Quantitative trait loci influencing pentacyclic triterpene composition in apple fruit peel

The chemical composition of pentacyclic triterpenes was analysed using a ‘Royal Gala’ x ‘Granny Smith’ segregating population in 2013 and 2015, using apple peels extracted from mature fruit at harvest and after 12 weeks of cold storage. In 2013, 20 compound isoforms from nine unique compound classes were measured for both treatments. In 2015, 20 and 17 compound isoforms from eight unique compound classes were measured at harvest and after cold storage, respectively. In total, 68 quantitative trait loci (QTLs) were detected on 13 linkage groups (LG). Thirty two and 36 QTLs were detected for compounds measured at harvest and after cold storage, respectively. The apple chromosomes with the most QTLs were LG3, LG5, LG9 and LG17. The largest effect QTL was for trihydroxy-urs-12-ene-28-oic acid, located on LG5; this was measured in 2015 after storage, and was inherited from the ‘Royal Gala’ parent (24.9% of the phenotypic variation explained).

Cell type-specific gene expression underpins remodelling of cell wall pectin in exocarp and cortex during apple fruit development

In apple (Malus×domestica) fruit, the different layers of the exocarp (cuticle, epidermis, and hypodermis) protect and maintain fruit integrity, and resist the turgor-driven expansion of the underlying thin-walled cortical cells during growth. Using in situ immunolocalization and size exclusion epitope detection chromatography, distinct cell type differences in cell wall composition in the exocarp were revealed during apple fruit development. Epidermal cell walls lacked pectic (1→4)-β-d-galactan (associated with rigidity), whereas linear (1→5)-α-l-arabinan (associated with flexibility) was exclusively present in the epidermal cell walls in expanding fruit and then appeared in all cell types during ripening. Branched (1→5)-α-l-arabinan was uniformly distributed between cell types. Laser capture microdissection and RNA sequencing (RNA-seq) were used to explore transcriptomic differences controlling cell type-specific wall modification. The RNA-seq data indicate that the control of cell wall composition is achieved through cell-specific gene expression of hydrolases. In epidermal cells, this results in the degradation of galactan side chains by possibly five β-galactosidases (BGAL2, BGAL7, BGAL10, BGAL11, and BGAL103) and debranching of arabinans by α-arabinofuranosidases AF1 and AF2. Together, these results demonstrate that flexibility and rigidity of the different cell layers in apple fruit during development and ripening are determined, at least in part, by the control of cell wall pectin remodelling.

Red to Brown: An Elevated Anthocyanic Response in Apple Drives Ethylene to Advance Maturity and Fruit Flesh Browning

The elevation of anthocyanin contents in fruits and vegetables is a breeding target for many crops. In some fruit, such as tomato, higher anthocyanin concentrations enhance storage and shelf life. In contrast, highly anthocyanic red-fleshed apples (Malus x domestica) have an increased incidence of internal browning flesh disorder (IBFD). To determine the mechanisms underlying this, 'Royal Gala' cultivar apples over-expressing the anthocyanin-related transcription factor (TF) MYB10 (35S:MYB10), which produces fruit with highly pigmented flesh, were compared with standard 'Royal Gala' Wild Type (WT) grown under the same conditions. We saw no incidence of IBFD in WT 'Royal Gala' but the over-expression of MYB10 in the same genetic background resulted in a high rate of IBDF. We assessed concentrations of potential substrates for IBDF and a comparison of metabolites in these apples showed that anthocyanins, chlorogenic acid, pro-cyanidins, flavon-3-ols, and quercetin were all higher in the MYB10 lines. For the flavol-3-ols sub-group, epicatechin rather than catechin was elevated in MYB10 lines compared with the control fruit. Internal ethylene concentrations were measured throughout fruit development and were significantly higher in 35S:MYB10 lines, and ethylene was detected at an earlier developmental stage pre-harvest. Expression analysis of key genes associated with ethylene biosynthesis (aminocyclopropane-1-carboxylic acid synthase and oxidase; ACS and ACO) and polyphenol oxidase (PPO) showed the potential for increased ethylene production and the mechanism for enhanced PPO-mediated browning. The expression of a transcription factor of the ethylene response factor (ERF) class, ERF106, was elevated in red flesh. Analysis of transcriptional activation by MYB10 showed that this transcription factor could activate the expression of apple ACS, ACO, and ERF106 genes. Our data show a link between the elevation of anthocyanin-related transcription factors and an undesirable fruit disorder. The accelerated advancement of maturity via premature ethylene induction has implications for the breeding and storage of these more highly pigmented plant products.

Delayed response to cold stress is characterized by successive metabolic shifts culminating in apple fruit peel necrosis

BACKGROUND

Superficial scald is a physiological disorder of apple fruit characterized by sunken, necrotic lesions appearing after prolonged cold storage, although initial injury occurs much earlier in the storage period. To determine the degree to which the transition to cell death is an active process and specific metabolism involved, untargeted metabolic and transcriptomic profiling was used to follow metabolism of peel tissue over 180 d of cold storage.

RESULTS

The metabolome and transcriptome of peel destined to develop scald began to diverge from peel where scald was controlled using antioxidant (diphenylamine; DPA) or rendered insensitive to ethylene using 1-methylcyclopropene (1-MCP) beginning between 30 and 60 days of storage. Overall metabolic and transcriptomic shifts, representing multiple pathways and processes, occurred alongside α-farnesene oxidation and, later, methanol production alongside symptom development.

CONCLUSIONS

Results indicate this form of peel necrosis is a product of an active metabolic transition involving multiple pathways triggered by chilling temperatures at cold storage inception rather than physical injury. Among multiple other pathways, enhanced methanol and methyl ester levels alongside upregulated pectin methylesterases are unique to peel that is developing scald symptoms similar to injury resulting from mechanical stress and herbivory in other plants.

Gene expression and metabolism preceding soft scald, a chilling injury of 'Honeycrisp' apple fruit

BACKGROUND

'Honeycrisp' is an apple cultivar that is susceptible to soft scald, a chilling injury expressed as necrotic patches on the peel. Improved understanding of metabolism associated with the disorder would improve our understanding of soft scald and contribute to developing more effective management strategies for apple storage. It was expected that specific gene expression and specific metabolite levels in the peel would be linked with soft scald risk at harvest and/or specific time points during cold storage.

