Dark Chilling Research Articles

The Effect Of Ultraviolet Light Treatment In Extend Shelf Life And Preserve The Quality of Strawberry (Fragaria x ananassa) cv. Festival

Strawberry (Fragaria x ananassa) is a highly perishable product and rarely to be kept for more than 7 days. Cold chain system is the only methods apply in Malaysia strawberry industry to prolong the shelf life and preserve the quality of strawberry. UV light treatment proved to be effective in inhibit microbial loads and delay ripening process of fruit products where short wavelength (254 nm) ultraviolet-C was proved in keeping the freshness and quality of fruits or vegetables. This experiment was conducted to determine the effect of UV-C irradiation on extending shelf life and to determine the optimum radiation intensity of UV-C treatment on postharvest quality of treated strawberry. A total of 399 of strawberries cv. Festival were harvested in red colour with maturity stage of >80 – 85% from Cameron Highlands’s strawberry farm. The strawberries were exposed to different doses (0, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 kJ/m2) of ultraviolet-C (254nm, UV-C) radiation. The treated strawberries were randomly placed in the polystyrene trays and stored in the dark chilling room at -5Cº for 9 days. The significant differences were found when the highest level of dosage was applied. UV-C treated strawberries with the highest doses (1.0 kJ/mº) are significantly firmer (0.557N), higher total soluble solids content (7.5 ºBrix) and ascorbic acid contain (0.518mg/ml) on day 9 (p

Strigolactones positively regulate chilling tolerance in pea and in Arabidopsis.

Strigolactones (SL) fulfil important roles in plant development and stress tolerance. Here, we characterized the role of SL in the dark chilling tolerance of pea and Arabidopsis by analysis of mutants that are defective in either SL synthesis or signalling. Pea mutants (rms3, rms4, and rms5) had significantly greater shoot branching with higher leaf chlorophyll a/b ratios and carotenoid contents than the wild type. Exposure to dark chilling significantly decreased shoot fresh weights but increased leaf numbers in all lines. Moreover, dark chilling treatments decreased biomass (dry weight) accumulation only in rms3 and rms5 shoots. Unlike the wild type plants, chilling-induced inhibition of photosynthetic carbon assimilation was observed in the rms lines and also in the Arabidopsis max3-9, max4-1, and max2-1 mutants that are defective in SL synthesis or signalling. When grown on agar plates, the max mutant rosettes accumulated less biomass than the wild type. The synthetic SL, GR24, decreased leaf area in the wild type, max3-9, and max4-1 mutants but not in max2-1 in the absence of stress. In addition, a chilling-induced decrease in leaf area was observed in all the lines in the presence of GR24. We conclude that SL plays an important role in the control of dark chilling tolerance.

Anionic Cerium Oxide Nanoparticles Protect Plant Photosynthesis from Abiotic Stress by Scavenging Reactive Oxygen Species.

Plant abiotic stress leads to accumulation of reactive oxygen species (ROS) and a consequent decrease in photosynthetic performance. We demonstrate that a plant nanobionics approach of localizing negatively charged, sub-11 nm, spherical cerium oxide nanoparticles (nanoceria) inside chloroplasts in vivo augments ROS scavenging and photosynthesis of Arabidopsis thaliana plants under excess light (2000 μmol m-2 s-1, 1.5 h), heat (35 °C, 2.5 h), and dark chilling (4 °C, 5 days). Poly(acrylic acid) nanoceria (PNC) with a hydrodynamic diameter (10.3 nm)-lower than the maximum plant cell wall porosity-and negative ζ-potential (-16.9 mV) exhibit significantly higher colocalization (46%) with chloroplasts in leaf mesophyll cells than aminated nanoceria (ANC) (27%) of similar size (12.6 nm) but positive charge (9.7 mV). Nanoceria are transported into chloroplasts via nonendocytic pathways, influenced by the electrochemical gradient of the plasma membrane potential. PNC with a low Ce3+/Ce4+ ratio (35.0%) reduce leaf ROS levels by 52%, including hydrogen peroxide, superoxide anion, and hydroxyl radicals. For the latter ROS, there is no known plant enzyme scavenger. Plants embedded with these PNC that were exposed to abiotic stress exhibit an increase up to 19% in quantum yield of photosystem II, 67% in carbon assimilation rates, and 61% in Rubisco carboxylation rates relative to plants without nanoparticles. In contrast, PNC with high Ce3+/Ce4+ ratio (60.8%) increase overall leaf ROS levels and do not protect photosynthesis from oxidative damage during abiotic stress. This study demonstrates that anionic, spherical, sub-11 nm PNC with low Ce3+/Ce4+ ratio can act as a tool to study the impact of oxidative stress on plant photosynthesis and to protect plants from abiotic stress.

