Ultrastructure Of Mesophyll Cells Research Articles

Elevated CO2 can modify the response to a water status gradient in a steppe grass: from cell organelles to photosynthetic capacity to plant growth.

BackgroundThe atmospheric CO2 concentration is rising continuously, and abnormal precipitation may occur more frequently in the future. Although the effects of elevated CO2 and drought on plants have been well reported individually, little is known about their interaction, particularly over a water status gradient. Here, we aimed to characterize the effects of elevated CO2 and a water status gradient on the growth, photosynthetic capacity, and mesophyll cell ultrastructure of a dominant grass from a degraded grassland.ResultsElevated CO2 stimulated plant biomass to a greater extent under moderate changes in water status than under either extreme drought or over-watering conditions. Photosynthetic capacity and stomatal conductance were also enhanced by elevated CO2 under moderate drought, but inhibited with over-watering. Severe drought distorted mesophyll cell organelles, but CO2 enrichment partly alleviated this effect. Intrinsic water use efficiency (WUEi) and total biomass water use efficiency (WUEt) were increased by elevated CO2, regardless of water status. Plant structural traits were also found to be tightly associated with photosynthetic potentials.ConclusionThe results indicated that CO2 enrichment alleviated severe and moderate drought stress, and highlighted that CO2 fertilization’s dependency on water status should be considered when projecting key species’ responses to climate change in dry ecosystems.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0846-9) contains supplementary material, which is available to authorized users.

Red and Blue Lights Significantly Affect Photosynthetic Properties and Ultrastructure of Mesophyll Cells in Senescing Grape Leaves

Light quality significantly affects photosynthetic efficiency in plants. The mechanisms for how light quality affects photosynthesis in grape is poorly understood. Therefore, to investigate the effects of different light qualities on chloroplast ultrastructure and photosynthesis efficiency, two grape cultivars ‘Italia’ (slower speed of leaf senescence) and ‘Centennial Seedless’ (faster speed of leaf senescence) grown under protected and delayed conditions were used. The three treatments, replicated three times, were control (no supplemental lighting), red light and blue light. Chlorophyll content, net photosynthetic rate, and the ratio of Fv/Fm significantly increased in red light relative to the control. The opposite trend was observed in blue light in the early phase of leaf senescence. At later stages, physiological indexes were gradually higher than that of control, resulting in a delay in leaf senescence. Compared to the control, red and blue light both significantly increased the chlorophyll a/b ratio. Electron microscopy showed that blue light caused severe damage to the fine structure of chloroplasts at early stages of leaf senescence, but effects at later stages of leaf senescence became less severe compared to the control. The degradation of chloroplast ultrastructure was apparently delayed in red light throughout the experimental timeframe compared to other treatments. In this experiment, ‘Italia’ showed higher chlorophyll content, net photosynthetic rate, ratios of Fv/Fm, chlorophyll a/b and better preserved chloroplast ultrastructure relative to ‘Centennial Seedless’, resulting in a slower rate of leaf senescence.

Structure, pigment content, and photosynthesis of Siberian larch needles in Northern and Sub-Arctic Urals

The structure and functional organization of the photosynthetic apparatus of Siberian larch growing on the western slope of Northern and Sub-Arctic Urals were studied. The needle morphostructure, the mesophyll cell ultrastructure, and the pigment complex of chloroplasts were quantitatively characterized. Active photosynthesis of larch was observed during warm days with a low deficit of humidity. Photoassimilation depression under hot and dry weather was followed by a decrease in the stomatal conductance of needles. Under extreme conditions of mountains, Siberian larch has low photosynthesis. It decreased gradually from Nothern to Sub-Arctic Urals.

Analysis of obtained chloroplast transformants of tobacco (Nicotiana tabacum L.) plants with marker expression cassette of aadA au gene, changing the color of leaves

Transplastomic tobacco Nicotiana tabacum cv. Petit Havana plants were obtained by ballistic transformation. The modified expression cassette aadA au was used as a marker, which confers the resistance to streptomycin and spectinomycin and causes the golden color of the leaf when planted in the soil after selection on selective medium. Plants were transferred into soil and screened for the golden leaf color. Molecular analysis was performed to confirm the transplastomic nature of the plants. The differences in plastid ultrastructure of mesophyll cells between the leaves of tobacco plants of wild-type (with green leaf fragments) and plastids with altered pigmentation (old leaves of wild-type and yellow pieces of the leaf with transformed chloroplasts) were analyzed by electron microscopy. It was shown that the ultrastructural organization of plastids of transplastomic plants with golden color had distinct differences from the chloroplasts of plants in the control group by the number and arrangement of thylakoids, the number and sizes of starch grains and plastoglobules. Decreased number of thylakoids and starch grain inclusions was marked in the mesophyll cells on a background of their increased number in the stroma and grana. There were also significantly more light areas of the stroma in transplastomic plants, which was typical for nucleoid areas.

