MECHANISTIC DIFFERENCES IN UTILIZATION OF ABSORBED EXCITATION-ENERGY WITHIN PHOTOSYNTHETIC APPARATUS OF NORWAY SPRUCE INDUCED BY THE VERTICAL-DISTRIBUTION OF PHOTOSYNTHETICALLY ACTIVE RADIATION THROUGH THE TREE CROWN
V. Spunda et al., MECHANISTIC DIFFERENCES IN UTILIZATION OF ABSORBED EXCITATION-ENERGY WITHIN PHOTOSYNTHETIC APPARATUS OF NORWAY SPRUCE INDUCED BY THE VERTICAL-DISTRIBUTION OF PHOTOSYNTHETICALLY ACTIVE RADIATION THROUGH THE TREE CROWN, PLANT SCI, 133(2), 1998, pp. 155-165
An attempt to reveal the causal relation between gradient of photosynt
hetically active radiation (PhAR) through Norway spruce crown and diff
erentiation of photosynthetic apparatus under field conditions is pres
ented. The exposure of exposed (E) needles to higher photosystem (PS)
II excitation pressure than for shaded (S) ones led to diminution of l
ight harvesting complexes (LHCs), increased photosynthetic capacity (P
-Nmax, by 70%) and increased capacity of nonradiative dissipation (NPQ
, by 30%). Further analyses of chlorophyll a (Chl a) fluorescence reve
aled several differences between S and E needles concerning NPQ: (a) f
or E needles the NPQ provides more efficient protection against overre
duction of PS II reaction centres; (b) the steeper dependence of F-0 q
uenching on NPQ (by 53%) in E needles than in S needles supports the v
iew that nonradiative dissipation localized in LHCs was enhanced for E
needles; (c) for E needles induction of NPQ was accompanied by a sign
ificant decrease in energy transfer from Ch1 b to Ch1 a (by 20% and/or
15%) as estimated from 77 K excitation spectra of Ch1 a fluorescence
measured from PS II and PS I, respectively. This implied that down-reg
ulation of light harvesting function operates in PS I as well as in PS
II. The physiological significance of these results regarding the ada
ptation of Norway spruce photosynthetic apparatus to the gradient of P
hAR through the tree crown is discussed. (C) 1998 Elsevier Science Ire
land Ltd. All rights reserved.