Identification,isolation and expression analysis of eight stress-related <Emphasis Type="Italic">R2R3</Emphasis>-<Emphasis Type="Italic">MYB</Emphasis> genes in tartary buckwheat (<Emphasis Type="Italic">Fagopyrum tataricum</Emphasis>)

Key message

Eight R2R3 - MYB genes in tartary buckwheat were identified, and their expression patterns were comprehensively analyzed, which reveals role in plant response to abiotic stresses.

Abstract

The proteins of the R2R3-MYB superfamily play key roles in the growth and development processes as well as defense responses in plants. However, their characteristics and functions have not been fully investigated in tartary buckwheat (Fagopyrum tataricum), a strongly abiotic resistant coarse cereal. In this article, eight tartary buckwheat R2R3-MYB genes were isolated with full-length cDNA and DNA sequences. Phylogenetic analysis of the members of the R2R3-MYB superfamily between Arabidopsis and tartary buckwheat revealed that the assumed functions of the eight tartary buckwheat R2R3-MYB proteins are divided into five Arabidopsis functional subgroups that are involved in abiotic stress. Expression analysis during abiotic stress and exogenous phytohormone treatments identified that the eight R2R3-MYB genes responded to one or more treatments. This study is the first comprehensive analysis of the R2R3-MYB gene family in tartary buckwheat under abiotic stress.

     

Chalcone synthase homologous genes cloning and expression pattern in flowering <Emphasis Type="Italic">Fagopyrum tataricum</Emphasis> Gaertn

Tartary buckwheat (Fagopyrum tataricum Gaertn.) is highly nutritious and an excellent dietary source of flavonoid compounds. Chalcone synthase (CHS) is the first key enzyme involved in flavonoid biosynthesis. Here, three putative CHS genes (designated as FtCHS1 (GU172165), FtCHS2 (KT284884), and FtCHS3 (KT284885) were isolated from tartary buckwheat. Nucleotide sequence analysis indicated that FtCHS1 and FtCHS2 each contained one intron of 444 bp and 157 bp, respectively. FtCHS3 included two introns, one of 86 bp and another of 73 bp. The results of quantitative real-time PCR (qRT-PCR) showed the FtCHSs expression presented the same pattern in the stems and flowers, with FtCHS1>FtCHS3>FtCHS2. A different tendency was found in leaves, with FtCHS3>FtCHS2>FtCHS1. However, there was no direct correlation between the three CHS expression and total flavonoids. Furthermore, high-performance liquid chromatography (HPLC) performance reveals rutin is the most abundant flavonoid in all tissues, leaves should be the main location for quercetin storage in tartary buckwheat.     

Nitrogen-induced variations in leaf gas exchange of spring triticale under field conditions

Nitrogen (N) is the key factor limiting photosynthetic processes and crop yield. Little is known about the response of leaf gas exchange of spring triticale (Triticosecale Wittm.) to N supply. The effect of N fertilizers on different gas exchange variables, i.e., photosynthetic rate (A), transpiration rate (E), stomatal conductance (g _s), instantaneous water use efficiency (WUE) and maximum quantum yield of photosystem II (PSII) (F _v/F _m), chlorophyll index (SPAD, soil–plant analysis development), and the relationship of these variables with yield were studied in spring triticale grown under field conditions. Six treatments of N—0, 90, 180, 90 + 30, 90 + 30 + 30 kg ha^?1 (applied as ammonium nitrate, AN) and one treatment of N 90 + 30 + 30 kg ha^?1 (applied as urea ammonium nitrate solution, UAN) were compared. The analysis of variance showed that throughout the triticale growing season, N fertilization had significant effects on A, WUE, g _s and SPAD. On average, N fertilizer application increased A values by 14–70%. E and F _v/F _m values were not influenced by N fertilization levels. The effect of growth stage and year on gas exchange variables and F _v/F _m and SPAD was found to be significant. At different growth stages, A values varied and maximum ones were reached at BBCH 31–33 (decimal code system of growth stages) and BBCH 59. With aging, values of A decreased independently of N fertilization level. The gas exchange variables were equally affected by both fertilizer forms. The interplay among grain yield, leaf gas exchange variables, F _v/F _m and SPAD of spring triticale was estimated. The statistical analysis showed that grain yield positively and significantly correlated with A and SPAD values throughout the growing season.     

