Turion as Dormant Structure in Spirodela polyrhiza

摘要: ABSTRACT Hydrophytes such as Spirodela polyrhiza form dormant turions to withstand cold winters. The turion is an anatomicallydistinct structure from which a vegetative frond arises later during germination. sink the bottom of thepond when temperatures drop and remain there throughout winter. In spring, they float surface germi-nate into new primordium. Unlike fronds, are known possess small aerenchyma, starchgrains, relatively dense cytoplasm. These features allow survive winter season at ofthe pond. has been investigated previously great extent, especially in its physiological, biochemical andecological attributes. However, little about structural deve-lopment. Thus, aim present study was reveal characteristics with regardto tissue differentiation, aerenchyma development, starch distribution, ultrastructure, use electron micro-scopy.A moderate degree mesophyll differentiation found frond, whereas did not exhibit suchdifferentiation. Within tissue, approximately 37~45% cellular volume occupied by large aeren-chyma, but only 9~15% taken up turion. cells, those turionprimordium, were derived contained Their cytoplasm densely packed plastids,mitochondria, endoplasmic reticulum, Golgi bodies, microtubules. Plasmodesmata also well developed withinthese cells. most striking feature observed distribution grains within plastids Before theturion sank pond, considerable amount accumulated plastid stroma. starchgrains dissolved rose this promptly provided nutrients primordiumneeded for therefore, appropriate free-floating, reducedhydrophytes like polyhriza due that aided purpose ofsinking below water fronds arose grew rapidlyin beginning life cycle. Keywords : Hydrophytes,