Leaf Sugar Research Articles

Nitrogen fertilization effects on the leaf chemical concentrations in Russet Burbank potato

The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), is a destructive pest of potato (Solanum tuberosum L.) crops. Leaf sugars are regarded as energy sources for the growth of the CPB, while glycoalkaloids are used to suppress the feeding behaviors of the CPB. The metabolic pathway of these leaf compounds is closely related to nitrogen (N) nutrition. Additionally, N plays an important role in determining tuber yield. The objective of this study was to investigate the effects of N fertilization on the concentrations of sugars and glycoalkaloids in potato leaves and on marketable tuber yield under field conditions in eastern Canada. Experiments were conducted at three sites and five N rates (0, 60, 120, 180, and 240 kg N ha−1) provided in a randomized complete block design. The potato cultivar “Russet Burbank” was used throughout the experiments. Twenty potato plants were randomly selected in each plot and the fourth leaf from the top of each plant was collected at 40, 54, 68, and 82 days after planting (DAP) for analyzing the concentrations of sugars (sucrose, glucose, and fructose) and glycoalkaloids (α-solanine and α-chaconine). Marketable tuber yield was determined along with the whole plant (vine + tuber) N accumulation. A significant decline of the averaged total sugar, including sucrose and glucose, was observed with increasing N rates. The average concentration of total glycoalkaloid, including α-chaconine, increased significantly in response to the increasing N rates. Based on our results, a rate of 205 kg N ha-1 was identified to obtain a maximum marketable tuber yield along with high concentrations of glycoalkaloid and low sugar concentrations which may influence the CPB feeding.

Differential effects of varied potassium and magnesium nutrition on production and partitioning of photoassimilates in potato plants.

Potassium (K) and magnesium (Mg) are essential macronutrients for plants; they play crucial roles for photoassimilate production and transport. The knowledge on both individual and interactive effects of K and Mg nutrition in potato (Solanum tuberosum L.) is limited. We aimed to determine whether K or Mg deficiencies impair photoassimilate production and transport, and consequently the development of tubers which are strong sink organs for photoassimilates. Potato plants were grown in pots using sand culture under various K and Mg supplies. Biomass production, CO2 net assimilation, leaf sugar concentrations and transcript levels of H+/sucrose symporters in leaves were measured. Both K and Mg deficiencies reduced CO2 net assimilation and biomass production, with stronger reductions during K deficiency. Sugars accumulated in K‐ and, more importantly, in Mg‐deficient leaves. Low K or Mg supplies resulted in increased transcript levels of H+/sucrose symporters, but the increase was less pronounced during Mg deficiency. The lower increase of transcript levels of H+/sucrose symporters under Mg deficiency was probably caused by an impaired sucrose transport already at an earlier step, namely the efflux of sucrose from mesophyll cells into the apoplast. Thus, we assume that K and Mg deficiencies caused sugar accumulation in separated cell compartments of source leaves leading to a different impact on the gene expression of sucrose transport systems. Tuber sugar and starch concentrations, however, remained unaffected under the various treatments. Nevertheless, the total amount of tuber sugar and starch per plant decreased significantly during K and Mg deficiencies.

Defense Compounds Rather Than Nutrient Availability Shape Aggressiveness Trait Variation Along a Leaf Maturity Gradient in a Biotrophic Plant Pathogen.

Foliar pathogens face heterogeneous environments depending on the maturity of leaves they interact with. In particular, nutrient availability as well as defense levels may vary significantly, with opposing effects on the success of infection. The present study tested which of these factors have a dominant effect on the pathogen’s development. Poplar leaf disks of eight maturity levels were inoculated with the poplar rust fungus Melampsora larici-populina using an innovative single-spore inoculation procedure. A set of quantitative fungal traits (infection efficiency, latent period, uredinia size, mycelium quantity, sporulation rate, sporulation capacity, and spore volume) was measured on each infected leaf disk. Uninfected parts of the leaves were analyzed for their nutrient (sugars, total C and N) and defense compounds (phenolics) content. We found that M. larici-populina is more aggressive on more mature leaves as indicated by wider uredinia and a higher sporulation rate. Other traits varied independently from each other without a consistent pattern. None of the pathogen traits correlated with leaf sugar, total C, or total N content. In contrast, phenolic contents (flavonols, hydroxycinnamic acid esters, and salicinoids) were negatively correlated with uredinia size and sporulation rate. The pathogen’s fitness appeared to be more constrained by the constitutive plant defense level than limited by nutrient availability, as evident in the decrease in sporulation.

