Abstract
The principal components of plant productivity and nutritional value, from the standpoint of modern agriculture, are the acquisition and partitioning of organic carbon (C) and nitrogen (N) compounds among the various organs of the plant. The flow of essential organic nutrients among the plant organ systems is mediated by its complex vascular system, and is driven by a series of transport steps including export from sites of primary assimilation, transport into and out of the phloem and xylem, and transport into the various import-dependent organs. Manipulating C and N partitioning to enhance yield of harvested organs is evident in the earliest crop domestication events and continues to be a goal for modern plant biology. Research on the biochemistry, molecular and cellular biology, and physiology of C and N partitioning has now matured to an extent that strategic manipulation of these transport systems through biotechnology are being attempted to improve movement from source to sink tissues in general, but also to target partitioning to specific organs. These nascent efforts are demonstrating the potential of applied biomass targeting but are also identifying interactions between essential nutrients that require further basic research. In this review, we summarize the key transport steps involved in C and N partitioning, and discuss various transgenic approaches for directly manipulating key C and N transporters involved. In addition, we propose several experiments that could enhance biomass accumulation in targeted organs while simultaneously testing current partitioning models.
Highlights
The principal components of plant productivity and nutritional value, from the standpoint of modern agriculture, are the acquisition and partitioning of organic carbon (C) and nitrogen (N) compounds among the various organs of the plant
When Arabidopsis was photosynthetically labeled with 14CO2 for 20 min followed by a 10 min chase period, only 2% of the label was incorporated into raffinose family oligosaccharides (RFO), while Suc contained up to 80% and up to 30% was in Glc and Fru
Rolletschek et al (2005) documented a 20% increase in seed N content and seed size as a result of the ectopic expression of the Vicia faba VfAAP1 amino acid transporter gene in the developing seeds of pea and Vicia narbonensis using the seed specific legumin B4 promoter. These results suggest that amino acid transport into the storage parenchyma of the developing seed is rate limiting
Summary
The principal components of plant productivity and nutritional value, from the standpoint of modern agriculture, are the acquisition and partitioning of organic carbon (C) and nitrogen (N) compounds among the various organs of the plant. Transgenic manipulation of assimilate partitioning into amino acids in the root or shoot for subsequent transport to import-dependent tissues. These “sinks” are the primary consumers of newly assimilated sugars and amino acids, and include many essential organ systems such as expanding leaves, roots, seeds and fruits, storage tissue and organs, and secondary growth. Human manipulation of C and N partitioning is evident from the earliest examples of crop domestication. Nutritional and other quality enhancements of feed/food crops are primary objectives that are in part dependent on C and N partitioning
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