Monday, November 5, 2007 - 2:45 PM
62-4
Carbon Metabolism in Grass Leaf Meristems.
Marie-Pascale Prud'Homme, Annette Morvan-Bertrand, Véronique Amiard, Bertrand Lasseur, Jérémy Lothier, and Nathalie Noiraud-Romy. Ecophysiologie Végétale Agronomie et Nutritions NCS, UMR INRA-UCN 950 EVA, Université de Caen, Esplanade de la Paix, Caen cedex, F-14032, France
In Lolium perenne, fructan polymers represent the main storage carbohydrates. Even if leaf meristems, located in elongating leaf bases, act as strong sink for imported assimilates, they also synthesize fructans in substantial amounts. Fructans are generally not evenly distributed. Their highest content is found in the growth zone (0-30 mm from the leaf base) and decreased strongly in the differentiation zone (30-60 mm ). Lp1-SST, Lp6G-FFT/1-FFT and Lp6-SFT, encoding the three main fructan synthesizing activities in Lolium perenne, were also predominantly expressed in the growth zone. Their expression declined along the leaf axis, in parallel with the spatial occurrence of fructans, sucrose and enzyme activities. As a response to defoliation, the decline in fructan content occurred not only in the differentiation zone, but also in the growth zone. Before defoliation, the activity of fructan exohydrolase (FEH) was maximal in the differentiation zone. After defoliation, it increased in all segments, but peaked in the growth zone. These data strongly indicate that fructans stored in the leaf growth zone were hydrolyzed and recycled in that zone to sustain refoliation immediately after defoliation. Leaf sheaths represent the other source of fructans. When the product of fructan degradation, fructose, was supplied as 13C-fructose to leaf sheaths at the time of defoliation, its fate showed that the relative supply of C to roots was transiently reduced for the benefit of the growth zone where 13C was allocated first to the proximal part (0-10 mm). This preferential allocation of C could be at least partly explained by a strong and specific increase of the SuSy activity in that zone after defoliation.The results will be discussed in relation to plant development and defoliation tolerance.