Amelioration of oxidative damage in Solanum melongena seedlings by 24-epibrassinolide during chilling stress and recovery

The effects of foliar application of 24-epibrassinolide (EBR) on chlorophyll content, oxidative damage, and antioxidant capacity in eggplant (Solanum melongena L.) seedlings during a short-term chilling stress and subsequent recovery were investigated. The eggplant seedlings pretreated with 0.1 μM EBR were exposed to 5 °C for 12 h in the dark and then recovered under a normal temperature for another 12 h. The results show that EBR alleviated a chilling-induced oxidative stress reflected by a decrease in malondialdehyde and H2O2 content, O2 ·− production rate, and an increase in chlorophyll content and activities of superoxide dismutase, guaicol peroxidase, and catalase. The EBR pretreatment also promoted activities of ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase, as well as the accumulation of ascorbic acid (AsA) and glutathione (GSH) involved in the AsA-GSH cycle. Moreover, after the12 h recovery, EBR plus chilling treated leaves showed no significant changes in content of MDA and chlorophyll a, lower reactive oxygen species (ROS) content, and greater activities of AsA-GSH cycle enzymes than in seedlings only chilled. The results suggest that EBR alleviated an oxidative damage caused by the dark chilling stress and accelerated a recovery rate mainly through increasing the ROS scavenging system including the AsA-GSH cycle.

Inhibition of photosystem II activities in soybean (Glycine max) genotypes differing in chilling sensitivity

Due to chilling sensitivity, minimum night temperatures represent the main constraint in soybean production in South Africa. In vivo quantification of photosystem II (PSII) function by direct chlorophyll fluorescence revealed that dark chilling (8°) inhibited PSII function in the extreme chill sensitive genotype, Java 29 (JAs) mainly by deactivating reaction centers and inhibiting the conversion of excitation energy to electron transport and electron transfer from reduced plastoquinone to the PSI end electron acceptors. Further analysis of the normalized fast fluorescence transients, revealed that in JAs, upon dark chilling, disengagement of the oxygen evolution complex (ΔVK band) occurred which coincided with a concomitant decrease in O2 evolution measured in vitro. The chilling resistant Maple Arrow (MAr), though one night cold stress lead to a decrease in fluorescence emission at 2ms (−ΔVJ band) indicating a decrease in the QA− concentration due to cold-induced slow-down of electron donation from P680, however showed clear signs of recovery after the second and third cold nights. The moderate chill sensitive genotype, Fiskeby V (FBm) responded in a fashion intermediate to above-mentioned extremes. A second experiment showed that in JAs the inhibitory effect increased with increasing time of exposure to light following dark chilling. Our data demonstrated that significant differences exist in the cold tolerance of different soybean genotypes: (a) In respect to activity criteria, expressed by the quantum yields for primary photochemistry φPo=TRo/ABS, for electron transport from photosystem II to photosystem I as φEo=ETo/ABS and the efficiency, φRo=REo/ABS, to reduce the end electron acceptors of photosystem I up to NADP; (b) In respect to stability criteria, dependent on structure and conformation, such as the capability of energetic cooperativity (grouping) among photosynthetic units quantified by the grouping probability for exciton movements within the energetically connected group of entire photosynthetic units. Therefore analyzing the O-J-I-P fluorescence transient according to the JIP-test offers a practical and sensitive in vivo screening test for dark chilling tolerance in soybean.

