Chlorophyllase Activity and Chlorophyll Degradation in Tobacco Chlorophyll Genotypes

Dark (Ky171) and Burley (Ky14) tobaccos, which differ in chlorophyll genotype at Yb₁ and Yb₂ loci, showed no difference in chlorophyllase activity in leaves of the same stalk position. Within a plant, the activity was comparable among three stalk positions in Ky14, whereas the top leaves had higher activity than bottom leaves in Ky171. Since these chlorophyll genes do not modify chlorophyllase activity, these results suggest their mode of action on chlorophyll accumulation is through biosynthesis rather than degradation. In contrast, chlorophyll-deficiency genes Py and yg showed higher chlorophyllase activity than dark and Burley genotypes. This was further substantiated by the loss of ¹⁴C-chlorophyll specific activity in a pulse-labelling experiment using ¹⁴C-d-aminolevulinic acid as chlorophyll precursor. The mode of action for Py and yg genes on chlorophyll degradation is in concert with polyphenol accumulation in tobacco leaf. A metabolic scheme showing the inter-relationship between chlorophyll biosynthesis and polyphenol accumulation is presented.