RESULTS

Fruit from nine 'Honeycrisp' apple orchards that would eventually develop different incidences of soft scald between 4 and 8 weeks of cold air storage were used to contrast and determine differential transcriptomic and metabolomic changes during storage. Untargeted metabolic profiling revealed changes in a number of distinct pathways preceding and concurrent with soft scald symptom development, including elevated γ-aminobutryic acid (GABA), 1-hexanol, acylated steryl glycosides, and free p-coumaryl acyl esters. At harvest, levels of sesquiterpenoid and triterpenoid acyl esters were relatively higher in peel of fruit that did not later develop the disorder. RNA-seq driven gene expression profiling highlighted possible involvement of genes and associated metabolic processes with soft scald development. These included elevated expression of genes involved in lipid peroxidation and phenolic metabolism in fruit with soft scald, and isoprenoid/brassinosteroid metabolism in fruit that did not develop soft scald. Expression of other stress-related genes in fruit that developed soft scald included chlorophyll catabolism, cell wall loosening, and lipid transport while superoxide dismutases were up-regulated in fruit that did not develop the disorder.

CONCLUSIONS

This study delineates the sequential transcriptomic and metabolomic changes preceding soft scald symptom development. Changes were differential depending on susceptibility of fruit to the disorder and could be attributed to key stress related and mediating pathways.

Lower cell wall pectin solubilisation and galactose loss during early fruit development in apple (Malus x domestica) cultivar 'Scifresh' are associated with slower softening rate

Substantial differences in softening behaviour can exist between fruit even within the same species. Apple cultivars 'Royal Gala' and 'Scifresh' soften at different rates despite having a similar genetic background and producing similar amounts of ethylene during ripening. An examination of cell wall metabolism from the fruitlet to the ripe stages showed that in both cultivars pectin solubilisation increased during cell expansion, declined at the mature stage and then increased again during ripening. This process was much less pronounced in the slower softening 'Scifresh' than in 'Royal Gala' at every developmental stage examined, consistent with less cell separation and softening in this cultivar. Both cultivars also exhibited a progressive loss of pectic galactan and arabinan side chains during development. The cell wall content of arabinose residues was similar in both cultivars, but the galactose residue content in 'Scifresh' remained higher than that of 'Royal Gala' at every developmental stage. The higher content of cell wall galactose residue in 'Scifresh' cell walls correlated with a lower β-galactosidase activity and more intense immunolabelling of RG-I galactan side chains in both microscopy sections and glycan microarrays. A high cell wall galactan content has been associated with reduced cell wall porosity, which may restrict access of cell wall-modifying enzymes and thus maintain better structural integrity later in development. The data suggest that the composition and structure of the cell wall at very early development stages may influence subsequent cell wall loosening, and may even predispose the wall's ensuing properties.

Chilling-related cell damage of apple (Malus × domestica Borkh.) fruit cortical tissue impacts antioxidant, lipid and phenolic metabolism

'Soggy breakdown' (SB) is an internal flesh disorder of 'Honeycrisp' apple (Malus × domestica Borkh.) fruit that occurs during low temperature storage. The disorder is a chilling injury (CI) in which visible symptoms typically appear after several weeks of storage, but information about the underlying metabolism associated with its induction and development is lacking. The metabolic profile of flesh tissue from wholly healthy fruit and brown and healthy tissues from fruit with SB was characterized using gas chromatography-mass spectrometry (GC-MS) and liquid chromatograph-mass spectrometry (LC-MS). Partial least squares discriminant analysis (PLS-DA) and correlation networks revealed correlation among ester volatile compounds by composition and differences in phytosterol, phenolic and putative triacylglycerides (TAGs) metabolism among the tissues. anova-simultaneous component analysis (ASCA) was used to test the significance of metabolic changes linked with tissue health status. ASCA-significant components included antioxidant compounds, TAGs, and phytosterol conjugates. Relative to entirely healthy tissues, elevated metabolite levels in symptomatic tissue included γ-amino butyric acid, glycerol, sitosteryl (6'-O-palmitoyl) β-d-glucoside and sitosteryl (6'-O-stearate) β-d-glucoside, and TAGs containing combinations of 16:0, 18:3, 18:2 and 18:1 fatty acids. Reduced metabolite levels in SB tissue included 5-caffeoyl quinate, β-carotene, catechin, epicatechin, α-tocopherol, violaxanthin and sitosteryl β-d glucoside. Pathway analysis indicated aspects of primary metabolism differed according to tissue condition, although differences in metabolites involved were more subtle than those of some secondary metabolites. The results implicate oxidative stress and membrane disruption processes in SB development and constitute a diagnostic metabolic profile for the disorder.

Transcriptomic events associated with internal browning of apple during postharvest storage

BACKGROUND

Postharvest ripening of apple (Malus x domestica) can be slowed down by low temperatures, and a combination of low O2 and high CO2 levels. While this maintains the quality of most fruit, occasionally storage disorders such as flesh browning can occur. This study aimed to explore changes in the apple transcriptome associated with a flesh browning disorder related to controlled atmosphere storage using RNA-sequencing techniques. Samples from a browning-susceptible cultivar ('Braeburn') were stored for four months under controlled atmosphere. Based on a visual browning index, the inner and outer cortex of the stored apples was classified as healthy or affected tissue.

RESULTS

Over 600 million short single-end reads were mapped onto the Malus consensus coding sequence set, and differences in the expression profiles between healthy and affected tissues were assessed to identify candidate genes associated with internal browning in a tissue-specific manner. Genes involved in lipid metabolism, secondary metabolism, and cell wall modifications were highly modified in the affected inner cortex, while energy-related and stress-related genes were mostly altered in the outer cortex. The expression levels of several of them were confirmed using qRT-PCR. Additionally, a set of novel browning-specific differentially expressed genes, including pyruvate dehydrogenase and 1-aminocyclopropane-1-carboxylate oxidase, was validated in apples stored for various periods at different controlled atmosphere conditions, giving rise to potential biomarkers associated with high risk of browning development.

CONCLUSIONS

The gene expression data presented in this study will help elucidate the molecular mechanism of browning development in apples at controlled atmosphere storage. A conceptual model, including energy-related (linked to the tricarboxylic acid cycle and the electron transport chain) and lipid-related genes (related to membrane alterations, and fatty acid oxidation), for browning development in apple is proposed, which may be relevant for future studies towards improving the postharvest life of apple.

