Testis Development and Ultrastructural Features During Spermatogenesis in Cultured Small Yellow Croaker,Larimichthys polyactis

The small yellow croaker Larimichthys polyactis is an economically important marine fish in Northeast Asia.Currently,its natural resources are threatened by overfishing and environmental pollution.Therefore,research on the reproductive system of the fish is crucial.Here,we studied the testis development and ultrastructural features of spermatogenesis in cultured L.polyactis using anatomical,histological,and ultrastructural techniques.A pair of testes,consisting of a central sperm duct and radial seminiferous lobules,were observed.The reproduction cycle of testes can be divided into stages I–VI.March to May was confirmed as the breeding season for male L.polyactis,while April is the ideal period for artificial breeding.The male L.polyactis can attain sexual maturity within 1 year.The spermatogenesis of L.polyactis comprised spermatogonium,spermatocyte,spermatid,and mature spermatozoon.The morphology of spermatogenic cells changed obviously during spermiogenesis,including nuclear shaping,midpiece and flagellum formation.The mature sperms consist of an ellipsoidal head,a short midpiece,and a long flagellum.The anterior of the head with a kidney-shaped nucleus can be distinguished.The midpiece is located posterior to the head and includes four to six spherical mitochondria.The flagellum has irregular lateral fins.The testis of L.polyactis is an unrestricted lobular type,with cystic spermatogenesis,type II spermiogenesis,and type II spermatozoa.These features are highly similar to those of other Sciaenid species.Our findings provide useful insights into the mechanism underlying testis development and spermatogenesis of L.polyactis,which can facilitate the artificial breeding of this species.

Physiology and Ultrastructure of Azolla imbricata as Affected by Hg 2+ and Cd 2+ Toxicity

The toxic effects of different gradient concentrations of Hg2+ and Cd2+ on chlorophyll content, chlorophyll a/b value, photosynthetic O-2 evolution, respiration rate, anti-oxidase system (superoxide dismulase (SOD), catalase (CAT), peroxidase (POD)) and ultrastructure of the cells of Azolla imbricata (Roxb.) Nakai were studied. The results showed that with Hg2+ and Cd2+ increase, chlorophyll content and chlorophyll a/b value, photosynthetic O-2 evolution decreased drastically; respiration rate peaked at 2 mg/L pollutant and declined afterwards. The activities of SOD, CAT and POD increased first and decreased afterwards except the activity of POD, which decreased with the increasing of Cd2+ concentration. Ultrastructural observation showed that the extent of ultrastructural damage was much more serious with higher pollutant concentration and longer time of stress. This resulted in swelling of chloroplast, disruption and disappearance of chloroplast membrane and disintegration of chloroplasts; swelling of cristae of mitochondria, deformation and vacuolization of mitochondria; condensation of chromatin in nucleus, dispersion of nucleolus and disruption of nuclear membrane. The experimental results showed: (1) Hg2+ and Cd2+ pollution not only destroyed physiological activities, but also caused irreversible damage to its ultrastructure, thus leading the cells to death; (2) With increase in the stress of Hg2+ and Cd2+, ultrastructural damage was related to the changes of plant physiology; (3) The toxic symptoms of plant showed an evident correlation between dose and effect; (4) The toxicity of Cd2+ on A. imbricata is heavier than that of Hg2+ under the same treatment time and concentration. The lethal concentration of Hg2+ to A. imbricata ranged from 3.5 to 4 mg/L, and that of Cd2+ ranged from 3 to 3.5 mg/L. The damage of cell ultrastructure on Anabaena azollae Strasburger was observed. The results indicated that tolerance of Azolla imbricata for Hg2+ and Cd2+ was higher than that of A. imbricata.

Ultrastructural Study of Secondary Wall Formation in the Stem Fiber of Phyllostachys pubescens

Ultrastructural changes in secondary wall formation of Phyllostachys pubescens Mazel fiber were investigated with transmission electron microscopy. Fiber developed initially with the elongation of cells containing ribosomes, mitochondria and Golgi bodies in the dense cytoplasm. During the wall thickening, the number of rough endoplasmic reticulum and Golgi bodies increased apparently. There were two kinds of Golgi vesicles, together with the ones from endoplasmic reticulum formed transport vesicles. Many microtubules were arranged parallel to the long axis of the cell adjacent to the plasmalemma. Along with the further development of fiber, polylamellate structure of the secondary wall appeared, with concurrent agglutination of chromatin in the nucleus, swelling and disintegration of organelles, while cortical microtubules were still arranged neatly against the inner side of plasmalemma. Lomasomes could be observed between the wall and plasmalemma. The results indicated that the organelles, such as Golgi bodies together with small vesicles, rough endoplasmic reticulum and lomasomes, played the key role in the thickening and lignification of the secondary wall of bamboo fiber, though cortical microtubules were correlative with the process as well.

