Effect of maturation and storage on asparagus (Asparagus officinalis) cell wall composition

Changes in the cell wall composition of stems of asparagus ( Asparagus officinalis L. cv. Connovor Collossus) during maturation and during storage in modified atmospheres were investigated. Alcohol-insoluble residues from portions of stems were analysed for changes in alkali-soluble phenolics and in the constituent sugars and their glycosidic linkages. Maturation-related changes down the stem involved increased levels of (l–4)-linked xylosyl residues from xylans, cellulose and phenolics, which arise from the lignified vascular and sclerenchyma tissues, and a decrease in the levels of (l–5)-linked arabinosyl residues from pectic arabinans from the parenchy-matous tissues. Storage under aerobic conditions permitted stem elongation in the apical sections and secondary thickening in the basal sections. This was due to continued tissue maturation. Storage under anaerobic conditions inhibited such changes. In accordance with these effects of storage on stem physiology, maturation-related changes in cell wall components were enhanced by storage only under aerobic conditions. However, levels of (1–4)-linked galactosyl residues which remained relatively constant during maturation, decreased substantially (ca 50%) in all stem sections during both aerobic and anaerobic storage.     

Cell wall biochemistry in Archaea and its phylogenetic implications

Cellularization of a precellular ancestral condition of life must have occured separately for each of the three domains of life resulting in a protoarchaeon, a protobacterium and a protocaryon. Accordingly, a first cell, ancestral to the three domains of life has never existed. This statement is based on a retrospective evaluation of the distribution patterns of membrane lipids and of cell wall polymers with their different chemical nature and modes of biosynthesis in a global phylogenetic tree based on 16S rRNA sequence comparison.Dedicated to Professor Peter Sitte on the occasion of his 65th birthday.     

Effects of the medium ammonium-nitrate ratio on competence for asparagus cell division induced by phytosulfokine-α

The effects of medium ammonium-nitrate ratio on cell proliferation were investigated using a low cell-density culture of Asparagus officinalis L., which was triggered by a peptidal plant growth factor, phytosulfokine-α (PSK-α). The asparagus cells proliferated the most in a medium with an ammonium-nitrate ratio of 0:30 mM and could be maintained without significant loss of responsiveness to PSK-α for at least 96 h from the beginning of culture. In this medium, single cells gave rise to microcalli at initial densities as low as 3.2×10² cells/ml as long as PSK-α was present in the medium. Increasing the ammonium-nitrate ratio resulted in severe inhibition of cell proliferation at a low cell density, even if PSK-α was added to the medium. Received: 6 May 1997 / Revision received: 5 August 1997 / Accepted: 2 September 1997     

Rheological analysis of viscoelastic cell wall changes in maize coleoptiles as affected by auxin and osmotic stress

The effects of auxin and osmotic stress on elongation growth of maize (Zea mays L.) coleoptile segments are accompanied by characteristic changes in the extensibility of the growth-limiting cell walls. At full turgor auxin causes growth by an increase in wall extensibility (wall looseining). Growth can be stopped by an osmotically produced step-down in turgor of 0.45 MPa. Under these conditions auxin causes the accumulation of a potential for future wall extension which is released after restoration of full turgor. Turgor reduction causes a reversible decrease in wall extensibility (wall stiffening) both in the presence and absence of auxin. These changes in vivo are correlated with corresponding changes in the rheological properties of the cell walls in vitro which can be traced back to specific modifications in the shape of the hysteretic stress-strain relationship. The longitudinally load-bearing walls of the coleoptile demonstrate almost perfect viscoelasticity as documented by a nearly closed hysteresis loop. Auxin-mediated wall loosening causes an increase of loop width and thus affects primarily the amount of hysteresis in the isolated wall. In contrast, turgor reduction by osmotic stress reduces loop length and thus affects primarily the amount of viscoelastic wall extensibility. Pretreatment of segments with anoxia and H₂O₂ modify the hysteresis loop in agreement with the conclusion that the wall-stiffening reaction visualized under osmotic stress in vivo is an O₂-dependent process in which O₂ can be substituted by H₂O₂. Cycloheximide specifically inhibits auxin-mediated wall loosening without affecting wall stiffening, and this is mirrored in specific changes of the hysteresis loop. Corroborating a previous in vivo study (Hohl et al. 1995, Physiol. Plant. 94: 491–498) these results show that cell wall stiffening in vivo can also be demonstrated by Theological measurements with the isolated cell wall and that this process can be separated from cell wall loosening by specific changes in the shape of the hysteresis loop.     

