Effect of aluminum toxicity and phosphorus deficiency on the growth and photosynthesis of oil tea (<Emphasis Type="Italic">Camellia oleifera</Emphasis> Abel.) seedlings in acidic red soils

Wild and cultivated varieties of Camellia oleifera Abel. were studied for the response of their photosynthetic apparatus to Al toxicity and low-P stress in pot experiments with medium of acidic red soil. The effect was measured using physiological processes (growth, photosynthesis, chlorophyll a fluorescence), and pigment contents. The results showed that Al toxicity and low-P stress affected the seedlings’ growth and leaves’ photosynthesis, and the differences could be found between the two varieties. Lime plus P fertilizer treatment led to higher increase in the net photosynthetic rate (Pn) in the cultivar than in the wild variety. Pn increase was positively related to the increase of stomatal conductance (gs) and negatively correlated to intercellular CO₂ concentration (Ci) in both varieties. The maximum PSII quantum yield (Fv/Fm), the efficiency of excitation energy capture by open PSII reaction centers (Fv’/Fm’), the photochemical quenching (qP) and the efficiency of open PSII centers (Φ_PSII) significantly increased almost in all the treatment groups of both varieties, with the exception of an insignificant change in qP value for P₁Al₁ group of cultivar. The insensitive qP and lower Pn for cultivar indicate a higher photosynthetic efficiency for the wild variety, though the Φ_PSII was not significant between the two varieties. The pigment contents of oil tea seedlings under treatments changed significantly when lime and P were added, especially the Car/Chl ratio, suggesting carotenoid plays the role of photoprotection under high-Al and low-P stresses.     

Effects of groundwater depth variation on photosynthesis and photoprotection of <Emphasis Type="Italic">Elaeagnus angustifolia</Emphasis> L.

Physiological and photosynthetic responses were investigated at three different depths of groundwater (DGW: 1.4, 2.4, and 3.4 m) in Elaeagnus angustifolia L., a locally adapted tree to the arid region in northwest China. Predawn leaf water potential and chlorophyll content declined gradually with the increasing DGW, whereas there was little effect on predawn variable-to-maximum chlorophyll fluorescence ratio F _v/F _m and leaf carotenoid compositions (xanthophyll cycle pool, neoxanthin, lutein, and β-carotene). Net photosynthetic rate (P _n), quantum yield of PSII electron transport (Φ_PSII), stomatal conductance (Gs), and intercellular CO₂ concentration (Ci) declined obviously; however, P _n decreased more than Φ_PSII at deeper DGW. The photoinhibition of PSII at all three DGW occurred at midday in summer and increased as DGW increased. The ΔpH-dependent thermal dissipation and the level of de-epoxidation of the xanthophyll cycle at all three DGW reached their maxima at midday with the increase of light intensity. However, the fraction of functional PSII and light intensity at deeper DGW (2.4, 3.4 m) showed a negative correlation. This correlation suggested that most of violaxanthin was converted into zeaxanthin at midday, and the reversible inactivation of partial PSII reaction centers took place at deeper DGW. These results together suggest that both the xanthophyll cycle-dependent thermal dissipation and the reversible inactivation of partial PSII might have played important roles in avoiding the excess light-induced energy damage in leaves of this tree species at deeper DGW.     

Diurnal cycle of chlorophyll fluorescence in <Emphasis Type="Italic">Phalaenopsis</Emphasis>

Chlorophyll (Chl) fluorescence of warm day/cool night temperature exposed Phalaenopsis plants was measured hourly during 48 h to study the simultaneous temperature and irradiance response of the photosynthetic physiology. The daily pattern of fluorescence kinetics showed abrupt changes of photochemical quenching (q_P), non-photochemical quenching (NPQ) and quantum yield of photosystem II electron transport (Φ_PSII) upon transition from day to night and vice versa. During the day, the course of Φ_PSII and NPQ was related to the air temperature pattern, while maximum quantum efficiency of PSII photochemistry (F_v/F_m) revealed a rather light dependent response. Information on these daily dynamics in fluorescence kinetics is important with respect to meaningful data collection and interpretation.     

