Comparison of Stomatal Structure and Distribution between Ovules and Leaves in Ginkgo biloba

Abstract

Stomata are plant epidermal structures that play essential roles in photosynthesis, respiration, and transpiration. Although stomata on plant leaves have been extensively studied, their structure and distribution on other organs remain poorly understood. The “living fossil “, Ginkgo biloba, has naked ovules that are thought to be primitive reproductive structures in ancient seed plants. Therefore, we hypothesized that there are some distinct stoma features in G. biloba ovules that have not been reported. In this study, we investigated the morphological development of stomata on ovules and leaves of Ginkgo biloba using scanning electron microscopy, then examined the anatomical characteristics of the general stalk and petiole using semi-thin sectioning. We found that stomata were distributed on the epidermis of the whole ovule, except near the micropyle; these stomata persisted until harvest, indicating that ovules perform gross photosynthesis to an extent similar to the photosynthesis observed in leaves, which is beneficial to ovule development. Ovule and leaf stomata share similar orientation, composition, and development; however, their distribution and subsidiary cell morphology significantly differ. The morphology of the general stalk was similar to the morphology of the petiole, but xylem cell development was minimal, and no sclerenchyma cells were present beneath the epidermis; these findings suggested that the general stalk is biomechanically weaker than the petiole. Overall, these results suggest that despite their differences, G. biloba ovules and leaves share many morphological and anatomical similarities in terms of stomatal architecture and stalk anatomy. These findings will help to elucidate the leaf origins of “flowers” in ancient plants.