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Indução de Tolerância à Alta Temperatura de Secagem em Sementes de Milho por Meio de Pré-Condicionamento à Baixa Temperatura

DOI: http://dx.doi.org/10.18512/1980-6477/rbms.v3n2p290-310

http://rbms.cnpms.embrapa.br/index.php/ojs/index 

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Sttela D. V. F. da Rosa1, Édila V. R. V. Pinho2, Maria das G. G. C. Vieira2 & Ruben D. Veiga3

 

Resumo: Sementes de milho maduras, sob condição de secagem natural, perdem água lentamente e tornam-se mais tolerantes a temperaturas de secagem mais elevadas, em conseqüência da ocorrência de mudanças físicas, fisiológicas e bioquímicas. O objetivo do presente trabalho foi investigar os efeitos do pré-condicionamento de sementes de milho, por meio de pré-secagem sob temperatura de 35ºC, sobre a tolerância à secagem a 50ºC. Para tanto, sementes de milho de três cultivares, colhidas com teores de água de 42,3%, de 37,2% e de 34,2%, foram submetidas à pré-secagem a 35ºC (précondicionamento), por períodos de 0, 4, 8 16, 24, 32, 40, 48 e 56 horas, antes da secagem conduzida a 50ºC até 12% de teor de água. Após os períodos de pré-condicionamento, embriões foram analisados quanto aos conteúdos de glicose, sacarose e estaquiose. Após a secagem a 50ºC, as sementes foram avaliadas por testes de germinação, de primeira contagem de germinação, de frio, de condutividade elétrica, de peso de matéria seca de plântula e de comprimento de plântula. Em uma das cultivares foi determinada a atividade da enzima a-amilase. As sementes recém colhidas são tolerantes a 35ºC e intolerantes a 50ºC, mas tornam-se tolerantes a essa temperatura após a pré-secagem a 35ºC (précondicionamento) até que atinjam teores de água entre 25,3 e 28,5%. As sementes intolerantes a 50ºC apresentam menores germinação, vigor e atividade enzimática. Coincidentemente com a aquisição de tolerância a 50ºC, ocorrem a diminuição de glicose e o aumento de rafinose; o conteúdo de sacarose parece não sofrer alteração durante a transição do estado de intolerância para o de tolerância.

Palavras-chave: secagem artificial, tolerância à dessecação, qualidade fisiológica, açúcares, Zea mays L.

 

Abstract: Mature corn seeds, under natural drying conditions, lose water slowly and become more tolerant to higher drying temperatures in consequence of the occurrence of physical, physiological and biochemical changes. The aim of the present work was to investigate the effect of the pre-conditioning of corn seeds by means of pre-drying, under temperature of 35ºC on the drying tolerance at 50ºC. So, corn seeds of three cultivars harvested with water contents of 42.3%, 37.2% and 34.2%, were submitted to pre-drying at 35ºC (pre-conditioning) for periods of 0, 4, 8 16, 24, 32, 40, 48 and 56 hours before the drying, conducted at 50ºC up to 12% of water content. After the pre-conditioning periods, embryos were analyzed as to the contents of glucose, sucrose and stachiose. After drying at 50ºC, the seeds were evaluated trough tests of germination, first count, cold test, test of electric conductivity, dry weight and seedling length. In one of the cultivars, the activity of the α-amilase enzyme was determined. The freshly collected seeds are tolerant at 35ºC and intolerant at 50ºC but they become tolerant to that temperature after pre-drying at 35ºC (pre-conditioning) till they reach water contents between 25.3 and 28.5%. The seeds intolerant at 50ºC present poorer germination, vigor and enzyme activity. Concomitantly with the acquisition of tolerance at 50ºC, the decrease of glucose and the increase of raffinose take place. Sucrose content seems not to suffer any changes during the transition of the state of intolerance to that of tolerance.

Key words: artificial drying, tolerance desiccation, physiological quality, sugars, Zea mays L.

 

1 Pesquisadora, Dra, Embrapa Café, CEPECAFÉ/DAG/Universidade Federal de Lavras. Caixa Postal 37, CEP. 37200- 000 Lavras, MG. E-mail: sttelaveiga@ufla.br (autora para correspondência).
2 Professores Drs., Dep. de Agricultura da Universidade Federal de Lavras. Caixa Postal 37, CEP. 37200-000 Lavras, MG.
3 Professor Dr., Dep. Ciências Exatas da Universidade Federal de Lavras. Caixa Postal 37, CEP. 37200-000 Lavras, MG.

 

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