ISHS Acta Horticulturae 517: XXV International Horticultural Congress, Part 7: Quality of Horticultural Products
ENDO-β-MANNANASE ACTIVITY DURING LETTUCE SEED GERMINATION AT HIGH TEMPERATURE CONDITIONS |
| Authors: | W.M. Nascimento, D.J. Cantliffe, D.J. Huber |
| Keywords: | Lactuca sativa L., dormancy, seed priming, thermoinhibition, thermotolerance |
| Abstract:
Continuous high temperature (above 30°C) in the greenhouse or field can lead to a reduction or complete inhibition of lettuce seed germination. Weakening of the endosperm tissue around the radicle tip prior to radicle protrusion and the role of some enzymes in endosperm modification have been associated with normal germination in this species. The galactomannan-containing polysaccharides in the lettuce endosperm cell wall are mobilized by endo-  -mannanase.
The role of endo--mannanase during germination of lettuce seeds at high temperature (35°C) was investigated by gel-diffusion assay utilizing thermotolerant and thermosensitive genotypes, and primed and nonprimed seeds.
Seeds from thermotolerant ('Everglades' and PI 251245) genotypes had higher endo--mannanase activity before radicle protrusion at 35°C than thermosensitive ('Dark Green Boston', 'Valmaine' and 'Floricos 83') genotypes.
During priming of 'Dark Green Boston', endo--mannanase activity increased between 24 and 72 hours after the beginning of osmotic imbibition.
Radical protrusion did not occur under these conditions.
Primed seeds germinated 100% at 35°C, whereas nonprimed seeds germinate only 4% at this temperature.
Higher enzyme activity was observed in primed seeds compared with nonprimed seeds.
A relationship between increased endo--mannanase activity before radicle protrusion was established for thermosensitive 'Dark Green Boston'.
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