Ethylene regulates Apple (Malus x domestica) fruit softening through a dose x time-dependent mechanism and through differential sensitivities and dependencies of cell wall-modifying genes

In fleshy fruit species that have a strong requirement for ethylene to ripen, ethylene is synthesized autocatalytically, producing increasing concentrations as the fruits ripen. Apple fruit with the ACC OXIDASE 1 (ACO1) gene suppressed cannot produce ethylene autocatalytically at ripening. Using these apple lines, an ethylene sensitivity dependency model was previously proposed, with traits such as softening showing a high dependency for ethylene as well as low sensitivity. In this study, it is shown that the molecular control of fruit softening is a complex process, with different cell wall-related genes being independently regulated and exhibiting differential sensitivities to and dependencies on ethylene at the transcriptional level. This regulation is controlled through a dose × time mechanism, which results in a temporal transcriptional response that would allow for progressive cell wall disassembly and thus softening. This research builds on the sensitivity dependency model and shows that ethylene-dependent traits can progress over time to the same degree with lower levels of ethylene. This suggests that a developmental clock measuring cumulative ethylene controls the fruit ripening process.

Genetic and environmental control of fruit maturation, dry matter and firmness in apple (Malus × domestica Borkh.)

For any given genotype, the environment in which an apple is grown can influence the properties of the fruit considerably. While there has been extensive research on the mechanism of the genetic control of fruit quality traits, less effort has been made to investigate the way that these genetic mechanisms interact with the environment. To address this issue, we employed a large 'Royal Gala' × 'Braeburn' population of 572 seedlings replicated over sites in three climatically diverse apple-growing regions in New Zealand. Phenotyping for traits including fruit maturation timing, firmness and dry matter content was performed at each of these three sites for a single growing season (2011), and at two sites (Motueka and Hawke's Bay) for two seasons (2009 and 2010). The phenotype data collected over 2 years at two sites enabled the detection of 190 quantitative trait loci (QTL) that controlled these traits regardless of year or growing location, as well as some chromosomal loci that influenced the traits in a single given environment or year. For those loci that were environmentally stable over three sites, there was an interdependency of fruit maturation date, dry matter content and storage potential within this population, with two regions on Linkage Groups (LGs) 10 and 16 strongly contributing. If these loci were used in a marker-assisted selection programme to select for progeny bearing firmer fruit, this would have the unintentional consequence of selecting, high dry matter content, later maturing apples. In addition, a further 113 new QTLs with a smaller effect were identified, some of which were exhibited only in a single growing environment, demonstrating the underlying complexity of control of traits determining fruit quality, in addition to the need for being aware of environmental effects when developing new apple varieties.

Cell wall structures leading to cultivar differences in softening rates develop early during apple (Malus x domestica) fruit growth

BACKGROUND

There is a paucity of information regarding development of fruit tissue microstructure and changes in the cell walls during fruit growth, and how these developmental processes differ between cultivars with contrasting softening behaviour. In this study we compare two apple cultivars that show different softening rates during fruit development and ripening. We investigate whether these different softening behaviours manifest themselves late during ethylene-induced softening in the ripening phase, or early during fruit expansion and maturation.

RESULTS

'Scifresh' (slow softening) and 'Royal Gala' (rapid softening) apples show differences in cortical microstructure and cell adhesion as early as the cell expansion phase. 'Scifresh' apples showed reduced loss of firmness and greater dry matter accumulation compared with 'Royal Gala' during early fruit development, suggesting differences in resource allocation that influence tissue structural properties. Tricellular junctions in 'Scifresh' were rich in highly-esterified pectin, contributing to stronger cell adhesion and an increased resistance to the development of large airspaces during cell expansion. Consequently, mature fruit of 'Scifresh' showed larger, more angular shaped cells than 'Royal Gala', with less airspaces and denser tissue. Stronger cell adhesion in ripe 'Scifresh' resulted in tissue fracture by cell rupture rather than by cell-to-cell-separation as seen in 'Royal Gala'. CDTA-soluble pectin differed in both cultivars during development, implicating its involvement in cell adhesion. Low pectin methylesterase activity during early stages of fruit development coupled with the lack of immuno-detectable PG was associated with increased cell adhesion in 'Scifresh'.

CONCLUSIONS

Our results indicate that cell wall structures leading to differences in softening rates of apple fruit develop early during fruit growth and well before the induction of the ripening process.

Investigation of ascorbate metabolism during inducement of storage disorders in pear

In pear and apple, depletion of ascorbate has previously been associated with development of stress-related flesh browning. This disorder occurs in intact fruit and differs from browning associated with tissue maceration and processing. We investigated changes in ascorbate content, ascorbate peroxidase (APX) activities and gene expression of l-galactose pathway genes, ascorbate recycling genes and APXs from harvest to 30 days storage for three pear varieties ['Williams Bon Chretien' (WBC), 'Doyenne du Comice' and 'Beurre Bosc']. The pears were stored at 0.5°C in air or controlled atmosphere (CA, 2 kPa O(2) and 5 kPa CO(2)). Storage in CA caused significant amounts of storage disorders in WBC only. Ascorbate content generally declined after harvest, although a transient increase in ascorbate in the form of dehydroascorbate (DHA) between harvest and 3 days was observed in CA stored WBC, possibly due to low at-harvest monodehydroascorbate reductase and CA-decreased dehydroascorbate reductase expression. Quantitative polymerase chain reaction indicated that all cultivars responded to CA storage by increasing transcripts for APXs, and surprisingly the pre-l-galactose pathway gene GDP-mannose pyrophosphorylase, of which the product GDP mannose, is utilized either for cell wall polysaccharides, protein N-glycosylation or ascorbate production. Overall, the small differences in ascorbate we observed suggest how ascorbate is utilized, rather than ascorbate content, determines the potential to develop internal browning. Moreover, a transitory increase in DHA postharvest may indicate that fruits are at risk of developing the disorder.

Down-regulation of POLYGALACTURONASE1 alters firmness, tensile strength and water loss in apple (Malus x domestica) fruit

BACKGROUND

While there is now a significant body of research correlating apple (Malus x domestica) fruit softening with the cell wall hydrolase ENDO-POLYGALACTURONASE1 (PG1), there is currently little knowledge of its physiological effects in planta. This study examined the effect of down regulation of PG1 expression in 'Royal Gala' apples, a cultivar that typically has high levels of PG1, and softens during fruit ripening.

RESULTS

PG1-suppressed 'Royal Gala' apples harvested from multiple seasons were firmer than controls after ripening, and intercellular adhesion was higher. Cell wall analyses indicated changes in yield and composition of pectin, and a higher molecular weight distribution of CDTA-soluble pectin. Structural analyses revealed more ruptured cells and free juice in pulled apart sections, suggesting improved integrity of intercellular connections and consequent cell rupture due to failure of the primary cell walls under stress. PG1-suppressed lines also had reduced expansion of cells in the hypodermis of ripe apples, resulting in more densely packed cells in this layer. This change in morphology appears to be linked with reduced transpirational water loss in the fruit.

