Xuecai Qiang, Qingzhen Jiang, David Hole and Dominique Roche

Department of plants, soils and biometeorology, Utah State University, Logan, UT 84321, USA

The physiological interaction of lemma and palea with the barley caryopsis is unique. During grain filling, photosynthesis rate of these glumelles and respiration rate of the caryopsis is very high.. Ten days after anthesis, lemma and palea fuse to the caryopsis and remain green for two more weeks. In recent studies we found that dark respiration of the filling grain led to significant underestimation of gross photosynthesis of the barley ear. In field conditions, albino lemma and other photosynthetic mutants for glumelles are used to monitor the contribution of glumelles to gas exchange of the ear. We will present data indicating that refixation of carbon released by grain respiration occurs in the lemma and palea. Finally, carbon isotope discrimination (Ä) of dissected glumelles (hull) and mature kernels were determined for several genetic lines grown along a gradient of irrigation (‘line source experimental design'). We found that Ä values between hull and mature kernel were similar under fully irrigated conditions. However, Ä values of grains were lower than those of hulls under less or non-irrigated conditions. These results will be discussed to assess the role of glumelles in water use efficiency of the whole ear.