Decrease In CO2 Assimilation Rate Research Articles

Loss of peroxisomal NAD kinase 3 (NADK3) affects photorespiration metabolism in Arabidopsis

Nicotinamide adenine dinucleotides (NAD+ and NADP+) are electron mediators involved in various metabolic pathways. NADP(H) are produced by NAD kinase (NADK) through the phosphorylation of NAD(H). The Arabidopsis NADK3 (AtNADK3) is reported to preferentially phosphorylate NADH to NADPH and is localized in the peroxisome. To elucidate the biological function of AtNADK3 in Arabidopsis, we compared metabolites of nadk1, nadk2 and nadk3 Arabidopsis T-DNA inserted mutants. Metabolome analysis revealed that glycine and serine, which are intermediate metabolites of photorespiration, both increased in the nadk3 mutants. Plants grown for 6 weeks under short-day conditions showed increased NAD(H), indicating a decrease in the phosphorylation ratio in the NAD(P)(H) equilibrium. Furthermore, high CO2 (0.15%) treatment induced a decrease in glycine and serine in nadk3 mutants. The nadk3 showed a significant decrease in post-illumination CO2 burst, suggesting that the photorespiratory flux was disrupted in the nadk3 mutant. In addition, an increase in CO2 compensation points and a decrease in CO2 assimilation rate were observed in the nadk3 mutants. These results indicate that the lack of AtNADK3 causes a disruption in the intracellular metabolism, such as in amino acid synthesis and photorespiration.

Differential physiological performance of two Eucalyptus species and one hybrid under different imposed water availability scenarios

Eucalyptus forest reproductive material responded differently to the imposed water scenarios through different water resistance mechanisms. Eucalyptus is amongst the most planted genera in the world. The focus of this study was to evaluate the ability of different forest reproductive material to withstand the occurrence of drought under different possible climate scenarios, both experienced by plants in the field: a long-term water deficit period (WS) and a short-term water deficit period followed by recovery, in comparison with a well-watered condition. The performance of two Eucalyptus species (Eucalyptus globulus and Eucalyptus nitens) and one hybrid (Eucalyptus globulus × Eucalyptus cypellocarpa), under such conditions, was assessed through several morphological and physiological traits. Under prolonged water stress, E. globulus, which experienced the lowest water potential values, suffered a decrease in CO2 assimilation rates as a result of stomatal limitations that, together with high oxidative damage, led to growth impairment. It also exhibited the slowest recovery from a short-term water stress period. The hybrid reacted to the prolonged water stress period through an active antioxidant system which allowed a higher photosynthetic assimilation rate and overall growth. Though it experienced a decrease in CO2 assimilation rate, due to non-stomatal limitations, E. nitens was able to maintain its growth under a prolonged water deficit period. Furthermore, under short-term drought stress followed by recovery, E. nitens was able to completely recover its gas-exchange parameters and increase overall growth production conferring a physiological advantage under the tested conditions. Our data demonstrate that, under the experimentally imposed water stress scenario, plants have different adaptive mechanisms to cope with continuous water deficit and recovery after a short-term stress situation.

Effects of Mild and Severe Drought Stress on Photosynthetic Efficiency in Tolerant and Susceptible Barley (Hordeum vulgare L.) Genotypes

AbstractDrought stress is one of the most important abiotic factors which adversely affect growth, metabolism and yield of crops worldwide. The objective of this study was to determine the effects of drought stress on photosynthesis in barley and examine the differential responses of photosynthetic apparatus in relatively tolerant (Yousof) and susceptible (Morocco) barley genotypes. Plants were subjected to different levels of soil water availability including control, mild and severe drought stress. In both genotypes, drought stress led to decrease in chlorophylls, β‐carotene and stomatal conductance accompanied by decrease in CO2 assimilation rate. Significant increase in α‐tochoperol content was only observed in Yousof cultivar under drought stress. Initial slope and plateau phase of CO2 response curve of drought‐stressed plants as well as polyphasic chlorophyll a fluorescence transient curve (OJIP test) and fast fluorescence induction kinetics were influenced by drought stress. These parameters were more affected in Morocco cultivar by drought stress compare with Yousof. Drought stress also resulted in reduction of D1 protein content in both genotypes and accelerated photoinhibition process. Based on our results, stomatal conductance is the main factor limiting photosynthesis in Yousof genotype under mild drought stress. However, in Morocco, in addition to stomatal limitation, damage to photosystem II (PSII), reduced electron transport and carboxylation efficiencies were important parts of limitation in photosynthesis. Severe drought stress resulted in structural and biochemical impairment of light‐dependent reactions as well as carboxylation process of photosynthesis in both genotypes. Alpha‐tocopherol showed an important protective role against drought stress in Yousof cultivar as a relatively drought‐tolerant cultivar.

Analysis of the photosynthetic response induced by variation potential in geranium

Electrical signals (action and variation potentials) caused by environmental stimuli induce a number of physiological responses in plants including changes in photosynthesis; however, mechanisms of these changes remain unclear. We investigated the influence of the variation potential on photosynthesis in geranium (Pelargonium zonale) under different conditions (control, low external CO₂ concentration, and actinic light absence). The variation potential caused by lamina burning induced a reduction in photosynthesis (decreases in effective quantum yields of photosystem I and II, CO₂ assimilation rate, and stomatal conductance) in unstimulated leaves under control conditions. Changes in the majority of light-stage parameters (photosystem I and II quantum yields, coefficients of photochemical and non-photochemical quenching, quantum yield of non-photochemical energy dissipation in photosystem I due to donor-side limitation) were correlated with a decrease in CO₂ assimilation rate. The changes were similar to those caused by lowering [CO₂]; their magnitudes decreased both under low external CO₂ concentration and without actinic light. These results support the hypothesis that Calvin cycle inactivation plays a key role in photosynthetic response induced by electrical signals. However, a decrease in electron transport through the PSI acceptor side also induced by variation potential was not correlated with a decrease in the CO₂ assimilation rate and did not depend on the external CO₂ concentration or actinic light intensity. Thus, we suggest that there are two different mechanisms of light-stage inactivation induced by the variation potential in geranium: one strongly dependent on dark-stage inactivation and one weakly dependent on dark-stage inactivation.

