Structural associations between organelle membranes in nectary parenchyma cells.

MAIN CONCLUSION: The close association between membranes and organelles, and the intense chloroplast remodeling in parenchyma cells of extrafloral nectaries occurred only at the secretion time and suggest a relationship with the nectar secretion. Associations between membranes and organelles have been well documented in different tissues and cells of plants, but poorly explored in secretory cells. Here, we described the close physical juxtaposition between membranes and organelles, mainly with chloroplasts, in parenchyma cells of Citharexylum myrianthum (Verbenaeceae) extrafloral nectaries under transmission electron microscopy, using conventional and microwave fixation. At the time of nectar secretion, nectary parenchyma cells exhibit a multitude of different organelle and membrane associations as mitochondria-mitochondria, mitochondria-endoplasmic reticulum, mitochondria-chloroplast, chloroplast-nuclear envelope, mitochondria-nuclear envelope, chloroplast-plasmalemma, chloroplast-chloroplast, chloroplast-tonoplast, chloroplast-peroxisome, and mitochondria-peroxisome. These associations were visualized as amorphous electron-dense material, a network of dense fibrillar material and/or dense bridges. Chloroplasts exhibited protrusions variable in shape and extension, which bring them closer to each other and to plasmalemma, tonoplast, and nuclear envelope. Parenchyma cells in the pre- and post-secretory stages did not exhibit any association or juxtaposition of membranes and organelles, and chloroplast protrusions were absent. Chloroplasts had peripheral reticulum that was more developed in the secretory stage. We propose that such subcellular phenomena during the time of nectar secretion optimize the movement of signaling molecules and the exchange of metabolites. Our results open new avenues on the potential mechanisms of organelle contact in parenchyma nectary cells, and reveal new attributes of the secretory cells on the subcellular level.

Combined elevated temperature and soil waterlogging stresses inhibit cell elongation by altering osmolyte composition of the developing cotton (Gossypium hirsutum L.) fiber.

Soil waterlogging events and high temperature conditions occur frequently in the Yangtze River Valley, yet the effects of these co-occurring stresses on fiber elongation have received little attention. In the current study, the combined effect of elevated temperature (ET) and soil waterlogging (SW) more negatively affected final fiber length (reduced by 5.4%-11.3%) than either stress alone by altering the composition of osmotically active solutes (sucrose, malate, and K+), where SW had the most pronounced effect. High temperature accelerated early fiber development, but limited the duration of elongation, thereby limiting final fiber length. Treatment of ET alone altered fiber sucrose content mainly through decreased source strength and the expression of the sucrose transporter gene GhSUT-1, making sucrose availability the primary determinant of final fiber length under ET. Waterlogging stress alone decreased source strength, down-regulated GhSUT-1 expression and enhanced SuSy catalytic activity for sucrose reduction. Waterlogging treatment alone also limited fiber malate production by down-regulating GhPEPC-1 & -2. However, combined elevated temperature and waterlogging limited primary cell wall synthesis by affecting GhCESAs genes and showed a negative impact on all three major osmotic solutes through the regulation of GhSUT-1, GhPEPC-1 & -2 and GhKT-1 expression and altered SuSy activity, which functioned together to produce a shorter fiber length.

Histochemical Analysis of Plant Secretory Structures.

Histochemical analysis is essential for the study of plant secretory structures whose classification is based, at least partially, on the composition of their secretion. As each gland may produce one or more types of substances, a correct analysis of its secretion should be done using various histochemical tests to detect metabolites of different chemical classes. Here I describe some of the most used methods to detect carbohydrates, proteins, lipids, phenolic compounds, and alkaloids in the secretory structures.

Plant development: cell movement relative to each other is both common and very important.

The common view that "plant cells cannot move relative to each other" is incorrect. Relative movement of plant cells relative to each other is expressed during fiber elongation, growth of arms of branched sclereids, intrusive growth of the tips of fusiform initials in the cambium, the increase in diameter of vessel members, growth in length of vessel-member elements in the secondary xylem of the few monocotyledons that express secondary growth, growth of laticifers, formation of tylosis, dilatation in the bark via parenchyma cell expansion, and growth of pollen tubes in the style. In all these cases, part of the plant cell remains in its original position, while other parts of the cell grow to the new locations, moving significantly relative to other cells. Not considering these movements will cause a delay in studying and understanding many aspects of differentiation of plant cells and tissues.

