Physiological and morphogenetic studies of fern gametophyte by aseptic culture. 3. Growth and differentiation of single cells isolated from callus tissues of Pteris vittata

Culture types and period impact gametophyte morphogenesis and sporophyte formation of eastern bracken

BACKGROUND

Liquid suspension culture efficiently proliferates plant cells and can be applied to ferns because it rapidly increases the fresh weight of gametophytes. This study assessed gametophyte proliferation and sporophyte production of Pteridium aquilinum var. latiusculum using a suspension culture method.

RESULTS

The growth curve linear phase of gametophyte cells was confirmed between 9 and 18 days of culture, and the subculture cycle was determined to be 2 weeks. A double-strength MS medium (fresh weight, 18.0 g) containing 2% sucrose and NH₄⁺:NO₃^- (120 mM, 40:80) was found to be the optimal liquid medium. Gametophytes obtained after suspension culture for 18 days did not normally form sporophytes in an ex vitro soil environment. However, this issue was resolved after changing the culture type or extending the culture period to 6 weeks. A short suspension culture period increased the fresh weight of fragmented and homogenized gametophytes but yielded numerous relatively immature gametophytes (globular forms of branching gametophytes, BG). Furthermore, differences in gametophyte morphogenesis and development were indicated by changes in endogenous phytohormone content. BG with immature development exhibited high accumulation of zeatin, jasmonic acid, and salicylic acid, and relatively low levels of abscisic acid and indole-3-acetic acid. The immature development of gametophytes directly affected sporophyte formation.

CONCLUSIONS

This study maximized the advantages of liquid suspension culture using eastern bracken gametophytes and provides data to resolve any associated issues, thus facilitating efficient bracken production.

[On regeneration capacity of isolated single cells and small groups of cells of Riella helicophylla]

1. Isolated single cells of the basal part of the gemma of Riella helicophylla regenerate to whole plants. Late developmental stages of rhizoid initials divide earlier after isolation than young rhizoid initials and "normal cells" of the basal part. 2. In isolated groups of two cells composed of one rhizoid initial and one "normal cell" only the rhizoid initial divides, and it divides much sooner than it does as a single cell. 3. If in isolated groups of two cells from the basal part of the gemma the divided cell is killed immediately after division, the second cell of the group also divides, just as soon, in fact, as it would have if it had been isolated as a single cell. If the first divided cell is killed 7 days after division, the division of the second cell of the group is delayed by 6 days. 4. After isolation of single cells and of small groups of cells from old as well as from young tissue of the wing, cell division occurs earliest in the largest cell groupe and latest in single cells. The regenerates develop the more quickly the larger the isolated cell group from which they derive. 5. Cells in fragments isolated from young tissue divide sooner after isolation than cells in fragments from old tissue. However, single cells isolated from old tissue divide earlier than single cells from young tissue. 6. Light is a prerequisite for regeneration of single cells and of small groups of cells from the marginal region of the wing. Only in relatively large tissue fragments do some cells also divide in the dark. 7. The existence and nature of correlations between the cells of a regenerating tissue fragment are discussed.