Shoji Amano

Water relations in fruit, leaves and stems of two apple cultivars that differ in susceptibility to watercore

Summary The intensity of watercore in apple (Malus domestica Borkh.) cv. ‘Orin’ increased from July to August when maximum air temperatures were above 30°C, then decreased as temperatures decreased and fruit ripened. In cv. ‘Fuji’, there was only a low incidence of the disorder in November and December. Tissue water potential ( ) was similar in the inner and outer flesh. Predawn and midday fruit decreased during fruit development and was lower in ‘Orin’ than in ‘Fuji’. Midday leaf and stem were higher in ‘Orin’ in late August and September. The gradient of midday between leaves or stems and fruit became positive earlier in ‘Orin’ than in ‘Fuji’. Soluble solids content (SSC) was also higher in ‘Orin’ than in ‘Fuji’. Seasonal fluctuations in sorbitol in ‘Orin’ paralleled the incidence of watercore and gradually increased during fruit development in ‘Fuji’.These results suggest that immature ‘Orin’ fruit have more favorable water relations than ‘Fuji’, resulting in a greater incidence of watercore.

Effects of ethylene and hydrogen cyanide on β-cyanoalanine synthase activity in satsuma mandarin (Citrus unshiu Marc.) fruit

Abstract Exogenous ethylene increased β-cyanoalanine synthase activity in satsuma mandarin fruit. An inward decreasing gradient in the activity was found in ethylene-treated fruit; the highest activity was in the flavedo and the lowest in the juice sacs. β-Cyanoalanine synthase activity in the peel (flavedo and albedo) increased in parallel with increasing ethylene concentrations up to 500 ppm and then leveled off. Green mature fruit were less responsive to ethylene in the induction of β-cyanoalanine synthase activity than more mature fruit. Regardless of ripening stage, the latter group of fruit responded to ethylene to reach similar maximum enzyme activities, which were approximately two-fold greater than those of green mature fruit. 2,5-Norbornadiene, a specific inhibitor of ethylene action, repressed the ethylene-induced increase in β-cyanoalanine synthase activity. Hydrogen cyanide did not induce β-cyanoalanine synthase but rather reduced the activity at high concentrations.

Seasonal changes in cellular compartmentation and membrane permeability to sugars in relation to early or high temperature-induced watercore in ‘Orin’ apples

Summary The intensity of watercore in ‘Orin’ apples (Malus domestica Borkh.) from the outer canopy increased from early-July to mid-August, followed by a decrease through late-October, while no watercore was detected in inner canopy fruit during the same period. Seasonal changes in sorbitol content in each cellular compartment paralleled the development of watercore. Significantly higher sorbitol, fructose and glucose contents in the vacuoles of cells in outer canopy fruit than in inner canopy fruit suggest that active metabolism and uptake of sorbitol might occur in watercored apples in mid-August. The permeability of sorbitol across the tonoplast was significantly higher in outer than in inner canopy fruit after mid-August, whereas no difference was observed between bearing position for the other sugars or for the plasma membrane. These data suggest that elevated sorbitol levels in the intercellular spaces might result from active apoplastic unloading and not from an inhibition of metabolism and/or an increase in leakage from cells.