Physical and chemical indices of cucumber seedling leaves under dibutyl phthalate stress.

Phthalic acid ester (PAE) pollution to soil can lead to phytotoxicity in plants and potential health risks to human being. Dibutyl phthalate (DBP) as a kind of PAE has a large usage amount and large residues in soil. To analyze antioxidant responses of plants to DBP stress, effects of varying DBP concentrations on cucumber seedlings growth had been investigated. Malonaldehyde (MDA), hydrogen peroxide (H2O2), chlorophyll, proline, glutathione (GSH), and oxidized glutathione (GSSH) contents and activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POD) were studied. The results showed that H2O2 content increased in cucumber seedlings with the increase of DBP concentration. The chlorophyll content in the higher DBP significantly declined compared to the control. In the present study, a disturbance of the GSH redox balance was evidenced by a marked decrease in GSH/GSSG ratio in cucumber seedlings subjected DBP stress. Our results indicated that DBP treatment not only inhibited antioxidant capacity and antioxidant enzyme activity in seedlings' leaves but might also induce chlorophyll degradation or reduce the synthesis of chlorophyll. Moreover, it could also enhance the accumulation of reactive oxygen species (ROS) which induced membrane lipid peroxidation. DBP also altered the ultrastructure of mesophyll cells, damaged membrane structure of chloroplast and mitochondrion, and increased the number and size of starch grains in chloroplasts reducing the photosynthetic capacity.

Genotypic variation of the responses to chromium toxicity in four oilseed rape cultivars

Heavy metal toxicity in soils has been considered as major constraints for oilseed rape (Brassica napus L.) production. In the present study, toxic effects of chromium (Cr) were studied in 6-d-old seedlings of four different cultivars of B. napus (ZS 758, Zheda 619, ZY 50, and Zheda 622). The elevated content of Cr inhibited seedling growth, decreased the content of photosynthetic pigments, and activities of antioxidant enzymes, as well as increased the content of malondialdehyde and reactive oxygen species in all the cultivars. The Cr content in different parts of plants was higher in Zheda 622 than in other cultivars. The electron microscopic study showed changes in ultrastructure of leaf mesophyll and root tip cells at 400 μmol Cr, and these changes were more prominent in Zheda 622. An increased size and number of starch grains and number of plastoglobuli, damaged thylakoid membranes, and immature nucleoli and mitochondria were observed in leaves. In roots, enlarged vacuoles, disrupted cell walls and cell membranes, an increased number of mitochondria and a size of nucleolus, as well as plasmolysis (in Zheda 622) were observed. On the basis of these findings, it can be concluded that cv. Zheda 622 was more sensitive to Cr as compared to other three cultivars.

Ultrastructural response of cabbage outer leaf mesophyll cells (Brassica oleracea L.) to excess of nickel

Changes in the structure and in the ultrastructure of cabbage outer leaf mesophyll cells [<em>Brassica oleracea</em> L.] cv. Sława from Enkhouizen were examined by means of light and electron microscopy. The examined plants were grown on the basic Murashige and Skoog medium with addition of excesive concentrations of nickel (added as NiSO<sub>4</sub> x 7H<sub>2</sub>O),i.e. Ni 5, Ni 10 and Ni 20 mg/dm<sup>3</sup>. In Ni 5 mg samples mainly adaptation changes to the conditions of stress were observed. These changes were manifested by the increase of cytoplasm content and by cytoplasm vacuolization, by the increase of nucleus and nucleous volume, nucleolus vacuolization, the increase of plasmalemma invaginations and of the amount of rough ER, by the central arrangement of smooth ER and of the thylakoids of chloroplasts; it was also shown by the growth of the number of mitochondria and of peroxisomes in the cell. In Ni 10 mg samples, apart from adaptation changes, such as the increase of the nucleus volume, increase of plasmalemma invaginations, cytoplasm and nucleolus vacuolization, degeneration changes were also observed. They concerned mainly the nucleus (the increasing amount of condensed chromatin), ER (swelling and fragmentation of rER and sER), mitochondrium (swelling and reduction of cristae), Golgi apparatus (disintegration and decay) and chloroplasts (changes of shape, swelling and reduction of thylakoids, disappearance of starch and presence of big plastoglobuli). In Ni 20 mg samples cell protoplasts were in different stages of degeneration and the cell organelles that were identifiable, were usually damaged.

