Growth Light Conditions Research Articles

Role of Thylakoid ATP/ADP Carrier in Photoinhibition and Photoprotection of Photosystem II in Arabidopsis

The chloroplast thylakoid ATP/ADP carrier (TAAC) belongs to the mitochondrial carrier superfamily and supplies the thylakoid lumen with stromal ATP in exchange for ADP. Here, we investigate the physiological consequences of TAAC depletion in Arabidopsis (Arabidopsis thaliana). We show that the deficiency of TAAC in two T-DNA insertion lines does not modify the chloroplast ultrastructure, the relative amounts of photosynthetic proteins, the pigment composition, and the photosynthetic activity. Under growth light conditions, the mutants initially displayed similar shoot weight, but lower when reaching full development, and were less tolerant to high light conditions in comparison with the wild type. These observations prompted us to study in more detail the effects of TAAC depletion on photoinhibition and photoprotection of the photosystem II (PSII) complex. The steady-state phosphorylation levels of PSII proteins were not affected, but the degradation of the reaction center II D1 protein was blocked, and decreased amounts of CP43-less PSII monomers were detected in the mutants. Besides this, the mutant leaves displayed a transiently higher nonphotochemical quenching of chlorophyll fluorescence than the wild-type leaves, especially at low light. This may be attributed to the accumulation in the absence of TAAC of a higher electrochemical H(+) gradient in the first minutes of illumination, which more efficiently activates photoprotective xanthophyll cycle-dependent and independent mechanisms. Based on these results, we propose that TAAC plays a critical role in the disassembly steps during PSII repair and in addition may balance the trans-thylakoid electrochemical H(+) gradient storage.

Variation in Photosynthetic Traits and Antioxidant Enzyme Activities of Wheat Seedlings Transferred from Low to High Light Growth Condition

When plants absorb excessive light energy, a large number of reactive oxygen species is generally produced resulting in the degradation of DNA, proteins, and pigments in plants. For wheat (Triticum aestivum L.) grown in North China, the photooxidation induced by high light (HL) during grain-filling period usually causes great losses in grain yield. It is important to understand the mechanism of wheat plant in response to HL for HL-tolerant breeding in wheat. Xiaoyan 54, a wheat cultivar with high resistance to HL, is an ideal material to disclose photosynthesis characteristics of wheat when exposed to HL. In this study, the third-leaf seedlings of Xiaoyan 54 were grown under the condition low light to HL in a growth chamber. The seedlings were sampled at 0, 1, 3, 8, 24, and 48 h after HL treatment. Simultaneously, the net photosynthetic rate (Pn), chlorophyll content (Chl), and fluorescence parameters were measured with the second leaf. The activities of antioxidant enzymes, such as superox-ide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR), were also determined. In addition, expression pattern of the pigment binding protein related genes were evaluated. The results showed that Pn increased in the photosynthetic induction stage that was from 0 h to 8 h of HL treatment, but decreased continuously during the photoinhibi-tion stage that was from 8 h to 48 h of HL treatment. The maximum Pn value of 18 μmol CO2 m?2 s?1 was observed at the 8 h timepoint of HL treatment. The parameters Gs, Ci, and Tr changed similarly to Pn and reached the peaks at the 8 h timepoint of treatment. The contents of total chlorophyll and chlorophyll a only changed slightly during the 48 h of HL treatment. In contrast, chlorophyll b reduced significantly from 24 h to 48 h of treatment, and the ratio of chlorophyll a/b increased from 8 h to 48 h of HL treatment. At the one hour timepoint of HL treatment, the maximum quantum efficiency of PSII (Fv/Fm), the maximum fluo-rescence (Fm), and variable fluorescence (Fv) were down-regulated significantly, when the heat dissipation was enhanced. The activities of SOD, CAT, APX, and GR were induced to higher levels with the highest value at the 24 h timepoint of HL treatment. From 8 h to 48 h of HL treatment, the Talhcb genes, encoding LHCII subunits, were down-regulated at the RNA levels. At early stage of HL treatment (0–3 h), TaELIP1 and TaELIP3 were induced, but repressed from 8 h to 48 h. As key enzymes in xantho-phyll cycle, the transcripts of TaVDE and TaZEP responded differently to HL treatment. The expression of TaVDE decreased remarkably at 8 h of HL treatment and maintained a rather low level till 48 h. However, the expression of TaZEP showed an increase trend from 3 h to 24 h, and decreased at 48 h. In conclusion, when wheat seedlings exposed to continuous HL for 48 h, photooxidative stress occurred resulting in reductions of Pn, Fv/Fm, Chl b, and the expressions of pigment binding protein genes, but activation of the antioxidant enzymes.