Snails prefer it sweet: A multifactorial test of the metal defence hypothesis.

Metal defence against insect herbivory in hyperaccumulator plants is well documented. However, there are contradictory results regarding protection against snails. According to the joint effects hypothesis, inorganic and organic defences cooperate in plant protection. To test this hypothesis, we explored the relationships between snail (Cantareus aspersus) feeding and multiple inorganic and organic leaf components in the Cd hyperaccumulator plant Noccaea praecox. Plants grouped by rosette size growing in nutrient solution supplemented or not with 50 μM Cd were offered to the snails. After 3 days of snail feeding, the plants and snails were analysed. In addition to Cd concentrations, we analysed leaves for nutritional factors (sugar and protein), defence-related compounds (glucosinolates, phenolics, tannins, salicylic acid and jasmonate) and essential mineral nutrients. Cadmium concentrations in the snails and in snail excrements were also analysed. Snails preferentially fed on plants grown without Cd. Medium-sized plants exposed to Cd were the least consumed. Snail excrements from this trial weighed less and had higher Cd concentrations than those from other treatments. Cadmium increased salicylate and jasmonate production. A positive relationship between jasmonate levels and the number of attacked leaves was found. Principal component analysis revealed that leaf sugar concentration was the main factor positively affecting snails' leaf consumption, while leaf Cd had a negative but weaker influence. In conclusion, leaf sugar concentration mainly governs snails' feeding preferences. High leaf Cd concentrations do not deter herbivores from attacking leaves, but they do reduce leaf consumption. Our results clearly support the joint effects hypothesis.

Grapevine leafroll disease alters leaf physiology but has little effect on plant cold hardiness.

Foliar sugar accumulation in grapevines with leafroll disease was correlated with lower photosynthesis, likely due to feedback inhibition. However, cold acclimation of dormant tissues remained unaffected by the virus status. Grapevine leafroll-associated viruses (GLRaV) contribute to losses in fruit yield and quality worldwide. Visually, leafroll disease symptoms appear similar to those associated with an imbalance in source/sink relations and a concomitant feedback inhibition of photosynthesis, which is often caused by an impasse in sugar translocation. In order to test this potential relationship and related physiological responses, leaf water status, gas exchange, non-structural carbohydrates, and dormant tissue cold hardiness were examined over 2years in healthy and GLRaV-3-infected, field-grown Merlot grapevines. Diurnal and seasonal changes in leaf water status and gas exchange were dominated by variations in water availability, temperature, and leaf age, while GLRaV-3 infection contributed less to the overall variation. By contrast, foliar carbohydrates increased markedly in infected plants, with starch accumulating early in the growing season, followed by soluble sugar accumulation, leaf reddening, and declining gas exchange. Photosynthesis correlated negatively with leaf sugar content. However, dormant-season cold hardiness of buds and cane vascular tissues was similar in healthy and infected vines. These findings support the idea that visible symptoms of grapevine leafroll disease are a consequence of carbohydrate accumulation which, in turn, may lead to feedback inhibition of photosynthesis. In addition, this study provided evidence that GLRaV-3 infection is unlikely to alter the susceptibility to moderate water deficit and winter damage in mature Merlot grapevines.

Physiological Evaluation of Wheat Genotypes for Tolerance to Water Deficit Stress

Four wheat genotypes (BARI Gom 25, E 28, BAW 1170, BAW1140) were grown under well water and water deficit stress condition to evaluate the sensitivity of physiological traits of wheat resulting reduced grain yield under water deficit stress. Wheat genotypes showed greater stability of flag leaf chlorophyll, greater ability to retain water in leaf, higher level of proline in flag leaf and kernel, higher level of soluble sugar in flag leaf and greater ability to keep the canopy cooler compared to sensitive genotype under water deficit condition. Greater spike dry matter accumulation at peak, longer grain growth duration, better yield components such as spikes m-2 and grains spike-1 under water deficit stress contributed to better tolerance of BARI Gom 25, E 28 and BAW 1170. The order of tolerance based on grain yield was BAW 1170 > BARI Gom 25 > E 28 > BAW 1140 and the order of tolerance based on above ground biological yield was BAW 1170 > E 28 > BARI Gom 25 > BAW 1140.Bangladesh Agron. J. 2017, 20(2): 37-52

Effects of plastic mulching film-induced leaf burning on seedling growth in tobacco cultivation: Different findings beyond conservation view

