RESUMO
Plant cell suspension cultures of Asclepias syriaca L. are morphologically homogeneous, that is, most cells in a suspension population are thin-walled, parenchyma-like cells. However, metabolic specialization of certain cells may occur in culture without morphological specialization. This study shows that a small number of suspension cells may synthesize secondary metabolites normally synthesized by a secretory cell, the non-articulated laticifer. The laticifer cell is an elongate, non-septate cell that is present in most intact plant tissues of Asclepias syriaca but which has not been observed to develop in vitro.
RESUMO
Starch biosynthesis and degradation was studied in seedlings and mature plants of Euphorbia heterophylla L. and E. myrsinites L. Mature embryos, which lack starch grains in the non-articulated laticifers, develop into seedlings that accumulate starch rapidly when grown either in the light or the dark. Starch accumulation in laticifers of dark-grown seedlings was ca. 47 and 43% of total starch in light-grown controls in E. heterophylla and E. myrsinites, respectively. In light-grown seedlings, starch was present in laticifers as well as parenchyma of stems and leaves, whereas in dark-grown seedlings starch synthesis was almost exclusively limited to laticifers. In 7-month-old plants placed into total darkness, the starch in chyma was depleted within 6 d, whereas starch in laticifers was not mobilized. The starch content of latex in plants during development of floral primordia, flowering, and subsequent fruit formation remained rather constant. The results indicate that laticifers in seedlings divert embryonal storage reserves to synthesize starch even under stress conditions (darkness) in contrast to other cells, and that starch accumulated in laticifers does not serve as a metabolic reserve. The laticifer in Euphorbia functions in the accumulation and storage of secondary metabolites yet retains the capacity to produce, but not utilize starch, a primary metabolite.