Comparison of the Drought Stress Responses of Tolerant and Sensitive Wheat Cultivars During Grain Filling: Changes in Flag Leaf Photosynthetic Activity,ABA Levels,and Grain Yield

Water status parameters, flag leaf photosynthetic activity, abscisic acid (ABA) levels, grain yield, and storage protein contents were investigated in two drought-tolerant (Triticum aestivum L. cv. MV Emese and cv. Plainsman V) and two drought-sensitive (cvs. GK élet and Cappelle Desprez) wheat genotypes subjected to soil water deficit during grain filling to characterize physiological traits related to yield. The leaf water potential decreased earlier and at a higher rate in the sensitive than in the tolerant cultivars. The net CO₂ assimilation rate (P _N) in flag leaves during water deficit did not display a strict correlation with the drought sensitivity of the genotypes. The photosynthetic activity terminated earliest in the tolerant cv. Emese, and the senescence of flag leaves lasted 7 days longer in the sensitive Cappelle Desprez. Soil drought did not induce characteristic differences between sensitive and tolerant cultivars in chlorophyll a fluorescence parameters of flag leaves during post-anthesis. Changes in the effective quantum yield of PSII (Φ_PSII) and the photochemical quenching (qP) depended on the genotypes and not on the sensitivity of cultivars. In contrast, the levels of ABA in the kernels displayed typical fluctuations in the tolerant and in the sensitive cultivars. Tolerant genotypes exhibited an early maximum in the grain ABA content during drought and the sensitive cultivars maintained high ABA levels in the later stages of grain filling. In contrast with other genotypes, the grain number per ear did not decrease in Plainsman and the gliadin/glutenin ratio was higher than in the control in Emese during drought stress. A possible causal relationship between high ABA levels in the kernels during late stages of grain filling and a decreased grain yield was found in the sensitive cultivars during drought stress.     

Leaf rolling and photosystem II efficiency in <Emphasis Type="Italic">Ctenanthe setosa</Emphasis> exposed to drought stress

Photochemical efficiency of PSII of Ctenanthe setosa was investigated to understand the photosynthetic adaptation mechanism under drought stress causing leaf rolling. Stomatal conductance (g _s), the levels of photosynthetic pigments and chlorophyll (Chl) fluorescence parameters were determined in leaves that had four different visual leaf rolling scores from 1 to 4, opened after re-watering and mechanically opened at score 4. g _s value gradually decreased in adaxial and abaxial surfaces in relation to scores of leaf rolling. Pigment contents decreased until score 3 but approached score 1 level at score 4. No significant variations in effective quantum yield of PSII (Φ_PSII), and photochemical quenching (q_p) were found until score 3, while they significantly decreased at score 4. Non-photochemical quenching (NPQ) increased at score 2 but then decreased. After re-watering, the Chl fluorescence and other physiological parameters reached to approximately score 1 value, again. As for mechanically opened leaves, g _s decreased during drought period. The decrease in adaxial surface was higher than that of the rolled leaves. NPQ was higher than that of the rolled leaves. Φ_PSII and q_p significantly declined and the decreases were more than those of the rolled leaves. In conclusion, the results indicate that leaf rolling protects PSII functionality from damage induced by drought stress.     

Cold Tolerance of the Photosynthetic Apparatus: Pleiotropic Relationship between Photosynthetic Performance and Specific Leaf Area of Maize Seedlings

