Endomitosis and the effect of gibberellic acid in different Pisum sativum L. cultivars

The distribution pattern of endopolyploidy in maize

We discovered that endopolyploidization is common in various organs and tissues of maize at different development stages. Endopolyploidy is not specific in maize germplasm populations. Endopolyploidy is caused by DNA endoreplication, a special type of mitosis with normal DNA synthesis and a lack of cell division; it is a common phenomenon and plays an important role in plant development. To systematically study the distribution pattern of endopolyploidy in maize, flow cytometry was used to determine the ploidy by measuring the cycle (C) value in various organs at different developmental stages, in embryos and endosperm during grain development, in roots under stress conditions, and in the roots of 119 inbred lines from two heterotic groups, Shaan A and Shaan B. Endopolyploidy was observed in most organs at various developmental stages except in expanded leaves and filaments. The endosperm showed the highest C value among all organs. During tissue development, the ploidy increased in all organs except the leaves. In addition, the endopolyploidization of the roots was significantly affected by drought stress. Multiple comparisons of the C values of seven subgroups revealed that the distribution of endopolyploidization was not correlated with the population structure. A correlation analysis at the seedling stage showed a positive relationship between the C value and both the length of the whole plant and the length of main root. A genome-wide association study (GWAS) identified a total of 9 significant SNPs associated with endopolyploidy (C value) in maize, and 8 candidate genes that participate in cell cycle regulation and DNA replication were uncovered in 119 maize inbred lines.

Hormonal control of endoreduplication in sugar beet (Beta vulgaris L.) seedlings growing in vitro

The effect on endoreduplication in sugar beet (Beta vulgaris L.) seedlings of five plant hormones in MS medium, ethylene, 24-epibrassinolide (EBR), gibberellic acid (GA(3) ), kinetin and 1-naphthaleneacetic acid (NAA), as well as a combination of kinetin and NAA at two different concentrations, was studied using flow cytometry. Analyses of DNA content in nuclei of the root, hypocotyl and cotyledons of seedlings growing in vitro were performed during their early development, starting from when the root was 0.5-1.0 cm long until expansion of the first pair of leaves. The proportions of nuclei with different DNA contents were established and the mean C-value calculated. The presence of exogenous plant hormones changed endoreduplication intensity, although to different extents, depending on the organ and developmental stage. Ethylene and NAA stimulated the process, while EBR and kinetin suppressed it and GA did not clearly affect it.

Endopolyploidy in seed plants

Two main attempts have been suggested for the biological significance of endopolyploidy: (i) provision of high DNA amounts to support high synthetic demands in certain cells and (ii) compensation for a lack of nuclear DNA in species with small genomes. However, in seed plants, the positive correlation between DNA content and cell volume of endopolyploid cells suggests other possibilities. Cell size paralleled by the endopolyploidy level has an impact on growth and development. Endopolyploidy levels in turn are characteristic for a given species and even families, reflecting the adaptation to certain habitats during phylogeny. Furthermore, endopolyploidy levels vary to some degree between individuals of one species in response to different environmental conditions. In addition, endopolyploidy differs between different tissues suggests that a certain cell size is advantageous for a given cell function. This article reviews these findings and discusses more conclusive possible functions of endopolyploidy.

Endopolyploidy in Vanda Miss Joaquim (Orchidaceae)

•  Occurrence of endopolyploidy in somatic tissues of the hybrid orchid Vanda Miss Joaquim (Vanda hookeriana × Vanda teres) was investigated with respect to tissue type and developmental stage. Effects of naphthaleneacetic acid (NAA) and gibberellic acid (GA₃ ) on endopolyploidy during embryo development were also studied. •  For the study of endopolyploidy, flow cytometric analysis was employed to determine nuclear DNA content of cells of somatic tissues. •  Multiploid cells were observed in leaves, roots and column, but not in shoot apex, stem, perianth and pedicel. Furthermore, differential distribution of multiploid cells was found among different parts of leaves and roots. The degree of endopolyploidy in embryos increased with development. NAA was shown to induce endoreduplication in germinating embryos to a much larger extent than GA₃ . •  The pattern of endopolyploidy was characteristic of tissue type and developmental stage. The implications of endopolyploidy during differentiation and development, as well as the relevance of endopolyploidy to somaclonal variation, are discussed.