The Positive Effect of Different 24-epiBL Pretreatments on Salinity Tolerance in Robinia pseudoacacia L. Seedlings

Abstract

As a brassinosteroid (BR), 24-epibrassinolide (24-epiBL) has been widely used to enhance the resistance of plants to multiple stresses, including salinity. Black locust (Robinia pseudoacacia L.) is a common species in degraded soils. In the current study, plants were pretreated with three levels of 24-epiBL (0.21, 0.62, or 1.04 µM) by either soaking seeds during the germination phase (Sew), foliar spraying (Spw), or root dipping (Diw) at the age of 6 months. The plants were exposed to salt stress (100 and 200 mM NaCl) via automatic drip-feeding (water content~40%) for 45 days after each treatment. Increased salinity resulted in a decrease in net photosynthesis rate (P n ), stomatal conductance (G s ), intercellular:ambient CO 2 concentration ratio (C i /C a ), water-use efficiency (WUE i ), and maximum quantum yield of photosystem II (PSII) (F v /F m ). Non-photochemical quenching (NPQ) and thermal dissipation (H d ) were elevated under stress, which accompanied the reduction in the membrane steady index (MSI), water content (RWC), and pigment concentration (Chl a, Chl b, and Chl). Indicators of oxidative stress (i.e., malondialdehyde (MDA) and antioxidant enzymes (peroxidase (POD) and superoxide dismutase (SOD)) in leaves and Na + content in chloroplasts increased accompanied by a reduction in chloroplastid K + and Ca 2+ . At 200 mM NaCl, the chloroplast and thylakoid ultrastructures were severely disrupted. Exogenous 24-epiBL improved MSI, RWC, K + , and Ca 2+ content, reduced Na + levels, maintained chloroplast and thylakoid membrane structures, and enhanced the antioxidant ability in leaves. 24-epiBL also substantially alleviated stress-induced limitations of photosynthetic ability, reflected by elevated chlorophyll fluorescence, pigment levels, and P n . The positive effects of alleviating salt stress in R. pseudoacacia seedlings in terms of treatment application was Diw > Sew > Spw, and the most positive impacts were seen with 1.04 µM 24-epiBL. These results provide diverse choice for 24-epiBL usage to defend against NaCl stress of a plant.

Role of Brassinosteroids in plants responses to salinity stress: A review

“…Similar results were also recorded in potatoes through BRS priming subjected to salinity stress which indicates the positive role of BRS in metigating the negative impact of salt stress on lipid peroxidation level (Efimova et al, 2018). Yue et al (2018) also reported that pretreatment of BRS declines the MDA content in Robinia pseudoacacia L. under salinity stress.…”

Effects of Arbuscular Mycorrhizal Fungi on Growth, Photosynthesis, and Nutrient Uptake of Zelkova serrata (Thunb.) Makino Seedlings under Salt Stress

“…The relative water content in the leaves was measured according to the previously method [19] using the following formula: RWC = (fresh weight − dry weight)/(turgor weight − dry weight. The membrane stability index was estimated using the formula [20], MSI = 1 − C1/C2, where C1 is the electrical conductivity bridge after the leaves were heated at 40 • C for 30 min in a water bath, and C2 is the electrical conductivity bridge after the leaves were boiled at 100 • C for 10 min in a water bath.…”

Physiological Responses to Abiotic and Biotic Stress in Forest Trees

“…An overabundance of ROS, which cannot be compensated by antioxidative systems, leads to damage symptoms such as chlorophyll degradation, membrane leakage, and eventually necrosis [13]. Some examples for salt damage symptoms at the tissue and organelle levels are also demonstrated in this Special Issue [14,15]. Since soil degradation with enhanced salinization is an increasing problem, identification of salt-tolerant plant species and measures to enhance the resistance of crops and horticultural plants are urgently needed.…”

“…The beneficial effect was concentration dependent and disappeared in plants exposed to 1 mM salicylic acid. In another study, Robinia pseudoacacia seeds or seedlings were treated with 24-epibrassinolide (a brassinosteroid) and subsequently exhibited enhanced antioxidative protection and enhanced salt tolerance [14]. To obtain deeper insights into the signal transduction pathway activated by stress, the TCP15 transcription factor (TEOSINTE BRANCHED1, CYCLOIDEA, and PROLIFERATION CELL FACTOR) was isolated from Fraxinus mandshurica (Mandchurian ash) [21].…”