Combined Effect of Water Deficit and Salt Stress on the Structure of Mesophyll Cells in Wheat Seedlings

The purpose of the work was to assess the combined effect of drought and salinity (50, 100, 200 mМ NaCl) on the meso- and ultrastructure of mesophyll cells of wheat seedlings. Stress development was estimated by a decrease in the relative water content (RWC) and CO2-dependent O2 evolution (An) in leaves. The decrease in the RWC and in An occurred rapidly in the absence of salt in the substrate and slowly in the presence of salt, especially at a treatment of 100 mM NaCl. The resumption of watering led to the recovery of the both parameters in all variants except one with 200 mM NaCl. Structural studies showed that a weak drought stress (RWC 60%) without salinity led to the destruction of cell membranes and hyaloplasm, which did not occur in all salt treatments. By contrast, the ultrastructure of nuclei in weak drought without salinity remained unchanged, whereas in all salt treatments chromatin changed substantially. Heterochromatin underwent a strong condensation followed by the fusion into a united mass with the simultaneous loss of electron density. A strong water stress (RWC 40%) in all variants led to cell destruction and the hydrolysis of cell compounds. Under the drought without salinity, vacuoles disappeared, whereas in salt-treated samples they were retained and filled with organelles being at different degrees of degradation. Cell nuclei under strong drought stress lost their rounded shape, nuclear envelopes were destroyed, and at the end only a finely dispersed substance remained. Thus, under the combined action of drought and salt, there is some critical level of salt concentration in substrate above which the effect of NaCl changes to the adverse, which enhances the action of drought. Among structural components of mesophyll cells, the most sensitive parts to NaCl are nuclei and their chromatin.

Influence of heat stress on leaf ultrastructure, photosynthetic performance, and ascorbate peroxidase gene expression of two pear cultivars (Pyrus pyrifolia)

Plants encounter a variety of stresses in natural environments. One-year-old pot-grown trees of pear (Pyrus pyrifolia Nakai cv. Cuiguan and Wonhwang) were exposed to two heat stress regimes. Under constant short-term heat stress, chloroplasts and mitochondria were visibly damaged. Relative chlorophyll content and maximum photochemical efficiency of photosystem II were significantly decreased, which indicated that the leaf photosynthetic capability declined. Under chronic heat stress, mesophyll cell ultrastructure was not obviously damaged, but leaf photosynthetic capability was still restrained. As chronic heat stress was a simulation of the natural environment in summer, further study of the responses under this stress regime was undertaken. Ascorbate peroxidase (APX) activity was increased in 'Cuiguan', but not in 'Wonhwang'. Inducible expression of PpAPX genes in the cytoplasm, chloroplasts and peroxisomes was consistent with increased APX activity in 'Cuiguan', whereas only weak induction of PpAPX genes was observed in 'Wonhwang'. The isoenzymes cytosolic APX1 (cAPX1) and stromal APX (sAPX) were confirmed to be localized in the cytoplasm and chloroplasts, respectively.

Effect of Heat Stress on the Photosynthetic Characteristics in Flag Leaves at the Grain‐Filling Stage of Different Heat‐Resistant Winter Wheat Varieties

