Insensitivity of Water-Oxidation and Photosystem II Activity in Tomato to Chilling Temperatures

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Impaired chloroplast function is responsible for nearly two-thirds of the inhibition of net photosynthesis caused by dark chilling in tomato (Lycopersicon esculentum Mill.). Yet the plant can eventually recover full photosynthetic capacity if it is rewarmed in darkness at high relative humidity. As a means of identifying potential sites of chilling injury in tomato, we monitored leaf protein synthesis in chilled plants during this rewarming recovery phase, since changes in the synthesis of certain proteins might be indicative of damaged processes in need of repair. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins pulse labeled with I35Slmethionine revealed discrete changes in the pattern of protein synthesis as a result of chilling. A protein of Mr = 27 kilodaltons (kD), abundantly synthesized by unchilled plants, declined to undetectable levels in chilled plants. Reillumination restored the synthesis of this protein in plants rewarmed for 8 hours. Peptide mapping analysis showed the 27 kD protein to be the major chlorophyll a/b binding protein of the photosystem II light-harvesting complex (LHCP-II). The identity of this protein was confirmed by its immunoprecipitation from leaf extracts by a monoclonal antibody specific for the major LHCP-II species. While chilling abolished the synthesis of the major LHCP-II species, it also induced the synthesis of an entirely new protein of M, = 35 kD. The protein was synthesized on cytoplasmic ribosomes, and twodimensional polyacrylamide gel electrophroesis showed it to exist as a single isoelectric species. This chilling-induced 35 kD protein is structurally distinct from the 27 kD LHCP-II and appears to be synthesized specifically in response to low temperature. While the 35 kD protein was found not to be associated with the chloroplast thylakoid membrane, chilling did cause selective changes in thylakoid membrane protein synthesis. The synthesis of two unidentified proteins, Mr = 14 and 41 kD, and the j-subunit of the chloroplast coupling factor were substantially reduced after chilling. These losses may provide clues as to the causes of the overall reduction in net photosynthesis caused by chilling.Plant species evolutionarily adapted to warm habitats are quite susceptible to injury by low, above-freezing temperatures (0 < T <1 2°C). For in darkness (26). While increased stomatal resistance accounts for some of the inhibition, the major portion of the decrease was due to direct impairment of chloroplast activity (26). Yet plants damaged by chilling in darkness can eventually recover full photosynthetic capacity if they are rewarmed in darkness at high RH (24). Presumably, the damaged biochemical processes are repaired under these conditions.Our research is directed toward identifying those elements that account for the susceptibility of chloroplast activity to chilling. Previous work has shown that dark chilling has vanishing little effect on water oxidation capacity (26), electron transfer reactions (20), or the regulation and activation...

Section: Discussioncontrasting

confidence: 64%

Changes in Protein Synthesis Induced in Tomato by Chilling

Cooper¹,

Ort²

1988

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“…Electron flow through PSII was measured spectrophotometrically by following the photoreduction of ferricyanide (420 nm) mediated by the lipophilic oxidant DAD,,X (20). The 2-ml reaction mixture (20 mm water was subsequently withheld (Fig.…”

Section: Methodsmentioning

confidence: 99%

Acclimation of Photosynthesis to Low Leaf Water Potentials

Matthews

Boyer²

1984

123

Photosynthesis is reduced at low leafwater potentials (*,) but repeated water deficits can decrease this reduction, resulting in photosynthetic acclimation. The contribution of the stomata and the chloroplasts to this acclimation is unknown. We evaluated stomatal and chloroplast contributions when soil-grown sunflower (Helianthus annuus L.) plants were subjected to water deficit pretreatments for 2 weeks. The relationship between photosynthesis and I,, determined from gas-exchange and isopiestic thermocouple psychometry, was shifted 3 to 4 bars towards lower '4's in pretreated plants. Leaf (2,32) and similarly reduce the sensitivity of stomata to low 1, (11,21). The acclimation of photosynthesis to these conditions in cotton (Gossypium hirsutum L.) plants was attributed to altered stomatal

“…The uppermost leaf on the plant that was almost fully expanded was enclosed in an assimilation chamber. The rate of light-saturated CO2 fixation was measured at 20°C in a closed compensating system at 300 ,lI/I or 1500 ,il/l ambient CO2 as described earlier (14).…”

mentioning

confidence: 99%

“…Total or gross photosynthesis was calculated by subtracting the rate of CO2 exchange in the light from the rate of dark respiration. The amount of incident radiation that was absorbed was calculated by correcting for the portion of light which was either reflected or transmitted as described previously (14). The measurements were performed in an atmosphere containing 21% 02 at 25°C and 90Yo RH.…”

mentioning

confidence: 99%

Comparison of Photosynthetic Performance in Triazine-Resistant and Susceptible Biotypes of Amaranthus hybridus

Ort¹,

Ahrens²,

Martín³

et al. 1983

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The rate of CO2 reduction in the S-triazine-resistant biotype of smooth pigweed (Amaranthus hybridus L.) was lower at all levels of irradiance than the rate of CO2 reduction in the susceptible biotype. The intent of this study was to determine whether or not the lower rates of CO2 reduction are a direct consequence of the same factors which confer triazine resistance. The quantum yield of CO2 reduction was 23 ± 2% lower in the resistant biotype of pigweed and the resistant biotype of pigweed had about 25% fewer active photosystem II centers on both a chlorophylH and leaf area basis. This quantum inefficiency of the resistant biotype can be accounted for by a decrease in the equilibrium constant between the primary and secondary quinone acceptors of the photosystem II reaction centers which in turn would lead to a higher average level of reduced primary quinone acceptor in the resistant biotype. Thus, the photosystem II quantum inefficiency of the resistant biotype appears to be a direct consequence of those factors responsible for triazine resistance but a caveat to this conclusion is discussed. The effects of the quantum inefficiency of photosystem II on CO2 reduction should be overcome at high light and therefore cannot account for the lower light-saturated rate of CO2 reduction in the resistant biotype. Chloroplast lameliar membranes isolated from both triazine-resistant and triazine-susceptible pigweed support equivalent rates of whole chain electron transfer and these rates are sufficient to account for the rate of light-saturated CO2 reduction. This observation shows that the slower transfer of electrons from the primary to the secondary quinone acceptor of photosystem II, a trait which is characteristic of the resistant biotype, is nevertheless still more rapid than subsequent reactions of photosynthetic CO2 reduction. Thus, it appears that the lower rate of light-saturated CO2 reduction of the resistant biotype is not limited by electron transfer capacity and therefore is not a direct consequence of those factors which confer triazine resistance.As many as one-half of all commercially available herbicides used in agriculture act by interfering with photosynthetic electron transfer reactions. The margin of selectivity of many of these herbicides between the crop and unwanted plant species is disappointingly low, although the metabolic detoxification of triazines by corn is an exception of immense economic importance. In recent years, dramatically lower sensitivities of photosynthesis to S-triazine herbicides have appeared in populations of numerous weed species growing on agricultural lands (for review, see 16). Investigations into the biochemical basis for the lower sensitivity of these weeds to triazine herbicides have clearly established that the mode of resistance is at the level of the interaction of the herbicide with the photosynthetic electron transport chain (16).Maternal inheritance (9,12) of triazine resistance indicates control by a chloroplast rather than a nuclear gene(s). The implic...