Development and Ultrastructure of the Phloem Ganglion in Bamboo Node

The development, cytological characters and ultrastructure of phloem ganglion in the nodal region of Phyllostachys edulis (Carr.) H. de Lehaie, a most economically important bamboo, were investigated and the possible physiological function of this special structure was proposed. The phloem ganglion derived directly from procambium is situated at the sites where the vascular bundle forks and is present in pairs. The phloem ganglion is spindle_like in appearance and usually consists of 4 to 6 layers. Two kinds of cells in the ganglion could be distinguished. In the middle, there are two layers of filiform cells with pointed ends so that there are no normal sieve plates. Nevertheless, there are many pits on the lateral wall of the filiform cells. The other type of cells located at both ends of the spindle which possess an intermediate form between the filiform cell and the normal sieve tube. The walls of these cells towards the filiform cells are strongly convex forming a special sieve plate. Ultrastructure study showed that cells in the ganglion are connected by enriched plasmodesma. During early differentiation, the paramural body and the ingrowth of cell wall could be observed. It indicates that the cells of phloem ganglion have the character of transfer cells. The organelles in the mature cells are mainly plastids with abundant accumulation of proteins of crystalline structure. The above_mentioned results suggest that the physiological function of the phloem ganglion is closely related with substance transport.

Ultrastructure of Epidermis and Flesh of the Developing Apple Fruit

The ultrastructure of the epidermis and flesh of apple ( Malus domestica Borkh cv. Red Fuji) fruit was systematically observed during the fruit development via transmission electron microscopy. The results showed that, in spite of the ultrastructural changes in many aspects of the developing fruit epidermal cells, it remained almost unchanged throughout the whole developmental process that the cytoplasm was filled with numerous endoplasmic reticula (ER). Most of these endoplasmic reticula were tube_like and rough_ER with enlarged cisterna from which many vesicles were produced. Some of the vesicles were shown to merge into vacuole. Some dynamic Golgi bodies were also found. All the ultrastructural characteristics showed that the epidermal cells have the features of excretory cells. The ultrastructure of the fruit flesh cells at the young fruit stage were shown to be metabolically active, characterized by the presence of numerous clustered plasmodesmata, cisterna enlarged_ and rough_ER filling the cytoplasm, plenty of vesicles and Golgi bodies, indicating their dynamic cellular transport function. Some giant_circular rough_ERs were found. All the ultrastructural features at this early developmental stage should be closely associated with the enlargement of the young fruit. At the rapid growing phase of the fruit the main changes were characterized by: the starch grain_filled amyloplasts, furcating of the single orifice of plasmodesmata, and the cytoplasm enrichment of both the Golgi body_formed vesicles and other vesicles. These features correspond well with those of a photoassimilate sink_cell. An ultrastructural degeneration phenomenon was observed at the fruit ripening stage, but the mitochondria and plasmalemma still remained intact, which might be related to the continuous development of fruit quality during the fruit ripening.

Ultrastructural Changes of Scolex on Cysticercus pisiformis during Relative Rest and Motion States

[Objective] This study aimed to research the ultra-morphological changes of scolex of Cysticercus pisiformis during the relative rest and motion states. [Method] The ultrastructure changes of scolex located in cyst and evaginated from cyst after cultivation were comparatively observed by scanning electron microscope. [Result] When the scolex was in the relative rest state, observed from the top, the rostel um with the tegument muscular column that connected to tooth-hook looked like the umbrel a and covered on the front end of the scolex. Viewed from the side of the scolex, the tooth-hook on the rostel um looked like the antler branch and had only one row. Four suckers looked like cavities, and were located in the back of the rostel um and distributed around the scolex in the equidistance. When the scolex was in the motion states, the tegument muscular column on the rostel um contracted, the antler-like tooth-hook extended to periphery, and the sucker also made the ring-like and longitudinal-like contraction. [Conclusion] Ultrastructure of the scolex of C. pisiformis changed apparently during relative rest and motion states. Those changes help scolex to invade the host tissue.