The objective of this study was to elucidate the genetic relationship between the specific leaf area (SLA) and the photosynthetic performance of maize (Zea mays L.) as dependent on growth temperature. Three sets of genotypes: (i) 19 S₅ inbred lines, divergently selected for high or low operating efficiency of photosystem II (Φ_PSII) at low temperature, (ii) a population of 226 F_2:3 families from the cross of ETH-DL3 × ETH-DH7, and (iii) a population of 168 F_2:4 families from the cross of Lo964 × Lo1016 were tested at low (15/13 °C day/night) or at optimal (25/22 °C day/night) temperature. The latter cross was originally developed to study QTLs for root traits. At 15/13 °C the groups of S₅ inbred lines selected for high or low Φ_PSII differed significantly for all the measured traits, while at optimal temperature the groups differed only with regard to leaf greenness (SPAD). At low temperature, the SLA of these inbred lines was negatively correlated with Φ_PSII (r = − 0.56, p < 0.05) and SPAD (r = − 0.80, p < 0.001). This negative relationship was confirmed by mapping quantitative trait loci (QTL) in the two mapping populations. A co-location of three QTLs for SLA with QTLs for photosynthesis-related traits was detected in both populations at 15/13 °C, while co-location was not detected at 25/22 °C. The co-selection of SLA and Φ_PSII in the inbred lines and the co-location of QTL for SLA, SPAD, and Φ_PSII at 15/13 °C in the QTL populations strongly supports pleiotropy. There was no evidence that selecting for high Φ_PSII at low temperature leads to a constitutively altered SLA.     

Comparison of photosynthetic damage from arthropod herbivory and pathogen infection in understory hardwood saplings

Arthropods and pathogens damage leaves in natural ecosystems and may reduce photosynthesis at some distance away from directly injured tissue. We quantified the indirect effects of naturally occurring biotic damage on leaf-level photosystem II operating efficiency (Φ_PSII) of 11 understory hardwood tree species using chlorophyll fluorescence and thermal imaging. Maps of fluorescence parameters and leaf temperature were stacked for each leaf and analyzed using a multivariate method adapted from the field of quantitative remote sensing. Two tree species, Quercus velutina and Cercis canadensis, grew in plots exposed to ambient and elevated atmospheric CO₂ and were infected with Phyllosticta fungus, providing a limited opportunity to examine the potential interaction of this element of global change and biotic damage on photosynthesis. Areas surrounding damage had depressed Φ_PSII and increased down-regulation of PSII, and there was no evidence of compensation in the remaining tissue. The depression of Φ_PSII caused by fungal infections and galls extended >2.5 times further from the visible damage and was ∼40% more depressed than chewing damage. Areas of depressed Φ_PSII around fungal infections on oaks growing in elevated CO₂ were more than 5 times larger than those grown in ambient conditions, suggesting that this element of global change may influence the indirect effects of biotic damage on photosynthesis. For a single Q. velutina sapling, the area of reduced Φ_PSII was equal to the total area directly damaged by insects and fungi. Thus, estimates based only on the direct effect of biotic agents may greatly underestimate their actual impact on photosynthesis.     

Influence of enhanced temperature on photosynthesis,photooxidative damage,and antioxidant strategies in <Emphasis Type="Italic">Ceratonia siliqua</Emphasis> L. seedlings subjected to water deficit and rewatering

Predicted future climatic changes for the Mediterranean region give additional importance to the study of photooxidative stress in local economic species subjected to combined drought and high-temperature conditions. Under this context, the impact of these stresses on photosynthesis, energy partitioning, and membrane lipids, as well as the potential ability to attenuate oxidative damage, were investigated in Ceratonia siliqua L. Two thermal regimes (LT: 25/18°C; HT: 32/21°C) and three soil water conditions (control, water stress, and rewetting) were considered. HT exacerbated the adverse effects of water shortage on photosynthetic rates (P _N) and PSII function. The decrease in P _N was 33% at LT whereas at HT it was 84%. In spite of this, the electron transport rate (ETR) was not affected, which points to an increased allocation of reductants to sinks other than CO₂ assimilation. Under LT conditions, water stress had no significant effects on yield of PSII photochemistry (Φ_PSII) and yields of regulated (Φ_NPQ) and nonregulated (Φ_NO) energy dissipation. Conversely, drought induced a significant decrease of Φ_PSII and a concomitant increase of Φ_NO in HT plants, thereby favouring the overproduction of reactive oxygen species (ROS). Moreover, signs of lipid peroxidation damage were detected in HT plants, in which drought caused an increase of 40% in malondialdehyde (MDA) content. Concurrently, a marked increase in proline content was observed, while the activities of catalase (CAT) and ascorbate peroxidase (APX) were unaffected. Despite the generation of a moderate oxidative stress response, C. siliqua revealed a great capability for photosynthetic recovery 36 h after rewatering, which suggests that the species can cope with predicted climate change.     

