Abstract
Heterophyllous aquatic plants produce aerial (i.e., floating and terrestrial) and submerged leaves—the latter lack stomata—while homophyllous plants contain only submerged leaves, and cannot survive on land. To identify whether differences in morphogenetic potential and/or physiological stress responses are responsible for variation in phenotypic plasticity between two plants types, responses to abscisic acid (ABA) and salinity stress were compared between the closely related, but ecologically diverse pondweeds, Potamogeton wrightii (heterophyllous) and P. perfoliatus (homophyllous). The ABA-treated (1 or 10 μM) P. wrightii plants exhibited heterophylly and produced leaves with stomata. The obligate submerged P. perfoliatus plants were able to produce stomata on their leaves, but there were no changes to leaf shape, and stomatal production occurred only at a high ABA concentration (10 μM). Under salinity stress conditions, only P. wrightii leaves formed stomata. Additionally, the expression of stress-responsive NCED genes, which encode a key enzyme in ABA biosynthesis, was consistently up-regulated in P. wrightii, but only temporarily in P. perfoliatus. The observed species-specific gene expression patterns may be responsible for the induction or suppression of stomatal production during exposure to salinity stress. These results suggest that the two Potamogeton species have an innate morphogenetic ability to form stomata, but the actual production of stomata depends on ABA-mediated stress responses specific to each species and habitat.Electronic supplementary materialThe online version of this article (doi:10.1007/s10265-016-0844-x) contains supplementary material, which is available to authorized users.
Highlights
Many organisms have evolved sophisticated stress response mechanisms, and have acquired the ability to alter their phenotypes to adapt to environmental changes. Bradshaw (1965) suggested that plants should be more plastic, tolerate a broader range of environmental conditions, and experience more persistent natural selection than animals
Under salinity stress, which often promotes abscisic acid (ABA) biosynthesis, stomata were induced in P. wrightii, but not in P. perfoliatus (Fig. 5)
These results suggested that, between the two Potamogeton plants, differences in the ABA-mediated stress responses, but not in the morphogenetic potential, were responsible for variation in phenotypic plasticity under natural conditions
Summary
Many organisms have evolved sophisticated stress response mechanisms, and have acquired the ability to alter their phenotypes to adapt to environmental changes. Bradshaw (1965) suggested that plants should be more plastic, tolerate a broader range of environmental conditions, and experience more persistent natural selection than animals. Aquatic plants are thought to have evolved from terrestrial ancestors, and to have adapted secondarily to aquatic habitats They include both heterophyllous and obligate submerged homophyllous (non-heterophyllous) species (Cook 1990, 1999). The structure of the aerial leaves is similar to that of land plants, while the submerged leaves are thin, elongated and lack differentiation of the stomata, cuticle and mesophyll layers. Many environmental factors, such as water stress, photoperiod, and temperature, affect heterophyllous leaf formation (reviewed by Kuwabara and Nagata 2002; Wells and Pigliucci 2000)
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