Brasinosteroidy as factors modifying the molecular dynamics of model membranes and membranes isolated from barley plants.

INTRODUCTION. During their life cycle, plants are usually exposed to different environmental factors: abiotic
(extreme temperature, a lack or excess of water, too low or too intense light) and biotic (pathogens,
parasites). Plants have developed various acclimation strategies to counteract the negative effects of
abiotic stresses (including extreme temperature stress) and the cell membrane is an important
element in these strategies. During acclimation to changing temperature conditions, modifications
in the cell membrane fluidity are connected with changes in the proportion of unsaturated fatty
acids, which results in a rearrangement of the membrane structure and its properties. Membrane
properties may also be modified by incorporating various components into their structure, for
example, tocopherols or sterols. Many of the physiological phenomena that occurs in cells is
controlled by multidirectional effect of hormones on the metabolism of plants, which is also the
basis for the adaptability of organisms in order to function in changing environmental conditions.
Brassinosteroids (plant steroid hormones) belongs to the group of hormones that are involved
among others in regulating of plant growth and plant metabolism in stressful conditions. Their
function in plants is still being explained and relatively little is known about their impact on the
plant cell membrane properties. Considering the role of membranes as the first cellular line to react
to changing temperatures, the aim of the proposed project is to broaden the knowledge about
changes in physicochemical properties of cell membranes during the plant acclimation to low/high
temperature and the influence of brassinosteroids on these properties. Studies of brassinosteroid
content in cell membranes will also be performed. The object of studies will be barley – species of
economic importance. Results obtained in the project will enrich knowledge about mechanisms of
action of brassinosteroids - the hormones that have perspectives to be used in agriculture for
protection of crop plants against environmental stress.

SELECTED RESULTS 

Sadura, I.; Latowski, D.; Oklestkova, J.; Gruszka, D.; Chyc, M.; Janeczko, A. Molecular Dynamics of Chloroplast Membranes Isolated from Wild-Type Barley and a Brassinosteroid-Deficient Mutant Acclimated to Low and High Temperatures. Biomolecules 2021, 11, 27. https://doi.org/10.3390/biom11010027

(1) In the chloroplasts that were isolated from the barley wild-type Delisa and the
mutant 522DK, regardless of the plant growth temperature, eight brassinosteroids at
different concentrations were identified. Their diverse presence may indicate that they play
some role in the functioning of these organelles.

(2) Mutant 522DK is a BR-deficient mutant that has a lower accumulation of BR
compared to the wild type in its leaf tissue. However, in the case of the chloroplasts,
this regularity has not been proven in present studies. The mutant’s chloroplasts had a
higher level of three brassinosteroids: homodolicholide (regardless of the plant growth
temperature), dolicholide (plants at 5C) and homodolichosterone (plants at 20C) than
the wild-type Delisa. On the other hand, the content of homocastasterone was lower in the
mutant’s chloroplasts (plants at 20C), while castasterone was unchanged (regardless of
the plant growth temperature). It is likely that the incorporation of BR into the chloroplast
membranes is driven by accumulation mechanisms that do not have much in common
with their biosynthesis process or the final BR production/concentration in cells.

(3) Although electron paramagnetic resonance has been used to study the cell membrane
properties and the influence of different factors on those properties, knowledge
about the influence of BR on the fluidity of cell membranes is still rudimentary. In the
current work, it was shown that the main components that are important for the chloroplast
membrane’s structure/properties, such as FA, carotenoids and chlorophylls, were
comparable in the chloroplasts of the wild type and mutant 522DK, but it cannot be unambiguously
stated that the BR that were present in the chloroplasts were responsible for the
differences in the chloroplast membrane molecular dynamics between the tested genotypes.
However, in the hydrophobic (but not hydrophilic) area, the chloroplast membranes of the
mutant 522DK that had been acclimated at 5C were more ordered (more rigid) than the
membranes of the wild-type Delisa. Slight differences between the mutant and wild type
were also observed after their growth at 20C. There was practically no difference in the
membrane dynamics between the mutant and the wild type after acclimation at 27C in
either the hydrophilic or hydrophobic area.