CONCLUSIONS

These findings confirm PG1's role in apple fruit softening and suggests that this is achieved in part by reducing cellular adhesion. This is consistent with previous studies carried out in strawberry but not with those performed in tomato. In apple PG1 also appears to influence other fruit texture characters such as juiciness and water loss.

An improved counterselection cassette for use in Haemophilus influenzae

Counterselectable cassettes are extremely useful in molecular biology and allow for the creation of unmarked deletion mutants or the introduction of point mutations. I have constructed an inducible sacB cassette, using the tetracycline repressor. When used in tandem with a kanamycin-resistance marker, the cassette was successful in creating unmarked mutants in Haemophilus influenzae. The inducible nature of the cassette avoids some of the common problems associated with the utilization of sacB in counterselection.

Effects of osmotic pretreatments on oxidative stress, antioxidant profiles and cryopreservation of olive somatic embryos

A three-day pretreatment of olive somatic embryos (SE) with 0.75 M sucrose, combined with cryoprotection (0.5M DMSO, 1M sucrose, 0.5M glycerol and 0.009 M proline) and controlled rate cooling, supported regrowth (as 34.6% fresh weight gain) and resumption of embryo development after cryopreservation. Pretreatment with mannitol or sorbitol did not support regrowth. Profiles of sugars, proline, antioxidant enzymes, Reactive oxygen species (ROS), secondary oxidation products and ethylene were constructed for the most successful (0.75 M) pretreatment series. Sucrose was the optimal pretreatment for supporting recovery, it also elevated glutathione reductase (GR) activity compared to controls, whereas superoxide dismutase (SOD), catalase and guaiacol peroxidase activities remained relatively unchanged. Superoxide dismutase activity was higher in SE pretreated with sucrose, compared with those pretreated with polyols; H(2)O(2) was enhanced in SE pretreated with sorbitol and sucrose compared to mannitol. The overall trend for ethylene and OH production revealed their levels were highest in SE pretreated with polyols albeit, for individual treatments this was not always the case. Generally, pretreatments did not significantly change embryo secondary oxidation profiles of ThioBarbituric Acid Reactive Substances (TBARS) and Schiff's bases. In combination these studies suggest oxidative processes may influence regrowth of cryopreserved olive SE and that optimal pretreatments could, in part, increase tolerance by an overall enhancement of endogenous antioxidants (particularly GR), proline and sugars.

Laboratory growth and maintenance of Haemophilus influenzae

Haemophilus influenzae is a non-spore forming, non-motile, pleomorphic Gram-negative coccobacilli. H. influenzae is a strict human pathogen that can cause a variety of systemic and localized infections, depending on the strain. The three Basic Protocols in this unit will describe how to culture and prepare H. influenzae for the use in biological studies of the organism.

Sialic acid transport and catabolism are cooperatively regulated by SiaR and CRP in nontypeable Haemophilus influenzae

Background

The transport and catabolism of sialic acid, a critical virulence factor for nontypeable Haemophilus influenzae, is regulated by two transcription factors, SiaR and CRP.

Results

Using a mutagenesis approach, glucosamine-6-phosphate (GlcN-6P) was identified as a co-activator for SiaR. Evidence for the cooperative regulation of both the sialic acid catabolic and transport operons suggested that cooperativity between SiaR and CRP is required for regulation. cAMP was unable to influence the expression of the catabolic operon in the absence of SiaR but was able to induce catabolic operon expression when both SiaR and GlcN-6P were present. Alteration of helical phasing supported this observation by uncoupling SiaR and CRP regulation. The insertion of one half-turn of DNA between the SiaR and CRP operators resulted in the loss of SiaR-mediated repression of the transport operon while eliminating cAMP-dependent induction of the catabolic operon when GlcN-6P was present. SiaR and CRP were found to bind to their respective operators simultaneously and GlcN-6P altered the interaction of SiaR with its operator.

Conclusions

These results suggest multiple novel features for the regulation of these two adjacent operons. SiaR functions as both a repressor and an activator and SiaR and CRP interact to regulate both operons from a single set of operators.

The role of ethylene and cold temperature in the regulation of the apple POLYGALACTURONASE1 gene and fruit softening

Fruit softening in apple (Malus x domestica) is associated with an increase in the ripening hormone ethylene. Here, we show that in cv Royal Gala apples that have the ethylene biosynthetic gene ACC OXIDASE1 suppressed, a cold treatment preconditions the apples to soften independently of added ethylene. When a cold treatment is followed by an ethylene treatment, a more rapid softening occurs than in apples that have not had a cold treatment. Apple fruit softening has been associated with the increase in the expression of cell wall hydrolase genes. One such gene, POLYGALACTURONASE1 (PG1), increases in expression both with ethylene and following a cold treatment. Transcriptional regulation of PG1 through the ethylene pathway is likely to be through an ETHYLENE-INSENSITIVE3-like transcription factor, which increases in expression during apple fruit development and transactivates the PG1 promoter in transient assays in the presence of ethylene. A cold-related gene that resembles a COLD BINDING FACTOR (CBF) class of gene also transactivates the PG1 promoter. The transactivation by the CBF-like gene is greatly enhanced by the addition of exogenous ethylene. These observations give a possible molecular mechanism for the cold- and ethylene-regulated control of fruit softening and suggest that either these two pathways act independently and synergistically with each other or cold enhances the ethylene response such that background levels of ethylene in the ethylene-suppressed apples is sufficient to induce fruit softening in apples.

Example of use of taqman real-time RT-PCR to analyze bacterial gene transcript levels: Haemophilus influenzae

The protocol in this unit describes the steps for gene expression analysis of Haemophilus influenzae in broth culture. Steps for hot acid phenol RNA extraction, RNA cleanup, quantitation, assessment, and preparation for TaqMan qRT-PCR are described. The validation, setup, and analysis of TaqMan qRT-PCR experiments are discussed.

Detection of 8-hydroxy-2-deoxyguanosine as a marker of oxidative damage in DNA and germplasm exposed to cryogenic treatments

An HPLC method has been optimised to measure 8-hydroxy-2-deoxyguanosine (8OHdG) in DNA and germplasm with the objective of using the adduct as a marker of cryostorage stability. The encapsulation-dehydration cryopreservation protocol was adapted as a model system for assessing the formation of 8OHdG from alginate-encapsulated DNA of calf thymus (CT) and currant species (Ribes) exposed to temperatures of -20 and -196 degree C. The presence of H2O2 exacerbated the formation of 8OHdG in encapsulated CT and Ribes DNA. Production of the oxidized adduct was lower in the plant system. A reduction in residual water following osmotic dehydration and evaporative desiccation was associated with reduced adduct formation in encapsulated DNA. No significant differences in 8OHdG adduct formation were observed in plants regenerated from cryopreserved Ribes meristems derived from genotypes known to have differential tolerance to cryopreservation.

