Fine structural quantification of drought-stressed Picea abies (L.) organelles based on 3D reconstructions

Ultrastructural investigations of cells and organelles by transmission electron microscopy (TEM) usually lead to two-dimensional information of cell structures without supplying exact quantitative data due to the limited number of investigated ultrathin sections. This can lead to misinterpretation of observed structures especially in context of their three-dimensional (3D) assembly. 3D investigations and quantitative morphometric analysis are therefore essential to get detailed information about the arrangement and the amount of subcellular structures inside a cell or organelle, respectively, especially when the plant sample was exposed to environmental stress. In the present research, serial sectioned chloroplasts, mitochondria, and peroxisomes from first year spruce needles (Picea abies (L.) Karst.) were 3D reconstructed and digitally measured using a computer-supported image analysis system in order to obtain a detailed quantitative characterization of complete cell organelles including precise morphological data of drought-induced fine structural changes. In control plants, chloroplast volume was composed of 56% stroma, 15% starch, 27% thylakoids, and 2% plastoglobules. In drought-stressed chloroplasts, the relative volume of both the thylakoids and the plastoglobules significantly increased to 37% and 12%, respectively. Chloroplasts of stressed plants differed from control plants not only in the mean thylakoid and plastoglobules content but also in the complete lack of starch grains. Mitochondria occurred in variable forms in both control and stressed samples. In stressed plants, mitochondria showed a significant smaller mean volume which was only 81% when compared with the control organelles. Peroxisomes were inconspicuous in both samples and their volume did not differ between control and drought-stressed samples. The present study shows that specific subcellular structures are subject to significant quantitative changes during drought stress of spruce needles giving a detailed insight in adaptation processes of the investigated cell organelles.     

Effects of drought and waterlogging on ultrastructure of Scots pine and Norway spruce needles

Effects of water stress on needle ultrastructure of 2-year-old Scots pine (Pinus sylvestris L.) and 5-year-old Norway spruce [Picea abies (L.) Karst.] seedlings were studied in greenhouse experiments. Drought stress was induced by leaving seedlings without watering, and waterlogging stress was produced by submerging the seedling containers in water. Needle samples for ultrastructural analyses were collected several times during the experiments, and samples for nutrient analyses at the end of the experiments. In drought stress, plasmolysis of mesophyll and transfusion parenchyma tissues, aggregation of chloroplast stroma and its separation from thylakoids and decreased size and abundance of starch grains in needles of both species were observed. The concentration of lipid bodies around the chloroplasts were detected in pine needles. Calcium and water concentrations in spruce needles were lower by the end of the experiments compared to controls. In waterlogging treatment, swelling of phloem cells in pine needles and large starch grains, slight swelling of thylakoids and increased translucency of plastoglobuli in chloroplasts of both species studied were observed. The phosphorus concentration in pine needles was higher while phosphorus, calcium and magnesium concentrations in spruce needles were lower in the waterlogging treatments compared to controls. Typical symptoms induced by drought stress, e. g. aggregation of chloroplast stroma and its separation from thylakoids, were detected, but, in waterlogging stress, ultrastructural symptoms appeared to be related to the developing nutrient imbalance of needles.     

Effect of water stress on cotton leaves : I. An electron microscopic stereological study of the palisade cells

Palisade cells from fully expanded leaves from irrigated and nonirrigated, field grown cotton (Gossypium hirsutum L. cv. Paymaster 266) were subjected to a microscopic examination to evaluate the effect of water stress on subcellular structures. The water potential difference between the two treatments was 13 bars at the time of sampling. The dimensions of the palisade cells and their density per unit leaf area were determined by light microscopy. Palisade cells from stressed plants had the same diameter, but were taller than their counterparts in irrigated plants. The density of the palisade cells was the same in both treatments as was the fractional volume of the intercellular space. It was concluded that the reduced leaf area observed in the stressed plants resulted primarily from a mitotic sensitivity to water stress. Further, expansion of palisade cells was not inhibited by the stress imposed in this study.

