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).
Highlights
Plant Steroid Hormones—BrassinosteroidsBrassinosteroids (BR) are plant steroid hormones that are structurally similar to the steroid hormones that are found in animals and insects
This review focuses mainly on the achievements in the study of the acclimation processes to frost and high temperature in barley (Hordeum vulgare L.) and its mutants with an impaired BR biosynthesis and an impaired perception of BR [13,34–37] in recent years
To verify the results of earlier studies, which were conducted using a Langmuir bath regarding the possibility that BR have an impact on the molecular dynamics of membranes, electronic paramagnetic resonance (EPR) was used to compare the molecular dynamics of the chloroplast membranes that had been isolated from a barley mutant with a disturbed biosynthesis of BR (522DK) and one that had been isolated from its reference cultivar Delisa [37]
Summary
Brassinosteroids (BR) are plant steroid hormones that are structurally similar to the steroid hormones that are found in animals (corticosteroids, estrogens, androgens, progesterone) and insects (ecdysteroids). Many conclusions about the role of BR in the plant response to low/high-temperature stress in the case of cereals, have been made according to a research model that uses exogenous BR In some cases, this state of knowledge may require some verification and/or confirmation, for example, in research using mutants. This review focuses mainly on the achievements in the study of the acclimation processes to frost and high temperature in barley (Hordeum vulgare L.) and its mutants with an impaired BR biosynthesis (a reduced content of BR from the C28 and C29 groups) and an impaired perception of BR (a defect of the BRI1 receptor and an increased content of BR from the C28 group) [13,34–37] in recent years. That is why our review is focused on the process of photosynthesis and the physicochemical properties of membranes, which are extremely important for the acclimation of plants to temperature stress and the possible regulatory role of the plant hormones, brassinosteroids
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