Diurnal changes in assimilate concentrations and fluxes in the phloem of castor bean (Ricinus communis L.) and tansy (Tanacetum vulgare L.)

Kallarackal, Jose; Bauer, Susanne N.; Nowak, Heike; Hajirezaei, Mohammad‐Reza; Komor, Ewald

doi:10.1007/s00425-012-1600-7

Cited by 26 publications

(20 citation statements)

References 31 publications

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“…4). As source tissues, mature leaves continually export amino acids to sink tissues, but the export rate and the indirect ATP cost of amino acid transport from leaves that occur at night have not been quantified, and experimental methods to address this question are lacking (Kallarackal et al, 2012). Therefore, it remains unclear whether this process is a cost that contributes greatly to the observed variation in R N .…”

Section: Protein Synthesis Is Not a Major Determinant Of Mature Arabimentioning

confidence: 99%

“…First, nighttime respiration is thought to function largely in an energy-generating capacity involving a cyclic flux through the citric acid cycle (Sweetlove et al, 2010;Cheung et al, 2014). Second, leaves continuously export Suc and amino acids throughout the diurnal cycle to support the growth of heterotrophic tissues at a substantial cost of ATP (Bouma et al, 1995;Kallarackal et al, 2012). Third, the assimilation of nitrogen and, thus, de novo amino acid synthesis at night is reduced greatly in leaves because nitrate reduction is low to nil and ammonium assimilation also is less than in daytime (Canvin and Atkins, 1974;Matt et al, 2001;Nelson et al, 2014).…”

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Variation in Leaf Respiration Rates at Night Correlates with Carbohydrate and Amino Acid Supply

et al. 2017

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Plant respiration can theoretically be fueled by and dependent upon an array of central metabolism components; however, which ones are responsible for the quantitative variation found in respiratory rates is unknown. Here, large-scale screens revealed 2-fold variation in nighttime leaf respiration rate (R N ) among mature leaves from an Arabidopsis (Arabidopsis thaliana) natural accession collection grown under common favorable conditions. R N variation was mostly maintained in the absence of genetic variation, which emphasized the low heritability of R N and its plasticity toward relatively small environmental differences within the sampling regime. To pursue metabolic explanations for leaf R N variation, parallel metabolite level profiling and assays of total protein and starch were performed. Within an accession, R N correlated strongly with stored carbon substrates, including starch and dicarboxylic acids, as well as sucrose, major amino acids, shikimate, and salicylic acid. Among different accessions, metabolite-R N correlations were maintained with protein, sucrose, and major amino acids but not stored carbon substrates. A complementary screen of the effect of exogenous metabolites and effectors on leaf R N revealed that (1) R N is stimulated by the uncoupler FCCP and high levels of substrates, demonstrating that both adenylate turnover and substrate supply can limit leaf R N , and (2) inorganic nitrogen did not stimulate R N , consistent with limited nighttime nitrogen assimilation. Simultaneous measurements of R N and protein synthesis revealed that these processes were largely uncorrelated in mature leaves. These results indicate that differences in preceding daytime metabolic activities are the major source of variation in mature leaf R N under favorable controlled conditions. Few plant metabolic fluxes are readily accessible to routine measurement. The major exceptions to this are fluxes involving gas exchange, such as respiration and photosynthesis. Measurements of respiratory gas exchange (i.e. mitochondrial oxygen uptake or CO 2 release in the absence of photorespiration) are useful from a metabolic perspective because they can be interpreted in terms of the underlying carbon fluxes and the generation of ATP by oxidative phosphorylation (Sweetlove et al., 2013). The biochemical reactions of respiration that produce CO 2 and lead to oxygen consumption are well understood (Plaxton and Podestá, 2006;Sweetlove et al., 2010;Millar et al., 2011;Tcherkez et al., 2012). The stoichiometries of the reactions and the connections between them are known, which provides us with a metabolic map of respiration that includes glycolysis, the oxidative pentose phosphate pathway, the citric acid cycle, the mitochondrial electron transport chain (mETC), ATP synthase, and several other surrounding reactions. In plants, carbohydrates are the dominant respiratory substrates, whereas lipids are rarely respired (Plaxton and Podestá, 2006). Carbohydrate oxidation proceeds via organic acids, which serve many purposes in plant...

