Chl a Fluorescence and 820 nm Transmission Changes Occurring During a Dark-to-Light Transition in Pine Needles and Pea Leaves: A Comparison

Abstract

In dark-adapted leaves and needles, inactive ferredoxin-NADP+-reductase (FNR) forms a transient block of electron transport. We show here that the activation of this enzyme during a dark-to-light transition in Pinus brutia needles (and other gymnosperms) is much faster than in pea leaves (and other angiosperms). At the same time, inactivation of FNR in darkness is a much slower process in P. brutia needles than in pea leaves. The consequences of this difference for the interpretation of saturating pulse experiments is discussed. The special properties of FNR in pine needles are used to confirm our earlier observation that it is not possible to determine Fm (all centers closed) in the presence of an active photosystem I acceptor side. A comparison of the first 900 s of illumination following a dark-to-light transition shows that the slow activation kinetics of FNR in pea leaves provide an additional means to control electron flow during the activation of photosynthesis.