Restriction endonuclease analysis of chloroplast (ct) DNA variation in two cultivated rice species, Oryza sativa and O. glaberrima, using three endonucleases, EcoRI, HindIII and PstI, indicated the differentiation of their chloroplast genome into three types. O. sativa differed from O. glaberrimain its EcoRI restriction pattern, whereas both O. sativa ecospecies Japonica and ecosp. Javanica were differentiated from ecosp. Indica by their HindIII and PstI restriction patterns. In contrast, no ctDNA variation was revealed in O, sativa ecosp. Japonica, Javanica, or Indica, or O. glaberrima (11, 4, 7 and 8 accessions, respectively). These findings demonstrated, for the first time, the existence of chloroplast genome diversity among cultivated rice species and ecospecies.
The degrees of dominance of amylase activity, responsiveness to inducing (or repressive) environment, the activity of one allozyme relative to that of the other duplicated locus, and trans- or cis-action of controlling elements were investigated using 10 homozygous lines from a natural population in Japan. The main findings are: (1) Genetic variation in specific activity, responsiveness as well as relative activity of duplicated genes were found. (2) The degree of dominance of amylase activity drastically changed in different environments. The heterozygous amylase activity in starch food was almost the same as the parental value with lower activity (h=1.29±0.39, complete recessive). On the other hand, the enzyme activity of heterozygote in normal food was closer to the parent with higher activity (h=0.26 ±0.07, high dominance), indicating that the manner of amylase regulation is trans-action and also is affected by the environments. (3) The relative activity of one of the two duplicated amylase loci on the same chromosome was affected by an allozyme on the homologous chromosome. In other words, the regulation of duplicated amylase genes was trans-action and partially differentiated, but high correlation of the enzyme activity between the two duplicated genes on the same chromosome also indicated the coordinated regulation.
Seven indica rice varieties with different amylose contents were crossed in all possible combinations including reciprocals. Single grains of parents and F1′s were analyzed to determine the dosage effects of genes responsible for different amylose contents. Different genes for amylose content showed differential effects on endosperm appearance and amylose production in the F1. A single dose of very low or low amylose gene was not capable of producing amylose to the level of their non-waxy parent in waxy/non-waxy crosses. The effect of one dose of gene for intermediate or high amylose was highly conspicious with relatively less dosage effect. Dosage effects were observed in both waxy/non-waxy and among non-waxy crosses. In general, amylose content increased with increase in gene dosage though not in a linear fashion. Cases where amylose content decreased with increase in dosage for higher amylose have also been observed. The importance of such results in understanding the inheritance pattern of this trait has been discussed.