Solving high-temperature plastic mulching film-induced leaf burning in the first week during tobacco cultivation would take much time and effort. In the present study, the growth as well as the leaf sugar and nicotine contents of seedlings with or without leaf burning induced by high-temperature plastic mulching film were tested at two independent sites in 2015 and 2016 to identify the influence of leaf burning on seedling growth. The results showed that the growth of seedlings with leaf burning was improved with increased leaf area, leaf number and plant height compared to those without leaf burning, combined with an increased seedling survival rate at two sites in two years. In seedlings with leaf burning, the contents of fructose and glucose increased and peaked at 11:00 and 13:00 in the leaf and root, respectively, with an increased root nicotine content beginning at 13:00, highlighting the signalling role of sugars. Activities of antioxidant enzymes including peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) were all increased in seedlings with leaf burning. More plant biomass was allocated to roots in seedlings with leaf burning with increased root volume compared to control seedlings, which might facilitate the absorption of water and nutrients from the soil. Our findings demonstrate that high-temperature plastic mulching film-induced leaf burning not inhibited but benefited seedling survival and growth, suggesting that the time and labour-consuming manual plucking of burnt leaves can be avoided during tobacco cultivation.

A cycad's non‐saturating response to carbon dioxide enrichment indicates Cenozoic carbon limitation in pre‐historic plants

AbstractCycads were a dominant plant functional type during the Mesozoic Era when atmospheric carbon dioxide [CO2] greatly exceeded current conditions. Cycads, now rare and endangered, are slow‐growing perennial gymnosperms that develop carbon‐rich structural biomass, such as sclerophyllous leaves, dense stems and massive reproductive cones. Is cycad carbon partitioning to specific organs a constraint of their high [CO2] evolutionary history (CO2 legacy hypothesis, CLH)? To explore changes in cycad growth, carbon partitioning and assimilation responses that could be expected during the CO2 depletion of the Cenozoic Era, individuals of the cycad species Encephalartos villosus plants were grown at four CO2 levels: 400, 550, 750 and 1000 μmol mol−1. The CLH predicts that cycad biomass and growth rates would increase in elevated [CO2] due to increased net assimilation rates, and that carbon‐dense structures would provide sufficient carbohydrate sinks to prevent photosynthetic down‐regulation even under super‐ambient [CO2] of 1000 μmol mol−1. Both hypotheses were confirmed, though the latter less strongly. Plant relative growth rates increased 23% and biomass accumulation increased 65% in 1000 μmol mol−1relative to 400 μmol mol−1 treatment groups. Mean net assimilation rates increased 130% at 1000 μmol mol−1 relative to 400 μmol mol−1 CO2, though there was some down‐regulation of maximum rate of carboxylation (Vcmax). Assimilation rates, relative growth rates, biomass and mean leaf sugar content were linearly related to [CO2] over the entire experimental range. Photosynthesis appears to be regulated by stomata at low CO2 levels and by non‐stomatal (i.e. biochemical limitations) at greater concentrations. In general, our results suggest that growth and physiological performance of cycads have been severely compromised by declining [CO2] during the Cenozoic Era, possibly contributing to the current rare and endangered status of this functional type.

The Potential Use of Metamitron as a Chemical Fruit-thinning Agent in Mandarin

Under conditions of profuse flowering and excessive fruit set, citrus (Citrus sp.) fruit need to be thinned to increase the size of remaining fruit, reduce the intensity of alternate bearing, or both. Metamitron was recently developed as a chemical fruit-thinning agent for apple (Malus ×domestica) and pear (Pyrus communis), and it inhibits photosynthesis and is thought to transiently reduce the carbohydrate pool in fruit trees. Citrus trees are sensitive to carbohydrate stress during and immediately after flowering, but the response of citrus to foliar treatment with a photosynthesis inhibitor, such as metamitron, is unknown. The purpose of this study was to evaluate metamitron for its effects on leaf carbohydrates and its ability to chemically thin citrus fruitlets. Significant fruit-thinning effects were found in all the experiments conducted over two seasons. A 300 mg·L−1 metamitron treatment reduced leaf sugars and leaf total carbohydrates, and consistently reduced the total number of fruit per tree in both seasons in ‘Nadorcott’ mandarin (Citrus reticulata), irrespective of the timing of application. In the second season, a reduction in fruit yield was reported with an increase in metamitron concentration, both in mass and number of fruit per tree. A 150 mg·L−1 metamitron treatment in November had no fruit-thinning effects, and fruit yield was not different from the control. The application of metamitron did not increase the fruit size of ‘Nadorcott’ mandarin and had no direct effect on other fruit quality attributes in either season. Metamitron can be used as a chemical fruit-thinning agent to reduce fruit numbers in ‘Nadorcott’ mandarin, but an increase in fruit size or quality should not be expected.

