The effect of light on pigment accumulation in germinating r-ch(Hopi) seeds

As outlined in the previous note, a characteristic feature of r-ch(Hopi) is its light dependent potential to accumulate anthocyanin in the scutellum and aleurone tissues of germinating seeds. A 24-hour period of illumination is in fact sufficient to allow complete pigmentation of the scutellum and the appearance of patches of pigment in the aleurone, similar to those exhibited by the light-inducible c-p allele of c1. To ascertain whether germination plays any role in this light mediated process, immature seeds (35 days after pollination) were placed in agar, embryos up, in plastic petri dishes as whole seed or as embryo together with its scutellum. Following 48 hours darkness they were exposed to light for another 48 hours and then scored for scutellum pigmentation. Under these conditions only embryos devoid of their endosperm germinate and accumulate anthocyanin in their scutellar tissues, while whole seeds neither germinate nor develop pigment. These results indicate that both light and germination are effective in triggering biochemical processes leading to pigment accumulation.

To see whether light quality affects the r-ch(Hopi) expression, homozygous r-ch seeds plated on wet filter paper in petri dishes were irradiated with continuous light of different qualities for 36 hours, and anthocyanins extracted from their scutella in a 1% HCI ethanol solution at the end of the irradiation time. Lamps Power stars HQ1-T400 W/DV OSRAM were the light source. The different light qualities obtained with gelatin or dielectric layer filters had fluence rates of 68, 19, 34 and 4.3 W m-2 for white, blue, red and far red light, respectively. The pigment content (A 530/scutellum) following irradiation with continuous light of different qualities is given below:
 
Dark White Blue Red Far Red
0.11 0.64 0.49 0.21  0.22

Each value is the average of the determination of two samples of five scutella each. These results suggest the involvement of at least two photoreceptors in mediating the light effects, one active in the red, far red and another one in the blue portion of the spectrum.

A similar interaction with light is observed in the presence of Sn (unpublished results), thus suggesting that the seed pigmentation conditioned by r-ch(Hopi) might represent the response of a modified Sn differing from standard Sn in its capacity to be expressed in the mature seed tissues following germination.

M. L. Racchi, G. Gavazzi and A. Gorrini
 
 


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