Green Phenotype Research Articles

Inhibition of TOR Represses Nutrient Consumption, Which Improves Greening after Extended Periods of Etiolation

Upon illumination, etiolated seedlings experience a transition from heterotrophic to photoautotrophic growth. During this process, the tetrapyrrole biosynthesis pathway provides chlorophyll for photosynthesis. This pathway has to be tightly controlled to prevent the accumulation of photoreactive metabolites and to provide stoichiometric amounts of chlorophyll for its incorporation into photosynthetic protein complexes. Therefore, plants have evolved regulatory mechanisms to synchronize the biosynthesis of chlorophyll and chlorophyll-binding proteins. Two phytochrome-interacting factors (PIF1 and PIF3) and the DELLA proteins, which are controlled by the gibberellin pathway, are key regulators of this process. Here, we show that impairment of TARGET OF RAPAMYCIN (TOR) activity in Arabidopsis (Arabidopsis thaliana), either by mutation of the TOR complex component RAPTOR1B or by treatment with TOR inhibitors, leads to a significantly reduced accumulation of the photoreactive chlorophyll precursor protochlorophyllide in darkness but an increased greening rate of etiolated seedlings after exposure to light. Detailed profiling of metabolic, transcriptomic, and physiological parameters revealed that the TOR-repressed lines not only grow slower, they grow in a nutrient-saving mode, which allows them to resist longer periods of low nutrient availability. Our results also indicated that RAPTOR1B acts upstream of the gibberellin-DELLA pathway and its mutation complements the repressed greening phenotype of pif1 and pif3 after etiolation.

Influence of nitrogen source on photochemistry and antenna size of the photosystems in marine green macroalgae, Ulva lactuca

Ulva lactuca is regarded as a prospective energy crop for biorefinery owing to its affluent biochemical composition and high growth rate. In fast-growing macroalgae, biomass development strictly depends on external nitrogen pools. Additionally, nitrogen uptake rates and photosynthetic pigment content vary with type of nitrogen source and light conditions. However, the combined influence of nitrogen source and light intensity on photosynthesis is not widely studied. In present study, pale green phenotype of U. lactuca was obtained under high light (HL) condition when inorganic nitrogen (nitrate) in the media was substituted with organic nitrogen (urea). Further, pale green phenotype survived the saturating light intensities in contrast to the normal pigmented control which bleached in HL. Detailed analysis of biochemical composition and photosynthesis was performed to understand functional antenna size and photoprotection in pale green phenotype. Under HL, urea-grown cultures exhibited increased growth rate, carbohydrate and lipid content while substantial reduction in protein, chlorophyll content and PSII antenna size was observed. Further, in vivo slow and polyphasic chlorophyll a (Chl a) fluorescence studies revealed reduction in excitation pressure on PSII along with low non-photochemical quenching thus, transmitting most of the absorbed energy into photochemistry. The results obtained could be correlated to previous report on cultivation of U. lactuca through saturating summer intensities (1000 µmole photons m-2 s-1) in urea based: poultry litter extract (PLE). Having proved critical role of urea in conforming photoprotection, the application PLE was authenticated for futuristic, sustainable and year-round biomass cultivation.

RAF2 is a RuBisCO assembly factor in Arabidopsis thaliana.

Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) catalyzes the reaction between gaseous carbon dioxide (CO2 ) and ribulose-1,5-bisphosphate. Although it is one of the most studied enzymes, the assembly mechanisms of the large hexadecameric RuBisCO is still emerging. In bacteria and in the C4 plant Zea mays, a protein with distant homology to pterin-4α-carbinolamine dehydratase (PCD) has recently been shown to be involved in RuBisCO assembly. However, studies of the homologous PCD-like protein (RAF2, RuBisCO assembly factor 2) in the C3 plant Arabidopsis thaliana (A. thaliana) have so far focused on its role in hormone and stress signaling. We investigated whether A. thalianaRAF2 is also involved in RuBisCO assembly. We localized RAF2 to the soluble chloroplast stroma and demonstrated that raf2 A. thaliana mutant plants display a severe pale green phenotype with reduced levels of stromal RuBisCO. We concluded that the RAF2 protein is probably involved in RuBisCO assembly in the C3 plant A. thaliana.

Heterologous expression of kiwifruit (Actinidia chinensis) GOLDEN2-LIKE homolog elevates chloroplast level and nutritional quality in tomato (Solanum lycopersicum).

