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

Abstract

Brassinolide (BL) mediates various physiological processes and improves plant tolerance to abiotic stresses. However, the effects and mechanism of exogenous BL on the salt tolerance of apple seedlings remain unclear. Herein, we investigated the role of BL in the salt stress response of Malus hupehensis Rehd., a widely grown apple rootstock. Saltstressed apple seedlings showed significant decline in chlorophyll content and photosynthetic rate, and the application of 0.2 mg/L exogenous BL alleviated salt stress and maintained photosynthetic capacity. Exogenous BL application can strengthen the activities of superoxide dismutase and catalase and thereby eliminates reactive oxygen species (ROS) production induced by salt stress and promote the accumulation of proline and soluble sugar, thus maintaining osmotic balance. Furthermore, exogenous BL application decreased Na + accumulation and increased K + content in shoots and roots under salt stress by regulating the expression levels of Na + (K +)/H + antiporter genes (MhNHXs). MhBZR1 and MhBZR2, which are the key transcription factors in the BR signal transduction pathway, can directly bind to the promoter of MhSOS1 and MhNHX4-1, respectively, and inhibit their expression. Our findings would provide a theoretical basis for analyzing the mechanism of exogenous BL application on the salt tolerance of apples.

Phylogenetic Diversity and Physiological Roles of Plant Monovalent Cation/H+ Antiporters

“…The initial cloning and overexpression of AtNHX1 in Arabidopsis firmly demonstrated its important role in salinity stress tolerance ( Apse et al., 1999 ), and many additional studies subsequently confirmed that NHX overexpression lead to improved salt tolerance in diverse species ( Zhang and Blumwald, 2001 ; Ohta et al., 2002 ; Rodriguez-Rosales et al., 2008 ). NHX transcript levels are induced by salt in both leaf ( Quintero et al., 2000 ; Venema et al., 2003 ; Kagami and Suzuki, 2005 ; Li et al., 2018 ; Sun et al., 2019 ; Su et al., 2020 ) and roots ( Fukuda et al., 2004a ; Fukuda et al., 2004b ; Zörb et al., 2004 ; Ye et al., 2009 ; Zhang et al., 2018 ). A similar increase was reported upon plant exposure to dehydration ( Li et al., 2006 ), hyperosmotic stress ( Fukuda et al., 2004a ; Fukuda et al., 2004b Yokoi et al., 2002 ), or ABA treatment ( Yokoi et al., 2002 ; Venema et al., 2003 ).…”

Genome-Wide Association Study (GWAS) Analysis of Camelina Seedling Germination under Salt Stress Condition

“…Four PPKLs were characterized in A. thaliana: BSU1, BSL1, BSL2, and BSL3 [55][56][57], which showed a functional relevance in interactively affecting brassinosteroid signaling [54]. Brassinosteroid signaling was found to mediate plant development and adaptation under salt stress [56,58]. An SNP located on chromosome 3 (S3_3511428) annotated as BSL2 was significantly associated germination rate at the 9-day seedling stage (Table 4, Figure 3), although no direct evidence showed that the increased activity of BSL2 was triggered by salt stress.…”

Resveratrol Improves the Iron Deficiency Adaptation of Malus Baccata Seedlings by Regulating Iron Absorption, Phytohormone Content, and ROS Migration

“…Plant growth regulators usually affect plant growth and development in a dose-dependent manner. Su et al (Su et al 2020). reported that the effect of applying 0.2 mg/L of BL on improving the salt tolerance of apple seedlings is much better than the effect of applying BL concentrations of 0.05 and 1.0 mg/L.…”

“…Then, the kilndried samples were digested with 12 mL of HNO 3 and HClO 4 and diluted with deionized H 2 O to 25 mL. Elemental analysis of Fe was performed via inductively coupled plasma-optical emission spectrometry (PerkinElmer, Waltham Massachusetts, USA) as described by Su et al (Su et al 2020). Each experiment was independently repeated three times.…”