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Flachmann (1997) studied the PS II antennae composition under varying light conditions in tobacc o plants transformed with antisense echnique. An increase of P S II antenna size was observed under low irradiance and also higher LHC II content. The results also suggested that LHC II biogenesis is perhaps not controlled by transcription. The foregone account of different studies using transgenics have inmmensely helped by adding new dimension in our understanding of the structure and function of the photosystem core complexes and of the antennae systems related to both PS II and PS I. A fairly larg e number of studies have also been directed using transgenic technology to understand the process of photoinhibition. Tyystjarvi et al., (1999b) have made a study of photoinhibition of PS II in tobacco an d poplar plants. The tobacco cultivars were expressed with bacterial gov gene in the cytosol and Fe SOD gene from Arabidopsis thaliana rather in the chloroplast. The transformations were affected as an overexpression of glutathione reductase in tobacco and superoxide dismutase in poplar. This transformation resulted in the activities of glutathione reductase in tobacco leaves and superoxide dismutase in poplars were five to eight times higher than in the untransformed plants. The experiments of the authors (Tyystjarvi et al., (1999b) with the transformed plants have led to some important clues regarding the identity of Active Oxygen Species and the mechanisms. There was a lack of protection by overproduction of SOD in the stroma, suggesting that superoxide is not accessible to dismutation by the stromal enzymes. Protection by glutathione reductase suggested that a soluble reductant has a limited chance to trap the species before it reacts with PS II RC. It was concluded (Tyystjarvi et al., 1999b) that much further work is required to understand the molecular mechanism of loss of PS II activity. H.Y.Yamamoto and his scholars have made several studies manipulating the levels of the enzymes of the xanthophyll cycle through transgenic techniques. Verhoeven et al., (2001) have investigated the effect of suppression of Z in tobacco plants with an antisense construct of VDE in growth chambers. Under short-term (2 or 3h) high light treatment, antisense plants had a greater reduction in Fv/Fm ratio relative to wild type, which implied a greater susceptibity to photoinhibition. In the long-term highlight stress experiment, the antisense plants had significant reduction in Fv/Fm. The authors concluded that XC-dependent energy dissipiation is critical for photoprotection in tobacco under excess light in the long term.
DOI link for Flachmann (1997) studied the PS II antennae composition under varying light conditions in tobacc o plants transformed with antisense echnique. An increase of P S II antenna size was observed under low irradiance and also higher LHC II content. The results also suggested that LHC II biogenesis is perhaps not controlled by transcription. The foregone account of different studies using transgenics have inmmensely helped by adding new dimension in our understanding of the structure and function of the photosystem core complexes and of the antennae systems related to both PS II and PS I. A fairly larg e number of studies have also been directed using transgenic technology to understand the process of photoinhibition. Tyystjarvi et al., (1999b) have made a study of photoinhibition of PS II in tobacco an d poplar plants. The tobacco cultivars were expressed with bacterial gov gene in the cytosol and Fe SOD gene from Arabidopsis thaliana rather in the chloroplast. The transformations were affected as an overexpression of glutathione reductase in tobacco and superoxide dismutase in poplar. This transformation resulted in the activities of glutathione reductase in tobacco leaves and superoxide dismutase in poplars were five to eight times higher than in the untransformed plants. The experiments of the authors (Tyystjarvi et al., (1999b) with the transformed plants have led to some important clues regarding the identity of Active Oxygen Species and the mechanisms. There was a lack of protection by overproduction of SOD in the stroma, suggesting that superoxide is not accessible to dismutation by the stromal enzymes. Protection by glutathione reductase suggested that a soluble reductant has a limited chance to trap the species before it reacts with PS II RC. It was concluded (Tyystjarvi et al., 1999b) that much further work is required to understand the molecular mechanism of loss of PS II activity. H.Y.Yamamoto and his scholars have made several studies manipulating the levels of the enzymes of the xanthophyll cycle through transgenic techniques. Verhoeven et al., (2001) have investigated the effect of suppression of Z in tobacco plants with an antisense construct of VDE in growth chambers. Under short-term (2 or 3h) high light treatment, antisense plants had a greater reduction in Fv/Fm ratio relative to wild type, which implied a greater susceptibity to photoinhibition. In the long-term highlight stress experiment, the antisense plants had significant reduction in Fv/Fm. The authors concluded that XC-dependent energy dissipiation is critical for photoprotection in tobacco under excess light in the long term.
Flachmann (1997) studied the PS II antennae composition under varying light conditions in tobacc o plants transformed with antisense echnique. An increase of P S II antenna size was observed under low irradiance and also higher LHC II content. The results also suggested that LHC II biogenesis is perhaps not controlled by transcription. The foregone account of different studies using transgenics have inmmensely helped by adding new dimension in our understanding of the structure and function of the photosystem core complexes and of the antennae systems related to both PS II and PS I. A fairly larg e number of studies have also been directed using transgenic technology to understand the process of photoinhibition. Tyystjarvi et al., (1999b) have made a study of photoinhibition of PS II in tobacco an d poplar plants. The tobacco cultivars were expressed with bacterial gov gene in the cytosol and Fe SOD gene from Arabidopsis thaliana rather in the chloroplast. The transformations were affected as an overexpression of glutathione reductase in tobacco and superoxide dismutase in poplar. This transformation resulted in the activities of glutathione reductase in tobacco leaves and superoxide dismutase in poplars were five to eight times higher than in the untransformed plants. The experiments of the authors (Tyystjarvi et al., (1999b) with the transformed plants have led to some important clues regarding the identity of Active Oxygen Species and the mechanisms. There was a lack of protection by overproduction of SOD in the stroma, suggesting that superoxide is not accessible to dismutation by the stromal enzymes. Protection by glutathione reductase suggested that a soluble reductant has a limited chance to trap the species before it reacts with PS II RC. It was concluded (Tyystjarvi et al., 1999b) that much further work is required to understand the molecular mechanism of loss of PS II activity. H.Y.Yamamoto and his scholars have made several studies manipulating the levels of the enzymes of the xanthophyll cycle through transgenic techniques. Verhoeven et al., (2001) have investigated the effect of suppression of Z in tobacco plants with an antisense construct of VDE in growth chambers. Under short-term (2 or 3h) high light treatment, antisense plants had a greater reduction in Fv/Fm ratio relative to wild type, which implied a greater susceptibity to photoinhibition. In the long-term highlight stress experiment, the antisense plants had significant reduction in Fv/Fm. The authors concluded that XC-dependent energy dissipiation is critical for photoprotection in tobacco under excess light in the long term.
ABSTRACT
Sun et al., (2001) have further extended the study of tobacco plants transformed with an antisense construct of VDE and the consequence of reduced XC activity on photoinhibition under field conditions. Antisense plants did not exhibit greater susceptibity to photoinhibition, in such circumstances. Their results indicated that the photoinhibition under field conditions is not dependent on the levels of Z and A. The authors have also stated that the antisense tobacco plants have a differential response to photoinhibition from the one shown by Arabidopsis NPQ1 mutants. The lack of photoinhibition under field conditions is presumably related to the characterstics of tobacco plants which are adapted to high light, unlike Aarbidopsis which is more of a shady plant.
