Developmental changes of sugar contents in the gall on the leaf of elm (Zelkowa serrata Makino) formed byParacolopha morrisoni Baker (homopetra)

To understand cell wall polysaccharide synthesis and the role of gall in interaction with aphids, the changes of sugar contents in the galls during their growth and development were determined from May 2 to June 8, 1996. The sugar content in the symplastic (MeOH and hot water) fractions decreased as the developmental stages progressed. In the cell wall fraction, the amount of pectic substances (2-3 mg per gram fresh weight) did not change. The hemicellulosic substance increased by 40% from May 14 to May 31. Among the neutral sugar components of hemicellulosic polysaccharides, xylose and arabinose contents increased during development of the gall, suggesting that xylans with arabinose residues were massively synthesized. On the other hand, glucose content decreased during development of the gall. The cellulose substance consistently increased 5 folds from May 2 to 31. The relationship between the aphid and the changes in sugar contents of cell walls during the development of aphid and the gall formation was discussed.     

Glycanase activities associated with cell walls ofCicer arietinum L. epicotyls

The effect of the proteins extracted with 1 M LiCl from theCicer arietinum etiolated epicotyl cell walls on the degradation of polysaccharides extracted with alkali was studied. The hemicellulosic polysaccharides were fractionated into three fractions extracted with 4 % KOH, 4 % KOH containing 8 M urea, and 24 % KOH. The protein extract showed exo-glycanase activity against all three hemicellulosic fractions whilst endo-glycanase activity was shown mainly against the hemicellulosic polysaccharides extracted with 4% KOH.     

Aphid galls accumulate high concentrations of amino acids: a support for the nutrition hypothesis for gall formation

The nutrition hypothesis for the adaptive significance of insect gall formation postulates that galls accumulate higher concentrations of nutritive compounds than uninfested plant tissue, resulting in a high performance of the gall former. This hypothesis has been supported by some taxa of gall insects, but not by taxa such as cynipid wasps. Aphid galls are expected to require higher levels of nitrogen than other insects’ galls with a single inhabitant, because aphid galls are required to sustain a number of aphids reproducing parthenogenetically over two generations. The present study tested this hypothesis by evaluating aphid performance and amino acid concentration in phloem sap, using the aphid Rhopalosiphum insertum (Walker) (Homoptera: Aphididae), which establishes colonies on leaves of Sorbus commixta Hedlund or in galls of the aphid Sorbaphis chaetosiphon Shaposhnikov (Homoptera: Aphididae). We prepared the gall and non‐gall treatments on trees of S. commixta, in which R. insertum fundatrices were reared and allowed to reproduce. In S. chaetosiphon galls, R. insertum colonies propagated more rapidly, and the second generation grew larger and more fecund than on ungalled leaves. The amount of amino acids exuding from cut galled leaves was fivefold that in ungalled leaves; however, there was no significant difference in the amino acid composition between galled and ungalled leaves. In the intact leaves, total amino acid concentration in the phloem sap declined rapidly from late April to late May; however, the galls retained this high amino acid concentration in developing leaves for 1 month. These results indicate that the improved performance in R. insertum is ascribed to the increased concentration of amino acids in galled leaves. We suggest that S. chaetosiphon galls function to promote the breakdown of leaf protein, leading to an increased performance of gall‐inhabiting aphids.     

Manipulation of food resources by a gall-forming aphid: the physiology of sink-source interactions

Summary We examined the capacity of the galling aphid, Pemphigus betae, to manipulate the sink-source translocation patterns of its host, narrowleaf cottonwood (Populus angustifolia). A series of ¹⁴C-labeling experiments and a biomass allocation experiment showed that P. betae galls functioned as physiologic sinks, drawing in resources from surrounding plant sources. Early gall development was dependent on aphid sinks increasing allocation from storage reserves of the stem, and later development of the progeny within the gall was dependent on resources from the galled leaf blade and from neighboring leaves. Regardless of gall position within a leaf, aphids intercepted ¹⁴C exported from the galled leaf (a non-mobilized source). However, only aphid galls at the most basal site of the leaf were strong sinks for ¹⁴C fixed in neighboring leaves (a mobilized source). Drawing resources from neighboring leaves represents active herbivore manipulation of normal host transport patterns. Neighboring leaves supplied 29% of the ¹⁴C accumulating in aphids in basal galls, while only supplying 7% to aphids in distal galls. This additional resource available to aphids in basal galls can account for the 65% increase in progeny produced in basal galls compared to galls located more distally on the leaf and limited to the galled leaf as a food resource. Developing furits also act as skins and compete with aphid-induced sinks for food supply. Aphid success in producing galls was increased 31% when surrounding female catkins were removed.     