Water relations, activities of antioxidants, ethylene evolution and membrane integrity of pigeonpea roots as affected by soil moisture

The plants of pigeonpea (Cajanus cajan L.) cv. H77-216 were subjected to moderate [soil moisture content (SMC) = 7.3 ± 0.5 %] and severe (SMC = 4.3 ± 0.5 %) drought by withholding the irrigation at vegetative stage (45 d after sowing). The control plants were maintained at SMC of 11.0 ± 0.5 %. Half of the stressed plants were re-irrigated and their recovery was studied after 2 d. Leaf water potential, osmotic potential, and relative water content of leaf and root decreased significantly while a sharp rise in proline and total soluble sugars contents were noticed. Drought induced a significant increase in 1-aminocyclopropane 1-carboxylic acid (ACC) content and ACC oxidase activity which caused a considerable increase in ethylene evolution. Malondialdehyde content and relative stress injury were increased under drought whereas reverse was true for ascorbic acid content. The membrane integrity of roots decreased during stress and recovered on rehydration. The specific activity of total superoxide dismutase, ascorbate peroxidase, glutathione reductase, and glutathione transferase decreased to 37 – 78 %, 17 – 62 %, 29 – 36 % and 57 – 79 % at moderate and severe drought, respectively. The increase in activity of catalase and peroxidase could not overcome the accumulation of H₂O₂ content in the roots.     

Growth and osmoregulation in Pisum sativum subhooks as affected by gibberellic acid and cotyledon excision

Growth stimulation by gibberellic acid (GA) of the Alaska pea ( Pisum sativum L.) subhook was observed within 6 h after its application; the stimulation being larger in cuttings with cotyledons than in decotylized ones. The osmotic potential in the subhook increased as it grew, the rate of its increase being faster in cuttings without than in cuttings with cotyledons. GA had no effect on the change in the osmotic potential until 8 h after GA application, but afterwards it suppressed the increase in cuttings with cotyledons. This GA effect was not observed in decotylized cuttings. Changes in the osmotic potential were well correlated with changes in the concentration of soluble sugars, but not with changes in amino acids and K⁺, Soluble sugars accumulated in the subhook of cuttings with and without cotyledons in proportion to growth, irrespective of the presence or absence of GA. Cotyledon excision suppressed sugar accumulation, and GA promoted it in cuttings with cotyledons but not in decotylized ones. These results suggest that GA stimulates the translocation of sugars from the cotyledons to the subhook and, thereby, maintains the osmotic potential low, resulting in enhanced growth.     

Cell wall glycoproteins and polysaccharides of mature runner beans

A novel use of chlorite-HOAc treatment (delignification procedure) for the isolation of hydroxyproline (HP) rich “glycoproteins” from the depectinated cell wall material of mature runner beans is described. This procedure can be used for the isolation of wall proteins even from heavily lignified tissues. Its main disadvantage is that some of the constituent amino acids are either destroyed or modified; the nature of these changes was studied using gelatine, lysozyme and “cytoplasmic proteins” of mature beans. The main amino acids to be affected were tyrosine, cystine, methionine and lysine. The chlorite-HOAc solubilized proteins were separated by PhOH-H₂O fractionation into two distinct “glycoprotein fractions”. The major fraction (isolated from the aqueous layer) contained most of the HP of the solubilized proteins. The sugars obtained on hydrolysis of both “glycoproteins” were galactose, arabinose, glucose, xylose, rhamnose and uronic acid. Most of the proteins remaining in the holocellulose could readily be extracted with cold alkali and were relatively poor in HP.     

