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SUMMARY: Plant adaptation from aquatic to terrestrial environments required modifications to cell wall structure and function to provide tolerance to new abiotic and biotic stressors. Here, we investigate the nature and function of red auronidin pigment accumulation in the cell wall of the liverwort Marchantia polymorpha. Transgenic plants with auronidin production either constitutive or absent were analysed for their cell wall properties, including fractionation of polysaccharide and phenolic components. While small amounts of auronidin and other flavonoids were loosely associated with the cell wall, the majority of the pigments were tightly associated, similar to what is observed in angiosperms for polyphenolics such as lignin. No evidence of covalent binding to a polysaccharide component was found: we propose auronidin is present in the wall as a physically entrapped large molecular weight polymer. The results suggested auronidin is a dual function molecule that can both screen excess light and increase wall strength, hydrophobicity and resistance to enzymatic degradation by pathogens. Thus, liverworts have expanded the core phenylpropanoid toolkit that was present in the ancestor of all land plants, to deliver a lineage‐specific solution to some of the environmental stresses faced from a terrestrial lifestyle. [ABSTRACT FROM AUTHOR]

SUMMARY: During fruit ripening, polygalacturonases (PGs) are key contributors to the softening process in many species. Apple is a crisp fruit that normally exhibits only minor changes to cell walls and limited fruit softening. Here, we explore the effects of PG overexpression during fruit development using transgenic apple lines overexpressing the ripening‐related endo‐POLYGALACTURONASE1 gene. MdPG1‐overexpressing (PGox) fruit displayed early maturation/ripening with black seeds, conversion of starch to sugars and ethylene production occurring by 80 days after pollination (DAP). PGox fruit exhibited a striking, white‐skinned phenotype that was evident from 60 DAP and most likely resulted from increased air spaces and separation of cells in the hypodermis due to degradation of the middle lamellae. Irregularities in the integrity of the epidermis and cuticle were also observed. By 120 DAP, PGox fruit cracked and showed lenticel‐associated russeting. Increased cuticular permeability was associated with microcracks in the cuticle around lenticels and was correlated with reduced cortical firmness at all time points and extensive post‐harvest water loss from the fruit, resulting in premature shrivelling. Transcriptomic analysis suggested that early maturation was associated with upregulation of genes involved in stress responses, and overexpression of MdPG1 also altered the expression of genes involved in cell wall metabolism (e.g. β‐galactosidase, MD15G1221000) and ethylene biosynthesis (e.g. ACC synthase, MD14G1111500). The results show that upregulation of PG not only has dramatic effects on the structure of the fruit outer cell layers, indirectly affecting water status and turgor, but also has unexpected consequences for fruit development. [ABSTRACT FROM AUTHOR]

Capsicums (bell peppers) are an important international crop that has specific postharvest handling requirements due to a high susceptibility to quality deterioration from water loss. When harvested green, capsicums are susceptible to chilling injury if stored below ∼7°C for long periods, although red fruit can withstand lower temperatures. Chilling injury usually manifests as spots of surface pitting that can develop into large regions of pitted areas. Extending storage life to enable sea freight from countries distant from their final market (such as New Zealand) means that fruit must be exceptionally well cleaned to allow high humidity to be maintained during storage so that rots do not develop. A range of postharvest treatments that might reduce chilling injury is discussed, although few if any of these have entered commercial practice. This review also covers biology and consumer attributes including colour, taste and flavour, and texture. [ABSTRACT FROM AUTHOR]

Visual symptoms of the onset of senescence in Sandersonia aurantiaca flowers begin with fading of flower colour and wilting of the tissue. When fully senescent, the flowers form a papery shell that remains attached to the plant. The cell walls of these flowers have been examined to determine whether there are wall modifications associated with the late stages of expansion and subsequent senescence‐related wilting. Changes in the average molecular size of pectin were limited through flower opening and senescence, although there was a loss of neutral sugar‐containing side‐branches from pectins in opening flowers, and the total amounts of pectin and cellulose continued to rise in cell walls of fully senescent sandersonia flowers. Xyloglucan endotransglycosylase activity increased in opening and mature flowers, but declined sharply as flowers wilted. Concomitantly, the proportion of hemicellulose polymers of increasing molecular weight increased from flower expansion up to the point at which wilting occurred. Approximately 50% of the non‐cellulosic neutral sugar in mature flower cell walls was galactose, primarily located in an insoluble cell wall fraction. Total galactose in this fraction increased per flower with maturity, then declined at the onset of wilting. β‐Galactosidase activity was low in expanding tepals, but increased as flowers matured and wilted. [ABSTRACT FROM PUBLISHER]

