Brassinosteroids and the Tolerance of Cereals to Low and High Temperature Stress: Photosynthesis and the Physicochemical Properties of Cell Membranes

Abstract

Cereals, which belong to the Poaceae family, are the most economically important group of plants. Among abiotic stresses, temperature stresses are a serious and at the same time unpredictable problem for plant production. Both frost (in the case of winter cereals) and high temperatures in summer (especially combined with a water deficit in the soil) can result in significant yield losses. Plants have developed various adaptive mechanisms that have enabled them to survive periods of extreme temperatures. The processes of acclimation to low and high temperatures are controlled, among others, by phytohormones. The current review is devoted to the role of brassinosteroids (BR) in cereal acclimation to temperature stress with special attention being paid to the impact of BR on photosynthesis and the membrane properties. In cereals, the exogenous application of BR increases frost tolerance (winter rye, winter wheat), tolerance to cold (maize) and tolerance to a high temperature (rice). Disturbances in BR biosynthesis and signaling are accompanied by a decrease in frost tolerance but unexpectedly an improvement of tolerance to high temperature (barley). BR exogenous treatment increases the efficiency of the photosynthetic light reactions under various temperature conditions (winter rye, barley, rice), but interestingly, BR mutants with disturbances in BR biosynthesis are also characterized by an increased efficiency of PSII (barley). BR regulate the sugar metabolism including an increase in the sugar content, which is of key importance for acclimation, especially to low temperatures (winter rye, barley, maize). BR either participate in the temperature-dependent regulation of fatty acid biosynthesis or control the processes that are responsible for the transport or incorporation of the fatty acids into the membranes, which influences membrane fluidity (and subsequently the tolerance to high/low temperatures) (barley). BR may be one of the players, along with gibberellins or ABA, in acquiring tolerance to temperature stress in cereals (particularly important for the acclimation of cereals to low temperature).

ICE-CBF-COR Signaling Cascade and Its Regulation in Plants Responding to Cold Stress

“…ERFs are known to bind COR genes (CORLTRECOREATCOR15 and MYBCORE) cis-elements, enhancing freezing tolerance by reducing ROS species, and increasing SOD and POD levels [136] As steroid hormones, brassinosteroids (BR) are synthesized from mass sterol campesterol through multiple hydroxylations and oxidations, further catalyzed with various cytochrome P450 enzymes, including DWARF4, CPD, ROT3, and the CYP85A2 BR6ox2 steroid, cumulatively known as BR-biosynthetic genes. BRs induce a multidirectional response in plants that include the regulation of cold-responsive genes (ICEs, CBFs, and CORs) and other hormonal cross-talks (ABA and JA) [137]. Nevertheless, cold treatment downregulates these BR-biosynthetic genes [32].…”

Genetic Mechanisms of Cold Signaling in Wheat (Triticum aestivum L.)

“…COR gene expression and cold tolerance in Arabidopsis are increased by exogenous BR treatment [ 94 ]. Exogenous BR treatment promotes growth recovery of maize seedlings following chilling treatment [ 95 ] and increases cold tolerance in winter rye and winter wheat [ 96 , 97 ]. BRASSINOSTEROID INSENSITIVE 2 (BIN2) negatively regulates the freezing tolerance in Arabidopsis [ 98 ].…”

Mechanisms of Cold Signaling in Wheat (<em>Triticum aestivum</em> L.)

“…COR gene expression and cold tolerance in Arabidopsis are increased by exogenous BR treatment [83]. Exogenous BR treatment promotes growth recovery of maize seedlings following chilling treatment [84] and increases cold tolerance in winter rye and winter wheat [85][86]. BRASSINOSTEROID INSENSITIVE 2 (BIN2) negatively regulates the freezing tolerance in Arabidopsis [87].…”