Do aphid galls provide good nutrients for the aphids?: Comparisons of amino acid concentrations in galls among Tetraneura species (Aphididae: Eriosomatinae)

Some aphid species induce leaf galls, in which the fundatrix parthenogenetically produces many nymphs. In order to ensure high performance, galls have to provide the aphids with sufficient nutrients, in particular, amino acids as a nitrogen source. We tested this hypothesis using six Tetraneura aphid species that induce closed galls. We extracted free amino acids from the whole gall tissues of unit weight and quantified the concentration of each amino acid. There were large differences in the total amino acid concentrations among galls of the Tetraneura species. Tetraneura species in which higher concentrations of total amino acids were found in the gall tended to produce larger numbers of offspring. Of the amino acids found, asparagine was predominant in the gall. The asparagine concentration in T. yezoensis galls was several hundred times as high as in control leaves. We discussed why such a high level of asparagine accumulates in aphid galls.     

Comparative characterization of degraded and non-degradative hemicelluloses from barley straw and maize stems: Composition, structure, and thermal properties

Three organic solvents and one aqueous alkaline solution for fully fractional dissolving hemicelluloses from mild ball-milled cell wall of lignified barley straw and maize stems are described: 90% neutral dioxane, 80% dioxane containing 0.05 M HCl, dimethyl sulfoxide (DMSO), and 8% aqueous KOH. The four successive extractions resulted in dissolution of 94.6% and 96.4% of the original hemicelluloses and 93.7% and 95.3% of the original lignin from barley straw and maize stems, respectively. The structures of the hemicellulosic fractions released during the treatment with the neutral solvents of 90% dioxane and DMSO was found to remain intact, while the extractions with 80% acidic dioxane and 8% KOH under the conditions used resulted in a partial depolymerization of dissolved polysaccharides by cleavage of the glycosidic bonds and saponification of the ester groups in the polymers. The 90% neutral dioxane-soluble hemicellulosic fractions consisted mainly of the more branched arabinoxylans and mixed-linkage glucans such as β-glucans, whereas the hemicellulosic fractions solubilized during the sequential treatments with 80% acidic dioxane, DMSO, and 8% KOH are composed of arabino-(4-O-methyl-d-glucurono) xylans as the major hemicellulosic materials. In addition, the hemicellulosic polymers contained small amounts of ferulic and p-coumaric acids and lignins, revealing that the hemicelluloses removed are mostly unbound to the lignins in the cell walls of cereal straws. This non-degradative cell wall dissolution offers the potential to analyze polysaccharide components for the first time, and improve current hemicellulosic isolation method by using high concentration of aqueous alkali from the delignified cell walls.     

Evolutionary relationships of Pemphigus and allied genera (Hemiptera: Aphididae: Eriosomatinae) and their primary endosymbiont,Buchnera aphidicola

Aphids harbor primary endosymbionts, Buchnera aphidicola, in specialized cells within their body cavities. Aphids and Buchnera have strict mutualistic relationships in nutrition exchange. This ancient association has received much attention from researchers who are interested in endosymbiotic evolution. Previous studies have found parallel phylogenetic relationships between non‐galling aphids and Buchnera at lower taxonomic levels (genus, species). To understand whether relatively isolated habitats such as galls have effect on the parallel relationships between aphids and Buchnera, the present paper investigated the phylogenetic relationships of gall aphids from Pemphigus and allied genera, which induce pseudo‐galls or galls on Populus spp. (poplar) and Buchnera. The molecular phylogenies inferred from three aphid genes (COI, COII and EF‐1α) and two Buchnera genes (gnd, 16S rRNA gene) indicated significant congruence between aphids and Buchnera at generic as well as interspecific levels. Interestingly, both aphid and Buchnera phylogenies supported three main clades corresponding to the galling locations of aphids, namely leaf, the joint of leaf blade and petiole, and branch of the host plant. The results suggest phylogenetic conservatism of gall characters, which indicates gall characters are more strongly affected by aphid phylogeny, rather than host plants.     