短期夜间低温胁迫对秋茄幼苗碳氮代谢及其相关酶活性的影响

The frequency,duration and intensity of extreme cold events have been hypothesized to explain the current latitudinal limits of mangrove distribution. At present,Kandelia obovata is the major mangrove species for forestation on the southeast coast of China,whose northern distribution boundary transplanted is in Yueqing county( 28°25'N). Therefore, the incidence of extreme cold events is likely to be a factor limiting mangrove survival ratio. Kandelia obovata seedling grown in a controlled-environment chamber equipped were exposed to two different night temperature regimes:( low temperature treatment)-2℃ and( control) 20℃ for 12 h. During the day,temperature were maintained in both treatments at a minimum of 5 ℃ and a maximum of 25 ℃ for 4 h. Our objective was to investigate the possible physiological mechanisms of Kandelia obovata in responses to the short-term chilling 16 hours. Kandelia obovata seedling were cultivated in the illuminating incubator to study the effects of short-term dark chilling on photosynthetic characteristic,photosynthetic pigment contents,antioxidation system,cell membrane permeability and involved activities of enzymes in carbon and nitrogen metabolism. The results obtained are as follows:( 1) The leaf net photosynthetic rate( Pn),stomatal conductance( Gs) and stomatatal limitation( Ls) of Kandelia obovata were significantly decreased at low temperature 16 h,while leaf intercellular CO 2 concentration was increased.( 2) The contents of chlorophyll,carotenoids,and Chl a / Chl b ratio in leaf had no significantly changes at low temperature less than 8 h,whereas leaf Car / Chl ratio was significantly improved. In addition,photosynthetic pigment contents were decreased at low temperature between 12 h and 16 h.( 3) The leaf total soluble sugars was increased during low temperature 16 h,while sucrose content,sucrose synthase( SS) and sucrose phosphate synthase( SPS) activities were decreased after low temperature 12 h.( 4) The contents of soluble protein and free amino acid and carboxypeptidase activity in leaf were increased during low temperature 16 h,while endopeptidase activity in leaf begun to drop at low temperature 8 h.( 5) During low temperature 16 h,the relative conductivity and malondialdehyde( MDA) content in leaf were increased,while activity of POD was decreased,especially in dark. Also, low temperature both 4 h and 16 h treatments suppressed leaf superoxide dismutase( SOD) activity. These results demonstrate that non-stomatal restriction was cause for reduced Kandelia obovata photosynthesis at low temperature 16 h, which was mainly associated with reduced photosynthetic pigment and depressed antioxidant enzyme activity. Moreover, short-term low night temperature restrained leaf carbon and nitrogen metabolic self-regulation in Kandelia obovata by affecting activities of SS,SPS,endopeptidase and carboxypeptidase.

High Root Temperature Blocks Both Linear and Cyclic Electron Transport in the Dark During Chilling of the Leaves of Rice Seedlings

The most photosynthetically active leaves of rice seedlings were severely damaged when shoots but not roots were chilled (10°C/25°C, respectively), but no such injury was observed when the whole seedling was chilled (10°C/10°C). To elucidate the mechanisms, we compared the photosynthetic characteristics of the seedlings during the dark chilling treatments. Simultaneous analyses of Chl fluorescence and the change in absorbance of P700 showed that electron transport almost disappeared in both PSII and PSI in the 10°C/25°C leaves, whereas the electron transport rate in PSI in the 10°C/10°C leaves was similar to or higher than that in non-chilled control leaves. Light-induced non-photochemical quenching in PSII was inhibited in the 10°C/25°C leaves, occurring at only half the level in the 10°C/10°C leaves, whereas non-light-induced non-photochemical quenching remained high in the 10°C/25°C leaves. The light induction of Chl a fluorescence (OJIP curves) in the 10°C/25°C leaves was similar to that in leaves treated with DCMU. The fluorescence decay after a single turnover saturating flash in the 10°C/25°C leaves was much slower than in the 10°C/10°C leaves. In vivo analyses of the 550-515 nm difference signal indicated decreased formation of a proton gradient across the thylakoid membrane and decreased zeaxanthin formation in the 10°C/25°C leaves. Our results suggest that electron transport was blocked between Q(A) and Q(B) in the dark 10°C/25°C leaves, but without irreversible damage to the components of this system. The consequent light-dependent losses of electron transport, proton gradient formation across the thylakoids and thermal dissipation may therefore be responsible for the visible injury.