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.     

Effect of long-term different fertilization on bacterial community structures and diversity in citrus orchard soil of volcanic ash

This study was conducted to assess bacterial species richness, diversity and community distribution according to different fertilization regimes for 16 years in citrus orchard soil of volcanic ash. Soil samples were collected and analyzed from Compost (cattle manure, 2,000 kg/10a), 1/2 NPK+compost (14-20-14+2,000 kg/10a), NPK+compost (28-40-28+2,000 kg/10a), NPK (28-40-28 kg/10a), 3 NPK (84-120-84 kg/10a), and Control (no fertilization) plot which have been managed in the same manners with compost and different amount of chemical fertilization. The range of pyrosequencing reads and OTUs were 4,687–7,330 and 1,790–3,695, respectively. Species richness estimates such as Ace, Chao1, and Shannon index were higher in 1/2 NPK+compost than other treatments, which were 15,202, 9,112, 7.7, respectively. Dominant bacterial groups at level of phylum were Proteobacteria, Acidobacteria, and Actinobacteria. Those were occupied at 70.9% in 1/2 NPK+compost. Dominant bacterial groups at level of genus were Pseudolabrys, Bradyrhizobium, and Acidobacteria. Those were distributed at 14.4% of a total of bacteria in Compost. Soil pH displayed significantly closely related to bacterial species richness estimates such as Ace, Chao1 (p<0.05) and Shannon index (p<0.01). However, it showed the negative correlation with exchangeable aluminum contents (p<0.05). In conclusion, diversity of bacterial community in citrus orchard soil was affected by fertilization management, soil pH changes and characteristics of volcanic ash.     

Assessment of photosynthetic potential of indoor plants under cold stress

Photosynthetic parameters including net photosynthetic rate (P_N), transpiration rate (E), water-use efficiency (WUE), and stomatal conductance (g_s) were studied in indoor C₃ plants Philodendron domesticum (Pd), Dracaena fragans (Df), Peperomia obtussifolia (Po), Chlorophytum comosum (Cc), and in a CAM plant, Sansevieria trifasciata (St), exposed to various low temperatures (0, 5, 10, 15, 20, and 25°C). All studied plants survived up to 0°C, but only St and Cc endured, while other plants wilted, when the temperature increased back to room temperature (25°C). The P_N declined rapidly with the decrease of temperature in all studied plants. St showed the maximum P_N of 11.9 μmol m^?2 s^?1 at 25°C followed by Cc, Po, Pd, and Df. E also followed a trend almost similar to that of P_N. St showed minimum E (0.1 mmol m^?2 s^?1) as compared to other studied C₃ plants at 25°C. The E decreased up to ≈4-fold at 5 and 0°C. Furthermore, a considerable decline in WUE was observed under cold stress in all C₃ plants, while St showed maximum WUE. Similarly, the g_s also declined gradually with the decrease in the temperature in all plants. Among C₃ plants, Pd and Po showed the maximum g_s of 0.07 mol m^?2 s^?1 at 25°C followed by Df and Cc. However, St showed the minimum g_s that further decreased up to ～4-fold at 0°C. In addition, the content of photosynthetic pigments [chlorophyll a, b, (a+b), and carotenoids] was varying in all studied plants at 0°C. Our findings clearly indicated the best photosynthetic potential of St compared to other studied plants. This species might be recommended for improving air quality in high-altitude closed environments.     

