Abstract
Long distance transport of 14C-labeled photoassimilate was studied in Macrocystis integrifolia Bory. Movement of label followed the source-sink relationship; mature blades closer to the holdfast with young 2° and 3° fronds transported mostly to the base, those closer to the frond apex transported mostly to the apex, and those in intermediate positions transported both acropetally and basipetally. The velocity of movement of 14C as computed both from study of intact fronds and exudate was in the range of 35 to 72 centimeters per hour and these estimates are on the low side. The composition of the translocate as determined from intact fronds was the same as that determined from exudate analysis; furthermore, this composition was nearly identical with that of the photosynthate (40 to 50% mannitol and 40 to 50% amino acids). From these data we conclude that the exudate represents the sieve tube sap and that there is little if any selectivity exercised in the loading and translocation of photoassimilate. An analysis of translocated label in the growing apex is presented and indicates that the synthesis of polymeric compounds such as laminaran, alginate, cellulose, lipids, and “protein” occurs in situ from the transported mannitol and amino acids. Detailed data on chemical composition of sieve tube sap from M. integrifolia and M. pyrifera (L.) C.A. Agardh are given and compared with the sieve tube sap from higher plants. Finally, we show that stipe segments, 60 to 100 centimeters long with three to six attached blades, are useful for translocation studies in Macrocystis.
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Selected References
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