Effects on both the roots and shoots of soybean during dark chilling determine the nature and extent of photosynthesis inhibition

The relative contribution of low soil and air temperatures towards the overall inhibition of photosynthesis in soybean is still unclear. The mechanisms involved in the dark chilling-induced inhibition of photosynthesis were explored further in a chilling tolerant (Highveld Top) and sensitive (PAN809) soybean genotype in experiments where low soil temperatures were present (whole plant chilling, WPC) or absent (shoot-localised chilling, SC). Initially (after three nights of chilling) both the WPC and SC treatments induced the same symptoms in PAN809. These symptoms could thus be ascribed to chilling stress effects on the shoots. Typical symptoms included reduced CO 2 assimilation capacity, inhibition of photosystem II function and lower chloroplast fructose-1,6-bisphosphatase (cFBPase) and sucrose-phosphate-synthase (SPS) activity. When the nodulated root systems of PAN809 were also exposed to low temperatures (WPC treatment), additional constraints gradually developed, which were not observed in Highveld Top. Novel evidence is provided showing that the response in PAN809 is influenced by whether whole-plant or shoot-localised dark chilling occurs and that cFBPase is specifically targeted resulting in severe inhibition of CO 2 assimilation capacity.

Dorsoventral variations in dark chilling effects on photosynthesis and stomatal function in Paspalum dilatatum leaves.

The effects of dark chilling on the leaf-side-specific regulation of photosynthesis were characterized in the C4 grass Paspalum dilatatum. CO2- and light-response curves for photosynthesis and associated parameters were measured on whole leaves and on each leaf side independently under adaxial and abaxial illumination before and after plants were exposed to dark chilling for one or two consecutive nights. The stomata closed on the adaxial sides of the leaves under abaxial illumination and no CO2 uptake could be detected on this surface. However, high rates of whole leaf photosynthesis were still observed because CO2 assimilation rates were increased on the abaxial sides of the leaves under abaxial illumination. Under adaxial illumination both leaf surfaces contributed to the inhibition of whole leaf photosynthesis observed after one night of chilling. After two nights of chilling photosynthesis remained inhibited on the abaxial side of the leaf but the adaxial side had recovered, an effect related to increased maximal ribulose-1,5-bisphosphate carboxylation rates (Vcmax) and enhanced maximal electron transport rates (Jmax). Under abaxial illumination, whole leaf photosynthesis was decreased only after the second night of chilling. The chilling-dependent inhibition of photosynthesis was located largely on the abaxial side of the leaf and was related to decreased Vcmax and Jmax, but not to the maximal phosphoenolpyruvate carboxylase carboxylation rate (Vpmax). Each side of the leaf therefore exhibits a unique sensitivity to stress and recovery. Side-specific responses to stress are related to differences in the control of enzyme and photosynthetic electron transport activities.

Novel insights into the inhibition of symbiotic nitrogen fixation by dark chilling in soybean root nodules

Novel insights into the inhibition of symbiotic nitrogen fixation by dark chilling in soybean root nodules

Regulation of respiration and the oxygen diffusion barrier in soybean protect symbiotic nitrogen fixation from chilling-induced inhibition and shoots from premature senescence.

