An analysis of the chlorophyll-fluorescence transients from pea leaves generated by changes in atmospheric concentrations of CO2 and O2

Fluorescence induction curves registered from individual microalgae cenobiums in the process of population growth

Registration of chlorophyll fluorescence induction curves (IC) from individual microalgae cenobiums was performed during Scenedesmus quadricauda culture growth. Emphasis was placed on the analysis of patterns of the slow phase of IC, since these slow fluorescence transitions reflect complex interactions between primary and secondary photosynthetic processes. A classification was performed of the ICs obtained according to the patterns of their slow phase. Four different types of such patterns were distinguished. The microalgae population structure with respect to IC patterns was investigated at different stages of culture growth. The distribution of microalgae cenobiums over the patterns of IC was found to change in accordance with the stage of population development. At the stage of the population growth enhancement, nonmonotonous IC dominated with a high steady-state level of fluorescence. The stage of linear growth was characterized by IC with monotonous decay kinetics and low steady-state level of fluorescence. At the third stage including the phases of growth inhibition, stationary state and the beginning of cell death the population structure was the most heterogeneous, with all IC patterns observed.

Chlorophyll fluorescence transients from the diatom Phaeodactylum tricornutum: relative rates of cyclic phosphorylation and chlororespiration

In Phaeodactylum tricornutum cells kept 30 min in the dark, induction of fluorescence showed the well-known levels OIDPSMT. The decrease of MT was the most important when the intensity of excitation light was high. It was mainly due to the photochemical quenching. After addition of DCMU (2 to 20 μM), a quenching qE was still observed: this quenching, cancelled by NH4Cl (2 to 20 mM) is attributed to ΔpH. This qE was also inhibited by antimycin, an inhibitor of cyclic phosphorylation and may be of chlororespiration above plastoquinones. Anaerobiosis also decreased it. We can infer that chlororespiration also plays a part in the formation of the ΔpH in the presence of DCMU. After 30 mn of preillumination in red light, the levels P and M were lower and the quenching in presence of DCMU was no more observed: thus, neither the chlororespiration nor the cyclic phosphorylation were active, unless the activity of ATPase was much more important. So, in diatoms, one at least of the above cited phenomena can be modulated by light.

The role of carbon dioxide and oxygen in determining chlorophyll fluorescence quenching during leaf development

Chlorophyll fluorescence emission at 680 nm (F680) and the rate of CO2 fixation were measured simultaneously in sections along the length of wheat and maize leaves. These leaves possess a basal meristem and show a gradation in development towards the leaf tip. The redox state of the primary electron acceptor, Q, of photosystem II was estimated using a non-invasive method. Distal mature leaf sections displayed typical F680 induction curves which were generally anti-parallel with CO2 fixation and during which Q became gradually oxidised. In leaf-base sections net assimilation of CO2 was not detectable, F680 quenched slowly and monotonously without displaying any of the oscillations typical of mature tissue and Q remained relatively reduced. Sections cut from mid-regions of the leaf showed intermediate characteristics. There were no major differences between the wheat and maize leaf in the parameters measured. The results support the hypothesis that generation of the transthylakoid proton gradient and associated ATP production is not a major limitation to photosynthesis during leaf development in either C3 or C4 plants. Removal of CO2 from the mature leaf sections caused little change in steady-state F680 and produced about 50% reduction of Q. When O2 was then removed, F680 rose sharply and Q became almost totally reduced. In immature tissue unable to assimilate CO2, removal of O2 alone caused a similar large rise in F680 and reduction of Q whilst removal of CO2 had negligible effects on F680 and the redox state of Q. It is concluded that in leaf tissue unable to assimilate CO2, either because CO2 is absent or the tissue is immature, O2 acts as an electron acceptor and maintains Q in a partially oxidised state. The important implication that O2 may have a role in the prevention of photoinhibition of the photochemical apparatus in the developing leaf is discussed.