Growth regulation, plastid differentiation and the development of a photosynthetic system in cultured carrot root explants as influenced by exogenous sucrose and various phytohormones

Abstract

Chromoplasts, which exist in the ceils of freshly isolated carrot root explants, seemed to be transformed in thylakoid containing plastids, and chlorophyll formation was initiated if the explants were cultured in a liquid medium containing inositol and IAA as a hormonal supplement. This process was intensified when kinetin was also added, but no dependence on a sucrose supply could be found.A sucrose supply of 2% in conjunction with the combination of all three hormones, however, was needed to achieve maximal thylakoid formation including stacking in individual chloroplasts and for the very extensive chloroplast multiplication in explants growing with high cell division activity. It should be noted that the number of plastids per cell is strongly increased by the sucrose supplement which leads also to starch accumulation. However, no transformation into chloroplasts occurred without the hormonal stimulus.

Ultrastructural and biochemical development of the photosynthetic apparatus during callus induction in carrot root explants

“…In the shoot apex of carrot seedlings grown in the dark such proplastids generally developed into etioplasts. However, when carrot root explants were cultured in the dark for 7-10 days no etioplasts could be detected and the only plastidal structures besides chromoplasts were amyloplasts with heavy starch accumulation as in stage 1 [7]. This may indicate that either in cells originally derived from root tissue proplastids do not develop into etioplasts or these proplastid-like structures are not developmental precursors of etioplasts and chloroplasts as they were in the shoot apex.…”

“…The tissue was explanted from the secondary phloem of the carrot tap root and grown for 28 days in a liquid medium [6,7]. For each set of experiments fresh explants were used.…”

“…At least during the initial period of cultivation the transformation of chromoplasts into chloroplasts may serve as the main route of plastidal development. During the log phase of cell division of the cultured explants the number of cells increased by a factor of 15-20 and the majority of these newly formed ceils contained 20 to 50 plastids each [7]. This requires a high rate of plastid propagation.…”

Germinação in vitro de embriões zigóticos de murmuru (Astrocaryum ulei)

“…Diante disso, a sacarose tem sido a fonte de carbono mais utilizada, estando presente em meios de cultura em concentrações que variam de 20 a 40 g.L -1 (FERREIRA et al, 2002). Portanto, variações na concentração deste carboidrato no meio de cultivo afetam as condições osmóticas e o metabolismo da planta in vitro, influenciando no crescimento e no metabolismo das culturas (KUMAR et al, 1984;OZAIAS-AKINS & VASIL, 1982).…”

Efeito da sacarose e do benomyl na multiplicação in vitro da macieira

“…A sacarose é o carboidrato mais utilizado em culturas de tecidos, e sua concentração nos meios de multiplicação varia de 2 a 3% (Ozaias- Akins & Vasil, 1982). Variações na concentração de sacarose no meio de cultura afetam as condições osmóticas e o metabolismo da planta in vitro, influenciando no crescimento e na diferenciação das culturas (Barg & Umiel, 1977;Ozaias-Akins & Vasil, 1982;Kumar et al, 1984). O benomyl é um fungicida sistêmico usado em culturas in vitro, principalmente para evitar a contaminação fúngica do meio e dos tecidos vegetais.…”