Morphometric analysis of electron micrographs was used to evaluate the subcellular structure of palisade cells from nonstressed and stressed plants. The fractional volumes of cell walls, total cytoplasm, chloroplasts, starch granules, intrachloroplast bodies, mitochondria, peroxisomes, and central vacuoles were determined. The surface densities of grana and stroma lamellae, outer chloroplast membranes, mitochondrial cristae, endoplasmic reticulum and Golgi cisternae were also measured. The number of chloroplasts, mitochondria, and peroxisomes were determined. These data were expressed as actual volumes, areas, and numbers per palisade cell for each treatment. Palisade cells from stressed plants had thinner cell walls, larger central vacuoles and approximately the same amount of cytoplasm compared to cells from nonstressed plants. Within the cytoplasm, stressed plants had more but smaller chloroplasts with increased grana and stroma lamellae surfaces, larger mithchondria with reduced cristae surfaces, smaller peroxisomes and reduced membrane surfaces of endoplasmic reticulum and Golgi cisternae.

     

Seasonal rhythmics of the leucoplast structure in bulb scales of Scilla sibirica L

A study was made of seasonal changes in plastids of ground tissue cells of bulb scales in early-spring ephemeroid Scilla sibirica L. In summer, plastids are represented by typical amyloplasts, with their main volume (97.0 +/- 4.3%) being occupied by one large starch grain. The volume fraction of plastid stroma is at its minimum. The stroma contains small plastoglobuli and no thylakoids. The same structure is characteristic of plastids in October. However, no starch is found in December, when some thylakoids are seen at the plastid periphery. In the early spring (March), when leaves still remain below the ground, the volume fraction of starch grains is 53.0 +/- 2.2%. In the stroma some structures superficially similar to those of microtubuli are revealed. The thylakoid system is fairly well developed, some of thylakoids being concentrically arranged. Some electron-opaque material is seen in the thylakoid lumen. Many plastids are sheathed with elements of the smooth endoplasmic reticulum. Based on the analysis of these and literature data, a conclusion is made that plastids of bulb scales not only store starch, but also seemingly participate in phytohormone biosynthesis.     

Green tissue within the haustorium of the dwarf mistletoe Korthalsella (Viscaceae). An ultrastructural comparison between chloroplasts of sucker and aerial stem tissues

Summary Korthalsella (Viscaceae) is a dwarf mistletoe attached to its host branch by a single haustorium. Plants are leafless with flattened or cylindrical stems that function in photosynthesis. When a fresh haustorium is cut the sucker within the host appears bright green. Transmission electron microscopy reveals that this greening is due to chloroplasts, but that their organization differs from those of the aerial stem. The three representatives of Korthalsella endemic to New Zealand were the main species investigated. In the stem, chloroplasts have short stacks of cylindrical grana interconnected by stroma thylakoids typical of normal chloroplasts. Sucker chloroplasts have a more variable organization, with most containing extensive granal stacks and poorly differentiated stroma thylakoids. These granal thylakoids exhibit extensive partitions formed by appression of adjacent membranes. Some sucker plastids also approach etioplasts in having a prominent prolamellar body from which radiate thylakoids with short partitions. Sucker chloroplasts usually contain a few large starch grains, plastoglobuli, and sometimes also a stroma centre. The extensive granal thylakoids in sucker chloroplasts of Korthalsella resemble that found in certain shade plants and tissue grown under low light conditions. Sucker chloroplasts probably have a low level of photosynthesis. This activity might provide a local source of osmotically active material used to assist transport between host and parasite.     

盐胁迫下芦苇叶肉细胞超微结构的研究

对青藏高原柴达木盆地柯柯盐湖边盐碱地上生长的芦苇叶肉细胞的超微结构进行了研究,并以西宁地区非盐碱地上生长的芦苇作对照。结果表明：西宁地区的芦苇叶肉细胞的叶绿体呈椭圆形,其膜系统完整,基粒片层和基质片层发育良好。在盐碱地上生长的芦苇叶肉细胞的叶绿体呈圆形,叶绿体内出现较大的淀粉粒,并发现有线粒体嵌入叶绿体的现象。叶绿体的类囊体膨大,线粒体的嵴也有膨大的现象。在盐湖水中生长的芦苇叶肉细胞,叶绿体的类囊体排列紊乱、扭曲、松散。类囊体膜局部被破坏,部分类囊体膜解体,空泡化,甚至消失,一些溶解了的类囊体流进细胞质中。综上所述,芦苇叶肉细胞超微结构的变化是该植物适应柯柯盐湖地区盐渍、低温、低气压、强辐射等环境因子的结果。     

