Underdeveloped embryos in dwarf seeds and implications for assignment to dormancy class

Abstract

Studies were conducted to determine if small embryos (i.e. low embryo length:seed length ratio) in mature dwarf seeds (0.2–2 mm) are underdeveloped. In this case, they would grow (inside the seed) prior to germination, and seeds would have morphological or morphophysiological dormancy. Prior to radicle emergence, embryo length in seeds ofDrosera anglica(Droseraceae),Campanula americana,Lobelia appendiculata,L. spicata(Campanulaceae) andSabatia angularis(Gentianaceae) increased 0, 103, 182, 83 and 57%, respectively. Since embryo growth did not occur in seeds ofD. anglicaprior to germination, embryos, although small, are fully developed; seeds have only physiological dormancy. The underdeveloped embryo in seeds ofC. americanahas little or no physiological dormancy; thus, seeds have morphological dormancy. On the other hand, underdeveloped embryos in seeds ofL. appendiculata,L. spicataandS. angularisare physiologically dormant, and seeds have morphophysiological dormancy. Therefore, since small embryos in dwarf seeds may or may not be underdeveloped, assignment of seeds to a dormancy class requires that studies be done to determine if embryos grow inside the seed before germination can occur. Such information is important in understanding the evolutionary relationship of the different kinds of seed dormancy.