Developmental and molecular genetic studies of roots in the fern Ceratopteris richardii

The homosporous fern Ceratopteris richardii is an excellent system for studies of root developmental biology in a non-seed plant due to its fast life cycle and semi-aquatic habit. In this dissertation, I first characterized variation in growth and development of the first six roots in young sporophyte of C. richardii, then briefly described certain related characters in later developmental stages (e.g. reproductive) during sporophyte ontogeny. The root plastochron and individual growth rate, organ size (diameter and final length), anatomy, and the onset of lateral root initiation all varied as a function of shoot age. However, one prominent character was that one root was always produced in association with one leaf at each node. This character continued into the adult shoot. Although there was significant heteroblastic variation among roots in young sporophytes of C. richardii, the results also showed that the pattern of development in roots located at equivalent positions along the young shoot was relatively uniform and therefore amenable for further developmental investigations. In particular, the fifth root presented a convenient organ for more detailed investigations.; The developmental anatomy of the fifth root in young sporophytes of C. richardii was described using histological and statistical techniques. All roots examined possessed a tetrahedral root apical cell. Three proximal division faces of this apical cell divided in a strict sequence to produce three merophyte orthostichies in the body of the root. Formative divisions in merophytes behind the apical cell produced initials that gave rise to a characteristic number of cell files in each merophyte. These formative divisions occurred also in a relatively regular order during merophyte ontogeny. The predictable cellular development and consequential structural pattern described for the fifth root in C. richardii will be very useful for subsequent molecular and genetic studies of the underlying mechanisms of root development in ferns.; Finally, molecular genetic studies of root development in C. richardii were undertaken. The differential display polymerase chain reaction (DD-PCR) technique was used to identify putative root specific cDNAs. Six root specific subclones were recovered from a display of six primer combinations. Northern analysis of the first subclone (designated as RSG1) had confirmed that it was specifically expressed in roots of C. richardii . Rapid amplification of cDNA ends (RACE) was unsuccessful in extending RSG1 sequence toward the 5′ unknown upstream regions. Efforts are in progress to construct a genomic DNA library of C. richardii to recover a full length RSG1 sequence.