Heterologous expression of a novel <Emphasis Type="Italic">Poa pratensis</Emphasis> gibberellin 2-oxidase gene, <Emphasis Type="Italic">PpGA2ox</Emphasis>, caused dwarfism,late flowering,and increased chlorophyll accumulation in <Emphasis Type="Italic">Arabidopsis</Emphasis>

Gibberellin 2-oxidases (GA2oxs) irreversibly convert bioactive gibberellins (GAs) and their immediate precursors into inactive GAs via 2-β hydroxylation and so regulate gibberellin content in plants. However, to the best of our knowledge, little has been known about the GA2oxs and its function in cool season turfgrass Poa pratensis. In this study, rapid amplification of cDNA end (RACE) was employed to isolate PpGA2ox from P. pratensis. The open reading frame of PpGA2ox was 1 047 bp in length, corresponding to 348 amino acids. PpGA2ox was localized in both nucleus and cytoplasm. The expression of PpGA2ox could be up-regulated by 10 μM gibberellic acid, 5 μM methyl jasmonate, or 10 μM indole-3-acetic acid. In addition, its native promoter could drive GUS expression in both leaf apex and shoot apical region. Moreover, overexpression of PpGA2ox in Arabidopsis led to GA-deficiency leading to dwarf phenotype, delayed flowering time, and increased chlorophyll content. Our study suggests that PpGA2ox could be a candidate gene for breeding new cultivars of P. pratensis.     

Effects of light intensity on leaf photosynthetic characteristics,chloroplast structure,and alkaloid content of <Emphasis Type="Italic">Mahonia bodinieri</Emphasis> (Gagnep.) Laferr.

The variation of light intensity has obvious effects on leaf external morphology, internal anatomy, and physiological characteristics; it even induces changes in secondary metabolite production. The effects of different irradiance levels on biomass, gas exchange parameters, and photosynthetic pigment contents in Mahonia bodinieri (Gagnep.) Laferr. were analyzed here. Combined analyses of physiology, cytology, and HPLC were used to study the differences in leaf morphology, structure, physiological characters, and alkaloid content in response to different irradiances. The results indicated that the highest foliar biomass was observed under I ₅₀ (50 % of full sunlight) followed by I ₃₀ (30 % of full sunlight), the highest net photosynthetic rate, stomatal conductance, transpiration rate values were observed under I ₃₀ followed by I ₅₀, and lower values occurred in I ₁₀ (10 % of full sunlight) and I ₁₀₀ (full sunlight). With increased light intensity, total leaf area and the contents of chlorophyll a (Chl a), chlorophyll b (Chl b), and chlorophyll (Chl a+b) per unit leaf area were clearly reduced, whereas leaf mass per area, carotenoid content, leaf thickness, thickness of palisade and spongy parenchyma, and stomatal density were all significantly increased. Electron microscopic observation revealed that the number of grana, stroma lamellae and the number of starch grains in chloroplasts were decreased, the number of plastoglobuli was increased when irradiance levels increased. The estimated total yield of alkaloids in a single plant was higher under I ₃₀ and I ₅₀ than under I ₁₀ or I ₁₀₀ as a result of the higher biomass of the plants. Therefore, I ₃₀ and I ₅₀ were not only beneficial to increase biomass, but also suitable for the synthesis and accumulation of the major secondary metabolites (alkaloids). Our findings provide valuable data for the determination and regulation of irradiance levels during artificial cultivation of M. bodinieri.     

Changes in the photosynthetic characteristics of cotton leaves infested by invasive mealybugs tended by native ant species

Herbivore injury has a direct effect on the growth and performance of host plants through photosynthetic suppression. However, changes in plant photosynthesis affected by ant tending of hemipteran sap feeders remain poorly understood. We investigated the effects of an invasive mealybug (Phenacoccus solenopsis) tended by native ants (Paratrechina longicornis) on the chlorophyll content and chlorophyll fluorescence characteristics of cotton (Gossypium hirsutum) leaves under greenhouse conditions. The results showed that the relative chlorophyll content of the infested cotton leaves significantly decreased after 10 days, and the chlorophyll contents were reduced by 26.4 and 34.9 % after 20 days in the without and with ant treatments compared to the control, respectively. In addition, the light utilization efficiency and maximum relative electron transport rate were reduced by 53.0 and 51.3 % compared to the control, respectively. However, no significant differences in these factors were found between the without and with ant treatments. The light saturation coefficient, describing the capacity of a sample to resist glare, exhibited no significant difference among treatments. The number of tending P. longicornis ants increased with P. solenopsis numbers, and the P. solenopsis numbers decreased after 20 days compared to the without ant treatment. We suggest that the tending ants may enhance the feeding ability of individual mealybugs in spite of the decreased number of mealybugs in this situation. Additionally, P. longicornis decrease the relative chlorophyll content of infested cotton leaves and may accelerate the damage caused by P. solenopsis to plants over time.     

