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.

尽管海草是无性系植物，但它们也在有性繁殖中投入了大量能量。然而，人们对海草生殖结构的发育及其与环境条件的复杂相互作用知之甚少。在这里，我们描述了热带海草Thalassia testudinum果皮发育过程中的结构和生理变化，以及它们在防御机制中的可能作用。果实外果皮发育具有单层表皮的突起。外果皮表皮下的薄壁组织由具有丰富叶绿体和细胞的绿组织组成，在果实发育的早期，积累了原花青素和其他多种酚类化合物，在发育过程中，其数量和溶解度各不相同。在发育的中后期，当果实出现在沉积物上方时，就会形成带有草酸盐晶体的成虫。果实发育过程中形态、酚类化合物和草酸盐晶体沉积物的变化可能与维持体内平衡的各种代谢过程有关，例如光合活性氧的下调。同时，这些变化也可能提供针对食草动物的防御机制。鹦鹉鱼似乎没有被手动暴露的幼果外果皮中的酚类化合物吓倒；但它们不消耗带有草酸盐晶体的成熟果实（自然出现在沉积物上方）的果皮。这些发现表明，果实发育过程中形态和代谢变化的时机和整合保证了种子的成功发育和保护。