Abstract
Streptophyte algae are the ancestors of land plants, and several classes contain taxa that are adapted to an aero-terrestrial lifestyle. In this study, four basal terrestrial streptophytes from the class Klebsormidiophyceae, including Hormidiella parvula; two species of the newly described genus Streptosarcina (S. costaricana and S. arenaria); and the newly described Streptofilum capillatum were investigated for their responses to radiation, desiccation and temperature stress conditions. All the strains showed low-light adaptation (Ik < 70 μmol photons m−2 s−1) but differed in photoprotective capacities (such as non-photochemical quenching). Acclimation to enhanced photon fluence rates (160 μmol photons m−2 s−1) increased photosynthetic performance in H. parvula and S. costaricana but not in S. arenaria, showing that low-light adaptation is a constitutive trait for S. arenaria. This lower-light adaptation of S. arenaria was coupled with a higher desiccation tolerance, providing further evidence that dehydration is a selective force shaping species occurrence in low light. For protection against ultraviolet radiation, all species synthesised and accumulated different amounts of mycosporine-like amino acids (MAAs). Biochemically, MAAs synthesised by Hormidiella and Streptosarcina were similar to MAAs from closely related Klebsormidium spp. but differed in retention time and spectral characteristics in S. capillatum. Unlike the different radiation and dehydration tolerances, Hormidiella, Streptosarcina and Streptofilum displayed preferences for similar thermal conditions. These species showed a temperature dependence of photosynthesis similar to respiration, contrasting with Klebsormidium spp. and highlighting an interspecific diversity in thermal requirements, which could regulate species distributions under temperature changes.
Highlights
Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.4 M.G
For H. parvula and S. costaricana, acclimation to moderate light (ML) was related to a lower α (t test, p = 0.0068; p = 0.0277), higher rETRmax (t test, p = 0.0408; p = 0.0226) and Ik values twice as high as in the CL (t test, p = 0.0247; p = 0.0311)
This study investigated how the photosynthetic apparatus of recently described members of basal streptophyte algae responds to changes of radiation, water availability and temperature
Summary
Streptophyte green algae separated from the Chlorophyta lineage more than 700 million years ago (MYA) [1, 2]. Following this split, streptophytes diversified into six paraphyletic classes, the basal (Mesostigmatophyceae, Chlorokybophyceae, Klebsormidiophyceae) and advanced streptophytes (Charophyceae, Coleochaetophyceae, Zygnematophyceae), which originated the land plants about 450–500 MYA [1, 3, 4]. Three members of basal terrestrial streptophytes, including the newly described genera Streptosarcina Mikhailyuk et Lukešová (sister lineage to Hormidiella Iyengar et Kanthamma) and Streptofilum.
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