抄録
1. A case of functional disturbance of the plastid system, found in Medicago truncatula Gaertn., is described. Its most striking aspect was a widely varying variegation, hence the term “variegation sensu lato” would be convenient.
2. The phenomenon is controlled by a variable recessive gene. The spectrum of its manifestations extended from colorless albina, bordering on xanthoid-over gradually varying degrees of variegation-to apparently homogeneous green.
3.Selection was successful in both directions. If practiced toward increasing participation of the green component, it resulted in a uniformly, somewhat lighter, green form which could be distinguished from the normal green of the Bright line mainly by ±quasi-chlorotic new growth. The selection was aided by a greening process imposed by the same gene. Selection in the opposite direction, toward the albina state, made the maintenance of variegated plants possible. But it was difficult to reach the albina state itself by selfing, unless strikingly variegated pods were used which offered the chance for the occurrence of ovules formed in colorless or ultra-chlorotic tissue. The easiest way to obtain highly variegated plants as well as albinas was to look out for them in crosses, for the former in the F2 generation and for the latter in any segregating offspring in F2-F5.
4. Crosses with the normal Bright line showed in both directions of the cross very similar results. In F1 (about 50 plants observed) normal green was completely dominant. In F2 segregation was monohybrid but a considerable part of the recessives were albina, more of them in the cross with normal green as the female parent of the cross, (among 42 recessives 20) than in the reciprocal direction (among 42 recessives 13).
5. In the further generations, F3-F5, albinas were almost the only representatives of the recessive class, i.e. variegated plants practically disappeared. Thus, the problem of the variable gene of the present case was, after the branching off of a normalized form, resolving itself in the course of generations into the old Mendelian example of 3 green: 1 albinotic segregation.
6. Segregation was recognized already among the seeds of hybrids, due to the “greenish” appearance of the albina seeds. The difference from normal seeds (homo- and heterozygotes) was much more pronounced in the first green stager1), in still green pods, where the contrast between the scarcely perceptible tint of the albina embryonal cotyledons and those, lusciously green, of the dominant homo- and heterozygotes was striking. Occasionally a variegated pattern of the cotyledons could be seen in the first green stage of F1-seeds.
7. The plastids seem to be potentially able to function. Only those in ultra-chlorotic and albina tissues remain inactive.
8. A tentative explanation of the albinas in the segregating offspring was sought in an eventual intra-pod competition. Their higher frequency when normal green was the female parent of the cross than in the reciprocal direction seems to be not inconsistent with this hypothesis.
9. The described case is gene-controlled. Crosses with normals gave in both directions of the cross the same results. Intra-cell mixture and its corollary, somatic segregation of plastids, seem not to occur. Plasma has no influence, in contradiction with variegation resulting from the fairly well understood chimeral developments inwhich a maternal plasma is involved. Both kinds of variegation could be simultaneously observed in the present investigation. The difference was striking.
