The role played by the R locus in anthocyanin biosynthesis is not known, even though studies on the activity of an enzyme involved in flavonoid biosynthesis (UDP glucose:flavonol 3-0-glucosyltransferase) point to a regulatory function (Dooner and Nelson, Biochem. Genet. 15:509-519, 1977). However, the information available is still too scant to attempt the formulation of a hypothesis on the gene action of R.
Pigment synthesis conditioned by a group of R accessions collectively known as R cherry is light dependent at least in some tissues like the cob or the mesocotyl, but the physiological basis of the photoinduction has not been explored. On the other hand in hybrid stocks of unknown R constitution it has been ascertained that at least two photoreceptor pigments are involved in photoinduction of anthocyanins in the mesocotyl (Duke, Fox and Naylor, Plant Physiol. 57:192-196, 1976). One of the two photoreceptors is phytochrome.
In this note we report some preliminary results on the effects of a hormone, benzyladenine (BA), on anthocyanin production in the mesocotyl of homozygous cherry seedlings. This work is aimed to elucidate R gene action through an analysis of its interaction with a hormone in the process leading to anthocyanin synthesis. We have tested three cherry accessions, designated bol-1, bol-2 and bol-3, originally present in a Bolivian population and now introduced in the W22 background (5 backcrosses). Surface sterilized seeds were incubated in BA solutions of increasing concentrations (10-6 to 10-4 M) on a rotary shaker for 24 hours, transferred to large glass vessels layered with agar and grown for 9 days in darkness at 30 C. Anthocyanins of the mesocotyl were then extracted by grinding mesocotyl in a mortar with liquid nitrogen, adding a fixed volume of 0.1 percent HCL ethanolic (v/v) solution. The extract was then centrifuged and the supernatant used for spectrophotometric reading. The same procedure was followed on 9 days etiolated seedlings exposed to light for 48 hours.
The results obtained with bol-3 (Table 1) show that increasing concentrations of BA lead to a proportional increase in the pigment content of the mesocotyl as well as an inhibition in the seedling length, both effects being dose dependent. The other two alleles (bol-2 and bol-3) do not develop any pigment under these growth conditions. The response of bol-3 seems thus to suggest that anthocyanin enhancement reflects, in this case, a specific interaction between BA and the genetic material of bol-3. This cherry accession appears thus as a good candidate for analyzing the mechanisms of action of a hormone at the gene level.
C. Tonelli, G. Gavazzi and N. Avogadro
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