engleski

Functional and molecular changes of the photosynthetic apparatus in developing spruce needles

The biogenesis of the photosynthetic apparatus during proliferation of vegetative buds and young needles of Norway spruce (Picea abies L. Karst.) under natural conditions was investigated by measurements of oxygen evolution, chlorophyll a fluorescence, photosynthetic pigment content and LHC II and Rubisco LSU expression. Low amounts of chlorophylls and carotenoids, LHC II and Rubisco were detected in the embrionic shoot of vegetative buds. Although PS II was functional, oxygen production was not sufficient to compensate for respiration. Shortly after bud break, compensation of respiration was only observed at high light levels of≥ 650 μ mol m-2 s-1 PPFD in young needles. As development proceeded, the light compensation point was successively lowered. At four weeks after bud break when needles already had a length of 19 mm light compensation was reached at low light levels of c. 30 μ mol m-2 s-1 PPFD similar to mature needles developed in the previous season. A significant increase in photosynthetic pigments as well as the high level of LHC II and Rubisco LSU expression was also observed in this last developmental stage of young needles. The observed delay in biogenesis of the photosinthetic apparatus as well as some irregular fluctuation of chlorophyll a fluorescence parameters during the early development of spruce needles suggest that environmental factors other than light could be critical during development of the photosynthetic apparatus in spruce needles.

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