Contrasting physiological plasticity in response to environmental stress within different cnidarians and their respective symbionts

Given concerns surrounding coral bleaching and ocean acidification, there is renewed interest in characterizing the physiological differences across the multiple host–algal symbiont combinations commonly found on coral reefs. Elevated temperature and CO₂ were used to compare physiological responses within the scleractinian corals Montipora hirsuta (Symbiodinium C15) and Pocillopora damicornis (Symbiodinium D1), as well as the corallimorph (a non-calcifying anthozoan closely related to scleractinians) Discosoma nummiforme (Symbiodinium C3). Several physiological proxies were affected more by temperature than CO₂, including photochemistry, algal number and cellular chlorophyll a. Marked differences in symbiont number, chlorophyll and volume contributed to distinctive patterns of chlorophyll absorption among these animals. In contrast, carbon fixation either did not change or increased under elevated temperature. Also, the rate of photosynthetically fixed carbon translocated to each host did not change, and the percent of carbon translocated to the host increased in the corallimorph. Comparing all data revealed a significant negative correlation between photosynthetic rate and symbiont density that corroborates previous hypotheses about carbon limitation in these symbioses. The ratio of symbiont-normalized photosynthetic rate relative to the rate of symbiont-normalized carbon translocation (P:T) was compared in these organisms as well as the anemone, Exaiptasia pallida hosting Symbiodinium minutum, and revealed a P:T close to unity (D. nummiforme) to a range of 2.0–4.5, with the lowest carbon translocation in the sea anemone. Major differences in the thermal responses across these organisms provide further evidence of a range of acclimation potential and physiological plasticity that highlights the need for continued study of these symbioses across a larger group of host taxa.     

UV-B induces biomass production and nonenzymatic antioxidant compounds in three cyanobacteria

In the present study, the impact of low fluence rate of UV-B (0.045 W.m^?2) on biomass production, photosynthetic pigments (chlorophyll a, carotenoids, and phycobiliproteins), chlorophyll fluorescence, nonenzymatic antioxidants: proline, ascorbate, cysteine, and nonprotein thiols, total phenolic contents, and antioxidant potential (radical scavenging activity) was investigated in three cyanobacteria, viz. Nostoc muscorum, Phormidium foveolarum, and Arthrospira platensis. Selected fluence rate of UV-B caused enhancing effect on these parameters; however, the increased values of these attributes were greater in A. platensis followed by P. foveolarum and N. muscorum. Results indicate that UV-B (at selected fluence rate) could be used as technique that may modify cyanobacterial system for efficient and economic production of natural food supplements and/or natural pharmaceuticals.     

Foliar-application of α-tocopherol enhanced salt tolerance of <Emphasis Type="Italic">Carex leucochlora</Emphasis>

Several different concentrations of α-tocopherol were applied to Carex leucochlora after plants had been treated with high salinity (0.8 % NaCl) in a greenhouse for one month. The results revealed that 0.8 mM α-tocopherol treatment showed the greatest alleviation of growth inhibition and cell membrane damage induced by salt stress. In comparison with NaCl alone, the 0.8 mM α-tocopherol application significantly decreased the content of hydrogen peroxide and the rate of superoxide radical generation, and increased the content of chlorophyll b, carotenoids, free proline, and soluble protein, but had no effect on the content of chlorophyll a and soluble sugar. These results suggest that α-tocopherol could effectively protect C. leucochlora plants from salt stress damage presumably by quenching the excessive reactive oxygen species to protect the photosynthetic pigments and by enhancing the osmotic adjustment.     

