Radioimmunoassay of phytochrome content in green, light‐grown oats

We measured phytochrome content by radioimmunoassay in green, light‐grown oats (Avena sativa L., cv. Garry) grown under several light regimes. Phytochrome content increased linearly to six times the light‐grown level during a 24‐h dark incubation and to fifty times the light‐grown level after 48 h darkness. Phytochrome content, in response to a cycle of 12‐h light, 12‐h dark photoperiods, increased to three times the light‐grown level in darkness and returned to the light‐grown level during the subsequent light period. Plants given far‐red light immediately prior to a 12‐h dark period contained about four‐fold more phytochrome than light‐grown oats, compared with a three‐fold increase in plants treated identically except given no far‐red light. We also attempted, unsuccessfully, to eliminate a general nonspecific interference by crude plant extracts with the radioimmunoassay.