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Section: Protein Synthesis Is Not a Major Determinant Of Mature Arabimentioning

confidence: 99%

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confidence: 99%

Variation in Leaf Respiration Rates at Night Correlates with Carbohydrate and Amino Acid Supply

et al. 2017

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“…Conversely, stylectomy yields more pure phloem sap because the sampling is less invasive, and although aphids can alter the amino acid composition of phloem exudates [44] there is no evidence that these changes directly affect sugar concentration. The disadvantage of this technique is that it is technically challenging and is susceptible to the effects of evaporation because of the small size of the exudate droplets [45]. Furthermore, it can only be used in plant species associated with sap-feeding insects [35], which could lead to biases in sample collection if these insects prefer certain types of plants.…”

Section: Phloem Sap Sugar Concentration Datamentioning

confidence: 99%

Optimal concentration for sugar transport in plants

Jensen

Savage

Holbrook

2013

J. R. Soc. Interface.

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Vascular plants transport energy in the form of sugars from the leaves where they are produced to sites of active growth. The mass flow of sugars through the phloem vascular system is determined by the sap flow rate and the sugar concentration. If the concentration is low, little energy is transferred from source to sink. If it is too high, sap viscosity impedes flow. An interesting question is therefore at which concentration is the sugar flow optimal. Optimization of sugar flow and transport efficiency predicts optimal concentrations of 23.5 per cent (if the pressure differential driving the flow is independent of concentration) and 34.5 per cent (if the pressure is proportional to concentration). Data from more than 50 experiments (41 species) collected from the literature show an average concentration in the range from 18.2 per cent (all species) to 21.1 per cent (active loaders), suggesting that the phloem vasculature is optimized for efficient transport at constant pressure and that active phloem loading may have developed to increase transport efficiency.

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“…Limited, and sometimes conflicting, data exist on the extent that phloem transport changes temporally during a plant's lifetime (Kallarackal et al, 2012). For example, diurnal variation in carbon assimilation is often predicted to influence phloem sugar concentration and/ or carbon flux because of changes in source activity.…”

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Phloem Transport Velocity Varies over Time and among Vascular Bundles during Early Cucumber Seedling Development

2013

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We use a novel dye-tracing technique to measure in vivo phloem transport velocity in cucumber (Cucumis sativus) plants during early seedling development. We focus on seedlings because of their importance in plant establishment and because they provide a simple source and sink model of phloem transport. The dye-tracing method uses a photodiode to track the movement of a bleach front of fluorescent dye traveling in the phloem from the cotyledons (source) to the roots (sink). During early seedling development, phloem transport velocity in this direction can change 2-fold depending on vascular connectivity and the number of actively growing sinks. Prior to leaf expansion, vascular bundles attached to the first developing leaf demonstrate a decline in basipetal phloem transport that can be alleviated by the leaf's removal. At this stage, seedlings appear carbon limited and phloem transport velocity is correlated with cotyledon area, a pattern that is apparent both during cotyledon expansion and after source area manipulation. When the first leaf transitions to a carbon source, seedling growth rate increases and basipetal phloem transport velocity becomes more stable. Because bundles appear to operate autonomously, transport velocity can differ among vascular bundles. Together, these results demonstrate the dynamic and heterogeneous nature of phloem transport and underline the need for a better understanding of how changes in phloem physiology impact growth and allocation at this critical stage of development.

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Diurnal changes in assimilate concentrations and fluxes in the phloem of castor bean (Ricinus communis L.) and tansy (Tanacetum vulgare L.)

Cited by 26 publications

References 31 publications

Variation in Leaf Respiration Rates at Night Correlates with Carbohydrate and Amino Acid Supply

Variation in Leaf Respiration Rates at Night Correlates with Carbohydrate and Amino Acid Supply

Optimal concentration for sugar transport in plants

Phloem Transport Velocity Varies over Time and among Vascular Bundles during Early Cucumber Seedling Development

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