The changing window of conditions that promotes germination of two fire ephemerals, Actinotus leucocephalus (Apiaceae) and Tersonia cyathiflora (Gyrostemonaceae)

BACKGROUND AND AIMS: Following a period of burial, more Actinotus leucocephalus (Apiaceae) and Tersonia cyathiflora (Gyrostemonaceae) seeds germinate in smoke water. The main aim of this study was to determine whether these fire-ephemeral seeds exhibit annual dormancy cycling during burial. This study also aimed to determine the effect of dormancy alleviation on the range of light and temperature conditions at which seeds germinate, and the possible factors driving changes in seed dormancy during burial. METHODS: Seeds were collected in summer, buried in soil in mesh bags in autumn and exhumed every 6 months for 24 months. Germination of exhumed and laboratory-stored (15 degrees C) seeds was assessed at 20 degrees C in water or smoke water. Germination response to light or dark conditions, incubation temperature (10, 15, 20, 25 and 30 degrees C), nitrate and gibberellic acid were also examined following burial or laboratory storage for 24 months. In the laboratory seeds were also stored at various temperatures (5, 15, 37 and 20/50 degrees C) for 1, 2 and 3 months followed by germination testing in water or smoke water. KEY RESULTS: The two species exhibited dormancy cycling during soil burial, producing low levels of germination in response to smoke water when exhumed in spring and high levels of germination in autumn. In autumn, seeds germinated in both light and dark and at a broader range of temperatures than did laboratory-stored seeds, and some Actinotus leucocephalus seeds also germinated in water alone. Dormancy release of Actinotus leucocephalus was slow during dry storage at 15 degrees C and more rapid at higher temperatures (37 and 20/50 degrees C); weekly wet/dry cycles further accelerated the rate of dormancy release. Cold stratification (5 degrees C) induced secondary dormancy. By contrast, no Tersonia cyathiflora seeds germinated following any of the laboratory storage treatments. CONCLUSIONS: Temperature and moisture influence dormancy cycling in Actinotus leucocephalus seeds. These factors alone did not simulate dormancy cycling of Tersonia cyathiflora seeds under the conditions tested.     

Hyaluronan facilitates transforming growth factor-β1-dependent proliferation via CD44 and epidermal growth factor receptor interaction

Fibroblast proliferation is an early feature of progressive tissue fibrosis and is largely regulated by the cytokine transforming growth factor-β1 (TGF-β1). In the oral mucosa, fibroblasts have a unique phenotype and demonstrate healing with no fibrosis/scarring. Our previous studies show that whereas dermal fibroblasts proliferate in response to TGF-β1, oral fibroblasts have an antiproliferative response to this cytokine. Hyaluronan (HA) was directly linked to this TGF-β1-dependent response. The aim of this study was to understand the underlying mechanism through which HA regulates TGF-β-dependent responses. Using patient-matched oral and dermal fibroblasts, we show that TGF-β1-dependent proliferation is mediated through the HA receptor CD44, whereas the TGF-β1-mediated antiproliferative response is CD44-independent. Furthermore, overexpression of HAS2 (HA synthase-2) in oral cells modifies their response, and they subsequently demonstrate a proliferative, CD44-dependent response to TGF-β1. We also show that epidermal growth factor (EGF) and its receptor (EGFR) are essential for TGF-β1/HA/CD44-dependent proliferation. Increased HA levels promote EGFR and CD44 coupling, potentiating signal transduction through the MAPK/ERK pathway. Thus, in a HA-rich environment, late ERK1/2 activation results from EGFR/CD44 coupling and leads to a proliferative response to TGF-β1. In comparison, in a non-HA-rich environment, only early ERK1/2 activation occurs, and this is associated with an antiproliferative response to TGF-β1. In summary, HA facilitates TGF-β1-dependent fibroblast proliferation through promoting interaction between CD44 and EGFR, which then promotes specific MAPK/ERK activation, inducing cellular proliferation.     