The Photosynthetic Properties of Rice Leaves Treated with Low Temperature and High Irradiance

Photosynthetic characteristics in rice (Oryza sativa L.) leaves were examined after treatment with low temperature (15 degrees C) and high irradiance (1,500 micromol quanta m(-2) s(-1)). Decreases in quantum efficiencies in PSII (PhiPSII) and PSI (PhiPSI) and in the rate of CO2 assimilation were observed with a decrease in the maximal quantum efficiency of PSII (F(v)/F(m)) by simultaneous measurements of Chl fluorescence, P700+ absorbance and gas exchange. The decreases in PhiPSII were most highly correlated with those in CO2 assimilation. Although the initial (the activity immediately measured upon extraction) and total (the activity following pre-incubation with CO2 and Mg2+) activities of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Rubisco) decreased slightly, the maximal activity (the activity following treatment with SO4(2-)) of Rubisco remained almost constant. These results indicate that the decrease in CO2 assimilation rate with the decreasing F(v)/F(m) was not caused by a decrease in Rubisco activity but rather by a decrease in RuBP regeneration capacity which resulted from the decrease in the rate of the linear electron transport. On the other hand, the decrease in PhiPSI was very small and the ratio of PhiPSI to PhiPSII increased. The de-epoxidation state of xanthophyll cycle pigments also increased. Thus, the cyclic electron transport around PSI occurred in photoinhibited leaves.

Dark chilling increases glucose‐6‐phosphate dehydrogenase activity in soybean leaves

Available evidence suggests that the stress‐induced increase in the activity of glucose‐6‐phosphate dehydrogenase (G6PDH, EC 1.1.1.49), the key regulatory enzyme of the oxidative pentose phosphate pathway, might often be related to the presence of plant water deficit. The response of G6PDH to dark chilling in chilling sensitive plant species is still unknown. In this communication we report on this response and its dependence on the presence of chill‐induced drought stress. A chilling sensitive soybean (Glycine max L. Merr.) genotype was exposed to dark chilling of the entire plant (whole‐chilled) or only the shoots and leaves (shoot‐chilled). The development of chill‐induced drought stress upon illumination was quantified by measurement of proline and relative water content (RWC). Chill‐induced drought stress (decrease in RWC and increase in proline content) developed with time in whole‐chilled plants, but not in shoot‐chilled plants. The response of the above‐mentioned treatments on G6PDH activity in fully expanded leaves was assessed. In parallel, the effects on CO2 assimilation, PSII activity and chloroplast fructose‐1,6‐bisphosphatase (FBPase EC 3.1.3.11) and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco EC 4.1.1.39) activity were quantified. A decrease in CO2 assimilation rate, FBPase activity and ribulose‐1,5‐bisphosphate (RuBP) content was observed in whole‐chilled but not in shoot‐chilled plants. However, in shoot‐chilled plants regulation of diurnal PSII activity was altered. The increase in the activation state of NADP‐dependent malate dehydrogenase (NADP‐MDH EC 1.1.1.82) in shoot‐chilled plants suggests an increase in stromal redox state. Although the two different dark chilling treatments resulted in distinct physiological and biochemical effects, both induced an increase in foliar G6PDH activity, suggesting an important role of this enzyme during and following dark chilling stress, irrespective of the presence of chill‐induced drought stress.

Assimilation of CO2 , enzyme activation and photosynthetic electron transport in bean leaves, as affected by high light and ozone.

• Bean seedlings (Phaseolus vulgaris cv. Pinto) were grown in the greenhouse at a light intensity of 400µmolm-2 s-1 . When the primary leaf was fully expanded, plants were divided into four groups and subjected to one of the following treatments: light intensity of 400µmolm-2 s-1 and filtered air (control); light intensity of 400µmolm-2 s-1 and ozone (O3 ) (150nll-1 for 5h) (ozonated); light intensity of 1000µmolm-2 s-1 for 5h and filtered air (HL); and light intensity of 1000µmol m-2 s-1 and O3 (150nll-1 ) for 5h (HL+O3 ). • At the end of the treatments (HL and/or O3 ) a strong decrease in CO2 assimilation rate as well a decrease in stomatal conductance were observed, while no changes in intercellular CO2 concentration were recorded. In addition the Fv :Fm ratio (maximal quantum yield for PSII photochemistry) decreased in the stressed leaves (HL and/or O3 ), indicating photoinhibition, and they showed a corresponding increase in minimal fluorescence (F0 ), indicating a higher number of deactivating photosystem II (PSII) centres. • The maximum catalytic activity of the Benson-Calvin cycle enzymes, fructose-1,6-bisphosphate phosphatase (FBPase) and Rubisco, decreased following HL+O3 stress but activation was enhanced. A linear relation was found between activation state of NADP-malate dehydrogenase (MDH) and the flux of electrons through PSII and in HL+O3 -treated plants NADP-MDH activity decreased at high irradiance levels, indicating a limitation in linear electron flux.