Deciphering growth inhibition mechanisms in Vicia faba L. under saline-alkaline salt stress in relation to apoplastic pH, nutrients, metabolites, and gene transcription

Soil salinization and alkalization co-occur in nature, causing severe problems in crop production. The plant responses to alkali stress are not fully understood because the effects of individual components of alkali salt stress (i.e. high pH, sodium and bicarbonate) on plant growth were never dissected. Hence, for the first time, we experimentally separated the individual components of alkali salt stress and investigated their effect on the growth and various physiological, metabolic, and transcriptional responses of Vicia faba. Moreover, the mechanisms underlying survival and long-term growth improvement in short-term ABA-primed plants under saline conditions were identified. In our first short term study, we found that plants exposed to alkali salt for 150 minutes induced various changes at the physiological and transcriptional levels, while alone alkaline pH did not show any of these changes. Accumulation of metabolites and fast upregulation of stress-responsive genes suggested the mechanism for early adaptation to alkali salt stress. In the second experiment, we hypothesized that the main growth-limiting factor is not the high pH or Na+, but rather excess bicarbonate, by inducing over-accumulation of organic acids (through dark fixation) in plant roots under mid-term alkali salt stress, was investigated. High bicarbonate induced over-accumulation of organic acid, causing growth inhibition via key nutrient imbalance and ROS accumulation. In the third experiment, the long-term (8d) effect of one-time 24h root priming treatment with  abscisic acid on growth response and survival, the transcriptional changes, and their effects on ion relations in Vicia faba grown under 50 mM NaCl salinity were investigated. One-time ABA priming mitigates salt stress in Vicia faba by persistently changing transcription patterns of ion transporters, stabilizing the ionic and osmotic balance, and improving photosynthesis and growth.



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