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.

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.

Rop GTPase-dependent dynamics of tip-localized F-actin controls tip growth in pollen tubes.

Tip-growing pollen tubes provide a useful model system to study polar growth. Although roles for tip-focused calcium gradient and tip-localized Rho-family GTPase in pollen tube growth is established, the existence and function of tip-localized F-actin have been controversial. Using the green fluorescent protein-tagged actin-binding domain of mouse talin, we found a dynamic form of tip-localized F-actin in tobacco pollen tubes, termed short actin bundles (SABs). The dynamics of SABs during polar growth in pollen tubes is regulated by Rop1At, a Rop GTPase belonging to the Rho family. When overexpressed, Rop1At transformed SAB into a network of fine filaments and induced a transverse actin band behind the tip, leading to depolarized growth. These changes were due to ectopic Rop1At localization to the apical region of the plasma membrane and were suppressed by guanine dissociation inhibitor overexpression, which removed ectopically localized Rop1At. Rop GTPase-activating protein (RopGAP1) overexpression, or Latrunculin B treatments, also recovered normal actin organization and tip growth in Rop1At-overexpressing tubes. Moreover, overexpression of RopGAP1 alone disrupted SABs and inhibited growth. Finally, SAB oscillates and appears at the tip before growth. Together, these results indicate that the dynamics of tip actin are essential for tip growth and provide the first direct evidence to link Rho GTPase to actin organization in controlling cell polarity and polar growth in plants.

fw2.2: a quantitative trait locus key to the evolution of tomato fruit size.

Domestication of many plants has correlated with dramatic increases in fruit size. In tomato, one quantitative trait locus (QTL), fw2.2, was responsible for a large step in this process. When transformed into large-fruited cultivars, a cosmid derived from the fw2.2 region of a small-fruited wild species reduced fruit size by the predicted amount and had the gene action expected for fw2.2. The cause of the QTL effect is a single gene, ORFX, that is expressed early in floral development, controls carpel cell number, and has a sequence suggesting structural similarity to the human oncogene c-H-ras p21. Alterations in fruit size, imparted by fw2.2 alleles, are most likely due to changes in regulation rather than in the sequence and structure of the encoded protein.

Pollen tube attraction by the synergid cell.

In flowering plants, guidance of the pollen tube to the embryo sac (the haploid female gametophyte) is critical for successful fertilization. The target embryo sac may attract the pollen tube as the final step of guidance in the pistil. We show by laser cell ablation that two synergid cells adjacent to the egg cell attract the pollen tube. A single synergid cell was sufficient to generate an attraction signal, and two cells enhanced it. After fertilization, the embryo sac no longer attracts the pollen tube, despite the persistence of one synergid cell. This cessation of attraction might be involved in blocking polyspermy.

Living with genome instability: plant responses to telomere dysfunction.

Loss of telomere function in metazoans results in catastrophic damage to the genome, cell cycle arrest, and apoptosis. Here we show that the mustard weed Arabidopsis thaliana can survive up to 10 generations without telomerase. The last five generations of telomerase-deficient plants endured increasing levels of cytogenetic damage, which was correlated with developmental anomalies in both vegetative and reproductive organs. Mutants ultimately arrested at a terminal vegetative state harboring shoot meristems that were grossly enlarged, disorganized, and in some cases, dedifferentiated into a callusoid mass. Unexpectedly, late-generation mutants had an extended life-span and remained metabolically active. The differences in plant and animal responses to dysfunctional telomeres may reflect the more plastic nature of plant development and genome organization.

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.

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.

[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.

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 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.

Intercellular signalling in the transition from stem cells to organogenesis in meristems.

Meristems continuously produce new cells to sustain plant growth. Stem cells are maintained in the centre of the meristem and provide the precursor cells for the initiation of new organs and tissues in the periphery. The structure of the meristem is maintained while cells are constantly displaced by new divisions. Recent advances have been made in understanding the intercellular signals that maintain meristem structure by adjusting gene expression according to cell position. In addition to refinements in our understanding of how the position and size of the stem-cell population is regulated, there have been advances in understanding how the location of new organ primordia is controlled and how the meristem influences organ polarity.

The actin-interacting protein AIP1 is essential for actin organization and plant development.

Cell division, growth, and cytoplasmic organization require a dynamic actin cytoskeleton. The filamentous actin (F-actin) network is regulated by actin binding proteins that modulate actin dynamics. These actin binding proteins often have cooperative interactions. In particular, actin interacting protein 1 (AIP1) is capable of capping F-actin and enhancing the activity of the small actin modulating protein, actin depolymerising factor (ADF) in vitro. Here, we analyze the effect of the inducible expression of AIP1 RNAi in Arabidopsis plants to assess AIP1s role in vivo. In intercalary growing cells, the normal actin organization is disrupted, and thick bundles of actin appear in the cytoplasm. Moreover, in root hairs, there is the unusual appearance of actin cables ramifying the root hair tip. We suggest that the reduction in AIP1 results in a decrease in F-actin turnover and the promotion of actin bundling. This distortion of the actin cytoskeleton causes severe plant developmental abnormalities. After induction of the Arabidopis RNAi lines, the cells in the leaves, roots, and shoots fail to expand normally, and in the severest phenotypes, the plants die. Our data suggest that AIP1 is essential for the normal functioning of the actin cytoskeleton in plant development.

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.

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.

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.

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.

Shaping in plant cells.

Plant cells adopt a diversity of different shapes that are adapted to their specific functions. Central to the development of specialised form is the modification of cell-wall composition and organisation. A number of recent papers emphasise the importance of the cell wall to cell shaping, in the definition of both localised regions that are expandable and regions that are more resistant to mechanical forces. The organisation and activity of the cytoskeleton, and the activity of signalling pathways, are also essential in defining regions of the cell wall that will grow and those that will not. Although turgor has long been assumed to be a rather passive contributor to cell shaping, recent reports show that, in some cells, differential changes in turgor may have a role in establishing specialised cell form.

Ultrasound: mechanical gene transfer into plant cells by sonoporation.

Development of nonviral gene transfer methods would be a valuable alternative of gene therapy or transformation. Ultrasound can produce a variety of nonthermal bioeffects via acoustic cavitation. Cavitation bubbles can induce cell death or transient membrane permeabilization (sonoporation) on cells. Application of sonoporation for gene transfer into cells or tissues develops quickly in recent years. Many studies have been performed in vitro exposure systems to a variety of cell lines transfected successfully. In vivo, cavitation initiation and control are more difficult, but can be enhanced by ultrasound contrast agents (microbubbles). The use of ultrasound for nonviral gene delivery has been applied for mammalian systems, which provides a fundamental basis and strong promise for development of new gene therapy methods for clinical medicine. In this paper, ultrasound applied to plant cell transformation or gene transfer is reviewed. Recently, most researches are focused on sonication-assisted Agrobacterium-mediated transformation (SAAT) in plant cells or tissues. Microbubbles are also proposed to apply to gene transfer in plant cells and tissues.