Features of anthocyanin biosynthesis in pap1-D and wild-type Arabidopsis thaliana plants grown in different light intensity and culture media conditions

The number of different anthocyanin molecules potentially produced by Arabidopsis thaliana and which anthocyanin molecule is the first product of anthocyanidin modification remain unknown. To accelerate the understanding of these questions, we investigated anthocyanin biosynthesis in rosette leaves of both pap1-D and wild-type (WT) A. thaliana plants grown in nine growth conditions, which were composed of three light intensities (low light, middle light, and high light) and three media derived from MS medium (medium-1, 2, and 3). These nine growth conditions differentially affected the levels of anthocyanins and pigmentation patterns of rosette leaves, which were closely related to the diversification levels of cyanin structures. The combined growth conditions of high light and either medium-2 or medium-1 induced the most molecular diversity of anthocyanin structures in rosette leaves of pap1-D plants. Twenty cyanin molecules, including five that were previously unknown, were characterized by HPLC-ESI-MS and HPLC-TOF-MS analyses. We detected that the A. thaliana anthocyanin molecule A11 was most likely the first cyanin derived from the multiple modification steps of cyanidin. In addition, in the same growth condition, rosette leaves of pap1-D plants produced much higher levels and more diverse molecular profiling of cyanins than those of WT plants. The transcript levels of PAP1, PAL1, CHS, DFR, and ANS cDNAs were much higher in pap1-D rosette leaves than in WT ones. Furthermore, on the same agar-solidified medium, an enhancement of light intensity increased levels and molecular diversity of cyanins in both pap1-D and WT rosette leaves. In the same light intensity condition, the responses of anthocyanin levels and profiling to medium alternation were different between pap1-D and WT plants.

Variation in Photosynthetic Traits and Antioxidant Enzyme Activities in Wheat Seedlings Transferred from Low to High Light Growth Condition

The photooxidation induced by high light (HL) during the grain-filling period usually causes great yield loss of wheat ( Triticum aestivum L.) in northern China. To understand the mechanism of wheat plant in response to HL, the photosynthetic characteristics of Xiaoyan 54, a winter wheat cultivar with high tolerance to HL, were investigated under HL condition. At third-leaf stage, seedlings of Xiaoyan 54 were transferred from low light to HL in a growth chamber and treated for 0, 1, 3, 8, 24, and 48 h. The net photosynthetic rate ( P n), chlorophyll content, and fluorescence parameters were measured with the second leaf. The activities of antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR), were also determined. In addition, the expression patterns of genes encoding pigment-binding proteins were also evaluated. The results showed that the P n increased gradually during the photosynthetic induction phase within 8 h of HL treatment, but decreased continuously during the photoinhibition phase longer than 8 h of HL treatment. The maximum P n value of 18 μmol CO 2 m −2 s −1 was observed at the 8 h timepoint. The G s, C i, and T r varied similarly to the P n and reached their peaks at the 8 h timepoint. The contents of total chlorophyll and chlorophyll a were changed slightly during 48 h of HL treatment. In contrast, chlorophyll b reduced significantly at the 24 and 48 h timepoints, but the ratio of chlorophyll a to b continuously increased from the 8 h timepoint. One hour of HL treatment significantly reduced the maximum quantum efficiency of PSII ( F v/ F m), the maximum fluorescence ( F m), and the variable fluorescence ( F v), but enhanced the heat dissipation process. The activities of SOD, CAT, APX, and GR were induced by HL stress and reached the highest values at 48 h timepoint. At the photoinhibition stage, the RNA transcripts of Talhcb genes that encode LHCII subunits declined. TaELIP1 and TaELIP3 encoding early light-induced protein were induced by short-term HL (within 3 h) and repressed by long-term HL. As the key enzymes in xanthophyll cycle, the transcripts of TaVDE and TaZEP responded differently to the HL stress. The transcripts of TaVDE decreased remarkably after 8 h timepoint and remained low level. However, the transcripts of TaZEP showed an increase trend from 3 to 24 h of HL, and decreased at 48 h timpoints. In conclusion, when wheat seedlings were exposed to continuous HL for 48 h, photooxidative stress occurred, which resulted in a series of variations in physiology and biochemistry, such as reductions of P n, F v/ F m, and Chl b, the down-regulated expressions of pigment-binding protein genes, and the activation of antioxidant enzymes.

