Microtubule pattern and the occurrence of pre-prophase bands in embryogenic cultures of black spruce (Pieca mariana Mill.) and non-embryogenic cultures of jack pine (Pinus banksiana Lamb.)

Abstract

The organization of microtubules during interphase and prophase in embryogenic cultures of black spruce (Picea mariana) was investigated by indirect immunofluorescence. Somatic embryos of black spruce possessed an extensively branched and interconnecting network of fine interphase cortical microtubules. The development of pre-prophase bands (PPBs) in embryogenic black spruce cultures was compared with that in non-embryogenic cell cultures of jack pine (Pinus banksiana). PPBs in both species were initially arranged as a very broad array of microtubules, later (early to mid-prophase) becoming narrower and more intensely fluorescent. The occurrence of pre-prophase bands in relation to the number of phragmoplasts (i.e. PPB index) of black spruce somatic embryos was significantly higher (p<0.01) than that found for jack pine cells.

Auxin deprivation induces a developmental switch in maize somatic embryogenesis involving redistribution of microtubules and actin filaments from endoplasmic to cortical cytoskeletal arrays

“…Note that cortical microtubules are arranged in the form of fine networks within pre-embryogenic cells (ec) in D, in contrast to dense arrays of cortical microtubules in non-embryogenic callus cells (cc and arrows) in D. After auxin deprivation for 5 days, embryogenic cells of transition units assemble dense cortical microtubules (arrows in E and F), while endoplasmic perinuclear microtubules are depleted or randomized both in meristematic and suspensor-like cells (asterisks in E and F). Bar in F is valid for all images and represents 12 mm for B and D; 15 mm for A, C and F; and 25 mm for E embryogenic cultures of black spruce (Tautorus et al 1992). Cortical microtubules were also observed in regions adjacent to the new cross-walls in cellular clumps of alfalfa (Meijer and Simmonds 1988).…”

Microtubule and actin filament organization during acentral divisions in potato suspension culture cells

“…Preprophase bands of microtubules also occurred and were similar to preprophase bands found in suspension cells of other species in that they were less organized and less clearly defined than in cells in whole plants (Simmonds et al 1983, Simmonds 1986, Gorst et al 1986, Tautorus et al 1992. A value for the PPB index of 0.50, indicating that preprophase bands were not common compared to phragmoplasts, is typical of nonembryogenic suspension culture cells (Gorst et al 1986, Tautorus et al 1992). On occasions, F-actin has also been observed in preprophase bands in suspension culture cells such as the tobacco BY-2 line (Kakimoto and Shibaoka 1987a, b).…”

“…In the preprophase cell, therefore, the "chamber" is the phragmosome. The phragmosome is large in nonembryogenic suspension culture cells that lack well formed preprophase band and have a low PPB index (Gorst et al 1986, Tautorus et al 1992; this study).…”

“…Early reports of microtubule localizations in suspension cultures noted an apparent absence of microtubule preprophase bands, with this being attributed to the general lack of organized growth within these cells (Fowke and Gamborg 1980). While subsequent observations have shown that microtubule preprophase bands are present in suspension culture cells of some species (Simmonds et al 1983, Simmonds 1986, Gorst et al 1986, Traas et al 1987, Sonobe and Shibaoka 1989, Tautorus et al 1992, these often appear less organized in suspension culture cells than in cells in whole plants (Simmonds et al 1983, Gorst et al 1986). Furthermore, the PPB index, defined as the ratio of cells with preprophase bands of microtubules to cells with phragmoplasts, is significantly lower in nonembryogenic suspension cultures compared to root tip cells or embryogenic suspension cultures that are capable of organized growth and cell differentiation (Gorst et al 1986, Tautorus et al 1992.…”

“…While subsequent observations have shown that microtubule preprophase bands are present in suspension culture cells of some species (Simmonds et al 1983, Simmonds 1986, Gorst et al 1986, Traas et al 1987, Sonobe and Shibaoka 1989, Tautorus et al 1992, these often appear less organized in suspension culture cells than in cells in whole plants (Simmonds et al 1983, Gorst et al 1986). Furthermore, the PPB index, defined as the ratio of cells with preprophase bands of microtubules to cells with phragmoplasts, is significantly lower in nonembryogenic suspension cultures compared to root tip cells or embryogenic suspension cultures that are capable of organized growth and cell differentiation (Gorst et al 1986, Tautorus et al 1992. Given the irregular cell patterning in suspension cells, the early stages of division, including the centring of the nucleus through the formation of the phragmosome and preprophase band, may indeed indicate crucial steps where suspension culture cells divert from the organized growth of cells in plants.…”