Combined effects of water stress and high temperature on photosynthesis, nitrogen metabolism and lipid peroxidation of a perennial grass Leymus chinensis

Drought and high-temperature stresses have been extensively studied; however, little is known about their combined impact on plants. In the present study, we determined the photosynthetic gas exchange, chlorophyll fluorescence, nitrogen level, and lipid peroxidation of the leaves of a perennial grass (Leymus chinensis (Trin.) Tzvel.) subjected to three constant temperatures (23, 29 and 32°C), and five soil-moisture levels (75–80%, 60–65%, 50–55%, 35–40% and 25–30% of field capacity, respectively). High temperature significantly decreased plant biomass, leaf green area, leaf water potential, photosynthetic rate (A), maximal efficiency of PSII photochemistry (F _v/F _m), actual PSII efficiency (Φ_PSII), the activities of nitrate reductase (NR; EC 1.6.6.1) and glutamine synthetase (GS; EC 6.3.1.2), but markedly increased the ratio of leaf area to leaf weight (SLA), endopeptidase (EP; EC 3.4.24.11) activity, and malondialdehyde (MDA) content, especially under severe water stress conditions. The A and F _v/F _m were significantly and positively correlated with leaf-soluble protein content, and the activities of NR and GS. However, both photosynthesis parameters were significantly and negatively correlated with EP activity and MDA content (P < 0.05). It is suggested that high temperature, combined with severe soil drought, might reduce the function of PSII, weaken nitrogen anabolism, strengthen protein catabolism, and provoke lipid peroxidation. The results also indicate that severe water stress might exacerbate the adverse effects of high temperature, and their combination might reduce the plant productivity and distribution range of L. chinensis in the future.     

Protective mechanism of desiccation tolerance in <Emphasis Type="Italic">Reaumuria soongorica</Emphasis>: Leaf abscission and sucrose accumulation in the stem

Reaumuria soongorica (Pall.) Maxim., a perennial semi-shrub, is widely found in semi-arid areas in northwestern China and can survive severe desiccation of its vegetative organs. In order to study the protective mechanism of desiccation tolerance in R. soongorica, diurnal patterns of net photosynthetic rate (Pn), water use efficiency (WUE) and chlorophyll fluorescence parameters of Photosystem II (PSII), and sugar content in the source leaf and stem were investigated in 6-year-old plants during progressive soil drought imposed by the cessation of watering. The results showed that R. soongorica was characterized by very low leaf water potential, high WUE, photosynthesis and high accumulation of sucrose in the stem and leaf abscission under desiccation. The maximum Pn increased at first and then declined during drought, but intrinsic WUE increased remarkably in the morning with increasing drought stress. The maximal photochemical efficiency of PSII (Fv/Fm) and the quantum efficiency of noncyclic electric transport of PSII(Φ_PSII) decreased significantly under water stress and exhibited an obvious phenomenon of photoinhibition at noon. Drought stressed plants maintained a higher capacity of dissipation of the excitation energy (measured as NPQ) with the increasing intensity of stress. Conditions of progressive drought promoted sucrose and starch accumulation in the stems but not in the leaves. However, when leaf water potential was less than −21.3 MPa, the plant leaves died and then abscised. But the stem photosynthesis remained and, afterward the plants entered the dormant state. Upon rewatering, the shoots reactivated and the plants developed new leaves. Therefore, R. soongorica has the ability to reduce water loss through leaf abscission and maintain the vigor of the stem cells to survive desiccation.     

Mapping quantitative trait loci associated with chlorophyll a fluorescence parameters in soybean (Glycine max (L.) Merr.)

