Embryogenic tissues of white spruce [Picea glauca (Moench) Voss] remain in an early developmental stage while cultured on 2,4-dichlorophenoxyacetic acid and N6-benzyladenine, but develop to cotyledonary embryos when these phytohormones are replaced by abscisic acid. Twenty-eight cDNAs were isolated from cotyledonary embryos by differential screening against immature embryo and non-embryonic tissues. Temporal expression patterns of these cDNAs during ABA-stimulated somatic embryo development were observed. This showed that clones could be allocated to various groups, including embryo-abundant, embryo-maturation-induced, and those whose expression was modulated during embryo development, germination or in non-embryogenic tissues. Expression corresponding to these cDNA clones showed that there were various responses to exogenous ABA or polyethylene glycol during a period of 48 h. Analyses of DNA and predicted amino acid sequence revealed that 12 of 28 cDNA clones had no known homologues, while others were predicted to encode different late-embryogenesis-abundant proteins, early methionine-labelled proteins, storage proteins, heat-shock proteins, glycine-rich cell wall protein, metallothionein-like protein and some other metabolic enzymes.
Cotyledons of various ages from seedlings of eight watermelon (Citrullus vulgaris) cultivars were cultured on MS medium supplemented with different combinations of phytohormones. High frequency shoot regeneration (60.0-92.0%) was induced from 5-day-old cotyledons of cultivars cultured on MS medium containing 5.0 mg/l 6-benzylaminopurine (BA) and 0.5 mg/l indole-3-acetic acid (IAA). Multiple shoot buds elongated on MS medium containing 0.2 mg/l kinetin (KT) and 5-10 shoots per expiant could be recovered depending on the cultivars. Elongated shoots rooted on MS medium with 0.1 mg/l α-naphthalene acetic acid (NAA). Zeatin riboside (ZT) had a similar efficiency as BA in shoot induction, and it was significantly more functional than 2-isopentenyladenine (2iP) or kinetin (KT). Cotyledons from 5-day-old seedlings were the most responsive to shoot induction.
Two cDNAs isolated from white spruce [Picea glauca (Moench) Voss] somatic embryos, are predicted to encode a basic class IV chitinase and a beta-1,3-glucanase, respectively corresponding to genes PgChi-1 and PgGlu-1. Each represents a multigene family in spruce. Transcripts homologous to PgChi-1 or PgGlu-1 genes were highly abundant in embryogenic tissues and gradually decreased after tissues were placed on abscisic acid-containing maturation medium, with lowest abundance in globular embryos. Transcripts related to PgGlu-1 became highly abundant again in early cotyledonary embryos but decreased thereafter, whereas transcripts related to PgChi-1 were also highly abundant in late cotyledonary embryos and plantlets in vitro; transcripts were either low (PgChi-1) or were not detectable (PgGlu-1) in needles. Wounding, drying and flooding stresses enhanced PgChi-1- and PgGlu-1-related gene expression. Fungal cell wall suspension enhanced PgGlu-1-related transcript accumulation, but reduced PgChi-1-related transcript abundance within 24 h. PgChi-1 and PgGlu-1 and their homologues may have roles in plant defense, and possibly developmental roles during spruce somatic embryo maturation.
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