Symbiotic nitrogen fixation is sensitive to dark chilling (7 degrees C-15 degrees C)-induced inhibition in soybean (Glycine max). To characterize the mechanisms that cause the stress-induced loss of nodule function, we examined nodule structure, carbon-nitrogen interactions, and respiration in two soybean genotypes that differ in chilling sensitivity: PAN809 (PAN), which is chilling sensitive, and Highveld Top (HT), which is more chilling resistant. Nodule numbers were unaffected by dark chilling, as was the abundance of the nitrogenase and leghemoglobin proteins. However, dark chilling decreased nodule respiration rates, nitrogenase activities, and NifH and NifK mRNAs and increased nodule starch, sucrose, and glucose in both genotypes. Ureide and fructose contents decreased only in PAN nodules. While the chilling-induced decreases in nodule respiration persisted in PAN even after return to optimal temperatures, respiration started to recover in HT by the end of the chilling period. The area of the intercellular spaces in the nodule cortex and infected zone was greatly decreased in HT after three nights of chilling, an acclimatory response that was absent from PAN. These data show that HT nodules are able to regulate both respiration and the area of the intercellular spaces during chilling and in this way control the oxygen diffusion barrier, which is a key component of the nodule stress response. We conclude that chilling-induced loss of symbiotic nitrogen fixation in PAN is caused by the inhibition of respiration coupled to the failure to regulate the oxygen diffusion barrier effectively. The resultant limitations on nitrogen availability contribute to the greater chilling-induced inhibition of photosynthesis in PAN than in HT.

Cysteine proteinases regulate chloroplast protein content and composition in tobacco leaves: a model for dynamic interactions with ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) vesicular bodies

The roles of cysteine proteinases (CP) in leaf protein accumulation and composition were investigated in transgenic tobacco (Nicotiana tabacum L.) plants expressing the rice cystatin, OC-1. The OC-1 protein was present in the cytosol, chloroplasts, and vacuole of the leaves of OC-1 expressing (OCE) plants. Changes in leaf protein composition and turnover caused by OC-1-dependent inhibition of CP activity were assessed in 8-week-old plants using proteomic analysis. Seven hundred and sixty-five soluble proteins were detected in the controls compared to 860 proteins in the OCE leaves. A cyclophilin, a histone, a peptidyl-prolyl cis-trans isomerase, and two ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activase isoforms were markedly altered in abundance in the OCE leaves. The senescence-related decline in photosynthesis and Rubisco activity was delayed in the OCE leaves. Similarly, OCE leaves maintained higher leaf Rubisco activities and protein than controls following dark chilling. Immunogold labelling studies with specific antibodies showed that Rubisco was present in Rubisco vesicular bodies (RVB) as well as in the chloroplasts of leaves from 8-week-old control and OCE plants. Western blot analysis of plants at 14 weeks after both genotypes had flowered revealed large increases in the amount of Rubisco protein in the OCE leaves compared to controls. These results demonstrate that CPs are involved in Rubisco turnover in leaves under optimal and stress conditions and that extra-plastidic RVB bodies are present even in young source leaves. Furthermore, these data form the basis for a new model of Rubisco protein turnover involving CPs and RVBs.

The role of low soil temperature in the inhibition of growth and PSII function during dark chilling in soybean genotypes of contrasting tolerance

Dark chilling affects growth and yield of warm-climate crops such as soybean [Glycine max (L.) Merr.]. Several studies have investigated chilling-stress effects on photosynthesis and other aspects of metabolism, but none have compared effects of whole-plant chilling (WPC; shoots and roots) with that of aboveground chilling in legumes. This is important because low root temperatures might induce additional constraints, such as inhibition of N(2) fixation, thereby aggravating chilling-stress symptoms. Effects of dark chilling on PSII, shoot growth, leaf ureide content and photosynthetic capacity were studied in two soybean genotypes, Highveld Top (chilling tolerant) and PAN809 (chilling sensitive), in experiments comparing effects of WPC with that of shoot chilling (SC). Both treatments inhibited shoot growth in PAN809 but not Highveld Top. Also, WPC in PAN809 caused a decrease in leaf ureide content followed by severe chlorosis and alterations in O-J-I-P fluorescence-rise kinetics, distinct from SC. A noteworthy difference was the appearance of a Delta K peak in the O-J-I-P fluorescence rise in response to WPC. These genotypic and treatment differences also reflected in the degree of inhibition of CO(2) assimilation rates. The appearance of a Delta K peak, coupled with growth inhibition, reduced ureide content, chlorosis and lower CO(2) assimilation rates, provides mechanistic information about how WPC might have aggravated chilling-stress symptoms in PAN809. We introduce a model explaining how chilling soil temperatures might trigger N-limitation in sensitive genotypes and how characteristic changes in O-J-I-P fluorescence-rise kinetics are linked to changes in carbon and nitrogen metabolism.