Ultrastructure of the Multicellular Nodules in Hypericum perforatum Leaves

With the development of the multicellular nodules in the leaves of Hypericum per plastids increased both in number and volume, and some plastids degenerated and were surrounded by dark tubular elements and vesicles. Some vesicles fused with vacuoles and secreted substances into vacuoles. There are many multivesicles, multimembrane structures and osmiophilic droplets in vacuoles of nodule cells. Meanwhile, dictyosome secreted vesicles into the vacuoles. However, there is a large central vacuole completely filled with secretory materials (hypericin) in matured multicellular nodules. This suggests that the osmiophilic droplets may be a precursor of hypericin originated from the degenerated plastids. There were abundant endoplasmic reticulums and dictyosomes between the plastids and osmiophilic droplets, suggesting that they may be involved in the synthesis and/or transport of the precursor of hypericin.

Ultrastructure of Oogenesis in Osmunda cinnamomea var. asiatica

The ultrastructure of oogenesis in the fern Osmunda cinnamomea L. var. asiatica Fernald has been studied by electron microscopy. During oogenesis, numerous vesicles not only moved towards the periphery, but also were arranged in line along the inside of plasmalemma, and in addition aggregated outside the plasmalemma by exocytosis. They released or excreted osmiophilic material. It was observed that a few vesicles containing lamellar osmiophilic material situated closely along the plasmalemma, seemed to break open. Simultaneously, a separation cavity between egg cell and archegonium wall formed. Its width was broader than the other advanced ferns reported previously, and an extra egg membrane occurred outside around the plasmalemma of the egg, its thickness being greater than in Pteridium and Dryopteris. Amyloplasts around the nucleus were filled with large triangular semicircular or subelliptical starch grains, but as the egg matured they progressively decreased. Nucleus was large and flattened, and paired membrane in two to three couples laid within the nucleus, close and parallel to the nuclear membrane. No nuclear evagination was observed. Mitochondria seemed to have been undeveloped, but finally recovered normally.

Ultrastructural Studies on the Sieve Elements in Root Protophleom of Arabidopsis thaliana

The ultrastructures of the root protophleom sieve element at different developmental stages of Arabidopsis thaliana L. were investigated using the technique of high pressure freezing and freeze substitution fixing specimen. The results show that in the development of the sieve elements, the nuclei undergo typical characteristics of the programmed cell death (PCD): the nuclear envelopes form emboli, the chromatin condenses and aggregates towards the nuclear envelope, which degrades and fully disappears later. Before the nucleus degradation, neither the nuclear envelope undulation, nucleus lobe nor marked dilation (or bleb) of perinuclear space could be observed. In the cytoplasm of the mature sieve element, there are starch-like granules separately sheathed with a layer of membrane and usually with mitochondria around. These gnanules seem to provide substrates to mitochondria in their function. Small vacuoles originate from endoplasmic reticulum (ER), and no bigger vacuole was found.

Ultrastructure of the Blepharoplast and the Multilayered Structure in Spermatogenesis in Osmunda cinnamomea var. asiatica

The ultrastructure of the blepharoplast and the multilayered structure (MLS) in the fern Osmunda cinnamomea var. asiatica Fernald have been studied by electron microscopy with respect to spermatogenesis. The blepharoplast appears in the young spermatid. The differentiating blepharoplast is approximately a spherical body, which is composed of densely stained granular material in the center and some cylinders outside of it. The differentiated blepharoplast is also a sphere, but without the densely stained material in the center, consisting of scattered or radially arranged cylinders. The MLS seen in the spermatid lies between the basal bodies and the giant mitochondrion. In the early developmental stage, the MLS only consists of lamellar layers, each of which runs parallel to one another and forms a strip. In the mid stage, the MLS is composed of the microtubular ribbon (MTr), the lamellar layers and a layer of plaque. In the late stage, the MLS forms accessory band, osmiophilic crest and a layer of osmiophilic material. The MTr grows out from the MLS and extends along the surface of the nucleus to unite with the nuclear envelope in a complex. The basal body coming from the cylinder produces the axoneme of the flagella in the distal end and the wedge-shaped structure in the proximal end, respectively. In the present study, the ultrastructural features of blepharoplast and the MLS of the protoleptosporangiopsida fern, O. cinnamomea var. asiatica, have been described and compared with those of other kinds of pteridophytes in detail. The lamellar layers appearing before the formation of the MTr was found and reported for the first time.

