Activity of the Fe-branch of tetrapyrrole biosynthesis in the chlorophyll-deficient plastome mutant of sunflower

The biosynthesis of heme, a plant tetrapyrrole, was studied in the leaves o f a chlorophyll-deficient plastome mutant of the sunflower (Helianthus annu us L, line 2-24, albina form). In the light, the content of 5-aminolevulini c acid (ALA) in white mutant leaves was, on the average, ten times less tha n in that of the wildtype form (line 3629). Chlorophyll content in mutant l eaves comprised only 0.3%, of that of control plants. The activities of Fe- chelatase and ALA dehydratase in the heme synthesis were either comparable to or even higher than those in the wild-type leaves. A normal respiration rate in white mutant leaves, the equal content of phytochrome apoproteins i n plants of both types, and the lack of noticeable morphogenetic difference s realized through the phytochrome system can indicate that mutant and wild -type leaves are similar in their levels of phytochrome and the cytochromes of mitochondrial respiration. Nevertheless, in the mutant, the content of heme noncovalently bound by apoproteins amounted to only one third of its c ontent in the wild-type plants. It seems that a dramatic decrease in the ca pability of white leaves for chlorophyll biosynthesis and for the formation of the photosynthetic apparatus is responsible for a low demand for chloro plast cytochromes, which is the major cause of a reduced heme content in th e mutant.