Abstract
Brassinosteroids (BRs) are involved in the regulation of many plant developmental processes and stress responses. In the presented study, we found a link between plant growth under salinity stress and sensitivity to 24-epibrassinolide (24-EBL, the most active phytohormone belonging to BRs), brassinazole (Brz) and bikinin (inhibitors of BR biosynthesis and signaling pathways, respectively). Plant sensitivity to treatment with active substances and salinity stress was genotype-dependent. Cv. Haruna Nijo was more responsive during the lamina joint inclination test, and improved shoot and root growth at lower concentrations of 24-EBL and bikinin under salinity stress, while cv. Golden Promise responded only to treatments of higher concentration. The use of Brz resulted in significant dose-dependent growth inhibition, greater for cv. Haruna Nijo. The results indicated that BR biosynthesis and/or signaling pathways take part in acclimation mechanisms, however, the regulation is complex and depends on internal (genotypic and tissue/organ sensitivity) and external factors (stress). Our results also confirmed that the lamina joint inclination test is a useful tool to define plant sensitivity to BRs, and to BR-dependent salinity stress. The test can be applied to manipulate the growth and stress responses of crops in agricultural practice or to select plants that are sensitive/tolerant to salinity stress in the plant breeding projects.
Highlights
Brassinosteroids (BRs) are a class of plant polyhydroxylated steroid hormones that control plant growth, architecture, leaf size and angle, and seed yield, adjust the processes from seed development through flowering to senescence, or regulate the physiology of stress signaling [1,2,3]
We report on the links between developmental changes, stress responses and sensitivity to 24-EBL, bikinin, and Brz in two barley cultivars grown under salinity stress
Golden Promise improved the angle of lamina inclination only at higher concentrations (Figure 1a, 0.5 μM–5 μM 24-EBL and Figure 1b, 50 μM–150 μM bikinin)
Summary
Brassinosteroids (BRs) are a class of plant polyhydroxylated steroid hormones that control plant growth, architecture, leaf size and angle, and seed yield, adjust the processes from seed development through flowering to senescence, or regulate the physiology of stress signaling [1,2,3]. The molecular processes of the BRs biosynthesis and signaling pathways were described for arabidopsis (Arabidopsis thaliana L.) and other plant species, including barley (Hordeum vulgare L.) [3]. The first step of biosynthesis, regulated by DWARF4 (DWF4, known as CYP90B1), initiates a cascade of reactions that allow for the transformation of episterol into the final product brassinolide (BL) [7]. The BL molecules are captured by a transmembrane receptor Brassinosteroid Insensitive 1—BRI1 Associated Receptor Kinase 1 (BRI1-BAK1) [11]. The active BRI1-BAK1 heterodimer initiates a cascade of phosphorylation and dephosphorylation of cytoplasmic relay proteins. BRI1-EMS-Suppressor 1 (BES1) and Brassinazole-Resistant 1 (BZR1) transcription factors (TFs) are activated and relocated from the cytoplasm to the nucleus. Dephosphorylation by Protein Phosphatase 2A (PP2A) allows BES1 and BZR1 to function with other TFs and cofactors to promote BR-induced gene expression and inhibit BR-repressed gene expression [14]
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