24-Epibrassinolide Promotes Carbohydrates Accumulation in Crowns of Perennial Ryegrass during Cold Acclimation by Regulation of Gene Expression and Enzyme Activities which Results in Increased Frost Tolerance

Abstract

Due to climate changes and global warming the knowledge about the role of hormones promoting cold acclimation will become increasingly important. Brassinosteroids (BR) are plant steroid hormones which control photosynthesis, affect carbohydrate metabolism and protect against environmental factors (Janeczko et al., 2011).In order to demonstrate if BR are essential for the cold acclimation of perennial ryegrass, we studied the effect 24- epibrassinolide (EBR) and brassinazole (BZ) a specific inhibitor of BR biosynthesis, on parameters associated with cold acclimation (CA). We also analyzed the influence of the length of CA on carbohydrate quality and quantity under EBR treatment. The endogenous BR level during cold acclimation was also studied.We had demonstrated that EBR treatment improved frost tolerance of perennial ryegrass. EBR upregulated while BZ downregulated the expression of Rubisco activase (RcaA) in leaves and crowns of Lolium perenne. EBR treatment decreased contents of total soluble carbohydrates (TSC) in leaves which coincided with increased level of TSC in crowns. At the same time the expression of sucrose-1-fructosyltransferase (1-SST) and sucrose synthase (SUS) genes in leaves and crowns were reduced by BZ. Gene expression level corresponded to changes in Rubiscoand sucrose synthase activities. Endogenous level of castasterone (CS), the only detected BR in plants, increased significantly after 3 weeks of CA and decreased to the control level after next 3 weeks at 4°C. Changes of different soluble sugars concentration including fructooligosacharides was dependent on lenght of CA. Concluding, EBR enhanced frost tolerance of perennial ryegrass through changes during cold acclimation. Particulary EBR upregulated RcaA, SUS and 1-SST genes and activated of Rubisco and SPS enzymes during cold acclimation, leading to increased carbohydrate accumulation in crowns which coincided with decline of TSC level in leaves Founding: National Science Centre (Poland) DEC-2011/03/D/NZ9/05548