Photosynthetic acclimation to different light levels in the brown marine macroalga, Hizikia fusiformis (Sargassaceae, Phaeophyta)

Hizikia fusiformis thalli experience dynamic incident light conditions during the period of growth. The present study was designed to examine how changing photon irradiance affects the photosynthesis both in the short and long terms by culturing H. fusiformis under three different light levels: 35 μmol photons m-2 s-1 (low light, LL), 85 μmol photons m-2 s-1 (intermediate light, IL), and 165 μmol photons m-2 s-1 (high light, HL). A similar relative growth rate was observed between IL- and HL-grown algae, but the growth rate was significantly reduced in LL-grown algae. The photosynthetic rates (Pn) measured at their respective growth light levels were found to be lowest in the thalli grown at LL and highest at HL. However, LL-grown algae exhibited much higher Pn in comparison with IL- and the HL-grown thalli at the same measuring photosynthetic photon flux density, indicating the photosynthetic acclimation to low growth light in H. fusiformis. The photosynthesis–light curves showed that LL-grown algae had a highest light-saturating maximum Pn (Pmax) in comparison with IL- or HL-grown algae when the photosynthetic rates were expressed on the biomass basis. However, Pmax was highest in HL-grown algae compared to IL- or LL-grown algae when the rates were normalized to chlorophyll a. The photosynthesis–inorganic carbon (Ci) response curves were also significantly affected by the growth light conditions. The highest value of apparent photosynthetic conductance occurred in LL-grown algae while the lowest value in HL-grown algae. Additionally, the activity of external carbonic anhydrase (CA) tended to increase while the total CA activity inclined to decrease in H. fusiformis thalli when the growth light level altered from 35 to 165 μmol photons per square meter per second. The external CA inhibitors showed a higher inhibition in HL-grown algae compared with LL-grown algae. It was proposed that photosynthetic acclimation to low light condition in H. fusiformis was achieved through an increase in the number of reaction centers and increased capacities of electron transport and of Ci transport within cells. The ability of photosynthetic acclimation to low light confers H. fusiformis thalli to overcome the environmental low light condition as a result of the attenuation of seawater or self-shading through enhancing its photosynthetic performance and carbon assimilation necessary for growth.

Short‐term dynamics of isotopic composition of leaf‐respired CO2 upon darkening: measurements and implications

Recent advances in understanding the metabolic origin and the temporal dynamics in delta(13)C of dark-respired CO(2) (delta(13)C(res)) have led to an increasing awareness of the importance of plant isotopic fractionation in respiratory processes. Pronounced dynamics in delta(13)C(res) have been observed in a number of species and three main hypotheses have been proposed: first, diurnal changes in delta(13)C of respiratory substrates; second, post-photosynthetic discrimination in respiratory pathways; and third, dynamic decarboxylation of enriched carbon pools during the post-illumination respiration period. Since different functional groups exhibit distinct diurnal patterns in delta(13)C(res) (ranging from 0 to 10 per thousand diurnal increase), we explored these hypotheses for different ecotypes and environmental (i.e. growth light) conditions. Mass balance calculations revealed that the effect of respiratory substrates on diurnal changes in delta(13)C(res) was negligible in all investigated species. Further, rapid post-illumination changes in delta(13)C(res) (30 min), which increased from 2.6 per thousand to 5 per thousand over the course of the day, were examined by positional (13)C-labelling to quantify changes in pyruvate dehydrogenase (PDH) and Krebs cycle (KC) activity. We investigated the origin of these dynamics with Rayleigh mass balance calculations based on theoretical assumptions on fractionation processes. Neither the estimated changes of PDH and KC, nor decarboxylation of a malate pool entirely explained the observed pattern in delta(13)C(res). However, a Rayleigh fractionation of (12)C-discriminating enzymes and/or a rapid decline in the decarboxylation rate of an enriched substrate pool may explain the post-illumination peak in delta(13)C(res). These results are highly relevant since delta(13)C(res) is used in large-scale carbon cycle studies.