Effect of Doubled-CO2 Concentration on the Ultrastructure of Chloroplasts from Medicago sativa and Setaria italica

It has been reported in quite a number of literatures that doubled CO2 concentration increased the photosynthetic rate and dry matter production of C3 plants, but substantially affected C4 plants little. However, why may CO2 enrichment promote growth and either no change or decrease reproductive allocation of the C3 species, but havinag no effects on growth characteristics of the C4 plants? So far, there has been no satisfactory explanation on that mentioned above, except the differences in their CO2 compensatory points. In the past, although some studies on ultrastructure of the chloroplasts under doubled CO2 concentration were limitedly conducted. Almost all the relevant experimental materials were only from C3 plants not from C4 plants, and even though the results were of inconsistancy. Thereby, it needs to verify whether the differences in photosynthesis of C3 and C4 plants at doubled CO2 level is caused by the difference in their chloroplast deterioration. Experiments to this subject were conducted at the Botanical Garden of Institute of Botany, Academia Sinica in 1993 and 1994. Both experimental materials from C3 plant alfalfa (Medicago sativa) and C4 plant foxtail millet (Setaria italica) were cultivated in the cylindrical open-top chambers (2.2 m in diameter × 2.4 m in height) with aluminum frames covered by polyethylene film. Natural air or air with 350× 10-6 CO2 were blown from the bottom of the chamber space with constant temperature between inside and outside of the chamber 〈0.2℃〉. Electron microscopic observation revealed that the ultrastructure of the chloroplasts from C3 plant Medicago sativa and C4 plant Seteria italica growing under the same doubled CO2 concentration were quite different from each other. The differential characteristics in ultrastructure of chloro plasts displayed mainly in the configuration of thylakoid membrances and the accumulation of starch grains. They were as follows: 1. The most striking feature was the building up of starch grains in the chloroplasts of the bundle sheath cells (BSCs) and the mesophyll cells (MCs) at doubled CO2 concentra tion. The starch grains appeared centrifugally first in the BSCs and then in the chloroplast of the other MCs. It was worthy to note that the starch grains in the chloroplasts of C4 plant Setaria ira/ica were much more than those of the C3 plant Medicago sativa . The decline of photosynthesis in the doubled CO2-grown C4 plants might be caused by an over accumulation of starch grains, that deformed the chloroplast even demaged the stroma thylakoids and grana. There might exsist a correlation between the comformation of thylakoid system and starch grain accumulation, namely conversion and transfer of starch need energy from ATP, and coupling factor (CF) for ATP formation distributed mainly on protoplastic surface (PSu) of stroma thylakoid membranes, as well as end and margin membranes of grana thylakoids. Thereby, these results could provide a conclusive evidence for the reason of non effectiveness on growth characteristics of C4 plant. 2. Under normal condition , the mature chlolroplats of higher plants usually develop complete and regularly arranged photosynthetic membrane systems . Chloroplasts from the C4 plant Setaria italica, however, exerted significant changes on stacking degree, grana width and stroma thylakoid length under doubled CO2 concentration; In these changes, the grana stacks were smaller and more numerous, and the number of thylakoids per granum was greatly increased, and the stroma thylakoid was greatly lengthened as compared to those of the control chloroplasts. But the grana were mutually intertwined by stroma thylakoid. The integrity of some of the grana were damaged due to the augmentation of the intrathylakoid space . Similarly, the stroma thylakoids were also expanded. In case. the plant was seriously effected by doubled CO2 concentration as observed in C4 plant Setaria italica , its chloroplasts contained merely the stroma (matrix) with abundant starch grains, while grana and stroma thylakoid membranes were unrecognizable, or occasionally a few residuous pieces of thylakoid membranes could be visualized, leaving a situation which appeared likely to be chloroplast deterioration. However, under the same condition the C3 plant Medicago sativa possessed normally developed chloroplasts, with intact grana and stroma thylakoid membranes. Its chloroplasts contained grana intertwined with stroma thylakoid membranes, and increased in stacking degree and granum width, in spite of more accumulated starch grains within the chloroplasts. These configuration changes of the thylakoid system were in consistant with the results of the authors another study on chloroplast function, viz. the increased capacity of chloroplasts for light absorption and efficiency of PSⅡ.     