Transforming acidic coiled-coil-containing protein 4 interacts with centrosomal AKAP350 and the mitotic spindle apparatus

AKAP350 is a multiply spliced family of 350-450-kDa protein kinase A-anchoring proteins localized to the centrosomes and the Golgi apparatus. Using AKAP350A as bait in a yeast two-hybrid screen of a rabbit parietal cell library, we have identified a novel AKAP350-interacting protein, transforming acidic coiled-coil-containing protein 4 (TACC4). Two-hybrid binary assays demonstrate interaction of both TACC3 and TACC4 with AKAP350A and AKAP350B. Antibodies raised to a TACC4-specific peptide sequence colocalize TACC4 with AKAP350 at the centrosome in interphase Jurkat cells. Mitotic cell staining reveals translocation of TACC4 from the centrosome to the spindle apparatus with the majority of TACC4 at the spindle poles. Truncated TACC4 proteins lacking the AKAP350 minimal binding domain found in the carboxyl coiled-coil region of TACC4 could no longer target to the centrosome. Amino-truncated TACC4 proteins could no longer target to the spindle apparatus. Further, overexpression of TACC4 fusion proteins that retained spindle localization in mitotic cells resulted in an increased proportion of cells present in prometaphase. We propose that AKAP350 is responsible for sequestration of TACC4 to the centrosome in interphase, whereas a separate TACC4 domain results in functional localization of TACC4 to the spindle apparatus in mitotic cells.     

Occurrence of physical dormancy in seeds of Australian Sapindaceae: a survey of 14 species in nine genera

Background and Aims

Sapindaceae is one of 16 angiosperm families whose seeds have physical dormancy (PY). However, the extent and nature of PY within this family is poorly known. The primary aims of this study were: (1) to evaluate seed characteristics and determine presence (or not) of PY within nine genera of Australian Sapindaceae; and (2) to compare the frequency of PY across the phylogenetic tree within Australian Sapindaceae.

Methods

Viability, imbibition and seed characteristics were assessed for 14 taxa from nine genera of Sapindaceae. For five species of Dodonaea, optimal conditions for germination and dormancy break were evaluated. An in situ burial experiment was performed on D. hackettiana seeds to identify the factor(s) responsible for overcoming PY. Classes of dormancy and of non-dormancy for 26 genera of Sapindaceae were mapped onto a phylogenetic tree for the family.

Key Results

Mean seed viability across all taxa was 69·7 %. Embryos were fully developed and folded (seven genera) or bent (two genera); no endosperm was present. Seeds of all five Dodonaea spp. and of Distichostemon hispidulus had PY. Hot-water treatment released PY in these six species. Optimal germination temperature for seeds of the four Dodonaea spp. that germinated was 15–20 °C. Following 5 months burial in soil, 36·4 % of D. hackettiana seeds had lost PY and germinated by the beginning of the winter wet season (May). Laboratory and field data indicate that dormancy was broken by warm, moist temperatures (≥50 °C) during summer.

Conclusions

PY occurs infrequently in genera of Sapindaceae native to Australia. Seeds of Dodonaea and Distichostemon had PY, whereas those of the other seven genera did not. Seeds of these two genera and of Diplopeltis (a previous study) are the only three of the 20 native Australian genera of Sapindaceae for which germination has been studied that have PY; all three belong to subfamily Dodonaeoideae.Key words: Dodonaea spp., physical dormancy, Sapindaceae, seed ecology, seed germination     

Synemin and vimentin are components of intermediate filaments in avian erythrocytes

