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Thomas E. Marler and Nirmala Dongol

an assemblage of loose sporophylls. The cycad megagametophyte is a large seed structure that is composed of haploid tissue ( Brenner et al., 2003 ; Norstog and Nichols, 1997 ). It serves a nutritive role for the cycad embryo in a manner that is

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Jules Janick, Christiane Cabral Velho, and Anna Whipkey

Mature seed weight of loblolly pine (Pinus taeda L.) averaged 25 mg (dry weight), of which 55.0% was seedcoat, 38.5% megagametophyte, and 6.4% embryo. Fatty acid (FA) content (dry-weight basis) was 17.5% for whole seed, 0.4% for seedcoat, 36.2% for megagametophyte, and 51.2% for embryo. Distribution of FAs (16:0; 18:0; 18:1; 18:2; 18:3 Δ5,9,12; 18:3 Δ9,12,15; 20:0; and 20:3) differed in seedcoat, megagametophyte, and embryo, but 18:2 was the predominant FA in all tissues. Seed development was analyzed for 110 days from 25 July, the year following pollination. Embryos could be macroscopically observed on or about day 30. Embryo dry weight, length, and FA accumulation increased until about day 50 and then remained constant. Embryo density decreased from day 30 to 50 and then stabilized at ≈1.0366 g·ml-1 or 10% sucrose equivalent. Excised zygotic embryos did not germinate in vitro until after day 51; germination increased linearly after this date, reaching 80% by day 72.

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Thomas E. Marler and Christopher A. Shaw

between cycad seed consumption on Guam and amyotrophic lateral sclerosis–parkinsonism dementia complex ( Borenstein et al., 2007 ; Whiting, 1963 ). Natural sterols and steryl glucosides extracted from cycad megagametophyte tissue ( Fig. 1 ) are among the

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Jonathan D. Mahoney, Thao M. Hau, Bryan A. Connolly, and Mark H. Brand

reproduce apomictically. Gametophytic apomixis occurs when a progenitor cell in the megasporangium forms a megagametophyte ( Grossniklaus et al., 2001 ; Richards, 2003 ). Gametophytic apomixis is further classified into two categories: diplospory and

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Audrey M. Sebolt and Amy F. Iezzoni

on the stigma; 4) pollen tube growth in the style; 5) sufficient ovule longevity; 6) fertilization of at least one of the two ovules present in the Prunus megagametophyte; and 7) at least initial zygote viability. In cherry, poor fruit set is likely

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Pablo Aleza, José Cuenca, José Juárez, José A. Pina, and Luis Navarro

diploid megagametophyte development in clementine ( Luro et al., 2004 ), whereas Chen et al. (2008) proposed first meiotic division restitution in sweet oranges. In Spain, the structure of mandarin cultivars poses several problems. Mandarins include

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José Cuenca, Andrés García-Lor, José Juárez, José A. Pina, Luis Navarro, and Pablo Aleza

; Cuenca et al., 2011 , 2015 ), where triploid hybrids arise usually from the union of an unreduced megagametophyte formed through a second-division restitution mechanism with a haploid pollen ( Cameron and Frost 1968 ; Cuenca et al., 2011 ; 2015; Esen

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Michele A. Stanton, Joseph C. Scheerens, Richard C. Funt, and John R. Clark

heat stress during the first 4 d after fertilization caused failure of fruit and seed development through a cessation of development occurring in the megagametophytes or carpels. In our study, detailed cytological examinations of pollen germinability at

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Thomas E. Marler

10570 Marler, T.E. Dongol, N. 2016 Seed ontogeny and nonstructural carbohydrates of Cycas micronesica megagametophyte tissue HortScience 51 1144 1147 Marler, T.E. Lawrence, J.H. 2012 Demography of Cycas micronesica on Guam following introduction of

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Atsu Yamasaki, Akira Kitajima, Norihiro Ohara, Mitsutoshi Tanaka, and Kojiro Hasegawa

. Sci. 71 394 400 (In Japanese with English summary). Herr J.M. Jr 1974 A clearing squash technique for the study of ovule and megagametophyte development in angiosperms 230 235 Raford A.E. Dickison W