Constitutive expression of AchGLK from A. chinensis in transgenic tomato (S. lycopersicum) confers fruits an elevated plastid biogenesis with intensified granule thylakoid stacks and increased content of nutritional compounds. Plastid development is regulated by multiple environmental and genetic factors. Golden2-like (GLK) genes, members from GARP subfamily of the MYB transcription factors, have been shown to regulate plastid biogenesis and development in several species. In tomato (S. lycopersicum), SlGLK2 gene is expressed in the fruit in a manner of latitudinal gradient and determines the green shoulder phenotype. Here, we report the isolation and characterization of a kiwifruit (A. chinensis) GLK homolog (AchGLK). Transcription analysis showed that AchGLK is highly expressed in mature leaves and in fruits 60-day post-anthesis. Overexpression of AchGLK in transgenic tomato resulted in dark green immature fruit with higher concentration of chlorophyll and overall increased chloroplast compartment, both number and size. The ripened fruit had higher levels of carotenoids and sugars as well. Nevertheless, no phenotypic changes were observed in the transgenic leaves, similar to the previously described overexpression of SlGLK2 in tomato. Our study suggests that AchGLK is functionally homologous to tomato GLK2 with a potential in regulating plastid level in fruit that could contribute to improvement of fruit quality.

Dimethylsulfonioproprionate (DMSP) content and antioxidant capacity in the host and endosymbionts of the sea anemone Entacmaea quadricolor are influenced by the host phenotype

Dimethylsulfoniopropionate (DMSP) is a key biogenic compound in marine algae and symbiotic cnidarians. Besides its role as a precursor of the climatically active dimethylsulfide, DMSP is a putative antioxidant through its capacity to scavenge reactive oxygen species. Here, the production of DMSP concurrently with the antioxidant capacity (AOC) among the host and endosymbionts of two colour phenotypes of the sea anemone Entacmaea quadricolor, that provides essential habitat for anemonefish, was investigated for 9days under heat stress (3.2°C and 6.3°C above control). Although visual signs of bleaching were observed on day 3 in all of the anemones at high temperature, cell density and chlorophyll a content did not vary among temperatures over time. The maximum quantum yield of endosymbionts decreased over time in medium and high temperature treatments in both phenotypes, indicating slight photoinhibition under thermal stress. Temperature had no or little effect on AOC and DMSP concentrations in the host and endosymbionts in both phenotypes, suggesting adaptation of subtropical E. quadricolor and associated symbionts to short-term abrupt changes in temperature, which is a regular occurrence in this region. However, host and endosymbiont AOC and DMSP concentrations were, at least partly, driven by the host phenotype, with overall greater AOC and lower DMSP concentrations being found in pink compared with green anemones. These results, along with stronger photoinhibition in the green phenotype under thermal stress suggest that green anemones could be more vulnerable to environmental pressure than the pink phenotype. As our oceans continue to warm, the differing responses of the colour phenotypes may influence their relative abundance on reefs, and have implications for reproductive success as the phenotypes correspond to different sexes. Furthermore, the selective disappearance of one phenotype could adversely affect anemonefish that preferentially associate with more sensitive colour morphs.

Impact of spat shell colour selection in hatchery-produced Pinctada margaritifera on cultured pearl colour

Beaded cultured pearl farming is a lengthy aquaculture process, particularly when the pearl oysters are produced through a hatchery propagation system, and includes the key steps of artificial breeding, larval and spat rearing before graft operations can take place. Within its genus, Pinctada margaritifera has the ability to produce the widest range of pearl colours, thanks to the donor colour polymorphism of the inner shell, which is mainly responsible for colour transmission. As hatchery spat production in P. margaritifera leads to several colour phenotypes (at 3 months old), the aim of this study was to determine whether a relation exists between the colour of the donors as spat and the final pearl colour. In the experiment, which took place over a four-year period, earlier spat colour selection was applied to two hatchery-produced P. margaritifera families. The spat were traced and then used as donors at the adult stage. A total of 1100 experimental grafts were made, using originally grey, green, red and yellow spat phenotypes as donors. The results showed that all spat colour phenotypes mainly produced pearls in the moderately dark (78.4%) and grey colour (56.7%) classes. Differences in darkness level were produced by red and yellow spat, whose pearls were about twice as pale as those from the grey and green phenotypes. Concerning the pearl colour categories, the results showed that the attractive green/blue pearls were obtained twice as often when using grey and green spat phenotypes and that aubergine/peacock pearls were obtained four times more often by using the red and yellow spat phenotypes. This preliminary study suggests that earlier phenotypic colour selection could be applied in P. margaritifera spat as a useful indicator in both pearl production cycles and family selection for donor oyster lines of specific colour propagation.

