Mutations in the HvDWARF, HvCPD and HvBRI1 Genes-Involved in Brassinosteroid Biosynthesis/Signalling: Altered Photosynthetic Efficiency, Hormonal Homeostasis and Tolerance to High/Low Temperatures in Barley

Abstract

Brassinosteroids (BR) are steroid phytohormones that are involved in the growth and stress response in plants, but the precise mechanisms of their action are still being discovered. In our study we have used BR-deficient barley mutants 522DK and BW084 (which carry missense mutations in the HvDWARF and HvCPD genes, respectively). We have also used a BR-signalling mutant that harbors missense substitutions in the HvBRI1 gene. Our aim was (1) to find out if the content of phytohormones in the mutants grown at 20 °C is different than in the wild types and whether/how the content of phytohormones changes after plant acclimation at temperatures of 5 °C and 27 °C?, (2) to characterise the effectiveness of the light reactions of photosynthesis of the barley mutants in comparison to wild types at various temperatures, and (3) to verify the impact of mutations on the tolerance of barley to high and low temperatures. Hormonal characteristics of the BR mutants of barley show the complexity of the interactions between BR and other plant hormones that are additionally modified by temperature and possibly by other factors. The results suggest the participation of BR in auxin catabolism. Further, BR appears to play a role in maintaining the ABA-ABAGlc balance. As for the gibberellin content in plants at a temperature of 20 °C, more in-depth studies will be required to explain the contradictory effects regarding the accumulation of GA3, GA4 and GA5, which appears to be dependent on the type of mutation and connected to the BR level. A fast-kinetic chlorophyll a fluorescence analysis has revealed that the mutants had lower values of energy absorption than the wild types, but the values of the energy transferred via the electron-transport chain was maintained at the wild-type level. We presumed that BR are involved in regulating plant acclimation to extreme (low/high) temperatures, thus the BR-deficient and BR-signalling mutants should be less tolerant to low/high temperatures when compared to the wild types. Unexpectedly, all of the mutants showed a higher tolerance to high temperatures than the wild types. The BW084 and BW312 mutants were less tolerant to frost than the wild type, but 522DK had a similar frost tolerance as the reference wild-type cultivar.

Involvement of homocastasterone, salicylic and abscisic acids in the regulation of drought and freezing tolerance in doubled haploid lines of winter barley

“…5a) but, in contrast to the majority of published data (e.g. Sadura et al 2019), ABA level in almost all studied DH lines of barley was not influenced significantly by cold hardening treatment. Only one of two studied DH lines with the highest freezing tolerance level (DH534) responded in accordance with the expected pattern, increasing ABA accumulation more than 1.5 times.…”

“…Values marked with the same letter do not differ significantly according to the Duncan test (p ≤ 0.05). which is in agreement with earlier studies on barley cultivars and their mutants (Sadura et al 2019;Gruszka et al 2016a).…”

“…ABA abscisic acid, SA salicylic acid, HCS homocastasterone, CS castasterone, TE teasterone, DL dolicholide, Sc control seedlings/heading plants sensitive to freezing/drought treatment, Tc control seedlings/heading plants tolerant to freezing/drought treatment, S H cold hardened seedlings sensitive to freezing stress, T H cold hardened seedlings tolerant to freezing stress, S D drought treated plants sensitive to drought stress, T D drought treated plants tolerant to drought stress 1 3 freezing tolerance, whereas disturbances in later stages of BR biosynthesis had no effect. According to literature, the content of BRs increased in cold hardened winter rye (Pociecha et al 2016) and spring barley (Sadura et al 2019), which is to some extent in accordance with data obtained in this study as significant increase in HCS content was noted for more freezing tolerant DH lines of barley. Previous studies with spring barley (Sadura et al 2019) and winter wheat (Janeczko et al 2019) also showed that cultivars less tolerant to freezing accumulated lower amounts of BRs (especially HCS) in response to cold hardening in comparison with more tolerant cultivars.…”

“…The content of HCS detected as the only BR in winter barley seedlings was comparable to that received by Sadura et al (2019) and Gruszka et al (2016a) with the use of spring barley varieties. These authors also reported a very low level of two other BRs (brassinolide and CS) detected in three to four leaf seedlings whereas in our study, the spectrum of identified BRs increased in plants entering the generative phase of development.…”

“…The role of BRs in the process of plant hardening to frost was investigated earlier by Eremina et al (2016), who revealed that BRs improved freezing tolerance of plants on the basis of a study on Arabidopsis thaliana mutants with impaired BR signalling. The importance of BR signalling for freezing tolerance was also confirmed for barley (Sadura et al 2019) as barley BR signalling mutants had lower freezing tolerance than the wild type. The results for BR biosynthesis mutants confirmed it partially, while a disturbance of early stages of biosynthesis resulted in lowered Fig.…”