Evolution of protein transport to the chloroplast envelope membranes

Comparing with other angiosperms, most members within the family Orchidaceae have lower photosynthetic capacities. However, the underlying mechanisms remain unclear. Cypripedium and Paphiopedilum are closely related phylogenetically in Orchidaceae, but their photosynthetic performances are different. We explored the roles of internal anatomy and diffusional conductance in determining photosynthesis in three Cypripedium and three Paphiopedilum species, and quantitatively analyzed their diffusional and biochemical limitations to photosynthesis. Paphiopedilum species showed lower light-saturated photosynthetic rate (A _N), stomatal conductance (g _s), and mesophyll conductance (g _m) than Cypripedium species. A _N was positively correlated with g _s and g _m. And yet, in both species A _N was more strongly limited by g _m than by biochemical factors or g _s. The greater g _s of Cypripedium was mainly affected by larger stomatal apparatus area and smaller pore depth, while the less g _m of Paphiopedilum was determined by the reduced surface area of mesophyll cells and chloroplasts exposed to intercellular airspace per unit of leaf area, and much thicker cell wall thickness. These results suggest that leaf anatomical structure is the key factor affecting g _m, which is largely responsible for the difference in photosynthetic capacity between those two genera. Our findings provide new insight into the photosynthetic physiology and functional diversification of orchids.     

Gas exchange,carbon balance and stomatal traits in wild and cultivated rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) genotypes

Carbon balancing within the plant species is an important feature for climatic adaptability. Photosynthesis and respiration traits are directly linked with carbon balance. These features were studied in 20 wild rice accessions Oryza spp., and cultivars. Wide variation was observed within the wild rice accessions for photosynthetic oxygen evolution or photosynthetic rate (A), dark (R _d), and light induced respiration (LIR) rates, as well as stomatal density and number. The mean rate of A varied from 10.49 μmol O₂ m^?2 s^?1 in cultivated species and 13.09 μmol O₂ m^?2 s^?1 in wild spp., The mean R _d is 2.09 μmol O₂ m^?2 s^?1 and 2.31 μmol O₂ m^?2 s^?1 in cultivated and wild spp., respectively. Light induced Respiration (LIR) was found to be almost twice in wild rice spp., (16.75 μmol O₂ m^?2 s^?1) compared to cultivated Oryza spp., Among the various parameters, this study reveals LIR and A as the key factors for positive carbon balance. Stomatal contribution towards carbon balance appears to be more dependent on abaxial surface where several number of stomata are situated. Correlation analysis indicates that R _d and LIR increase with the increase in A. In this study, O. nivara (CR 100100, CR 100097), O. rufipogon (IR 103404) and O. glumaepatula (IR104387) were identified as potential donors which could be used in rice breeding program. Co-ordination between gas exchange and patchiness in stomatal behaviour appears to be important for carbon balance and environmental adaptation of wild rice accessions, therefore, survival under harsh environment.     

Methylation of the genes for the microRNAs miR-129-2 and miR-9-1, changes in their expression,and activation of their potential target genes in clear cell renal cell carcinoma

Methylation of promoter CpG islands and microRNA (miRNA) interactions with mRNAs of target genes are epigenetic mechanisms that play a crucial role in deregulation of gene expression and signaling pathways in tumors. Altered expression of six chromosome 3p genes (RARB(2), SEMA3B, RHOA, GPX1, NKIRAS1, and CHL1) and two miRNA genes (MIR-129-2 and MIR-9-1) was observed in primary clear cell renal cell carcinomas (ccRCCs, 31–48 samples) by RT-PCR and qPCR. Significant downregulation (p < 0.05, Fisher’s exact test) was observed for SEMA3B, NKIRAS1, and CHL1; and differential expression, for the other chromosome 3p and miRNA genes. Methylation-specific PCR with primers to RARB(2), SEMA3B, MIR-129-2, and MIR-9-1 showed that their methylation frequency was significantly (p < 0.05, Fisher’s exact test) elevated in the ccRCC samples. Significant correlations between promoter methylation and expression were confirmed for SEMA3B and observed for the first time for RARB(2), GPX1, and MIR-129-2 in ccRCC (Spearman’s correlation coefficient r _s ranging 0.31–0.60, p < 0.05). The MIR-129-2 and RARB(2) methylation frequencies significantly correlated with ccRCC progression. MIR-129-2 methylation correlated with upregulation of RARB(2), RHOA, NKIRAS1, and CHL1 (r _s ranging 0.35–0.53, p < 0.05). The findings implicate methylation in regulating RARB(2), SEMA3B, GPX1, and MIR-129-2 and indicate that miR-129-2 and methylation of its gene affect RARB(2), RHOA, NKIRAS1, and CHL1 expression.     

