Adapted from a brief review on turion formation by Klaus-J. Appenroth and Eric Lam (see the 14th issue of Duckweed Forum)
Turion formation in Spirodela polyrhiza is possible in light and in darkness. In order to compare different clones or a particular clone under different conditions, the ratio between formed turions and the number of fronds has to be calculated at the time when no new turions are formed in the cultivation flask. Light intensity, nutrient composition, temperature and medium volume are important factors. Phosphate is needed to support the inoculum for vegetative growth. During active growth phosphate from the medium is rapidly taken up. The resulting lack of external phosphate due to this uptake is sensed by the plant as a signal to start the developmental process of turion formation when a threshold of external phosphate concentration is reached. Turions can be most easily formed when the nutrient medium contains a low concentration of phosphate, e.g. 60 µM or less. Other signals (low sulphate concentrations, low temperature, and addition of the natural phytohormone abscisic acid) also can be a switch for turion formation. Only when all conditions are strictly standardized and the plants are carefully pre-cultivated under the same cultivation conditions, reproducible quantitative results can be obtained and the results can be compared with those of other research groups.
References:
- Appenroth K-J. 2002. Co-action of temperature and phosphate in inducing turion formation in Spirodela polyrhiza (Great duckweed). Plant, Cell and Environment 25: 1079–1085.
- Appenroth K-J, Adamec L. 2015. Specific turion yields of different clones of Spirodela polyrhiza depend on external phosphate thresholds. Plant Biology 17 (Suppl. 1): 125-129.
- Appenroth K-J, Nickel G. 2010. Induction of turion formation in Spirodela polyrhiza under close-tonature conditions: the environmental signals that induce the developmental process in nature. Physiologia Plantarum 138: 312–320.
- Appenroth K-J, Teller S, Horn M. 1996. Photophysiology of turion formation and germination in Spirodela polyrhiza. Biologia Plantarum 38: 95–106.
- Kuehdorf K, Jetschke G, Ballani L, Appenroth K-J. 2013. The clonal dependence of turion formation in the duckweed Spirodela polyrhiza – an ecogeographical approach. Physiologia Plantarum 150: 46–54.