title: Contribution of current carbon assimilation in supplying root exudates of Lolium perenne measured using steady-state C labelling.
abstract: Coupling growth of Lolium perenne L. in sterile solution culture with steady-state (13)CO(2) labelling allowed quantification of the contribution of C, assimilated either before or after a specific time point, both to plant compartments and root exudates. Plants were grown for 27 days in atmospheres containing CO(2) with delta(13)C signatures of either -13.5 or -36.1 per thousand. Air supplies to plants were then reciprocally switched to the opposing signature (day 0), plants were destructively harvested and root exudates collected over the next 8 days. Following the switch, C assimilated after day 0 and transported to the roots initially only appeared in root tips, later appearing in both tip and non-tip material. The delta(13)C signature of the root exudate changed exponentially with time. Assimilation pre- and post-day 0 contributed equally to exudate C at 4.5 days. Beyond day 8, assimilation pre-day 0 still contributed 41.7% of exudate C. Over all 8 days, a linear relationship existed between the delta(13)C signatures of root tips and exudate, suggesting that all newly assimilated C in the exudate was from root tips. Results imply pulse-labelling approaches to study root exudates are discriminative in the sources of exudates labelled and in the sites from which exudation occurs.
authors.affiliation: The Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, UK.
authors.forename: Barry
authors.initials: B
authors.lastname: Thornton
authors.forename: Eric
authors.initials: E
authors.lastname: Paterson
authors.forename: Andrew J.
authors.initials: AJ
authors.lastname: Midwood
authors.forename: Allan
authors.initials: A
authors.lastname: Sim
authors.forename: Shona M.
authors.initials: SM
authors.lastname: Pratt