Plants are continuously exposed to various environmental stresses and they respond to them in different ways. Ambient temperature is among the most important environmental cues that directly influence plant growth and yield. Research in recent years has revealed that epigenetic mechanisms play a key role in plants' response to temperature stress. Changes in gene expression evoked by stress signals follow post-translational histone modifications, DNA methylation, histone variant incorporation, and the action of chromatin remodeling factors and Polycomb group proteins. The majority of epigenetic modifications induced by temperature stress are reversible in nature; thus, chromatin returns to its previous state after the stress has passed. Some modifications seem stable, however, due presumably to so-called stress memory. Epigenetic modifications can be inherited through mitosis and meiosis. By dint of epigenetic memory, plants can more efficiently respond to future stressful conditions, thereby increasing their potential for environmental adaptation. Recognition of the epigenetic mechanisms that take part in plants' response to changes of ambient temperature will increase our understanding of adaptations to stress conditions.
Application of 1-naphthaleneacetic acid (NAA) or 1-aminocyclopropane-1-carboxilic acid (ACC) to maize roots growing in hydroponic solution inhibited root elongation, and increased radial growth, but the responses to those treatments differed in degree. Auxin was more effective than ACC as an elongation inhibitor and root swelling promoter. Whereas NAA fully inhibited elongation and maintained swelling over 48 h, ACC inhibited elongation partially (50%) and only promoted swelling for 24 h. It is well-known that auxin, like ACC, promotes ethylene production, but similar levels of ethylene production reached by means of NAA or ACC treatments did not elicit the same response, the response being always stronger to NAA than to ACC. These results suggest that the effect of auxin on root growth is not mediated by ethylene. Elongation and swelling of roots appear to be inversely related: usually a reduction in elongation was accompanied by corresponding swelling. However, these two processes showed different sensitivities to growth regulators. After 24 h treatment with 0.5 μM NAA or 5 μM ACC, root elongation was inhibited by 90% and 53% respectively, but the same treatments promoted swelling by 187% and 140% respectively. Furthermore, 1 μM ACC was shown to promote inhibition of root elongation without affecting swelling. The ethylene antagonist STS (silver thiosulfate) did not affect elongation in control or NAAtreated roots, but increased ethylene production and swelling. These results indicate that longitudinal and radial expansion could be independently controlled.
We compared the biochemical profiles of Physalis ixocarpa hairy roots transformed with Agrobacterium rhizogenes ATCC and A4 strains with non-transformed root cultures. The studied clones of A4- and ATCC-induced hairy roots differed significantly; the latter showed greater growth potential and greater ability to produce secondary metabolites (tropane alkaloids) and to biotransform hydroquinone to arbutin. We compared glucose content, alanine and aspartate aminotransferase activity, and L-phenylalanine ammonia-lyase activity. We analyzed markers of prooxidant/antioxidant homeostasis: catalase, ascorbate peroxidase, oxidase, glutathione peroxidase and transferase activity, and the levels of ascorbate, glutathione, tocopherol and lipid peroxidation. We found that transformation induced strain-specific regulation, including regulation based on redox signals, determining the rate of allocation of carbon and nitrogen resources to secondary metabolism pathways. Our results provide evidence that A. rhizogenes strain-specific modification of primary metabolites contributed to regulation of secondary metabolism and could determine the ability of P. ixocarpa hairy root clones to produce tropane alkaloids and to convert exogenously applied hydroquinone to pharmaceutically valuable arbutin. Of the studied parameters, glucose content, L-phenylalanine ammonia-lyase activity and alanine aminotransferases activity may be indicators of the secondary metabolite-producing potential of different P. ixocarpa hairy root clones.
Arbuscular mycorrhizal fungi are the most widespread root fungal symbionts, forming associations with the vast majority of plant species. Ectomycorrhizal development alters gene expression in plant symbionts. In this work we examined the effect of arbuscular mycorrhizal fungi spores on the growth and development of Brassica and on the expression of BnMT2 in winter rape. In a pot experiment, rape seedlings growing on different types of sterile and nonsterile soils were inoculated simultaneously with mycorrhizal fungi spores of Acaulospora longula,Glomus geosporum, Glomus mosseae and Scutellospora calospora. As compared with control plants growing in the absence of spores, ten-week-old seedlings of Brassica napus L. in sterile soil inoculated with arbuscular spores had longer shoots and higher fresh biomass of above-ground plant parts. In other types of substrates enriched with mycorrhizal fungi spores, the plants were smaller than non-inoculated plants. The presence of AMF spores stimulated the elongation growth of hypocotyls in both analyzed substrates. BnMT2 expression was highest in plants growing on the sterile substrate. Generally, the presence of mycorrhizal fungi spores appeared to have an adverse effect on the growth of rape plants.