Rearrangement of leaf traits with changing source-sink relationship in blueberry (Vaccinium corymbosum L.) leaves

The source-sink relationship is one of major determinants of plant performance. The influence of reproductive sink demand on light-saturated photosynthesis (P_max), dark respiration (R_D), stomatal conductance (g_s), intrinsic water-use efficiency (WUE_i), contents of soluble sugar (SSC), nitrogen, carbon, and photosynthetic pigments was examined in blueberry (Vaccinium corymbosum L. cv. ‘Brigitta’) during the final stage of rapid fruit growth. Measurements were performed three times per day on developed, sun-exposed leaves of girdled shoots with 0.1, 1, and 10 fruit per leaf (0.1F:L, 1F:L, and 10F:L, respectively) and nongirdled shoots bearing one fruit per leaf (NG). Girdling and lower fruit amount induced lower P_max, g_s, N, and total chlorophyll (Chl) and higher WUE_i, SSC, R_D, Chl a/b ratio and carotenoids-to-chlorophylls ratio (Car/Chl) for the 1F:L and 0.1F:L treatments. The impact of girdling was counterbalanced by 10F:L, with NG and 10F:L having similar values. Variables other than P_max, R_D, g_s, WUE_i, and SSC were unaffected throughout the course of the day. P_max and g_s decreased during the course of the day, but g_s decreased more than P_max in the afternoon, while WUE_i was increasing in almost all treatments. SSC increased from the morning until afternoon, whereas R_D peaked at noon regardless of the treatment. Generally, P_max was closely and negatively correlated to SSC, indicating that sugar-sensing mechanisms played an important role in regulation of blueberry leaf photosynthesis. With respect to treatments, P_max and N content were positively related, while R_D was not associated to substrate availability. The enhanced Car/Chl ratio showed a higher photoprotection under the lower sink demand. Changes in the source-sink relationship in ‘Brigitta’ blueberry led to a rearrangement of physiological and structural leaf traits which allowed adjusting the daily balance between carbon assimilation and absorbed light energy.     

Photosynthetic acclimation and leaf traits of <Emphasis Type="Italic">Stipa bungeana</Emphasis> in response to elevated CO<Subscript>2</Subscript> under five different watering conditions

Although plant performance under elevated CO₂ (EC) and drought has been extensively studied, little is known about the leaf traits and photosynthetic performance of Stipa bungeana under EC and a water deficiency gradient. In order to investigate the effects of EC, watering, and their combination, S. bungeana seedlings were exposed to two CO₂ regimes (ambient, CA: 390 ppm; elevated, EC: 550 ppm) and five levels of watering (?30%, ?15%, control, +15%, +30%) from 1 June to 31 August in 2011, where the control water level was 240 mm. Gas exchange and leaf traits were measured after 90-d treatments. Gas-exchange characteristics, measured at the growth CA, indicated that EC significantly decreased the net photosynthetic rate (P _N), water-use efficiency, nitrogen concentration based on mass, chlorophyll and malondialdehyde (MDA) content, while increased stomatal conductance (g _s), intercellular CO₂ concentration (C _i), dark respiration, photorespiration, carbon concentration based on mass, C/N ratio, and leaf water potential. Compared to the effect of EC, watering showed an opposite trend only in case of P _N. The combination of both factors showed little influence on these physiological indicators, except for g _s, C _i, and MDA content. Photosynthetic acclimation to EC was attributed to the N limitation, C sink/source imbalance, and the decline of photosynthetic activity. The watering regulated photosynthesis through both stomatal and nonstomatal mechanisms. Our study also revealed that the effects of EC on photosynthesis were larger than those on respiration and did not compensate for the adverse effects of drought, suggesting that a future warm and dry climate might be unfavorable to S. bungeana. However, the depression of the growth of S. bungeana caused by EC was time-dependent at a smaller temporal scale.     