AFM Investigations of Cellulose Fibers in Bintje Potato (Solanum tuberosum L.) Cell Wall Fragments

Atomic force microscopy (AFM) has been used to image the cellulose networks in moist fragments of the cell walls of Bintje potato (Solanum tuberosum L.). The interfiber spacing in hydrated native cell wall fragments was found to be 26.2 nm. This value is consistent with published estimates of the contour length of xyloglucan cross-links determined by transmission electron microscopy (TEM) studies of cell walls. Sequential extraction of the pectin using CDTA and Na₂CO₃ led to shrinkage of the cell wall fragment and a reduction in interfiber spacing to 20.2 nm. Partial extraction of xyloglucan using 1 M KOH caused a small decrease in interfiber spacing to 19.5 nm. Finally, the almost complete removal of xyloglucan with 4 M KOH substantially reduced the interfiber spacing to 11 nm. The results are consistent with a model for the cell wall in which the cellulose–xyloglucan network is immersed in a swollen, hydrated pectin network.     

Cell-wall polysaccharides and glycoproteins of parenchymatous tissues of runner bean (Phaseolus coccineus).

1. Polymers were solubilized from the cell walls of parenchyma from mature runner-bean pods with minimum degradation by successive extractions with cyclohexane-trans-1,2-diamine-NNN'N'-tetra-acetate (CDTA), Na2CO3 and KOH to leave the alpha-cellulose residue, which contained cross-linked pectic polysaccharides and Hyp-rich glycoproteins. These were solubilized with chlorite/acetic acid and cellulase. The polymers were fractionated by anion-exchange chromatography, and fractions were subjected to methylation analysis. 2. The pectic polysaccharides differed in their ease of extraction, and a small proportion were highly cross-linked. The bulk of the pectic polysaccharides solubilized by CDTA and Na2CO3 were less branched than those solubilized by KOH. There was good evidence that most of the pectic polysaccharides were not degraded during extraction. 3. The protein-containing fractions included Hyp-rich and Hyp-poor glycoproteins associated with easily extractable pectic polysaccharides, Hyp-rich glycoproteins solubilized with 4M-KOH+borate, the bulk of which were not associated with pectic polysaccharides, and highly cross-linked Hyp-rich glycoproteins. 4. Isodityrosine was not detected, suggesting that it does not have a (major) cross-linking role in these walls. Instead, it is suggested that phenolics, presumably linked to C-5 of 3,5-linked Araf residues of Hyp-rich glycoproteins, serve to cross-link some of the polymers. 5. There were two main types of xyloglucan, with different degrees of branching. The bulk of the less branched xyloglucans were solubilized by more-concentrated alkali. The anomeric configurations of the sugars in one of the highly branched xyloglucans were determined by 13C-n.m.r. spectroscopy. 6. The structural features of the cell-wall polymers and complexes are discussed in relation to the structure of the cell walls of parenchyma tissues.     

Life history strategy and taxonomic position of gall midges (Diptera: Cecidomyiidae) inducing leaf galls on Styrax japonicus (Styracaceae)

Four gall midge species (Diptera: Cecidomyiidae) that induce leaf galls on Styrax japonicus (Styracaceae) were identified to generic level based on larval morphology. Three of these gall midges, which induce whitish hemiglobular galls, flattened subglobular galls, and purple globular galls, respectively, were identified as three genetically distinct species of Contarinia, and the remaining species, which induces globular galls with dense whitish hairs, was identified as a species of Dasineura. Field surveys in Fukuoka, Japan, revealed that adults of these gall midges emerged and oviposited in late March to mid‐April at Mount Tachibana (approximately 200 m a.s.l.) and in late April to early May at Mount Sefuri (about 1050 m a.s.l.), coinciding with the leaf‐opening season of S. japonicus. Larvae of these gall midges mostly developed into third instars by June and then left their galls and dropped to the ground. These species therefore have a life history strategy that differs from that of another S. japonicus‐associated gall midge, Oxycephalomyia styraci, which overwinters as the first instar in ovate swellings, matures rapidly in spring, and emerges directly from the galls.     

Developmental anatomy and immunocytochemistry reveal the neo-ontogenesis of the leaf tissues of Psidium myrtoides (Myrtaceae) towards the globoid galls of Nothotrioza myrtoidis (Triozidae)

Key message

The temporal balance between hyperplasia and hypertrophy, and the new functions of different cell lineages led to cell transformations in a centrifugal gradient that determines the gall globoid shape.