Reference gene selection for quantitative real-time PCR normalization in tomato subjected to nitrogen, cold, and light stress

We examined eight putative consistently expressed genes—actin (ACT), β-tubulin, elongation factor 1α (EF1), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), phosphoglycerate kinase (PGK), ribosomal protein L2 (RPL2), ubiquitin (UBI), and a catalytic subunit of protein phosphatase 2A (PP2Acs)—for their potential as references for the normalization of gene expression in tomato leaves. Expression stability of candidate reference genes was tested during growth conditions of nitrogen (N) starvation, low temperature, and suboptimal light. The geNorm algorithm, using reciprocal cross-validation among a larger group of candidate references, was applied for this purpose. The widely used reference genes GAPDH and PGK were top ranked during light stress but poorly ranked during N and cold stress. In contrast, EF1 was top ranked during N and cold stress but poorly ranked during light stress. The novel references RPL2 and PP2Acs, as well as the traditional references ACT and UBI, appeared to be stably expressed when looking at the data set as a whole. No gene was identified that exhibited such a constant level of expression as to outperform the other candidates under all experimental conditions. Thus, the results highlight the need for normalizing gene expression in tomato using the geometric average of multiple carefully selected reference genes.

Novel Nuclear-encoded Subunits of the Chloroplast NAD(P)H Dehydrogenase Complex

The NAD(P)H dehydrogenase (NDH) complex functions in photosystem I cyclic electron transfer in higher plant chloroplasts and is crucial for plant responses to environmental stress. Chloroplast NDH complex is a close relative to cyanobacterial NDH-1L complex, and all fifteen subunits so far identified in NDH-1L have homologs in the chloroplast NDH complex. Here we report on the identification of two nuclear-encoded proteins NDH48 and NDH45 in higher plant chloroplasts and show their intimate association with the NDH complex. These two membrane proteins are shown to interact with each other and with the NDH complex enriched in stroma thylakoids. Moreover, the deficiency of either the NDH45 protein or the NDH48 protein in respective mutant plants leads to severe defects in both the accumulation and the function of the NDH complex. The NDH48 and NDH45 proteins are not components of the hydrophilic connecting domain of the NDH complex but are strongly attached to the hydrophobic membrane domain. We conclude that NDH48 and NDH45 are novel nuclear-encoded subunits of the chloroplast NDH complex and crucial both for the stable structure and function of the NDH complex.

CALLUS CULTURE OF TRIGONELLA FOENUM GRAECUM AS A PLANT TISSUE CULTURE ALTERNATIVE OF ANTIBACTERIAL ACTIVITY

In the present study, Fenugreek (Trigonella foenum graecum) seeds were surface sterilized and allowed to germinate on hormone free Murashige and Skoog's culture media for one week. Hypocotyls were cut into 0.5 mm length segments. Callus morphogenesis was achieved from the hypocotyls segments Using Murashige and Skoog's culture media supplemented with benzyl adenine and naphthalene acetic acid. The best callus biomass was obtained with 2 mg/l (BA) plus 1.5 mg/L (NAA) and the growth biomass was measured after 4 weeks. This concentration was then used to plot the growth curve of callus under both dark and light growth conditions. Calli obtained under light conditions exhibited a greenish yellow pigmentation, generally accumulated better biomass and their cells contained numerous and well formed discoid plastids. Calli obtained after 3, 6 and 9 weeks of growth were harvested, dried, and grinded into a fine powder and then extracted with ethanol 80%. Antibacterial activity of various calli extracts was checked by the disc-plate diffusion method and the results obtained have indicated that both hypocotyls and calli obtained from these explants exhibited activity against the tested bacteria and it was generally observed that calli were more potent than hypocotyls and that calli induced under light conditions were more potent in some cases than dark-induced calli in inhibiting the bacterial growth.