AbstractHeat stress has become an increasingly important factor in limiting wheat yields. In northernChina, high temperature (>30 °C) during the grain filling is one of the major constraints in increasing wheat productivity. We used two winter wheat (Triticum aestivumL.) cultivars with different sensitivities to heat stress (Jimai 22 ‘JM22’, low sensitivity and Xinmai 26 ‘XM26’, high sensitivity) to study the various aspects of photosynthetic characteristics during the grain filling stage under heat stress. The results showed that photosynthesis rates (Pn) in flag leaves ofXM26 decreased faster than inJM22 under heat stress during the grain‐filling stage.Pndecreased more rapidly under heat stress than without stress, by up to 69.9% and 59.3%, respectively, at 10 days following heat stress (10DAS). This decline ofPnwas not caused by heat‐induced stomatal limitation, but rather by a decline in Rubisco activity and a functional drop in photosystemII(PSII). After heat stress, the grain yield ofJM22 decreased by 6.41%, butXM26 decreased by 11.43%, when compared with their respective controls. Heat stress also caused an alteration of mesophyll cell ultrastructure. Injury caused by heat stress to organelles inXM26 was more severe thanJM22. Moreover, theJM22 cultivar showed some self‐repair capacity following heat stress injury. These results indicate that declines in photosynthetic performance caused by heat stress were cultivar‐dependent. Compared withXM26, theJM22 cultivar had superior heat stability in terms ofPSIIfunction and carboxylation activity, both of which are susceptible to heat stress.

Chloroplast ultrastructure of Hypericum perforatum plants regenerated in vitro after cryopreservation

The ultrastructure of leaf mesophyll cells of in vitro cultured Hypericum perforatum L. plants regenerated after cryopreservation was studied. Electron microscopy analysis revealed that the chloroplasts in plants pretreated with abscisic acid and regenerated after cryopreservation were round, with increased amount of starch, rather small volume of the thylakoid system, and destroyed envelope. Plants pretreated with 0.3 M mannitol and cooled at rates of 0.1 or 0.3 °C min−1 possessed chloroplasts with high starch content that resulted in a reduction of a membrane system. However, the pretreatment with 0.3 M mannitol and cooling at a rate of 0.2 °C min−1 was the best as chloroplast ultrastructure resembled the controls regenerated without cryopreservation.

Spent metal working fluids produced alterations on photosynthetic parameters and cell-ultrastructure of leaves and roots of maize plants

In this work we assess the capacity of maize (Zea mays) plants to phytoremediate spent metal working fluids (MWFs) and its effects on photosynthesis and ultrastructure of mesophyll and root cells. A corn-esparto fibre system patented by us has been used to phytoremediate MWFs in hydroponic culture. Furthermore, a plant growth promoting rhizobacteria (PGPR) has been used to improve the process. The results show that this system is capable of significantly reducing the chemical oxygen demand, under local legislation limits. However, plant systems are really damaged, mainly its photosynthetic system, as shown by the photosynthetical parameters. Nevertheless, strain inoculated improves these parameters, especially Hill reaction. The ultrastructure of photosynthetic apparatus was also affected. Chloroplast number decreased and becomes degraded in the mesophyll of MWFs treated plants. In some cases even plasmolysis of chloroplast membrane was detected. Early senescence symptoms were detected in root ultrastructural study. Severe cellular damage was observed in the parenchymal root cells of plants grown with MWFs, while vascular bundles cell remained unchanged. It seems that the inoculation minimises the damage originated by the MWFs pollutants, appearing as less degenerative organelles and higher chloroplast number than in non-inoculated ones.

Specific ultrastructure of the leaf mesophyll cells of Deschampsia antarctica Desv. (Poaceae) / Ultrastruktura komórek mezofilu liści Deschampsia antarctica Desv. (Poaceae)

The ultrastucture of mesophyll cells of Deschampsia antarctica Desv. (Poaceae) leaves was investigated using the standard method of preparing material for examination in transmission electron microscopy (TEM). The investigated leaves were collected from the Antarctic hairgrass growing in a tundra microhabitat and representing xermorphic morphological and anatomical features. The general anatomical features of mesophyll cells are similar to those in cells of another grass leaves. The observations of the ultrastructure of mesophyll cells have shown that the organelles are located close to each other in a relatively small amount of the cytoplasm or closely adhere to each other. Organelles such as mitochondria, peroxisomes, and Golgi apparatus, as well as osmiophilic materials are gathered close to the chloroplasts. The chloroplast of the mesophyll cells of the D. antarctica leaf can form concavities filled with the cytoplasm. Such behaviour and ultrastructure of organelles facilitate exchange/flow of different substances engaged in the metabolic activity of the cell between cooperating organelles.

