NIF GENE-TRANSFER AND EXPRESSION IN CHLOROPLASTS - PROSPECTS AND PROBLEMS

The engineering of plants capable of fixing their own nitrogen is an e xtremely complex task, requiring the coordinated and regulated express ion of 16 nif genes in an appropriate cellular location. We suggest th at plastids may provide a favourable environment for nif gene expressi on provided that the nitrogenase enzyme can be protected from oxygen d amage. Using the non-heterocystous cyanobacteria as a model, we argue that photosynthesis could be temporally separated from nitrogen fixati on in chloroplasts by restricting nitrogenase synthesis to the dark pe riod. We report preliminary data on the introduction and expression of one of nitrogenase components, the Fe protein, in transgenic tobacco and Chlamydomonas reinhardtii. Finally we discuss potential avenues fo r further research in this area and the prospects for achieving the ul timate goal of expressing active nitrogenase in cereal crops such as r ice.