Mature seeds of Ilex species usually contain immature embryos and are extremely difficult to germinate. Ilex latifolia and I. rotunda, two species that are grown as ornamentals, also produce seeds that are difficult to germinate. In the present study, we investigated some factors affecting seed germination in those species. Although seeds of I. latifolia and I. rotunda could imbibe water, they did not germinate. When embryos were cultured in vitro, germination was observed in I. latifolia but not in I. rotunda. Interestingly, a transient decrease in germination frequency occurred in I. latifolia embryos isolated from seeds collected in September or October. Among five types of I. latifolia seeds that differed in the presence of the endocarp, testa, and endosperm, germinability of isolated embryos was highest. Good germination was also observed in quarter-seeds with or without endocarp followed by half-seeds. Treatment of seeds with sodium hydroxide (NaOH) had no effect on seed germination in I. latifolia. Cold stratification at 5 °C increased the germination frequency of I. latifolia embryos. In conclusion, the data suggested a mechanical barrier by the endocarp and inhibitors contained in the endosperm, testa, and/or endocarp inhibited seed germination in I. latifolia. Although no seeds or embryos of I. rotunda germinated, cold stratification in combination with other treatments deserves further investigation. Chemical name: sodium hydroxide (NaOH).
Adventitious shoots can be regenerated from the cut surface of the primary shoot and lateral branches in decapitated plants in vivo. This inherent regenerative ability of plants is useful for mass propagation. In the present study, we conducted histological observations of shoot regeneration and applied auxin and cytokinin to decapitated seedlings in four tomato cultivars. The cultivars produced different numbers of adventitious shoots after decapitation; ‘Petit’ produced the largest number of adventitious shoots (78.5 ± 10.2) and ‘Momotaro’ produced the fewest (12.1 ± 3.3). Histological observation of ‘Petit’ revealed that adventitious shoots regenerated from calli formed at the cut surface of stems. Adventitious shoot formation was inhibited by the presence of lateral branches. Shoot regeneration was prevented by application of 1-naphthaleneacetic acid to ‘Petit’. Application of 6-benzyladenine promoted shoot regeneration in ‘Momotaro’. These results suggest auxin synthesized de novo from the lateral branches inhibited shoot regeneration after decapitation and endogenous cytokinin might stimulate shoot regeneration. Chemical names: 1-naphthaleneacetic acid (NAA); 6-benzyladenine (BA)