ULTRASTRUCTURE OF THE VEGETATIVE CELLS OF NOSTOC FLAGELLIFORME PREPARED WITH HIGH PRESSURE FREEZING AND FREEZE SUBSTITUTION TECHNIQUE

The ultrastructure of the vegetative cells of Nostoc flagelliforme Born. et Flah. was investigated with high pressure freezing and freeze substitution technique and compared with the results obtained by using conventional preparation methods. During the processes of chemical fixation, dehydration and embedding, the cell structures might be more artificially modified than that obtained from high pressure freezing and freeze substitution. With the present method, the sheath of N. flagelliforme could be well penetrated and no extra big space could exist between the cell and the sheath. The cell protoplasm rarely shrinked. Some fine structures of cell inclusions and unit membranes became visualized. Many bacteria were harbored in the sheath. In addition, the presence of big vacuoles in the cell of N. flagelliforme as well as the presence of bacteria in the sheath shown in the present preparation for cyanobacteria has not been described so far in the literature.

Effects of CO_2 Enrichment on Microstructure and Ultrastructure of Two Species of Freshwater Green Algae

order to investigate the morphological response of freshwater green algae to elevated CO2 concentration, Chlamydomonas reinhardtii Dang and Scenedesmus obliquus Kutz were cultured with enriched CO2, and their microstructure and ultrastructure were examined by microscopy and electron microscopy. The effect of CO2 enrichment to 186 mumol/L, was insignificant on the shape and size of C. reinhardtii, but significant in reducing the volume of S. obliquus. High-CO2 increased the amount of chloroplast. The pyrenoids occurred in low-CO2-grown cells but not in high-CO2-grown ones and more starch granules were observed in the former.

Evidence of Ultrastructure and Physiology of F-actin as Component of Plasmodesmata

The characters and ultrastructure of the intercellular connection were revealed in the outer epidermis of the garlic clove sheath by means of fluorescent probe TRITC_Phalloidin (TRITC_Ph) labeling combined with confocal laser scanning microscopy (CLSM), immuno_gold labeling and transmission electron microscopy. These results show that transcellular channel is a complex of rod_like cytoplasm channel and grouped plasmodesmata (PDs) in pit. The former remains a portion of the cell protoplast. The diameter of PD is normally 60-70 nm. The PDs are the real intercellular symplasmic connections of the cells. The transcellular fibers labeled with the TRITC_Ph obviously become narrow in the primary pit fields, which is the same as the characters observed under the electron microscope. The bright fluorescent spot in the primary wall reflects the grouped PDs in pit, and hence the presence of F_actin in the PDs can be confirmed. In immuno_gold labeling experiment, a lot of gold particles were massively distributed in the rod_like cytoplasm channel and grouped PDs. The result provides effective support that these fluorescent filaments possibly are the existing form of F_actin.

Ultrastructural Study on Development of Needle Resin Ducts in Pinus elliottii Engel.

The development of needle resin ducts of Pinus elliottii was studied using electron microscope. The results indicate that the resin duct development encompasses at least three distinctive development stages: the stage of initial cells, the stage of middle lamellae expansion and intercellular space appearance, and the stage of cavity enlargement and the resin duct formation. During the whole development stages, all kinds of organells in the duct cells show different ultrastructural features and regularity, among them the plastids' changing is the most striking one. On the basis of analysing the ultrastructural features of developing resin duct cells, the pattern of duct cavity formation, possible sites of resin synthesis, the manner and way of the resin elimination from the protoplast are discussed.

