Heterogeneity of dormancy in the turions of <italic>Spirodela polyrrhiza</italic>

Abstract

Spirodela polyrrhiza exhibits at least two different types of dormancy in turions induced by nitrogen deficiency, i.e., Y (young)- and O (old)-type turions produced at early and late stages in the formation process, respectively. On the other hand, turions induced by relatively low temperature are mainly the Y type. O-type turions germinate rapidly under darkness with the addition of NO3-. However, under semi-anaerobic and anaerobic conditions they germinate only when exposed to light in the presence of NO3-. Y-type turions germinate in air after a definite dormant period only under light and in the presence of NO3-. The dormancy is broken by light regardless of the presence of NO3-, although the germination phase requires both. This dormancy is also broken when a definite period of darkness is given in the absence of NO3-, and the germination proceeds in the presence of NO3- with or without light. Thus, an alternative process exists for the Y type in which the dormancy is released by either light or darkness.