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R Geeta

Publications and source records attributed to R Geeta.

4 recordsLinked to original sources
PubMed2006

Endophytic Phomopsis species: host range and implications for diversity estimates.

Foliar endophyte assemblages of teak trees growing in dry deciduous and moist deciduous forests of Nilgiri Biosphere Reserve were compared. A species of Phomopsis dominated the endophyte assemblages of teak, irrespective of the location of the host trees. Internal transcribed spacer sequence analysis of 11 different Phomopsis isolates (ten from teak and one from Cassia fistula) showed that they fall into two groups, which are separated by a relatively long branch that is strongly supported. The results showed that this fungus is not host restricted and that it continues to survive as a saprotroph in teak leaf, possibly by exploiting senescent leaves as well as the litter. Although the endophyte assemblage of a teak tree growing about 500 km from the forests was also dominated by a Phomopsis sp., it separated into a different group based on internal transcribed spacer sequence analysis. Our results with an endophytic Phomopsis sp. reinforce the earlier conclusions reached by others for pathogenic Phomopsis sp., i.e., that this fungus is not host specific, and the species concept of Phomopsis needs to be redefined.

Ascomycota↗
PubMed2003

The origin and maintenance of nuclear endosperms: viewing development through a phylogenetic lens.

The endosperm develops in fertilized ovules of angiosperms following fertilization of the central cell and nuclei in the female gametophyte. Endosperms differ in whether, and which, nuclear divisions are followed by cellular divisions; the variants are classified as cellular, nuclear or helobial. Functional correlates of this variation are little understood. Phylogenetic methods provide a powerful means of exploring taxonomic variation and phylogenetic patterns, to frame questions regarding biological processes. Data on endosperms across angiosperms were analysed in a phylogenetic context in order to determine homologies and detect biases in the direction of evolutionary transitions. Analyses confirm that neither all nuclear nor all helobial endosperms are homologous, raise the possibility that cellular development is a reversal in some derived angiosperms (e.g. asterids) and show that a statistically significant bias towards evolution of nuclear endosperms (and against reversals) prevails in angiosperms as a whole. This bias suggests strong selective advantages to having nuclear endosperm, developmental constraints to reversals or both. Homologies suggest that the microtubular cycle and cellularization pattern characteristic of reproductive cells across land plants may have been independently co-opted during multiple origins of nuclear endosperms, but information on cellular endosperms is essential to investigate further.

Cell Division↗
PubMedDate not supplied

Structure trees and species trees: what they say about morphological development and evolution.

The evolutionary history of morphological structures generally is equated with that of the taxa that carry them. It is argued here that, analogous to genes, developmental genetic pathways underlying morphological structures may be subject to developmental evolutionary changes that result, for instance, in duplication (serial homology analogous to gene duplication and paralogy). Entities that undergo evolution are expected to be related to each other as a tree. Just as with molecular evolution, "structure trees" and species trees sometimes may be incongruent, with implications for morphological homology concepts. Detection of structure trees through morphological evolutionary analyses may point to an entity that is maintained through evolution, possibly in part because it is a developmentally integrated structure ("individualized"). This idea is illustrated in a morphological evolutionary analysis of leaf primordia. These analyses suggest that leaf primordia in monocots and close relatives are related to each other as a tree and, therefore, are developmentally integrated, evolving entities. Among monocot primordia this tree structure breaks down, and it is concluded that there is no entity, the "monocot leaf primordium." However, one group of primordia is identified within monocots that have uniform characteristics and that are well represented by model species maize and rice. Such analyses of structure trees can facilitate the extrapolation and interpretation of results from molecular developmental and other comparative studies.

Flowers↗