Ecophysiological changes and spore formation: two strategies in response to low‐temperature and high‐light stress in Klebsormidium cf. flaccidum (Klebsormidiophyceae, Streptophyta)¹

Abstract

Members of the cosmopolitan streptophycean genus Klebsormidium live in various habitats, including sand dunes and polar/alpine environments. To survive in these harsh conditions they must possess an array of adaptive physiological and structural mechanisms, for example, to deal with chilling and photochilling stresses. Since these mechanisms have not been studied in detail, the objectives of this study were (i) to determine the physiological and biochemical responses of Klebsormidium cf. flaccidum (K. cf. flaccidum) to chilling (low temperature [LT]) and photochilling (LT in combination with high light [HL]) stresses; and (ii) to understand the cross‐link between biochemical parameters and cellular ultrastructural changes. The results indicated that 5°C is a temperature threshold (i.e., at 5°C) but not at higher temperatures, physiological changes were observed (Fv/Fm and ETR decreased and energy‐partitioning distribution changed, with an increase in Y[NPQ] under LT and an increase in Y[NO] under HL‐LT). Also, pigment contents changed significantly, with increased concentrations of photoprotective pigments such as antheraxanthin, zeaxanthin, and total carotenes. All of these responses occurred under LT and, to a greater extent, under LT‐HL, indicating that the two stresses (temperature and light) are additive. The cold treatment applied here induced the formation of spores under both LL and HL. The degree of photoinhibition was higher in spores than in vegetative cells, indicating that spores are less susceptible to photodamage. This study demonstrated a broad acclimation potential in different developmental stages of K. cf. flaccidum, which helps to explain the ecological success of this genus.

Cell Wall Reinforcements Accompany Chilling and Freezing Stress in the Streptophyte Green Alga Klebsormidium crenulatum

“…The physiological explanation for this acclimation can be found in enhanced concentrations of soluble sugars (glucose and sucrose), a putative glycoside and amino acids, including gama-aminobutyric acid (GABA) accumulated in this alga during cold acclimation (Nagao et al, 2008). Similar observations were made by Miguez et al (2020), indicating an initial increase of sucrose during cold acclimation at 5 • C.…”

“…Desiccation stress caused subcellular rearrangements ( Holzinger et al, 2011 ) and cell wall modifications in K. crenulatum , with an increase in total callose content ( Herburger and Holzinger, 2015 ). Also cold stress ( Rippin et al, 2019 ; Miguez et al, 2020 ), freezing stress ( Elster et al, 2008 ; Nagao et al, 2008 ) and osmotic stress ( Kaplan et al, 2012 ) were previously investigated in different Klebsormidium strains. In K. crenulatum , plasmolysis occurred after a treatment with 800 mM sorbitol, indicating a very negative osmotic potential (i.e., Ψ = −2.09 MPa; Kaplan et al, 2012 ).…”

Cold Stress Response: An Overview in Chlamydomonas

“…Similarly, Chlamydomonas nivalis and Haematococcus pluvialis in response to cold stress become cysts ( de Carpentier et al, 2019 ). Interestingly, in some filamentous green algae ( Klebsormidium ), the cold treatment induces the formation of spores, which show a significantly less susceptibility to photodamage compared to vegetative filaments ( Míguez et al, 2020 ).…”

“…Low-temperature stress affects many aspects of photosynthesis in land plants ( Huner et al, 1998 ; Ensminger et al, 2006 ; Hajihashemi et al, 2018 ; Zhu et al, 2018 ) and green algae ( Míguez et al, 2017 ; Míguez et al, 2020 ; Zheng et al, 2020 ). In terrestrial green algae, down-regulation of photochemical processes is a controlled mechanism that favors the dissipation of excess energy to protect the photosynthetic apparatus under low temperature conditions ( Míguez et al, 2017 ).…”

“…Due the imbalanced absorption and utilization of light induced by cold treatment, over-accumulation of ROS occurs in plants ( O’Kane et al, 1996 ; Ensminger et al, 2006 ; Barati et al, 2019 ). Some cold-exposed green algae significantly increase the content of photoprotective pigments such as antheraxanthin, zeaxanthin, and total carotenes ( Míguez et al, 2020 ). During cold adaptation, ROS-scavenging enzymes are essential for ROS detoxification ( Suzuki and Mittler, 2006 ; Distelbarth et al, 2013 ).…”