Co-ordination of early and late ripening events in apples is regulated through differential sensitivities to ethylene

In this study, it is shown that anti-sense suppression of Malus domestica 1-AMINO-CYCLOPROPANE-CARBOXYLASE OXIDASE (MdACO1) resulted in fruit with an ethylene production sufficiently low to be able to assess ripening in the absence of ethylene. Exposure of these fruit to different concentrations of exogenous ethylene showed that flesh softening, volatile biosynthesis, and starch degradation, had differing ethylene sensitivity and dependency. Early ripening events such as the conversion of starch to sugars showed a low dependency for ethylene, but a high sensitivity to low concentrations of ethylene (0.01 microl l(-1)). By contrast, later ripening events such as flesh softening and ester volatile production showed a high dependency for ethylene but were less sensitive to low concentrations (needing 0.1 microl l(-1) for a response). A sustained exposure to ethylene was required to maintain ripening, indicating that the role of ethylene may go beyond that of ripening initiation. These results suggest a conceptual model for the control of individual ripening characters in apple, based on both ethylene dependency and sensitivity.

A rapid method of fruit cell isolation for cell size and shape measurements

BACKGROUND

Cell size is a structural component of fleshy fruit, contributing to important traits such as fruit size and texture. There are currently a number of methods for measuring cell size; most rely either on tissue sectioning or digestion of the tissue with cell wall degrading enzymes or chemicals to release single cells. Neither of these approaches is ideal for assaying large fruit numbers as both require a considerable time to prepare the tissue, with current methods of cell wall digestions taking 24 to 48 hours. Additionally, sectioning can lead to a measurement of a plane that does not represent the widest point of the cell.

RESULTS

To develop a more rapid way of measuring fruit cell size we have developed a protocol that solubilises pectin in the middle lamella of the plant cell wall releasing single cells into a buffered solution. Gently boiling small fruit samples in a 0.05 M Na2CO3 solution, osmotically balanced with 0.3 M mannitol, produced good cell separation with little cellular damage in less than 30 minutes. The advantage of combining a chemical treatment with boiling is that the cells are rapidly killed. This stopped cell shape changes that could potentially occur during separation. With this method both the rounded and angular cells of the apple cultivars SciRos 'Pacific Rose' and SciFresh 'Jazz' were observed in the separated cells. Using this technique, an in-depth analysis was performed measuring cell size from 5 different apple cultivars. Cell size was measured using the public domain ImageJ software. For each cultivar a minimum of 1000 cells were measured and it was found that each cultivar displayed a different distribution of cell size. Cell size within cultivars was similar and there was no correlation between flesh firmness and cell size. This protocol was tested on tissue from other fleshy fruit including tomato, rock melon and kiwifruit. It was found that good cell separation was achieved with flesh tissue from all these fruit types, showing a broad utility to this protocol.

CONCLUSION

We have developed a method for isolating single cells from fleshy fruit that reduces the time needed for fruit cell separation. This method was used to demonstrate differences in cell size and shape for 5 different apple cultivars. While firmness between the different cultivars is independent of cell size, apples with more angular cells appear to be firmer.

Cryopreservation induces temporal DNA methylation epigenetic changes and differential transcriptional activity in Ribes germplasm

The physiological and molecular mechanisms associated with acclimation and survival have been examined in four Ribes genotypes displaying differential cryotolerance. Changes in DNA methylation, nucleic acid and nucleoside composition were determined during acclimation and recovery of in vitro shoot-meristems from cryopreservation. DNA methylation was induced in the tolerant genotype, while demethylation was evident in sensitive genotypes. This response initially occurred during sucrose simulated acclimation, with progressive changes as shoots recovered from successive stages of the encapsulation-dehydration protocol. These methylation patterns existed in the initial vegetative cycle but regressed to control values following subculture, indicating the changes in DNA methylation to be a reversible epigenetic mechanism. RNA levels indicating transcriptional activity during the acclimation of nodal tissue are inversely linked to methylation changes, where activity appears to be up-regulated in the cryosensitive genotypes. Conversely, cryopreserved shoots show increased levels of both RNA and DNA methylation in the cryotolerant genotypes. Other nucleosides show post-transcriptional activity corresponds with tolerance during acclimation and cryopreservation. These observations connect physiological attributes to differential molecular changes in Ribes, the implications of which are discussed in relation to cryopreservation-induced apoptosis and genetic stability.

Regulation of sialic acid transport and catabolism in Haemophilus influenzae

Virulence of nontypeable Haemophilus influenzae (NTHi) is dependent on the decoration of lipooligosaccharide with sialic acid. This sugar must be derived from the host, as NTHi cannot synthesize sialic acids. NTHi can also use sialic acid as a carbon source. The genes encoding the sialic acid transporter and the genes encoding the catabolic activities are localized to two divergently transcribed operons, the siaPT operon and the nan operon respectively. In this study, we identified SiaR as a repressor of sialic acid transport and catabolism in NTHi. Inactivation of siaR resulted in the unregulated expression of the genes in both operons. Unregulated catabolism of sialic acid in the siaR mutant resulted in the reduction of surface sialylation and an increase in serum sensitivity. In addition to SiaR-mediated repression, CRP, the cAMP receptor protein, was shown to activate expression of the siaPT operon but not the nan operon. We describe a model in which SiaR and CRP work to modulate intracellular sialic acid levels. Our results demonstrate the importance of SiaR-mediated regulation to balance the requirement of surface sialylation and the toxic accumulation of intracellular sialic acid.

Evaluation of the 1-methyl-2-phenylindole colorimetric assay for aldehydic lipid peroxidation products in plants: malondialdehyde and 4-hydroxynonenal

The 1-methyl-2-phenylindole colorimetric assay is considered specific for malondialdehyde (MDA) and 4-hydroxynonenal (HNE) in mammalian systems, but its specificity in plant tissues is unknown. This study demonstrates that the assay produces a purple/blue chromophore with an absorbance peak at 586 nm for a malondialdehyde standard, while aqueous extractions from Ribes spp. Beta vulgaris, and Lycopersicon esculentum tissues produce an orange chromophore with an absorbance maximum at 450 nm and a large shoulder that extends to 700 nm. No distinctive MDA peak was discernable in plant samples at lambda=586 nm and absorbance was attributed to background interference. The reaction between sucrose and 1-methyl-2-phenylindole produced an orange chromophore with a spectrum similar to those obtained from plant extractions, suggesting that simple sugars are the likely source of background interference. This study demonstrates that the 1-methyl-2-phenylindole colorimetric assay is non-specific for detecting MDA and HNE in plants and its use is cautioned due to interference, particularly from sugars.

