|Pigments in Plants
1. The anthocyanins are common plant pigments. They are water-soluble glycosides with some or all of the sugar groups removed. The colour comes from a positive charge distributed over the chemical ring system. The colours of the charged anthocyanin pigments are dependent on the pH of the intracellular medium containing these pigments.
. Many leaves frequently develop red coloration during development, at maturity, and during senescence. Most plants produce anthocyanins (usually cyanidin glycosides) as the basis of this colour, but members of the Caryophyllales produce nitrogenous pigments, betacyanins.
3. The betacyanin pigment of beet roots is normally sequestered in the vacuole and, by means of the properties of the tonoplast and cell membrane, does not leak into the cytosol or the extra-cellular sap of the beet root. Of course if the beet root is cut cells are sliced open and the pigment spills out, but if the membrane is altered (phospholipid bilayer + proteins) more subtly leakage (diffusion) of betacyanin is induced.
Betalains: What are betalains?
Betalains are alkaloid pigments that are found in some families of plants belonging to the order Caryophyllales, but in no other plants.
Betalains are not found in plants containing anthocyanin pigments. Structurally they are unrelated
They have also been found in some fungi
They can be divided into betacyanins and betaxanthins based upon their molecular structure.
betacyanins generally appear red to red violet in colour
betaxanthins generally appear yellow in colour
They cause colour in both flowers, fruits and sometimes vegetative organs
They are found in the vacuole
They are aqueous in solubility
Betacyanins absorb in the 535-550nm range
Betaxanthins absorb in the 475-480nm range
Beetroot contains 2 Betacyanins Betanin and a derivative
Little is known about the role of betalains but it is thought they may protect against pathogens
The basic structure of betacyanins