Over-expression of a pepper plastid lipid-associated protein in tobacco leads to changes in plastid ultrastructure and plant development upon stress.

Proteins homologous to fibrillin, a pepper plastid lipid-associated protein involved in carotenoid storage in fruit chromoplasts, have been recently identified in leaf chloroplasts from several species and shown to be induced upon environmental stress. To further investigate the role of the protein, transgenic Nicotiana tabacum plants over-expressing fibrillin using a constitutive promoter were generated. Transgenics grown under standard light intensities (300 micromol photons m-2 sec-1) were found to contain substantial amounts of fibrillin in flowers and leaves. In leaves, the protein was immunolocalized within chloroplasts in both stromal and thylakoid subfractions. No change was noticed in thylakoid structures from transgenics, but chloroplasts contained an increased number of plastoglobules organized in clusters. In petals, leucoplasts were also found to contain more agglutinated plastoglobules. The effects of environmental factors on fibrillin gene expression and protein localization were studied in tobacco leaves. Less fibrillin was present in plants grown under low light intensities, which can be explained by the involvement of a light-dependent splicing step in the control of fibrillin gene expression in leaves. Analysis of protein subfractions from plants subjected to drought or high light showed that both stresses resulted in fibrillin association with thylakoids. Whereas no growth difference between wild-type (WT) and transgenic plants was noticed under low light conditions, transgenics exhibit a longer main stem, enhanced development of lateral stems and accelerated floral development under higher light intensities. These data suggest that fibrillin-related proteins fulfil an important function in plant development in relation to environmental constraints.

Effect of CO2 and O2 on development and fructification of wheat in closed systems.

The cultivation of wheat (Triticum aestivum L.) was performed in controlled environment chambers with the continuous monitoring of photosynthesis, dark respiration, transpiration and main nutrient uptakes. A protocol in twin chambers was developed to compare the specific effects of low O2 and high CO2. Each parameter is able to influence photosynthesis but different effects are obtained In the development, fructification and seed production, because of the different effects of each parameter on the ratio of reductive to oxidative cycle of carbon. The first main conclusion is that low level of O2, at the same rate of biomass production, strongly acts on the rate of ear appearance and on seed production. Ear appearance was delayed and seed production reduced with a low O2 treatment (approximately 4%). The O2 effect was not mainly due to the repression of the oxidative cycle. The high CO2 treatment (700 to 900 microl l-1) delayed ear appearance by 4 days but did not reduce seed production. High CO2 treatment also reduced transpiration by 20%. Two hypothesis were proposed to explain the similarities and the difference in the O2 and CO2 effects on the growth of wheat.