Characterization of Blue-Green Fluorescence in the Mesophyll of Sugar Beet (Beta vulgaris L.) Leaves Affected by Iron Deficiency

Abstract

The mesophyll of sugar beet (Beta vulgaris 1.) leaves emits red (chlorophyll a ) fluorescence and blue-green fluorescence when excited with ultraviolet light. The intensity of blue-green fluorescence was increased in mesophylls affected by iron deficiency. This increase was large and progressive. It was concomitant with a decrease of photosynthetic pigments per unit of leaf area. Most of the increase in blue-green fluorescence can be explained by the decrease of the screening of ultraviolet light by chlorophylls and carotenoids. In addition, chlorophylls selectively reabsorb blue fluorescence, which leads to a change in the form of the fluorescence emission spectra. This effect induces an increase of the blueto-green fluorescence ratio in control mesophylls that was concomitant with the decrease of chlorophyll per unit of leaf area. Iron deficiency induced a decrease of the blue-to-green fluorescence ratio that may be attributed to an accumulation of flavins fluorescing in the green. Time-resolved fluorescence measurements indicate that they are mostly riboflavin and/or flavin mononucleotide phosphate. Our data also indicate that the blue-green fluorescence emitted from the mesophyll contains fluorescence of nicotinamide nucleotides.In the last decade several spectroscopic methods have been considered for the characterization of the physiological state of plants. Among them, the use of the fluorescence signal emitted by plants has been the object of intense research activity. Measurements of red (Chl a ) fluorescence have become a useful investigational tool in photosynthesis research, plant physiology, and early detection of stress conditions in plants ( Weis, 1984, 1991). Red fluorescence is usually excited in the visible part of the spectrum. Upon excitation with UV light, leaves also emit blue (maximum at 450 nm) and green (shoulder at 530 nm) fluorescence (Chappelle et al., 1984b(Chappelle et al., , 1991Goulas et al., 1990;Lang et al., , 1992. The intensity and form of the emission spectra of the UV light-induced fluorescence are influenced by environmental conditions (Chappelle et al., 1984a(Chappelle et al., , 1984bTheisen, 1988), or by stage of development. For instance, an increase in green fluorescence has been reported in pine needles as a result of exposure to pollutants (Schneckenburger and Frenz, 1986). An increased BGF was also recorded in senescent soybean leaves (Chappelle et al., 1984b), senescent (Stober and Lichtenthaler, 1992). The common feature of these reports was a reduced amount of Chl per unit of leaf area. This is also the most obvious characteristic of leaves affected by iron deficiency (Bolle-Jones and Notton, 1953;Terry, 1980; Abadia et al., 1989;Morales et al., 1990). Therefore, we used iron deficiency as a model system to investigate the effect of Chl on the BGF.Chl's and carotenoids absorb UV light (Lichtenthaler, 1987;Chappelle et al., 1990Chappelle et al., , 1991. This absorption attenuates the UV light that reaches the fluorophores fluorescing bluegreen. The result is a si...

Fluorescence excitation spectra of drought resistant and sensitive genotypes of triticale and maize

“…The blue and green fluorescence originates from plant phenolics, primarily from ferulic acid covalently bound to sugars of epidermal cell walls (Morales et al 1994, Schweiger et al 1996, Cerovic et al 2002, Meyer et al 2003. Phenolic compounds may function as UVfilter for the mesophyll tissues and can change radiation falling on leaf through absorption of UV-radiation and its transformation into the blue and/or green fluorescence.…”

Fluorescence images of soybean leaves grown under increased O 3 and CO 2

“…Recent studies have attributed the most variable portion of blue fluorescence to nicotinamide-adenine dinucleotide phosphate (NADP) in the reduced form ' 12,13,14,15 The more static portion is speculated to be due to relatively inert structural compounds such as polyphenolics and lignin 16,17,18 The dominant plant constituent that fluoresces in the red and far-red regions at 685 nm and 735 nm is chlorophyll a. Chlorophyll a fluorescence intensities are associated with the concentration of this pigment, and are inversely related to the rate and efficiency of photosynthesis 10, 19 Laser induced fluorescence (LIF) techniques have been demonstrated as a feasible active remote sensing method for plant species identification and determination ofplant vigor that may vary due to various plant stress '°' " '19, 20 Most previous fluorescence studies have involved point-source measurement techniques to assess fluorescence characteristics ofplant leaves. Recent studies have attributed the most variable portion of blue fluorescence to nicotinamide-adenine dinucleotide phosphate (NADP) in the reduced form ' 12,13,14,15 The more static portion is speculated to be due to relatively inert structural compounds such as polyphenolics and lignin 16,17,18 The dominant plant constituent that fluoresces in the red and far-red regions at 685 nm and 735 nm is chlorophyll a. Chlorophyll a fluorescence intensities are associated with the concentration of this pigment, and are inversely related to the rate and efficiency of photosynthesis 10, 19 Laser induced fluorescence (LIF) techniques have been demonstrated as a feasible active remote sensing method for plant species identification and determination ofplant vigor that may vary due to various plant stress '°' " '19, 20 Most previous fluorescence studies have involved point-source measurement techniques to assess fluorescence characteristics ofplant leaves.…”

Cd, Fe, and Light Sensitivity: Interrelationships in Cd-Treated Populus

“…6). The F 510 compound, which accumulated under L80 + Cd treatment, may belong to flavonols (Cerovic et al, 2002;Morales et al, 1996), whereas F 530 -F 560 compounds, which accumulated under L250-Cd but partially also under L80 + Cd treatment, are most probably flavins Morales et al, 1994).…”

“…Among flavonoids, flavonols are the main emitters in the green region (Morales et al, 1996;Roshal et al, 1999), whereas flavins perform a higher wavelength, yellow region fluorescence Morales et al, 1994). The synthesis of flavonoids is known to be induced by UV stress (Harborne and Williams, 2000).…”