Plastid photodamage and Cab gene expression in barley leaves

The effects of norflurazon (NF) and amitrole (AM), two bleaching herbicides which inhibit carotenogenesis, were compared in leaves of 7-day-oId barley (Hordeum vulgare L, cv Express) plants grown in damaging light, The herbic ide effects were analysed with respect to chloroplast organization, photosy nthetic functionality and nuclear photodependent expression of the Lhcb1 ge ne, which codes for the Lhcb1 light-harvesting chlorophyll a/b binding prot ein of photosystem II. Both herbicides caused dramatic photooxidation of or ganelles, which were photosynthetically unfunctional, Plastids of NF-treate d plants lacked thylakoids and pigments. Plastids of AM- treated plants had some strikingly altered membranes and contained only very small quantities of chlorophylls. Despite the presence of severely photodamaged plastids, c ells of AM-treated leaves contained high levels of Lhcb1 transcript. This t ranscript, on the contrary, was completely absent in the cells of NF-treate d plants, These findings suggest that in order to block expression of nucle ar genes coding for plastid-resident proteins, photodamage leading to the c omplete dismantling of thylakoids and to the total absence of any form of p hotosynthetic pigment is required.