A. Sangaré

Photosynthetic ability of in vitro grown coconut (Cocos nucifera L.) plantlets derived from zygotic embryos

Photosynthetic parameters have been investigated using complementary approaches throughout the in vitro development of coconut zygotic embryos into plantlets. Patterns of chlorophyll fluorescence were comparable in in vitro grown coconut plantlets (OFAx = 0.72 and O, = 0.45) and in autotrophic adult palms (OpAX = 0.76 and Bp=0.5O). Chlorophyll content was lower in in vitro-cultured plantlets (0.92 mg/g fresh weight (FW)) than in autotrophic plants (2.43 mg/g FW). The photosynthetic rate (1.14 pmol CO,/m’ per s) of autotrophic palms was half that of in vitro grown plantlets, while transpiration rates were similar in both. Changes in the PEPC:RubisCO ratio during the development of in vitro grown plantlets (from 89.17 to 0.04 pmol COJh per mg total soluble protein (TSP)) reflected a transition from a heterotrophic towards a RubisCO-mediated mode of CO, fixation. The RubisCO enzyme capacity (2.83 pmol CO,/h per mg TSP) and content (172.8 mg/g TSP) measured in in vitro-cultured plantlets were lower than those measured in autotrophic palms (6.60 pmol CO,/h per mg TSP and 217.6 mg/g TSP respectively). Transmission electronic microscopy (TEM) observations showed a complete ultrastructural organisation of chloroplasts in plantlets at the end of the in vitro culture process (6 weeks under light). All the studied parametersj Abbreoiatiotis: Chl a, Chlorophyll a; Chl b, Chlorophyll b; FW, Fresh weight; PAR, Photosynthesis active radiations; PEPC, Phosphoenolpyruvate carboxylase; PVP, Polyvinyl pyrrolidone; RH, Relative humidity; RubisCO, Ribulose 1,5-bisphosphate carboxylase oxygenase; To, Temperature; TCA cycle, Tricarboxylic acid or Krebs cycle; TEM, Transmission electronic microscopy; TSP, Total soluble proteins.

Recent progress on coconut micropropagation through a joined effort involving different countries

Coconut is one of the most important perennial crops for the economy of intertropical countries (Persley, 1992). Thanks to breeding, high-performance hybrids can be achieved. However, conventional selection methods have some constraints derived from the features of the reproduction of these perennial plants: great variability among progeny (consequence of the allogamy), very long selection cycle, low multiplication rate (coconut is only multiplied from seeds), and absence of natural vegetative propagation.