Tissue localization of betacyanins in cactus stems

Resumen

Betalains are soluble pigments found only in the suborder Chenopodiniae, while in all other Angiospermae
they are replaced by anthocyanins. The convergent evolution of the presence of anthocyanins and betalains in
vegetative tissues supports the hypothesis of a similar function, based on the absorption properties of these pigments.
The screening effect of anthocyanins results in the reduction of the amount of photoinhibition. Betalains, being the
anthocyanin counterpart in most families of Caryophyllales, were also suggested to have a screening role. This study
is aimed at identifying in which Cactaceae stem tissues betacyanins, reddish to violet betalain pigments, accumulate.
Stem accumulation of betacyanins was observed in cacti both in their natural habitat and in cultivation. The localization
of betacyanins was assessed by light microscope studies on tubercle transverse sections. During 2 field trips in distinct
years to the Mexican plateau in March, many cactus species, belonging to different genera, were observed displaying
a reddish stem. Light microscope studies on cultivated plants showed that betacyanins accumulate in the hypodermis
and in the outer layers of the chlorenchyma, where they may act as a screen, thus protecting the photosystems present
in the underlying chlorenchyma, and have a possible antioxidant function in the cortex.