Polyploidy in Changing Environment

Abstract

In nature, polyploidy is essential for diversity of new species (maintenance and emergence). Moreover, the environment might also play a role in creating polyploids as they have been found more in extreme environments such as high-altitude, subarctic and xeric areas (Love and Love 1949; Love 1953; Hanelt 1966; Grant 1971). It has been proposed that polyploids can establish better than diploids, and various studies on morphology, physiology and development have been conducted to verify the higher stress tolerance/resistance. It has been seen morphologically that polyploids have large cell sizes (Melaragno et al. 1993) and larger stomata (Hodgson et al. 2010). It has been suggested that genome duplication in polyploids might help to predict the water relations in them by showing changes in stomatal pore size, e.g. in Betula papyrifera (birch), polyploids have lesser stomata than diploids resulting in decreased gaseous exchange (Li et al. 1996). Furthermore, other morphological factors such as leaf, cuticle thickness and cell wall composition also play a role in maintaining water potential and gaseous exchange (Johnson 1975; Li et al. 1996). Thus, the polyploids being more adaptive than diploids are still inconclusive because of the lack of extreme experimentation. Maherali et al. (2009) studied how genome doubling affected water relations by comparing the natural diploid and tetraploid with neotetraploids (colchicine-induced) of Chamerion angustifolium (firewood). They reported that all tetraploids had large size stomata, increased stem and wall diameter and decreased specific hydraulic conductivity than the diploid ones. However, they noted that the natural tetraploids were significantly drought tolerant than diploids and neotetraploids suggesting that tolerance trait did not evolve instantaneously but evolved later on independent of the genome duplication (Maherali et al. 2009). However, Ramsey (2011) performed the transplant experiment in the field by transferring seedlings from greenhouse to dry dune habitat and noted that there were fivefold increases in survivorship of hexaploid seedlings raised from seeds collected from the field compared with the tetraploid seedlings. He also observed that there was 70% increase in survivorship of spontaneous neohexaploid seedlings. Thus, polyploids adapt better to changing environments. Furthermore, an integrative experimentation using Arabidopsis for examining the role of ecophysiological conditions on morphological alterations in polyploids for finding the mechanisms of cell size variability between diploids and tetraploids (Li et al. 2012).