The paper describes anatomical and physiological features of photobionts and mycobionts in Bryoria forsteri Olech & Bystrek, Caloplaca regalis (Vain.) Zahlbr., Cetraria aculeata (Schreb.) Fr., Ramalina terebrata Hook f. & Taylor, Sphaerophorus globosus (Huds.) Vain. and Usnea antarctica Du Rietz, collected in the Antarctic under varied weather conditions. Green algae from the genera Lobosphaera and Trebouxia were gathered in depressions of the cortex under the more resistant mycobiont hyphae. In photobiont cells a large amount of highly osmiophilic electron-dense PAS-negative material, lipid-like in character, was of particular interest. Similar material also filled certain areas of the aerial apoplast. A star-shaped chromatophore with central and lateral pyrenoids encompassed most of the photobiont protoplast in all the studied species. Regularly arranged thylakoids with evenly widened lumina along their entire length and osmiophilic lipid droplets adhering to their outer surfaces were visible within the pyrenoid. Inside the chloroplast, large protein inclusions tightly joined with the thylakoids were observed. The mycobionts were closely attached to each other another and with the photobionts by means of an outer osmiophilic wall layer, and formed intramural haustoria. Their protoplasts were filled with PAS-positive polysaccharides and a large amount of lipid-like substances. The photobionts were physiologically active and produced a large amount of electron-dense osmiophilic material, and PAS-positive starch grains were visible around their pyrenoids in the thalli collected in different weather conditions. The permanent reserves of nutritive materials deposited in the thalli enable these organisms to quickly begin and continue indispensable physiological processes in the extreme Antarctic conditions.
Three problems in the taxonomy of Pancratium in Egypt are the lack of publications, a lack of clarity about the relationships between recently distinguished species, and the lack of markers for examining the levels and patterns of variation in rare and endemic species; the latter hinders work in plant conservation genetics. In this study we reassessed the taxonomic status of the Pancratium species of Egypt, and examined morphological and genetic variation within and between species, using specimens from different populations collected throughout its distribution range in the country. Our assessment was based on 38 macromorphological characters mainly representing vegetative parts, flowers, fruits and seeds, in addition to RAPD data. The results revealed five morphologically distinguished Pancratium species in Egypt, of which P. trianthum Herb. is newly recorded. Species identification was confirmed by two phenetic dendrograms generated with 26 quantitative morphological characters and RAPD data, while species delimitation was verified by principal component analysis. The diagnostic floral characters are those of the perianth, corona teeth, pistil, stamens, aerial scape, spathe, and number of flowers. The retrieved RAPD polymorphic bands show better resolution of the morphologically and ecologically closely allied Pancratium species (P. arabicum and P. maritimum), and also confirm the morphological and ecological divergence of P. tortuosum from the other studied species. These results are supported by the constructed UPGMA dendrogram.
The stigma of Ornithogalum sigmoideum is of dry and papillate type. The papillae are covered by a cuticle-pellicle layer, as revealed by staining. The activity of nonspecific esterase, acid phosphatase and peroxidase increases in the pellicle during the receptivity period. The style of O. sigmoideum is of the hollow type. Ultrastructural study of the cells lining the canal indicated that they are secretory cells and contain abundant endoplasmic reticulum, dictyosomes, mitochondria, plastids and ribosomes. After anthesis these organelles show degeneration at the end of the secretory phase. In canal cells, cytochemical tests showed the presence of acidic polyanions, insoluble and acidic polysaccharides, proteins and lipids. Before anthesis the canal cells are rich in polysaccharides, proteins and lipids. At maturity the cuticle is ruptured and secretory materials from the canal cells are released into the canal. In the unpollinated style of O. sigmoideum the exudates accumulated in the center of the canal; in pollinated pistils the same secretion materials were dispersed through the canal, which became wider.
