ORIGINAL ARTICLE Endoreduplication level affects flower size and development by increasing cell size in Phalaenopsis and Doritaenopsis Thanh-Tam Ho 1 • A-Reum Kwon 1 • Yeo-Joong Yoon 2 • Kee-Yoeup Paek 1 • So-Young Park 1 Received: 6 February 2016 / Revised: 20 July 2016 / Accepted: 21 July 2016 / Published online: 23 July 2016 Ó Franciszek Go ´rski Institute of Plant Physiology, Polish Academy of Sciences, Krako ´w 2016 Abstract Endoreduplication is an alternative form of the cell cycle that is common in approximately 90 % of angiosperm species. Endoreduplication, determined using flow cytometry, occurs in various tissues of Phalaenopsis and Doritaenopsis species belonging to the Phalaenopsis (Phal.) alliance. In this study, flowers and leaves of nine cultivars from the small, middle, and large flower groups of the Phal. alliance were used to investigate the relationship between endoreduplication level and flower size. Some degree of endoreduplication was detected in all cultivars. A higher level of endoreduplication (2C–16C) was observed in cultivars from the large flower group than in those from the middle and small flower groups (2C–8C). In the leaves, endoreduplication tended to be found in middle and large flower group cultivars, but it varied with the cultivar rather than the flower group. Different patterns of endoredupli- cation were recorded at various stages of flower develop- ment in the Phal. hybrids ‘Queen Beer’ (small flower group) and ‘KV01’ (large flower group). Endoreduplication during flower development caused an increase in ploidy levels from 2C–4C to 2C–8C in ‘Queen Beer’, and from 2C–8C to 2C–16C in ‘KV01’; thus higher ploidy levels were detected in cultivars from the large flower group. Endoreduplication levels affected flower size and devel- opment by increasing cell size, indicating a positive relationship between endoreduplication and petal size in the Phal. alliance. Controlling flower size via the adjust- ment of the level of endoreduplication should be consid- ered in breeding programs aimed at developing new cultivars. Keywords DNA content Á Endocycle Á Flow cytometry Á Orchidaceae Á Petal Á Ploidy level Introduction The genus Phalaenopsis (Phal.) belongs to the Orchi- daceae (orchids, the largest family in the plant kingdom) and includes approximately 63 species (Christenson 2001). Phal. orchids are native to tropical and subtropical Asia, including South China, India, Indo-China, and Southeast Asia, and to Northern Australia (Christenson 2001; Tsai 2011). These plants have a monopodial growth form (no lateral shoots) in which the main stem grows throughout the year and usually one spray of flowers develops from each leaf axil. The elegant flowers of Phal. makes it a much desired plant. Recently, due to the development of novel hybrids, Phal. and Doritaenopsis (Dpts; a genus formed by hybridization between Doritis and Phalaenop- sis) have become an important ornamental orchids in the floriculture industry (Park and Paek 2006; Park et al. 2010). These genera look very similar, and many subspecies or cultivars have been produced by cross-breeding and selection without classification into either genus. Endopolyploidy is estimated to occur in more than 90 % of angiosperms (D’Amato 1989; Joube `s and Chevalier 2000) and is a highly regulated developmental process in both plants and animals (Lee et al. 2009). Endoreduplica- tion consists of the replication of nuclear DNA without Communicated by B. Zheng. & So-Young Park soypark7@cbnu.ac.kr 1 Division of Animal, Horticulture and Food Sciences, Department of Horticultural Science, Chungbuk National University, Cheongju 361-763, Republic of Korea 2 Yuni PlanTech Co., Umsung, Chungbuk 113-342, Republic of Korea 123 Acta Physiol Plant (2016) 38:190 DOI 10.1007/s11738-016-2222-7