© 1990 Heron Publishing—Victoria, Canada
Distribution and metabolism of current photosynthate by single-flush northern red oak seedlings
Richard E. Dickson, J. S. Isebrands and Patricia T. Tomlinson
USDA Forest Service, North Central Forest Experiment Station, P.O. Box 898, Rhinelander, WI 54501, USA /
Summary
Carbon distribution and metabolism by northern red oak seedlings (Quercus rubra L.) were followed for 72 h after a 30-min photosynthetic exposure to 14CO2. Approximately 50% of the assimilated carbon was lost during this time, presumably through respiration. Most of the 14C recovered in the plant remained in the source leaf. Most of the exported 14C was found in stems and especially roots. Position of the source leaf did not affect distribution of translocated 14C; however, upper source leaves retained slightly more 14C than lower source leaves.
Most 14C in all tissues was found initially in sugars. Labeled carbon in this fraction decreased rapidly and increased in other chemical
fractions, particularly residue (structural carbohydrates and lignin). More 14C was incorporated into residue than into any other chemical fraction, indicating continued growth by each of the tissues
during the lag stage of seedling development. Labeled carbon increased in proteins for 6 to 12 h after treatment, then remained
essentially constant for the remainder of the transport period, indicating both rapid incorporation of the pulsed 14C into, and slow turnover of, the labeled protein components. In source leaves, 14C incorporated into starch in the light was lost during the dark period, a typical diurnal storage pattern. In stems, 14C in starch increased for 12 h, then decreased during the dark period, and then increased during the rest of the transport
period. This pattern indicates that stems have both diurnal and long-term storage pools of starch. In roots, 14C in starch increased rapidly for 12 h, then remained constant for the rest of the transport period, indicating primarily
long-term storage in this tissue. Peak 14C in amino acids in taproot preceded that in stem tissue, indicating recycling of 14C from the roots to the shoot in amino acids.