Plastic responses of 4 tree species of successional subalpine coniferous forest serals to different light regimes

The morphological and physiological plasticity to 6 light conditions was investigated for seedlings of 4 tree species dominating at different successional serals in subalpine coniferous forests in eastern Qinghai-Tibet Plateau, China. Abies faxoniana is a late successional species, while Betula albo-sinensis is a pioneer tree species, with Picea asperata and Acer davidii among other mid-late successional species. To compare the responses of photosynthetic characters to different growth light conditions, the seedlings were potted and placed in artificially shaded chambers with gradients of 100%, 55%, 40%, 25%, 15% and 7% of the full sunlight, respectively. During two and a half years' cultivation, various morphological and photosynthetic parameters were measured and analyzed. The results were: 1) all seedlings of the four species under the low growth light conditions showed decrease in root collar diameter, relative growth rate, leaf thickness, root mass ratio, leaf area-based photosynthetic capacity, dark respiration rate, light saturation point and light compensation point, while showed increase in specific leaf area, above-ground to under-ground mass ratio, specific stem length, leaf mass ratio and stem mass ratio; 2) under most light conditions, A. faxoniana of the two conifers revealed lower values in both leaf area-based photosynthetic capacity and respiration rates than P. asperata; the same fact held true for the two broad-leaved trees with lower values observed in B. albo-sinensis; 3) under higher light conditions, relative growth rates of P. asperata and B. albo-sinensis got higher values than those of A. faxoniana and A. davidii, while contrary results were obtained under lower light regimes; 4) the means of phenotypic plastic indices of the eleven morphological and physiological parameters of P. asperata and B. albo-sinensis were higher than those of A. faxoniana and A. davidii, respectively. The findings indicate that A. faxoniana has better adaptation to low light regimes, but as a shade-tolerant species, it is not so adapted to low light regimes as the trees of earlier successional serals, especially P. asperata and B. albo-sinensis. Of the four tree species, physiological plastic indices were higher than morphological plastic indices, suggesting that morphological plasticity plays an important role in their adaptation to different growth light conditions. The results also support the hypothesis that ecophysiological traits of tree species determine their successional status and associate habitats of their seedlings.

Towards understanding the functional difference between the two PsbO isoforms in Arabidopsis thaliana—insights from phenotypic analyses of psbo knockout mutants

The extrinsic PsbO subunit of the water-oxidizing photosystem II (PSII) complex is represented by two isoforms in Arabidopsis thaliana, namely PsbO1 and PsbO2. Recent analyses of psbo1 and psbo2 knockout mutants have brought insights into their roles in photosynthesis and light stress. Here we analyzed the two psbo mutants in terms of PsbOs expression pattern, organization of PSII complexes and GTPase activity. Both PsbOs are present in wild-type plants, and their expression is mutually controlled in the mutants. Almost all PSII complexes are in the monomeric form not only in the psbo1 but also in the psbo2 mutant grown under high-light conditions. This results either from an enhanced susceptibility of PSII to photoinactivation or from malfunction of the repair cycle. Notably, the psbo1 mutant displays such problems even under growth-light conditions. These results together with the finding that PsbO2 has a threefold higher GTPase activity than PsbO1 have significance for the turnover of the PSII D1 subunit in Arabidopsis.