Plastid differentiation during androgenesis in albino and non-albino producing cultivars of barley (Hordeum vulgare L.)

In order to better understand androgenic albinism in barley, we compared plastid differentiation during anther culture in two cultivars, an albino (spring cultivar Cork) and a non-albino (winter cultivar Igri) producing cultivar. The ultrastructure of plastids and the relative amount of DNA containing plastids were followed in both cultivars during the androgenic process and correlated with the proportion of regenerated chlorophyllous plantlets. For androgenesis, anthers were collected at the uninucleate stage, during mid- or late-microspore vacuolation. At this stage DNA was detected in 15.3 ± 2. 7% of microspore plastid sections in the winter cultivar Igri, compared to 1.7 ± 0.5% in the spring cultivar Cork. In the winter cultivar Igri, starch was broken down after anther pretreatment but plastids divided rapidly during anther culture and thylakoids developed in the stroma. Prior to regeneration, plastids contained 2.0 ± 0.2 thylakoids per plastid and starch represented 26.1 ± 3.3% of the plastid volume. In the spring cultivar Cork, plastids followed a different developmental pathway. After anther pretreatment, microspore plastids differentiated exclusively into amyloplasts, accumulating starch and losing their thylakoids as well as their capacity to divide. This developmental pattern became progressively more marked, so that by the end of anther culture plastids contained 0.5 ± 0.4 thylakoids per plastid and starch represented up to 90.3 ± 4.3% of plastid volume. Following androgenesis, the response was similar in both cultivars except that the winter cultivar Igri provided 87.8% of chlorophyllous plantlets compared to 99.7% albino plantlets in the cultivar Cork. The results presented here suggest that the exclusive regeneration of albino plantlets in the spring cultivar Cork may be due to degradation of microspore plastid DNA during early pollen development, preventing the plastids from differentiating into chloroplasts under culture conditions. Received: 13 March 2000 / Revision accepted: 6 June 2000     

Ultrastructural changes of radish leaf exposed to cadmium

Cadmium (Cd²⁺) is one of the most toxic heavy metal pollutants in nature. Mesophyll cells from the leaf of radish seedlings exposed to 0.25 and 1.0 mM of CdCl₂ during 24 h exhibited structural changes of chloroplasts, mitochondria and nuclei when compared to non-treated control plants. Chloroplasts from Cd²⁺-exposed samples exhibited changes in the organelle shape, an increase in the stroma volume and a deposition of electron-dense material in the double membrane. The changes in the chloroplast membranes were not very drastic, however and reorganization of the thylakoids and stroma was observed. In contrast, the breakdown of the nuclear envelope of the plant cells treated with Cd²⁺ was very clear. The accumulation of electron-dense granules was also observed in mitochondria. No alterations were observed in the vacuoles of radish seedlings grown at different Cd²⁺ concentrations for the periods tested.     

Drought-induced male sterility in rice: Changes in carbohydrate levels and enzyme activities associated with the inhibition of starch accumulation in pollen

Male reproductive development of rice (Oryza sativa L.) is very sensitive to drought. A brief, transitory episode of water stress during meiosis in pollen mother cells of rice grown under controlled environmental conditions induced pollen sterility. Anthers containing sterile pollen were smaller, thinner, and often deformed compared to normal anthers of well-watered plants. Only about 20% of the fully developed florets in stressed plants produced grains, compared to 90% in well-watered controls. Water stress treatments after meiosis were progressively less damaging. Levels of starch and sugars and activities of key enzymes involved in sucrose cleavage and starch synthesis were analyzed in anthers collected at various developmental stages from plants briefly stressed during meiosis and then re-watered. Normal starch accumulation during pollen development was strongly inhibited in stress-affected anthers. During the period of stress, both reducing and non-reducing sugars accumulated in anthers. After the relief of stress, reducing sugar levels fell somewhat below those in controls, but levels of non-reducing sugars remained higher than in controls. Activities of acid invertase and soluble starch synthase in stressed anthers were lower than in controls at comparable stages throughout development, during as well as after stress. Stress had no immediate effect on ADP-glucose pyrophosphorylase activity, but had an inhibitory aftereffect throughout post-stress development. Sucrose synthase activity, which was, relatively speaking, much lower than acid invertase activity, was only slightly suppressed by stress. The results show that it is unlikely that pollen sterility, or the attendant inhibition of starch accumulation, in water-stressed rice plants are caused by carbohydrate starvation per se. Instead, an impairment of enzymes of sugar metabolism and starch synthesis may be among the potential causes of this failure.     

