Fruit Development In The Seagrass Thalassia Testudinum: Possible Relationships Between Structure, Physiology And Defense

Even though seagrasses are clonal plants, they also invest substantial energy in sexual reproduction. However, little is known about the development of the reproductive structures of seagrasses and their complex interactions with ambient conditions. Here, we describe the structural and physiological changes during development in the fruit pericarp of the tropical seagrass Thalassia testudinum, and their possible role in defense mechanisms. The fruit exocarp develops protuberances with a monostratified epidermis. The parenchyma below the exocarp epidermis, consists of chlorenchyma with abundant chloroplasts and cells that, in the early stages of development of the fruit, accumulate proanthocyanins and other diverse phenolic compounds, in the course of development, vary in quantity and solubility. During the intermediate and late stages of development, when the fruit emerges above the sediment, idioblasts with oxalate crystals are formed. Changes during the fruit development in morphology, phenolic compounds and oxalate crystal deposits, may be related to various metabolic processes to maintain homeostasis, such as downregulation of photosynthetic ROS. At the same time, these changes may also provide defense mechanisms against herbivores. Parrotfish appear undeterred by phenolic compounds in the exocarp of young manually exposed fruits; but they do not consume the pericarp of mature fruits (naturally emerged above the sediments) with oxalate crystals. These findings suggest that timing and integration of morphological and metabolic changes during fruit development guarantee both successful development and protection of the seeds.