Pathways of auxin transport in the intact pea seedling (Pisum sativum L.)

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Abstract
When small colonies of the pea aphid [Acyrthosiphon pisum (Harris)] were established on the stem of Meteor Dwarf Pea seedlings (Pisum sativum L.), 14C was found in the honeydew 4.5 h after applying IAA-1-14C to a fully-expanded foliage leaf. In contrast, no activity was found in the honeydew or aphids 4.5 h after the application of IAA-1-14C to the intact apical bud even though the internode upon which the aphids were feeding contained high levels of 14C. The lack of radio-activity in aphids feeding on stems to which IAA-1-14C was applied via the apical bud was found not to be influenced by the internode position or by the transport interval allowed (up to 24 h). Radioactivity derived from either foliar or apical applications of IAA-1-14C was not transported through stem tissues killed by heat treatment. Xylem function was shown not to be impared by the heat treatment employed. It was concluded that the long-distance transport of IAA from the apical bud of intact pea seedlings does not take place in the phloem sieve tubes involved in the transport of metabolites from foliage leaves, or in the non-living tissues of the xylem.