Exposure of high-light-grown cultures of Chlorella vulgaris to darkness inhibits the relaxation of excitation pressure: uncoupling of the redox state of the photosynthetic electron transport chain and phenotypic plasticity

Chlorella vulgaris acclimated to high light (HL) conditions exhibited a pale-green phenotype characterized by reduced chlorophyll and light harvesting polypeptide abundance compared with the dark green phenotype of the control, low-light-grown (LL) cultures. We hypothesized that if chloroplast redox status was the sole regulator of phenotype, exposure to darkness should cause reversion of the HL to LL phenotype. Surprisingly, HL cells transferred to darkness or dim light failed to green. Thus, phenotypic reversion is light-dependent with an optimal photon flux density (PFD) of 110 μmol photons·m−2·s−1. HL cells shifted to this PFD exhibited increased chlorophyll and light harvesting polypeptide abundance, which were inhibited by 2,5-dibromo-3-methyl-6-isopropyl-benzoquinone but not by 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea. We conclude that photoacclimation of HL-grown cells to LL is governed by the redox state of the intersystem photosynthetic electron transport chain (PETC) at this PFD. At lower light levels, cells maintained the HL phenotype, despite an oxidized status of the PETC. Because 110 μmol photons·m−2·s−1 was the optimal PFD for protochlorophyllide oxidoreductase accumulation, we suggest that stabilization of light-harvesting polypeptides by chlorophyll binding may also govern photoacclimation in C. vulgaris. The possible role of the metabolic balance between respiration and photosynthesis is also discussed.

Deficient glutamate biosynthesis triggers a concerted upregulation of ribosomal protein genes in Arabidopsis

Biomass production requires the coordination between growth and metabolism. In a large-scale screen for mutants affected in leaf morphology, we isolated the orbiculata1 (orb1) mutants, which exhibit a pale green phenotype and reduced growth. The combination of map-based cloning and next-generation sequencing allowed us to establish that ORB1 encodes the GLUTAMATE SYNTHASE 1 (GLU1) enzyme, also known as FERREDOXIN-DEPENDENT GLUTAMINE OXOGLUTARATE AMINOTRANSFERASE 1 (Fd-GOGAT1). We performed an RNA-seq analysis to identify global gene expression changes in the orb1–3 mutant. We found altered expression levels of genes encoding enzymes involved in nitrogen assimilation and amino acid biosynthesis, such as glutamine synthetases, asparagine synthetases and glutamate dehydrogenases, showing that the expression of these genes depends on the levels of glutamine and/or glutamate. In addition, we observed a concerted upregulation of genes encoding subunits of the cytosolic ribosome. A gene ontology (GO) analysis of the differentially expressed genes between Ler and orb1–3 showed that the most enriched GO terms were ‘translation’, ‘cytosolic ribosome’ and ‘structural constituent of ribosome’. The upregulation of ribosome-related functions might reflect an attempt to keep protein synthesis at optimal levels even when the pool of glutamate is reduced.

Distinct growth light and gibberellin regimes alter leaf anatomy and reveal their influence on leaf optical properties

Light capture by leaves is a key component for plant surveillance, and it has been accepted that blue and red lights are captured by palisade cells. However, the importance of green light absorption remains to be fully understood. Herein, wild-type tobacco plants treated with distinct gibberellin (GA) regimes [increased by gibberellic acid (GA3)] supplementation and reduced by paclobutrazol [PAC, (GA biosynthesis inhibitor) treatment] and light intensity (full sunlight and low light – 91.5% shading) to induce variations in leaf thickness, photosynthetic pigment content and leaf anatomy were used to evaluate leaf optical properties. Gibberellin supplementation promotes an etiolated phenotype with thinner leaves. On the other hand, the use of PAC induces the growth of smaller plants with a dark green phenotype. GA3-treated plants showed greater leaf area, thinner leaves and reduced pigment content expressed on a leaf area basis, but not on a dry weight basis, independently of light level. PAC-treated plants showed increased pigment content and two layers of palisade parenchyma cells in full sunlight-grown plants, but similar leaf thickness when compared to the controls. PAC-treated plants grown in the low light environment showed a dense spongy parenchyma and increased leaf thickness. All plants, including low light-grown individuals, displayed similar and high absorption of blue and red lights. GA3-treated plants presented increased green light reflectance and transmittance, and reduced absorbance. The opposite behavior was observed for PAC-treated plants. Green light is more absorbed by leaves with high pigment content (on a leaf area basis), but leaf thickness is the major component that drives green light absorption. Taken together, these results indicate that blue and red light are very efficiently absorbed, despite low chlorophyll content by adaxial structures of the leaf (palisade parenchyma), while green light is proposed to penetrate deeper in leaf cells and is suggested as driving light reactions in the spongy parenchyma.

