Morphology and anatomy of mature embryos and seedlings in parasitic angiospermCuscuta japonica

Abstract

Morphological and anatomical features of mature embryos and seedlings were observed at different growth stages in the parasitic angiosperm Cuscutajaponica Choisy. The spirally coiled embryos from scarified seeds had no cotyledons but possessed blunt radicles. Seeds germinated at 30~ in the dark. Although most embryo cells incubated for 16 h did not have starch grains, the shoot cells of three-day-old seedlings possessed numerous starch grains. After these seedlings were transferred to a lightened growth chamber, all the shoot apical regions of seedlings grown for 6, 8, and 10 days became greenish and hooked. Most of the shoot cells, including the green apical parts, contained abundant starch grains. The hooks opened only when one seedling made contact with another seedling, This suggested that the green and hooked shoot apical regions played an important role in searching for and twining about their host plants. In some two-day-old seedlings, the massive roots were circular or semi-circular. This enabled the shoot axes to stand erect on some substratum. It would assist the shoots in making contact with the host plant. In eight-day-old seedlings, the green apical regions also were hooked and the roots were considerably degraded.Keywords: Anatomy, Cuscuta japonica, Embryo, Morphology, Parasitic angiosperm, SeedlingThe seedlings of Cuscuta have chlorophyll that enables photosynthesize (Zimmermann, 1962;Pattee et al., 1965). Although all the Cuscuta species still contain chlorophyll a and b while exploiting their host plants (Macleod, 1963;Ismail and Obeid, 1976), the rate of photosynthesis is decreased (Pattee et al., 1965). The excised stem tips of C. campestris, grown in vitro, produce a considerable amount of chlorophyll. This probably plays an important role in maintaining the growth of the culture (Loo, 1946). Fujita (1964) has characterized the mature embryo of C. japonica as a spirally coiled, yellow cylindrical structure, with a tapering apex, no cotyledon, and having a blunt radicle without a root cap. Truscott (1966) has suggested that in embryo culture of C.gronovii, the loss of both cotyledons and roots was a single embryonic event in the evolution of Cuscuta from its autotrophic ancestors. The morphology and anatomy of early seedlings in C. pedicellata has been studied by Lyshede (1985), who has also observed the fine structures of the tuberous radicular end (Lyshede, 1986) and the one-week-old seedlings in the same species (Lyshede, 1989). However, the function of organs during their autotrophic growth *Corresponding author; fax +82-62-230-7363 e-mail leekb@mail.chosun.ac.kr period is not yet clearly understood. The present study attempts to describe some morphological and anatomical features of C. japonica embryos and seedlings at various developmental stages, and to evaluate these features in view of their parasitic roles. MATERIALS AND METHODS Seed GerminationWe scarified mature, dormant seeds of C. japonicaChoisy with concentrated sulfuric acid for 25, 35, or 45 min, then rinsed them in tap water a...

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“…For example, in C. europaea it lacks both root cap and root apical meristem ( Fig. 1B and C) as observed by other authors (Lyshede 1986;Lee et al 2000;Behdarvandi et al 2015). Several days after germination this root-like organ degrades through a senescence-like process from apex towards the stem base ( Fig.…”

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“…Although no starch-containing plastids exist in C. japonica embryonic cells (Lee, 2006), anatomical study has revealed that numerous starch grains are present in the subapical ground meristem cells of 3-d-old dark-grown seedlings (Lee et al, 2000). This feature was ultrastructurally confirmed here ( Fig.…”

“…4 in Lee et al, 2000), it may be assumed that those stored starch grains are digested and supplied to the embryo during the germination and early-growth stages. Second, starch grains in the subapical cells of the seedling shoot may result from certain biochemical pathway(s), e.g., gluconeogenesis, by which sugars are converted from lipid and protein bodies stored in the embryo cells (Li and Ross, 1990;Eastmond et al, 2000;Rylott et al, 2003;Cornah et al, 2004).…”

“…Most developed chloroplasts have well-organized granal thylakoids in C. pentagona seedling tips grown for up to 10 d during their pre-parasitic stage (Sherman et al, 1999). Seedling tips in Cuscuta japonica also have been examined at various growth stages (Lee et al, 2000). I-or example, the shoot subapical cells of 3-d-old '~:Corresponding author; fax +82-62-230-7363 e-mail leekb@chosun.ac.kr dark-grown seedlings and 6-d-old seedlings (grown under sunlight for an additional 3 d after that dark period) contain abundant starch-containing amyloplasts.…”

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“…It was then scraped with a blade until the epidermal layer was reached (Ogundpie and Olatunji, 1991;Lee et al, 2000). The tissue was then washed in clean water and temporarily mounted in glycerin.…”