The rate of protein synthesis in needles of Norway spruce (Picea abies): Light stimulation, regulation through photophosphorylation, stress enhancement.

The incorporation of ¹⁴C‐leucine into the total‐protein fraction of needles of Norway spruce (Picea abies [L.] Karst.) during short time incubation was used as a measure of protein synthesis in the light and in the dark. Light saturation curves, obtained for needles of different ages (new flush and 1 and 2 years old) or at different seasons (summer‐winter) followed the Michaelis‐Menten algorithm, exhibiting marked differences with regard to light saturation (V_max) and the half‐saturation constant (K_S/2). The light saturation curves of ATP level (mg g⁻¹ fresh weight) and of leucine incorporation into protein (nmol mg⁻¹ h⁻¹) matched each other, suggesting that photophosphorylation may be decisive for the rate of protein synthesis in the light. This is confirmed by the action spectrum of leucine incorporation. which resembled an action spectrum of leaf photosynthesis, and also by partial inhibition of protein synthesis by 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU), an inhibitor of non‐cyclic photophosphorylation. Light stimulated protein synthesis showed pronounced seasonal fluctuations with a summer maximum. Furmigation of 5 years old spruce trees for 3 months with SO₂ in combination with O₃ and/or NO₂ caused a distinct enhancement of the protein synthesis rate in the light and, at a reduced absolute level, also in the dark. A similar result was obtained for 40 to 70 years old spruce stands when healthy and sick trees were compared: the latter being afflicted by the novel type of forest decline, which is characterized by yellowish bronze discolouration of sun‐exposed older needles and partial loss of older needle generations (3 to 4 years old). The 1 year old needles of the unhealthy trees showed a markedly increased ¹⁴C‐leucine incorporation rate which, in the dark, was even more pronounced than in the light. Stress‐physiological mechanisms, which could possibly explain this stimulation, are discussed. [ABSTRACT FROM AUTHOR]