Ultrastructural Studies on the Development of Oil Cells in Litsea pungens

The developmental process of oil cells in the shoot of Litsea pungens Hemsl. has been studied with transmission electron microscopy. According to the development of the three layers of cell wall, the developmental process could be divided into 4 stages. In stage 1, the cell wall consisted only of a primary (the outmost) cellulose layer, which might further be divided into two substages, the oil cell initial, and the vacuolizing oil cell. During this stage, there were some small electron translucent vesicles and dark osmiophilic droplets of variant sizes in the different-shaped plastids. It was observed that some dark and gray osmiophilic materials coalesced to vacuoles in the cytoplasm. In stage 2, a lamellated suberin layer accumulated inside the primary cellulose layer. In stage 3, a thicker and looser inner cellulose wall layer was formed gradually inside the suberin layer. Some dark osmiophilic droplets have been observed in this loose inner cellulose wall layer. The plasmodesmata were blocked up and became a special structure. Then, the big vacuole, which is the oil sac, was full of osmiophilic oil. In stage 4, the oil cell became matured and the cytoplasm disintegrated. The oil sac enveloped from plasmalemma was attached to the cupule, which was formed by the protuberance of the inner cellulose wall layer into the lumen. After the maturity of oil cell, the ground cytoplasm began to disintegrate and became electron opaque or exhibited in a disordered state, and the osmiophilic oil appeared light gray.

Effects of Weak Light on the Ultrastructural Variations of Phloem Tissues in Source Leaves of Three-Year-Old Nectarine Trees(Prunus persica L.var. nectarina Ait.)

Leaves from three_year_old solar greenhouse nectarine trees ( Prunus persica L. var. nectarina Ait. “Zao Hong Yan”) were used as materials in this study. It was the first time that the ultrastructural characteristics of phloem tissues of source leaves were observed and compared in normal and weak light intensities using the transmission electron microscopy. Results showed that the average diameters of companion cells (CC) and sieve elements (SE) of all kinds of veins were bigger in normal than that in weak light intensity, indicating that light could influence the cell development and growth. Dense cytoplasm with abundant mitochondria, endoplasmic reticulums, multivesicular bodies, vesicles and plastids were observed in normal light intensity. On the contrary, CC with small vacuolar structures and few mitochondrias, endoplasmic reticulums were shown in weak light. Misalignment of grana thylakoid margins of nectarine leaves also was seen in weak light. The sieve pores of SEs were obstructed in weak light. Chloroplasts with numerous starch grains and few mitochondrias were noticed in the mesophyll cell (MES) surrounding the bundle sheath in weak light. The storage of starch grains appeared to result from an unbalance between photosynthate production and export of photosynthates. This observation provided a strong support to the point that most leaves export the most of assimilates in the light time. Plasmodesmal densities between SE/CC, CC/PP (phloem parenchyma cell), PP/PP and PP/BSC (bundle_sheath cell) decreased in weak light. Plasmodesmata were observed between CC/SE (NS) (nacreous_walled sieve element), PP/BSC in branch veins in normal light intensity, but not in weak light. Thus apoplasmic pathway may be the main mode of transport of assimilates in weak light, however symplasmic pathway may be the main mode of transport of assimilates in normal light intensity. These results demonstrated that the solar greenhouse nectarine trees could be adapted to the weak light via the ultrastructure variation of phloem tissues of the source leaves.

THE SECRETORY STIGMAS IN POPULUS: DEVELOPMENT, CYTOCHEMISTRY, ULTRASTRUCTURE AND THEIR RELATION TO INTERSECTIONAL INCOMPATIBILITY *

The stigmas of five species, Populus euphratica Oliv., P. alba L., P. simonii Carr., P. lasiocarpa Oliv. and P. nigra L. have been studied. Scanning electron microscopy re veals that exudates are present in the intercellular spaces, in the clefts between the multicel lular papillae and on the receptive surface. Release and movement of exudates can be visual ized when the fresh stigmas are stained with sudan Ⅲ and auramine O. Paraffin and semi thin resin sections of stigmas after glutaraldehyde osmium fixation evidence the lipidic nature of the exudates. Transmission electron microscopy reveals the glandular features of the stigmatic papillae cells, such as abundance of rough and smooth endoplasmic reticulum, polyribosomes, and well developed dictyosomes with secretory vesicles. Pellicle and epicuticular lamellate layers which have been considered as typical features of the dry type stigmas are also present in the species where stigmas appear extremely wet. It is concluded that stigmas in all of the five species are secretory at the receptive stage. Well developed generative and sperm cells were observed in the pollen tubes penetrating through the deep layers of the stigmatic tissue in the reciprocal crosses between P. euphratica and P. simonii, which indicated that there is no significant barrier in the stigma.

