Some of the chlorophyll mutants change their character expression under high or low temperature conditions. The author screened the world collection of barley varieties to find out high temperature sensitive chlorophyll mutants. Out of about 5,000 barley varieties, an Italian variety "2541" (Accession No. OUU 311) segregated albino and normal plants when the variety was grown at higher temperature than 27{o}C and higher light intensity than 11,000 lux, whereas it appeared normal at lower than 21°C or less than 2,000 lux, indicating that the OUU 311 included a mutant for chlorophyll formation responsible to high temperature under normal light condition. When the mutant was germinated for two or three days under high temperature (25-30{o}C) and then reared under low temperature, chlorophyll formation of the primary leaf was inhibited but not in the second and succeeding leaves. In this way, the heat sensitive mutant was clearly distinguished from the normal or wild type of 0UU 311, and a mutant line was bred true as OUM 407 and the normal counterpart as OUM 406

Chlorophyll-a, -b, and carotenoid content of both of the OUM 407 and OUM 406 were determined under different temperature and light conditions. In the mutant plants, carotenoid formation was restricted under high temperature irrespective of the light intensity for the first step, and then the chloroplast formation was inhibited under a strong light irrespective of the temperature condition at the second step. The mechanism of the chlorosis mav be re w rted elsewhere.

OUM 407 was crossed with several linkage testers to study the inheritance and linkage relationship of the causal gene(s). F₂ plants were germinated at 25-30{o}C to distinguish the mutant type from the normal one, then they were transplanted into the field to check other marker characters. Segregation mode in F₂ populations revealed that the mutant character was controlled by a recessive gene named hsa (heat sensitive albino). Independent inheritance of the mutant gene was confirmed by the F₂ tests of the crosses involving the following marker genes: v (kernel rows), li (liguleless), e (wide outer glume) and sk (subjacent hood) on chromosome 2; uz ("uzu" semi-brachytic) and al (albino lemma) on chromosome 3; K (hooded lemma), gl3 (glossy seedling) and Hs (hairy sheath) on chromosome 4; B (black lemma and pericarp) and trd (third outer glume) on chromosome 5; o (orange lemma base and internode) on chromosome 6; and s (short rachilla hairs), dsk (dusky), and fs (fragile stem) on chromosome 7. On the other hand, hsa was with linked with n (naked kernel), l (dense spike) and lk2 (short awn) on chromosome 1. According to the F₂ data shown in Table 1, the four genes mentioned above were arranged on the long arm of chromosome 1 as illustrated in Figure 1. As the gene hsa is closely linked with 1 in the repulsion phase, no recombinant was obtained in the F₂ population. Therefore, distance between hsa and l was determined from F₃ data (Table 2). The three point order of the genes l hsa, and n was confirmed according to the method described by Smith (1947).

As hsa is easily identified at the earlier growth stage, it may be a useful marker gene for the linkage analysis of barley. Furthermore, hsa may be a useful marker for cell engineering, because it is clearly identified under specific temperature and light conditions.

Reference:

Smith, L. 1947. A simple method for estimating the three-point order of genes from F₃ data. Jour. Amer. Soc. Agron. 37:353-355.