Article

Phenotypic Plasticity Among Ecological Populations of Polygonum equisetiforme Sm. in the Northern Geographical Areas, Egypt

International Journal of Botany 01/2007;
Source: DOAJ

ABSTRACT The main objective of present study is to provide some clue on how the different populations of Polygonum equisetiforme species respond to different environmental conditions. Plant individuals were chosen from 22 sites representing different geographical areas: The western section, Nile Delta and north Sinai. Ripe seeds were collected from the sampling sites. Soil analyses were performed to collected soil samples from each site. Preliminary germination experiments were conducted to determine the optimum conditions for germination of seeds. Two ex situ cultivation experiments were carried out in two successive years under uniform conditions. Morphological and seed attributes have been measured for the wild populations and the cultivated progenies. Protein content of seeds and seed coat morphology as well as the anatomical structure of the different organs of the investigated species were also studied. Germination experiments showed that seeds of Polygonum equisetiforme Sm. require a storage period before starting to germinate for most sites, while further variability in germination percentages did occur with extending the storage period of seeds. This period exceeded two months for active germination of seeds representing most of the sites. The present study points out many important remarks, of which: population of Nile Delta section exhibited the most plastic response among different conditions; Seed size and reserve of P. equisetiforme are environmentally induced rather than genetically fixed characters. Seed coat is characterized by two patterns of ornamentation, wavy and papillate, the wavy ornamented is more frequent. Electrophoresis separation of protein bands in the sampled of Polygonum equisetiforme showed that all samples has the same protein bands. This may reflect the consistency of the same kinds of protein and suggests the absence of genetic variation within different individuals collected from different geographical areas. It also reveals that the protein pattern of the study species tends to be genetically fixed. Wild and cultivated progenies of the western province showed tendency of their individuals to contain the highest amount of protective tissues in their leaves; supporting tissues in their stems and conductive tissues in their roots. This probably reflects the great response of this population to environmental conditions. Fluctuation in the thickness of these tissues in the cultivated progenies leads to the assumption that thickness of layer is an environmentally affected. However, arrangement of layers in Polygonum equisetiforme is mostly genetically fixed as they exhibited the least change affected by the environmental changes. There was a plastic response in the timing of flowers production for the plants of the ex situ experiments to ensure faster reproduction and complete life history in the new environment. Meanwhile, wild individuals produce a large number of flowers to encounter numerous interacting stresses for survival. The present study also showed that individuals of P. equisetiforme allocate resources to support vegetative growth rather than reproductive output in the successive progenies in response to ex situ cultivation.

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