Abstract
The unicellular freshwater alga Micrasterias denticulata is an exceptional organism due to its complex star-shaped, highly symmetric morphology and has thus attracted the interest of researchers for many decades. As a member of the Streptophyta, Micrasterias is not only genetically closely related to higher land plants but shares common features with them in many physiological and cell biological aspects. These facts, together with its considerable cell size of about 200 μm, its modest cultivation conditions and the uncomplicated accessibility particularly to any microscopic techniques, make Micrasterias a very well suited cell biological plant model system. The review focuses particularly on cell wall formation and composition, dictyosomal structure and function, cytoskeleton control of growth and morphogenesis as well as on ionic regulation and signal transduction. It has been also shown in the recent years that Micrasterias is a highly sensitive indicator for environmental stress impact such as heavy metals, high salinity, oxidative stress or starvation. Stress induced organelle degradation, autophagy, adaption and detoxification mechanisms have moved in the center of interest and have been investigated with modern microscopic techniques such as 3-D- and analytical electron microscopy as well as with biochemical, physiological and molecular approaches. This review is intended to summarize and discuss the most important results obtained in Micrasterias in the last 20 years and to compare the results to similar processes in higher plant cells.
Highlights
Among the placoderm desmids the genus Micrasterias has an exceptional position due to its highly ornamented, star-shaped morphology with deep indentations and furcated lobe tips (Figure 1A)
Based on earlier results briefly outlined in the Section “Introduction” and on a more detailed survey on results obtained in the last 20 years, this review aims to provide an overview on our present knowledge on the cell biological basis for growth and cell shape formation as well as on responses of Micrasterias to different abiotic stress scenarios
Thereafter photosynthesis drops to zero at 40◦C after pre-cultivation at 15◦ but declines less distinctly after pre-cultivation at 20 or 25◦C. These results show that the optimum temperature for photosynthesis in Micrasterias is similar to that determined in higher plants of temperate areas (Larcher, 2001) and that primary energy balancing processes such as photosynthesis and respiration are less affected by elevated temperature than cell division rates and cell shaping (Weiss et al, 1999)
Summary
Plant Physiology Division, Cell Biology Department, University of Salzburg, Salzburg, Austria. As a member of the Streptophyta, Micrasterias is genetically closely related to higher land plants but shares common features with them in many physiological and cell biological aspects These facts, together with its considerable cell size of about 200 μm, its modest cultivation conditions and the uncomplicated accessibility to any microscopic techniques, make Micrasterias a very well suited cell biological plant model system. The review focuses on cell wall formation and composition, dictyosomal structure and function, cytoskeleton control of growth and morphogenesis as well as on ionic regulation and signal transduction It has been shown in the recent years that Micrasterias is a highly sensitive indicator for environmental stress impact such as heavy metals, high salinity, oxidative stress or starvation.
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