Allantoin accumulation in response to increased growth irradiance in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Excess radiation is one of frequent natural environmental stresses that plants have to cope with on a daily basis. Therefore, plants have evolved many short- and long-term mechanisms to acclimate to high irradiance and tolerate it. Ureides, generated from purine degradation, have been proposed as compounds involved in environmental stress responses, including altered irradiance. In the present study, high irradiance was used to investigate ureide content and gene expression in Arabidopsis thaliana. Arabidopsis plants shifted to high irradiance showed high content of a specific ureide compound, allantoin. The accumulation of allantoin was associated with increased expression of uricase, an enzyme involved in its production. When an Arabidopsis mutant (aln-3), which constitutively accumulates elevated amounts of allantoin, was exposed to high irradiance, mutant plants demonstrated enhanced tolerance to the stress conditions compared to the wild-type plants. Our results provide evidence that accumulation of the allantoin might contribute in plants response to increased growth irradiance.     

Effect of low irradiance on the photosynthetic performance and spiking of Phalaenopsis

Lowering irradiance can delay the flower stalk, i.e., spike development, in order to schedule flowering time of Phalaenopsis; however, the effect on photosynthetic performance and spiking inhibition remains poorly understood. We compared light and shade treatments of Phalaenopsis aphrodite subsp. formosana in order to determine how limiting light affects day-night changes in the photosynthetic capacity of leaves and the carbon pool of leaves and stems resulting in delayed spiking. The low irradiance treatment [20 μmol(photon) m^?2 s^?1] for six weeks did not affect potential functions of photosynthetic apparatus estimated by chlorophyll a fluorescence analysis, but it significantly reduced the net CO₂ uptake and O₂ evolution rates, carbohydrate and organic acid concentrations, and amplitudes of CAM activity in new and fully expanded leaves of Phalaenopsis and delayed the spiking compared with the control kept at 150 μmol(photon) m^?2 s^?1. The shortened stem contained a remarkably high sucrose concentration, accounting for more than 80% of total soluble sugars for both treatments throughout the day. Moreover, the sucrose concentration was unaffected by the lowering of irradiance. The relationship between the sucrose content and spiking seemed to be loose; the major factor(s) for spiking in Phalaenopsis remained to be ascertained as the flower stalk bud is attached to the shortened stem.     

Effects of different levels of water stress on leaf photosynthetic characteristics and antioxidant enzyme activities of greenhouse tomato

Two greenhouse experiments were conducted in order to investigate the effects of different levels of water stress on gas exchange, chlorophyll fluorescence, chlorophyll content, antioxidant enzyme activities, lipid peroxidation, and yield of tomato plants (Solanum lycopersicum cv. Jinfen 2). Four levels of soil water content were used: control (75 to 80% of field water capacity), mild water stress (55 to 60%), moderate water stress (45 to 50%), and severe water stress (35 to 40%). The controlled irrigation was initiated from the third leaf stage until maturity. The results of two-year trials indicated that the stomatal conductance, net photosynthetic rate, light-saturated photosynthetic rate, and saturation radiation decreased generally under all levels of water stress during all developmental stages, while compensation radiation and dark respiration rate increased generally. Water stress also declined maximum quantum yield of PSII photochemistry, electron transfer rate, and effective quantum yield of PSII photochemistry, while nonphotochemical quenching increased in all developmental stages. All levels of water stress also caused a marked reduction of chlorophyll a, chlorophyll b, and total chlorophyll content in all developmental stages, while activities of antioxidant enzymes, such as superoxide dismutase, peroxidase, and catalase, and lipid peroxidation increased.     

Cotton genotypic variation in the photosynthetic response to irradiance

The photosynthetic response of 8 cotton (Gossypium hirsutum L.) genotypes to changing irradiance was investigated under field conditions during the 1998 through 2000 growing seasons. Equations developed to describe the response of net photosynthetic rate (P_N) to photosynthetic photon flux density (PPFD) demonstrated that, across all irradiances, the two okra leaf-type genotypes photosynthesized at a greater rate per unit leaf area than all of the six normal leaf-type genotypes. This superior photosynthetic performance of the okra leaf-type genotypes can be partially explained by their 13 % greater leaf chlorophyll content relative to that of the normal leaf-type genotypes. The 37 % reduction in leaf size brought upon by the okra leaf trait may have concentrated the amount of photosynthetic machinery per unit leaf area. Nevertheless, the lack of sufficient canopy leaf surface area suppressed the potential yield development that could accompany the higher P_N per unit leaf area.     

