Seed aging affects ethylene production and endo-β-mannanase activity during lettuce seed germination at high temperature
The lettuce endosperm can delay or prevent germination, acting as a physical barrier to radicle protrusion, especially under high temperatures. Weakening of the endosperm layer of lettuce seeds is a prerequisite to radicle protrusion at high temperatures. Cell wall-associated endo-β-mannanase was expressed in lettuce seed endosperm prior to radicle protrusion. Ethylene overcomes thermoinhibition of lettuce seeds. The involvement of ethylene and endo-β-mannanase during germination of lettuce seeds was investigated by a gel-diffusion assay. Thermotolerant 'Everglades' lettuce seeds were aged at 41°C and 100% humidity for 0, 1, 3 and 5 days and examined for germination capacity at 20 and 35°C. At 20°C, all seeds germinated 100%. At 35°C, germination was lowest in seeds aged 3 or 5 days. Aged seeds produced low ethylene levels, whereas non-aged seeds produced high ethylene levels at 35°C. Higher endo-β-mannanase activity before radicle protrusion was observed in nonaged seeds. Seed aging can lead to some physiological and biochemical changes such as reduced ethylene and endo-β-mannanase activity and thus lead to thermoinhibition in lettuce seed germination.
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Document Type: Research Article
Publication date: April 1, 2005
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