We previously isolated a cDNA clone, pTIP13, whose homologous mRNA rapidly declined in abundance in the tips of harvested asparagus (Asparagus officinalis L.) spears [King and Davies (1992) Plant Physiol. 100: 1661]. In order to identify factors regulating the postharvest deterioration of asparagus, we have now sequenced the pTIP13 cDNA, derived the encoded amino acid sequence and determined the cellular location of pTIP13 mRNA by in situ hybridization. pTIP13 encodes a derived protein that is rich in proline (22.3%), but also has a high content of lysine (15.2%) and threonine (14.1%). The proline residues are located in motifs at the amino-terminal region of the protein. The carboxyl-terminal region of the derived protein has a high leucine content and shares >64% amino acid identity with derived proteins identified from cDNA clones to cell wall protein precursor mRNAs obtained from soybean hypocotyls, alfalfa roots, and tomato fruit. Genomic Southern analysis suggests that pTIP13 is encoded by a single-copy gene in asparagus. pTIP13 mRNA was localized to specific cell types in the young bracts of the asparagus spear tip. The results provide new information on the complexity of tissue responses in the tips of asparagus spears following harvest. [ABSTRACT FROM AUTHOR]

• Growth of bell pepper fruit is distinguished by a large release of cell wall galactan. • Cell wall polysaccharide modification is minimal during ripening and postharvest. • Sizeable expression of some cell wall-modifying genes with ripening. • No distinctive cell wall change with postharvest water loss and whole-fruit softening. We have investigated the cell wall polysaccharides of a commercially grown blocky-type red bell pepper (Capsicum annuum L. 'Funky') during on-plant growth and ripening, and after postharvest water loss. There was no evidence of substantial depolymerisation of cell wall pectic polysaccharides or hemicelluloses at any ripening stage. The onset of fruit ripening was accompanied by a slightly increased solubilisation of very high molecular weight polyuronides. Measurable polygalacturonase activity was absent, despite an endo -polygalacturonase mRNA being present as fruit turned red. The largest cell wall change was a substantial loss of galactose (primarily from Na 2 CO 3 -soluble rhamnogalacturonan-I) as green fruit approached full size, which could not be directly correlated with conventionally assayed β-galactosidase/galactanase activities. The majority of β-galactosidase/galactanase gene expression and enzyme activity was found in fully ripe fruit, although by this stage galactose loss was comparatively minimal. This suggests that the upregulation in activity has significance beyond wall rheology, or is vestigial. Severe water-stress applied to harvested ripe fruit did not result in any cell wall changes suggestive of cell wall breakdown, compared with cell walls of fruit stored under high humidity conditions. We conclude that this commercial line of bell pepper, which was bred for intensive glasshouse production, has wall characteristics that result in retention of typical crisp texture and extended postharvest storage life. [ABSTRACT FROM AUTHOR]

The localization of cell wall polysaccharides of the fused petals of monocotyledonous Sandersonia aurantiaca flowers has been identified using antibodies directed to pectin and xyloglucan epitopes and detection by fluorescence microscopy. Cross sections of the petal tissue were taken from cut flowers in bud and at various stages of maturity and senescence. Patterns of esterification in pectin backbones were identified by JIM5 and 2F4 labelling. Pectic galactan and arabinan side branches were detected by LM5 and LM6, respectively, while fucosylated xyloglucan was identified by CCRC-M1. The labelling patterns highlighted compositional differences between walls of the outer/inner epidermis compared to the spongy parenchyma cells of the interior mesophyll for fucosylated xyloglucan and arabinan. Partially esterified homogalacturonan was present in the junction zones of the outer epidermis and points of contact between cells of the mesophyll, and persisted throughout senescence. Pectic galactans were ubiquitous in the outer and inner epidermal cell walls and walls of the interior mesophyll at flower opening, whereas pectic arabinan was found predominantly in the epidermal cells. Galactan was lost from walls of all cells as flowers began to senesce, while fucosylated xyloglucan appeared to increase over this time. Such differences in the location of polysaccharides and the timing of changes suggest distinct combinations of certain polysaccharides offer mechanical and rheological advantages that may assist with flower opening and senescence.