Photosynthesis is a pivotal process in plant physiology, and its regulation plays an important role in plant defense against biotic stress. Interactions with pathogens and pests often cause alterations in the metabolism of sugars and sink/source relationships. These changes can be part of the plant defense mechanisms to limit nutrient availability to the pathogens. In other cases, these alterations can be the result of pests manipulating the plant metabolism for their own benefit. The effects of biotic stress on plant physiology are typically heterogeneous, both spatially and temporarily. Chlorophyll fluorescence imaging is a powerful tool to mine the activity of photosynthesis at cellular, leaf, and whole-plant scale, allowing the phenotyping of plants. This review will recapitulate the responses of the photosynthetic machinery to biotic stress factors, from pathogens (viruses, bacteria, and fungi) to pests (herbivory) analyzed by chlorophyll fluorescence imaging both at the lab and field scale. Moreover, chlorophyll fluorescence imagers and alternative techniques to indirectly evaluate photosynthetic traits used at field scale are also revised.
The effect of viral infection on photosynthesis was investigated infected plants. The CP accumulation level was dependent upon both the post-infection time and the virus analyzed, but in Nicotiana benthamiana Gray plants infected with different strains of pepper and paprika mild mottle viruses (PMMoV independent of the CP itself since hybrid viruses did not behave as their parental viruses with the same CP, with and PaMMoV) and chimeric viral genomes derived from them. In both symptomatic and asymptomatic leaves of virus-respect to PSII inhibition, CP accumulation rates and OEC infected plants, photosynthetic electron transport in photosys-protein levels. Modulated chlorophyll (Chl) fluorescence and tem II (PSII) was reduced. In all cases analyzed, viraloxygen evolution measurements carried out in both types of infection affected the polypeptide pattern of the oxygen-evolv-leaves showed that the quantum yield of PSII electron transport was diminished in infected plants with respect to those of ing complex (OEC) in thylakoid membranes. The levels of control plants. The decrease in electron transport efficiency both the 24 and 16 kDa proteins were reduced to a differing extent when compared with the levels in healthy control. This was mainly caused by a reduction in the fraction of open loss of the OEC extrinsic proteins affected the oxygen evolu-reaction centers. The infected plants also showed a reduction tion rates of thylakoid membranes and leaves from infected in the efficiency of excitation capture in PSII by photoprotecplants. Additionally, viral coat protein (CP) was found associ-tive thermal dissipation of excess excitation energy. ated with the chloroplasts and the thylakoid membranes of the phenomenon under biotic stress, as is also observed under abiotic stress conditions. However, the mechanism of action of the viral infection upon PSII remains unclear (see Balachandran et al. 1997).Chlorophyll (Chl) fluorescence measurements show that the PSII photochemical efficiency was decreased by the viral infection (Hodgson et al. 1989, van Kooten et al. 1990, Balachandran and Osmond 1994, Balachandran et al. 1994a). Studies of imaging PSII fluorescence quenching (Balachandran et al. 1994b) also demonstrated that in the youngest, most susceptible leaves of tobacco plants systemically infected with tobbaco mosaic virus (TMV), distur-
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.