Benzyladenine Affects Cell Division and Cell Size during Apple Fruit Thinning

Abstract

<jats:p>Benzyladenine (BA), carbaryl (CB), daminozide (DM), and naphthaleneacetic acid (NAA) were applied postbloom as fruitlet thinning agents to mature `Empire' apple <jats:italic>(Malus domestica</jats:italic> Borkh.) trees. BA, NAA, and CB reduced fruit set and yield per tree, and increased fruit size, percent dry weight, soluble solidscontent and return bloom. Fruit size was reduced, return bloom, length: diameter ratio and flesh firmness were increased, and fruit set and yield unaltered by DM. Although fruit set and yield were similar for BA, NAA, and CB, BA treated fruit were larger, indicating that BA increased fruit size beyond the effect attributable to chemical thinning alone. BA increased the rate of cell layer formation in the fruit cortex, indicating that BA stimulated cortical cell division. NAA, CB and DM had no effect on cell division rate. Mean cortical cell diameter at harvest was increased by NAA and CB and reduced by DM. Cell diameter at harvest in BA-treated fruit was similar to the control. These data support the hypothesis that BA-induced fruit size increase in `Empire' apple results from greater numbers of cells in the fruit cortex, whereas the fruit size increase due to NAA or CB is a consequence of larger cell size. Chemical names used: <jats:italic>N</jats:italic>-(phenylmethyl)-1H-purine-6-amine [benzyladenine (BA)]; 1-napthaleneacetic acid (NM); 1-naphthalenyl methylcarbamate [carbaryl (CB)]; butanedioic acid mono (2,2dimethyl hydrazide) [daminozide (DM)].</jats:p>

Cytokinins increase fruit size of ‘Delicious’ and ‘Golden Delicious’ (Malus domestica) apple in a warm climate

“…BA applied at concentrations above 50 mg l -1 at the 10 mm fruit diameter stage is known as a chemical thinner for some apple cultivars, increasing the size of the remaining fruits (Greene, 1993b;Elfving and Cline, 1993;Wismer et al, 1995;Yuan and Greene, 2000;; however, it is also known to increase the rate of cell division in the apple fruit cortex (Wismer et al, 1995). Therefore, it may increase fruit size independently of its effect on crop load.…”

“…The synthetic cytokinin benzyladenine (BA) is known to be an effective thinner of apples, thus increasing fruitsize (Elfving and Cline, 1993;Moran and Southwick, 2000), but it also increases fruit-size independently of this effect, by stimulating additional cell division within the fruit (Greene, 1993b;Wismer et al, 1995;. Cell division during the early stage of fruit development has a major effect on final fruit size (Westwood, 1993;Looney, 1993;Harada et al, 2005).…”

A dynamic interplay between phytohormones is required for fruit development, maturation, and ripening

“…Although cytokinins are generally considered to play a critical role in the stimulation of cell division during fruit development (Wismer et al, 1995; Srivastava and Handa, 2005), very few experimental data support the involvement of this hormone in the initial cell division phase of fruit growth (Mariotti et al, 2011). It is well known that cytokinin promotes cell proliferation at shoot apical meristems and interact closely with auxin (Murray et al, 2012) and are likely to function in a similar manner in the developing gynoecia (Lindsay et al, 2006; Bartrina et al, 2011).…”

Synthetic cytokinins extend the phase of division of parenchyma cells in developing pear (Pyrus communisL.) fruits

“…a prolonged period of mitotic activity, suggesting that external application of cytokinins affected pear fruit size by extending the duration of cell division. In apple, a single application of BA, for chemical thinning, increased the rate of cell division in the fruit cortex, but did not influence the duration of this process (Wismer and Proctor, 1995). In Arabidopsis it was shown that cytokinin regulated the cell cycle transition through CycD3 (Frank and Schmulling, 1999).…”