We compared by chlorophyll (Chl) fluorescence imaging the effects of two strains of the same virus (Italian and Spanish strains of the Pepper mild mottle virus - PMMoV-I and-S, respectively) in the host plant Nicotiana benthamiana. The infection was visualized either using conventional Chl fluorescence parameters or by an advanced statistical approach, yielding a combinatorial set of images that enhances the contrast between control and PMMoV-infected plants in the early infection steps. Among the conventional Chl fluorescence parameters, the non-photochemical quenching parameter NPQ was found to be an effective PMMoV infection reporter in asymptomatic leaves of N. benthamiana, detecting an intermediate infection phase. The combinatorial imaging revealed the infection earlier than any of the standard Chl fluorescence parameters, detecting the PMMoV-S infection as soon as 4 d post-inoculation (dpi), and PMMoV-I infection at 6 dpi; the delay correlates with the lower virulence of the last viral strain. and M. Pineda ... [et al.].
We demonstrate the feasibility of assaying and predicting post-harvest damage in lemons by monitoring chlorophyll (Chl) fluorescence. Fruit quality was assayed using a commercial instrument that determines photosynthetic performance by imaging Chl fluorescence parameters under different irradiances. Images of Chl fluorescence from individual lemons reveal that photosynthesis is active throughout the post-harvest ripening process. Because photosynthesis is highly sensitive to biotic and abiotic stress, variations in Chl fluorescence parameters over the surface of a lemon fruit can be used to predict areas that will eventually exhibit visible damage. The technique is able to distinguish between mould-infected areas that eventually spread over the surface of the fruit, and damaged areas that do not increase in size during ripening. This study demonstrates the potential for using rapid imaging of Chl fluorescence in post-harvest fruit to develop an automated device that can identify and remove poor quality fruit long before visible damage appears. and L. Nedbal ... [et al.].
The sensitivity of marine algal biotest ISO 10253 to the photosystem 2 (PS2) herbicide diuron (DCMU) was determined. Using the diatom Phaeodactylum tricornutum, we found that the algal growth rate was reduced to 50 % of the control value (EC50) for ca. 200 nM DCMU. This value is too high to allow a practical application of the biotest for concentrations of the PS2 herbicides found in natural waters. The mechanisms causing the low sensitivity of the biotest to the PS2 herbicide were investigated by measuring parameters of photosynthetic apparatus in the diatom prior and during the biotest. The apparent dissociation constant for DCMU in P. tricornutum found by measurements of inhibition of oxygen evolution and of variable fluorescence was in the range 60-90 nM. This should lead to a much higher sensitivity of the biotest than found in our experiments. The low biotest sensitivity is caused by an acclimation to sub-lethal DCMU concentrations. The acclimation is manifested by the chlorophyll content per cell that is increasing with the DCMU concentration. During a prolonged exposure to sub-lethal herbicide concentrations, we observed also a selection of DCMU resistant organisms indicating that also an adaptation may decrease the test sensitivity. The biotest sensitivity may increase when the acclimation and adaptation are limited by shortening of the experiment duration. and J. Soukupová ... [et al.].