Photooxidative damage to plastids affects the abundance of nitrate-reductase mRNA in mustard cotyledons.

It was found previously that in the mustard (Sinapis alba L.) seedling (Schuster et al. 1989, Planta 177, 74-83) the action of nitrate and phytochrome on the appearance of cytosolic nitrate reductase (NR) is abolished if the plastids are damaged by photooxidation. In the present study this finding has been corroborated by the following results: (i) the appearance and disappearance of NR activity are strictly correlated with the appearance and disappearance of immunoresponsive NR protein; (ii) the appearance of NR correlates with the appearance of translatable NR mRNA; (iii) photodestruction of the plastids strongly reduces the level of NR mRNA. It is concluded that the dependence of the NR level on the state of the plastids can be detected at the level of its mRNA and is not attributable to an inactivation of the enzyme.