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Phloem unloading and ‘sink strength’: The parallel between the site of attachment of Cuscuta and developing legume seeds

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Abstract

Sink regions play a central role in determining assimilate distribution patterns. Two factors are discussed which have a strong effect on the ‘sink strength’ of a sink, viz. phloem unloading and turgor-sensitive transport. ‘Sink strength’ may be defined as the capacity of phloem in the sink region to import assimilates from other parts of the plants and to release the imported substances into the sink apoplast.

A stem parasitized by Cuscuta represents a very strong sink. A review is presented of data on enhanced phloem unloading, at the site of attachment of Custuta. Recent data on metabolically controlled sucrose and amino acid unloading into the seed coat apoplast of developing legume seeds show a remarkable parallel with phloem unloading in a parasitized Vicia faba stem. Data on turgor-sensitive sucrose and amino acid transport into developing seeds are presented, which throw new light on the pressure flow theory of phloem transport.

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  1. Botanical Laboratory, State University of Utrecht, Lange Nieuwstraat 106, 3512 PN, Utrecht, The Netherlands

    P. Wolswinkel

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Wolswinkel, P. Phloem unloading and ‘sink strength’: The parallel between the site of attachment of Cuscuta and developing legume seeds. Plant Growth Regul 2, 309–317 (1984). https://doi.org/10.1007/BF00027290

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