Physiological Responses of Alfalfa to High-level Salt Stress: Root Ion Flux and Stomatal Characteristics

Abstract

Alfalfa is an important salt-tolerant leguminous forage-plant in salinity areas worldwide, but its performance in high level of salt stress cannot meet the satisfactory requirement. Especially, the short-term response of alfalfa to high-level salt stress is still not clear. In the present study, thirty-day-old alfalfa Gongnong No. 1 (Medicago sativa L. cv. Gongnong No.1) seedlings were exposed to NaCl treatments at concentrations of 0 (control), 50 (moderate level), 150 (high level), and 250 mM (extremely high level). Twenty-four hours after salt stress treatment, with the increase of NaCl level plant height was slightly decreased but both shoot biomass and root length were substantially declined to a dramatic extent. Also decreased was root K + concentration. In contrast, both Na + concentration and ratio of K + /Na + showed increased trends. Root K + flux was determined using non-invasive micro-test technique (NMT) around apical root tips, wherein a clear K + influx was observed at the rate of about 0.5 nmol cm -2 s -1 under the condition without salt stress, while under salt stress at the rate of 2-3 nmol cm -2 s -1 did occur K + efflux. Accordingly, stomatal length and breadth and stomatal aperture breadth decreased with the increase of NaCl concentration, while stomatal aperture density increased with time in the first 24 h after NaCl treatment. In conclusion, as a species-specific test, alfalfa is sensitive to high-level salinity with NaCl concentrations above 150 mM in the first 24 h post salt-exposure. The key mechanism was found to be presented as the pressed stamatal conductance induced by K + -Na + unbalance which was caused by root K + efflux.

Physiological, biochemical, and antioxidant properties of two genotypes of Vicia faba grown under salinity stress

“…Salinity stress tolerance in plants is reportedly conferred by K + retention and Na + exclusion from the shoots (Shabala, 2017). Positive correlations between K + retention in plant tissues and salinity tolerance have been reported in wheat (Wu et al, 2015), alfalfa (Guo et al, 2016), cotton (Wang et al, 2016), mustard (Chakraborty et al, 2016), and cucumber (Redwan et al, 2016). Salt tolerant genotypes maintain high K + /Na + ratios under salinity stress; this has been reported by Wu et al, (2015) in barley and by Xiong et al, (2018) in melon.…”

Research advances of MYB transcription factors in plant stress resistance and breeding

“…Under salt stress, the roots of the plant absorb water difficulty, and the water infiltration in the body reduces the supply of water in the plant, causing cell dehydration and threatening the survival of the plant, 48,49 which seriously affects normal growth. 50 When plants are subjected to salt stress, the ion dynamic balance of the plants is disturbed, [51][52][53][54][55][56][57] and high salt seriously affects the membrane permeability, [58][59][60][61] and the absorbed salt ions are toxic to plants 62 . Excessive salinity leads to osmotic stress in cells, destroying normal metabolism and seed germination.…”

Characterization of Salt Tolerant Wheat (Triticum aestivum) Genotypes on the Basis of Physiological Attributes

“…Salt stress caused a significant reduction in leaf photosynthetic pigments as well as alterations in ionic balance which limits vegetative growth and economic productivity in wheat (Mahboob et al, 2016). However, several plant growth and development processes influenced by salinity results in low grain yield and poor quality of crops (Turki et al, 2012;Desoky and Merwad, 2015;Guo et al, 2016).…”