Physiological dissection of blue and red light regulation of apical dominance and branching in M9 apple rootstock growing in vitro

This paper presents the results of the interaction of red light (R) with blue light (B), applied to shoots of M9 apple ( Malus pumila paradisiaca Schmid) rootstock, on the regulation of stem growth, apical dominance and branching. These results are compared with the active form of phytochromes (PHYs) under monochromatic and dichromatic light treatments. The inhibition of internode elongation was determined by PHY photoequilibrium, with the additional effect of B, by means of a separate photoreceptor. The development of phytomers appeared to be primarily due to the active form of PHY, with a marginal effect from B. Shoot growth, which combines internode elongation and development of the phytomer, was highest under R and lowest under B and far red light (FR), showing the largely positive role of PHY photoequilibrium. Under FR, reduced stem elongation was due to the very small number of phytomers formed. Apical dominance was inhibited, while branching was increased under R, corresponding to the highest values of PHY photoequilibrium determined. Apical dominance was increased and branching was reduced by B, indicating a complex interaction between PHY and B receptor. In the shoot cluster system, photomorphogenic behavior was dependent on the time of exposure to the different light qualities. The information gained from the study will be helpful in improving the set up of in vitro growth light conditions, and in providing useful insights into research of the development of the woody plant canopy, an important factor in ecological plant communities.

Growth characteristics of two tropical forest species Warburgia ugandensis and Polyscias fulva seedlings grown under contrasting light conditions

Growth parameters for seedlings of two forest trees, Warburgia ugandensis andPolyscias fulva, were measured under various light growth conditions. Leaf area and plant height were significantly higher under low light (< 42% full sunlight) than high light (65% of sunlight) growth conditions (P<0.001). Plant leaf area ranged from 238 cm² under full sunlight to 376 cm² under dense shade in P. fulva and from 33 cm² under full sunlight to 178 cm² under dense shade in W. ugandensis.Plant heights ranged from about 20 mm under full sunlight to 38 mm under dense shade in P. fulva; and from about 36 mm under full sunlight to 89 mm under dense shade in W. ugandensis. P. fulva had more leaves than W. ugandensis but both species increased their leaf numbers from 28 (full sunlight) to 37 (dense shade) and 21 (full sunlight) to 29 (dense shade) respectively (P< 0.05). P. fulva accumulated more biomass (from 4 to about 9g) than W. ugandensis (from 0.6 to 2.4g) under all light conditions (P<0.05). The shoot/root ratios were highest (1.84 for P. fulva and 6.42 for W. ugandensis) under low light conditions in the two species (P<0.05). Highest specific leaf areas were recorded under low light growth conditions for the two species (198 cm² g-1 forP. fulva and 220 cm² g-1 for W. ugandensis). W. ugandensis was found to be more shade tolerant than P. fulva. Key words: Forest tree seedlings, Warburgia, Polyscias, light, growth

Molecular Design of Photosynthesis-Elevated Chloroplasts for Mass Accumulation of a Foreign Protein

In order to increase production of a useful protein by the chloroplast transformation technique, it seems to be necessary to determine the upper limit for the accumulation of a biologically active foreign protein in chloroplasts and then improve photosynthetic capacity and plant productivity. Here we show that the stromal fractions of tobacco chloroplasts could accommodate an additional 200-260 mg ml(-1) of green fluorescent protein in the stroma without any inhibition of gas exchange under various light intensity and growth conditions. The minimum amount of fructose-1,6-/sedoheptulose-1,7-bisphosphatase (FBP/SBPase) limiting photosynthesis was then calculated. Analyses of the photosynthetic parameters and the metabolites of transformants into which FBP/SBPase was introduced with various types of promoter (PpsbA, Prrn, Prps2 and Prps12) indicated that a 2- to 3-fold increase in levels of FBPase and SBPase activity is sufficient to increase the final amount of dry matter by up to 1.8-fold relative to the wild-type plants. Their increases were equivalent to an increase of <1 mg ml(-1) of the FBP/SBPase protein in chloroplasts and were calculated to represent <1% of the protein accumulated via chloroplast transformation. Consequently, >99% of the additional 200-260 mg ml(-1) of protein expressed in the chloroplasts could be used for the production of useful proteins in the photosynthesis-elevated transplastomic plants having FBP/SBPase.

