Download DEVELOPMENT OF CAROTENOID PIGMENTS

BRIEF PAPERS
DEVELOPMENT OF CAROTENOID PIGMENTS WITHOUT
TIIE AID OF LIGHT
Xanthophyll and carotene are usually associated in plants and are present before the formation of chlorophyll. Their formulae suggest genetic
relationship. Xanthophyll can be reduced to carotene and the transformation is reversible. Together they may represent a respiratory mechanism
similar to the haemoglobin-oxyhaemoglobin complex in animal forms.
No chlorophyll develops in seedlings not exposed to light as was first
recorded by JOANNES RAJUS in 1693. BONNET called such plants " etiollees"
and the condition is now known as etiolation.
ARNAUD in 1889 first suggested that etiolated leaves contain carotene.
The carotenoids are in leucoplastids which are generally assumed to be identical with the chloroplastids that contain the chlorophyll of normal plants.
KRAUS first studied the alcoholic extract of etiolated leaves spectroscopically
and concluded that the yellow pigments and the chlorophyll of normal plants
are genetically related. PRINGSHEIM made similar studies in 1874 and concluded that a special pigment was present which he called "etiolin." This
substance seems to be identical with protochlorophyll.
The results of experiments by the writer and by others before him, prove
that chlorophyll forms within less than 30 seconds after etiolated plants are
exposed to light. Protochlorophyll is probably the precursor.
According to observations of the writer the yellow color of etiolated sunflower seedlings is limited almost entirely to the cotyledons. The stems are
white except for a small zone directly below the cotyledons. Upon exposure to light, this zone increases downward, the yellow extending beyond
the green when chlorophyll forms. In time, however, the yellow and green
colors become confused. It appears that some material is translocated in the
stem which is converted into pigment in the plastid by the metabolic processes of the protoplasm.
The writer's experiments further show that the carotenoids are formed
in sunflower seedlings without the aid of light. Some seeds contain carotenoid pigment, but attempts to extract them from sunflower seeds failed.
Even if it is assumed that an initial amount was present, careful studies by
the writer proved that the pigment forms in the absence of light. The
greatest rate of development was between the fourth and seventh days of
sprouting. The rate of increment in that time was much greater for carotene than for xanthophyll, and the decline from the seventh to the fourteenth day was much greater for the carotene. The amount of carotene
developed, in comparison with the amount of xanthophyll, was always small.
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PLANT PHYSIOLOGY
The xanthophyll: carotene ratio increased during the period from the
fourth to the seventh day, from 9 to 12, and during the period from the
seventh day to the fourteenth day, from 13 to 20.
It may be concluded that the origin and the function of carotene and
xanthophyll are probably related. The material stored in the seed probably
is the source of the necessary material and energy required for the formation of the carotenoid pigments.
Carotene appears to have a stimulating effect on the production of roots,
which suggests that carotene may be a precursor of auxin.-WILLIAM A.
BECK, Institutum Divi Thomae, Graduate School of Scientific Research,
Cincinnati, Ohio.
Downloaded from on June 17, 2017 - Published by www.plantphysiol.org
Copyright © 1937 American Society of Plant Biologists. All rights reserved.