Pl effect on young seedlings

Stocks segregating for Pl, collected from different sources and selfed for several generations, yield plants differing in their anther pigmentation and easily classifiable into 2 groups, strong and weak red anther colour. We presume this effect is due to Pl. From each stock we derived two sublines breeding true for strong and weak red anther colour respectively. Seedlings of the former develop an intense red pigmentation in their roots even in darkness, while those of the latter turn red only after light exposure. Their pigment content, however, remains much lower than that of their sibling sublines. One Pl source (originally from Dr. Brink) differs from the others in conditioning a very weak root pigmentation while maintaining the intensive anther coloration, suggesting the existence of Pl alleles that differ in their tissue specificity of expression. An example of the effect of different Pl sources on root pigmentation is given in the table below where results referring to a weak and strong Pl source are given.
 
Root pigment
Pl Source Pl Constitution A 530/g fwt.
Brink Pl/Pl 2.3
Brink pl/pl 0.7
Co-op (l*-4120) Pl/Pl 58.9
Co-op (l*-4120) pl/pl 2.7

Two effects should be noted: 1) within each Pl source the Pl subline develops more pigment than the pllpl subline; 2) the intensifying Pl over pl effect is more than 20 fold for Pl (Co-op) but only 3.3 for Pl (Brink).

By crossing two Pl stocks differing in their colour marker constitution, i.e. A1 a2 C1 C2 R-g Pl (from Dr. Coe) with A1 A2 c1 C2 r-r Pl (from Dr. Phillips, in A188 background) we obtained, upon 2 successive rounds of selfing, colourless seeds, r-r/r-r Pl/Pl A2/a2 in genotype. Their progeny, obtained by selfing, yield seedlings with red and nonred roots in a 3:1 rato. The one-quarter of seedlings devoid of anthocyanin (r-r/r-r a2/a2 Pl/Pl) exhibit an unusual yellow pigmentation in their roots. Chromatographic results on hydrolyzed extracts of such roots indicate that the major component present in the extracts is quercetin. This compound is not found in coleoptiles of the same seedlings. Since a2 is blocking one step of the conversion of dihydroflavonol to anthocyanins, it might well be that conversion of dihydroflavonols to flavonols is enhanced by the presence of Pl, leading to an accumulation of flavonols in roots, an event generally not observed.

G. Gavazzi, M.L. Racchi and G. Todesco


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