How do 'housekeeping' genes control organogenesis?--Unexpected new findings on the role of housekeeping genes in cell and organ differentiation.

In recent years, an increasing number of mutations in what would appear to be 'housekeeping genes' have been identified as having unexpectedly specific defects in multicellular organogenesis. This is also the case for organogenesis in seed plants. Although it is not surprising that loss-of-function mutations in 'housekeeping' genes result in lethality or growth retardation, it is surprising when (1) the mutant phenotype results from the loss of function of a 'housekeeping' gene and (2) the mutant phenotype is specific. In this review, by defining housekeeping genes as those encoding proteins that work in basic metabolic and cellular functions, we discuss unexpected links between housekeeping genes and specific developmental processes. In a surprising number of cases housekeeping genes coding for enzymes or proteins with functions in basic cellular processes such as transcription, post-transcriptional modification, and translation affect plant development.

Involvement of AtMinE1 in plastid morphogenesis in various tissues of Arabidopsis thaliana.

While it has been established that binary fission of leaf chloroplasts requires the prokaryote-derived, division site determinant protein MinE, it remains to be clarified whether chloroplast division in non-leaf tissues and the division of non-colored plastids also involve the MinE protein. In an attempt to address this issue, plastids of cotyledons, floral organs, and roots were examined in the Arabidopsis thaliana mutant of the MinE (AtMinE1) gene, which was modified to express the plastid-targeted cyan fluorescent protein constitutively, and were quantitatively compared with those in the wild type. In the cotyledons, floral organs, and root columella, the plastid size in the atminE1 mutant was significantly larger than in the wild type, while the plastid number per cell in atminE1 appeared to be inversely smaller than that in the wild type. In addition, formation of the stroma-containing plastid protrusions (stromules) in the cotyledon epidermis, petal tip, and root cells was more active in atminE1 than in the wild type.

Elaiophores in Gomesa bifolia (Sims) M.W. Chase & N.H. Williams (Oncidiinae: Cymbidieae: Orchidaceae): structure and oil secretion.

BACKGROUND AND AIMS: Oils are an unusual floral reward in Orchidaceae, being produced by specialized glands called elaiophores. Such glands have been described in subtribe Oncidiinae for a few species. The aims of the present study were to identify the presence of elaiophores in Gomesa bifolia, to study their structure and to understand how the oil is secreted. Additionally, elaiophores of G. bifolia were compared with those of related taxa within the Oncidiinae. METHODS: Elaiophores were identified using Sudan III. Their structure was examined by using light, scanning electron and transmission electron microscopy. KEY RESULTS: Secretion of oils was from the tips of callus protrusions. The secretory cells each had a large, centrally located nucleus, highly dense cytoplasm, abundant plastids containing lipid globules associated with starch grains, numerous mitochondria, an extensive system of rough and smooth endoplasmatic reticulum, and electron-dense dictyosomes. The outer tangential walls were thick, with a loose cellulose matrix and a few, sparsely distributed inconspicuous cavities. Electron-dense structures were observed in the cell wall and formed a lipid layer that covered the cuticle of the epidermal cells. The cuticle as viewed under the scanning electron microscope was irregularly rugose. CONCLUSIONS: The elaiophores of G. bifolia are of the epithelial type. The general structure of the secretory cells resembles that described for other species of Oncidiinae, but some unique features were encountered for this species. The oil appears to pass through the outer tangential wall and the cuticle, covering the latter without forming cuticular blisters.

Isolation of dihydrocurcuminoids from cell clumps and their distribution in various parts of turmeric (Curcuma longa).

