CHANGES IN PHOTOSYNTHETIC PARAMETERS DURING IN VITRO GROWTH AND SUBSEQUENT ACCLIMATIZATION OF COCONUT (COCOS NUCIFERA L.) ZYGOTIC EMBRYOS

In coconut, in vitro development and acclimatization of plantlets still constitute the major bottlenecks for the implementation of tissue culture protocols.
In the present paper, the photosynthetic status of in vitro grown plantlets resulting from zygotic embryo culture is investigated, combining various complementary approaches, both in vitro and in planta.

Patterns of chlorophyll fluorescence were similar in in vitro grown coconut plantlets (Ø_P^MAX=0.72 and Ø_P = 0.45) and in autotrophic adult palms (Ø_P^MAX=0.76 and Ø_P= 0.50), whereas the chlorophyll content was lower in in vitro-cultured plantlets (0.92 mg.g^-1 _FW) than in autotrophic plants (2.43 mg.g^-1_FW).

The photosynthetic rate (1.14 μmol CO₂ m^-2s^-1) was two times lower in in vitro grown plantlets, while transpiration rates were similar in both in vitro-cultured plantlets and in autotrophic palms.

Changes in the PEPC: RubisCO carboxylase ratio during the development of in vitro grown zygotic embryos (from 89.17 to 0.04 μmol CO₂ h^-1mg^-1 _TSP) reflected an early transition towards a RubisCO-mediated mode of CO₂ fixation.
The RubisCO content (172.8mg.g^-1) measured in in vitro-cultured plantlets was lower than in autotrophic palms (217.6 mg.g^-1).

During the acclimatisation phase, the in vitro grown coconut plantlets showed a faster decrease in their PEPC: RubisCO ratio than the seedlings, suggesting that an earlier transition from a heterotrophic to an autotrophic mode of carbon fixation takes place in the in vitro-derived material.
Just before acclimatization, the RubisCO activity in in vitro-derived plantlets was lower than that in seedlings of the same age.
After acclimatisation, RubisCO activities were comparable in both in vitro and in planta germinated material.

In vitro grown plantlets displayed several photosynthetic characteristics (Ø_P^MAX, Ø_P, PEPC: RubisCO ratio and transpiration rates) similar to those of acclimatized plants.
These results suggest an early establishment of a photosynthetic metabolism during the in vitro development of coconut plantlets.

International Symposium on Biotechnology of Tropical and Subtropical Species Part 2

K. Triques, A. Rival, T. Beulé, F. Morcillo, V. Hocher, J.-L. Verdeil, S. Hamon

Arecaceae, autotrophy, carboxylases, chl fluorescence, PEPC, RubisCO

https://doi.org/10.17660/ActaHortic.1998.461.30