Deciphering the possible mechanism of exogenous NO alleviating alkali stress on cucumber leaves by transcriptomic analysis

Alkali stress is a major factor that limits crop yield, and nitric oxide (NO) is involved in the regulation of plants tolerant to abiotic stress. In the present study, sodium nitroprusside (SNP), a NO donor, reversed the chlorosis of cucumber leaves caused by alkali stress. Physiological analysis indicated that application of SNP protected mesophyll cell ultrastructure from damage by alkali stress. SNP increased nutrient element utilization, pigment content, photosynthetic capacity and accumulation of organic acids. In this study, Solexa sequencing was used to investigate the effect of SNP on expression of genes involved in cucumber response to alkali stress. About 5.9 million (M) and 5.8M 21-nt cDNA tags were sequenced from the cDNA library of the alkali treatment and SNP treatment, respectively. When annotated, a total of 10,271 genes for the alkali stress treatment from the Solexa sequencing tags and 10,288 genes for SNP treatment were identified. We detected 901 differentially expressed genes in two samples, of which 437 and 464 of them were up- or down-regulated by SNP under alkali stress, respectively. The expression levels of 11 differentially expressed genes were confirmed by real-time RT-PCR. The trends observed agreed well with the Solexa expression profiles, although the degree of change was diverse in amplitude. Gene ontology analysis revealed that differentially expressed genes were mainly involved in response to abiotic stress, cellular metabolic process, photosynthesis, transmembrane transportation and organelle development, which were in accordance with physiological results.

Soil cadmium toxicity and nitrogen deposition differently affect growth and physiology in Toxicodendron vernicifluum seedlings

To ultimately determine whether different levels of soil nitrogen (N) deposition can modify the detrimental effects of cadmium (Cd), the seedlings of Toxicodendron vernicifluum (Strokes) F. A. Barkley were exposed to soil Cd stress (0, 5 and 15 mg kg(-1) dry soil), N deposition (0, 13 and 40 mg kg(-1) dry soil) and their combinations. Soil Cd stress caused damage in plant growth, photosynthesis and other physiological indexes, and in the ultrastructure of mesophyll cells. The effects of N deposition on growth, lipid peroxidation and enzyme activities depended on the relative amounts of N supplied. The combination of low N deposition and Cd stress was positive to plant growth, photosynthesis and enzyme activities, and it caused lower levels of Cd accumulation and lipid peroxidation compared with the effect of Cd stress alone. The combination of high N deposition and Cd stress led to a higher Cd accumulation and lipid peroxidation, and to lower enzyme activities, as compared with the effect of Cd stress alone. T. vernicifluum was found to be sensitive to soil Cd stress. Soil Cd had detrimental effects on T. vernicifluum seedlings, but the tolerance of T. vernicifluum to Cd increased under low N deposition.

Drought, high temperature, and their combination affect ultrastructure of chloroplasts and mitochondria in wheat (Triticum aestivum L.) leaves

Plants experience a number of limiting factors, as drought and heat, which are often coinciding stress factors in natural environment. This study evaluated the changes in mesophyll cell ultrastructure in the leaves of two varieties of winter wheat (Triticum aestivum L.), differing in their drought tolerance, under individual or combined drought and heat treatment. Although the individual stress factors affected leaf ultrastructure, the damaging effect of the combined drought and heat was more pronounced and manifested certain differences between genotypes. Chloroplasts and mitochondria were affected in a variety-specific manner under all adverse treatments. The organelles of the drought-tolerant Katya were better preserved than those in the sensitive variety Sadovo. Leaf ultrastructure can be considered as one of the important characteristics in the evaluation of the drought susceptibility of different wheat varieties.

Reciprocal grafting separates the roles of the root and shoot in sex‐related drought responses in Populus cathayana males and females

Drought stress responses and sensitivity of dioecious plants, such as Populus cathayana Rehd., are determined by different mechanisms in each sex. In general, males tend to be more resistant while females are more sensitive. Here, we used reciprocal grafting between males and females to determine the relative importance of roots and shoots when plants are exposed to drought stress. Total dry matter accumulation (DMA), photosynthetic capacity, long-term water-use efficiency (Δ), water potential and ultrastructure of mesophyll cells were evaluated to determine the different roles of root and shoot in sex-related drought responses. Plants with male roots were found to be more resistant and less sensitive to water stress than those with female roots under drought conditions. On the contrary, plants with female shoots grew better than those with male shoots under well-watered conditions. These results indicated that the sensitivity of males and females to water stress is primarily influenced by root processes, while under well-watered conditions sexual differences in growth are primarily driven by shoot processes. Furthermore, grafting female shoot scion onto male rootstock was proved to be an effective mean to improve resistance to water stress in P. cathayana females.

