Polyphenol oxidase (PPO, catecholase) activity during germination and early seedling growth of Cicer milkvetch (<em>Astragalus cicer</em> L.)

Abstract

Mature seeds of the legume Astragalus cicer L. form a homogeneous seed pool in size and weight. They occur either brown coloured or yellow coloured. They reveal an expressed dormancy but they germinate readily after mechanical scarification. Time span of germination and early seedling development under defined conditions were followed and compared to the activity and potential activation of polyphenol oxidase (PPO, catecholase). The yellow seeds developed without difficulties, but on the brown coloured seeds in the course of germination hyphal growth was visible which was linked with the death of the seedlings. Quantitative experiments with the yellow seeds revealed that scarified seeds formed more than 98 % of seedlings within seven days. There was no difference of germination rate between dark and daylight incubations. The polyphenol oxidase of the seeds occurs in two forms, a preformed testa localized enzyme and an induced PPO activity of the seedling. The initially high activity of the testa related PPO (1.32 μM O2/h x g fresh weight) decreases during the first days after germination, the activity of the seedling related PPO becomes detectable four to five days after onset of germination. After seven days the activity in roots is about 3.6 μM O2/h x g fresh weight. The cotyledons reveal 2.3 and the hypocotyl 1.9 μM O2/h x g fresh weight, respectively. There is an indication that autoinhibitory components interfere with the germination process. The importance of the polyphenol oxidase as a component of the plants’ protection system during germination is discussed.