Genetic characterization and high efficiency photosynthesis of an aurea mutant of tobacco

A new tobacco (Nicotiana tabacum) aurea mutant was isolated from the progeny of a selfed variegated tobacco plant. The new mutant is termed Su/su var. Aurea. If the mutant is selfed, the seeds obtained give rise to four types of plants: green seedlings which correspond to the wild type; yellow-green seedlings which correspond to the earlier described Su/su; yellow seedlings which correspond to the new tobacco aurea mutant Su/su var. Aurea; and white lethal seedlings. The frequency ratio of the four phenotypes is 1:1:1:1. It appears that the mutation is due to two independent nuclear factors, su and aur, both of which have to be present in a heterozygous conditions, Su/su Aur/aur, to give rise to the new aurea phenotype. The aurea mutant Su/su var. Aurea has a reduced photosynthetic unit size which is approximately one-eighth of the wild type. Despite its chlorophyll deficiency, the plant grows well and exhibits maximal photosynthetic rates on a chlorophyll basis which are at least seven times higher than those of the green wild type provided the temperature and the light intensities are high enough. In contrast to the earlier described Su/su, the new mutant does not exhibit more photorespiration than the wild type. It appears that the factor aur causes either repression of photorespiration or an increase in the number of functioning photosynthetic units.