Photosynthetic responses of a wheat (Asakaze)–barley (Manas) 7H addition line to salt stress

The photosynthetic responses to salt stress were examined in a wheat (Triticum aestivum L. cv. Asakaze)–barley (Hordeum vulgare L. cv. Manas) 7H addition line having elevated salt tolerance and compared to the parental wheat genotype. For this purpose, increasing NaCl concentrations up to 300 mM were applied and followed by a 7-day recovery period. Up to moderate salt stress (200 mM NaCl), forcible stomatal closure, parallel with a reduction in the net assimilation rate (P _N), was only observed in wheat, but not in the 7H addition line or barley. Since the photosynthetic electron transport processes of wheat were not affected by NaCl, the impairment in P _N could largely be accounted for the salt-induced decline in stomatal conductance (g _s), accompanied by depressed intercellular CO₂ concentration and carboxylation efficiency. Both, P _N and nonstomatal limitation factors (L_ns) were practically unaffected by moderate salt stress in barley and in the 7H addition line due to the sustained g _s, which might be an efficient strategy to maintain the efficient photosynthetic activity and biomass production. At 300 mM NaCl, both P _N and g _s decreased significantly in all the genotypes, but the changes in P _N and L_ns in the 7H addition line were more favourable similar to those in wheat. The downregulation of photosynthetic electron transport processes around PSII, accompanied by increases in the quantum yield of regulated energy dissipation and of the donor side limitation of PSI without damage to PSII, was observed in the addition line and barley during severe stress. Incomplete recovery of P _N was observed in the 7H addition line as a result of declined PSII activity probably caused by enhanced cyclic electron flow around PSI. These results suggest that the better photosynthetic tolerance to moderate salt stress of barley can be manifested in the 7H addition line which may be a suitable candidate for improving salt tolerance of wheat.     

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.     

The lignin synthesis related genes and lodging resistance of <Emphasis Type="Italic">Fagopyrum esculentum</Emphasis>

Lignin is closely related to the lodging resistance of common buckwheat (Fagopyrum esculentum Moench.). However, the characteristics of lignin synthesis related genes have not yet been reported. We investigated the lignin biosynthesis gene expression, activities of related enzymes, and accumulation of lignin monomers during branching stage, bloom stage, and milky ripe stage by real-time quantitative PCR, UVspectrophotometry, and gas chromatography-mass spectrometry in the 2^nd internode of three common buckwheat cultivars with different lodging resistance. The results showed that lignin content and the activity of phenylalanine ammonia lyase (PAL), 4-coumarate: CoA ligase (4CL), cinnamyl alcohol dehydrogenase (CAD) and peroxidase (POD) were closely related to the lodging resistance of common buckwheat. Further, we studied gene expression of cinnamate 4-hydroxylase (C4H), caffeoyl-CoA O-methyltransferase (CCoAOMT), ferulate 5-hydroxylase (F5H), cinnamoyl-CoA reductase (CCR), and caffeic acid O-methyltransferase (COMT). The lignin biosynthesis genes were divided into three classes according to their expression pattern: 1) expression firstly increasing and then descending (PAL, 4CL, CAD, C4H, CCoAOMT, F5H, and CCR), 2) expression remaining constant during maturation (C3H), and 3) expression decreasing with maturation (COMT). The present study provides preliminary insights into the expression of lignin biosynthesis genes in common buckwheat, laying a foundation for further understanding the lignin biosynthesis.     