Chlorophyll a fluorescence parameters can provide qualitative and quantitative information about photosynthetic processes in chloroplasts. JIP-test and modulated fluorescence (MF) parameters are commonly used chlorophyll a fluorescence parameters. This study was conducted to identify quantitative trait loci (QTLs) associated with JIP-test parameters, MF parameters, and photosynthetic rate (P_N), and to examine the relationships among them in soybean (Glycine max (L.) Merr.). Pot and field experiments were performed to evaluate 184 recombinant inbred lines (RILs) for five JIP-test parameters (ABS/RC, TR_o/ABS, ET_o/TR_o, RE_o/ET_o, and PI_ABS), four MF parameters (Fv/Fm, Fv′/Fm′, ΦPSII, and qP), and P_N. Significant correlations were commonly observed among JIP-test parameters, MF parameters, and P_N. QTL mapping analysis identified 13, 9, and 4 QTLs for JIP-test parameters, MF parameters, and P_N, respectively, of which 13 were stable. Four major genomic regions were detected: LG A2 (19.81 cM) for JIP-test parameters, LG C1 (94.31 and 97.61 cM) for P_N and MF parameters, LG M (100.51 cM) for JIP-test and MF parameters, and LG O (30.61–49.91 cM) for P_N, JIP-test, and MF parameters. These results indicate that chlorophyll fluorescence parameters, especially ΦPSII and qP, could play an important role in regulating P_N, and that JIP-test and MF parameters could be controlled by the same or different genes. The QTLs identified in this study will help in the understanding of the genetic basis of photosynthetic processes in plants. They will also contribute to the development of marker-assisted selection breeding programs for photosynthetic capacity in soybean.     

Comparative study on energy partitioning in photosystem II of two <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> mutants with reduced non-photochemical quenching capacity

Lhcb1-2 and PsbS proteins of photosystem II (PSII) have important roles in photoprotective thermal energy dissipation of the absorbed excess light energy. The light responses of chlorophyll fluorescence parameters were analyzed to examine how the absence of Lhcb1-2 or PsbS proteins can modify the energy allocation patterns of absorbed light energy in PSII using an antisense construct of lhcb2 and a psbS deletion (npq4-1) mutant of Arabidopsis thaliana. Both mutants exhibit reduced Stern–Volmer non-photochemical chlorophyll fluorescence quenching (NPQ). Here, we have adopted an approach, presented by Hendrickson et al. (Photosynth Res 82:73–81, 2004), to gain a better insight into the mechanism of the NPQ in these mutants. We have found no significant differences in the quantum yields of photochemical energy conversion (Φ_PSII) between the mutants and the wild type. Nevertheless, as it was expected, the fraction of the energy, which is dissipated as heat via regulated pathways in PSII (Φ_NPQ) for both mutants, were reduced as compared to the wild type. In a complementary way, the extent of non-regulated non-photochemical energy loss in PSII (Φ_NO) for both mutants was significantly higher than that in the wild type. This reflects, together with the lower Φ_NPQ (or NPQ) values, suboptimal capacity of photoprotective reactions at higher light intensities.     

Rapid upregulation ofDehyrin3 andDehydrin4 in response to dehydration is a characteristic of drought-tolerant genotypes in barley

The identification of molecular markers and marker-aided selection are essential to the efficient breeding of drought-tolerant plants. However, because that characteristic is controlled by many quantitative trait loci, such markers that can screen and trace desirable barley genotypes in a segregating population or germplasm have not yet been determined. Relative water content has been used to estimate drought tolerance in plants because it is highly correlated with the drought index of yield. To develop reliable gene-specific markers for identifying tolerant versus susceptible genotypes, we performed suppression subtractive hybridization to identify candidate genes. We used two domestic barley cultivars, one having the highest RWC (drought-tolerant ‘Chalbori’) and the other having the lowest (drought-susceptible ‘Daebaekbori’). In response to dehydration at the early seedling stage, rapid upregulation ofDehydrin3 (Dhn3) andDhn4 occurred in the drought-tolerant genotypes, but not in the susceptible ones. Similar results were obtained with mature plants growing under frequent drought stress in the greenhouse. In addition,Dhn3 andDhn4 conferred higher drought tolerance when they were over-expressed in transgenicArabidopsis. Thus, in addition to using assessments of RWC, we propose thatDhn3 andDhn4 expressions can serve as drought-induced gene-specific markers to determine drought-tolerant barley genotypes at the seedling stage.     

