The chl a fluorescence intensity is remarkably insensitive to changes in the chlorophyll content of the leaf as long as the chl a/b ratio remains unaffected
2012
Dinç, Emine | Ceppi, M Georgina | Tóth, Szilvia Z. | Bottka, Sándor | Schansker, Gert
The effects of changes in the chlorophyll (chl) content on the kinetics of the OJIP fluorescence transient were studied using two different approaches. An extensive chl loss (up to 5-fold decrease) occurs in leaves suffering from either an Mg²⁺ or SO₄ ²⁻ deficiency. The effects of these treatments on the chl a/b ratio, which is related to antenna size, were very limited. This observation was confirmed by the identical light intensity dependencies of the K, J and I-steps of the fluorescence rise for three of the four treatments and by the absence of changes in the F₆₈₅ ₙₘ/F₆₉₅ ₙₘ-ratio of fluorescence emission spectra measured at 77K. Under these conditions, the F₀ and FM-values were essentially insensitive to the chl content. A second experimental approach consisted of the treatment of wheat leaves with specifically designed antisense oligodeoxynucleotides that interfered with the translation of mRNA of the genes coding for chl a/b binding proteins. This way, leaves with a wide range of chl a/b ratios were created. Under these conditions, an inverse proportional relationship between the FM values and the chl a/b ratio was observed. A strong effect of the chl a/b ratio on the fluorescence intensity was also observed for barley Chlorina f2 plants that lack chl b. The data suggest that the chl a/b ratio (antenna size) is a more important determinant of the maximum fluorescence intensity than the chl content of the leaf.
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