W h e n t h e axial g r o w t h of b e a n roots (Vicia /aba, L., v a r i e t y B r o a d Windsor) was i m p e d e d b y a barrier, t h e rate of e t h y l e n e evolution increased b y as m u c h as six t i m e s t h a t of u n i m p e d e d controls. This h i g h r a t e was m a i n t a i n e d for a t least 30 hours. W h e n t h e b a r r i e r was removed, t h e rate of e t h y l e n e evolution decreased to near t h e r a t e of control roots. E x o g e n o u s applications of v e r y low c o n c e n t r a t i o n s were inhibitory. E x o g e n o u s e t h y l e n e also resulted in a n increase in radial diameter. These results indicate t h a t e t h y l e n e evolved b y b e a n roots in response to h i g h m e c h a n i c a l resistance m a y act as an endogenous g r o w t h regulator.
Premature ripening and/or senescence and
abscission induced by exposure to ethylene are significant postharvest
problems. Banana fruit and grevillea and Geraldton waxflower flowers are among
affected commodities. Treatment with 1-methylcyclopropene gas or silver
thiosulfate liquid can be used to prevent ethylene perception and response.
Treatment of banana fruit with 10 nL 1-methylcyclopropene/L for 12 h at
20˚C afforded protection against subsequent serial treatments over 13
days of subsets with 100 L ethylene/L for 24 h at 20˚C. Protection of
Grevillea ‘Sylvia’ inflorescences was
effective only for 2 days. Thereafter, fruit and inflorescences regained
sensitivity to ethylene. In contrast, neither banana fruit nor grevillea
inflorescences treated with 10 nL 1-methylcyclopropene/L for 12 h at
2˚C were protected against ethylene. 1-Methylcyclopropene binding to
ethylene receptors was apparently not achieved at the lower temperature.
Increasing the 1-methylcyclopropene concentration to 100 nL/L, applied at
2.5˚C to banana fruit, achieved protection against ethylene. Waxflower
sprigs treated with 10 nL 1-methylcyclopropene/L for 12 h at 2 or
20˚C regained full sensitivity to ethylene after about 2 and 4 days,
respectively. In contrast, pulsing waxflower with 0.5 mmol
Ag+/L as silver thiosulfate for 12 h at 2 or
20˚C afforded protection against ethylene for the 10 days duration of the
experiment.
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