Acclimation of shade-tolerant and light-resistant <Emphasis Type="Italic">Tradescantia</Emphasis> species to growth light: chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence,electron transport,and xanthophyll content

In this study, we have compared the photosynthetic characteristics of two contrasting species of Tradescantia plants, T. fluminensis (shade-tolerant species), and T. sillamontana (light-resistant species), grown under the low light (LL, 50–125 µmol photons m^?2 s^?1) or high light (HL, 875–1000 µmol photons m^?2 s^?1) conditions during their entire growth period. For monitoring the functional state of photosynthetic apparatus (PSA), we measured chlorophyll (Chl) a emission fluorescence spectra and kinetics of light-induced changes in the heights of fluorescence peaks at 685 and 740 nm (F ₆₈₅ and F ₇₄₀). We also compared the light-induced oxidation of P₇₀₀ and assayed the composition of carotenoids in Tradescantia leaves grown under the LL and HL conditions. The analyses of slow induction of Chl a fluorescence (SIF) uncovered different traits in the LL- and HL-grown plants of ecologically contrasting Tradescantia species, which may have potential ecophysiological significance with respect to their tolerance to HL stress. The fluorometry and EPR studies of induction events in chloroplasts in situ demonstrated that acclimation of both Tradescantia species to HL conditions promoted faster responses of their PSA as compared to LL-grown plants. Acclimation of both species to HL also caused marked changes in the leaf anatomy and carotenoid composition (an increase in Violaxanthin?+?Antheraxantin?+?Zeaxanthin and Lutein pools), suggesting enhanced photoprotective capacity of the carotenoids in the plants grown in nature under high irradiance. Collectively, the results of the present work suggest that the mechanisms of long-term PSA photoprotection in Tradescantia are based predominantly on the light-induced remodeling of pigment-protein complexes in chloroplasts.     

Influence of Nitrogen,Phosphorus, and Potassium Fertilization on Flowering and Expression of Flowering-Associated Genes in White Birch (<Emphasis Type="Italic">Betula platyphylla</Emphasis> Suk.)

Fertilization treatments can promote the growth and development of tree plants. In the present study, we evaluated the combined effects of different doses of nitrogen, phosphorous, and potassium on the blossoming and the expression of five flowering-associated genes, including BpMADS1, BpMADS3, BpMADS5, BpSPL1, and BpSPL2. The results showed that balanced NPK (nitrogen, phosphorous, and potassium) fertilization cannot only promote the transition from juvenility to maturity but also can increase the inflorescence production of white birch. Furthermore, some fertilizing treatments not only increase the expression levels of all the five flowering-associated genes, but also change their expression patterns during the growth season. These results indicated that NPK fertilization have remarkable effects on flowering of white birch.     

Effect of drought on ear and flag leaf photosynthesis of two wheat cultivars differing in drought resistance

We investigated net photosynthetic rate (P_N) of ear and two uppermost (flag and penultimate) leaves of wheat cultivars Hongmangmai (drought resistant) and Haruhikari (drought sensitive) during post-anthesis under irrigated and non-irrigated field conditions. The P_Nof ear and flag leaf were significantly higher and less affected by drought in Hongmangmai than in Haruhikari. The rate of reduction in stomatal conductance (g_s) was similar for the two cultivars, but intercellular CO₂concentration (C_i) in the flag leaf of Hongmangmai was lower than that of Haruhikari in non-irrigated treatment. No differences were observed in leaf water potential (ψ₁) and osmotic adjustment of the flag leaf of the cultivars. These results imply that differences in photosynthetic inhibition on the flag leaf at low leaf ψ₁between the cultivars were primarily due to non-stomatal effects. Hence the main physiological factor associated with yield stability of Hongmangmai under drought stress may be attributed to the capacity for chloroplast activity in the flag leaf, which apparently allows sustained P_Nof flag leaf during grain filling under drought stress. The higher P_Nof ear in Hongmangmai under drought could also be related to its drought resistance.     