Cell elongation and metabolic turnover of the cell wall as affected by auxin and cell wall degrading enzymes

A cell wall fraction (pectic substances) of oat coleoptile segmentsfed with ¹⁴C-glucose contained more radioactivity under theeffect of auxin than did the control. When labeled segmentswere grown for 6 hr in auxin or glucanase solution the labelin the hemicellulose fraction decreased as growth increased.ß-1,3-Glucanase prepared from the culture of a fungus,Sclerotinia libertiana, induces elongation of segments of thepea stem and the oat coleoptile. Traces of cellulase and pectinmethylesterase contaminating the enzyme preparation are notresponsible for the stimulatory effect. Cellulase seemed tobe rather inhibitory and pectin methylesterase showed only aslight effect on coleoptile elongation. A possible relationshipbetween the metabolic turnover of hemicellulosic polysaccharideand cell wall extension is suggested. (Received February 5, 1968; )     

Diverse effects of bacterial cell wall components on mast cell degranulation,cysteinyl leukotriene generation and migration

Nowadays there is more and more evidence that mast cells take part in antibacterial defence. Mast cells have the ability to kill bacteria via phagocytose‐dependent or phagocytose‐independent ways and express antimicrobial peptides that can directly kill pathogens at their site of entry. What is more, mast cells are capable of processing bacterial antigens for presentation through class I and II MHC molecules. Some data indicate that these cells can release various proinflammatory mediators in response to activation with bacteria and/or their products, however this information is still far from complete. Therefore, in this study we examined the ability of PGN from Staphylococcus aureus, LPS from Eschericha coli and LAM from Mycobacterium smegmatis to stimulate mature rat mast cell degranulation as well as cysteinyl LT generation. We also studied the influence of these bacterial components on mast cell migration. We found that PGN, LPS and LAM all failed to induce mast cell degranulation and histamine release. At the same time, activation of mast cells with these bacterial antigens resulted in generation and release of significant amounts of LT. Moreover, we documented that, even in the presence of laminin, none of the bacterial antigens used stimulated mast cell migration. However, PGN did induce migration of RANTES‐primed mast cells, and LPS did stimulate mast cell migratory response after priming with IL‐6. Our results show that PGN, LPS and LAM might be among the important bacterial antigens involved in mast cell activation during bacterial infection.     

Cell wall composition of the carrageenophyte Kappaphycus alvarezii (Gigartinales, Rhodophyta) partitioned by wet sieving

The cortical and medullary cells of Kappaphycus alvarezii fractions were screened by wet sieving after aqueous extraction of carrageenans. The cell populations obtained showed a clear partition between these two cell types. The main monosaccharide in hydro-insoluble cell walls was cellulosic glucose (70% dry weight), the crystallinity of which was shown torange from 20% in the cortical cells to 45% in the large medullary cells (over 250 μm diameter). Minor monosaccharides in the insoluble fraction were galactose, 3,6-anhydrogalactose (indicating presence of residual carrageenans), mannose and xylose. However, the major part of the remaining galactose probably originated from another galactoglycan strongly linked to insoluble polymers in the large medullarycell walls. The mannose concentration was maximum in the cortical cells and decreased with increasing size of the medullary cells. Thus, besides cellulose, two other types of polysaccharides were detected in insolublecell walls, mannoglycans and galactoglycans in cortical and medullary cellwalls, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genotypic covariations of traits underlying sorghum stem biomass production and quality and their regulations by water availability: Insight from studies at organ and tissue levels