Biochemical changes in soybean root nodules during development and senescence — effects of dark chilling

Biochemical changes in soybean root nodules during development and senescence — effects of dark chilling

Effects of dark chilling on components of Calvin cycle metabolism in soybean genotypes of contrasting chilling tolerance

Effects of dark chilling on components of Calvin cycle metabolism in soybean genotypes of contrasting chilling tolerance

Dark chilling lowers the content and catabolism of ureides in soybean leaves: Long-term effects on nitrogen status and vegetative growth

Dark chilling lowers the content and catabolism of ureides in soybean leaves: Long-term effects on nitrogen status and vegetative growth

Ranking of dark chilling tolerance in soybean genotypes probed by the chlorophyll a fluorescence transient O-J-I-P

In the experiments reported in this paper, we demonstrate how the chlorophyll a fluorescence transient O-J-I-P can be utilised in screening for dark chilling tolerance in large numbers of soybean [ Glycine max (L.) Merr.] genotypes. Thirty South African soybean genotypes of unknown chilling tolerance, and two foreign genotypes of well known, but contrasting chilling tolerance, were grown in growth chambers under rigorously controlled environmental conditions. Plants were dark chilled (6 °C) for seven consecutive nights but kept at normal day temperatures (26 °C). Root zone temperatures were kept at 20 °C to minimise the occurrence of chill-induced drought stress. Before the end of each night of dark chilling chlorophyll a fluorescence transients were recorded in fully dark-adapted attached leaves of control and dark chilled plants. The recorded chlorophyll a fluorescence transients were analysed by the so-called JIP-test that translates stress-induced alterations in these transients to changes in biophysical parameters quantifying the energy flow through photosystem II (PSII). The performance index (PI ABS), a multi-parametric expression that combines the three main functional steps taking place in PSII (light energy absorption, excitation energy trapping, and conversion of excitation energy to electron transport), was used as measure of dark chilling tolerance. Large genotypic differences in the extent by which dark chilling affected the shape of the O-J-I-P fluorescence transients, and thus the PI ABS, were observed. Elaboration of the PI ABS resulted in the formulation of a novel parameter, the so-called chill factor index (CFI), capable of revealing large differences in dark chilling response among the genotypes. The CFI of the two reference genotypes, Maple Arrow (chilling tolerant) and Java 29 (chilling sensitive) correlated with their known difference in chilling tolerance. We used the CFI to rank the 30 genotypes according to dark chilling tolerance and identified five genotypes with comparable dark chilling response to Maple Arrow under experimental conditions that excluded low root temperatures.

Reduction of dark chilling stress in N-fixing soybean by nitrate as indicated by chlorophyll a fluorescence kinetics.