Abstract

Plant galls develop by the redifferentiation of new cell types originated from those of the host plants, with new functional and structural designs related to the composition of cell walls and cell contents. Variations in cell wall composition have just started to be explored with the perspective of gall development, and are herein related to the histochemical gradients previously detected on Psidium myrtoides galls. Young and mature leaves of P. myrtoides and galls of Nothotrioza myrtoidis at different developmental stages were analysed using anatomical, cytometrical and immunocytochemical approaches. The gall parenchyma presents transformations in the size and shape of the cells in distinct tissue layers, and variations of pectin and protein domains in cell walls. The temporal balance between tissue hyperplasia and cell hypertrophy, and the new functions of different cell lineages led to cell transformations in a centrifugal gradient, which determines the globoid shape of the gall. The distribution of cell wall epitopes affected cell wall flexibility and rigidity, towards gall maturation. By senescence, it provided functional stability for the outer cortical parenchyma. The detection of the demethylesterified homogalacturonans (HGAs) denoted the activity of the pectin methylesterases (PMEs) during the senescent phase, and was a novel time-based detection linked to the increased rigidity of the cell walls, and to the gall opening. Current investigation firstly reports the influence of immunocytochemistry of plant cell walls over the development of leaf tissues, determining their neo-ontogenesis towards a new phenotype, i.e., the globoid gall morphotype.     

The effects of host-plant properties on gall density,gall weight and clone size in the aphidAploneura lentisci (Pass.) (Aphididae: Fordinae) in Israel

Summary Samples of shoots ofPistacia lentiscus carrying galls of the aphid,Aploneura lentisci, were collected at three localities in Israel. Shoots growing near pruning scars carried more galls than elsewhere on the plant, but these galls weighed less and contained fewer aphids (smaller clones). The proportion of empty galls increased with gall density. Crowding of galls at such sites may be due to the early burst of buds at the time of aphid emergence from the overwintering eggs, and not to active search for preferred sites. Shoots bearing larger numbers of leaves carried heavier galls, which contained larger aphid clones. The position of the galled leaf on the shoot had no effect on gall weight nor on clone size. The physiological condition of the plant may be an important environmental (ecological) factor affecting the variation in clone-size and in aphid morphology among galls.     

Structural characterization of cell wall polysaccharides from two plant species endemic to central Africa,Fleurya aestuans and Phragmenthera capitata

Fleurya aestuans (Linnaeus) Miquel and Phragmenthera capitata (Spreng) are two plants endemic to central Africa that are used in traditional medicine. However, information on their molecular constituents is lacking. In the present study and as part of our research on the structure/bioactivity relationship of plant cell wall molecules, we investigated the structure of polysaccharides isolated from leaf cell walls of both plant species. To this end, we used sequential extraction of polysaccharides, gas chromatography, matrix assisted laser desorption ionisation-time of flight mass spectrometry (MALDI-TOF MS) and immuno-dot assays. Our data indicate the presence of both pectin and hemicellulosic polysaccharides in the cell walls of both plants. In particular, cell wall of F. aestuans leaves appears to contain much more pectin than those of P. capitata. Structural analysis of hemicellulosic polysaccharides revealed differences in the structure of xyloglucan isolated from both species. While only the XXXG-type was found in P. capitata, both XXXG and XXGG types were detected in F. aestuans. No arabinosylated subunits were found in any of the xyloglucan isolated from both plant species. In addition, xylan structure with non methylated-α-d-glucuronic acid on side chains was only detected in F. aestuans leaf cell walls. Finally, structural analysis of rhamnogalacturonan-I (RG-I) and rhamnogalacturonan-II (RG-II) shows that unlike RG-II, RG-I is qualitatively different between F. aestuans and P. capitata leaves.     

ANATOMY OF SOME LEAF GALLS OF ROSA WOODSII (ROSACEAE)

Infection of Rosa woodsii by some members of the order Hymenoptera results in neoplasmic outgrowths on the leaves. One type of outgrowth produces a spherical swelling (leaf gall) while the other has extensive hair-like proliferations (hairy gall). The anatomy and ultrastructure of these galls were examined by light microscopy and transmission electron microscopy. The leaf gall cells were considerably larger than normal cells, lacked well-developed chloroplasts and were loosely arranged with prominent intercellular spaces. Vascular bundles were scattered throughout the gall tissue. The upper three cell layers of the leaf gall tissue resembles a periderm, having many suberin lamellae. The suberin lamellae were often traversed by pores which may represent incomplete plasmodesmata. Phenolic compounds were commonly seen both in the normal and gall cells. A layer of internal cells of the hairy galls have remarkably thickened cell walls, presumably due to the deposition of cellulosic substances. Unlike leaf galls, the epidermal cells of the hairy galls were not heavily cuticularized and no periderm was found. The hair-like outgrowths present on the outer surface of these galls had a central vascular bundle. The epidermis of the outgrowths also had thickened cell walls, and trichomes occurred on the outer surface. The structural modifications brought about by the insect invasion in these two galls are compared and their roles in gall formation are discussed.     