In addition to well-known curcuminoids, three colored metabolites were isolated from cultured cell clumps that had been induced from buds on turmeric rhizomes. The isolated compounds were identified as dihydro derivatives of curcuminoids, dihydrocurcumin (dihydroCurc), dihydrodesmethoxycurcumin-a (dihydroDMC-a), and dihydrobisdesmethoxycurcumin (dihydroBDMC). The cell clumps did not contain dihydroDMC-b, an isomer of dihydroDMC-a. A comparison of the distribution profiles of curcuminoids and dihydrocurcuminoids in the cell clumps with those in the rhizomes, leaves, and roots revealed the following differences: Unlike rhizomes, the cell clumps, leaves, and roots contained dihydrocurcuminoids as the major colored constituents. Whereas dimethoxy compounds, curcumin and dihydrocurcumin, respectively, were most abundant in the rhizomes and leaves, one of the monomethoxy derivatives, dihydroDMC-a, was found most abundantly in the cell clumps and roots. While both dihydroDMC-a and b were detected in the rhizomes, dihydroDMC-b was not detectable in the cell clumps, leaves, or roots. The occurrence of only one of the two possible isomers of dihydroDMC suggests biosynthetic formation of dihydrocurcuminoids in turmeric.

[Germplasm resources of Polygala tenuifolia and determination of presenegenin in processing products].

OBJECTIVE: To research the germplasm resources and the contents of senegenin in processing products of Polygala tenuifolia. METHOD: The contents of senegenin in wild Polygala tenuifolia and cultivated samples of Polygala tenuifolia were determined by RP-HPLC, and compared. RESULT: The contents of senegenin in wild reduce gradually along Shaanxi, Shanxi, Hebei to Dongbei. The contents of senegenin in cultivated three-year samples of three year Polygala tenuifolia from five main place was similar, 0.44%-0.49%. The content of senegenin were 0.44%-0.64% in the wand and 0.03%-0.09% in the residual part of stem, and the content of senegenin in Polygala tenuifolia was more than that in processing products. CONCLUSION: There is a correlation between the content of senegenin in Polygala tenuifolia and ecology environment that show a is inverse proportion with the quality grade, and the contents in the processing products were decreased. Senegenin can be used as a characteristic marker in range. This research provides a reference for search a index for quality control of Radix polygala and its processing products.

Evidence of ceased programmed cell death in metaphloem sieve elements in the developing caryopsis of Triticum aestivum L.

Transmission electron microscopy (TEM) and fluorescence microscopy studies revealed that the metaphloem sieve elements (MSEs) in the ventral vascular bundle of the caryopses of developing wheat (Triticum aestivum L.) undergo a unique type of programmed cell death (PCD). Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive nuclei were observed at 3 and 4 days after flowering (DAF). Transmission electron microscopy studies of differentiating MSEs revealed increased vacuolation, nuclear degeneration, chromatin condensation and localization to the periphery of the nucleus, and partly dilated perinuclear spaces, all typical characteristics of PCD in plant cells. In addition, vacuoles were disrupted at the last stages of differentiation. These results demonstrate that MSE differentiation is a unique type of PCD with highly selective autophagic processes, in which PCD ceases just prior to death. During this cessation of PCD, vacuoles and the endoplasmic reticulum appear to be associated with selective organelle digestion.

[Cell elongation as an inseparable component of growth in terrestrial plants].

The review is dedicated to the role of cell elongation in plant growth and morphogenesis. The ratios of cell division to elongation, cell competence for the initiation of elongation, main features of the metabolism of elongating cells, and physiological processes realizing elongation have been considered on the examples of seed germination and growth of roots, stems, and leaves. A special attention was paid to the vacuole as a specific feature of plant cells, pathways of its formation, and its role in maintenance of ion and water homeostasis in the elongating cell. The plant can modify its morphology according to changes in the environmental conditions via cell elongation.

Structural and immunocytochemical characterization of the adhesive tendril of Virginia creeper (Parthenocissus quinquefolia [L.] Planch.).

The tendrils of Virginia creeper (Parthenocissus quinquefolia) do not coil around their supports. Rather, they adhere to supporting objects by flattening against the support surface and secreting an adhesive compound which firmly glues the tendril to the support. In this study, microscopic and immunocytochemical techniques were utilized to determine the nature of this adhesive. Following touch stimulation, epidermal cells of the tendril elongate toward the support substrate, becoming papillate in morphology. Following contact with the support surface, an adhesive is produced at the base of the papillate cells. The adhesive appears as a highly heterogeneous, raftlike structure and consists of pectinaceous, rhamnogalacturonan (RG) I-reactive components surrounding a callosic core. In addition, more mobile components, composed of arabinogalactans and mucilaginous pectins, intercalate both the support and the tendril, penetrating the tendril to the proximal ends of the papillate cells. Following adherence to the support, the anticlinal walls of the papillate cells are devoid of RG I side-chain reactivity, indicating that extensive debranching of RG I molecules has taken place. Furthermore, a large amount of RG I backbone reactivity was observed in the contact area. These results may indicate that the debranched RG I molecules diffuse into and permeate the contact region, forming an integral part of the adhesive compound. These results indicate that Virginia creeper adheres to objects by a composite adhesive structure consisting of debranched RG I, callose, and other, less-well characterized mucilaginous pectins and that this structure subsequently becomes lignified and very weather-resistant upon the ultimate senescence of the tendril.

