REGULATION OF PHYTOCHROME MESSENGER-RNA ABUNDANCE IN GREEN OAT LEAVES

Avena sativa L. (oat) seedlings were grown 4d in continuous white light followed by 3 d in darkness. Probes derived from an oat phytochrome cDNA clone (pAP 3.2) were used in slot blot analyses to measure the abundance of phytochrome mRNA in the distinct etiolated and green portions of the leaves produced by these seedlings. Both the green and etiolated portions accumulated phytochrome mRNA to a level of about 85% of the etiolated seedling level. Subsequent experiments with similar seedlings showed that both the green and etiolated portions were capable of inducing a dramatic decline in phytochrome mRNA abundance in response to a saturating red light pulse. Despite the ability of green portions of oat leaves to accumulate phytochrome mRNA and to down-regulate phytochrome mRNA abundance in response to light, no substantial variation in phytochrome mRNA abundance was observed in green oat seedlings e maintained on a 12-h day/12-h night cycle. In the same oat seedlings, the abundance of chlorophyll a/b binding protein mRNA fluctuated dramatically during the day/night cycle.