Tuberaphis owadai (Homoptera), a new aphid species forming a large gall on Styrax tonkinensis in northern Vietnam

Tuberaphis owadai sp. nov., an aphid species forming coral‐shaped galls on Styrax tonkinensis in northern Vietnam, is described. We found that the species produces many sterile second‐instar soldiers in the gall. The colony size of a large gall was estimated to be 178 000, approximately half of which were soldiers. Alates emerging from galls contained sexual embryos, indicating that the life cycle is monoecious (non‐host‐alternating). Predaceous larvae of the pyralid moth Assara seminivalis were found in several galls.     

Lygodium japonicum fern accumulates copper in the cell wall pectin

The present work reports the results of a study on the growth kinetics and characterization of matrix polysaccharides in the cell walls of Lygodium japonicum prothallium grown in the presence of copper (Cu). When the prothallium was cultured in the media containing 0.2 mM or 0.4 mM CuSO(4), it showed a rapid accumulation of Cu with a maximum uptake of Cu measured in the cells up to 20 d of culture. The maximum rate of Cu uptake into the prothallium was greater for 0.4 mM Cu-treated cells (17.2 micromol g(-1) DW) than for 0.2 mM Cu-treated cells (3.2 micromol g(-1) DW). Cell walls were isolated from both untreated control and Cu-treated cells and then extracted sequentially with cyclohexane-trans-1,2-diaminetetra-acetate (CDTA), Na(2)CO(3), 1 M KOH, and 4 M KOH. The amount of pectin solubilized from 0.4 mM Cu-treated cell walls decreased to 53% of its level in the control, whereas the amount of hemicellulose solubilized from the Cu-treated cell walls represented 82% of that from control cell walls. When the polysaccharides were fractionated by anion-exchange chromatography into four carbohydrate components, considerable increases in fractions PI-3 and PII-3 eluted with 0.5 M NaCl were observed in CDTA-soluble (PI) and Na(2)CO(3)-soluble (PII) pectic polymers from Cu-treated cell walls. Fractions PI-3 and PII-3 were composed predominantly of uronic acid (more than 71% of total sugars). Approximately 66% of Cu within the cell walls was released from the 0.4 mM Cu-treated cells with the endo-pectate-lyase treatment, suggesting that most of the Cu that accumulated into the Lygodium prothallium is tightly bound to the homogalacturonan of the cell wall pectin.     

Isolation and characterisation of cell wall polysaccharides from cocoa (Theobroma cacao L.) beans

 Cell wall material (CWM) was prepared from sun-dried cocoa (Theobroma cacao L.) bean cotyledons before and after fermentation. The monosaccharide composition of the CWM was identical for unfermented and fermented beans. Polysaccharides of the CWM were solubilised by sequential extraction with 0.05 M trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CDTA), 0.05 M Na₂CO₃, and 1 M, 4 M and 8 M KOH. The non-cellulosic sugar composition for each fraction was similar for unfermented and fermented samples, indicating that fermentation caused no significant modification of the structural features of individual cell wall polysaccharides. Pectic polysaccharides accounted for 60% of the cell wall polysaccharides but only small amounts could be solubilised in solutions of CDTA, Na₂CO₃, and 1 M and 4 M KOH. The bulk of the pectic polysaccharides were solubilised in 8 M KOH and were characterised by a rhamnogalacturonan backbone heavily substituted with side-chains of 5-linked arabinose and 4-linked galactose. Linkage analysis indicated the presence of additional acidic polysaccharides, including a xylogalacturonan and a glucuronoxylan. Cellulose, xyloglucan and a galactoglucomannan accounted for 28%, 8% and 3% of the cell wall polysaccharides, respectively. It is concluded that the types and structural features of cell wall polysaccharides in cocoa beans resemble those found in the parenchymatous tissue of many fruits and vegetables rather than those reported for many seed storage polysaccharides. Received: 29 May 1999 / Accepted: 19 October 1999     