Cryopreservation of shoot tips and meristems

Shoot-tip meristem cryopreservation methodologies are reported for the complementary cryoprotective strategies of vitrification and equilibrium freezing using traditional controlled-rate freezing and chemical additive cryoprotection. Pregrowth, pretreatment, and cold acclimation approaches for the improvement of tolerance to liquid nitrogen are also presented. The chapter concludes by reporting an analytical protocol that profiles volatile hydrocarbon stress markers (for ethylene, hydroxyl radicals, and lipid peroxidation products) during cryopreservation. This method uses noninvasive headspace sampling and gas chromatography, and it is widely applicable across cryogenic systems.

Optimisation of the azinobis-3-ethyl-benzothiazoline-6-sulphonic acid radical scavenging assay for physiological studies of total antioxidant activity in woody plant germplasm

A robust spectroscopic method for determining total antioxidant activity in aqueous extractions has been applied to tissues from diverse woody plant species, including seeds of Coffea arabica and in vitro shoots from Ribes nigrum, Picea sitchensis and Shorea leprosula. The assay involves scavenging of an ABTS [2,2'-azinobis-(3-ethyl-benzothiazoline-6-sulphonic acid)] radical generated by the reaction of potassium persulphate with ABTS to produce an ABTS*(+) chromophore (lambda=734 nm). Antioxidants reduce ABTS*(+) back to ABTS with a concomitant decrease in absorbance. Aqueous extractions from C. arabica and S. leprosula had considerably higher (110-205 micromol Trolox eq. g(-1) FW) total antioxidant activities than P. sitchensis and R. nigrum (6-11 micromol Trolox eq. g(-1) FW). Further studies in two of these species showed that the inclusion of water-insoluble polyvinylpyrrolidone during aqueous tissue extraction enabled the combined phenolic and alkaloid antioxidant activity to be determined. These fractions accounted for 85% and 60% of total antioxidant activity for C. arabica seeds and R. nigrum shoots, respectively. The ABTS radical scavenging assay is presented herein as a robust method for determining total antioxidant activity in germplasm from diverse woody plant tissues and species. Its applicability to study oxidative stress in tissue cultures and germplasm employed in plant biotechnology, breeding and stress physiology programmes is discussed.

Mn2+-dependent regulation of multiple genes in Streptococcus pneumoniae through PsaR and the resultant impact on virulence

The concentration of Mn2+ is 1,000-fold higher in secretions than it is at internal sites of the body, making it a potential signal by which bacteria can sense a shift from a mucosal environment to a more invasive site. PsaR, a metal-dependent regulator in Streptococcus pneumoniae, was found to negatively affect the transcription of psaBCA, pcpA, rrgA, rrgB, rrgC, srtBCD, and rlrA in the presence of Mn2+. psaBCA encode an ABC-type transporter for Mn2+. pcpA, rrgA, rrgB, and rrgC encode several outer surface proteins. srtBCD encode a cluster of sortase enzymes, and rlrA encodes a transcriptional regulator. Steady-state RNA levels are high under low Mn2+ concentrations in the wild-type strain and are elevated under both high and low Mn2+ concentrations in a psaR mutant strain. RlrA is an activator of rrgA, rrgB, rrgC, and srtBCD (D. Hava and A. Camilli, Mol. Microbiol. 45:1389-1406, 2002), suggesting that PsaR may indirectly control these genes through rlrA, while PsaR-dependent repression of psaBCA, pcpA, and rlrA transcription is direct. The impact of Mn2+-dependent regulation on virulence was further examined in mouse models of pneumonia and nasopharyngeal carriage. The abilities of DeltapsaR, pcpA, and DeltapsaR DeltapcpA mutant strains to colonize the lung were reduced compared to those of the wild type, confirming that both PcpA-mediated gene regulation and PsaR-mediated gene regulation are required for full virulence in the establishment of pneumonia. Neither PcpA nor PsaR was found to be required for colonization of the nasopharynx in a carriage model. This is the first demonstration of Mn2+ acting as a signal for the expression of virulence factors within different host sites.

Novel sialic acid transporter of Haemophilus influenzae

Nontypeable Haemophilus influenzae is an opportunistic pathogen and a common cause of otitis media in children and of chronic bronchitis and pneumonia in patients with chronic obstructive pulmonary disease. The lipooligosaccharides, a major component of the outer membrane of H. influenzae, play an important role in microbial virulence and pathogenicity. N-Acetylneuraminic acid (sialic acid) can be incorporated into the lipooligosaccharides as a terminal nonreducing sugar. Although much of the pathway of sialic acid incorporation into lipooligosaccharides is understood, the transporter responsible for N-acetylneuraminic acid uptake in H. influenzae has yet to be characterized. In this paper we demonstrate that this transporter is a novel sugar transporter of the tripartite ATP-independent periplasmic transporter family. In the absence of this transporter, H. influenzae cannot incorporate sialic acid into its lipooligosaccharides, making the organism unable to survive when exposed to human serum and causing reduced viability in biofilm growth.

HPLC analysis of plant DNA methylation: a study of critical methodological factors

HPLC analysis of nucleosides is important for determining total DNA methylation in plants and can be used to help characterise epigenetic changes during stress, growth and development. This is of particular interest for in vitro plant cultures as they are highly susceptible to genetic change. HPLC methodologies have been optimised for mammalian and microbial DNA, but not for plants. This study examines critical methodological factors in the HPLC analysis of plant DNA methylation using in vitro cultures of Ribes ciliatum. HPLC revealed that complete removal of RNA from plant DNA extractions is difficult using RNase (A and T1) digestions and LiCl precipitation. This suggests that base analysis should be avoided when using these RNA removal techniques, as bases from residual RNA fragments will inflate peak areas for DNA-derived bases. Nucleoside or nucleotide analysis is therefore recommended as a more suitable option as RNA and DNA constituents can be readily separated. DNA digestion was also a critical factor as methylation was under-estimated following incomplete nuclease digestion and over-estimated following incomplete phosphatase digestion. The units of enzyme required for complete DNA digestion was optimised and found to be 20-200 times less for nuclease P1 and 15 times less for alkaline phosphatase as compared with previous protocols. Digestion performance was conveniently monitored using marker peaks that indicate incomplete digestion products. This study identifies critical components of HPLC analysis and offers a comprehensive guide for the stringent analysis of DNA methylation in plants.

