In the present study, the influence of 50 and 100 µM CuSO₄ was investigated starting from 3 h till 72 h treatment of 4-weeks Brassica napus plants. High CuSO₄ concentrations in nutrient medium ...resulted in the rapid copper accumulation in plants, especially in roots, much slower and to lower degree in leaves. Copper excess induced early decrease in the leaf water content and temporary leaf wilting. The decrease in content of photosynthetic pigments became significant to 24 h of excessive copper treatments and reached 35 % decrease to 72 h, but there were no significant changes in maximum quantum efficiency of photosystem II photochemistry. The copper excess affected the expression of ten genes involved in heavy metal homeostasis and copper detoxification. The results showed the differential and organ-specific expression of most genes. The potential roles of copper-activated genes encoding heavy metal transporters (ZIP5, NRAMP4, YSL2, and MRP1), metallothioneins (MT1a and MT2b), low-molecular chelator synthesis enzymes (PCS1 and NAS2), and metallochaperones (CCS and HIPP06) in heavy metal homeostasis and copper ion detoxification were discussed. The highest increase in gene expression was shown for NRAMP4 in leaves in spite of relatively moderate Cu accumulation there. The opinion was advanced that the NRAMP4 activation can be considered among the early reactions in the defense of the photosystem II against copper excess.
A spectral quasilinear approach to the problem of TEM-Weibel instability in an anisotropic collisionless plasma is developed, which takes into account only the integral nonlinear interaction of modes ...through the joint variation of the spatially averaged particle velocity distribution induced by these modes. Within this approximation, a closed system of equations is obtained for the one- and two-dimensional evolution of spatial modes (harmonics) of the distribution function of particles and the electromagnetic field under conditions when the plasma anisotropy axis, the wave vector, and the magnetic field of the modes are orthogonal to each other. The numerical solution of this system of equations is compared with the available results of one-dimensional analytical quasilinear theory in the region of its applicability, as well as with the results of two-dimensional simulation by the particle-in-cell method, which also takes into account the direct four-wave interaction of modes. It is established that in the simplest cases of one-dimensional and axially symmetric two-dimensional problems for a bi-Maxwellian plasma, quasilinear phenomena play the leading role at a quite long stage of nonlinear development of turbulence. It is noted that at a later stage of decay of turbulence and in a more general formulation of the problem, in particular, in the presence of an external magnetic field, the direct nonlinear interaction of modes can manifest itself along with quasilinear phenomena. Based on the analysis carried out, the contribution of certain nonlinear effects to the evolution of the spatial spectrum of Weibel turbulence is revealed, and the properties of this turbulence are studied, including the self-similar character and qualitatively different stages of the dynamics of unstable modes.
Light-dependent transcription factors GLKs of
Arabidopsis thaliana
are involved in the anterograde regulation of chloroplast biogenesis during deetiolation: they regulate the expression of ...photosynthetic nuclear-encoded genes and also mediate the transcription of plastid genes. Chloroplast biogenesis is determined at the same time by light and by endogenous factors (phytohormones), among which cytokinins significantly accelerate the formation of photosynthetically active chloroplasts. In this work, it was shown that
trans
-factors GLKs function as cytokinin-dependent regulators, mediating the positive cytokinin effect on the plastome expression through the activation of transcription of the
SCA3
nuclear gene encoding the plastid RNA polymerase RPOTp.
The review considers the role of H2O2, 1O2, O 2 ·− , and the products of lipid peroxidation as signaling molecules in the processes of stress signal transduction in plants. The data concerning ...possible ROS participation in transduction of stress signals from chloroplasts to the nuclear genome, H2O2 involvement in transduction stress signals in cyanobacteria, and also the interactions between ROS and other signaling systems within the cell are presented. It is suggested that redox regulators, protein kinases/protein phosphatases, and transcription factors play a crucial role in the functioning of ROS-dependent signaling systems in the plant cell.
Melatonin is a signaling molecule that mediates multiple stress-dependent reactions. Under photooxidative stress conditions generating intensive ROS production, exogenous melatonin (50 µM) ...contributed to maintaining the expression of mitochondrial encoded genes and up-regulation of RNA-polymerase genes
RPOTm
and
RPOTmp
, operating through the CAND2 receptor and α-subunit of the heterotrimeric G protein GPA1 coupled with CAND2. Unlike wild-type plants, mutants with defective
CAND2
and
GPA1
genes exhibited no decrease in the alternative pathway of leaf respiration, as well as the activity of an alternative oxidase, and the expression of the
AOX1a
gene. At the same time, the protective effect of exogenous melatonin on some physiological indicators did not depend on the receptor and was associated with the direct antioxidant function of the regulator. Thus, melatonin under photooxidative stress conditions can act as an antioxidant and as a hormone capable of regulating the expression of nuclear and organelle genes through the components of melatonin signal perception.
The expression profiles of the
PAP
genes, encoding proteins associated with plastid multisubunit RNA polymerase, were studied in dry seeds, during germination, and at the early stages of
Arabidopsis ...thaliana
seedling formation. A detailed analysis of the
PAP
transcript levels by RT-PCR showed that the transition of seeds from dormancy to active growth is accompanied by a drastic increase in the transcript accumulation of all studied genes on the first day of germination, both in the light and in the dark. Further changes in transcript levels differed among
PAP
genes and were apparently determined by their functional specificity. It was established for the first time that the expression of individual
PAP
genes is regulated by circadian rhythms, in addition to factors of ontogenetic and light nature.
