Vol 66, No 1 (2019)

Ethylene is an important phytohormone that regulates many important biological processes in plant. ERF (ethylene response factor) proteins are key transcription factors that activate the ethylene signaling pathway. However, our knowledge about the mechanism of the ERF transcription factors in regulating nuclear genes expression is limited. Retrograde signaling pathway in chloroplast is a novel kind of mechanism that regulates nuclear gene expression by different signals in plastid. Based on our former research we analyzed the components related with retrograde signaling from plastid in the transgenic tobacco overexpressing TERF1, a member of ERF family transcription factors, to elucidate the interaction between ethylene signaling pathway and different retrograde signaling pathway in plastid under normal growth condition. Results show that TERF1 regulates different retrograde signals in plastid and thus regulates different nuclear genes expression under normal growth condition. We propose a new mechanism that links ethylene signaling pathway and retrograde signaling pathway as well as new potential of TERF1 in regulating nuclear genes expression at post-transcriptional level.

Rosa chinensis Jacq., originating from China, occupied a pivotal position in the floral industry all over the world. Drought and soil salinization is a major problem in the Chinese rose planting industry. Therefore, the study on resistance is important to improve R. chinensis breeding. In this work, leaves of twelve samples with three biological repetitions were collected for transcriptome sequencing. In total 83.14 Gigabyte (G) Illumina sequence data were generated and 74 850 unigenes were successfully annotated. Differentially expressed gene (DEG) analysis was performed by comparing the transcriptomes of the 0, 2, 4 and 7 days salt treatment, based upon which several potential candidate genes involved in salt tolerance response had been identified. DEGs involved in plant hormone signal transduction, photosynthesis, and catalytic activity were examined in depth. The experimental result indicated that the R. chinensis showed strong stress signals after being subjected to salt stress. In the initial stage of salt treatment (two days), plant protective process began to take effect, which was embodied in the regulation of oxidoreductase activities and plant hormone signal transduction pathway. In addition, the expression level of P5CS was up-regulated in R. chinensis, but the proline metabolic pathway was not affected. In the late stage of salt treatment (four and seven days), the photosynthesis – antenna proteins pathway has been greatly affected, and the down-regulated PYL, Snrk2 and MRP lead to the salt tolerance decline, which was consistent with the leaf wilting performance of the R. chinensis in four and seven days of treatment. All the candidate genes were verified by RT-qPCR.

Cadmium (Cd) pollution was becoming more and more serious; there is an urgent need for an effective solution to inhibit the harm of cadmium stress. Chitosan (CTS) is a biologically active polysaccharide that plays a unique role under abiotic stress. So it was of much improtance to explore the effects of CTS on maize resistance ability. The results showed that maize (Zea mays L.) seedling growth was significantly inhibited, root system was the first organ that contact with cadmium stress, so the roots accumulated a lot of cadmium content, reducing the root activity, root growth was blocked, which led a reduction in nutrients to the leaves, and the chlorophyll content and photosynthetic enzyme activity were decreased. Additionally, the antioxidant enzyme activity was reduced. Under cadmium stress, CTS treatments significantly increased the growth rate and compensated for the function of root system, and which increased SOD, POD, CAT, APX and GR activities and AsA, GSH contents of leaves, but reduced \({\text{O}}_{2}^{{\centerdot \, - }}\), H₂O₂ and MDA contents. CTS increased chlorophyll content, P_n, G_s, T_r, F_v/F_m, Φ_PSII, qP and NPQ, reduced C_i, avoided excessive light damage and maintained higher PSII activity. CTS alleviated the destruction of antioxidant enzymes and inhibited the production of reactive oxygen species, which improved the chlorophyll content and photosynthesis of plants. Our results showed that CTS could be used in cadmium-contaminated areas to reduce the toxicity of cadmium stress. The study results provide a theoretical and experimental basis for the safe production of maize in cadmium-contaminated areas.

