Size Of Plastoglobuli Research Articles

Changes in chloroplast ultrastructure in leaves of drought-stressed maize inbred lines

Chloroplasts are commonly the site of the earliest abiotic injury visible in plant ultrastructure. In this study, six inbred lines of maize (Zea mays L.) were used to analyze changes in the ultrastructure of chloroplasts and related physiological parameters under conditions of drought stress simulated by 20% polyethylene glycol 6000 (−0.6 MPa) for two days. Chloroplasts of three maize lines proved to be more sensitive. They showed changes in the ultrastructure in response to drought, including damage of thylakoid membranes, an increase in the number and size of plastoglobuli, swelling of thylakoid membranes both stromal and granal, disorganization of the thylakoid membrane system, an obvious increase in the intrathylakoid space, and a decrease in the length-to-width ratio and area of chloroplasts. In addition, the contents of malondialdehyde increased markedly in the sensitive lines. Contrary to the sensitive lines, stable structures and shapes of chloroplasts were observed in the drought-resistant lines; it could be considered as an advantage contributing to drought tolerance in the plants. In addition, the drought index of leaf fresh mass (LMDI) in the drought-sensitive lines was ≤ 0.5, which was also associated with a lower content of leaf chlorophyll. In contrast, drought tolerance coincided with lesser growth reduction, and higher LMDI and leaf chlorophyll content.

Soil metals, chloroplasts, and secure crop production: a review

An increasing number of soils of poor quality with unbalanced metal concentrations are used worldwide for crop cultivation. Even though plants are able to develop strategies to cope with metal stress, either metal deficiency or excess, this unbalance affects the whole plant. Chloroplasts are key organelles for organic matter synthesis and biomass production. Under metal stress, chloroplasts suffer severe alterations of their ultrastructure, associated with profound molecular and metabolic damages. These alterations are accompanied by unbalanced metal distribution in plants, in particular in edible crop organs. Toxic metals get either accumulated or there is a deficiency of nutrients, resulting in a weak nutritional value. Nonetheless, there is more and more knowledge on the functioning and regulation of metal transporters in plants. Such knowledge will allow growing crops with well-balanced metal concentrations in edible parts even on metal unbalanced soils. This review shows that almost all vital functions of chloroplasts, such as photosynthesis, CO2 fixation, nitrogen and sulfur assimilation, and protein and nucleic acid metabolism, require metals. Therefore, the uptake of essential metals is necessary for the proper functioning of chloroplasts and, in turn, for crop productivity. We describe nutrient uptake mechanisms of plants and processes that influence essential and non-essential metal concentrations in different plant organs. We present an overview of metal transporters in chloroplasts. Several questions still need to be elucidated about the uptake and the trafficking of essential and non-essential metals into and within chloroplasts. Similarly to transporters present in other cellular compartments, the carriers are often not metal-specific. Therefore, essential and non-essential metals may compete for carriers. As a result, unbalanced soil metal concentrations can be reflected in the plants and in the chloroplasts. Metal deficiency or excess causes reduced growth and decreased productivity of crops. It can lead to human malnutrition. Several complex physiological processes can be responsible for the reduced biomass observed in plants with unbalanced metal concentration. In this review, we have focused on the structural and functional alterations of chloroplasts under metal deficiency or excess. Interestingly, besides specific differences, our data indicate several similarities in the response of chloroplasts to metal deficiency or excess. Indeed, oxidative stress and several ultrastructural alterations, e.g., increase in the number and size of plastoglobuli, disorganized grana and disturbed thylakoids, and swelling of the intrathylakoidal space, are observed in both cases. This indicates that changes in chloroplast ion homeostasis rather than the specific effect of a metal are responsible for decreased plant productivity. Therefore, sustainable agriculture has to take into consideration solutions that enable undisturbed metal and ion homeostasis in chloroplasts of crop plants grown even in soils with unbalanced metal concentrations.

