Fluorescence induction in whole leaves: Differentiation between the two leaf sides and adaptation to different light regimes.

In a variety of plants, the induction kinetics of chlorophyll fluorescence vary substantially depending on whether measured on the upper or lower side of the same leaf. The responses are comparable to those of plants grown under sun and shade conditions. Leaf morphology appears not to be the primary cause of the differences since inversion of the leaves can lead to reversed fluorescence responses. Fluorescence induction was analyzed in control and inverted leaves, and in one case, in chloroplasts from sun and shade leaves. It is concluded from the data that the major differences between the chloroplasts of the upper and lower leaf side reflect ionic and thylakoidmembrane conformational factors, rather than structural differences. Mg(2+) flux probably plays a significant role in the adjustment of the thylakoid membrane to high or low light conditions.