Ultraviolet-B radiation (UV-B) can boost the accumulation of terpenoids in plants. Here, Ach-yranthes bidentata Blume plantlets were exposed to UV-B radiation for different durations (1, 2, 3 and 4 h) to understand its effect on the accumulation of the medicinally important secondary metabolites oleanolic acid and ecdysterone. Our results showed that UV-B radiation led to reduced chlorophyll a, chlorophyll b and carotenoid production. Additionally, enzymatic antioxidants accumulated in the plant to detoxify ROS under UV-B radiation. Nine known enzyme-encoding genes (HMGS, HMGR, PMK, FPS, SS, SE, GGPPS, β-AS and CAS) involved in secondary metabolism in A. bidentata were analyzed at the transcriptional levels post-UV-B treatment from 0 to 4 h. RT-qPCR analysis revealed an upregulation in the HMGS, HMGR, PMK, FPS, SS, SE, β-AS and CAS genes that are related to the production of oleanolic acid and ecdysterone. We observed a significant increase in oleanolic acid and ecdysterone content at 3 and 2 h UV-B radiation exposure, respectively. The present work provides evidence that UV-B radiation in mild doses can enhance the concentration of these secondary metabolites by upregulating the relative expression levels of key enzyme genes involved in oleanolic acid and ecdysterone biosynthesis. This study provides evidence that short-term UV-B treatments can increase A. bidentata secondary metabolite content and may be a safe approach for generating high oleanolic acid and ecdysterone producing plantlets.

Nitric oxide (NO), phospholipase D (PLD) and plasma membrane (PM) H⁺-ATPase play crucial roles in plant response to drought stress, but the mechanisms of their function and their relationships in this process are still unclear. Here, we investigated how NO regulate PM H⁺-ATPase activity in maize (Zea mays L.) root tips in drought stress via inducing PLD-derived phosphatidic acid (PA) formation. Our results showed that drought stress stimulated NO production, up-regulated ZmPLD gene expression and stimulated PLD activity, coupled with PA production. With the elevation of PA content in a specific period (6 to 24 h after treatment), the PM H⁺-ATPase was stimulated. The NO scavenger impaired drought-induced PLD activation, PA formation and PM H⁺-ATPase activation at 12 h after treatment. The PLD inhibitor impaired drought-induced PA formation and PM H⁺-ATPase activation at 12 h after treatment. The NO scavenger, PLD inhibitor and PM H⁺-ATPase inhibitor aggravated the injury caused by drought stress. Exogenous NO alleviated the injury through a further elevation and a longer maintenance of ZmPLD gene expression, PLD activity, PA content and PM H⁺-ATPase activity in drought stress. The stimulation effect of exogenous NO on PA formation and PM H⁺-ATPase activation at 12 h after treatment were partly inhibited by the PLD inhibitor. The results suggested that as an early signal, NO triggers maize plant response to drought stress through increasing PM H⁺-ATPase activity in root tips. PLD-derived PA acts downstream of NO in this process.

The purpose of the present work was to compare calluses of European cranberry (Oxycoccus pal-ustris Pers.) and American cranberry (O. macrocarpus (Ait.) Pers.) by their ability to accumulate biomass and phenolic compounds in the presence of different cytokinins in nutrient medium. In European cranberry, callusogenesis appeared to be more intensive upon the addition of kinetin (Kin) to the medium, while accumulation of phenolic compounds and biomass was most pronounced on the medium with isopentenyladenine (iP). In American cranberry, callusogenesis appeared to be more intensive upon the addition of iP to the medium and in respect to accumulation of biomass and phenolic compounds (in the onset of the cultivation), somewhat higher values were obtained upon addition of benzylaminopurin (BAP). Maximum of phenolic compounds accumulation was observed upon the transition of callus cultures to the stationary growth phase, during the fifth week of the passage on average, except on the medium with BAP. The content of soluble phenolic compounds in European cranberry calluses did not exceed 11 mg/g fr wt, while that in American cranberry calluses did not exceed 17 mg/g fr wt. Cranberry callus cultures under long-term cultivation displayed a decrease in the level of all groups of phenolic compounds, including flavonoids to a higher extent. For European cranberry calluses after 6–10 passages, stabilization of the secondary synthesis was noted, first of all on the medium with iP. In general, more stable accumulation of phenolic compounds in calluses of both cranberry species was observed in the presence of Kin.