Analysis of photoprotection and apparent non-photochemical quenching of chlorophyll fluorescence in <Emphasis Type="Italic">Tradescantia</Emphasis> leaves based on the rate of irradiance-induced changes in optical transparence

The kinetics of irradiation-induced changes in leaf optical transparence (ΔT) and non-photochemical quenching (NPQ) of chlorophyll fluorescence in Tradescantia fluminensis and T. sillamontana leaves adapted to different irradiance in nature was analyzed. Characteristic times of a photoinduced increase and a dark decline of ΔT in these species were 12 and 20 min, respectively. The ΔT was not confirmed to be the main contributor to the observed middle phase of NPQ relaxation kinetics (τ = 10-28 min). Comparison of rate of photoinduced increase in ΔT and photosystem II quantum yield recovery showed that the former did not affect the tolerance of the photosynthetic apparatus (PSA) to irradiances up to 150 μmol PAR·m^–2·s^–1. Irradiance tolerance correlated with the rate of “apparent NPQ” induction. Considering that the induction of apparent NPQ involves processes significantly faster than ΔT, we suggest that the photoprotective mechanism induction rate is crucial for tolerance of the PSA to moderate irradiance during the initial stage of light acclimation (first several minutes upon the onset of illumination).     

Effects of nitrogen source and irradiance on <Emphasis Type="Italic">Porphyridium cruentum</Emphasis>

We determined the effects of two nitrogen sources (ammonium and nitrate) and two irradiance levels (50 and 200 μmol photons m^?2 s^?1) on the growth rate, cell size, proximate composition, pigment content, and photosynthesis of the unicellular red alga, Porphyridium cruentum. Irradiance significantly affects growth rate, as well as carbohydrate, protein, and phycoerythrin content. Nitrogen form significantly affects cell size, total dry weight, organic dry weight, ash content, carotene content, phycocyanin content, allophycocyanin content, maximum relative electron transport rate (rETRm), and photosynthetic efficiency (α). However, the irradiance and nitrogen source had significantly interaction with the content of lipids and chlorophyll a content, relative electron transport rate (rETR), and irradiance of saturation (I_k). These findings demonstrate that irradiance and nitrogen source influence the metabolism of P. cruentum and that the combination of these two variables induces the production of chemical products for biotechnological, aquaculture, and nutraceutical industry.     

Responses of clonal growth and photosynthesis in Amomum villosum to different light environments

Clonal growth is of great importance for survival, growth, expansion, and resource utilization of some species. Knowing how clonal plants respond morphologically and physiologically to different light environments can be useful to explain their occurrence and abundance patterns under specific environmental conditions. Responses of clonal growth, leaf gas exchange, fluorescence emission, and photosynthetic pigment concentrations to different light environments (100, 60, 30, and 15%) were studied in Amomum villosum, grown in the traditional way for economic purpose in Xishuangbanna, southwest China. The results showed that A. villosum attained vigorous clonal growth under 30% and 60% light, with a higher plant height, number of ramets, stolon length, thicker stems and stolons. Shade-grown A. villosum possessed a larger leaf area than that of the sun-grown plants in order to capture more light. For A. villosum, the higher light-saturated net photosynthetic rate, light-saturation point, larger fresh and dry biomass can explained the better clonal growth for A. villosum under 30% and 60% light. Amomum villosum attained the highest values of minimal chlorophyll fluorescence under 100% light and the lowest values of maximum photochemical efficiency of PSII under 15% light. Our findings indicated that the full irradiance was too strong and 15% light was too weak for A. villosum plants. It was also verified by higher concentrations of photosynthetic pigments in the shaded plants compared to those grown under full sun light. Our results suggested that A. villosum seemed to be adapted to moderate light environment (60–30%) which was indicated by vigorous clonal growth and higher photosynthesis. This information is very useful to select clonal species for rainforest or understory projects. The cultivation of A. villosum in rainforest should not be done under too strong (100%) or too weak light environment (less than 15%).     

Plant growth promotion and suppression of <Emphasis Type="Italic">Phytophthora drechsleri</Emphasis> damping-off in cucumber by cellulase-producing <Emphasis Type="Italic">Streptomyces</Emphasis>

Phytophthora drechsleri damping-off is one of the most important diseases of cucumber (Cucumis sativus). Salinity is a serious problem for crop production and affects diversity and activity of soil microorganisms. Application of salt-tolerant biocontrol agents may be beneficial in order to protect plants against pathogenic fungi in saline soils. In this study, a total of 717 Streptomyces isolates were isolated from the rhizosphere of cucumber, out of which two isolates showed more than 70% inhibitory effect against P. drechsleri and had cellulase activity in the presence and absence of NaCl. In a greenhouse experiment, two Streptomyces isolates with the highest antagonistic activity, strains C 201 and C 801, reduced seedling damping-off of cucumber caused by P. drechsleri by 77 and 80%, respectively, in artificially infested soils. Strain C 201 increased dry weight of seedlings up to 21% in greenhouse experiments. Phylogenetic analyses of 16S rRNA gene sequence reveals that strains C 201 and C 801 are closely related to S. rimosus and S. monomycini respectively. Increased activity of polyphenol oxidase (PPO) and peroxidase (POX) enzymes in Streptomyces-treated plants proved the biocontrol-induced systemic resistance (ISR) in cucumber plants against P. drechsleri.     

