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Abscisic acid signalling when soil moisture is heterogeneous: decreased photoperiod sap flow from drying roots limits abscisic acid export to the shoots
- DODD, IAN C., EGEA, GREGORIO, DAVIES, WILLIAM J.
- Plant, cell and environment 2008 v.31 no.9 pp. 1263-1274
- Helianthus annuus, abscisic acid, deficit irrigation, irrigation rates, leaves, photoperiod, root systems, root zone drying, roots, sap flow, shoots, simulation models, soil water, soil water content, xylem
- To investigate the contribution of different parts of the root system to total sap flow and leaf xylem abscisic acid (ABA) concentration ([X-ABA]leaf), individual sunflower (Helianthus annuus L.) shoots were grafted onto the root systems of two plants grown in separate pots and sap flow through each hypocotyl measured below the graft union. During deficit irrigation (DI), both pots received the same irrigation volumes, while during partial root zone drying (PRD) one pot ('wet') was watered and another ('dry') was not. During PRD, once soil water content (θ) decreased below a threshold, the fraction of sap flow from drying roots declined. As θ declined, root xylem ABA concentration increased in both irrigation treatments, and [X-ABA]leaf increased in DI plants, but [X-ABA]leaf of PRD plants actually decreased within a certain θ range. A simple model that weighted ABA contributions of wet and dry root systems to [X-ABA]leaf according to the sap flow from each, better predicted [X-ABA]leaf of PRD plants than either [X-ABA]dry, [X-ABA]wet or their mean. Model simulations revealed that [X-ABA]leaf during PRD exceeded that of DI with moderate soil drying, but continued soil drying (such that sap flow from roots in drying soil ceased) resulted in the opposite effect.