Activity of the photosynthetic apparatus and antioxidant enzymes in leaves of transgenic Solanum lycopersicum and Nicotiana tabacum plants, with FeSOD1 gene

Introduction of the FeSOD gene enhanced the stability of the photosynthetic apparatus of plants to the action of oxidative stress caused by UV irradiation. The expression of Arabidopsis thaliana FeSOD gene, targeting the enzyme in chloroplasts due to a signal sequence, leaded to significant changes in ultrastructure of cell subcompartments of tobacco and tomato leaves. The activity of superoxide dismutase in leaves of transgenic tomato plants exceeded the value of activity of this enzyme of control plants. Transgenic tobacco plants showed increasing in SOD activity compared with control non-transgenic tobacco. The activity of AP in the leaves of transgenic tobacco and tomato plants was similar with that of control non-transgenic plants, but activity of one accession of transgenic tomato, which is also characterized by high values of SOD activity, exceeded the value of control plant. Differences in ultrastructural organization of chloroplasts in the cells of transgenic and control tobacco and tomato plants have been manifested in a strong enlargement in the size of plastoglobuli. These distinctions were evident especially in the cells of the leaf parenchyma of transgenic tomato as well as transgenic tobacco. Also, a quantity of starch grains in the plastids of guard cells was increased. Chloroplasts in the cells of leaf parenchyma in transgenic plants contained less a starch grains than in wild-type plants.

Changes in chloroplast ultrastructure, fatty acid components of thylakoid membrane and chlorophyll a fluorescence transient in flag leaves of a super-high-yield hybrid rice and its parents during the reproductive stage

In plants, it is well established that chloroplast is one of the early targgeted organelles to breakdown during leaves senescing. Here we applied a newly developed super-high-yield hybrid rice ( Oryza sativa) LiangYouPeiJiu (LYPJ) and its parents lines to investigate changes in ultrastructure of chloroplasts, fatty acid composition of thylakoid membrane lipids and chlorophyll (Chl) a fluorescence transient in natural senescing leaves. We found that at full expansion of flag leaves in three lines, chloroplasts often showed oblong shapes with a typical membrane system of stroma and grana thylakoids, whereas their shapes had been changed from oblong to spherical during senescence. Our data showed that the initiation of senescence displayed accumulation of starch and an increase in the number and size of plastoglobuli with the damaged thylakoid membranes; subsequently, swollen thylakoid membranes in stroma and in grana with a significant increase in MDA content, and disorganization of thylakoid membrane system with significant changes in fatty acid composition of thylakoid membrane lipids were developed. Compared with its parents, the newly developed hybrid rice LYPJ had the highest capacity of carbohydrate transport from leaves (sources) to ears (sink), marked with the lowest accumulation of starch grains in the leaf chloroplasts, and the slowest senescing rate of chloroplast in overall leaf senescence process. Chl a fluorescence transients of three kinds of flag leaves were analyzed by so-called JIP-test. The results of analysis suggest that these findings inculding a high inherited activity of antioxidant enzymes and high photosynthetate transport to pretect chloroplast structure in the hybrid rice LYPJ have close relations to its super-high yield.

Copper and Cadmium Tolerance, Uptake and Effect on Chloroplast Ultrastructure. Studies on Salix purpurea and Phragmites australis

We have compared the effect of toxic Cu and Cd concentrations on growth, metal accumulation, and chloroplast ultrastructure of willow (Salix purpurea L.) and reed [Phragmites australis (Cav.) Trin. ex Steud.]. After a 10-day treatment, both species have tolerated to some extent the lowest concentration of both metals; however, plant growth was strongly reduced at the highest Cu and Cd concentrations. These plants could be described as Cu-tolerant at the lowest concentration tested, showing a higher tolerance index in reed than in willow; in contrast, willow exhibited higher tolerance against Cd. Both plants appeared to be moderate root accumulators of Cu and Cd. Ultrastructural studies revealed special features that can provide some protection against heavy metals stress, such as ferritin aggregates in the stroma. In addition, Cu and Cd induced distortion of thylakoids, reduction of grana stacks, as well as an increased number and size of plastoglobuli and peripheral vesicles.

Oxidative stress induced by long‐term plum pox virus infection in peach (Prunus persica)