Nitric oxide associated protein 1 is associated with chloroplast perturbation and disease symptoms in Nicotiana benthamiana infected with South African cassava mosaic virus

Nitric oxide associated 1 (NOA1) in plants is a cyclic GTPase involved in protein translation in the chloroplast and has been indirectly linked to nitric oxide (NO) accumulation and response to biotic stress. The association between NOA1 and NO accumulation in Arabidopsis noa1 mutants has been linked to the inability of noa1 mutants to accumulate carbon reserves such as fumarate, leading to chloroplast dysfunction and a pale green leaf phenotype. To understand the role played by NOA1 in response to South African cassava mosaic virus infection in Nicotiana benthamiana, the expression of NbNOA1 and the accumulation of NO in leaf samples was compared between south african cassava mosaic (SACMV)-infected and mock-infected plants at 14 and 28 dpi. Real-time qPCR was used to measure SACMV viral load which increased significantly by 20% from 14 to 28 dpi as chlorosis and symptom severity progressed. At 14 and 28 dpi, NbNOA1 expression was significantly lower than mock inoculated plants (2-fold lower at 14 dpi, p-value=0.01 and 5-fold lower at 28, p-value=0.00). At 14 dpi, NO accumulation remained unchanged in infected leaf tissue compared to mock inoculated, while at 28 dpi, NO accumulation was 40% lower (p-value=0.01). At 28 dpi, the decrease in NbNOA1 expression and NO accumulation was accompanied by chloroplast dysfunction, evident from the significant reduction in chlorophylls a and b and carotenoids in SACMV-infected leaves. Furthermore, the expression of chloroplast translation factors (chloroplast RNA binding, chloroplast elongation factor G, translation elongation factor Tu, translation initiation factor 3-2, plastid-specific ribosomal protein 6 and plastid ribosome recycling factor) were found to be repressed in infected N. benthamiana. GC–MS analysis showed a decrease in fumarate and an increase in glucose in SACMV-infected N. benthamiana in comparison to mock samples suggesting a decrease in carbon stores. Collectively, these results provide evidence that in response to SACMV infection, a decrease in photopigments and carbon stores, accompanied by an increase in glucose and decrease in fumarate, leads to a decline in NbNOA1expression and NO levels. This is manifested by suppressed translation factors and disruption of chloroplast function, thereby contributing to chlorotic disease symptoms.

Fine mapping of BoGL1, a gene controlling the glossy green trait in cabbage (Brassica oleracea L. Var. capitata)

The cuticular wax covering epidermal cells causes the glaucous appearance in cabbage. As a protective barrier, cuticular wax plays various roles in protection against biotic and abiotic stresses. This is the first gene mapping report of a dominant glossy green cabbage mutant. In the present paper, scanning electron microscopy (SEM) demonstrated that the wax crystals were severely reduced in the mutant, which indicates that the glossy green phenotype is caused by cuticular wax reduction. Genetic analysis revealed that the glossy trait is controlled by a single dominant gene. Through primer screening and fine mapping, the mutant gene BoGL1 (Brassica oleracea glossy 1) was delimited to the end of chromosome C08 by the flanking marker SSRC08–76 at a genetic distance of 0.2 cM. Two genes homologous to CER1 (ECERIFERUM 1), a gene related to wax biosynthesis in Arabidopsis, were located in the mapped region. Expressional analysis revealed that the Bol018504 gene was severely suppressed but that no nucleotide variation was found by sequencing. These results lay the foundation for the functional analysis of BoGL1, and they will accelerate the research on wax metabolism in cabbage.

