Abstract
During grain filling in barley (Hordeum vulgare L. cv. Barke) reserves are remobilized from vegetative organs. Glumes represent the vegetative tissues closest to grains, senesce late, and are involved in the conversion of assimilates. To analyse glume development and metabolism related to grain filling, parallel transcript and metabolite profiling in glumes and endosperm were performed, showing that glume metabolism and development adjusts to changing grain demands, reflected by specific signatures of metabolite and transcript abundances. Before high endosperm sink strength is established by storage product accumulation, glumes form early, intermediary sink organs, shifting then to remobilizing and exporting source organs. Metabolic and transcriptional transitions occur at two phases: first, at the onset of endosperm filling, as a consequence of endosperm sink activity and assimilate depletion in endosperm and vascular tissues; second, at late grain filling, by developmental ageing and senescence. Regulation of and transition between phases are probably governed by specific NAC and WRKY transcription factors, and both abscisic and jasmonic acid, and are accompanied by changed expression of specific nitrogen transporters. Expression and metabolite profiling suggest glume-specific mechanisms of assimilate conversion and translocation. In summary, grain filling and endosperm sink strength coordinate phase changes in glumes via metabolic, hormonal, and transcriptional control. This study provides a comprehensive view of barley glume development and metabolism, and identifies candidate genes and associated pathways, potentially important for breeding improved grain traits.
Highlights
During seed filling carbon (C) and nitrogen (N) compounds are remobilized from vegetative organs and transported to the seeds
Total N in glumes increased until 8 days after pollination (DAP), followed by a sharp decline at 8 DAP without further changes until 20 DAP and a slight decrease thereafter (Fig. 1B)
The results indicate a sudden decrease of most free amino acids in glumes at 8 DAP
Summary
During seed filling carbon (C) and nitrogen (N) compounds are remobilized from vegetative organs and transported to the seeds. Vegetative organs in barley and wheat are photosynthetically active, providing carbohydrates until late grain filling. 60–90% of grain N originates from remobilization out of vegetative organs (Hirel et al, 2007). Among the photosynthetically active tissues, glumes hold an exceptional role, as the organs nearest the grains. Glumes have a unique cellular and chloroplast distribution associated with their particular metabolism and supporting. Up to 30% of photosynthates imported into grains derive from photosynthetic activity of glumes (Grundbacher, 1963)
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