In this study, the effect of long‐term plum pox virus (PPV) infection on the response of certain antioxidant enzymes at the subcellular level was studied in peach plants (Prunus persica (L.) Batch) (cv. GF305), which are characterized by great susceptibility to the virus. In infected plants, a decrease in the efficiency of excitation energy capture by PSII (Fv′/Fm′) was observed, which was accompanied by a decrease in non‐photochemical quenching (NPQ). p‐Hydroxy‐mercury benzoic acid (pHMB)‐insensitive ascorbate peroxidase (APX) activity (class III peroxidase) was detected in both chloroplast and soluble fractions. In soluble fractions from inoculated peaches, a significant increase in pHMB‐sensitive APX activity and a significant decrease in superoxide dismutase (SOD) activity were observed. These changes were correlated with the observations in isolated chloroplasts, where an increase in both pHMB‐sensitive and pHMB‐insensitive APX activities was observed, whereas significant decreases in SOD, monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR) activities were produced. According to these results, as a consequence of PPV infection, an oxidative stress, indicated by an increase in lipid peroxidation and protein oxidation, was produced in peach leaves, which was monitored by the diaminobenzidine (DAB) peroxidase‐coupled H2O2 probe. PPV infection produced an alteration in chloroplast ultrastructure, giving rise to dilated thylakoid membranes. PPV‐infected peach leaves showed a decreased amount of starch in chloroplasts from palisade parenchyma, as well as an increase in the number and size of plastoglobuli, in relation to control plants. The results suggest that long‐term PPV infection produces an oxidative stress, and that an antioxidative metabolism imbalance may be related to the progress of PPV infection and symptoms in peach plants.

A role for diacylglycerol acyltransferase during leaf senescence.

Lipid analysis of rosette leaves from Arabidopsis has revealed an accumulation of triacylglycerol (TAG) with advancing leaf senescence coincident with an increase in the abundance and size of plastoglobuli. The terminal step in the biosynthesis of TAG in Arabidopsis is catalyzed by diacylglycerol acyltransferase 1 (DGAT1; EC 2.3.1.20). When gel blots of RNA isolated from rosette leaves at various stages of development were probed with the Arabidopsis expressed sequence tag clone, E6B2T7, which has been annotated as DGAT1, a steep increase in DGAT1 transcript levels was evident in the senescing leaves coincident with the accumulation of TAG. The increase in DGAT1 transcript correlated temporally with enhanced levels of DGAT1 protein detected immunologically. Two lines of evidence indicated that the TAG of senescing leaves is synthesized in chloroplasts and sequesters fatty acids released from the catabolism of thylakoid galactolipids. First, TAG isolated from senescing leaves proved to be enriched in hexadecatrienoic acid (16:3) and linolenic acid (18:3), which are normally present in thylakoid galactolipids. Second, DGAT1 protein in senescing leaves was found to be associated with chloroplast membranes. These findings collectively indicate that diacylglycerol acyltransferase plays a role in senescence by sequestering fatty acids de-esterified from galactolipids into TAG. This would appear to be an intermediate step in the conversion of thylakoid fatty acids to phloem-mobile sucrose during leaf senescence.

Differences in growth, leaf senescence and injury, and stomatal density in birch ( Betula pendula Roth.) in relation to ambient levels of ozone in Finland

The differences in growth, leaf senescence, visible ozone injuries and stomatal density between one coastal site (natural ozone) and two inland sites (natural and elevated ozone) in Finland were determined for saplings of Betula pendula clones grown under open-field conditions during two growing seasons. Responses in growth, leaf senescence, visible injuries, and stomatal density were determined in relation to cumulative ozone exposure accumulated over the thresholds of 30, 40 and 50 ppb (10 9) during the exposure period. In addition, the effects of the different ozone exposures on ultrastructure of chloroplasts were studied. Increasing ozone exposure resulted in reduced shoot dry weight, stimulated (first year) or reduced (second year) height growth, accelerated autumn yellowing of leaves, increased stomatal density, visible symptoms and chloroplast injuries, and increased number and size of plastoglobuli. Newly expanded mature leaves in midsummer were more sensitive to ozone episodes than younger developing leaves in the early growing season. In most parameters, the best correlation was achieved with the exposure index AOT30. Ozone risk for birch is highest in the southern coastal area of Finland, where background ozone concentrations are higher than in inland sites.

Cell ultrastructural evidence of accelerated ageing of Norway spruce needles in industrial areas

summaryNeedle mesophyll cell ultrastructure of 1st to 9th yr needles from Norway spruce (Picea abies (L.) Karst.) trees of different ages was studied at three different sites to determine the normal features of needle ageing, and the impact of air pollution on the needle ageing process. The sites included one rural area and two industrial environments, of which one contained SO2 emissions and the other SO2 and F emissions. The ultrastuctural features of needle mesophyll cells of different ages were found to be remarkably similar when young (20‐yr‐old) and mature (> 50‐yr‐old) trees were compared. Senescence‐related ultrastructural symptoms such as increase in the number and size of plastoglobuli and an increase in the large lipid accumulations were observed with increasing needle age. In addition, the occurrence of lipid bodies in the central vacuole and an increased number of dark grains in the cell wall were detected in ageing needles. No changes in chloroplast length were observed during the ageing of needles, although the width of the chloroplasts showed a tendency to increase. A poor differentiation of granal membranes and an increase in small cytoplasmic lipid bodies and irregularly‐shaped lipid material were symptoms typical of needles in the industrial areas. The ageing symptoms appeared in younger needles and were more evident in industrial areas than at the control site, suggesting an accelerated ageing process in the industrial areas.