Our cytomorphological study of various populations of Elsholtzia ciliata (Lamiaceae) collected from high-altitude sites of Kashmir Himalaya revealed two euploid cytomorphotypes, diploid (n=8) and tetraploid (n=16), growing sympatrically but inhabiting two different habitats. This is the first report of tetraploid (4×) E. ciliata from the Indian subcontinent. We found the course of meiois to be normal in diploids, but tetraploid individuals showed chromosome and meiotic irregularities: cytomixis at early prophase I, stickiness at metaphase I, and chromosome bridges at anaphase I. In tetraploids, 23 of the 26 pollen mother cells observed at metaphase I showed 0-6 quadrivalents, suggesting that the tetraploid is a segmental allopolyploid. Microsporogenesis was also abnormal in tetraploids, showing the formation of triads. All these anomalies are conducive to lower reproductive potential (40.70%) in tetraploids than in diploids (90.50%). Significant morphological differences between the two cytotypes are presented.
Hladnikia pastinacifolia RCHB., a narrow endemic, has an extremely restricted distribution in Trnovski gozd (Slovenia), despite the presence of many sites with suitable habitats. We compared the morphological traits of plants from different populations and habitats. The overall pattern showed that the smallest plants, with low fruit number, are found on Èaven (locus classicus or type locality); the largest individuals, with high fruit number, grow in the Golobnica gorge. As judged by plant size and seed set, the optimal habitats are screes. We used RAPD markers to estimate genetic variation between and within populations, as well as between and within the northern and the southern parts of the distribution area. Hladnikia showed only a low level of RAPD variability. AMOVA partitioned the majority of genetic diversity within selected populations. The low genetic differentiation between populations and their genetic depauperation indicates survival in situ, since the Trnovski gozd plateau most likely was a nunatak region in the southern Prealps during Pleistocene glaciations. Later range expansion of extant populations was limited by poor seed dispersal. We also analyzed the cpDNA trnL-F intergenic spacer to check whether the sequence is useful for studying the phylogenetic relationships of Hladnikia within the family Apiaceae (Umbelliferae). Our results support the assertion that H. pastinacifolia is an old taxon.
Plant viruses create many changes in the morphology of the plant cell once the infection process has begun. This paper describes and compares the ultrastructural changes induced in maize cells by two isolates of Maize dwarfmosaic virus (MDMV), Spanish (MDMV-Sp) and Polish (MDMV-P), and one isolate of Sugarcane mosaic virus (SCMV) at 10 and 42 days post-inoculation: the concentration and arrangement of virus particles, inclusion bodies associated with infection, and other cytological alterations. The most important difference between maize cells infected with MDMV isolates and with SCMV-P1 was in the form of cytoplasmic cylindrical inclusions. In cells infected with MDMV only typical inclusions such as pinwheels and scrolls were observed, but laminar aggregates were also present in SCMV-infected cells. No virus particles were found in plant cell organelles. Specific virion arrangements occurred in cells infected with MDMV-Sp and SCMV. The most interesting new finding was of specific amorphous inclusions in the cytoplasm of MDMV-Sp-infected cells, which clearly differentiated the two MDMV isolates studied.
We determined the level of flavonoids, citric acid and ascorbic acid in hips of rose species from the Caninae section occurring in Poland. We performed phytochemical analyses of 75 samples representing 11 species: Rosaagrestis Savi, R. canina L., R. dumalis Bechst., R. glauca Pourret, R. inodora Fries, R. jundzillii Besser, R. rubiginosa L., R. sherardii Davies, R. tomentosa Sm., R. villosa L. and R. zalana Wiesb. Flavonoid content was determined spectrophotometrically, and organic acid concentrations by HPLC. The content of the studied compounds varied greatly. Interspecific differences in the amount of flavonoids and ascorbic acid were highly significant. The most common species, Rosa canina, showed low average content of vitamin C (0.51 g/100 g of dry matter) and flavonoids (41 mg/100 g DM) and high content of citric acid (3.48 g/100 g DM). Ascorbic acid was highest in R. villosa hips (avg. 2.25 g/100 g DM), flavonoids were highest in R. rubiginosa (72 mg/100 g DM), and citric acid was highest in R. tomentosa (4.34 g/100 g DM). Flavonoid level correlated negatively with the amount of citric acid (r=-0.47, p<0.001). Cluster analysis of rose species based on the content of the investigated compounds confirmed the validity of the division of sect. Caninae into three subsections: Rubiginosae, Vestitae and Rubrifoliae. The phytochemical variation of these roses reflects their probable phylogenetic relationships as determined from morphology.
