Changes in Catechol Oxidase and Permeability to Water in Seed Coats of Pisum elatius during Seed Development and Maturation

Abstract

In the developing seed coat of Pisum elatius, o-dihydroxyphenols are present in appreciable amounts at all stages of development. However, catechol oxidase activity rises sharply during the later stages of development, shows a further abrupt rise during dehydration of the seed coat, and then decreases. It is suggested that a tanning reaction is induced by the contact of enzyme with its substrate while cell membranes are ruptured, and that this reaction renders the seed coats impermeable. The entire chain of events does not occur in Pisum sativum which has permeable seed coats.The germination of many species of seeds, especially of the Leguminoseae, is controlled by "hard seededness" (10,11,13). Conditions during seed storage (7) and environmental conditions during seed development and maturation may affect "hard seededness" (1) and permeability (7). For some seeds of the Leguminoseae it has been shown that there is a connection between the color of the seed coats and their permeability to water (1, 9).In a previous paper (9) we hypothesized that during dehydration of seeds, oxidation of phenolic compounds in seed coats catalyzed by catechol oxidase might render the seed coat impermeable to water. In order to test this hypothesis, we followed the content of catechol oxidase activity and of phenolic compounds during development and maturation of pea seeds. We have used wild peas, Pisum elatius, which have an impermeable seed coat and cultivated peas P. sativum, which have a permeable seed coat. We will show that changes in seed coat permeability are correlated with a change in the level of catechol oxidase, and suggest a mechanism by which permeability is changed. MATERIALS AND METHODSSeeds of Pisum sativum var. Alaska and Pisum elatius were grown outdoors in Jerusalem. Pods and seeds were collected at different stages of seed development and maturation as described in Tables I and II. Samples of seed coats, cotyledons, and whole seeds were taken for determination of fresh and dry weight (10 samples of 10 seeds were taken for each determination).Catechol oxidase activity was determined in homogenates of the seed coats, cotyledons, and entire seed. Usually, 3 g of seed coats or 5 g of cotyledons or whole seeds were used for preparing the homogenates which were prepared as previously described (8). The homogenate was fractionated by centrifugation to give a particulate-20,000g precipitate-and a supernatant fraction. The precipitate was resuspended in the same buffer used for preparing the homogenate, using 1 ml buffer per gram original fresh weight.Catechol oxidase activity was determined according to Harel and Mayer (2), using 5 nm 4-methylcatechol as substrate at pH 7.3. Only the activity of the particulate fraction at pH 7.3 is given, because previous results (8) showed that activity in the soluble cell fraction is negligible. This result was reconfirmed in the present investigation.The o-diphenol content of the tissue was measured according to Mapson et al. (8) using the sodium molybdate method. The tot...

Import, Targeting, and Processing of a Plant Polyphenol Oxidase

“…4B). The seed coats of wild pea, Pisum elatius, possess PPO activity during seed ripening, contrary to cultivated pea (Marbach and Mayer, 1975). However, thylakoids from P. elatius leaves did not react with the tomato antibodies (Fig.…”

Intensidade de dormência durante a maturação de sementes de mucuna-preta

“…No presente trabalho como as sementes de todos os estádios de maturação, com diferentes graus de desenvolvimento (Tabela 1) sofreram secagem no interior das vagens, houve a oxidação e impermeabilização do tegumento, como observado por Marbach e Mayer (1974, 1975 em ervilha silvestre (Pisum elatius), resultando porém diferenças de intensidade na impermeabilidade à água (Tabelas 2 e 3), que podem estar relacionadas à estruturação e maturação do tegumento por ocasião da colheita (Rolston, 1978) ou também, à desidratação do tegumento no interior das vagens durante a secagem (Baskin e Baskin, 1998;Samarah et al, 2004) e disponibilidade de oxigênio durante a secagem (Marbach e Mayer, 1974).…”

“…A formação de compostos de coloração escura, resultante da oxidação de substâncias fenólicas, pode contribuir para a impermeabilização do tegumento (Bewley e Black, 1985), tal como foi observado para sementes de Pisum elatius, e cujas modificações puderam ser relacionadas ao aumento da atividade da catecol oxidase, catalisando a oxidação de compostos fenólicos na presença de O 2 , durante a fase de desidratação do tegumento (Marbach e Mayer, 1974, 1975. Em mucuna-preta a secagem das sementes no interior das vagens, destacadas da planta, resultou no escurecimento e na impermeabilização do tegumento das sementes, e isso ocorreu de forma independente do estádio de maturação (Nakagawa et al, 2005).…”

Secagem e formação de sementes duras em mucuna-preta

“…NAKAGAWA et al (2003) Pelos resultados obtidos e as informações contidas em trabalhos com outras espécies de sementes duras (QUINLIVAN, 1965;MARBACH e MAYER, 1974, 1975SIDHU e CAVERS, 1977;ROLSTON, 1978;CHAVES e KAGEYAMA, 1980;MURDOCH e ELLIS, 1993;DEMIR, 1997;BASKIN e BASKIN, 1998), pode-se inferir que a secagem das sementes de mucuna-preta, realizada no interior das vagens, ocasionou a oxidação do tegumento, causando seu escurecimento e o surgimento de sementes duras em decorrência da impermeabilização do tegumento.…”

“…Durante a desidratação das sementes, na fase final de maturação, substâncias fenólicas são oxidadas resultando em compostos de coloração escura, os quais podem contribuir para a impermeabilização do tegumento (BEWLEY e BLACK, 1985); em sementes de Pisum elatius (MARBACH e MAYER, 1974, 1975, por exemplo, o escurecimento do tegumento foi devido à maior atividade da catecol oxidase catalisando a oxidação de compostos fenólicos em presença de O 2 .…”