Salt-induced oxidative stress in chloroplasts of pea plants

The possible involvement of activated oxygen species in the mechanism of damage by NaCl strees was studied in chloroplasts from leaves of two cultivars of pea (Pisum sativum L.) with differential sensitivity to NaCl. Intact organelles were purified by centrifugation in density-gradients of Percoll. In chloroplasts from tolerant plants, NaCl stress produced a significant increase of CuZn-SOD II and ascorbate peroxidase activities as well as in ascorbate content, while in those from sensitive plants NaCl produced increases in the H2O2 content and lipid peroxidation and no changes were observed in the enzymatic activities. Chlorophyll content significantly decreased in chloroplasts from sensitive plants and chloroplast integrity was lower in sensitive than in tolerant plants. Electron microscopy showed that the thylakoidal structure of chloroplast was notably disorganized in the NaCl-treated leaves. In purified chloroplasts, an increase in the number and size of plastoglobuli was produced by NaCl in chloroplasts from tolerant plants and to a lesser extent, in chloroplasts from sensitive plants. The relative starch content only decreased in chloroplasts from tolerant plants by NaCl-treatment. Results obtained suggest that in the cellular toxicity of NaCl in pea plants, superoxide- and H2O2-mediated oxidative damage in chloroplasts may play an important role.

Cell Membrane Permeability and Ultrastructural Effects of Difenzoquat on Wild Oats (Avena fatua)

Effects of difenzoquat on wild oats grown under controlled environmental conditions were studied. Seedling height and fresh weight were significantly reduced 5 days after postemergence treatment. Dose-dependent increase in cell membrane permeability was detected after a 12-h exposure to the herbicide. Scanning electron micrographs showed normal leaf hairs and cuticular wax but swollen guard cells 10 days after treatment. Ultrastructural changes occurred before the visible symptoms. The primary effect of difenzoquat appears to be the disruption of the tonoplast and plasmalemma. The tonoplast showed greater damage than the plasmalemma. Secondary effects included damage to mitochondria and chloroplasts. Mitochondria were swollen and often ruptured, but the effect did not increase with the duration of exposure. Chloroplasts became spherical in shape, and their contents were also affected. The changes included: accumulation and then disappearance of starch granules, swelling of frets, fusion of granal thylakoids, detachment and then rupture of the outer membrane of the envelope, and clumping of ribosomes. By contrast, natural senescence caused greater injury of the plasmalemma than the tonoplast, a marked increase in size of plastoglobuli, and loss of starch grains without early accumulation.

INFLUENCE OF AGE AND MICROCLIMATE ON THE PHOTOCHEMISTRY OF RHODODENDRON MAXIMUM LEAVES II. CHLOROPLAST STRUCTURE AND PHOTOSYNTHETIC LIGHT RESPONSE

The influence of age on chloroplast structure and photosynthetic light response of Rhododendron maximum L. was studied in three different microhabitats. The three microhabitats constituted a gradient of low, intermediate, and high irradiance levels. The most dramatic change in chloroplast structure with increasing age was the proliferation of the number and size of plastoglobuli. The magnitude and age specific rate of chloroplast occlusion by plastoglobuli increased in habitats with higher irradiance. Photosynthetic responses to light differed among the age categories of leaves. Light saturated photosynthesis and quantum yield decreased as leaves aged. However, in high light environments the rate of reduction of quantum yield or light saturated photosynthetic rate was more rapid than in the low light environment. The quantity of plastoglobuli increased in association with reduced light reaction capacity. The presence and abundance of plastoglobuli in R. maximum chloroplasts and their association with reduced photosynthetic performance indicates that the photosynthetic apparatus of the R. maximum chloroplast is sensitive to photodestruction by high irradiance: commonly a winter phenomenon in these environments.