Lipoprotein PsaA in virulence of Streptococcus pneumoniae: surface accessibility and role in protection from superoxide

PsaA of Streptococcus pneumoniae, originally believed to be an adhesin, is the lipoprotein component of an Mn2+ transporter. Mutations in psaA cause deficiencies in growth, virulence, adherence, and the oxidative stress response. Immunofluorescence microscopy shows that PsaA is hidden beneath the cell wall and the polysaccharide capsule and only exposed to antibodies upon cell wall removal. A psaBC deletion mutant, expressing PsaA normally, was as deficient in adherence to Detroit 562 cells as were strains lacking PsaA. Thus, PsaA does not appear to act directly as an adhesin, but rather, psaA mutations indirectly affect this process through the disruption of Mn2+ transport. The deficiency in Mn2+ transport also causes hypersensitivity to oxidative stress from H2O2 and superoxide. In a chemically defined medium, growth of the wild-type strain was possible in the absence of Fe2+ and Mn2+ cations after a lag of about 15 h. Addition of Mn2+ alone or together with Fe2+ allowed prompt and rapid growth. In the absence of Mn2+, the addition of Fe2+ alone extended the 15-h lag phase to 25 h. Thus, while Fe2+ adversely affects the transition from lag phase to log phase, perhaps through increasing oxidative stress, this effect is relieved by the presence of Mn2+. A scavenger specific for superoxides but not those specific for hydroxyl radicals or H2O2 was able to eliminate the inhibition of growth caused by iron supplementation in the absence of Mn2+. This implies that superoxides are a key player in oxidative stress generated in the presence of iron.

Antiendotoxin agents share molecular homology within their lipopolysaccharide binding domains

BACKGROUND

The purpose of this study was to determine whether antiendotoxin agents exhibit molecular homology within their lipopolysaccharide (LPS) binding domains, suggesting a common mechanism of action. We hypothesized that the presence of positively charged basic amino acids or a paucity of negatively charged acidic amino acids, or both, would be a critical characteristic of that portion of the molecule that binds to the highly negatively charged deep core/lipid A (DCLA) region of LPS.

MATERIALS AND METHODS

We analyzed the amino acid sequences of the variable light (VL) and heavy (VH) chain complementarity-determining regions (CDRs) of anti-DCLA monoclonal antibodies (mAbs) 1B6, 5A5, and 7C5 and compared them with (1) the CDRs of three irrelevant control mAbs and (2) the LPS binding region of bactericidal permeability-increasing protein (BPI). We purified and amplified the specific nucleotide sequences of the variable regions using reverse transcriptase polymerase chain reaction. DNA was sequenced by dideoxy termination, and protein sequences were deduced and analyzed. The percentages of acidic, basic, polar, and hydrophobic amino acids within VH and VL chain CDRs were determined.

RESULTS

We identified a paucity of negatively charged acidic amino acids exclusively within VL chain CDRs of anti-DCLA mAbs (P < 0.005). Although increased, the number of positively charged basic residues was not statistically significantly different; neither was the number of polar or hydrophobic amino acids. Conclusions. Our data suggest that the near absence of negatively charged acidic residues is critical for LPS binding. This characteristic appears to reside exclusively in the VL chain CDRs of anti-DCLA mAbs.

Immunization with antibodies that mimic LPS protects against gram negative bacterial sepsis

We developed 9H1.B11, an anti-idiotypic anti-deep core/lipid A (DCLA), murine monoclonal antibody (mAb) that mimics the conserved DCLA region of lipopolysaccharide (LPS). It recognizes an epitope in the variable region of an DCLA mAb, binds to the murine macrophage cell surface, and inhibits LPS-induced macrophage cytokine secretion. We hypothesized that (1) active immunization with mAb 9H1.B11 would be associated with the development of anti-DCLA antibodies and (2) immunization would protect against subsequent gram negative bacterial challenge. Mice were immunized for 8 weeks before intraperitoneal (ip) challenge with Escherichia coli O111:B4 bacteria. Control animals were immunized with an irrelevant IgM antibody 8133 (negative control) or with LPS derived from Salmonella minnesota Re bacteria (positive control). Sera from immunized mice were collected, and titers against the core region of LPS (Re) and against LPS derived from the infecting E. coli strain were determined. Mice immunized with mAb 9H1.B11 developed measurable titers against S. minnesota Re LPS but not against the challenge strain of E. coli. However, immunization with 9H1.B11 on S. minnesota Re LPS protected against subsequent infection due to E. coli O111:B4 (100% survival). The group of mice immunized with IgM 8133 exhibited only 25% survival. The development of an anti-S. minnesota Re LPS titer after immunization with 9H1.B11 provides further evidence that a portion of 9H1.B11 mimics the conserved DCLA region of LPS. We believe that this approach holds considerable promise and plan further studies to define the mechanism by which protective capacity occurs.

Macrophages expressing a fusion protein derived from bactericidal/permeability-increasing protein and IgG are resistant to endotoxin

OBJECTIVES

To generate a recombinant fusion protein (FP) based on the endotoxin-binding domain of bactericidal/permeability-increasing protein (BPI) and the constant domain of IgG and to test its ability to inhibit lipopolysaccharide (LPS)-induced macrophage tumor necrosis factor alpha (TNF-alpha) secretion.

DESIGN

A murine macrophage cell line, RAW 264.7, was transfected with a BPI-IgG FP before incubation with LPS. The amount of LPS-induced TNF-alpha protein secreted was measured and compared with that secreted by cells transfected with a control construct.

SETTING

Basic science research laboratory.

MAIN OUTCOME MEASURES

Secreted TNF-alpha protein concentration.

RESULTS

After transfection, RAW 264.7-cell FP expression was detected in cell lysates and supernatants. At each LPS dose tested, cells transfected with the FP gene secreted less TNF-alpha than did cells transfected with a control construct.

CONCLUSIONS

The FP possesses substantial antiendotoxin activity, as delineated by inhibition of LPS-induced TNF-alpha secretion by murine macrophages transfected with the fusion gene construct. In the future, such FP may be used as a clinical reagent to reduce the morbidity and mortality associated with serious gram-negative bacterial infections in surgical patients.

