Anomalous electron transport activity in a Photosystem I-deficient maize mutant.

Photosynthesis mutations were induced in maize lines bearing the transposable DNA element system, Mutator. Two Photosystem I mutants (hcf101 and hcf104) which were isolated are described here. Maize plants homozygous for the hcf104 mutation are seedling lethal and exhibit a high in vivo chlorophyll fluorescence yield. They lack ∼60% of CP1, P700 and PSI-specific electron transport activity relative to normal sibling plants. The comparable depletion of these three measures of PS I content conforms to the pattern reported for many other PS I-deficient mutants. Maize plants homozygous for hcf101 are seedling lethal and also exhibit high in vivo chlorophyll fluorescence yield. They lack 80-90% of CP1 and P700 but sustain steady state levels of PS I-specific electron transport activity at 70% of normal. Previous reports of similar apparent PS I hyperactivity are discussed and an explanation for the elevated steady state level of PS I electron transport activity in hcf101 is proposed.