Seasonal and diurnal monitoring of leaf polyamine content in Quercus ilex L. resprouts after fire in relation to changes in irradiation and photosynthetic parameters

Seasonal variations in free putrescine, spermidine and spermine content, gas-exchange and chlorophyll fluorescence parameters were followed during winter and summer on leaves of a similar age from undisturbed holm oak trees (control, C) and resprouts (R) originated after fire. We observed a general trend of putrescine content decrease with increasing irradiance. Putrescine content decreased markedly from winter to summer, especially in R, which were located on a site with much higher irradiation. Daily summer variations in putrescine showed a decline at midday from morning values, and they were also more accentuated in R. Measurement of gas-exchange and chlorophyll fluorescence parameters showed marked differences between C and R under their respective light conditions. R showed higher values of PSII quantum yield (Φ_PSII), photochemical quenching (qP) and intrinsic efficiency of open PSII centres () The Φ_PSII/PPFD response curve showed that under the same irradiance, Φ_PSII was enhanced in R and mainly under high light conditions. In spite of increasing irradiance from winter to summer, and especially in burned areas, the mentioned chlorophyll fluorescence parameters were maintained indicating the adaptation of the photosynthetic apparatus. Results derived from A/C _i and A/PPFD response curves showed enhanced photosynthetic capacity and lower non-stomatal limitation of photosynthesis in R during summer stress. The contribution of putrescine decline in the photoadaptation of the photosynthetic apparatus of species growing in natural forest habitats is considered.     

Protective mechanism of desiccation tolerance in Reaumuria soongorica: Leaf abscission and sucrose accumulation in the stem

Reaumuria soongorica (Pall.) Maxim., a perennial semi-shrub, is widely found in semi-arid areas in northwestern China and can survive severe desiccation of its vegetative organs. In order to study the protective mechanism of desiccation tolerance in R. soongorica, diurnal patterns of net photosynthetic rate (Pn), water use efficiency (WUE) and chlorophyll fluorescence parameters of Photosystem II (PSII), and sugar content in the source leaf and stem were investigated in 6-year-old plants during progressive soil drought imposed by the cessation of watering. The results showed that R. soongorica was characterized by very low leaf water potential, high WUE, photosynthesis and high accumulation of sucrose in the stem and leaf abscission under desiccation. The maximum Pn increased at first and then declined during drought, but intrinsic WUE increased remarkably in the morning with increasing drought stress. The maximal photochemical efficiency of PSII (Fv/Fm) and the quantum efficiency of noncyclic electric transport of PSII(Φ_PSII) decreased significantly under water stress and exhibited an obvious phenomenon of photoinhibition at noon. Drought stressed plants maintained a higher capacity of dissipation of the excitation energy (measured as NPQ) with the increasing intensity of stress. Conditions of progressive drought promoted sucrose and starch accumulation in the stems but not in the leaves. However, when leaf water potential was less than −21.3 MPa, the plant leaves died and then abscised. But the stem photosynthesis remained and, afterward the plants entered the dormant state. Upon rewatering, the shoots reactivated and the plants developed new leaves. Therefore, R. soongorica has the ability to reduce water loss through leaf abscission and maintain the vigor of the stem cells to survive desiccation. Supported by the Program of the Research of Vegetation Restoration in Arid Areas of Lanzhou (Grant No. 03-2-27) and the National Natural Science Foundation of China (Grant No. 30270243)     

Photosynthetic performance of regenerated protoplasts from disintegrated cells of <Emphasis Type="Italic">Bryopsis hypnoides</Emphasis> (Chlorophyta)

The photosynthetic performances of regenerated protoplasts of Bryopsis hypnoides, which were incubated in seawater for 1, 6, 12, and 24 h, were studied using chlorophyll (Chl) fluorescence and oxygen measurements. Results showed that for the regenerated protoplasts, the pigment content, the ratios of photosynthetic rate to respiration rate, the maximal photosystem II (PSII) quantum yield (F_v/F_m), and the effective PSII quantum yield (Φ_PSII) decreased gradually along with the regeneration progress, indicated that during 24 h of regeneration there was a remarkable reduction in PSII activity of those newly formed protoplasts. We assumed that during the cultivation progress the regenerated protoplasts had different photosynthetic vigor, with only some of them able to germinate and develop into mature thalli. The above results only reflected the photosynthetic features of the regenerated protoplasts at each time point as a whole, rather than the actual photosynthetic activity of individual aggregations. Further investigation suggested a relationship between the size of regenerated protoplasts and their viability. The results showed that the middle-sized group (diameter 20–60 μm) retained the largest number of protoplasts for 24 h of growth. The changes in F_v/F_m and Φ_PSII of the four groups of differently sized protoplasts (i.e. < 20, 20–60, 60–100, and > 100 μm) revealed that the protoplasts 20–60 μm in diameter had the highest potential activity of the photosynthetic light energy absorption and conversion for several hours.     