Immunocytochemical localization of Pisum sativum TRXs f and m in non-photosynthetic tissues.

Plants are the organisms containing the most complex multigenic family for thioredoxins (TRX). Several types of TRXs are targeted to chloroplasts, which have been classified into four subgroups: m, f, x, and y. Among them, TRXs f and m were the first plastidial TRXs characterized, and their function as redox modulators of enzymes involved in carbon assimilation in the chloroplast has been well-established. Both TRXs, f and m, were named according to their ability to reduce plastidial fructose-1,6-bisphosphatase (FBPase) and malate dehydrogenase (MDH), respectively. Evidence is presented here based on the immunocytochemistry of the localization of f and m-type TRXs from Pisum sativum in non-photosynthetic tissues. Both TRXs showed a different spatial pattern. Whilst PsTRXm was localized to vascular tissues of all the organs analysed (leaves, stems, and roots), PsTRXf was localized to more specific cells next to xylem vessels and vascular cambium. Heterologous complementation analysis of the yeast mutant EMY63, deficient in both yeast TRXs, by the pea plastidial TRXs suggests that PsTRXm, but not PsTRXf, is involved in the mechanism of reactive oxygen species (ROS) detoxification. In agreement with this function, the PsTRXm gene was induced in roots of pea plants in response to hydrogen peroxide.

Cell wall sheath surrounding calcium oxalate crystals in mulberry idioblasts.

The distribution and ultrastructural features of idioblasts containing calcium oxalate crystals were studied in leaf tissues of mulberry, Morus alba L. In addition to the calcium carbonate crystals formed in epidermal idioblasts, large calcium oxalate crystals were deposited in cells adjacent to the veins and surrounded by a cell wall sheath which had immunoreactivity with an antibody recognizing a xyloglucan epitope. The wall sheath formation indicates exclusion of the mature crystal from the protoplast.

Formation of archegonium chamber is associated with nucellar-cell programmed cell death in Ginkgo biloba.

The archegonium chamber in Ginkgo biloba L. is a pathway for spermatozoids swimming towards the archegonium for fertilization. The objective of this study was to elucidate the mechanism of archegonium chamber formation. The terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay and DNA ladder demonstrated that the nucellar cell death, coordinated with the archegonium chamber formation, was a process of programmed cell death. Cytochemical localization of Ca(2+) in these nucellar cells was determined by means of in situ precipitation with potassium pyroantimonate and electron microscopic visualization, in order to study the relation between Ca(2+) and programmed cell death. The results showed an early uptake of the mitochondrial calcium particles in the nucellar cells undergoing programmed cell death. Together with other dynamic changes in Ca(2+) subcellular distribution, this indicates that Ca(2+) may play a role in the regulation of mitochondria-mediated programmed events in the nucellar cells.

Glycosylation of tocopherols by cultured cells of Eucalyptus perriniana.

Cultured suspension cells of Eucalyptus perriniana converted exogenously administered alpha-tocopherol into alpha-tocopheryl 6-O-beta-d-glucopyranoside (46mug/gfr. wt of cells) and two biotransformation products: alpha-tocopheryl 6-O-(6-O-beta-d-glucopyranosyl)-beta-d-glucopyranoside (19mug/gfr. wt of cells) and alpha-tocopheryl 6-O-(6-O-alpha-l-rhamnopyranosyl)-beta-d-glucopyranoside (6mug/gfr. wt of cells). On the other hand, two other compounds, i.e., delta-tocopheryl 6-O-(6-O-beta-d-glucopyranosyl)-beta-d-glucopyranoside (27mug/g fr. wt of cells) and delta-tocopheryl 6-O-(6-O-alpha-l-rhamnopyranosyl)-beta-d-glucopyranoside (12mug/g fr. wt of cells), together with delta-tocopheryl 6-O-beta-d-glucopyranoside (63mug/g fr. wt of cells) were isolated from suspension cells following the administration of delta-tocopherol.

