THE ISOLATION AND CHARACTERIZATION OF MUTANTS OF THE C-4 PLANT AMARANTHUS-EDULIS

Azide generated mutants of the C-4 plant Amaranthus edulis have been s creened for their inability to grow in normal air a process that is re versed following exposure to 0.7% CO2. Three classes of mutants have n ow been characterized (1) LaC4 2.16 lacks the major C-4 form of PEP ca rboxylase protein found in the leaf. PEP carboxylase activity in non-p hotosynthetic tissue is unchanged in the mutant; (2) LaC4 73 lacks NAD -malic enzyme activity located in the bundle sheath mitochondria, but contains the normal 2 subunits of the enzyme protein; (3) LaC4 2.11, 2 5 and 30 that accumulate glycine following exposure to air. A common c haracteristic of all the mutant plants is that they are only able to c arry out photosynthetic CO2 assimilation at very low rates when expose d to air. In a heterozygous mutant of LaC4 2.16 containing 55% of the PEP carboxylase activity, the maximum photosynthetic rate and carboxyl ation efficiency is reduced by approximately 20%. Using the glutamine synthetase inhibitor phosphinothricin, in the presence of aminoacetoni trile, the rate of ammonia accumulation has been determined. in the mu tants that accumulate glycine, the amount of ammonia production is low , indicating that in the wild-type C-4 plant Amaranthus edulis, there is a significant measurable rate of photorespiration.