Diversity of the endophytic filamentous fungal leaf community at different development stages of eucalyptus

Fungal endophytic species inhabiting the leaves of eucalypts are capable of utilising leaf sugars and can influence both plant growth and health. Endophytic fungal symbionts can use simple soluble sugars in leaves as their main carbon source. This study set out to determine the diversity and distribution of the endophytic filamentous fungal leaf community in the hybrid Eucalyptus urograndis due to its economic importance. The fungal leaf community was characterised using denaturing gradient electrophoresis (DGGE) and correlated with levels of leaf nutrients and sugars throughout plant development. Sequencing of DGGE bands revealed the presence of Basidiomycota and Ascomycota phyla. Fourteen species and three genera of filamentous fungi were identified, and the population structure was affected by the plant developmental stage. Levels of K, Cu, N and Mn influenced communities from the clonal garden, whereas leaves in the field had higher glucose, fructose and sucrose. Many fungi were found to be specific to a certain development stages: Diplomitoporus crustulinus, Podosphaera tridactyla and Aspergillus restrictus to the clonal garden stage; Chaetomella acutiseta and Ascotricha chartarum to the shading stage; Erratomyces patelii and Saxomyces sp. to the shading output stage; Lepidostroma sp. and Saxomyces sp. to the dispatch stage; and Mycosphaerella populicola to the field stage. Teratosphaeria toledana and Teratosphaeria acidotherma were found at more than one developmental stage. Cladosporium sp. and Rhodosporidium fluviale colonized and persisted in plants at the dispatch and field stages. This is the first report of P. tridactyla, A. restrictus, E. patelii, Saxomyces and Lepidostroma sp. as endophytes in eucalipt.

Does cross-acclimation between drought and freezing stress persist over ecologically relevant time spans? A test using the grass Poa pratensis.

Despite evidence that prior exposure to drought can increase subsequent plant freezing tolerance, few studies have explored such interactions over ecologically relevant time spans. We examined the combined effects of drought and subsequent freezing on tiller growth and leaf sugar concentrations in the grass, Poa pratensis. We exposed tillers to no drought (-0.04 MPa), moderate drought (-0.19 MPa) or severe drought (-0.42 MPa) for 3weeks in summer. Tillers were then frozen in autumn or spring at -5°C (frost damage) or at 0°C (control) for 3days and harvested after a re-growth period. For shoot growth, there was a significant interaction between drought and autumn freezing, whereby the relative effect of freezing on growth was least for the plants previously exposed to severe drought; however, there was no significant interaction between drought and spring freezing. For root growth, there were no significant interactions between drought and freezing in either season. Leaf sugar concentrations increased significantly with drought intensity, but these effects dissipated within a month, prior to the onset of the autumn freezing treatment. Overall, our results suggest that interactions between prior drought and subsequent freezing in P.pratensis may be most relevant in the context of autumn freezing, and despite the important role of soluble sugars in increasing both drought and freezing tolerance in this species, the retention of these compounds after drought stress does not appear to explain the occurrence of drought-frost interactions at ecologically relevant time scales.

Regulation of Sucrose Transporters and Phloem Loading in Response to Environmental Cues.

Suc transporters (SUTs) play a key role in the allocation and partitioning of photosynthetically fixed carbon in plants. While a function could be assigned to many members of the SUT family, almost no information is available on their regulation. Here, the transcriptional regulation of SUTs in response to various environmental stimuli in the leaves of five dicots (Arabidopsis [Arabidopsis thaliana], soybean [Glycine max], potato [Solanum tuberosum], tomato [Solanumlycopersicum], and poplar [Populus spp.]) and four monocots (maize [Zeamays], rice [Oryza sativa], wheat [Triticum aestivum], and barley [Hordeum vulgare]) was investigated. Extensive data on expression of SUTs in relation to changes of environmental conditions were obtained through a global analysis of 168 transcriptomics data sets. Results were validated by quantitative PCR measurements and extended by the measurement of photosynthesis rate and phloem sugar content to draw insight on the correlation of SUT expression and sugar export from leaves. For the apoplasmic phloem loaders, a clear difference in transcriptional regulation in response to different environmental stimuli was observed. The consistent patterns of SUT expression under abiotic stress indicates which types of SUTs are involved in the regulation of leaf sugar status and in stress signaling. Furthermore, it is shown that down-regulation of phloem loading is likely to be caused by transcriptional regulation of SUTs, while up-regulation depends on post-transcriptional regulation. In poplar, expression of PtaSUT4 was found to consistently respond to environmental stimuli, suggesting a significant role in the regulation of sugar export from leaves in this passive symplasmic phloem loader.

