Transgenic tobacco plants expressing antisense ferredoxin‐NADP(H) reductase transcripts display increased susceptibility to photo‐oxidative damage

Abstract

SummaryFerredoxin-NADP(H) reductase (FNR) catalyses the ®nal step of the photosynthetic electron transport in chloroplasts. Using an antisense RNA strategy to reduce expression of this¯avoenzyme in transgenic tobacco plants, it has been demonstrated that FNR mediates a rate-limiting step of photosynthesis under both limiting and saturating light conditions. Here, we show that these FNR-de®cient plants are abnormally prone to photo-oxidative injury. When grown under autotrophic conditions for 3 weeks, specimens with 20±40% extant reductase undergo leaf bleaching, lipid peroxidation and membrane damage. The magnitude of the effect was proportional to the light intensity and to the extent of FNR depletion, and was accompanied by morphological changes involving accumulation of aberrant plastids with defective thylakoid stacking. Damage was initially con®ned to chloroplast membranes, whereas Rubisco and other stromal proteins began to decline only after several weeks of autotrophic growth, paralleled by partial recovery of NADPH levels. Exposure of the transgenic plants to moderately high irradiation resulted in rapid loss of photosynthetic capacity and accumulation of singlet oxygen in leaves. The collected results suggest that the extensive photo-oxidative damage sustained by plants impaired in FNR expression was caused by singlet oxygen building up to toxic levels in these tissues, as a direct consequence of the over-reduction of the electron transport chain in FNR-de®cient chloroplasts.

Singlet Oxygen Is the Major Reactive Oxygen Species Involved in Photooxidative Damage to Plants

“…In tobacco (Nicotiana tabacum), a pathogeninduced mitogen-activated protein kinase cascade disrupts chloroplast metabolism and leads to a rapid shutdown of CO 2 fixation, a phenomenon that is expected to favor light-dependent excess excitation energy conditions in thylakoids and ROS production (Liu et al, 2007). It is also worth mentioning that compromised linear electron transport in transgenic tobacco plants with reduced ferredoxin-NADP(H) reductase levels also led to increased generation of 1 O 2 , eventually followed by cell death (Palatnik et al, 2003). Apparently, environmental stresses that initiate cell death programs converge at halted chloroplast metabolism.…”

Transgenic Tobacco Plants Overexpressing Chloroplastic Ferredoxin-NADP(H) Reductase Display Normal Rates of Photosynthesis and Increased Tolerance to Oxidative Stress

“…Plants Accumulating FNR Display Increased Tolerance to Photooxidative Damage and Redox-Cycling Herbicides FNR-deficient plants were highly sensitive to photoinactivation, undergoing leaf bleaching, lipid peroxidation, and membrane damage even under moderate irradiation (Palatnik et al, 2003). The magnitude of the effect was directly dependent on the light intensity and the extent of FNR depletion.…”

“…Plants containing 20% to 70% of the reductase present in nontransformed siblings displayed growth arrest, chlorophyll (chl) degradation, and impaired CO 2 uptake. They were also abnormally prone to photooxidative damage (Palatnik et al, 2003). Control analysis revealed that FNR mediates a rate-limiting step of photosynthesis under both limiting and saturating light conditions (Hajirezaei et al, 2002), raising the possibility that overexpression of this flavoprotein could stimulate photosynthesis and ultimately lead to increased biomass production.…”

Photosynthetic Redox Imbalance Governs Leaf Sectoring in theArabidopsis thalianaVariegation Mutantsimmutans,spotty,var1, andvar2

“…Furthermore, tobacco (Nicotiana tabacum) plants deficient in ferredoxin-NADP(H) reductase exhibit a yellow-green phenotype due to the overreduction of the intersystem PET chain. The extent of this phenotype is directly dependent upon the irradiance to which the plants are exposed (Palatnik et al, 2003). Consequently, it has been suggested that the chloroplast has a dual role.…”