Gas exchanges of an endangered species <Emphasis Type="Italic">Syringa pinnatifolia</Emphasis> and a widespread congener <Emphasis Type="Italic">S. oblata</Emphasis>

Net photosynthetic rate (P_N), transpiration rate (E), water use efficiency (WUE), stomatal conductance (g_s), and stomatal limitation (L_s) were investigated in two Syringa species. The saturation irradiance (SI) was 400 µmol m^-2s^-1 for S. pinnatifolia and 1 700 µmol m^-2s^-1 for S. oblata. Compared with S. oblata, S. pinnatifolia had extremely low g _s . Unlike S. oblata, the maximal photosynthetic rate (P_max) in S. pinnatifoliaoccurred around 08:00 and then fell down, indicating this species was sensitive to higher temperature and high photosynthetic photon flux density. However, such phenomenon was interrupted by the leaf development rhythms before summer. A relatively lower P_N together with a lower leaf area and shoot growth showed the capacity for carbon assimilation was poorer in S. pinnatifolia.     

The effect of methanol on photosynthetic parameters of bean (Phaseolus vulgaris L.) under water deficit

Water availability is the main factor limiting crop growth and productivity in dry regions. This study was carried out in order to determine the effect of spraying methanol solution on the photosynthetic characteristics of bean plants. The main aim of our experiment was to improve plant performance under stress caused by water shortage. Two factors were involved: water-deficit stress, such as severe stress (25% of field capacity), mild stress (75% of field capacity), and no stress (100% of field capacity), and application of methanol solution spray at four concentrations: control (without spraying), 10, 20, and 30%. Methanol was applied three times at different growth stages (seedling, flowering, and podding stage) in 10-d intervals. The treatment with 20% methanol at the seedling stage resulted in increased net photosynthesis (P_N), intercellular CO₂ concentration (C_i), and decreased transpiration rate (E) under no stress and mild stress conditions. Under severe stress, 10 and 20%-methanol treatments resulted in increased C_i, maximal quantum yield of PSII photochemistry, and decreased E. At the flowering stage, methanol treatments resulted in decreased E and increased C_i under mild and severe stress. At the podding stage, 10 and 20%-methanol treatments resulted in increased P_N, C_i, and total chlorophyll content under mild stress. In conclusion, we suggested that foliar application of methanol had a positive role in enhancing photosynthetic performance.     

Effects of macrophyte leachate on <Emphasis Type="Italic">Anabaena</Emphasis> sp. and <Emphasis Type="Italic">Chlamydomonas moewusii</Emphasis> growth in freshwater tropical ecosystems

This study reports on the effects of dissolved organic matter (DOM) derived from the aquatic macrophyte Pistia stratiotes (collected from a tropical reservoir) on the mixotrophic growth of two phytoplankton species (Chlamydomonas moewusii and Anabaena sp.). The DOM from P. stratiotes had a mainly aliphatic structure, low molecular weight, low cellulose and lignin content and high carbon content. The addition of DOM (5% v/v) significantly decreased the growth rate of Anabaena sp. but increased the chlorophyll a concentration of C. moewusii. Higher light intensity (100 versus 30 µmol m^?2 s^?1) was important for Anabaena sp., increasing its growth rate and chlorophyll content. The use of DOM from P. stratiotes to mitigate cyanobacterial blooms should be further explored in future studies.     

