Ultrastructural Changes in the Cell Walls of Ripening Apple and Pear Fruit

Abstract

Ultrastructural changes in the cell walls of "Calville de San Sauveur" apples (Mahn sylvestris Mi) and "Spadona" pear (Pyrs conunws L.) frit were folowed during rpening. In apple, structural alteratons in cell walls became apparent at advanced stages of softening and showed predominantly disolution of the middle lamella. In pears softening was also associated with the dissolutio of the middle lamella, and in addition a gradual disintegration of fibria material throughout the cell wall. In fully ripe fruit almost al of the frilbar arrangement in the cell wall was lost.Application ofenzyme solutios containig polygalacturonase and cellulase to tissue discs from firm pear fruit led to ultrastructural changes observed in naturally ripening pears. In apple polygalacturonase alone was sufficient to dissolve the middle lamella region of the cell walls, as was also found to occur in naturaly ripening frit. In both apple and pear the cell wall areas containing ploata maintained their structural integrity tbroughout the ripening process. At advanced stages of ripening vesicles appeared in the vicinity of plasmodesmata.A characteristic of the ripening process common to most fruits is a decrease in fruit firmness. Loss in firmness is shown to be associated with the activity of cell wall-degrading enzymes (9, 16) and it is a reasonable hypothesis that this activity could lead to the chemical and structural alterations in cell walls. In an early microscopic study of cell walls from developing apple fruits, no differences were observed in thickness or structure during storage and softening of the fruit (14). Other studies in pear showed that although in lignified walls of stone cells there was no change during fruit maturation, in overripe fruit the parenchymatous cell walls became extremely thin and tenuous (18). Recent studies in avocado (15) also suggested that in softening fruit cell walls lose their structure. In the present work we extend these studies aimed at: (a) using ultrastructural techniques to observe the detailed microscopic changes occurring in the walls of apple and pear, MATERIALS AND METHODS Plant Material. "Calville de San Sauveur" apples (Malus sylvestris, Mill) and "Spadona" pears (Pyrus communis L.) ofuniform size and color were harvested at the mature stage and allowed to ripen at 20 C. Tissue samples from mature and soft apples and pears were then used for the EM2 study. Prior to sampling for EM, the firmness of the fruit was determined with a "Hunter" penetrometer, equipped with an 11. 1-mm tip for apples or a 7.9-mm tip for pears. The tissue firmness of the mature hard apples was from 6.5 to 5 kg and of soft fruit 3.3 kg. In pears the firmness at the mature hard stage was 7 kg and in soft fruit 2.5 kg.Ultrastructural studies were also made on fruit discs treated with applied enzymes. Small discs, 1-cm diameter, 3 mm thick, from mature hard fruit were incubated for 1 to 2 h in acetate buffer solutions containing commercial enzyme preparations. The enzyme solutions consisted of 25 mg/ml tomat...

Effect of maturity on the phenolic compositions of pear juice and cell wall effects on procyanidins transfer

“…Pear cell walls contained also high quantities of lignin (212e232 mg/g). The high concentrations of glucose, xylose and lignin reflected the presence of lignified cell walls rich in xylans and cellulose, typical of EC: (À)-epicatechin, PCA: procyanidins, DPn: average degree of polymerization of procyanidins, CQA: 5 0 -caffeoylquinic acid, Flavonols: sum of flavonols, Total: sum of polyphenols, n.d.: not detected, Pooled SD: pooled standard deviation, ns: not significant (P > 0.05), ***: P < 0.0001, **: P < 0.01, *: P < 0.1. stone cells (Ben-Arie, Kislev, & Frenkel, 1979;Martin-Cabrejas, Waldron, Selvendran, Parker et al, 1994). Le Bourvellec et al (2013) detected more galacturonic acid and less xylose in the AIS from the flesh of William pears.…”

The intersection between cell wall disassembly, ripening, and fruit susceptibility to Botrytis cinerea

“…Fruit that soften significantly at the fully ripe stage typically have CWs that appear swollen, both in planta and in vitro, and this ripeningassociated wall swelling correlates with pectin solubilization (27,28). CWs were isolated from LR and RR AC and transgenic fruit and suspended in water.…”

Cell Wall Metabolism in Ripening Fruit (IX. Synthesis of Pectic and Hemicellulosic Cell Wall Polymers in the Outer Pericarp of Mature Green Tomatoes (cv XMT-22)

“…This has led to the suggestion that certain hydrolytic enzymes are responsible for the dissolution of the middle lamella as well as for the degradation of the cell wall itself, thereby leading to a general loss of cohesion of the tissue, perceived as softening. This model is supported by anatomical work that demonstrated the breakdown of middle lamella polymers (Ben-Arie et al, 1979), by numerous studies characterizing the ripening-related changes in cell wall polymers (Gross and Wallner, 1979;Ahmed and * Corresponding author; e-mail jmlabavitch@ucdavis.edu; fax 1-916 -752-8502. Labavitch, 1980;Gross, 1984), and by studies that demonstrated increases in the activities of some putative cell wall polysaccharide hydrolases during ripening (Hobson, 1968;Tucker et al, 1982;Brady et al, 1983;Pressey, 1989; for review, see Fischer and Bennett, 1991).…”