RESUMO
The two cDNAs coding for the cytosolic (cyt) and the chloroplast-located (chl) Cu,Zn superoxide dismutases (SODs) of tomato (Perl-Treves et al. 1988) were cloned into respective binary vectors and mobilized into Agrobacterium strains. Potato tuber discs were infected with either of the two agrobacterial strains and cultured on selective medium containing kanaymcin. The integration of either of the cyt or the chl SOD transgenes was verified by Southern-blot hybridization. The enzymatic activity of the additional tomato chl Cu,Zn SOD could be distinguished from endogenous SOD activity since the latter isozyme migrated faster on SOD-activity gels. Several transgenic potato lines harboring either the cyt or the chl SOD genes of tomato showed elevated tolerance to the superoxide-generating herbicide paraquat (methyl viologen). After exposure of shoots to paraquat, tolerance was recorded either by scoring symptoms visually or by measurements of photosynthesis using the photoacoustic method. Root cultures from transgenic lines that harbored the additional cyt Cu,Zn SOD gene of tomato were tolerant to methyl viologen up to 10(-5) M; a lower tolerance was recorded in roots of transgenic lines that expressed the additional chl Cu,Zn SOD of tomato.
RESUMO
Energy storage measurements by modulated photothermal radiometry (PTR) were carried out on intact leaves to assess the value of the PTR method for photosynthesis research. In particular, correlations to the redox state of P700 under various conditions were examined. PTR monitors modulated light conversion to heat by sensing the resulting modulated infra-red radiation emitted from the leaf. It is, therefore, a complementary method to photoacoustics for estimating energy storage and its time variation, particularly under controlled leaf atmosphere.With modulated light-1 (λ>690 nm) the energy storage approached zero and P700 was maximally oxidized. When background light of shorter wavelength (λ<690 nm-light-2) was added, energy storage momentarily increased (a manifestation of Emerson enhancement) while P700 was reduced. The values of both parameters varied as a function of the background light intensity, keeping a mutual linear relationship. Following the initial change, there was a slow reversal transient of P700 oxidation with a parallel decrease in energy storage. Temporal correlation to P700 redox state after dark adaptation was observed also for the energy storage measured in modulated light 2 when combined with background actinic light of medium intensity (about 50 W m(2)). Under these circumstances P700 was almost totally oxidized initially and then gradually reduced while energy storage was initially low and then increased parallel to P700 reduction.A comparison between the maximum energy storage in modulated light 1, enhanced by background light 2, to the energy storage with short wavelength light (where light tends to be more evenly distributed) indicates a comparable contribution to energy storage from each active photosystem. The above experiments indicate that energy storage contribution from PS I is directly related to the extent of openness of its reaction-centers.While some aspects of the data call for more experimentation, these experiments already establish PTR as a valuable method to monitor photosynthetic energy storage activity in vivo, particularly when used simultaneously with other non-invasive methods.
