Phloem Pressure Differences and 14C-Assimilate Translocation in Ecballium elaterium

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Abstract
The role of phloem turgor pressure in 14C-assimilate translocation in E. elaterium A. Rich was studied. The direction of translocation was manipulated by 2 methods: darkening, or defoliation, of the upper or lower halves of the shoots. After 24 h of labeled assimilate movement, sieve tube turgor levels were measured with the phloem needle technique. Distribution of label, determined by autoradiography and counting, revealed a direct correlation between the direction of assimilate transport and the pressure difference. Phloem turgor levels always decreased in the stem of darkened shoots; this resulted in greater pressure differences in the stem between the source leaf receiving 14CO2 and treated regions.