Inducible growth mode switches influence Valonia rhizoid differentiation
- 170 Downloads
Cell differentiation and cell type commitment are an integral part of plant growth and development. Investigations on how environmental conditions affect the formation of shoots, roots, and rhizoids can help illustrate how plants determine cell fate and overall morphology. In this study, we evaluated the role of substratum and light on rhizoid differentiation in the coenocytic green alga, Valonia aegagropila. Elongating rhizoids displayed varying growth modes and cell shape upon exposure to different substrata and light conditions. It was found that soft substrata and dark incubation promoted rhizoid elongation via tip growth while subsequent exposure to light prevented tip growth and instead induced swelling in the apical region of rhizoids. Swelling was accompanied by the accumulation of protoplasm in the rhizoid tip through expansion of the cell wall and uninhibited cytoplasmic streaming. Subsequent diffuse growth led to the transformation from slender, rod-shaped rhizoids into spherical thallus-like structures that required photosynthesis. Further manipulation of light regimes caused vacillating cell growth redirections. An elongating V. aegagropila rhizoid cell thus appears capable of growth mode switching that is regulated by immediate environmental conditions thereby influencing ultimate cell shape and function. This is the first description of inducible, multiple growth mode shifts in a single intact plant cell that directly impact its differentiation.
KeywordsCytoplasmic streaming Growth mode Light Rhizoid Thallus Valonia aegagropila
We thank Dr. Ichiro Mine of Kochi University, Japan, for technical suggestions. This study was supported by the “Monbukagakusho,” Ministry of Education, Science, Sports, and Culture, Japanese Government, as part of doctoral research of P.R.E.
Conflicts of interest
The authors declare that they have no conflict of interest.
Formation of a bulb-tipped rhizoid from a rod-shaped V. aegagropila rhizoid and subsequent resumption of tip growth. A cell was incubated in darkness for 14 days at 22°C then exposed to 96 h continuous light at 40 μmol photons m−2 s−1 and then 24 h of continuous light at 10 μmol photons m−2 s−1. Photomicrographs were taken at 10-min intervals (MPG 2980 kb)
- Bold H, Wynne MJ (1985) Introduction to the algae. Prentice-Hall Inc, Englewood CliffsGoogle Scholar
- Chihara M (1959) Studies on the life history of the green algae in the warm seas around Japan (9). Supplementary note on the life history of Valonia macrophysa Kutz. J Jpn Bot 34:257–268Google Scholar
- Dazy AC, Puiseux-Dao S, Borghi H (1989) The effects of blue and red light on Acetabularia mediterranea after long exposure to darkness. Biol Cell 67:227–234Google Scholar
- Elvira PR, Sekida S, Okuda K (2012) Rhizoid formation in Valonia (Siphonocladales, Chlorophyceae). PhycologiaGoogle Scholar
- Fritsch FE (1935) The structure and reproduction of the alga. Cambridge Univ Press, LondonGoogle Scholar
- Kanda T (1940) Studies on the genus Valonia from Palao. Kagaku Nanyo 3:23–32Google Scholar
- Kawai H, Motomura T, Okuda K (2005) Isolation and purification techniques for macroalgae. In: Andersen A (ed) Algal culture techniques. Elsevier, Amsterdam, pp 133–143Google Scholar
- Maclean N, Hall BK (1987) Cell commitment and differentiation. Cambridge University Press, LondonGoogle Scholar
- Okuda K, Ueno S, Mine I (1997) Cytomorphogenesis in coenocytic green algae. IV. The construction of cortical microtubules during lenticular cell formation in Valonia utricularis. Mem Fac Sci Kochi Univ Ser D 18:17–25Google Scholar
- Provasoli L (1968) Media and prospects for the cultivation of marine algae. In: Watanabe A, Hattori A (eds) Proceedings of the US-Japan Conference, Hakone, September 1966. Japanese Society of Plant Physiologists, Japan, pp 63–75Google Scholar