Increase in fruit size of a spontaneous mutant of ‘Gala’ apple (Malus×domestica Borkh.) is facilitated by altered cell production and enhanced cell size

Abstract

Fruit size regulation was studied in the apple cultivar ‘Gala’ and a large fruit size spontaneous mutant of ‘Gala’, ‘Grand Gala’ (GG). GG fruits were 15% larger in diameter and 38% heavier than ‘Gala’ fruits, largely due to an increase in size of the fruit cortex. The mutation in GG altered growth prior to fruit set and during fruit development. Prior to fruit set, the carpel/floral-tube size was enhanced in GG and was associated with higher cell number, larger cell size, and increased ploidy through endoreduplication, an altered form of the cell cycle normally absent in apple. The data suggest that the mutation in GG promotes either cell production or endoreduplication in the carpel/floral-tube cells depending on their competence for division. Ploidy was not altered in GG leaves. During fruit growth, GG fruit cells exited cell production earlier, and with a DNA content of 4C suggesting G2 arrest. Cell size was higher in GG fruits during exit from cell production and at later stages of fruit growth. Final cell diameter in GG fruit cortex cells was 15% higher than that in ‘Gala’ indicating that enhanced fruit size in GG was facilitated by increased cell size. The normal progression of cell expansion in cells arrested in G2 may account for the increase in cell size. Quantitative RT-PCR analysis indicated higher MdCDKA1 expression and reduced MdCYCA2 expression during early fruit development in GG fruits. Together, the data indicate an important role for cell expansion in regulating apple fruit size.

Analysis of the dynamic mechanical properties of apple tissue and relationships with the intracellular water status, gas distribution, histological properties and chemical composition

“…It was within values observed for other apple parenchyma tissue such as Gala, (Malladi and Hirst, 2010), Jonagored (Oey et al, 2007) and apple progenies (Galvez-Lopez et al, 2011). Objects volume, estimated from their diameters, and elongation factor are presented in Table 1A with the statistics regarding cultivar differences.…”

Fruit Quality Traits Have Played Critical Roles in Domestication of the Apple

“…It is presumed that genes associated with key traits for apple domestication are present in the regions with most loci under selection (Table 2). Besides clusters of disease resistance, quantitative trait loci (QTLs) for fire blight disease (Calenge et al, 2005; Durel et al, 2009; Khan et al, 2006; Khan et al, 2012b), and QTLs for plant vigor and fruit quality traits of apple have also been reported to be present along these LGs (King et al, 2001; Liebhard et al, 2003; Longhi et al, 2012). Quantitative trait loci with moderate effects for variation in fruit texture (sensory traits, crispiness, and firmness, among others) on LGs 7, 5, and 12 have been reported (King et al, 2001).…”

Optical properties of developing pip and stone fruit reveal underlying structural changes

“…the thickness of the cortex, ranges from 7 mm at 51 days after full bloom (dafb) in cv. 'Granny Smith' (Bain and Robertson 1951) to 15-19 mm at maturity for different cultivars (Bain and Robertson 1951, Drazeta et al 2004, Malladi and Hirst 2010.…”