Local damages induce a wide spectrum of functional responses in intact parts of the plant, including changes in transpiration and CO₂ assimilation, which may be associated with propagating variation potential (VP). In the present work carried out on pea (Pisum sativum L.) plants, an analysis of the influence of local burn leading to generation of VP on transpiration and CO₂ assimilation under conditions of different air humidity was conducted. It was shown that VP induced multiphase changes in these physiological functions in intact pea leaf, including rapid lowering their parameters, slow elevation of them, and prolonged dropping transpiration and assimilation. Analysis of the impact of air humidity on these processes showed that quick and long lowering transpiration was significantly suppressed under the conditions of high humidity, while slowly increasing transpiration hardly depended on air humidity. Dependence of VP-induced CO₂ assimilation response on air humidity exhibited a similar character. Additional correlation analysis of amplitudes of VP-induced transpiration and CO₂ assimilation changes showed that prolonged stomata closing may be the mechanism of long-term lowering assimilation of intact leaves after the action of local burn. In general, it was established that the VP-induced transpiration response is a complex combination of activation and suppression of transpiration, and the contribution of different components to the observed responses depends on air humidity.

Photosynthetic activities of a chilling-sensitive species, Nicotiana tabacum L. (cv. Samsun), and a chilling-resistant plant, Arabidopsis thaliana Heynh. (L) (ecotype Columbia), were examined in young seedlings exposed to low temperatures. Functional parameters were determined after 1- to 6-day exposure of tobacco and arabidopsis plants at 8 and 2°C, respectively. In tobacco leaves sampled by the end of the experiment, the chlorophyll content decreased by 30%, the ratio of variable to maximum Chl a fluorescence (F_v/F_m) decreased by 5%, and the rate of net (apparent) photosynthesis diminished almost twofold. The concentration of soluble sugars in tobacco leaves increased by 30% approaching 130 mg/g dry wt. In arabidopsis, unlike tobacco, the content and proportions of photosynthetic pigments, as well as the F_v/F_m ratio changed insignificantly upon cooling, whereas net photosynthetic rates decreased to a lesser extent (by a factor of 1.6). The content of sugars in arabidopsis leaves increased fourfold by the end of the low-temperature treatment and reached 90 mg/g dry wt. Thus, the photosynthetic apparatus in chill-sensitive and cold-resistant plants responded differently to chilling temperatures. The data provide evidence that the photosynthetic apparatus in arabidopsis is well preserved upon chilling and can function effectively at cold-hardening temperatures. The thylakoid processes and the reactions of photosynthetic carbon metabolism in leaves of heat-loving tobacco plants are more sensitive to chilling temperatures and undergo changes in a more or less coordinated manner, helping chloroplasts to avoid the excessive generation of reactive oxygen species.

Sucrose synthase (EC 2.4.1.13) (SS) is the enzyme that regulates participation of sucrose in metabolism of the cells of the cambial zone of woody plants, thereby governing the structure and quality of wood. Much data have been accumulated about the role of SS in the formation of cell wall components and synthesis of storage metabolites. However, the majority of investigations were carried out with herbaceous plants. In this review, possible mechanisms of the enzyme activity regulation are examined and the isoenzyme composition and expression profiles of the genes encoding SS in woody plants are shown. We have analyzed literature data about the possible role of SS in phloem unloading, synthesis of the components of xylem cell walls, and its participation in starch accumulation in woody plants during different scenarios of xylogenesis.