Trichoderma asperellum Strain T34 Controls Fusarium Wilt Disease in Tomato Plants in Soilless Culture Through Competition for Iron

Trichoderma asperellum strain T34 has been reported to control the disease caused by Fusarium oxysporum f.sp. lycopersici (Fol) on tomato plants. To study the importance of iron concentration in the growth media for the activity and competitiveness of T34 and the pathogen, we tested four iron concentrations in the nutrient solution [1, 10, 100, and 1000 μM provided as EDTA/Fe(III)] in a biological control experiment with T34 and Fol in tomato plants. The reduction of the Fusarium-infected shoot by T34 was only significant at 10 μM Fe. We hypothesized that Fe competition is one of the key factors in the biocontrol activity exerted by T34 against Fol, as an increase in Fe concentration over 10 μM would lead to the suppression of T34 siderophore synthesis and thus inhibition of Fe competition with Fol. T34 significantly reduced the populations of Fol at all the doses of Fe assayed. In contrast, Fol enhanced the populations of T34 at 1 and 10 μM Fe. Nevertheless, several plant physiological parameters like net CO₂ assimilation (A), stomatal conductance (g _s), relative quantum efficiency of PSII (Φ _PSII), and efficiency of excitation energy capture by open PSII reactive centers (Fv′/Fm′) demonstrated the protection against Fol damage by treatment with T34 at 100 μM Fe. The first physiological parameter affected by the disease progression was g _s. Plant dry weight was decreased by Fe toxicity at 100 and 1,000 μM. T34-treated plants had significantly greater heights and dry weights than control plants at 1,000 μM Fe, even though T34 did not reduce the Fe content in leaves or stems. Furthermore, T34 enhanced plant height even at the optimal Fe concentration (10 μM) compared to control plants. In conclusion, T. asperellum strain T34 protected tomato plants from both biotic (Fusarium wilt disease) and abiotic stress [Fe(III) toxic effects].     

Relations between electron transport rates determined by pulse amplitude modulated chlorophyll fluorescence and oxygen evolution in macroalgae under different light conditions

The relationship between O₂-based gross photosynthesis (GP) and in vivo chlorophyll fluorescence of Photosystem II-based electron transport rate (ETR) as well as the relationship between effective quantum yield of fluorescence (Φ_PSII) and quantum yield of oxygen evolution (Φ_{O_2}) were examined in the green algae Ulva rotundata and Ulva olivascens and the red alga Porphyra leucosticta collected from the field and incubated for 3 days at 100 μmol m⁻² s⁻¹ in nutrient enriched seawater. Maximal GP was twice as high in Ulva species than that measured in P. leucosticta. In all species ETR was saturated at much higher irradiance than GP. The initial slope of ETR versus absorbed irradiance was higher than that of GP versus absorbed irradiance. Only under absorbed irradiances below saturation or at values of GP <2 μmol O₂ m⁻² s⁻¹ a linear relationship was observed. In the linear phase, calculated O₂ evolved /ETR molar ratios were closed to the theoretical value of 0.25 in Ulva species. In P. leucosticta, the estimated GP was associated to the estimated ETR only at high irradiances. ETR was determined under white light, red light emitting by diodes and solar radiation. In Ulva species the maximal ETR was reached under red light and solar radiation whereas in P. leucosticta the maximal ETR was reached under white light and minimal under red light. These results are in agreement with the known action spectra for photosynthesis in these species. In the case of P. leucosticta, GP and ETR were additionally determined under saturating irradiance in algae pre-incubated for one week under white light at different irradiances and at white light (100 μmol m⁻² s⁻¹) enriched with far-red light. GP and growth rate increased at a growth irradiance of 500 μmol m⁻² s⁻¹ becoming photoinhibited at higher irradiances, while ETR increased when algae were exposed to the highest growth irradiance applied (2000 μmol m⁻² s⁻¹). The calculated O₂ evolved /ETR molar ratios were close to the theoretical value of 0.25 when algae were pre-incubated under 500–1000 μmol m⁻² s⁻¹. The enrichment by FR light provoked a decrease in both GP and ETR and an increase of nonphotochemical quenching although the irradiance of PAR was maintained at a constant level. In addition to C assimilation, other electron sinks, such as nitrogen assimilation, affected the GP–ETR relationship. The slopes of GP versus ETR or Φ_PSII versus Φ_{O_2} were lower in the algae with the highest N assimilation capacity, estimated as nitrate reductase activity and internal nitrogen contents, i.e., Ulva rotundata and Porphyra leucosticta, than that observed in U. olivascens. The possible mechanisms to explain this discrepancy between GP and ETR are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

