The effects of light quality and non-steady-state, localized14CO2pulse labeling on net assimilation and14C translocation profiles inHeracleum lanatum

摘要

Red, green, blue, and white light of equivalent intensities of photosynthetically active radiation (PAR) (400ndash;700ensp;nm) had no effect upon leaf diffusion resistance, net assimilation, or translocation of leaves ofHeracleum lanatumMichx. at 20 deg;C. Regardless of light quality at 80ensp;mu;Eensp;mminus;2ensp;sminus;1PAR, 5ensp;min and 40ensp;min after the start of a 2-min application of 70ensp;mu;Ci of14CO2to a 1.33-cm2spot on a leaflet, the major ethanol-soluble labeled assimilates were sucrose and glutamic acid while sucrose was the only labeled translocate. Regardless of light quality at 80ensp;mu;Eensp;mminus;2ensp;sminus;1PAR, 5ensp;min after the start of a 2-min spot tag, well defined lsquo;wave-likersquo; translocation profiles consisting of five peaks, 3 to 6ensp;cm apart, were observed along 20ensp;cm of petiole. Regardless of light quality, in 40-min experiments, the lsquo;wave-likersquo; profiles were replaced by typical, linear semilogarithmic translocation profiles. It is concluded that the initial lsquo;wave-likersquo; profiles were induced by perturbing the steady-state kinetics of synthesis and vein loading labeled sucrose by pulse labeling a small spot with an unusually high concentration of14CO2. It is possible that pulsed profiles reported by others may have originated in similar fashion.