Abstract:

This study aimed to investigate the effects of nitric oxide (NO) fumigation on cottony softening of postharvest
wax apple fruit. ‘Black Pearl’ wax apple fruit (Syzygium samarangense Merr. et Perry) were treated with different
concentrations of exogenous NO (5, 10 and 20 μL/L), with 0 μL/L nitric oxide as control. The fruit quality, cottony softening
index, cell wall metabolism and lignin metabolism were determined. The results indicated that compared with control,
different concentrations of exogenous NO fumigation inhibited significantly fruit cottony softening development and weight
loss, maintained fruit firmness, reduced effectively the decrease of cellulose content. NO fumigation at 10 μL/L decreased
the activities of polygalacturonase (PG), pectin methylesterase (PME), and β-galactosidase (β-Gal). Meanwhile, different
concentrations of exogenous NO fumigation also retarded effectively the rise of lignin content. NO at 10 μL/L decreased the
activities of phenylalanin ammonia-lyase (PAL), peroxidase (POD) and 4-coumarate:coenzyme A ligase (4-CL). Correlation
analysis indicated that weight loss, fruit firmness, and the contents of cellulose and lignin were significantly correlated
with cottony softening index, and that cottony softening index was correlated significantly negatively with the content of
protopectin but significantly positively with the content of soluble pectin. Taken together, NO treatment decreased the activities
of cell wall-degrading enzymes, and effectively postponed fruit ripening and senescence process of postharvest wax apple, and
prolonged its storage life. Among different concentrations tested, 10 μL/L NO treatment presented the best effect.

Key words: wax apple, nitric oxide, cottony softening, quality, cell wall metabolism, lignin metabolism