Turion formation and behaviour inSpirodela polyrhiza at two levels of phosphate supply

The clone SJ of Spirodela polyrhiza (L.) Schleiden forms turions under various nutritive conditions. As compared to 1500 μmol 1 −1 phosphate (P+), growth and frond yield of mixotropic cultures decreased, when 60 μol 1 −1 phosphate (P-) were available. By contrast, P-conditions increased the number, individual size, dry matter content, and total turion yield (mg turions per ml of the nutrient medium) of P-turions as compared to P+ ones. Germination behaviour of P-turions is characterized by fairly low zero levels in the controls, and by low heterogeneity in individual size as well as in the response patterns concerning the influence of light and/or phytoactive substances. P-turions from young Spirodela cultures are extremely dormant. However, they undergo an after-ripening process if kept inside ageing cultures.