Phloem unloading in developing leaves of sugar beet. II. Termination of phloem unloading

Journal Article · Wed Dec 31 23:00:00 EST 1986 · Plant Physiol.; (United States)

DOI:https://doi.org/10.1104/pp.83.1.49· OSTI ID:6528082

Schmalstig, J G; Geiger, D R

Phloem unloading in developing leaves of Beta vulgaris L. occurred from successively higher order branches of veins as leaves matured. Phloem unloading was studied in autoradiographs of leaf samples taken at various times during the arrival of a pulse of /sup 14/C-labeled photoassimilate. Extension of mass flow of sieve element contents into leaf vein branches was determined from the high level of radiolabel in veins soon after first arrival of the pulse. Rapid entry, indicative of mass flow through open sieve pores, occurred down to the fourth division of veins in young, importing leaves and to the fifth or terminal branch in importing regions near the zone of transition from sink to source. The rate of unloading decreased with leaf age, as evidenced by the increased time required for the vein-mesophyll demarcation to become obscured. The rate of import per unit leaf area, measures by steady state labeling with /sup 14/CL/sub 2/ also decreased as a leaf matured. The decline in import appeared to result from progressive changes that increased resistance to unloading of sieve elements and eventually terminated phloem unloading.

• Research Organization: Univ. of Dayton, OH
• OSTI ID: 6528082
• Journal Information: Plant Physiol.; (United States), Journal Name: Plant Physiol.; (United States) Vol. 83:1; ISSN PLPHA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
AGE DEPENDENCE
AUTORADIOGRAPHY
BEETS
BODY
CARBON 14 COMPOUNDS
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
FOOD
LABELLED COMPOUNDS
LEAVES
MASS TRANSFER
MEMBRANE TRANSPORT
OXIDES
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOSYNTHESIS
PLANT TISSUES
PLANTS
SUGAR BEETS
SYNTHESIS
TISSUES
VEGETABLES