Sweet and biomass sorghum are expected to contribute increasingly to bioenergy production. Better understanding the impacts of the genotypic and environmental variabilities on biomass component traits and their properties is essential to optimize energy yields. This study aimed to evaluate whether traits contributing to stem biomass growth and biochemical composition at different biological scales (co)vary with the genotype and the water status in sorghum. Height genotypes were studied over two years in field conditions in southern France under two water treatments (well watered vs. 25 days’ dry down during stem elongation). Main stem internode number, size, (non)structural carbohydrate, and lignin contents were measured at the end of the stress period and/or at final harvest, together with biochemical and histological analyses of the youngest expanded internode. The tallest genotypes showed the highest stem dry weights and lignin contents. Stem (structural) biomass density was positively correlated with lignin content, particularly in internode parenchyma. Stem soluble sugar and lignin contents were inversely proportional across genotypes and water conditions. Genotypes contrasted for drought sensitivity and recovery capacity of stem growth and biochemical composition. The length and cell wall deposition of internodes expanding under water deficit were reduced and did not recover, these responses being weakly correlated. Genotypic variability was pointed out in the growth recovery of internodes expanding under re‐watered conditions. According to the observed genotypic variability and the absence of antagonistic correlations between the responses of the different traits to water availability, it is suggested that biomass sorghum varieties optimizing their responses to water availability in terms of growth and cell wall deposition can be developed for different bioenergy targets.     

Cell wall glucomannan in Arabidopsis is synthesised by CSLA glycosyltransferases, and influences the progression of embryogenesis

Mannans are hemicellulosic polysaccharides that have previously been implicated as structural constituents of cell walls and as storage reserves but which may serve other functions during plant growth and development. Several members of the Arabidopsis cellulose synthase-like A (CSLA) family have previously been shown to synthesise mannan polysaccharides in vitro when heterologously expressed. It has also been found that CSLA7 is essential for embryogenesis, suggesting a role for the CSLA7 product in development. To determine whether the CSLA proteins are responsible for glucomannan synthesis in vivo , we characterised insertion mutants in each of the nine Arabidopsis CSLA genes and several double and triple mutant combinations. csla9 mutants showed substantially reduced glucomannan, and triple csla2csla3csla9 mutants lacked detectable glucomannan in stems. Nevertheless, these mutants showed no alteration in stem development or strength. Overexpression of CSLA2, CSLA7 and CSLA9 increased the glucomannan content in stems. Increased glucomannan synthesis also caused defective embryogenesis, leading to delayed development and occasional embryo death. The embryo lethality of csla7 was complemented by overexpression of CSLA9 , suggesting that the glucomannan products are similar. We conclude that CSLA2, CSLA3 and CSLA9 are responsible for the synthesis of all detectable glucomannan in Arabidopsis stems, and that CSLA7 synthesises glucomannan in embryos. These results are inconsistent with a substantial role for glucomannan in wall strength in Arabidopsis stems, but indicate that glucomannan levels affect embryogenesis. Together with earlier heterologous expression studies, the glucomannan deficiency observed in csla mutant plants demonstrates that the CSLA family encodes glucomannan synthases.     

Differential effect of temperature on mitrochondrial activity in shoots from freshly harvested and moderately aged kernels of maize (Zea mays L.)

This paper reports on a study of mitochondrial activity in etiolated shoots of freshly harvested and moderately aged kernels of maize. Activity was investigated after incubation at a favourable temperature (25°C), sub-optimal temperature (13°C) and after a heat shock (46°C for 2h). Although impaired mitochondrial activity in shoots from moderately aged maize kernels was not detected at 25°C, deficiencies became evident under low temperature stress (13°C). State 3 oxygen uptake, cyanide-insensitive oxygen uptake and cytochrome oxidase activity were lower in mitochondria from these shoots at 13°C than in mitochondria from shoots of freshly harvested kernels at this temperature. After a heat shock, cyanide-insensitive oxygen uptake was higher, and cytochrome oxidase activity lower, in shoots of aged kernels than in shoots of fresh kernels. No significant differences in ADP: O ratio or succinate dehydrogenase activity occurred between mitochondria from shoots of the two seed lots in any of the temperature treatments.     