Miscanthus ×giganteus Greef et Deu. (Poaceae), a hybrid of Miscanthus sinensis and M. sacchariflorus native to Japan, is an ornamental and a highly lignocellulosic bioenergy crop, cultivated in the European Union as an alternative source of energy. This grass reproduces exclusively vegetatively, by rhizomes or via expensive in vitro micropropagation. The present study was aimed at finding the barriers that prevent sexual seed production, based on detailed embryological analyses of the whole generative cycle, including microsporogenesis, pollen viability, megasporogenesis, female gametophyte development, and embryo and endosperm formation. Sterility of M. ×giganteus results from abnormal development of both male and female gametophytes. Disturbed microsporogenesis (laggard chromosomes, univalents, micronuclei) was further highlighted by low pollen staining. The frequency of stainable pollen ranged from 13.9% to 55.3% depending on the pollen staining test, and no pollen germination was observed either in vitro or in planta. The wide range of pollen sizes (25.5-47.6 μm) clearly indicated unbalanced pollen grain cytology, which evidently affected pollen germination. Only 9.7% of the ovules developed normally. No zygotes nor embryos were found in any analyzed ovules. Sexual reproduction of M. ×giganteus is severely hampered by its allotriploid (2n=3x=57) nature. Hybrid sterility, a strong postzygotic barrier, prevents sexual reproduction and, therefore, seed formation in this taxon.
Annual and interannual phenomena and canopy behavior of prickly comfrey (Symphytum asperum Lep.) were studied in a 10-year experiment with 25 measurement sessions during the growing season. The results confirm the importance of long-term experiments in studying plant phenomena, biometrics and behavior. Prickly comfrey produced a green canopy each year and growth started very early in spring. Maximum plant height was less than 160 cm. Annual phenomena (growth initiation, seedling phase, flower phase, seed phase, senescent phase), interannual phenomena (initiation and youth, reproduction, new generation formation, plant death) and two population cycles (colonization and expansion) were measured. The duration of annual development up to canopy death can be expressed as x+2x+3x+2x, where x is initial growth. The genetic structure and activity of prickly comfrey promotes generative development of the species. Its age can be measured over a single and several vegetation generations. The ability to change the angle of vertical stem growth after 9 weeks can be considered a functional behavior of prickly comfrey and part of its life strategy. The differences between the organs in the upper and lower parts are very considerable and should be taken into account in morphological descriptions of this species. The upper and lower stems and leaves showed differential growth. Both stem and leaves were densely setose. Old leaves were 3.8 times longer, 4 times broader and 2.4 times thicker than young leaves. Hairs were on average 3 times longer on old than on young leaves. Flowers had contact with pollinators making relatively long visits to them.
Allium cepa var. agrogarum L. seedlings grown in nutrient solution were subjected to increasing concentrations of Cd2+ (0, 1, 10, 100 μM). Variation in tolerance to cadmium toxicity was studied based on chromosome aberrations, nucleoli structure and reconstruction of root tip cells, Cd accumulation and mineral metabolism, lipid peroxidation, and changes in the antioxidative defense system (SOD, CAT, POD) in leaves and roots of the seedlings. Cd induced chromosome aberrations including C-mitoses, chromosome bridges, chromosome fragments and chromosome stickiness. Cd induced the production of some particles of argyrophilic proteins scattered in the nuclei and even extruded from the nucleoli into the cytoplasm after a high Cd concentration or prolonged Cd stress, and nucleolar reconstruction was inhibited. In Cd2+-treated Allium cepa var. agrogarum plants the metal was largely restricted to the roots; very little of it was transported to aerial parts. Adding Cd2+ to the nutrient solution affected mineral metabolism. For example, at 100 μM Cd it reduced the levels of Mn, Cu and Zn in roots, bulbs and leaves. Malondialdehyde content in roots and leaves increased with treatment time and increased concentration of Cd. Antioxidant enzymes appear to play a key role in resistance to Cd under stress conditions.
We explored the use of the medicinally important plant Centella asiatica for expression of hemagglutinin-neuraminidase (HN) protein of Newcastle disease virus (NDV) strain AF2240. HN protein is the principal target for subunit vaccine development against NDV. The full-length HN gene was cloned into a plant expression construct driven by the CaMV 35S promoter and C-terminal fusion of green fluorescence protein (GFP) as reporter system. The recombinant expression construct was transformed via particle bombardment into C. asiatica callus. Transformants were screened using GFP and selected on MS medium supplemented with 15 mg/l hygromycin. The ~1.8 kb HN mRNA transcript was detected on the putative transformants using RT-PCR. The presence of HN protein expression was further confirmed through dot blot analysis using anti-NDV chicken serum. Here we report, for the first time, the use of a novel medicinal plant as a new platform for HN protein expression.
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