Article

Planta

, Volume 192, Issue 2, pp 239-248

Phloem transport and differential unloading in pea seedlings after source and sink manipulations

  • Alexander SchulzAffiliated withBotanisches Institut der Universität

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Abstract

Phloem transport was investigated in pea seedlings after application of [14C]sucrose to the cotyledons. The accumulation of the label in segments of young seedlings shows a differential unloading along the plant axis. Shoot and root exhibit tip-to-base gradients of sink strength. In the primary root, the sink-strength profiles reflect not only the importance of the apical meristem, but show also the starting points of cambial activity and production of secondary vascular elements. Experiments including partial removal of the source and manipulations of the sink strength indicate that translocation of pea seedlings is sink-regulated and responds rapidly to changed apoplastic conditions in the apical root region. Here, a lowered water potential leads to an increase of phloem unloading that is suggested to supply the assimilate demand for the short-term osmoregulation of affected cells via the symplasmic pathway.

Key words

Osmoregulation Phloem transport Phloem unloading Pisum Sink strength Source/sink relations