A novel endotoxin antagonist attenuates tumor necrosis factor-alpha secretion

Twenty-seven amino acid peptides with sequences corresponding to a proposed endotoxin binding region of bactericidal permeability increasing protein (BPI):1) inhibit lipopolysaccharide induced macrophage tumor necrosis factor-alpha (TNF-alpha) secretion, 2) have bactericidal activity against gram-negative bacteria, and 3) protect mice from a lethal lipopolysaccharide (LPS) challenge. Unfortunately, peptides have a short halflife in vivo. Therefore, we have chemically conjugated the BPI based peptide, BG38, to a larger carrier protein, keyhole limpet hemocyanin (KLH), and characterized its ability: 1) to inhibit LPS induced macrophage TNF-alpha secretion and 2) to decrease plasma endotoxin and TNF-alpha levels following an i.v. injection of E. coli 0111:B4 LPS. BG38-KLH inhibited cultured macrophage TNF-alpha secretion in response to LPS derived from four pathogenic strains of gram-negative bacteria in a dose dependent manner (>90% inhibition at 50 microgram/ml, P < 0.05 Student's t test). BG38-KLH also decreased serum endotoxin (>90%, P < 0.05 Student's t test) and peak TNF-alpha levels (>30% inhibition, P < 0.05 Student's t test) following E. coli LPS challenge in a murine gram-negative bacterial sepsis model. Novel endotoxin antagonists based upon a small domain of BPI represent promising reagents for the treatment of serious gram-negative bacterial infections.

Peptide derivatives of three distinct lipopolysaccharide binding proteins inhibit lipopolysaccharide-induced tumor necrosis factor-alpha secretion in vitro

BACKGROUND

Bactericidal permeability increasing protein (BPI), Limulus anti-lipopolysaccharide factor (LALF), and lipopolysaccharide binding protein (LBP) are three distinct proteins that bind to lipopolysaccharide (LPS). Intriguingly, binding of BPI and LALF to LPS results in neutralization of LPS activity, whereas the binding of LBP to LPS creates a complex that results in augmentation of LPS activity. Despite their different effector functions, we hypothesized that peptides based on the sequences of the proposed LPS-binding motif from each protein would neutralize LPS in vitro.

METHODS

Three peptide sequences, each 27 amino acids in length, of the proposed LPS-binding motif of BPI (BG38), LALF (BG42), and LBP (BG43) were synthesized. These peptides were then tested for their: (1) ability to inhibit macrophage secretion of TNF-alpha after stimulation by LPS derived from Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Serratia marcescens; and (2) bactericidal activity against these same four gram-negative bacteria in vitro.

RESULTS

Synthetic peptides BG38 (BPI-derived), BG42 (LALF-derived), and BG43 (LBP-derived) but not control peptide significantly inhibited LPS-induced tumor necrosis factor-alpha secretion by macrophages and mediated the lysis of gram-negative bacteria in vitro. In addition, preincubation of LPS with peptide BG38 mediated complete protection subsequent to lethal endotoxin challenge.

CONCLUSIONS

These data demonstrate that small peptides derived from BPI, LALF, and LBP retained significant endotoxin-neutralizing and bactericidal activity against many different gram-negative bacteria in vitro. Identification of this conserved LPS-binding region within each protein may aid in the development of new immunomodulatory reagents for use as adjuvant therapy in the treatment of gram-negative bacterial sepsis.

Lymphocyte-derived cytokines augment macrophage tumor necrosis factor-alpha and interleukin-6 secretion during experimental gram-negative bacterial sepsis

Although lymphocyte-derived cytokines are known to augment macrophage cytokine production in vitro, their effect on macrophage tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) secretion during gram-negative bacterial sepsis has not been characterized. The purpose of this study was to examine the effect of lymphocyte-derived cytokines on macrophage TNF-alpha and IL-6 secretion during gram-negative bacterial peritonitis. To examine this problem, uninfected and infected mice were studied. Mice were infected with Escherichia coli O111:B4 and two subgroups were examined consisting of those pretreated iv 1 hr prior to bacterial challenge with either (1) saline or (2) anti-E. coli O111:B4 LPS mAb 2A3, the latter administered to abrogate the effects of LPS in vivo. Thus, three groups of mice were studied in relation to pretreatment and infectious challenges: (1) saline/saline (control); (2) saline/E. coli (saline); and (3) mAb 2A3/E. coli (mAb 2A3). Nonadherent splenocytes (> 95% lymphocytes by histologic staining criteria) harvested 16 hr later from mice in each group were incubated in culture ex vivo for 3 hr to obtain supernatants containing lymphocyte-derived cytokines. These supernatants containing lymphocyte-derived cytokines then were incubated in vitro with naive splenic macrophages with or without E. coli O111:B4 LPS. Macrophage TNF-alpha and IL-6 levels were determined using L929 and B9 bioassays.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative properties of tobacco hornworm, Manduca sexta, carbonic anhydrases

Comparative properties of midgut, fat body and integumentary carbonic anhydrases (CAs) were measured as functions of CA-catalyzed CO2 hydration or p-nitrophenylacetate (pNPA) hydrolysis in feeding larvae and pharate pupae. Alkali metal cations fully reverse the halide anion inhibition of CA catalyzed CO2 hydration during the larval but not the pharate pupal stages in development. Concentrations of acetazolamide required to inhibit 50% of tissue-specific CA-catalyzed CO2 hydration (I50) were approximately 10(-8) M. The activity profiles between pH 6.0 and 9.0 had well-defined optima around pH 8.0 with activity declining dramatically above the optima. When CA-catalyzed pNPA hydrolysis was measured between 4 and 37 degrees C, insect enzymes failed to exhibit positive Q10 values between 25 and 37 degrees C. The affinities of the hornworm CAs toward pNPA were determined with stage- and tissue-specific Km ranging from 0.42 to 8.0 X 10(-3) M. It is concluded that tissue and stage-specific CAs exist in M. sexta, whose properties appear to differ markedly with those previously reported for mammalian enzymes.

Comparative properties of mammalian and insect carbonic anhydrases: effects of potassium and chloride on the rate of carbon dioxide hydration

1. Carbonic anhydrase (E.C.4.2.1.1) catalysed CO2 hydration was studied with enzymes from mammalian and insect sources at CO2 concentrations of 7.6-30.8 mM. 2. At 0.01-0.15 M, potassium chloride (KCl) or choline chloride (ChCl) markedly inhibited all 8 mammalian enzymes studied. 3. Inhibition by KCl is always greater than that associated with ChCl. 4. KCl non-competitively inhibits and choline chloride competitively inhibits bovine carbonic anhydrase. 5. Carbonic anhydrase obtained from fat body, integumentary epithelium and midgut tissues of larval tobacco hornworms, Manduca sexta, is greatly stimulated by KCl and slightly inhibited by ChCl. 6. We propose that the effect of K+ on mammalian and insect carbonic anhydrases if fundamentally different.