A genetic basis for the manipulation of sink–source relationships by the galling aphid <Emphasis Type="Italic">Pemphigus batae</Emphasis>

We examined how the galling aphid Pemphigus batae manipulates resource translocation patterns of resistant and susceptible narrowleaf cottonwood Populus angustifolia. Using carbon-14 (¹⁴C)-labeling experiments in common garden trials, five patterns emerged. First, although aphid galls on resistant and susceptible genotypes did not differ in their capacity to intercept assimilates exported from the leaf they occupied, aphids sequestered 5.8-fold more assimilates from surrounding leaves on susceptible tree genotypes compared to resistant genotypes. Second, gall sinks on the same side of a shoot as a labeled leaf were 3.4-fold stronger than gall sinks on the opposite side of a shoot, which agrees with patterns of vascular connections among leaves of the same shoot (orthostichy). Third, plant genetic-based traits accounted for 26% of the variation in sink strength of gall sinks and 41% of the variation in sink strength of a plant’s own bud sinks. Fourth, tree susceptibility to aphid gall formation accounted for 63% of the variation in ¹⁴C import, suggesting strong genetic control of sink–source relationships. Fifth, competition between two galls was observed on a susceptible but not a resistant tree. On the susceptible tree distal aphids intercepted 1.5-fold more ¹⁴C from the occupied leaf than did basal aphids, but basal aphids compensated for the presence of a distal competitor by almost doubling import to the gall from surrounding leaves. These findings and others, aimed at identifying candidate genes for resistance, argue the importance of including plant genetics in future studies of the manipulation of translocation patterns by phytophageous insects.     

Phase Separation of Plant Cell Wall Polysaccharides and Its Implications for Cell Wall Assembly

Concentrated binary mixtures of polymers in solution commonly exhibit immiscibility, resolving into two separate phases each of which is enriched in one polymer. The plant cell wall is a concentrated polymer assembly, and phase separation of the constituent polymers could make an important contribution to its structural organization and functional properties. However, to our knowledge, there have been no published reports of the phase behavior of cell wall polymers, and this phenomenon is not included in current cell wall models. We fractionated cell walls purified from the pericarp of unripe tomatoes (Lycopersicon esculentum) by extraction with cyclohexane diamine tetraacetic acid (CDTA), Na2CO3, and KOH and examined the behavior of concentrated mixtures. Several different combinations of fractions exhibited phase separation. Analysis of coexisting phases demonstrated the immiscibility of the esterified, relatively unbranched pectic polysaccharide extracted by CDTA and a highly branched, de-esterified pectic polysaccharide present in the 0.5 N KOH extract. Some evidence for phase separation of the CDTA extract and hemicellulosic polymers was also found. We believe that phase separation is likely to be a factor in the assembly of pectic polysaccharides in the cell wall and could, for example, provide the basis for explaining the formation of the middle lamella.     

Galactose loss and fruit ripening: high-molecular-weight arabinogalactans in the pectic polysaccharides of fruit cell walls

Cell wall material (CWM) was prepared from nine fruit species at two ripening stages (unripe and ripe) and extracted sequentially with 0.05 M trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CDTA), 0.05 M Na₂CO₃ and 4 M KOH. Each solubilised fraction and the CWM-residue remaining after 4 M KOH extraction was analysed for non-cellulosic sugar composition. A common pattern of distribution for polyuronide and pectin-associated neutral sugar was observed for all unripe fruit. Most polyuronide was extracted in the CDTA/Na₂CO₃ fractions while 70–93% of the neutral sugar was located on pectic polysaccharides in the 4 M KOH-soluble and CWM-residue fractions. During ripening, most of the galactose was lost from pectic polysaccharides in the CWM-residue. Partial solubilisation of these polysaccharides was achieved by treating the CWM-residue with endopolygalacturonase. The solubilised polysaccharides were separated into two fractions by ion-exchange chromatography. One of these contained polysaccharides with average molecular weights of 400 kDa or larger and consisted of between 70 and 90% arabinogalactan. The galactosyl residues were 80–90% β-1→4 linked, indicating largely unbranched side-chains. The arabinosyl residues were distributed among terminal, 3-, 5-, 2,5-, and 2,3,5-linked residues, indicating a highly ramified structure. The results are discussed with regard to the relationship between pectin solubilisation and galactose loss and their respective contribution to fruit softening. Received: 28 January 1997 / Accepted: 11 March 1997