Sub-optimal night temperatures below 15 degrees C (dark chilling) frequently reduce soybean [Glycine max (L.) Merrill] production. Nitrate application is known to alleviate some of the negative effects of low root zone temperatures, probably by counteracting the inhibition caused by decreased symbiotic nitrogen fixation (SNF). Under field conditions, however, dark chilling is frequently not accompanied by low root zone temperatures. The possibility that nitrate might increase dark-chilling tolerance under these conditions is still largely unexplored. In addition to quantifying vegetative development by means of the plastochron index, O-J-I-P (O-I(1)-I(2)-P) chlorophyll a fluorescence transients were recorded in soybean genotypes of contrasting chilling tolerance during and following exposure to dark chilling in the absence of low root zone temperatures. Plants, inoculated with the N(2)-fixing bacteria, Bradyrhizobium japonicum, were grown with and without nitrate supplementation. The recorded O-J-I-P chlorophyll a fluorescence transients were analysed by the so-called JIP-test which translates stress-induced alterations in these transients to changes in biophysical parameters that quantifies the energy flow through photosystem II (PSII). One of these parameters, the performance index (PI(ABS)), combines the three main functional steps (light energy absorption, excitation energy trapping, and conversion of excitation energy to electron transport) of photosynthetic activity by a PSII reaction centre complex into a single multiparametric expression. By using the PI(ABS) we could convincingly show that nitrate supplementation considerably enhances dark-chilling tolerance and recovery capacity of plants in the absence of low root zone temperatures. This was especially true for the chilling-sensitive genotype ('Java 29'), suggesting that the response of SNF to dark chilling might be an important factor contributing towards genotypic differences in chilling tolerance. Our results corroborated previous reports about the superior chilling tolerance of 'Maple Arrow', a chilling-tolerant genotype. The results obtained indicated that the PI(ABS) is a far more sensitive indicator of dark-chilling stress than the maximum quantum yield of primary photochemistry (F(V)/F(M)).

Limitation of photosynthetic carbon metabolism by dark chilling in temperate and tropical soybean genotypes

In the experiments reported in this paper, we characterised the physiological and biochemical factors involved in the chilling-induced inhibition of photosynthetic carbon metabolism in soybean [ Glycine max (L.) Merr.] genotypes of temperate and tropical adaptation. Plants of Maple Arrow (temperate genotype) and Java 29 (tropical genotype) were exposed to a single night at 8 °C. Dark chilling resulted in the inhibition of diurnal CO 2 assimilation rate and decreased stomatal conductance in both genotypes. Further analysis, however, revealed a difference in the response of the two genotypes. Stomatal limitation was largely responsible for the inhibition of CO 2 assimilation in Maple Arrow, whereas mesophyll limitation dominated the inhibition in Java 29. The results indicate that inhibition of stromal fructose-1,6-bisphosphatase (sFBPase; EC 3.1.3.11) activity and impaired electron transport capacity were responsible for the decrease in ribulose-1,5-bisphosphate (RuBP) regeneration capacity in Java 29. Sucrose-phosphate synthase (SPS; EC 2.4.1.14) activity was progressively inhibited during the light period in this genotype and might impose an additional constraint on photosynthesis. Maple Arrow appears to possess, at least with respect to photosynthetic carbon metabolism, physiological and biochemical characteristics that contribute towards its superior dark chilling tolerance.

Dark chilling inhibition of photosynthesis and symbiotic nitrogen fixation in soybean during pod filling

The growth stage of a soybean [Glycine max (L.) Merrill] plant may influence its physiological response to dark chilling. Opposed to vegetative development, the intense nutrient and energy requirements of the developing seeds during pod filling could cause additional chilling damage and decreased recovery capacity. Previously, we investigated dark chilling tolerance during vegetative development in two soybean genotypes, 'Maple Arrow' and 'Fiskeby V' and consistently found that photosynthesis and symbiotic nitrogen fixation (SNF) was less affected by dark chilling in 'Maple Arrow'. In this study we describe the dark chilling response of the same genotypes during pod filling. Our aim was to establish whether the potential selection criteria for dark chilling tolerance, identified during vegetative development, was equally sensitive during pod filling. The results indicate that photosynthesis is less affected by dark chilling in 'Maple Arrow' than in 'Fiskeby V', not only during vegetative development, but also during the critical reproductive stage of pod filling. 'Fiskeby V' also lacks the ability to restore normal photosynthetic capacity during an extended recovery treatment. The decrease of nodule ureide content indicates that SNF was inhibited to a similar extent in both genotypes. Nodule ureide content was reduced more than stem ureide content, suggesting that the former is a more sensitive indicator of chilling stress effects on SNF. The results indicate that certain photosynthetic and fluorescence parameters are sensitive indicators of dark chilling tolerance throughout plant development and should prove valuable in future breeding programmes aimed at increasing the chilling tolerance of soybean.