Leaf colour patterns, vegetative and sexual reproduction of Episcia ...

Proof of Anthocyanins and Analysis of the Colouring Agents with the UV/VIS-Spectrometry
Anthocyanins are secondary metabolites and are part of the large phenolic family collectively
known as the flavonoids. The anthocyanin molecule consists of an anthocyanidin (the aglycone
chromophore), tied to one or more glycosides (Paech 1950). The maximum absorption of
anthocyanins lies between 500 to 550 nm (Harborne 1967).
Anthocyanins have the ability to change their colour in correspondence with changes of the
pH-value. The experiments described below were conducted to prove that anthocyanins are
responsible for the leaf colouration of Episcia lilacina as well as to check if there are anthocyanins
even in the bright green leaves.
Materials and Methods: To be sure that anthocyanins are responsible for the red
colouration, the pH-value has been increased from low to high. Leaves of the red morphs were
cut and anthocyanins were extracted with aqua. Hydrochloric acid (0,01mol/l) was added until
the pH-value reached the level of 2. Afterwards, Ammonium hydroxide (50 per cent) was added
until a pH-value of 9 was obtained. By comparison, the same experiment was performed with the
leaves of African violet (Saintpaulia ionantha).
To demonstrate a difference in the content of anthocyanins between the green and the redmorphs
of Episcia lilacina, the UV/VIS-spectrometry was used. 15 plants were taken from Costa
Rica to Austria to accomplish experiments, which were not possible in the laboratory of the Field
Station La Gamba. In Austria the plants were kept in a greenhouse of the Botanical Garden of
the University of Vienna. The following method was modified after Strigl et al (1995).
To receive the clearest possible results, the two most extreme leaf-morphs were chosen.
From the green leaves 2,15 g were weighed, from the red ones 1,14 g. The leaves were cut and
grinded in a mortar with about 10 ml of 70% methanol and sea sand. The solid parts were
separated through a filter. From the supernatant the methanol was distilled on the rotary
evaporator. The solution was shaken out twice with benzine to separate the covalent parts and
then with ethyl acetate to extract the flavonoids and other phenolic compounds. To eliminate the
ethyl acetate the rotary evaporator was used. One more time the solution was filtered (0,2µm).
The measurement of the extinction took place in the UV/VIS spectrometer with a wavelength of
522 nm. The absorption maximum of 522 nm was determined in a previous measurement.
Results: At low pH-values a change in colour to red in the solutions could be observed with
Episcia lilacina as well as with Saintpaulia ionantha. After addition of base, the colour of both
solutions changed to brownish.
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