Effects of light and ethylene on endogenous hormones and development of Catasetum fimbriatum (Orchidaceae)

Abstract

This study attempted to clarify the effects of dark, light and ethylene on plant growth and endogenous levels of indole-3-acetic acid (IAA), cytokinins and abscisic acid in Catasetum fimbriatum. Dark-incubation fully inhibited root and pseudobulb formation as well as leaf growth, but favored shoot elongation. The results of continuous and active growth in dark-incubated shoots (stolons) were induced by strong apical meristem sink activity and by the significantly increased levels of cytokinins in shoots. In fact, shoot length, cytokinin and IAA levels in dark-incubated shoots were about twice as great as for those grown under light conditions. Moreover, the total cytokinin level in shoots of C. fimbriatum under light conditions without ethylene was significantly higher than that found in roots. High levels of cytokinins in dark-grown stolons may be closely related to the absence of roots in C. fimbriatum. Under light conditions, the increased IAA level in shoots is mediated by ethylene. However, ethylene caused a significant increase of cytokinins in roots of light-treated plants, which may be involved in the retardation of root growth. Since the difference of cytokinins in shoots between ethylene-treated and non-treated plants under light conditions is small, it is concluded that the marked inhibition of leaf growth in ethylene-treated plants can be attributed to ethylene. Zeatin and zeatin riboside are the major cytokinins in C. fimbriatum regardless of the light conditions, ethylene treatment or organ types. Key words: auxin, cytokinins, etiolation, plant growth, plant hormones Efeitos da luz e etileno sobre hormônios endógenos e o desenvolvimento de plantas de Catasetum fimbriatum (Orchidaceae): Neste estudo, procurou-se esclarecer os efeitos do escuro, da luz e do etileno no crescimento vegetal e nos teores endógenos de ácido indolil acético (AIA), citocininas e ácido abscísico em Catasetum fimbriatum. A incubação no escuro inibiu completamente a formação de pseudobulbos e raízes, e reduziu drasticamente o crescimento foliar, porém estimulou substancialmente o alongamento caulinar. Os resultados do crescimento ativo e contínuo dos caules incubados no escuro (estolões) dessa orquídea foram induzidos por um aumento intenso da atividade de dreno do meristema apical e pelo aumento significativo nas quantidades de citocininas nos caules. De fato, o comprimento caulinar e os teores de citocininas e de AIA foram mais de duas vezes maior nos caules incubados no escuro do que naqueles crescidos à luz. Além disso, é importante notar que o teor de citocininas totais nos caules de C. fimbriatum crescidos sem etileno, no claro, foi significativamente maior do que o encontrado nas raízes. Altas concentrações de citocininas nos estolões crescidos no escuro podem estar intimamente relacionadas à ausência de raízes em C. fimbriatum. À luz, o aumento dos teores de AIA nos caules foi mediado pelo etileno. Entretanto, o etileno promoveu um aumento significativo de citocininas nas raízes das plantas à luz, que poderiam estar en...

The content of endogenous hormones and sugars in the process of early somatic embryogenesis in the tree fern Cyathea delgadii Sternb.

“…In view of this, the reduction in ABA concentration in response to darkness seems to be related to changes in the structure and/or function of chloroplasts. Researchers also agree that the exposure of plants to darkness increases the concentration of endogenous IAA, even twice (Liu et al 1996;Volmaro et al 1998;Suzuki and Kerbauy 2006), and it is in agreement with the results obtained for C. delgadii. The negative effect of the light on IAA concentration is presumably because light induces IAA-peroxidase and IAA-oxidase activity, the key enzymes involved in the breaking down of IAA (Liu et al 1996).…”

“…Dark treatment also greatly stimulates cytokinin accumulation. In shoots of dark-grown Catasetum fimbriatum, the total cytokinin concentration was almost threefold greater than in those growing under photoperiodic conditions (Suzuki and Kerbauy 2006). In stipe explants of C. delgadii, this difference reached more than 9 in favour of the dark.…”

“…Phytohormone concentrations and their signalling pathways can also be regulated by changes in the photoperiodic conditions (Symons and Reid 2003;Pacholczak et al 2005). As a result of the light deficit, plants show a dramatic elongation of the stem (Suzuki and Kerbauy 2006). The plant response is often linked to reduced leaf development, enhanced apical dominance, and a re-allocation of resources from storagefavouring shoot elongation to reproductive growth (Suzuki and Kerbauy 2006;Mikuła et al 2015b).…”

“…As a result of the light deficit, plants show a dramatic elongation of the stem (Suzuki and Kerbauy 2006). The plant response is often linked to reduced leaf development, enhanced apical dominance, and a re-allocation of resources from storagefavouring shoot elongation to reproductive growth (Suzuki and Kerbauy 2006;Mikuła et al 2015b). Dark treatment of donor plantlets was reported to favour SE in Helianthus annuus L. (Fiore et al 1997), Dendranthema grandiflora Tzvelev.…”

Ethylene Modulates the Developmental Plasticity and the Growth Balance Between Shoot and Root Systems in the In Vitro Grown Epiphytic Orchid Catasetum fimbriatum

“…In addition, it was shown that root tips isolated from Catasetum species are able to directly convert into buds, which in turn, give rise to new plants (Kerbauy 1984;Kraus and Monteiro 1989). Interestingly, previous evidence has also indicated that these events of morphogenesis described for Catasetum are affected by ethylene to some extent (Kerbauy and Colli 1997;Peres and others 1999;Suzuki and Kerbauy 2006). The above mentioned results suggest that modulation of ethylene concentration and/or signaling could be important for regulating some architectural traits in both shoot and root systems of Catasetum species; however, the influence of this hormone on the developmental plasticity of these plants is still unclear.…”