Some aspects of geotropism in coleoptiles

Summary Auxin transport was studied in coleoptile sections that were stimulated geotropically. The early time course of auxin-transport asymmetry was measured. An initial phase in which more IAA was delivered into the receptor for the upper half was found after 5 min of horizontal exposure. After about 15 min this was followed by the expected known asymmetry in which more auxin flows in the lower side of the coleoptile. Upon return of the coleoptile to a vertical position, this asymmetry disappeared within 30 min.Earlier correlations of geosensitivity of the auxin transport system with sedimentation of amyloplasts in comparisons of wild type corn and an amylomaize mutant were confirmed and extended. It was also shown that, in contrast to the geotropic effect, phototropically induced lateral auxin asymmetry was not significantly different in wild type and amylomaize. Eleven other single-gene endosperm starch mutants of corn were compared to their corresponding normals. In all pairs, if a difference in geosensitivity of lateral auxin transport was present, it was correlated with a parallel difference in amyloplast sedimentation: e.g., sugary 1 (67) had an amyloplast asymmetry index of 0.32 and a 13% gravity effect on auxin transport; the paired wild-type had both a greater amyloplast asymmetry (0.61) and a greater gravity effect on transport (23%).Correlations between gravity effects on auxin transport and amyloplasts were also shown in comparisons of apical and basal sections of corn, oat and Sorghum coleoptiles.Further results, confirming the increased effect of centrifugal acceleration greater than 1xg on lateral auxin transport and on curvature, are in agreement with the hypothesis that the pressure exerted by amyloplasts, acting as statoliths, locally stimulates the auxin transport system in the individual cells.with participation by Charles steele and Vicky fan     

Gene expression patterns to define stages of post-harvest senescence in Alstroemeria petals

Petal senescence in many species is regulated by ethylene but some flowers, such as those on the monocotyledonous plant Alstroemeria, var. Rebecca are ethylene insensitive. Changes in gene expression during the post-harvest senescence of Alstroemeria flowers were investigated using several different techniques. Suppressive subtractive hybridization (SSH) was used to obtain cDNA libraries enriched for genes expressed at selected stages of petal senescence. Sequencing of the EST clones obtained resulted in over 1000 sequences that represent approximately 500 different genes. Analysis of the potential functions of these genes provides a snapshot of the processes that are taking place during petal development. Both cell wall related genes and genes involved in metabolism were present at a higher proportion in the earlier stages. Genes encoding metal binding proteins (mostly metallothionein-like) were the major component of senescence enhanced libraries. This limited the diversity of genes identified showing differential expression at the later stages. Changes in the expression of all genes were analysed using microarray hybridization, and genes showing either up or down-regulation were identified. The expression pattern of a selection of genes was confirmed using Northern hybridization. Northern hybridization confirmed the up-regulation of metallothioneins after floral opening, however, this was not detected by the microarray analysis, indicating the importance of using a combination of methods to investigate gene expression patterns. Considerably more genes were up-regulated than down-regulated. This may reflect the need during Alstroemeria petal senescence for the expression of a whole new set of genes involved with degradation and mobilization. The potential uses of expression profiling to improve floral quality in breeding programmes or as a diagnostic tool are discussed.     

Signaling Networks Converge on TORC1-SREBP Activity to Promote Endoplasmic Reticulum Homeostasis

The function and capacity of the endoplasmic reticulum (ER) is determined by multiple processes ranging from the local regulation of peptide translation, translocation, and folding, to global changes in lipid composition. ER homeostasis thus requires complex interactions amongst numerous cellular components. However, describing the networks that maintain ER function during changes in cell behavior and environmental fluctuations has, to date, proven difficult. Here we perform a systems-level analysis of ER homeostasis, and find that although signaling networks that regulate ER function have a largely modular architecture, the TORC1-SREBP signaling axis is a central node that integrates signals emanating from different sub-networks. TORC1-SREBP promotes ER homeostasis by regulating phospholipid biosynthesis and driving changes in ER morphology. In particular, our network model shows TORC1-SREBP serves to integrate signals promoting growth and G1-S progression in order to maintain ER function during cell proliferation.     

Seasonality and interindividual variation in mandrill feeding ecology revealed by stable isotope analyses of hair and blood