The role of the photosynthetic apparatus in cold acclimation of <Emphasis Type="Italic">Lolium multiflorum</Emphasis>. Characteristics of novel genotypes low-sensitive to PSII over-reduction

During cold acclimation by higher plants, temperature perception via changes in redox state of Photosystem II (PSII) and subsequent acclimation of the photosynthetic apparatus to cold is very important for achieving freezing tolerance. These properties were studied in two groups (A and B) of the same backcross 3 (BC₃) progeny derived from a triploid hybrid of Festuca pratensis (2×) × Lolium multiflorum (4×) backcrossed three times onto diploid L. multiflorum cultivars. Leaves of Group A plants formed at 20°C at medium-low light were unable to acclimate their photosynthetic apparatus to cold. Compared to Group B, the Group A plants were also more frost sensitive. This acclimation ability correlated with the freezing tolerance of the plants. However, leaves of the same Group A plants developed at 20°C, but under higher-light conditions had increased ability to acclimate their photosynthetic apparatus to cold. It was concluded that Group A plants may have impaired PSII temperature perception, and this then resulted in their poor capability to cold acclimate.     

Enhanced thermotolerance of photosystem II in salt-adapted plants of the halophyte<Emphasis Type="Italic"> Artemisia anethifolia</Emphasis>

Thermotolerance of photosystem II (PSII) in leaves of salt-adapted Artemisia anethifolia L. plants (100–400 mM NaCl) was evaluated after exposure to heat stress (30–45°C) for 30 min. After exposure to 30°C, salt adaptation had no effects on the maximal efficiency of PSII photochemistry (F_v/F_m), the efficiency of excitation capture by open PSII centers (F_v/F_m), or the actual PSII efficiency (_PSII). After pretreatment at 40°C, there was a striking difference in the responses of F_v/F_m, F_v/F_m and _PSII to heat stress in non-salt-adapted and salt-adapted leaves. Leaves from salt-adapted plants maintained significantly higher values of F_v/F_m, F_v/F_m and _PSII than those from non-salt-adapted leaves. The differences in F_v/F_m, F_v/F_m and _PSII between non-salt-adapted and salt-adapted plants persisted for at least 12 h following heat stress. These results clearly show that thermotolerance of PSII was enhanced in salt-adapted plants. This enhanced thermotolerance was associated with an improvement in thermotolerance of the PSII reaction centers, the oxygen-evolving complexes and the light-harvesting complex. In addition, we observed that after exposure to 42.5°C for 30 min, non-salt-adapted plants showed a significant decrease in CO₂ assimilation rate while in salt-adapted plants CO₂ assimilation rate was either maintained or even increased to some extent. Given that photosynthesis is considered to be the physiological process most sensitive to high-temperature damage and that PSII appears to be the most heat-sensitive part of the photosynthetic apparatus, enhanced thermotolerance of PSII may be of significance for A. anethifolia, a halophyte plant, which grows in the high-salinity regions in the north of China, where the air temperature in the summer is often as high as 45°C.