Photoinhibition in a C4 plant, Zea mays L.: a minireview

Abstract

Light and oxygen are both essential to life but can also cause some damage to plant photosynthesis and productivity, particularly excess light in the presence of oxygen. This phenomenon is called photoinhibition, i.e. the photooxidative damage of photosystems due to excess light associated or not with abiotic stresses. To tolerate photoinhibition, the plant needs to be able to avoid or tolerate excess light or to repair the photodamage by maintaining the de novo D1 protein synthesis that is essential for PS II complex activity. When the electron transport of the photosystems is diminished because the use of final electron acceptors, ferredoxin or NADPH 2 , via the Calvin cycle is reduced, electrons from water photolysis are captured by O 2 forming ROS, which inhibits protein synthesis, even in C 4 plants. To tolerate excess light or repair photodamage under photoinhibitory conditions, several mechanisms exist to reduce ROS and/or maintain ATP production and use for protein synthesis and growth: the scavenging systems (reducing ROS activity), such as the xanthophyll (thermal dissipation of excitation energy) and ascorbate cycle (associated with the Mehler reaction, in the waterwater cycle) or the activity of antioxidants compounds, such as carotenoids; the maintenance of cyclic electron flow (only ATP production); and the photorespiration cycle (consuming reducing equivalents and ATP). Photoinhibition is a phenomenon that occurs in C 3 and C 4 plants, such as corn, under PPFD above 1,000 lmol m -2 s -1 , and photooxidative damage seems to be more accentuated in mesophyll chloroplasts than in bundle sheath agranal chloroplasts.

Water stress effects on chlorophyll fluorescence and chlorophyll content in sugarcane cultivars with contrasting tolerance

“…Therefore, it can be observed that Fv/Fm is strongly correlated with the physiological characteristic of genotype tolerance to water deficit. This is due to the fact that water is the major donor of electrons to photosystem II by means of the oxidation process; thus, a reduction in water content may decrease the electrochemical potential of ATP synthase and photosystem I, compromising the formation of ATP and NADPH, respectively, and negatively affecting the photosynthetic apparatus (PIMENTEL, 2014).…”

“…The intensity of the photoinhibition can be measured by the reduction of the potential quantum efficiency of photosystem (PS) II (Fv/Fm) (LONG et al, 1994). This index represents the energy transmitted to the PSI by the electron transport chain and is converted into chemical energy (PIMENTEL, 2014). The Fv/Fm ratio can vary within a range of 0.75 to 0.85 for normal plants in optimum conditions (KRAUSE;WEIS, 1991).…”

Photosynthetic Potential and Productivity of Common Beans under Herbicide Effect

“…Plants have some protective mechanisms to prevent severe damages to the photosynthetic apparatus, which include repairing and replacing D 1 proteins in the Reaction Centers of Photosystem II (PSII), until dissipation of excess light energy (Baker, 2008), as in the xanthophyll cycle, which seems to be one of the most important mechanisms of PSII excess energy dissipation, in the form of heat. In addition to these, other processes, such as the pseudocyclic photophosphorylation, the ascorbate glutathione cycle and the photorespiration, contribute to reduce the photoinhibitory effect, by the consumption of the NADPH 2 produced in photosystems (Pimentel, 2014). In the xanthophyll cycle, violaxanthin is epoxidized and reduced to zeaxanthin during the day under high PPFD and stresses, consuming part of the excess electrons in the photosystem, and at night, with a lower metabolism, zeaxanthin is gradually de-epoxidized to violaxanthin, thus reducing the photoinhibitory effect (Takahashi and Badger, 2011).…”

“…The analysis of the variables obtained by the emission of chlorophyll a fluorescence is already a well known technique, and is used in several work areas to discriminate between the effects of stress (Pimentel, 2014). Studies conducted to better understand the relationship between 3 these chlorophyll a fluorescence emission variables and the photosynthetic potential associated with the physiological conditions of the plant under study became frequent, due to the development and commercial availability of fast and low cost portable fluorometers, compared to other photosynthetic activity measuring equipments, which helped the use of this methodology in evaluations and in the selection of a large number of plants (Murchie and Lawson, 2013).…”

“…In the morning, plants normally present greater photosynthetic activity than in the hours with higher PPFD (Pimentel, 2006), starting from the middle of the day, because environmental stresses may occur, due to high temperature or high transpiration associated to a higher PPFD at that specific moment; thus, the photosynthetic activity may be reduced, and plants may or may not express their photosynthetic potential, depending on the intensity of the stress associated with high PPFD (Rohácek et al, 2008;Takahashi and Badger, 2011). Therefore, the lower the ΔF v /F m values of the day, the greater the photoinhibition associated with environmental or chemical stresses during that particular day (Pimentel, 2014). In this study, only the treatment with bentazon showed significant differences, with a reduction of mean ΔF v /F m value of the day to -0.532 at 0 DAA ( Figure 6), and a positive value on the day after the application of the herbicide.…”