Mandrills are large-bodied terrestrial forest primates living in particularly large social groups of several hundred individuals. Following these groups in the wild to assess differences in diet over time as well as among individuals is demanding. We here use isotope analyses in blood and hair obtained during repeated captures of 43 identified free-ranging mandrills (Mandrillus sphinx) from Southern Gabon, to test how dietary variation relates to the season as well as an individual's age and sex. We measured the stable carbon (δ¹³C‰) and nitrogen (δ¹⁵N‰) isotope ratios in 46 blood and 214 hair section samples as well as from a small selection of mandrill foods (n = 24). We found some seasonal isotopic effects, with lower δ¹³C values but higher δ¹⁵N values observed during the highly competitive long dry season compared to the fruit-rich long rainy season. Variation in δ¹³C was further predicted by individual age, with higher δ¹³C values generally found in younger individuals suggesting that they may consume more high canopy fruit than older individuals, or that older individuals consume more low canopy foliage. The best predictor for δ¹⁵N values was the interaction between age and sex, with mature and reproductively active males revealing the highest δ¹⁵N values, despite the observation that males consume substantially less animal food items than females. We interpret high δ¹⁵N values in these mature male mandrill blood and hair sections to be the result of nutritional stress associated with intense male–male competition, particularly during mating season. This is the first study showing isotopic evidence for nutritional stress in a free-ranging primate species and may spark further investigations into male mandrill diet and energy balance.     

Leaf senescence in Brassica napus: cloning of senescence related genes by subtractive hybridisation

A subtractive hybridisation technique was developed to clone cDNAs representing genes that showed enhanced expression during leaf senescence in Brassica napus. A number of different genes were identified that, when analysed by northern hybridisation, showed different patterns of expression during leaf development but were all expressed at increased levels during senescence. Sequence analysis of these cDNAs showed that several types of genes were found including two different proteases, glutamine synthetase, ATP sulphurylase, catalase, metallothionein, ferritin and an antifungal protein. The possible roles of these gene products in the senescence process are discussed.     

Modulation of intra-oral processing in mammals and lepidosaurs

The mammalian masticatory apparatus is distinguished from theintra-oral processing systems of other amniotes by a numberof morphological and functional features, including transversemovements of the teeth during the power stroke, precise occlusion,suspension of the teeth in the socket by a periodontal ligament,diphyodonty (reduction to two generations of teeth), a hardpalate, and the presence of a single bone (the dentary) in thelower jaw which articulates with the skull at the temporomandibularjaw joint. The evolution of these features is commonly arguedto have improved the efficiency of food processing in the oralcavity. The present aricle highlights the existence in mammalsof the fusimotor system and afferent fibers from the periodontalligament through which the CNS modulates the responses by themuscle spindles. Published data suggest that the fusimotor systemand the periodontal afferents are important components in feed-forward(or anticipatory) control of chewing behavior. We hypothesizethat this feed-forward control is used to maintain relativelyconstant cycle lengths in mammals in the face of intra-sequenceand inter-sequence variation in material properties of the food,and that this enables them to maintain a higher average chewingfrequency than that of lizards. These predictions were evaluatedusing data on mean cycle length and its variance from the literatureand from our own files. On average, mammals have less variablecycle lengths than do lizards and shorter cycle lengths thando lizards of similar size. We hypothesize that by decreasingvariance in cycle length, presumably close to the natural frequencyof their feeding systems, mammals minimize energy expenditureduring chewing, allowing them to chew for longer, thereby maintainingthe high rates of food intake required for their high metabolicrates.     

BMP‐9 regulates the osteoblastic differentiation and calcification of vascular smooth muscle cells through an ALK1 mediated pathway

The process of vascular calcification shares many similarities with that of physiological skeletal mineralization, and involves the deposition of hydroxyapatite crystals in arteries. However, the cellular mechanisms responsible have yet to be fully explained. Bone morphogenetic protein (BMP‐9) has been shown to exert direct effects on both bone development and vascular function. In the present study, we have investigated the role of BMP‐9 in vascular smooth muscle cell (VSMC) calcification. Vessel calcification in chronic kidney disease (CKD) begins pre‐dialysis, with factors specific to the dialysis milieu triggering accelerated calcification. Intriguingly, BMP‐9 was markedly elevated in serum from CKD children on dialysis. Furthermore, in vitro studies revealed that BMP‐9 treatment causes a significant increase in VSMC calcium content, alkaline phosphatase (ALP) activity and mRNA expression of osteogenic markers. BMP‐9‐induced calcium deposition was significantly reduced following treatment with the ALP inhibitor 2,5‐Dimethoxy‐N‐(quinolin‐3‐yl) benzenesulfonamide confirming the mediatory role of ALP in this process. The inhibition of ALK1 signalling using a soluble chimeric protein significantly reduced calcium deposition and ALP activity, confirming that BMP‐9 is a physiological ALK1 ligand. Signal transduction studies revealed that BMP‐9 induced Smad2, Smad3 and Smad1/5/8 phosphorylation. As these Smad proteins directly bind to Smad4 to activate target genes, siRNA studies were subsequently undertaken to examine the functional role of Smad4 in VSMC calcification. Smad4‐siRNA transfection induced a significant reduction in ALP activity and calcium deposition. These novel data demonstrate that BMP‐9 induces VSMC osteogenic differentiation and calcification via ALK1, Smad and ALP dependent mechanisms. This may identify new potential therapeutic strategies for clinical intervention.