The mode of action of thidiazuron: auxins, indoleamines, and ion channels in the regeneration of Echinacea purpurea L.

The biochemical mechanisms underlying thidiazuron (TDZ)-induced regeneration in plant cells have not been clearly elucidated. Exposure of leaf explants of Echinacea purpurea to a medium containing TDZ results in undifferentiated cell proliferation and differentiated growth as mixed shoot organogenesis and somatic embryogenesis. The current studies were undertaken to determine the potential roles of auxin, indoleamines, and ion signaling in the dedifferentiation and redifferentiation of plant cells. E. purpurea leaf explants were found to contain auxin and the related indoleamine neurotransmitters, melatonin, and serotonin. The levels of these endogenous indoleamines were increased by exposure to TDZ associated with the induction of regeneration. The auxin-transport inhibitor 2,3,5-triiodobenzoic acid and auxin action inhibitor, p-chlorophenoxyisobutyric acid decreased the TDZ-induced regeneration but increased concentrations of endogenous serotonin and melatonin. As well, inhibitors of calcium and sodium transport significantly reduced TDZ-induced morphogenesis while increasing endogenous indoleamine content. These data indicate that TDZ-induced regeneration is the manifestation of a metabolic cascade that includes an initial signaling event, accumulation, and transport of endogenous plant signals such as auxin and melatonin, a system of secondary messengers, and a concurrent stress response.

Thidiazuron-induced regeneration of Echinacea purpurea L.: micropropagation in solid and liquid culture systems.

The goals of this study were to investigate thidiazuron (TDZ)-induced morphogenesis of Echinacea purpurea L. and to assess the possibility of developing a liquid-based protocol for rapid micropropagation. Callus development and root organogenesis were observed on leaf explants cultured on media containing 2,4-dicholorophenoxyacetic acid or dicamba, but no plantlets were regenerated. Addition of TDZ to the culture medium as the sole growth regulator resulted in the production of regenerable callus cultures. The highest rate of regeneration was observed for explants cultured on medium with TDZ at 2.5 microM or higher. Tissue derived from 1.0 microM TDZ treatments was used to initiate liquid cultures. All liquid treatments produced a similar number of regenerants but significantly more healthy plants were obtained from cultures grown in the presence of 0.1 and 1.0 microM TDZ. This TDZ-based micropropagation system is the first liquid, large-scale propagation protocol developed for the mass production of E. purpurea plants.

A histochemical and ultrastructural study of lipofuscin accumulation in thyroid follicular cells of aging domestic cats.

Enzyme activity and fine structure of thyroid follicular cells were investigated in domestic cats at ages: 2 and 8 months, and 1, 3, 5 and 8 years. The following major changes in the follicular cells with advancing age were observed: with histochemistry--an increase in acid phosphatase and beta-glucuronidase activities confined to numerous granules (vesicles); with electron microscopy -- an increase in colloid vesicles, the appearance and increase in size and number of lipofuscin vesicles, and the increase in number of follicular cells containing numerous colloid or lipofuscin vesicles. It is our opinion that the numerous enzymatically active granules of the older groups, observed with histochemistry, are synonymous with the lipofuscin vesicles and many of the colloid vesicles observed with electron microscopy. The cellular changes involving increased enzymatic activity and lipofuscin accumulation with advancing age would correlate with decreased thyroid function reported in the literature. These observations, therefore, would suggest increased autophagic activity involving organelle or unneeded product degradation.