Solute patterns and diurnal variation of photosynthesis and chlorophyll fluorescence in Korean coastal sand dune plants

Four plant species, Elymus mollis Trin., Carex kobomugi Ohwi, Glehnia littoralis F. Schmidt ex Miq., and Vitex rotundifolia L.f., are dominant perennial species in coastal sand dunes of Korea. We examined a physiological adaptation of these species by measurements of diurnal variation in photosynthesis and chlorophyll (Chl) fluorescence and solute patterns in leaves during one season (June), which is favorable for plant growth of all four species. All four species adopted different strategies in order to utilize radiation and to maintain water status under a fluctuating microclimate. Although the lowest water contents among four plant species was found, E. mollis with a high Chl and K⁺ content showed better photosynthetic performance, with high stomatal conductance (g _s), net photosynthetic rate (P _N), instantaneous carboxylation efficiency (CE), and water-use efficiency. Midday depression of P _N in E. mollis and G. littoralis, without a reduction of gs, was associated with a reduction in CE and maximum photochemical efficiency of PSII, indicating nonstomatal limitation. Photosynthesis depression in both C. kobomugi and V. rotundifolia, with relatively low g _s values, could be attributed to both stomatal and nonstomatal limitations. The high storage capacity for inorganic ions in E. molli, C. kobomugi, and G. littoralis may play an efficient role in regulating photosynthesis and maintaining leaf water status through stomatal control, and can also play an important role in osmotic adjustment.     

Modelling photosynthesis in shallow algal production ponds

Shallow ponds with rapidly photosynthesising cyanobacteria or eukaryotic algae are used for growing biotechnology feedstock and have been proposed for biofuel production but a credible model to predict the productivity of a column of phytoplankton in such ponds is lacking. Oxygen electrodes and Pulse Amplitude Modulation (PAM) fluorometer technology were used to measure gross photosynthesis (P _G) vs. irradiance (E) curves (P _G vs. E curves) in Chlorella (chlorophyta), Dunaliella salina (chlorophyta) and Phaeodactylum (bacillariophyta). P _G vs. E curves were fitted to the waiting-in-line function [P _G = (P _Gmax × E/E_opt) × exp(1 — E/E_opt)]. Attenuation of incident light with depth could then be used to model P _G vs. E curves to describe P _G vs. depth in pond cultures of uniformly distributed planktonic algae. Respiratory data (by O2-electrode) allowed net photosynthesis (P _N) of algal ponds to be modelled with depth. Photoinhibition of photosynthesis at the pond surface reduced P _N of the water column. Calculated optimum depths for the algal ponds were: Phaeodactylum, 63 mm; Dunaliella, 71 mm and Chlorella, 87 mm. Irradiance at this depth is ≈ 5 to 10 μmol m^?2 s^?1 photosynthetic photon flux density (PPFD). This knowledge can then be used to optimise the pond depth. The total net P _N [μmol(O2) m^?2 s^?1] were: Chlorella, ≈ 12.6 ± 0.76; Dunaliella, ≈ 6.5 ± 0.41; Phaeodactylum ≈ 6.1 ± 0.35. Snell’s and Fresnel’s laws were used to correct irradiance for reflection and refraction and thus estimate the time course of P _N over the course of a day taking into account respiration during the day and at night. The optimum P _N of a pond adjusted to be of optimal depth (0.1–0.5 m) should be approximately constant because increasing the cell density will proportionally reduce the optimum depth of the pond and vice versa. Net photosynthesis for an optimised pond located at the tropic of Cancer would be [in t(C) ha^?1 y^?1]: Chlorella, ≈ 14.1 ± 0.66; Dunaliella, ≈ 5.48 ± 0.39; Phaeodactylum, ≈ 6.58 ± 0.42 but such calculations do not take weather, such as cloud cover, and temperature, into account.