Characteristics of the Photosynthetic Apparatus of Copper Non-tolerant Spinach Exposed to Excess Copper

Summary Individual spinach plants ( Spinacia oleracea L., c.v. Matador) sensitive to excess copper were grown on a nutrient medium containing toxic amounts of the metal, and the characteristics of its photosynthetic apparatus were examined. In chloroplasts isolated from Cu-treated plants the accumulation of plastid pigments and lipoquinones was lower than in controls and it decreased with the increase of copper toxicity. The loss of photochemical activity of photosystem I and photosystem II was observed at the late stage of leaf degradation (the leaves turned yellow). The loss of photosystem II activity was faster than that of photosystem I. Consequently, changes in chlorophyll distribution of light harvesting chlorophyll-protein complexes were observed. The CPa level, being the presumable reaction center of photosystem II, decreased significantly. The fine structure of chloroplasts revealed degradation of grana stacks and stroma lamellae depending on the stage of their degeneration, an increase in the number and size of plastoglobuli and intrathylakoidal inclusions. The results obtained have been discussed with regard to direct or indirect effects of copper in chloroplasts of plants sensitive to excess copper.

The function of carotenoids during chloroplast development. V. Correlation between carotenoid content, ultrastructure and chlorophyll b to chlorophyll a ratio

The ultrastructural effect of carotenoid deficiency in wheat (Triticum aestivum L.) was studied after adding the herbicide SAN‐9789 to the growth medium. The presence of SAN‐9789 (28 mg I‐1) resulted in an almost complete absence of carotenoids. For plants grown in darkness the lack of carotenoids was accompanied by a reduction in partitions between primary thylakoids as well as a change in appearance of the plastoglobuli from small and black (osmiophilic) to large and greyish white (less osmiophilic). When plants were grown in weak red light (16 mW m‐2), the presence of SAN‐9789 also resulted in an almost complete absence of grana, a decrease in the ratio of chlorophyll b/chlorophyll a from 0.25 to 0.1, and an almost complete absence of prolamellar bodies. The greatest differences in carotenoid content, in amount of grana, in chlorophyll b/chlorophyll a ratio, and in number of prolamellar bodies, all occurred between 0.28 and 2.8 mg I‐1 of SAN‐9789. The change in appearance of plastoglobuli occurred at a lower SAN‐9789 concentration, between 0.028 and 0.28 mg I‐1. The ultrastructural responses to the SAN‐9789 treatment could be related to the effect on the carotenoid synthesis in different ways. The disappearance of thylakoid partitions was connected to a structural role of carotenoids, while the disappearance of the prolamellar bodies was dependent on the photoprotective role of carotenoids. The change in shape and size of plastoglobuli was not correlated to the presence of carotenoids. However, a connection to the accumulation of the carotenoid precursors is still possible.

Phenolic Synthesis in Relation to Chloroplast Ultrastructure in Flax Callus and Cell Suspension Cultures

Summary The distribution of phenolic compounds, chlorophyll content and enzymes of phenolic synthesis were studied in relation to the ultrastructure of chloroplasts in cotyledons, callus tissue and cell suspension cultures of the oil flax (Linum usitatissimum L.). Significant biochemical changes were observed in the cultured tissues as compared with the intact cotyledons which involved: (a) a marked decrease in the amounts of p-coumaric, caffeic and ferulic acids, as well as the chlorophyll content, and a concomitant decrease in phenolic acid/chlorophyll ratios; (b) a significant drop in the activity of enzymes of phenylpropanoid metabolism (phenylalanine ammonia-lyase, cinnamate-4-hydroxylase and caffeate-O-methyltransferase); (c) the absence of chalcone-flavanone isomerase activity and a resulting loss of potential for the synthesis of C-glycoflavones; (d) the disappearance of sinapic acid and the formation of a number of unidentified phenolic compounds. While the chloroplast ultrastructure of intact cotyledons exhibited the normal features of light-grown tissues those of the cultured tissues appeared to be partially differentiated and exhibited marked ultrastructural changes which involved: (a) the absence of starch grains and an increase in the number and size of plastoglobuli; (b) a loosely packed thylakoidal system with few lamellae and occassional granal stackings in callus-tissue chloroplasts; (c) a rather “primitive” type of chloroplast with vesiculated lamellar structure and containing phytoferritin bodies in the cultured cells. The parallelism between the biochemical modifications and the changes in chloroplast ultrastructure of callus tissues and cultured cells is discussed in relation to the possible involvement of chloroplasts in penylpropanoid and flavonoid biosynthesis in cultured flax tissues.