The physiological and molecular responses of
Arabidopsis thaliana
plants to cold stress were studied. Exposure to a low non-freezing temperature (4°C, 5 days) caused a decrease in the physiological ...functions and activity of a number of photosynthetic genes and elevation in expression of the cold stress gene
COR15a
, the product of which protects chloroplasts. It was shown for the first time that in parallel to a general inhibition of physiological functions under hypothermia, an increase in the expression of most genes for the chloroplast transcription apparatus was observed. This is obviously one of the compensatory mechanisms of adaptation aimed to maintain cellular homeostasis and physiological functions under hypothermia.
The antioxidant balance, photochemical activity of photosystem II (PSII), and photosynthetic pigment content, as well as the expression of genes involved in the light signalling of callus lines of
...Eutrema salsugineum
plants (earlier
Thellungiella salsuginea
) under different spectral light compositions were studied. Growth of callus in red light (RL, maximum 660 nm), in contrast to blue light (BL, maximum 450 nm), resulted in a lower H
2
O
2
content and thiobarbituric acid reactive substances (TBARS). The BL increased the activities of key antioxidant enzymes in comparison with the white light (WL) and RL and demonstrated the minimum level of PSII photochemical activity. The activities of catalase (CAT) and peroxidase (POD) had the highest values in BL, which, along with the increased H
2
O
2
and TBARS content, indicate a higher level of oxidative stress in the cells. The expression levels of the main chloroplast protein genes of PSII (
PSBA
and
PSBD
), the NADPH-dependent oxidase gene of the plasma membrane (
RbohD
), the protochlorophyllide oxidoreductase genes (
POR B, C
) involved in the biosynthesis of chlorophyll, and the key photoreceptor signalling genes (
CIB1, CRY2, PhyB, PhyA
, and
PIF3
) were determined. Possible mechanisms of light quality effects on the physiological parameters of callus cells are discussed.
A two-dimensional quasilinear theory of saturation of the transverse magnetic Weibel instability in a collisionless plasma is developed. A closed system of equations is obtained to describe the ...evolution of the interacting spatial harmonics of the particle distribution function perturbations and magnetic field when the plasma anisotropy axis and wave vectors of the harmonics, as well as the electric field vectors in them, lie in the same calculation plane. Based on the numerical solution of this system, the dependence of the mean-square average of the saturating magnetic field on the initial anisotropies of the bi-Maxwellian and various bikappa velocity distributions of particles is found. It is shown that the magnitude of the saturating field substantially depends on the kappa parameter of the product bikappa particle distribution, i.e., on its energy profile, when the anisotropy parameters are small compared to unity. The results are compared with the published results of calculation by the less efficient particle-in-cell method.
The ability of brassinosteroids (BS) of different chemical structures (for example, 24-epibrassinolide (EBL) and 24-epicastasterone (ECS)) to induce priming in rapeseed (
Brassica napus
L.) plants, ...increasing resistance to “delayed” salt stress (150 mM NaCl), was studied. After 2 weeks of growth of rapeseed seedlings in a hydroponic setup in Hoagland-Snyder (HS) medium, they were transferred to the same medium supplemented with EBL or ECS (10 nM) for 4 h. The plants were then kept on the HS medium without BS for 20 h. Then they were grown on HS nutrient medium in the absence or in the presence of 150 mM NaCl for 6 days. Salinization inhibited growth processes (stem length, number of leaves, assimilating surface area, raw mass of plants (by 30–35%)); decreased levels of chlorophylls
a
and
b
and carotenoids (by 38–44%), tissue water content (by 3.54%), and osmotic potential of cells (1.7 times); and increased lipid peroxidation (LPO) (by 62%) in leaves. At the same time, salt stress stimulated the level of proline in leaves by six times and in stems and roots by 11 times, the activity of superoxide dismutase (SOD) by 2.3 times, and the activity of peroxidase by 26%. The concentration (at %) of Na and Cl under salinization increased in all parts of the plants, but the concentration of K, Ca, Mg, S, P, Al, and Fe ions decreased. Treatment of plants with BS (10 nM, 4 h) stimulated growth processes under optimal conditions, which was more typical for ECS, which also increased the content of chlorophyll
a
and carotenoids (by 11 and 18% in leaves, respectively). BS stimulated the activity of antioxidant enzymes (EBL increased the activity of SOD by 4.6 times, ECS increased the activity of SOD and peroxidase (by 48%)), which could affect the development of the priming state in plants. Pretreatment of rape seedlings with BS increased their resistance to subsequent salt stress. The protective effect of BS manifested at the levels of growth responses (primarily in ECS), water status, and osmotic potential of leaves. The LPO level decreased due to the activation of SOD and peroxidase in the case of EBL and ECS, respectively. The accumulation of ions in plants subjected to hormonal priming depended on the chemical structure of BS. It has been suggested that the protective effect of BS priming is explained by the ability of hormones to activate antioxidant enzymes before stress and to influence the inorganic ion transport system in such a way that plants accumulate ions more actively with subsequent salinization, resulting in a decrease in the osmotic potential of cells and maintenance of the water status. The obtained results can be useful in the development of technology for increasing the salt tolerance of rapeseed.
