The first proline auxotroph we isolated is easily recognized on the basis of its endosperm morphology and its lethality as seedling before the first leaf emergence (Gavazzi et al., 1975, Theor. Appl. Genetics 46:339). We relied on the collapsed endosperm phenotype as a criterion for recognizing other pro mutants. By screening populations of M2 ears, originally derived from seeds mutagenized with EMS or NG, we isolated six independent mutants resembling pro-1 in their endosperm morphology. A complementation test was then run by making each mutant heterozygous with pro-1 and scoring for production of collapsed endosperm phenotype as a proof of allelism between the mutant and pro-1. This test led to the identification of three additional alleles at the pro locus. They are tentatively symbolized pro-2, pro-3 and pro-4. They were originally isolated in an EMS (pro-2), control (pro-3) and NG (pro-4) treated population.
Nutritional tests have been performed on pro-2 and pro-3. Each mutant has been grown as excised shoot tips on liquid F media (Racchi et al., 1978, Plant Sci. Lett. in press) supplemented with different groups of amino acids at 1 mM concentration.
The only group of amino acids growth promoting was the glutamate family (glu, arg, pro). Further tests on media with single additions of each of the three amino acids at 5 mM confirms that proline is the amino acid required by the mutants to resume normal growth (see Fig. 1).
Milvia Luisa Racchi and Giuseppe Gavazzi
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