Synemin, a high-molecular-weight protein associated with intermediate filaments in muscle, and vimentin, an intermediate-filament subunit found in many different cell types, have been identified by immunologic and electrophoretic criteria as components of intermediate filaments in mature avian erythrocytes. Desmin, the predominant subunit of intermediate filaments in muscle, has not been detected in these cells. Two dimensional immunoautoradiography of proteolytic fragments of synemin and vimentin demonstates that the erythrocyte proteins are highly homologous, if not identical, to their muscle counterparts. Double immunoflurorescence reaveals that erythrocyte synemin and vimentin co-localize in a cytoplasmic network of sinuous filaments that extends from the nucleus to the plasma membrane and resists aggregation by colcemid. Erythrocytes that are attached to glass cover slips can be sonicated to remove nuclei and nonadherent regions of the plasma membrane; this leaves elliptical patches of adherent membrane that retain mats of vimentin- and synemin-containing intermediate filaments, as seen by immunofluorescence and rotary shadowing. Similarly, mechanical enucleation of erythrocyte ghosts in suspension allows isolation of plasma membranes that retain a significant fraction of the synemin and vimentin, as assayed by electrophoresis, and intermediate filaments, as seen in thin sections. Both synemin and vimentin remain insoluble along with spectrin and actin, in solutions containing nonionic detergent and high salt. However, brief exposure of isolated membrane to distilled water releases the synemin and vimentin together in nearly pure form, before the release of significant amounts of spectrin and actin. These data suggest that avian erythrocyte intermeditate filaments are somehow anchored to the plasma membrane; erythrocytes may thus provide a simple system for the study of intermediate filaments and their mode of interaction with membranes. In addition, these data, in conjunction with previous data from muscle, indicate that synemin is capable of associating with either desmin or vimentin and may thus perform a special role in the structure or function of intermediate filaments in erythrocytes as well as muscle.     

Abscisic Acid in tobacco plants: tentative identification and its relation to stunting induced by pseudomonas solanaccarum

In tobacco plants inoculated with the wilt-inducing bacterium, Pseudomonas solanacearum, there was a correlation between decreased internode elongation, maximum multiplication of the bacterium, and an increase in the growth inhibitor content of stems 4 to 12 days after inoculation, as determined by a wheat coleoptile assay. Initial wilting of the upper leaves was also correlated with an increase in inhibitor content of these tissues.     

Leukotriene B4 generation by human monocytes and neutrophils stimulated by uropathogenic strains of Escherichia coli

The generation of the 5-lipoxygenase product, leukotriene B4 (LTB4) by human mononuclear phagocytes (monocytes) following incubation with 25 different uropathogenic strains of Escherichia coli correlated with the haemolytic activity of the strains (r = 0.572, P less than 0.01). LTB4 generation by human neutrophils (PMN), however, was unrelated to this haemolytic potential (r = 0.164). In contrast, both prelabelled monocytes and PMN were stimulated by haemolytic strains of E. coli and by haemolytic culture supernatants to release significant amounts of [3H]arachidonic acid. There was a significant correlation between haemolytic activity and [3H]arachidonic acid release generated by individual strains from monocytes (r = 0.804, P less than 0.001) and PMN (r = 0.888, P less than 0.001). In addition, nonhaemolytic strains but not their culture supernatants were capable of causing slow release of both [3H]arachidonic acid and LTB4 from PMN and mononuclear cells. These results suggest that both the possession of haemolytic activity, and the direct interaction of bacteria with the leukocyte surface are mechanisms by which uropathogenic strains of E. coli may cause the release and metabolism of arachidonic acid. In addition, there was synergistic augmentation by nonhaemolytic bacteria of the PMN LTB4 response to haemolytic culture supernatants or to low doses of the calcium ionophore A23187. These results support an ionophore-like mechanism for the activation of the cell by haemolysin. LTB4 generation by PMN incubated with haemolytic supernatants was also augmented by particulate zymosan in a manner dependent on the dose of zymosan, suggesting that the direct interaction of E. coli with PMN may involve an activation mechanism similar to that for zymosan. These results demonstrate differing responses of peripheral mononuclear cells and PMN from the same donors to identical strains of E. coli and suggest that the generation of the potent chemotactic agent LTB4 in response to E. coli infection in vivo need not depend solely on the elaboration of cytotoxic haemolysins by individual strains.