Influence of light on health‐promoting phytochemicals of broccoli sprouts

AbstractBACKGROUND: Broccoli (Brassicaceae) is a rich source of phytochemicals (glucosinolates and phenolic compounds) and micronutrients (vitamins and minerals). Germinated broccoli sprouts contain much higher levels (10–100 times) of aliphatic (glucoraphanin) and indolic glucosinolates than the inflorescences. This quality characteristic of broccoli sprouts plays an important role in human health and disease prevention. Although it is known that genetic and environmental factors can affect the composition of broccoli inflorescences, the influence of such factors on the seeds and sprouts has not been widely reported. Therefore the aim of this study was to determine the effect of light versus dark growth conditions on the phytochemical composition (vitamin C, phenolic compounds and glucosinolates) of broccoli sprouts.RESULTS: Broccoli sprouts grown in the light were found to have much higher concentrations of vitamin C (by 83%), glucosinolates (by 33%) and phenolic compounds (by 61%) than those grown in the dark. During a 7 day period there was a clear and analogous trend in both treatments, with a general reduction in concentrations over time. Among the different organs studied (seeds, cotyledons, stems and roots), the cotyledons contained the highest levels of bioactive compounds, while the roots contained the lowest.CONCLUSION: Light treatment of sprouting broccoli seeds increased their concentration of health‐promoting phytochemicals, mainly during the first 3–5 days of development. Therefore the younger broccoli sprouts are a better source of bioactive compounds for the consumer than the inflorescences. Copyright © 2008 Society of Chemical Industry

伊勢いもの組織培養における多芽体およびマイクロチューバーの形成に及ぼす植物成長調節物質， 光条件および培地の影響

伊勢いもの茎頂および節切片を材料として, 固形および液体のMS培地による組織培養によって多芽体を作成し, それらを分割して増殖・成長させ, さらにマイクロチューバーを作出した. 茎頂外植片はベンジルアデニン(BA)0.1～2 mg L-1とナフタレン酢酸(NAA)0.1～0.5 mg L-1, 節切片はBA 0.1～5 mg L-1の添加で多芽体を分化した. 多芽体はBAのみ5mg L-1を添加した培地に移植すると, そのまま維持し続けることができ, また, 植物成長調節物質無添加の培地に移植すると, 多芽体からシュートが伸長した. ある程度伸長したシュートにジャスモン酸(JA)を添加すると, マイクロチューバーは速やかに形成されたが, 無添加でも時間が経つと形成された. その形成数は暗黒下でより多く, 肥大は光照射下でより良好であった. 得られた生体重120 mg以上のマイクロチューバーは, 8℃に保った冷蔵庫内で1ヶ月貯蔵した後, 通常の栽培に用いることができた.

Differential regulation of psbA and psbD gene expression, and the role of the different D1 protein copies in the cyanobacterium Thermosynechococcus elongatus BP-1

In Thermosynechococcus elongatus BP-1 , which is the preferred organism in recent structural studies of PSII, three psbA and two psbD genes code for three D1 and one D2 protein isoforms, respectively. The regulation and function of these genes and protein products is largely unknown. Therefore, we used quantitative RT-PCR to follow changes in the mRNA level of the respective genes, in combination with biophysical measurements to detect changes in the electron transport activity of Photosystem II under exposure to different visible and UV light, and temperature conditions. In cells which are acclimated to 40 μmol m − 2 s − 1 growth light conditions at 40 °C the main populations of the psbA and psbD transcripts arise from the psbA1 and psbD1 genes, respectively. When the temperature is raised to 60 °C psbA1 becomes the single dominating psbA mRNA species. Upon exposure of the cells to 500 μmol m − 2 s − 1 intensity visible light psbA3 replaces psbA1 as the dominating psbA mRNA species, and psbD2 increases at the expense of psbD1. UV-B radiation also increases the abundance of psbA3, and psbD2 at the expense of psbA1 and psbD1, respectively. From the different extent of total D1 protein loss in the absence and presence of lincomycin it was estimated that the PsbA3 protein isoform replaces PsbA1 in about 65% of PSII centers after 2 h of high light acclimation. Under the conditions of different psbA transcript distributions chlorophyll fluorescence and thermoluminescence measurements were applied to monitor charge recombination characteristics of the S 2Q A − and S 2Q B − states. We obtained faster decay of flash-induced chlorophyll fluorescence in the presence of DCMU, as well as lower peak temperature of the Q and B thermoluminescence bands when PsbA3 replaced PsbA1 as the main D1 protein isoform. The relevance of dynamic changes in the abundance of psbA and psbD transcript levels, as well as D1 protein isoforms in the acclimation of T. elongatus to changing environmental conditions is discussed.