Metabolic Flux Redirection and Transcriptomic Reprogramming in the Albino Tea Cultivar \u2018Yu-Jin-Xiang\u2019 with an Emphasis on Catechin Production

In this study, shade-induced conversion from a young pale/yellow leaf phenotype to a green leaf phenotype was studied using metabolic and transcriptomic profiling and the albino cultivar ‘Yu-Jin-Xiang’ (‘YJX’) of Camellia sinensis for a better understanding of mechanisms underlying the phenotype shift and the altered catechin and theanine production. Shaded leaf greening resulted from an increase in leaf chlorophyll and carotenoid abundance and chloroplast development. A total of 1,196 differentially expressed genes (DEGs) were identified between the ‘YJX’ pale and shaded green leaves, and these DEGs affected ‘chloroplast organization’ and ‘response to high light’ besides many other biological processes and pathways. Metabolic flux redirection and transcriptomic reprogramming were found in flavonoid and carotenoid pathways of the ‘YJX’ pale leaves and shaded green leaves to different extents compared to the green cultivar ‘Shu-Cha-Zao’. Enhanced production of the antioxidant quercetin rather than catechin biosynthesis was correlated positively with the enhanced transcription of FLAVONOL SYNTHASE and FLAVANONE/FLAVONOL HYDROXYLASES leading to quercetin accumulation and negatively correlated to suppressed LEUCOANTHOCYANIDIN REDUCTASE, ANTHOCYANIDIN REDUCTASE and SYNTHASE leading to catechin biosynthesis. The altered levels of quercetin and catechins in ‘YJX’ will impact on its tea flavor and health benefits.

McMYB12 Transcription Factors Co-regulate Proanthocyanidin and Anthocyanin Biosynthesis in Malus Crabapple

The flavonoid compounds, proanthocyanidins (PAs), protect plants from biotic stresses, contribute to the taste of many fruits, and are beneficial to human health in the form of dietary antioxidants. In this study, we functionally characterized two Malus crabapple R2R3-MYB transcription factors, McMYB12a and McMYB12b, which co-regulate PAs and anthocyanin biosynthesis. McMYB12a was shown to be mainly responsible for upregulating the expression of anthocyanin biosynthetic genes by binding to their promoters, but to be only partially responsible for regulating PAs biosynthetic genes. In contrast, McMYB12b showed preferential binding to the promoters of PAs biosynthetic genes. Overexpression of McMYB12a and McMYB12b in tobacco (Nicotiana tabacum) altered the expression of flavonoid biosynthetic genes and promoted the accumulation of PAs and anthocyanins in tobacco petals. Conversely, transient silencing their expression in crabapple plants, using a conserved gene region, resulted in reduced PAs and anthocyanin production a green leaf phenotype. Meanwhile, transient overexpression of the two genes and silenced McMYB12s in apple (Malus domestica) fruit had a similar effect as overexpression in tobacco and silenced in crabapple. This study reveals a new mechanism for the coordinated regulation of PAs and anthocyanin accumulation in crabapple leaves, which depends on an auto-regulatory balance involving McMYB12a and McMYB12b expression.

Fine-Mapping and Analysis of Cgl1, a Gene Conferring Glossy Trait in Cabbage (Brassica oleracea L. var. capitata)

Cuticular waxes covering the outer plant surface impart a whitish appearance. Wax-less cabbage mutant shows glossy in leaf surface and plays important roles in riching cabbage germplasm resources and breeding brilliant green cabbage. This is the first report describing the characterization and fine-mapping of a wax biosynthesis gene using a novel glossy Brassica oleracea mutant. In the present paper, we identified a glossy cabbage mutant (line10Q-961) with a brilliant green phenotype. Genetic analyses indicated that the glossy trait was controlled by a single recessive gene. Preliminary mapping results using an F2 population containing 189 recessive individuals revealed that the Cgl1 gene was located at the end of chromosome C08. Several new markers closely linked to the target gene were designed according to the cabbage reference genome sequence. Another population of 1,172 recessive F2 individuals was used to fine-map the Cgl1 gene to a 188.7-kb interval between the C08SSR61 simple sequence repeat marker and the end of chromosome C08. There were 33 genes located in this region. According to gene annotation and homology analyses, the Bol018504 gene, which is a homolog of CER1 in Arabidopsis thaliana, was the most likely candidate for the Cgl1 gene. Its coding and promoter regions were sequenced, which indicated that the RNA splice site was altered because of a 2,722-bp insertion in the first intron of Bol018504 in the glossy mutant. Based on the FGENESH 2.6 prediction and sequence alignments, the PLN02869 domain, which controls fatty aldehyde decarbonylase activity, was absent from the Bol018504 gene of the 10Q-961 glossy mutant. We inferred that the inserted sequence in Bol018504 may result in the glossy cabbage mutant. This study represents the first step toward the characterization of cuticular wax biosynthesis in B. oleracea, and may contribute to the breeding of new cabbage varieties exhibiting a brilliant green phenotype.

