Reactive Oxygen Species and Alternative Respiration in the Developing Flowers of Two Subtropical Woody Plants

Abstract

Petals, sepals, pistils, and stamens from flowers of two landscape tree species (Elaeocarpus hainanensis Oliv and Michelia alba DC) were analyzed to determine the changes in levels of reactive oxygen species (ROS), lipoxygenase (LOX) activity, and alternative pathway respiration throughout flower development. Histochemical and quantitative analyses revealed that ROS levels differed among tissues and stages of flower development. ROS levels were high in all flower tissues early in development and then declined to low levels late in development. ROS levels were highest in the stamen. In contrast, LOX activity, heat energy evolution, and the percentage of total respiration represented by alternative respiration in M. alba petals increased with flower development. The results suggest that ROS are involved in the growth of various flower tissues at early developmental stages and not only located on the tip site of growing tissues. The reduction in ROS generation later in development is probably due to the significant elevation in alternative respiration. The increase in LOX activity and heat energy evolution might contribute to the formation and release of some aromatic compounds and to flower opening. LOX, however, might not mediate ROS generation in the petal during development.