Progesterone: Its occurrence in plants and involvement in plant growth

Progesterone is a mammalian gonadal hormone. In the current study, we identified and quantified progesterone in a range of higher plants by using GC–MS and examined its effects on the vegetative growth of plants. The growth of Arabidopsis ( Arabidopsis thaliana) seedlings was promoted by progesterone at low concentrations but suppressed at higher concentrations under both light and dark growth conditions. The growth of the gibberellin-deficient mutant lh of pea ( Pisum sativum) was also promoted by progesterone. An earlier study demonstrated that progesterone binds to MEMBRANE STEROID BINDING PROTEIN 1 (MSBP1) of Arabidopsis. In this work, we cloned the homologous genes of Arabidopsis, MSBP2 and STEROID BINDING PROTEIN ( SBP), as well as of rice ( Oryza sativa), OsMSBP1, OsMSBP2 and OsSBP and examined their expression in plant tissues. All of these genes, except OsMSBP1, were expressed abundantly in plant tissues. The roles of progesterone in plant growth were also discussed.

Plasmodesmata density in vascular bundles in leaves of C4 grasses grown at different light conditions in respect to photosynthesis and photosynthate export efficiency

The study was conducted with young plants of four species of C4 grasses of three photosynthetic sub-types: Panicum miliaceum (NAD-ME), Panicum maximum (PEP-CK), and Zea mays and Digitaria sanguinalis (both NADP-ME) with the aim to verify the hypothesis that light growth conditions affect the density of plasmodesmata connecting the photosynthetically active chlorenchymatous Kranz mesophyll (KMS) and bundle sheath (BS), as well as vascular parenchyma (VP) cells, and that the density of the plasmodesmata limits the efficiency of photosynthesis and photosynthate export from the leaf. The most important ultrastructural difference between the LL (grown at 50 μmol quanta m −2 s −1), ML (grown at 200 μmol quanta m −2 s −1) and HL (grown at 1000 μmol quanta m −2 s −1) plants was the increase, with increasing growth illumination, in the density of plasmodesmata connecting KMS and BS cells and, to a lesser extent, of those between BS and VP cells. This tendency was observed for all C4 grasses tested, although the magnitude of the reaction was species-specific, with the weakest and highest increase noted for P. miliaceum and D. sanguinalis, respectively. The maximum net photosynthesis rate (measured at saturating photon flux) was much higher in HL than in ML plants (except for P. miliaceum) and it was correlated very well with the density of the KMS/BS plasmodesmata. The photosynthate export capacity of the plants, as characterized by the time of 14C-photosynthate transfer into the transport path, the fraction of newly synthesized photosynthates exported from the leaf, and the transport speed in the leaf blade showed that ML plants were source-limited and HL plants were sink-limited. Apparently, C4 grasses are able to adjust their photosynthetic apparatus to light growth conditions by changing the number of plasmodesmata connecting cells of Kranz mesophyll, bundle sheath and vascular parenchyma in proportion to the intensity of illumination, so that for plant grown at high illumination the transport of photosynthates ceases to be a bottleneck limiting the efficiency of photosynthesis.

Pigment apparatus in Ajuga reptans plants as affected by adaptation to light growth conditions

Mechanisms of adaptation of the photosynthetic apparatus at the level of pigment complex in a shade-tolerant bugle plant (Ajuga reptans L.) grown at full solar irradiation in an open plot were studied. In “sun” plants, the content of photosynthetic pigments decreased markedly as compared to “shade” plants grown under a forest canopy at 5–10% of the full solar irradiation. In leaves of sun plants, the portion of β-carotene and lutein in the carotenoid spectrum was higher than in shade plant leaves, antheraxanthin and zeaxanthin were present, and de-epoxidation of violaxanthin was by an order of magnitude higher in sun plant leaves reaching 40%. The data obtained indicate the role of the violaxanthin cycle in the protection of photosynthetic apparatus in a shade-tolerant plant against destruction under excessive irradiation.