Algumas respostas de mono- e dicotiledôneas a auxinas associadas à ação do etileno

• Autor(a) principal: Medina, Eduardo Ferreira
• Data de Publicação: 2013
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/4336
• topic: Auxinas; Etileno; Monocotiledônea; Dicotiledônea; Resposta diferencial; Auxin; Ethylene; Monocot; Dicot; Differential response; CNPQ::CIENCIAS BIOLOGICAS::BOTANICA::FISIOLOGIA VEGETAL

The auxins IAA (indole-3-acetic, natural), 2,4-D (2,4-dichlorophenoxyacetic acid) and 2,4,5-T (2,4,5-trichlorophenoxyacetic acid, the latter two synthetic) were sprayed on corn (Zea mays, monocot) and beans (Phaseolus vulgaris, dicot), in order to investigate some differential responses of the two plant groups as associated to ethylene metabolism. Corn plants treated with the auxins did not produce ethylene, not exhibiting also any senescence symptom. Beans plants, on the other hand, produced large amounts of ethylene following treatment with auxins. Aminoethoxyvinylglycine (AVG) plus Co2+ (ethylene biosynthesis inhibitors) were not able to relieve the epinasty, drying and leaf wrinkling effects in bean plants, but leaf yellowing was considerebly reduced, suggesting this was an ethylene effect. Following spraying with auxins, corn plants showed no production of 1-aminocyclopropane-1-carboxylic acid (ACC), a response shown by beans plants. Therefore in the monocot, auxins seemed not to induce the expression of ACC synthase (ACS) or its activity. When treated with ACC, corn plants failed to produce any trace of ethylene, unlikely bean plants. This suggested that in monocot, auxins seemed also not to induce the expression or activity of ACC oxidase (ACO) or the enzyme is not activated. Potassium ferrocyanide, employed as a source of cyanide ions, was much more toxic to bean plants than to corn and so the monocot seemed to be more resistant than bean plants. Maximum quantum yield of photosystem II (Fv/Fm) and photosynthetic pigments contents kept unchanged in corn plants treated with the auxins. Bean plants showed significant decreases in both variables following spraying with 2,4-D and 2,4,5-T. Decreases in chlorophyll contents in bean plants treated with 2,4-D and 2,4,5-T correlated well with leaf chlorosis what was shown to be due to a more pronounced fall of chlorophyll contents rather than to an increase in carotenoid contents. The xanthophylls (neoxanthin, violaxanthin and anteraxantina) also showed a higher degradation than the alpha and beta carotenes in bean plants treated with 2,4-D and 2,4,5-T. When AVG and Co2+ were supplied together with auxin, no appreciable decrease in either the Fv/Fm ratio or pigment contents was observed, with the exception of alpha carotene. Also the ratio of chlorophyll a to chlorophyll b was also larger in bean plants treated with 2,4-D and 2,4,5-T than in the plants treated with 2,4-D and 2,4,5-T plus AVG and Co2+. The ratio of chlorophyll a to chlorophyll b did not show any significance in bean plants upon treatment with IAA.