Evolutionary Lineages, Inherently Conserved Within the Genome of Isoetes L (Isoetaceae: Pteridophyta) Express in Heterosporangia of Isoetes Pantii Goswami & Arya: Brief Review: A Five Decades’ Study

Heterosporous sporangia discovered in Isoetes pantii Goswami & Arya are known as heterosporangia. Heterosporangia produce thousands of alete, monolete and trilete microspores and a few dozen megaspores. This trait is inherent within the genome of I pantii because plants collected from a location in South Gujarat also exhibit this feature. Additionally, initial collections and followup studies since 1966 have been consistently showing two types of megaspores within the heterosporangia. While microspores and megaspores develop in each and every hetrosporangium, additional unusual megaspores, variable in shape and size (180-220 micron), do not occur in all heterosporangia of all plants. These spores closely resembling fossil ancestral spores are being now termed as “Chalonospores”. Thus, a living spore genus Chalonospora is being named and defined as a spore discovered in a living plant which recall fossil ancestry of the genus but are never found in any other extant species of the genus. Since Chalanospores also originate from spore mother cells, as other microspores and megaspores do, this indicates that spore mother cells found in heterosporangia are genetically variable in expressions. Quite likely, a few megaspore mother cells must be possessing gene combinations with “revitalized relic DNA sequences”. As different types of chalonospres have been observed, variable gene combinations must be representing sporadic expressions of different lycopods of the vast geological past. Germination studies prove that these spores are endowed with different genetic make-up, as the gametophyte produced on soil culture produce unique single cell rhizoids with spiny outer layer. This apparent genomic reshuffle is related with frequently encountered chromosome breaks, translocations and irregular presence of 2n=36 –to 39 chromosomes in such plants. However, Isoetes pantii plants possess 2n=48 chromosomes with X-Y mechanism. No other species in the world flora of the genus has exhibited sex chromosomal mechanism and possessed n=12 chromosome series. With greater probability this appears plausible to imagine that naturally imposed chromosomal aberrations have rejuvenated genes which might have been regular expressions within the genome of some of the lycopods of Carboniferous and thereafter