in unprimed, whereas sucrose was dominant in the primed plants. We conclude that one-time ABA priming mitigates salt stress in Vicia faba by persistently changing transcription patterns of key genes, stabilizing the ionic and osmotic balance, and improving photosynthesis and growth.
| INTRODUCTIONSalinity is characterized by excessive soluble salts in the growth medium, which impose osmotic and ionic stress in plants (Munns & Tester, 2008).Key processes of photosynthesis, respiration, and transpiration are affected, thus limiting shoot and root growth (Munns & Tester, 2008).Field bean (Vicia faba) grown with an excess of sodium chloride (NaCl) has been reported to show severe growth retardation due to a high accumulation of Na + that interferes with K + uptake (Slabu et al., 2009). It possibly disrupts the regulation of cytoplasmic enzymes and stomatal conductance (Isayenkov & Maathuis, 2019). Moreover, in Vicia faba grown under NaCl stress, higher accumulation of chloride (Cl − ) in the chloroplast is thought to impair the photosynthetic machinery and thus to induce chloroplast degeneration leading to chlorosis or necrosis of the leaf tissue (Geilfus, 2018). To resist salt stress, plants have evolved mitigating mechanisms at different organizational levels. Many of these