Participation of the cyanide-resistant pathway in respiration of winter rape leaves as affected by plant cold acclimation

Leaf slices sampled from winter rape plants ( Brassica napus L., var. oleifera L., cv. GórczaánAski), grown in cold (5°C), showed an increase in the dark respiration rate (measured at 25°C) as compared to slices cut from control plants (grown at 20/15°C). The effect of low temperature was most pronounced after 4 days of plant growth in the cold. Oxygen uptake by control slices was 60% inhibited by 1 m M KCN and was insensitive to 2.5 m M salicylhydroxamic acid (SHAM). On the contrary, respiration of leaf slices from cold-pretreated plants was more resistant to cyanide (35% inhibition after 4 days of cold treatment) and was 30% inhibited by SHAM. The patterns of cold-induced changes in total respiratory activity and in the estimated activity of alternative pathway were similar. It seems that in leaf slices from plants grown in the cold, the cyanide-resistant, alternative pathway participates in oxygen uptake. Cold treatment of plants also brought about a 4-fold increase in the level of soluble sugars, which reached a maximum on day 4 of exposure to cold. Addition of sucrose to the incubation medium resulted in an immediate increase in oxygen uptake by slices with low endogenous sugar level. The respiration stimulated by sucrose addition was more resistant to cyanide than the basal respiration and it was inhibited by SHAM. It is concluded that the operation of the alternative pathway is responsible for the increased oxygen uptake by the cold-grown winter rape leaves and it may be induced by an increased sugar supply for respiratory processes.     

Freezing pattern in apple seeds as affected by the temperature of fruit storage

Storage of apple fruits ( Pyrus malus L. cv. Golden Delicious) at different temperatures (0, 12 and 35°C) markedly altered the pattern of water freezing in the seeds. Higher temperatures of storage brought about a shift from the sequential to the discontinuous type of freezing in seeds, the low temperature exotherm (LTE) being much more pronounced than the high temperature one (HTE). The occurrence of LTE was highly correlated with embryo death. Fruit storage at higher temperatures also caused a decrease in the threshold super cooling temperature of seeds and of naked embryos, removed from the seed coat and endosperm. The decrease was less pronounced in naked embryos than in intact seeds. The results presented show that the frost resistance of apple seeds relies mainly on the supercooling ability of the embryos and is increased by the presence of seed coat and endosperm. The broad peak of the LTE indicates that, in contrast with other seeds and many super cooling organs, massive ice nucleation in apple seeds occurs within the embryo tissues and that extra organ freezing seems to be of less importance. Therefore, the increased super cooling ability of apple seeds, isolated from fruits stored at higher temperatures, seems to rely on those seed properties that protect embryo cells against heterogeneous ice nucleation.     

Cell wall and cell growth characteristics of giant‐celled algae

Because of their large sizes and simple shapes, giant‐celled algae have been used to study how the structural and mechanical properties of cell walls influence cell growth. Here we review known relationships between cell wall and cell growth properties that are characteristic of three representative taxa of giant‐celled algae, namely, Valonia ventricosa, internodal cells of characean algae, and Vaucheria frigida. Tip‐growing cells of the genus Vaucheria differ from cells undergoing diffuse growth in V. ventricosa and characean algae in terms of their basic architectures (non‐lamellate vs. multilamellate) and their dependence upon pH and Ca²⁺ for cell wall extensibility. To further understand the mechanisms controlling cell growth by cell walls, comparative analyses of cell wall structures and/or associated growth modes will be useful. The giant‐celled algae potentially serve as good models for such investigations because of their wide variety of developmental processes and cell shapes exhibited.     

