Articles
CARBON ASSIMILATION, ACTIVITIES OF CARBOXYLATING ENZYMES AND CHANGES IN TRANSCRIPT LEVEL OF GENES ENCODING ENZYMES OF THE CALVIN CYCLE AND CARBON PARTITIONING OF BANANA PLANTLETS DURING TRANSITION FROM HETEROTROPHIC TO AUTOTROPHIC EXISTENCE
As a consequence, the rate of photosynthetic activity is limited, although all the components involved in carbon assimilation are presumably present.
To support this assumption we followed the rates of photosynthetic activities, the activity of carboxylating enzymes ribulose, 1,5-biphosphate carboxylase (RuBISCO) and phosphoenolpyruvate carboxylase (PEP-C) and the expression of genes encoding several enzymes of the Calvin cycle as well as sucrose biosynthetic pathway during in vitro culture and at the first stages of hardening of banana plantlets.
A dramatic increase in the rate of photosynthesis occurred ten days after the transfer to the ex vitro photoautotrophic conditions.
Leaves which developed during the in vitro stage doubled their rates of photosynthesis, while new leaves which developed during the ex vitro period showed an increase of approximately ten folds.
Concomitant with the sharp increase in net photosynthesis during the ex vitro stage, a parallel increase in the activity of RuBISCO and a mild increase in the activity of PEP-C have been observed.
To examine the effect of transition to photoautotrophic conditions on the expression of genes involved in photosynthesis and carbon partitioning we have isolated cDNAs encoding the small subunit of RuBISCO, the cytosolic fructose 1,6-biphosphatase (FBPase) from a banana leaf cDNA library.
Northern blot analysis revealed a very significant increase in the level of FBPase and RuBISCO small subunit transcripts upon transition from photoheterotropic to photo-autotrophic conditions.