Effects of Molybdenum Application on Plant Growth, Molybdoenzyme Activity and Mesophyll Cell Ultrastructure of Round Leaf Cassia in Red Soil

ABSTRACT Round leaf cassia (Chamaecrista rotundifolia) cv. ‘Wynn’, a species of leguminous forage, was introduced into China from the Australian Centre for International Agricultural Research in 1989. It possesses strong resistance to adversity and is suited for planting in the red soil area of Southern China. The purpose of this study is to investigate the effects of molybdenum (Mo) application with different concentrations on plant growth, molybdoenzyme activity and mesophyll cell ultrastructure of C. rotundifolia in red soil. The results showed that, plant height, number of branches, and dry matter weight of C. rotundifolia under varying Mo applications (0.5, 1.0, 2.0, 4.0 mg kg−1) increased by 2.7%∼11.5%, 0.92%∼28.68%, and 52.9%∼115.2% compared with the control group, respectively, and they all increased with the increase of Mo concentration. Molybdenum contents in plants were also increased significantly with increasing the concentration of Mo, but Mo contents in plants at 4 mg kg−1 Mo application were lower than that at 2 mg kg−1 Mo application. The activities of nitrate reductase in leaf and nitrogenase in root nodule both reached the maximum at 1.0 mg/kg Mo, which increased by 57.77% and 113.1% than the control group respectively. However, their activities began to decrease at 2 and 4 mg kg−1 Mo. The observation on mesophyll cell ultrastructure showed that, Mo application could increase the number of chloroplasts, enhance the stability of lipid bilayer of chloroplast membrane and increase the density of chloroplast lamellae and grana. Simultaneously, the total number of mitochondria and the density of inner cristae were decreased, but there was no significant influence on mitochondrial outer membrane. Moreover, the right amount of Mo fertilizer could enhance the stability of mesophyll cell wall and cell membrane. Although the molybdoenzyme activity decreased at the higher concentration (e.g., 2 and 4 mg kg−1), the application of Mo fertilizer in this test (0.5∼4 mg kg−1) could promote the growth and development of C. rotundifolia.

Effects of Soil Drought with Nocturnal Warming on Leaf Stomatal Traits and Mesophyll Cell Ultrastructure of a Perennial Grass

ABSTRACTWhile water deficit and rising temperatures are progressive global problems, their combined effect on plants has received less attention. Stomatal traits, mesophyll cell ultrastructure, net photosynthetic rate, lipid peroxidation, and ion leakage were examined in leaves ofLeymus chinensis(Trin.) Tzvel. plants using native Castanozem soil. Stomatal traits and mesophyll cell ultrastructure were studied using light microscopy and transmission electron microscope. Under severe water stress, malondialdehyde and ion leakage increased, especially at high night temperatures of 30/25°C (day/night). Mild water stress increased stomatal density, especially with normal night temperatures of 30/20°C (day/night). Moderate and severe water stress did not affect stomatal density. Under water stress, mesophyll cell ultrastructures were disturbed, and the membrane systems of chloroplasts and mitochondria were broken, particularly at high night temperatures. Leaf net photosynthetic rate and stomatal conductance were negatively correlated with ion leakage and malondialdehyde. The results suggested that high night temperature may aggravate the adverse effects of soil water deficit on leaf stomatal traits and mesophyll cell ultrastructure and also enhance lipid peroxidation.

Effect of fucoidan on potato virus X accumulation and ultrastructure of mesophyll cells of Datura stramonium L.

The accumulation of potato virus X (PVX) in mesophyll cells of detached Datura stramonium L. leaves treated with fucoidan from brown algae Fucus evanescens C. Ag. have been evaluated by electron microscopy during the early infection period (three days after infection). It was found that cells of the leaves treated with fucoidan 24 h before infection accumulated virus less than untreated control. Ultrastructure-morphometric assay showed that fucoidan treatment causes an increase in the protein-synthesizing capability of cells (nucleolus dimention and amount of both mitochondria and rough endoplasmic reticulum membranes increased). At the same time, fucoidan treatment slightly activates the lytic compartment, which leads to the destruction of virus particles. Therefore, it may be considered that fucoidan induces a cellular defense mechanism that limits virus accumulation. Stimulation by the fucoidan of the formation of PVX-specific laminar structures able to bind virus particles may be another antiviral cell defense mechanism induced by the virus that prevents PVX reproduction and its intra- and intercellular transport.