Frost resistance and water status of winter rape leaves as affected by differential shoot/root temperature

Twenty day-old winter rape ( Brassica napus L. var. oleifera L. cv. Jantar) seedlings, grown in nutrient solution, were exposed to different shoot/root temperature (i. e. 20/20, 20/3, 3/20 and 3/3°C) for 2 or 4 weeks. Chilling treatments modified markedly the pattern of plant growth as indicated by changes in dry matter accumulation in individual plant parts (leaves, hypocotyls, roots) and decreased leaf specific area. Growth of roots was less sensitive to low temperature than that of shoots. This was reflected by a decrease in shoot/root biomass ratio. Chilling treatments increased freezing resistance, decreased water content and water potential and modified reducing sugar, soluble protein and phospholipid contents in the leaves. A biphasic character of tissue responses to chilling temperature was observed, the most remarkable changes being registered during the first 7 or 14 days of the treatment. Effects of root or shoot exposure to chilling temperature on ice nucleation temperature, LT₅₀, water potential, accumulation of sugars and phospholipids in leaves were additive. All the observations point to the important role of the root system in plant acclimation to cold. Its impact on water status of leaves is emphasized and some mechanisms of root involvement in acclimation processes are proposed.     

Cell wall thickness and the molecular mechanism of heterogeneous vancomycin-intermediate Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) with reduced sensitivity to vancomycin (VAN) has caused many clinical cases of VAN treatment failure, but the molecular mechanism underlying the reduced sensitivity to VAN is still unclear. We isolated a heterogeneous VAN-intermediate Staphylococcus aureus (hVISA), which was also a MRSA strain with reduced sensitivity to VAN. To investigate the molecular mechanism underlying the reduced sensitivity to VAN exhibited by the hVISA strain, we compared the hVISA strain with a VAN-sensitive MRSA strain, known as the N315 strain. The images captured by transmission electron microscopy showed that the cell wall of the hVISA strain was significantly thicker than that of the N315 strain (36·72 ± 1·04 nm vs 28·15 ± 1·25 nm, P < 0·05), and the results of real-time quantitative PCR analysis suggested that the expression levels of the cell wall thickness related genes (glmS, vraR/S, sgtB, murZ and PBP4) of the hVISA strain were significantly higher than those of the N315 strain (P < 0·05). In conclusion, this study indicated that the upregulation of the expression of the genes related to cell wall synthesis might be the molecular mechanism underlying the cell wall thickening of the hVISA strain and might be related to its resistance to VAN.     

Ectopic expression of a novel OsExtensin‐like gene consistently enhances plant lodging resistance by regulating cell elongation and cell wall thickening in rice

Plant lodging resistance is an important integrative agronomic trait of grain yield and quality in crops. Although extensin proteins are tightly associated with plant cell growth and cell wall construction, little has yet been reported about their impacts on plant lodging resistance. In this study, we isolated a novel extensin‐like (OsEXTL) gene in rice, and selected transgenic rice plants that expressed OsEXTL under driven with two distinct promoters. Despite different OsEXTL expression levels, two‐promoter‐driven OsEXTL‐transgenic plants, compared to a rice cultivar and an empty vector, exhibited significantly reduced cell elongation in stem internodes, leading to relatively shorter plant heights by 7%–10%. Meanwhile, the OsEXTL‐transgenic plants showed remarkably thickened secondary cell walls with higher cellulose levels in the mature plants, resulting in significantly increased detectable mechanical strength (extension and pushing forces) in the mature transgenic plants. Due to reduced plant height and increased plant mechanical strength, the OsEXTL‐transgenic plants were detected with largely enhanced lodging resistances in 3 years field experiments, compared to those of the rice cultivar ZH11. In addition, despite relatively short plant heights, the OsEXTL‐transgenic plants maintain normal grain yields and biomass production, owing to their increased cellulose levels and thickened cell walls. Hence, this study demonstrates a largely improved lodging resistance in the OsEXTL‐transgenic rice plants, and provides insights into novel extensin functions in plant cell growth and development, cell wall network construction and wall structural remodelling.