Onion is regarded as a non-climacteric vegetable. In onions, however,
ethylene can suppress sprouting while the ethylene binding inhibitor, 1-MCP (1-
methylcyclopropene) can also suppress sprout growth yet, it is unknown how ethylene
and 1-MCP elicit the same response. In this study, onions were treated with 10 μL L-1
ethylene or 1 μL L-1 1-MCP individually or in combination for 24 h at 20°C before or
after curing (six weeks) at 20 or 28°C then stored at 1°C. Following curing, a subset
of these same onions was stored separately under continuous air or ethylene (10 μL L-
1) at 1°C
Onions treated with ethylene and 1-MCP in combination after curing for 24 h
had reduced sprout growth as compared with the control 25 weeks after harvest.
Sprout growth following storage beyond 25 weeks was only reduced through
continuous ethylene treatment. This observation was supported by a higher proportion
of down-regulated genes characterised as being involved in photosynthesis measured
using a newly developed onion microarray. Physiological and biochemical data
suggested that ethylene was being perceived in the presence of 1-MCP since sprout
growth was reduced in onions treated with 1-MCP and ethylene applied in
combination but not when applied individually. A cluster of probes representing
transcripts up-regulated by 1-MCP alone but down-regulated by ethylene alone or in
the presence of 1-MCP support this suggestion. Ethylene and 1-MCP both down52
regulated a probe tentatively annotated as an ethylene receptor as well as EIN3,
suggesting that both treatments down-regulate the perception and signalling events of
ethylene
