Ploidy Effects in Isogenic Populations of Alfalfa

Abstract

Photosynthetically-active protoplasts isolated from isogenic sets of diploid-tetraploid and tetraplold-octoplold alfalfa (Medicago sativa L.) leaves were used to investigate the consequences of polyploidization on several aspects related to photosynthesis at the cellular level. Protoplasts from the tetraploid population contained twice the amount of DNA, ribulose-1,5-bisphosphate carboxylase (RuBPCase), chlorophyll (Chi), and chloroplasts per cell compared to protoplasts from the diploid population. Although protoplasts from the octoploid population contained nearly twice the number ofchloroplasts and amount of ChW per cell as tetraploid protoplasts, the amount of DNA and RuBPCase per octoploid cell was only 50% higher than in protoplasts from the tetraploWd population. The rate of C02-dependent 02 evolution in protoplasts nearly doubled with an increase in ploidy from the diploid to tetraploid level, but increased only 67% with an increase in ploidy from the tetraplold to octoploid level. Whereas leaves and-protoplasts had simflar increases in RuBPCase, DNA, and Chi with increase in ploidy level, it was concluded that increased cell volume rather than increased cell number per leaf is responsible for the increase in leaf size with ploidy.A better understanding of the physiological consequences of polyploidization should facilitate the development of agronomically useful genotypes from experimental polyploids. A principal difficulty inherent in physiological comparisons of polyploids is that cell volume (18), chloroplast number per cell (2), and the amount of DNA per nucleus (5) have been shown, in some cases, not to increase in exact proportion to an increase in genome size. In these instances, data expressed on a fresh weight, leaf area, or Chl basis may be misleading if the increase in these characteristics in relation to ploidy level has not been determined. The preferred method of comparing polyploids is to isolate protoplasts so that the amount of DNA can be correlated with genome size, and physiological data can be expressed on a per cell basis. Protoplast isolation also eliminates variability resulting from differences such as stomatal density (14) or anatomical characteristics (3).Allopolyploids (3,7,12) and colchicine-induced polyploids (14, 18) have been used to study the effects of polyploidization on biochemical and physiological processes. Results from these studies are confounded by genetic differences in the case of allopolyploids and problems associated with inbreeding depression in colchicine-induced and spontaneously appearing polyploids. 'To whom correspondence should be addressed. topolyploids of alfalfa (11) avoid these influences and allow a more direct study of polyploidization. These polyploids consist of an isogenic diploid-tetraploid (DDC 2X-4X) population of alfalfa to which maximum heterozygosity was restored and an isogenic tetraploid-octoploid (IC 4X-8X) population that was passed through a single sexual cycle, thus restoring some heterozygosity to the plants. These isogeni...

Sugar beet (Beta vulgarisL.) growth at different ploidy levels

“…Polyploid individuals may not always be superior to diploid ones: in some cases polyploid plants have slower growth rates (Ranney 2006) which could be attributed to difficulties in the cell cycle and slow cell division (Comai 2005), causing lower cell numbers and smaller organs. For example, it was reported that the overall chlorophyll content in polyploid plants is higher than diploid ones with lower chromosome numbers (Molin et al 1982;Warner et al 1987;Mathura et al 2006), while total chlorophyll content of tetraploid sugar beet genotypes ("AD 440" and "CBM 315") in our study were found to be lower than that of diploid ones ("Agnessa" and "Felicita").…”

“…The number of photosynthetic cells per unit leaf area decreases with increasing ploidy level (Warner and Edwards 1989). Although chloroplasts (Beck, Dunlop et al 2003;) and chlorophyll content (Molin et al 1982) are higher in polyploid genotypes, increased chlorophyll content with increasing ploidy level is not always apparent. For instance, chlorophyll content remained constant in different ploidy levels of Atriplex confertifolia (Warner and Edwards 1989).…”

“…Shoots of polyploid genotypes are thicker with short internodes and wider crotch angles. As the chromosome number increases, DNA content per cell, enzyme activity per cell and cell volume all increases (Molin et al 1982;Warner et al 1987). In addition, polyploids are used as sources of variability and new genotypes for plant improvement (Jan 1988;Hussain et al 1997).…”

Transgressive physiological and transcriptomic responses to light stress in allopolyploid Glycine dolichocarpa (Leguminosae)

“…Studies involving a wide range of polyploid species, including auto-and allopolyploids in both C3 and C4 species, have shown that polyploids often have larger mesophyll cells with more chloroplasts, higher chlorophyll and rubisco contents and greater photosynthetic capacities per cell than their diploid counterparts (for example, Dunstone and Evans, 1974;Molin et al, 1982;citations in Warner and Edwards, 1993;Coate et al, 2012). At the whole-leaf level, the effects of polyploidy are highly variable and not all polyploids examined exhibit greater photosynthetic capacities per unit leaf area (for example, Coate et al, 2012).…”

Stereology, an Unbiased Methodological Approach to Study Plant Anatomy and Cytology: Past, Present and Future

“…This technique was used by many authors (Possingham and Smith, 1972;Boffey et al, 1979;Lamppa et al, 1980;Molin et al, 1982;Tymms et al, 1983;Sung and Chen, 1989;Pyke and Leech, 1991;Yamasaki et al, 1996;Marrison et al, 1999;Ivanova and P'yankov, 2002;Meyer et al, 2006;Stettler et al, 2009). This estimation is unbiased since counting is done in the whole cell, provided the chloroplasts in the specimen are not overlapping and the cells used for chloroplast counting are selected in an unbiased way.…”