Effect of medium sucrose on the photosynthetic capacity of coconut vitroplants formed from zygotic embryos
1999
Santamaria, J.M. | Talavera, C. | Lavergne, Danielle | Trabelsi, S. | Verdeil, Jean-Luc | Huet, C. | Rival, Alain | Hamon, Serge | Nato, Aimé
Previous studies in coconut has shown severe reductions in photosynthetic rates, chlorophyll concentrations, activity and the amount of Rubisco in vitroplants derived from zygotic embryos when compared to greenhouse acclimatised palms. The objective of the present study was to determine if sucrose in the medium can be responsible for a low photosynthetic ability in vitroplants derived from coconut zygotic embryos cultured in vitro. Zygotic embryos were cultured in vitro in a Y3 medium containing 45 g l-1 of sucrose or containing no sucrose. The following parameters were analysed: Photosynthetic pigment concentrations, totals soluble proteins content, carboxylases capacities. Immunological approaches using specific polyclonal antibodies raised against the two carboxylases were performed to estimate the quantity of the two proteins. Sucrose had no effect on the pigment concentration of young leaf parts. However, in older leaf parts, the concentration of both chlorophylls (a and b) and carotenoids were larger in tissues from plant in sucrose-rich medium than in those from plants grown without sucrose in the medium. In all tissues grown with sucrose in the medium, the concentration of total soluble proteins was reduced compared to those grown without sucrose. These reduction in TSP was particularly high in young leaf parts. In coconut vitroplants derived from zygotic embryos, sucrose in the medium promoted the activity of PEPC in tissues, while decreased the activity of Rubisco. Immunological techniques revealed that the decreased Rubisco activity is due to some kind of degradation of the carboxylase. Similarly, they show that the increased activity of PEPC is related to an increased concentration of the carboxylase in those tissues
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