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

Ng JK, Schröder R, Sutherland PW, Hallett IC, Hall MI, Prakash R, Smith BG, Melton LD, Johnston JW - BMC Plant Biol. (2013)

Bottom Line: 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'.

View Article: PubMed Central - HTML - PubMed

Affiliation: Food Science, School of Chemical Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand. jovyn.ng@plantandfood.co.nz.

ABSTRACT

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.

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Size and density of cortical cells of ‘Royal Gala’ and ‘Scifresh’ at the fruitlet and mature stage. Cryo-scanning electron micrographs of fruitlet (A, C) and mature fruit (B, D) of ‘Royal Gala’ (A, B) and ‘Scifresh’ (C, D), and cortical density of cells at the mature fruit stage (E). Bars = 200 μm for all micrographs. Apples were matched for size at each stage of development. Values in (E) are the mean of 15 measurements ± SE.
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Figure 3: Size and density of cortical cells of ‘Royal Gala’ and ‘Scifresh’ at the fruitlet and mature stage. Cryo-scanning electron micrographs of fruitlet (A, C) and mature fruit (B, D) of ‘Royal Gala’ (A, B) and ‘Scifresh’ (C, D), and cortical density of cells at the mature fruit stage (E). Bars = 200 μm for all micrographs. Apples were matched for size at each stage of development. Values in (E) are the mean of 15 measurements ± SE.

Mentions: Cryo-scanning electron micrographs of cortex tissue showed that both cultivars had similar cell size at the fruitlet stage (Figure 3A, C), but cells were larger in ‘Scifresh’ than in ‘Royal Gala’ at the mature stage (Figure 3B, D) for fruit of equivalent size. Mature ‘Scifresh’ fruit had an average cell diameter of 166 ± 13.8 μm (n = 15), while mature ‘Royal Gala’ fruit had an average cell diameter of 107 ± 11.7 μm (n = 15). These findings were in agreement with[27] who found, using a different method, that ‘Scifresh’ cells were 49% larger by area than ‘Royal Gala’. Our results show that the cells in ‘Scifresh’ expanded at a greater rate during fruit growth than in ‘Royal Gala’, yet both cultivars result in a similar fruit size. In both cultivars, development of larger intercellular air spaces was observed between the fruitlet and mature stage (Figure 3). An estimate of air space volume showed that ‘Scifresh’ had a higher cortical tissue density than ‘Royal Gala’, once fruit were mature (Figure 3E).


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

Ng JK, Schröder R, Sutherland PW, Hallett IC, Hall MI, Prakash R, Smith BG, Melton LD, Johnston JW - BMC Plant Biol. (2013)

Size and density of cortical cells of ‘Royal Gala’ and ‘Scifresh’ at the fruitlet and mature stage. Cryo-scanning electron micrographs of fruitlet (A, C) and mature fruit (B, D) of ‘Royal Gala’ (A, B) and ‘Scifresh’ (C, D), and cortical density of cells at the mature fruit stage (E). Bars = 200 μm for all micrographs. Apples were matched for size at each stage of development. Values in (E) are the mean of 15 measurements ± SE.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4225529&req=5

Figure 3: Size and density of cortical cells of ‘Royal Gala’ and ‘Scifresh’ at the fruitlet and mature stage. Cryo-scanning electron micrographs of fruitlet (A, C) and mature fruit (B, D) of ‘Royal Gala’ (A, B) and ‘Scifresh’ (C, D), and cortical density of cells at the mature fruit stage (E). Bars = 200 μm for all micrographs. Apples were matched for size at each stage of development. Values in (E) are the mean of 15 measurements ± SE.
Mentions: Cryo-scanning electron micrographs of cortex tissue showed that both cultivars had similar cell size at the fruitlet stage (Figure 3A, C), but cells were larger in ‘Scifresh’ than in ‘Royal Gala’ at the mature stage (Figure 3B, D) for fruit of equivalent size. Mature ‘Scifresh’ fruit had an average cell diameter of 166 ± 13.8 μm (n = 15), while mature ‘Royal Gala’ fruit had an average cell diameter of 107 ± 11.7 μm (n = 15). These findings were in agreement with[27] who found, using a different method, that ‘Scifresh’ cells were 49% larger by area than ‘Royal Gala’. Our results show that the cells in ‘Scifresh’ expanded at a greater rate during fruit growth than in ‘Royal Gala’, yet both cultivars result in a similar fruit size. In both cultivars, development of larger intercellular air spaces was observed between the fruitlet and mature stage (Figure 3). An estimate of air space volume showed that ‘Scifresh’ had a higher cortical tissue density than ‘Royal Gala’, once fruit were mature (Figure 3E).

Bottom Line: 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'.

View Article: PubMed Central - HTML - PubMed

Affiliation: Food Science, School of Chemical Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand. jovyn.ng@plantandfood.co.nz.

ABSTRACT

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.

Show MeSH
Related in: MedlinePlus