Plasmolysis and recovery of different cell types in cryoprotected shoot tips of Mentha X piperita.

Successful cryopreservation of plant shoot tips is dependent upon effective desiccation through osmotic or physical processes. Microscopy techniques were used to determine the extent of cellular damage and plasmolysis that occurs in peppermint (Mentha x piperita) shoot tips during the process of cryopreservation, using the cryoprotectant plant vitrification solution 2 (PVS2) (30% glycerol, 15% dimethyl sulfoxide, 15% ethylene glycol, 0.4 M sucrose) prior to liquid-nitrogen exposure. The meristem cells were the smallest and least plasmolyzed cell type of the shoot tips, while the large, older leaf and lower cortex cells were the most damaged. When treated with cryoprotectant solutions, meristem cells exhibited concave plasmolysis, suggesting that this cell type has a highly viscous protoplasm, and protoplasts have many cell wall attachment sites. Shoot tip cells were most severely plasmolyzed after PVS2 treatment, liquid-nitrogen exposure, and warming in 1.2 M sucrose. Successful recovery may be dependent upon surviving the plasmolytic conditions induced by warming and diluting treated shoot tips in 1.2 M sucrose solutions. In peppermint shoot tips, clumps of young meristem or young leaf cells survive the cryopreservation process and regenerate plants containing many shoots. Cryoprotective treatments that favor survival of small, meristematic cells and young leaf cells are most likely to produce high survival rates after liquid-nitrogen exposure.

Seasonal change in the drought response of wood cell development in poplar.

Field-grown poplar trees (Populus nigra L. x P. maximowiczii Henry, clone Kamabuchi) were exposed to severe drought twice during the growing season to evaluate the impact on wood cell development. The drought treatment caused a reduction in leaf water potential, leaf wilting and a decreased concentration of osmotically active solutes in the cambial zone. Drought-induced changes in the anatomy of developing xylem cells were examined in stem sections and macerated wood samples. In early summer, drought significantly reduced the length and cross-sectional area of newly formed fibers, whereas no such effects were observed in late summer. In well-watered trees, fiber cross-sectional area declined between early and late summer. Similarly, drought reduced the cross-sectional area of vessel elements in early summer but not in late summer, whereas in both control and drought-treated trees, the cross-sectional area of vessel elements decreased between early and late summer. The vessel area to xylem area ratio was unaffected by drought because the drought-induced decrease in vessel size was matched by an increase in the number of newly formed vessel cells. In contrast to its effect in early summer, late-summer drought had no significant effect on fiber and vessel cell development, indicating that sensitivity of wood cell development to drought varies seasonally.

Calcium carbonate deposition in a cell wall sac formed in mulberry idioblasts.

Although calcium carbonate is known to be a common biomineral in plants, very little attention has been given to the biological control of calcium carbonate deposition. In mulberry leaves, a subcellular structure is involved in mineral deposition and is described here by a variety of cytological techniques. Calcium carbonate was deposited in large, rounded idioblast cells located in the upper epidermal layer of mulberry leaves. Next to the outmost region ("cap") of young idioblasts, we found that the inner cell wall layer expanded to form a peculiar outgrowth, named cell wall sac in this report. This sac grew and eventually occupied the entire apoplastic space of the idioblast. Inside the mature cell wall sac, various cellulosic membranes developed and became the major site of Ca carbonate deposition. Concentrated Ca2+ was pooled in the peripheral zone, where small Ca carbonate globules were present in large numbers. Large globules were tightly packed among multiple membranes in the central zone, especially in compartments formed by cellulosic membranes and in their neighboring membranes. The maximum Ca sink capacity of a single cell wall sac was quantified using enzymatically isolated idioblasts as approximately 48 ng. The newly formed outgrowth in idioblasts is not a pure calcareous body but a complex cell wall structure filled with substantial amounts of Ca carbonate crystals.