Exogenously Applied 24-Epibrassinolide (EBL) Ameliorates Detrimental Effects of Salinity by Reducing K+ Efflux via Depolarization-Activated K+ Channels

Abstract

This study has investigated mechanisms conferring beneficial effects of exogenous application of 24-epibrassinolides (EBL) on plant growth and performance under saline conditions. Barley seedlings treated with 0.25 mg l-1 EBL showed significant improvements in root hair length, shoot length, shoot fresh weight and relative water content when grown in the presence of 150 mM NaCl in the growth medium. In addition, EBL treatment significantly decreased the Na+ content in both shoots (by approximately 50%) and roots. Electrophysiological experiments revealed that pre-treatment with EBL for 1 and 24 h suppressed or completely prevented the NaCl-induced K+ leak in the elongation zone of barley roots, but did not affect root sensitivity to oxidative stress. Further experiments using Arabidopsis loss-of-function gork1-1 (lacking functional depolarization-activated outward-rectifying K+ channels in the root epidermal cells) and akt1 (lacking inward-rectifying K+ uptake channel) mutants showed that NaCl-induced K+ loss in the elongation zone of roots was reduced by EBL pre-treatment 50- to 100-fold in wild-type Col-0 and akt1, but only 10-fold in the gork1-1 mutant. At the same time, EBL treatment shifted vanadate-sensitive H+ flux towards net efflux. Taken together, these data indicate that exogenous application of EBL effectively improves plant salinity tolerance by prevention of K+ loss via regulating depolarization-activated K+ channels.

Melatonin-Stimulated Triacylglycerol Breakdown and Energy Turnover under Salinity Stress Contributes to the Maintenance of Plasma Membrane H+–ATPase Activity and K+/Na+ Homeostasis in Sweet Potato

“…First, compared with non-MT-treated Xu 32, MT pretreatment resulted in an evidently enhanced H + efflux that coincided with a decreased K + efflux upon NaCl shock ( Figure 2 ). This pattern of K + /H + flux under NaCl shock has been ascribed to enhanced PM H + –ATPase activity ( Sun et al, 2009b ; Yu et al, 2016 ; Azhar et al, 2017 ). Second, the PM H + –ATPase inhibitor enlarged the salt shock-induced K + efflux in MT-treated Xu 32 root and MCs (Supplementary Figure S2 ).…”

Exogenous Brassinolide Alleviates Salt Stress in Malus hupehensis Rehd. by Regulating the Transcription of NHX-Type Na+(K+)/H+ Antiporters

“…Given that exogenous BL was applied to the leaves, we inferred that the increased K + content in roots was caused by the transportation and distribution of K + between shoots and roots, which was affected by exogenous BL to the leaves. Recently, Azhar et al (2017) showed that BL in the growth medium prevented salt-induced K + leak from shoots and roots. They also noted that BL decreased K + efflux under salt stress by controlling depolarization-activated GORK channels.…”

“…The accumulation of osmolytes, such as sorbitol, proline, and lycine, is critical to osmotic balance (Shahid et al, 2014;Yusuf et al, 2017). Maintaining homeostasis of Na + and K + in cells by activating Na + and K + transporters is vital for plant salt stress tolerance (Azhar et al, 2017).…”

24-Epibrassinolide Improves Root Anatomy and Antioxidant Enzymes in Soybean Plants Subjected to Zinc Stress

“…The exogenous application of 24-epibrassinolide (EBR) can be a possible solution to mitigate the damage caused by deficiencies and excess Zn in plants because EBR is one of the most bioactive forms of brassinosteroids (BRs); it is extracted from plants and is biodegradable (Azhar et al 2017). This steroid presents a broad spectrum of systemic action on plant metabolism (Oh et al 2012), including CO 2 (Li et al 2016b), gas exchange (Swamy and Rao 2009), photochemical efficiency (Thussagunpanit et al 2015), antioxidant metabolism (Xia et al 2009) and growth rate (Abdullahi et al 2003).…”