Sucrose supplementation suppressed the growth inhibition in polyhydroxyalkanoate-producing plants.

Polyhydroxyalkanoate (PHA) is a thermoplastic polymer with several advantageous properties, including biomass origin, biocompatibility, and biodegradability. PHA is synthesized in transgenic plants harboring 3 enzymatic genes: phaA, phaB, and phaC (collectively referred to as phaABC). PHA-producing plants exhibit severe growth inhibition that leads to extremely low PHA accumulation when these enzymes are localized in the cytosol. This growth inhibition could be attributed to the deleterious effects of the PHA biosynthetic pathway on endogenous essential metabolites or to PHA cytotoxicity itself. We performed precise morphological observations of phaABC-overexpressing Arabidopsis (ABC-ox), which displayed typical growth inhibition. On growth medium without sucrose, ABC-ox exhibited a pale green phenotype, dwarfism, including small cotyledons and true leaves, and short roots. ABC-ox partially recovered from this growth inhibition when the growth medium was supplemented with 1% sucrose. This recovery was reversed after ABC-ox grown on 1% sucrose medium was transferred to soil. ABC-ox grown on 1% sucrose medium not only demonstrated recovery from growth inhibition but were also the only examined plants with PHA accumulation, suggesting that growth inhibition was not caused by PHA cytotoxicity but rather by a lack of essential metabolites.

Inheritance of leaf and flower morphologies in Kalanchoe spp.

Members of the genus Kalanchoe are morphologically diverse; this increases their commercial value. Understanding the genetic mechanism of development of morphological characters could contribute to parent screening and offspring selection in future breeding programs. In this study, we investigated the inheritance of leaf color, leaf shape, anther color, and flower orientation of Kalanchoe species or varieties. Kalanchoe garambiensis, K. garambiensis G., K. gracilis, K. spathulata, and K. manginii ‘Wendy’ were used as experimental parents to establish self and interspecific crosses. The separation ratios of the leaf and flower traits were analyzed using Chi square tests. The results showed that all progenies produced by selfing of K. garambiensis (purple leaf phenotype) had purple leaves, whereas those from selfing of K. garambiensis G. (green leaf phenotype) exhibited green and purple leaves at a ratio of approximately 3:1. The S1 and S2 populations of K. garambiensis G. exhibited an expected 3:1 ratio of leaf color, whereas the S3 populations produced all green leaf inbred lines. Reciprocal hybridization of the progenies of K. gracilis (deeply lobed leaf) with K. garambiensis G. (shallowly lobed leaf) resulted in a 1:1 ratio of shallowly lobed leaves to deeply lobed leaves. The progenies of the two cross combinations (K. garambiensis G. × K. manginii ‘Wendy’ and K. garambiensis × K. manginii ‘Wendy’) produced upright-type flowers and anthers having purplish red color. These findings suggested that leaf color, leaf shape, anther color, and flower orientation of Kalanchoe are controlled by a single pair of alleles. Green leaf, deeply loped leaves, purplish red anthers, and upright-type flowers were found to be dominant traits.

Genotype × environment interaction for morphological and quality traits of wheat varieties under different nitrogen regimes in the foothills of Shivalik range of Himalayas

Variation among twelve winter wheat varieties with respect to N efficiency (NE) were assessed in field trial planned as per factorial experimental design (two years × three nitrogen doses × twelve genotypes) in which treatments were randomized in three replications under three nitrogen levels (control, 150, 250 kg/ha) for two successive years at N. E. Borlaug Crop Research Center, Pantnagar. Stability analysis of nitrogen efficiency contributing traits was performed using mean performance, linear regression and the deviation from regression. No single genotype performed well enough for all the traits under study. QLD 33, HD 2967 and QLD 39 were stable for root length showing good performance for nitrogen uptake. HD 3112 was most stable variety for most of the characters whereas, QLD 33 was found to perform best under higher levels of nitrogen fertilisation, thus, not efficient enough. But, QLD 33 showed delayed maturity which could be linked with an increase in grain yield thus, it could be said that functional stay green phenotypes should increase the grain filling period and boost yield.