Seasonal Changes in the Ultrastructure of the Vascular Cambium in Shoots of Populus tomentosa

Wood is the product of cambial activity in trees, and the seasonal activity style of cambium directly influences wood biomass production, structures and properties. The seasonal changes in the ultrastructure of the vascular cambium activity of Populus tonientosa Carr. planted in Beijing area were examined in shoot tissues collected during 15 months by means of transmission electron microscopy. Before xylem mother cells reactivated completely, the dividing fusiform cells in cambium and new phloem cells had appeared at the same time. The initiation of cambial activity may be related to the bud sprouting and the young leaf growth in shoots. More details about the ultrastructural changes of cambial cells at the onset of cambial activity have been gained. When the large vacuole in active cambial cells divided into smaller ones during the dormant phase, proteinaceous material that disappeared in active cambial cells refilled many of these small vactioles. In addition, lipid droplets and starch granules had the same cycles as proteinaceous material. The plasmalemma invaginations of fusiform cells were observed not only in active phase but also in dormancy. The endomembrane system consisting of nuclear membrane, endoplasmic reticulum (ER), dictyosomes and their secretory vesicles, changed in form and distribution at different phases during a cycle and performed important roles at the onset of active cambium and during the wall formation process of secondary xylem cells. The tangential walls remained relatively thin throughout the year but the radial walls thickened markedly when the cambium was dormant. During the transition from dormancy to activity, a partial autolysis occurred in the radial walls of the cambial cells, especially at the cell wall junctions. A notable feature of the cells at the onset of cambial activity was the thinning of the radial walls.

Effects of Doubled_CO_2 Concentration on Ultrastructure, Supramolecular Architecture and Spectral Characteristics of Chloroplasts from Wheat

Wheat ( Triticum aestivum L.) plants were grown under ambient and doubled_CO 2(plus 350 μL/L) concentration in cylindrical open_top chamber to examine their effects on the ultrastructure, supramolecular architecture, absorption spectrum and low temperature (77 K) fluorescence emission spectrum of the chloroplasts from wheat leaves. The results were briefly summarized as follows: (1) The wheat leaves possessed normally developed chloroplasts with intact grana and stroma thylakoid membranes; The grana intertwined with stroma thylakoid membranes and increased slightly in stacking degree and the width of granum, in spite of more accumulated starch grains within the chloroplasts than those in control; (2) The particle density in the stacked region of the endoplasmic fracture face (EFs) and protoplasmic fracture face (PFs) and in the unstacked region the endoplasmic fracture face (EFu) and the protoplasmic fracture face (PFu) was significantly higher than that of control. Furthermore, in some cases many more particles on EFs faces of thylakoid membranes appeared as a paracrystalline particle array; (3) The variations in the structure of chloroplasts were consistent with the absorption spectra and the low temperature (77 K) fluorescence emission spectra of the chloroplasts developed under the doubled_CO 2 concentration. Results indicate that the capability of light energy absorption of chloroplasts and regulative capability of excitation energy distribution between PSⅡ and PSⅠ were raised by doubled_CO 2 concentration. This is very favorable for final productivity of wheat.

Obsevation for Epidermal Ultrastructure of Nostoc sphaeroides Kutzing under Scanning Electron Microscope

[Objective]The experiment aimed to explore a new way for observing surface structure of Nostoc sphaeroides Kutzing. [Method] The scanning electron microscope was used to observe the epidermal ultrastructure of wild and cultured Nostoc sphaeroides Kutzing. [ Result] The epidermis of wild and cultured Nostoc sphaeroides Kutzing showed mixture structure of fibril colloid which was reticular arranged. The difference between wild and cultured Nostoc sphaeroides Kutzing was that the outer epidermis of cultured Nostoc sphaeroides Kutzing had trichome distribution but the wild Nostoc sphaeroides Kutzing did not has such distribution. The obsevation results of under smaller than 10 μm by scanning electron microscope was touched thick and showed many folds and distortions. [ Conclusion] The scanning electron microscope was an effective way to study development of Nostoc sphaeroides Kutzing colony and it was worth popularizing.