Greening of peas: Parallel measurements of 77 K emission spectra, OJIP chlorophyll a fluorescence transient, period four oscillation of the initial fluorescence level, delayed light emission, and P700

Abstract

Irradiation of etiolated leaves leads to their greening. Although this problem has a long history, the question of whether the intermittent irradiation (IMI) grown plants have fully functional reaction centres as well as the oxygen clock, before exposure to continuous irradiation (CI), had not been resolved. To answer this question, as well as to analyze the development of the two photosystems, the following parallel measurements were made: (1) Emission spectra at 77 K; (2) OJIP chlorophyll (Chl) a fluorescence transient; (3) period 4 oscillation in the flash number dependence of initial fluorescence F0 (at 50 μs) and F(J) (at 2 ms); and (4) P700. In the 1-ms-flash (FL) grown pea, that has a different biogenesis of the photosynthetic apparatus, delayed light emission (DLE) and Chl a fluorescence transient were measured in parallel. Quantitative analysis of Chl a fluorescence values provided the following conclusions: (1) IMI, not FL, plants have almost fully developed reaction centres and the oxygen clock. (2) Further greening of IMI plants under CI involves two phases: (a) during 3-4 h of CI, the number of PS2 units and connectivity between them increase, and then (b) light-harvesting antenna increases. (3) In FL, 10 min CI activates fully the oxygen clock.