Ultrastructure Changes Induced by Stem Nematodes in Hypocotyl Tissue of Alfalfa

Scarified seeds of Medicago sativa L. ''Ranger'' and ''Lahontan'' alfalfa were allowed to imbibe water for 36 hr and then were inoculated with stem nematodes, Ditylenchus dipsaci Kühn. Seedlings were grown in sterilized Provo sand at 20 C and hypocotyl sections harvested at 1, 3 and 7 days. Evidence from electron micrographs indicated that cells of noninfected control plants contained normally developing chloroplasts bearing stroma, thylakoids, starch grains and plastoglobuli. The cytoplasm contained a nucleus, endoplasmic reticulum, vacuoles, mitochondria, ribosomes and dictyosomes. No morphological symptoms of nematode infection were observed in infected plants of either Ranger of Lahontan alfalfa 1 day after inoculation. Electron micrographs of tissue from the infected plants, however, indicated more osmiophilic bodies (lipid bodies) per cell than did the noninfected control, with more lipid bodies present in Ranger than in Lahontan. Three and 7 days after planting, swollen hypocotyls could be seen; the degree of swelling was greater in Ranger than in Lahontan. Electron micrographs of infected tissues indicated that both cultivars were undergoing the same kind of damage. Injured organelles were endoplasmic reticulum, chloroplasts and the nucleus. Histochemical staining indicated no changes in the middle lamellae.     

Ultrastructure of amyloplasts and intercellular transport of old and new scales inFritillaria ussuriensis

Amyloplast structure and intercellular transport in old and new scales ofFritillaria ussuriensis were observed by means of electron microscope. Most amyloplasts in old scales contained one starch grain, which was constructed by the layered deposition of starch around the hilum. Membrane systems and stroma of amyloplasts were pushed aside to form a shell surrounding the starch grain. In contrast, amyloplast shells in new scales contained a relatively light stroma and few internal membranes that were not organized into grana and stroma thylakoids. Active intercellular transport was observed in both new and old scales. Encytosis and exocytosis were common in the cell membrane and produced many vesicles containing numerous particles and filaments. These results lay the foundation for the further study on the mechanisms of growth and development in     

Chloroplast ultrastructure in leaves of tobacco plants with the introduced gene for the acyl-lipid Δ9-desaturase from <Emphasis Type="Italic">Synechococcus vulcanus</Emphasis> at normal and low temperature

Ultrastructural changes in chloroplasts of tobacco plants (Nicotiana tabacum L.) with the introduced desC gene for the acyl-lipid Δ9-desaturase from the thermophilic cyanobacterium Synechococcus vulcanus were investigated during plant acclimation to cold. Control plants were transformed with an empty pGA482 binary vector. At optimum growth temperature, a decreased number of grana and thylakoids and an increased number of plastoglobules and their larger area were observed in transgenic plants when compared to control ones. In control plants, acclimation to cold (6 days at 10°C) resulted in the larger areas of chloroplasts and grana. These changes indicated starting cold-induced injuries manifested in swelling of the stroma and a slight decrease in the total number of thylakoids in the chloroplast. In contrast, transgenic plants responded to cold by reducing the chloroplast, granal, and plastoglobule areas. Meantime, the number of thylakoids per granum increased noticeably. The total number of thylakoids in the chloroplast increased from 123 to 203. It was concluded that expression of the acyl-lipid Δ9-desaturase gene in tobacco plants provided for the formation of the cell ultrastructure similar to one characteristic of cold-tolerant plants.     

The ultrastructure of micropropagated and greenhouse rose plant stomata

Stomata of leaves from in vitro grown rose plantlets remain opened in the dark. The ultrastructure of their guard cells was studied after a 7 h light and a 7 h dark period, and compared to that of functional stomata from plants which have been acclimatized to greenhouse conditions. Qualitative and quantitative observations concerning the shape of the guard cells, mitochondria, plastids and starch grains, demonstrated the similarity in guard cell ultrastructure. The peculiarity of guard cell ultrastructure of in vitro cultured plants was the inability to close in the dark; vacuolar area was 40% of the whole guard cell area during both light and dark period whereas, in guard cells from greenhouse plants, the vacuolar area was 40% of the whole guard cell area during the light and only 25% during the dark period. These results indicate that stomata from in vitro plants are duly developed and possess an ultrastructure suitable for a typical functioning. The inability to close in the dark results from atypical water relation.     

