Spatial distribution and temporal regulation of phytochromes A and B levels in maize seedlings

Phytochrome distribution and putative level in dark- and light-grown maize (Zea mays L.) seedlings were analyzed using antibodies against oat phytochrome A (PHYA) and tobacco phytochrome B (PHYB) by immunoblotting. During the course of leaf elongation (4–8 d), the putative level of both PHYA and PHYB declined with age. Exposure of etiolated seedlings to light induced severe down-regulation of PHYA level, and transfer of light-grown seedlings to darkness induced reaccumulation of PHYA. For PHYB, no large effect of dark to light, or light to dark, transitions could be observed. Immunoblotting and spectroscopy of phytochromes along the length of 7-d old leaves showed that the level of both PHYA and PHYB was maximal at the leaf base and in the upper half of the leaf, but their level was low in the lower half of the leaf. In light-grown leaves, PHYB distribution was similar to the dark-grown leaves, though its overall level was lower. In light-grown leaves, PHYA could not be detected by immunoblotting, but when the leaves were transferred to darkness, PHYA reappeared with a distribution pattern more or less similar to that of dark-grown leaves. These results indicate that the temporal regulation and spatial distribution of PHYA and PHYB levels in maize appear to be governed by a common regulatory element during the development of seedlings.