A MORPHOLOGICAL STUDY OF THE X-RAY INDUCED CAULIFLOWER-HEAD AND SINGLE-LEAF MUTATION IN MEDICAGO SATIVA L.

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Abstract
The morphology of a spontaneous and an X-ray induced cauliflower-head and single-leaf mutation is compared with normal alfalfa. Chromosome numbers were 32 in the normal and the spontaneous mutation, 31 in some, but not all, of the X-ray induced lines. The cauliflower mutant is unrelated to the trisomic tetraploid condition of the B45 line. In normal flower development the pistils are homologues of the apical meristem of buds, while stamens and accessory floral structures are homologues of bud leaves. Flower development in X-ray induced cauliflower-head is restricted to profusely branched floral axes which produce only meristem primordia, and under treatment with gibberellic acid, rudimentary pistils, but still no stamens, petals or sepals. Flower development in the spontaneous mutation shows sparingly branched floral axes, which produce rudimentary pistils, and linear bracts homologous with sepal-petal primordia. With gibberellic acid treatment, pistil development approaches normal, but no stamens, petals or sepals are produced. Leaf development, which is trifoliate in normal alfalfa, is unifoliate in both mutants. The unifoliate leaf appears to result from suppression of lateral leaflet primordia. The study suggests that the X-ray induced mutation, although similar, is more extreme and rudimentary, in tissue differentiation, than the spontaneous mutation.