Subcellular volumes and metabolite concentrations in barley leaves

Metabolite concentrations in subcellular compartments from mature barley (Hordeum vulgare L. cv. Apex) leaves after 9 h of illumination and 5 h of darkness were determined by nonaqueous fractionation and by the stereological evaluation of cellular and subcellular volumes from light and electron micrographs. Twenty one-day-old primary leaves of barley with a total leaf volume of 902 μL per mg chlorophyll were found to be composed of 27% epidermis, 42% mesophyll cells, 6% veins, 4.5% apoplast and 23% gas space. While in epidermal cells 99% of the volume was occupied by the vacuole, mesophyll cells with an average volume of 31.3 pL consisted of 23 pL (73%) vacuole, 4.6 pL (19%) chloroplasts, 2.06 pL (6,7%) cytosol (including smaller organelles and vesicles), 0.34 pL (1%) mitochondria and 107 fL (0.34%) nucleus. The differences between leaves harvested after 9 h of illumination and after 5 h of darkness were in the size of the stromal compartment and the starch grains therein. Subcellular metabolite concentrations were calculated from the compartmental volumes and metabolite contents of the compartments as determined by nonaqueous fractionation. The amino-acid concentrations in stroma and cytosol were rather similar after 9 h of illumination and 5 h of darkness. In contrast, the vacuolar amino-acid concentrations were about one order of magnitude lower than the stroma and cytosol values, and there was a slight increase in concentration after 5 h of darkness.     

Immunocytolocalization of CDSP 32 and CDSP 34, two chloroplastic drought-induced stress proteins in Solanum tuberosum plants

Two chloroplastic proteins, named CDSP 32 and CDSP 34 for chloroplastic drought-induced stress protein of 32 and 34 kDa, were previously shown to be substantially synthesized in Solanum tuberosum plants subjected to water deficit. We investigated the localization of CDSPs in leaf chloroplasts from control and wilted potato plants using immunocytochemistry. Observation of electron micrographs did not reveal any important change in plastid structures of drought-stressed plants, except an increased number and a larger size of plastoglobuli. In well-watered plants, very little labeling corresponding to CDSP 32 was detected. Consecutively to water stress, a higher abundance of CDSP 32 was revealed, the protein being exclusively localized in the stroma. Immunocytochemical data indicated the presence of some CDSP 34 protein in well-watered plants and confirmed its accumulation upon water deficit. CDSP 34 was found to be preferentially associated with stromal lamellae thylakoids, but some protein was revealed in the stroma. No association of CDSP 34 with grana and plastoglobuli was noticed in chloroplasts from control and stressed plants.     

The effect of isoproturon on root growth and ultrastructure of the photosynthetic apparatus of two wheat cultivars and a weed

The effect of isoproturon [N,N-dimethyl N'4-(1-methyl-ethyl) phenyl urea] on the germination, growth of root and ultrastructure of the photosynthetic apparatus was investigated in two wheat cultivars ( Triticum sativum L. cvs Castan and Esquilache) and a weed ( Lolium rigidum Gaud.). No inhibition of germination was apparent in any of the three plants studied. The inhibition of root growth was considerably significant, especially in cv. Esquilache. After 48 h treatment with isoproturon (340 μ M ), the chloroplasts of the two wheat cultivars were found to be similar, showing a higher number of grana with fewer thylakoids per granum (lower stacking degree), broader grana stacks than in the control and an absence of starch. However, after 60 h of treatment, swelling of the thylakoids occurred in the Esquilache cultivar.
The rye grass was the most affected by the herbicide; at low concentration (3.4 μ M ) the number and size of the grana decreased considerably and the stroma thylakoids were destroyed. At higher concentration (17 μ M ), there was a strong accumulation in certain areas of the stroma of a substance with a lipid-like appearance, probably derived from the disintegrating thylakoids. At the same concentrations some chloroplast envelopes were completely desintegrated.
The Hill reaction of the three plants exhibited a similar sensitivity towards the herbicide.     

