02576naa a2200361 a 450000100080000000500110000800800410001902000180006010000210007824501250009926000090022430000160023352015490024965000130179865000200181165000160183165000120184765000100185965000110186965000260188065000150190665000150192165000170193665000190195365000120197265000160198465300150200065300210201570000220203670000130205870000170207177301260208817676262024-06-11       2000    bl uuuu     u00u1 u    #d  a0-85199-404-01 aCANTLIFFE, D. J.  aLettuce endosperm weakeningba role for endo-B-mannanase in seed germination at high temperature.h[electronic resource]  c2000  ap. 277-285.  aUnder high temperatures, seed germination of most lettuce genotypes can be erratic or completely inhibited. Weakening of the endosperm layer is a prerequisite to radicle protrusion at high temperatures. Enzyme-mediated degradation of endosperm cell walls may be a crucial factor for lettuce germination at high temperatures. The galactomannan polysaccharides in lettuce endosperm cell wall are mobilized by endo-b-mannanase. The involvement of endo-b-mannanase during germination of lettuce seeds at high temperature (35°C) was investigated by gel-diffusion assay. Genotype, seed maturation temperature, and seed priming enhanced lettuce seed germination at high temperature. Less force to penetrate the endosperm was required by seeds of thermotolerant genotypes or primed seeds, and structural alterations of endosperm in the micropylar area were also observed before radicle protrusion. Higher endo-b-mannanase activity in lettuce endosperm before radicle protrusion was verified in these situations. Moreover, at high temperature, thermotolerant genotypes produced more ethylene, more endo-b-mannanase, and germinated better than thermosensitive genotypes. An inhibitor of ethylene action, silver thiosulphate, inhibited both mannanase activity and germination. A precursor of ethylene, ACC, induced endo-b-mannanase activity and germination of thermosensitive ‘Dark Green Boston’ at 35°C. These results suggest that increased endo-b-mannanase activity might contribute to lettuce endosperm weakening, especially at high temperatures.  adormancy  aenzyme activity  agermination  alettuce  aseeds  aAlface  aAtividade Enzimática  aDormência  aEndosperma  aGerminação  aLactuca Sativa  aSemente  aTemperatura  aEndosperms  aHigh temperature1 aNASCIMENTO, W. M.1 aSUNG, Y.1 aHUBER, D. J.  tIn: BLACK, M.; BRADFORD, K.J.; VAZQUEZ-RAMOS, J., (Ed.). Seed biology: advances and applications. Wallingford: CAB, 2000.