Effects of light on production of camptothecin and expression of key enzyme genes in seedlings of <Emphasis Type="Italic">Camptotheca acuminate</Emphasis> Decne

Camptotheca acuminata (C. acuminata) is utilized in preparation of drugs and as constituent in functional foods of China due to high camptothecin (CPT) content in different plant parts. Light intensity is one of the most critical factors which affect plant growth and secondary metabolites. Pot experiment was conducted to study the effect of light intensity (i.e., 100 % irradiance (control), 75 % irradiance, 50 % irradiance and 25 % irradiance) on contents of CPT, activity of enzymes and genes expression related to CPT biosynthesis of C. acuminata seedlings. The study examined total leaf biomass, CPT content, activities of tryptophan synthase (TSB) and tryptophan decarboxylase (TDC), and relative expression of TSB, TDC1, and TDC2 genes. Plants grown in 75 % irradiance possessed the greatest leaf biomass compared with 100 % light irradiance. Highest values of CPT contents were found after 60 days in plants grown in 50 % irradiance, followed by 25, 75 % and full sunlight. Furthermore, activities of TSB, TDC and relative expression of genes of TSB, TDC1, and TDC2, were significantly increased after 60 days of 50 % irradiance compared with full sunlight. Irradiance of 50 % up-regulated the expression of CPT biosynthesis-related genes and induced CPT biosynthesis. In addition to that lower or higher irradiance inhibited the expression of CPT biosynthesis-related genes and CPT biosynthesis. It is concluded that manipulating light intensity can be an effective means to achieve highest CPT yield in medicinal plants.     

A morphophysiological analysis of the effects of drought and shade on <Emphasis Type="Italic">Catalpa bungei</Emphasis> plantlets

The interactive effects of shade and drought on the morphological and physiological traits of Catalpa bungei plantlets were assessed. Seedling growth, biomass, biomass allocation, leaf morphology, chlorophyll (Chl) content and gas-exchange parameters were measured in plants raised for 3 months under three light levels [80% (HI), 50% (MI), 30% (LI)] and two water levels [moisture (M) and drought (D)]. The results showed that shade greatly decreased growth, biomass, leaf area (LA) and Chl a/b; increased specific leaf area (SLA) and Chl content; and reduced photosynthetic rate (P _n). Drought reduced the growth, biomass, LA, SLA, Chl a/b, P _n, stomatal conductance (G _s), transpiration rate (T _r) and intercellular carbon dioxide concentration (C _i) and increased the Chl content. Stomatal closure was an early physiological response to water stress. Light, water and their interaction significantly affected plant traits and their bivariate relationships. The phenotypic plasticity index of light (0.47) was much higher than that of water (0.21), indicating that light was the main driver of the variations observed. Under drought stress, growth, biomass, leaf and stem biomass allocation significantly decreased in the HI and MI environments, whereas no significant difference was observed in growth or biomass parameters under the LI condition. Furthermore, no significant difference was observed in P _n, G _s, or T _r under the LI condition under water stress. Our results showed that shade did not alter the negative effects caused by drought stress in MI but did alleviate the negative effects of the LI condition. In summary, the effect of drought on C. bungei plantlets depends on the irradiance conditions.     

Effects of low nocturnal temperature on photosynthetic characteristics and chloroplast ultrastructure of winter rapeseed

We investigated the effects of low nocturnal temperature on photosynthetic apparatus of winter rapeseed (Brassica campestris L.). An artificial climate chamber was used to simulate the effects of low nocturnal temperature on seedling and stomatal morphology, chloroplast ultrastructure, photosynthetic parameters, and dry matter distribution and accumulation in two winter rapeseed cultivars, Longyou-7 (ultra coldresistant) and Tianyou-2 (weak cold resistance). Compared with those at diurnal/nocturnal temperatures of 20°/10°C (control), rapeseed seedlings at 20°/5°C had increased leaf chlorophyll content, deepened green leaf color, decreased stomatal conductance (G_s), intercellular CO₂ concentration (C_i), and photosynthetic rate (P_n), and improved root/shoot ratio; the majority of stomata remained open in Longyou-7 while those in Tianyou-2 were mostly closed or semi-closed. At diurnal/nocturnal temperatures of 20°/–5°C, rapeseed seedlings had decreased leaf chlorophyll content with increased C_i but decreased G_s and P_n; Tianyou-2 exhibited ruptured chloroplast membrane, dissolved grana, broken stroma lamella, and decreased root/shoot ratio, whereas Longyou-7 had chloroplasts retaining partial structure of grana with a small amount of starch granules in guard cells. Low nocturnal temperature damaged the photosynthetic membrane of chloroplasts and reduced P_n in the leaves of winter rapeseed influencing photosynthetic processes in this crop. The reduction of P_n was mainly related to stomatal limitation at diurnal/nocturnal temperatures of 20°/5°C and non-stomatal limitation at diurnal/nocturnal temperatures of 20°/–5°C.