Assessing the performance of fruit colour based phenotypes of tall (Typica) coconuts (Cocos nucifera L.) in Sri Lanka

Sri Lanka tall (variety Typica, form typica) is the most widely cultivated coconut form in Sri Lanka. Sri Lanka tall coconuts display variation in fruit colour ranging from green to divergent brownish red (rathi). The growers' perception is that rathi seedlings are more vigorous and higher yielding than the green phenotype. A study was conducted to evaluate and compare the nut and copra yield and seedling vigour of phenotypic groups of green, rathi and intermediate coloured fruits. Secondary data for nut yield recorded over 21 years and husked nut weight of 30 nuts per palm collected over a year in 30 palms in each of the three phenotypes were used for analysis. Furthermore, primary data for seedling girth, height and leaf number in 30 palms each of rathi and green phenotypes were collected for analysis. The data was subjected to Analysis of variance using MINITAB 16. Nut yield or the husked nut weight of the three phenotypes was not significantly different. Significant differences were observed in seedling collar girth between rathi and green phenotypes, with rathi seedlings appearing more vigorous as indicated by the thicker stem compared to the green seedlings. It is concluded that, there are no differences in the nut and copra yield among different colour forms of Sri Lanka Tall coconuts while the rathi seedlings appear superior due to their thicker seedling girth.

Arabidopsis phosphatidylglycerophosphate phosphatase 1 involved in phosphatidylglycerol biosynthesis and photosynthetic function.

Phosphatidylglycerol (PG) is an indispensable lipid constituent of photosynthetic membranes, whose function is essential in photosynthetic activity. In higher plants, the biological function of the last step of PG biosynthesis remains elusive because an enzyme catalyzing this reaction step, namely phosphatidylglycerophosphate phosphatase (PGPP), has been a missing piece in the entire glycerolipid metabolic map. Here, we report the identification and characterization of AtPGPP1 encoding a PGPP in Arabidopsis thaliana. Heterologous expression of AtPGPP1 in yeast Δgep4 complemented growth phenotype and PG-producing activity, suggesting that AtPGPP1 encodes a functional PGPP. The GUS reporter assay showed that AtPGPP1 was preferentially expressed in hypocotyl, vasculatures, trichomes, guard cells, and stigmas. A subcellular localization study with GFP reporter indicated that AtPGPP1 is mainly localized at chloroplasts. A T-DNA-tagged knockout mutant of AtPGPP1, designated pgpp1-1, showed pale green phenotype with reduced PG and chlorophyll contents but no defect in embryo development. In the pgpp1-1 mutant, ultrastructure of plastids indicated defective development of chloroplasts and measurement of photosynthetic parameters showed impaired photosynthetic activity. These results suggest that AtPGPP1 is a primary plastidic PGPP required for PG biosynthesis and photosynthetic function in Arabidopsis.

Chlorophyll Measurement as a Quantitative Method for the Assessment of Cytokinin-Induced Green Foci Formation in Tissue Culture

Tissue culture systems have long been exploited to study the process of organogenesis. In response to externally applied cytokinins, pluripotent cells proliferate into green calli and subsequently regenerate shoots. Conventionally, the cytokinin-induced greening phenotype has been evaluated by counting numbers of green foci or to present photographic evidence of morphological changes. However, because the structure of calli is disorganized and the development of pigmentation takes place gradually from pale white through yellow to green, adequately defining and counting green foci remains difficult. In this study, we employed chlorophyll measurement as an alternative method to statistically assess the greening phenotype in tissue culture material. We found that N,N-dimethylformamide was the most effective solvent for the extraction of chlorophylls from callus tissue and that bead disruption of the structured tissue improved solvent penetration and the consistency of results. The sensitivity of the method facilitated the quantification of chlorophylls in single-cultured root explants and the use of a spectrophotometer increased the efficiency of measuring multiple samples. Our measurements showed that chlorophyll contents from calli of wild-type and altered cytokinin response mutants (cre1; ahk3, or cytokinin hypersensitive 2 (ckh2)/pickle (pkl) were statistically distinguishable, validating the method. Our proposed procedure represents gains in efficiency and precision and leads to more robust standardization than the conventionally used counting of green foci.