Ultrastructural and Morphological Characteristics of Cultivated Wheat Growing on Copper-Polluted Fields

A cultivated Greek variety of wheat (Triticum aestivum L. cv. Vergina) growing in fields naturally polluted by outcrops of copper ores was investigated. Wheat plants show a negative response to increasing quantities of soil copper, including reduced growth and chlorosis. Copper toxicity was demonstrated in the laboratory by a rooting test; the frequency of mitoses declines sharply with increasing copper concentration in the nutrient solution. The mesophyll cells of polluted plants display a circular shape (in transverse sections) with a few chloroplasts parietally distributed, in contrast with the elongate or pleomorphic shape of control leaves that contain numerous chloroplasts crowded at the cell periphery. Ultrastructurally, the chloroplasts of polluted plants contain a poorly developed internal membrane system consisting of thylakoids arranged parallel to each other with only a few, rudimentary grana. In addition, a number of statistically significant differences were found, including the number of starch grains and plastoglobuli, chloroplast surface area, volume fraction of starch grains and, most important, the volume fraction of the internal membrane system. All ultrastructural changes are attributed to the toxic effect of high concentrations of soil copper.     

EFFECT OF SHORT-TERM SHADING ON THE CYTOLOGY OF PALISADE TISSUE IN MATURE LEAVES OF THE SUNFLOWER HELIANTHUS ANNUUS

Mature sunflower leaves were exposed to partial shading (35 or 14% of normal sun) or darkness (0% of normal sun) for approximately 8 hr. During this period one-half of each test leaf was shaded; the other half was used as a normal sun control. Palisade cell structure from both halves of each leaf was compared. Shading of leaves had little effect on organelle percent volume values (V_v) with exception of the starch compartment which decreased as shading increased. The surface to volume ratio (S_v) of the chloroplast thylakoids increased while the S_v of the mitochondrial membranes decreased as shading increased. Palisade cell volume did not change in shaded portions of the leaf, except in the fully shaded (dark) tissues where cell volume decreased. Changes in the actual volume of organelle compartments were strongly correlated with changes in cell volume. Thus a general osmotic response may account for some of the volume changes associated with differences in light intensity. Shading increased thylakoid surface areas 10–30% over the full sun controls. The ratio of stromal to granal thylakoid surface area remained constant in both the control and partially shaded samples. However, in darkened samples this ratio decreased as stromal membranes increased more than granal membranes. Changes observed in thylakoid surface areas associated with shading did not support thylakoid models which propose the interconversion of granal membranes to stromal membranes and vice versa.     

Ultrastructural aspects of kranz anatomy inDigitaria sanguinalis andSetaria viridis (poaceae)

Structural differentiation of Kranz anatomy has been investigated in leaf cross sections of two C-4 Poaceae:Digitaria sanguinalis andSetaria viridis. The study mainly focused on cellular and interfacial features of bundle sheath (BS) and mesophyll (MS) cells of the C-4 structure. Prominent BS, spaced by only two MS cells apart, were surrounded concentrically by a layer of MS cells. BS cells ofS. viridis had centrifugally arranged relatively large chloroplasts containing much starch, but the chloroplasts had agrana to rudimentary grana. Structural and size dimorphisms, when starch was present, were detected between BS and MS chloroplasts. Loosely arranged MS cells had peripherally displaced smaller chloroplasts containing little to none starch. BS chloroplasts ofD. sanguinalis were similar to those ofS. viridis, but had very little starch and well-developed long agranal stroma lamella. Features of MS cells were similar in both species, but well-defined peripheral reticulum (PR) was easily recognized in MS chloroplasts ofS. viridis. Virtually no PR was developed in BS chloroplasts examined. BS cells contained more mitochondria and microbodies, but no structural dimorphism was noticed. The electron-dense suberized lamella were often observed between BS and MS cells, especially in the primary wall of BS cells. It was most frequently found at the BS and MS cell interfaces and terminated in radial walls of the adjacent BS cells. Prominent pits with plasmodesmata (pd) were seen in the walls of both cells. There also were numerous pd in outer tangential walls of the BS cells. The number of pd ranged from 20 to 60. The pd trasversed a segment of cell wall much thinner than the adjacent wall. The current cellular data have been compared to the ultrastructural features known in leaves of other C-4 plants, especially NADP-ME species.