Redox Control of Aphid Resistance through Altered Cell Wall Composition and Nutritional Quality.

The mechanisms underpinning plant perception of phloem-feeding insects, particularly aphids, remain poorly characterized. Therefore, the role of apoplastic redox state in controlling aphid infestation was explored using transgenic tobacco (Nicotiana tabacum) plants that have either high (PAO) or low (TAO) ascorbate oxidase (AO) activities relative to the wild type. Only a small number of leaf transcripts and metabolites were changed in response to genotype, and cell wall composition was largely unaffected. Aphid fecundity was decreased significantly in TAO plants compared with other lines. Leaf sugar levels were increased and maximum extractable AO activities were decreased in response to aphids in all genotypes. Transcripts encoding the Respiratory Burst Oxidase Homolog F, signaling components involved in ethylene and other hormone-mediated pathways, photosynthetic electron transport components, sugar, amino acid, and cell wall metabolism, were increased significantly in the TAO plants in response to aphid perception relative to other lines. The levels of galactosylated xyloglucan were decreased significantly in response to aphid feeding in all the lines, the effect being the least in the TAO plants. Similarly, all lines exhibited increases in tightly bound (1→4)-β-galactan. Taken together, these findings identify AO-dependent mechanisms that limit aphid infestation.

Seasonal changes in leaf chemistry and leaf selection of the Japanese giant flying squirrel upon two tree species.

Tree leaves are important food sources for arboreal herbivores, such as primates, rodents, and marsupials. These animals do not eat leaves randomly in habitats with many tree species but rather choose based on the chemical components of leaves, such as sugars, fibers, proteins, and toxins. However, the effects of the microscale distribution of these chemicals within each leaf have not been examined for these animals. The giant flying squirrels Petaurista leucogenys are entirely arboreal, nocturnal herbivores, usually feeding on leaves and dropping leaf debris on the ground after partially consuming them. Therefore, we could easily assess which species of trees and which parts of the individual leaves they preferred to eat. We also examined microscale distributions of phenolics, sugar, and water within individual leaves. Of the two dominant food tree species, the deciduous Quercus acutissima was preferred over the evergreen Q. sessilifolia. The latter tree is only used during winter to early spring when the former had no leaves. Our chemical analyses revealed that Q. acutissima contained much more glucose than Q. sessilifolia in all seasons. Three types of leaf debris, eaten apically, basally, or centrally with a hole, were found. In Q. sessilifolia, which had low phenolic concentrations, apical eating was most common, whereas central eating was rare. In Q. acutissima, which had high phenolics, basal or central eating was common. Central feeding may be caused by avoiding the periphery because of a higher phenolic concentration in the leaf margin. Thus, microscale distributions of phenolics within individual leaves affect which parts P. leucogenys eats, whereas leaf sugar concentration is an important factor affecting which species of leaves they eat.

Herbivory-induced jasmonates constrain plant sugar accumulation and growth by antagonizing gibberellin signaling and not by promoting secondary metabolite production.

Plants respond to herbivory by reconfiguring hormonal networks, increasing secondary metabolite production and decreasing growth. Furthermore, some plants display a decrease in leaf energy reserves in the form of soluble sugars and starch, leading to the hypothesis that herbivory-induced secondary metabolite production and growth reduction may be linked through a carbohydrate-based resource trade-off. In order to test the above hypothesis, we measured leaf carbohydrates and plant growth in seven genetically engineered Nicotiana attenuata genotypes that are deficient in one or several major herbivore-induced, jasmonate-dependent defensive secondary metabolites and proteins. Furthermore, we manipulated gibberellin and jasmonate signaling, and quantified the impact of these phytohormones on secondary metabolite production, sugar accumulation and growth. Simulated herbivore attack by Manduca sexta specifically reduced leaf sugar concentrations and growth in a jasmonate-dependent manner. These effects were similar or even stronger in defenseless genotypes with intact jasmonate signaling. Gibberellin complementation rescued carbohydrate accumulation and growth in induced plants without impairing the induction of defensive secondary metabolites. These results are consistent with a hormonal antagonism model rather than a resource-cost model to explain the negative relationship between herbivory-induced defenses, leaf energy reserves and growth.

Fruit-load-induced starch accumulation causes leaf chlorosis in “off” ‘Nadorcott’ mandarin trees

Leaf chlorosis often develops in low-fruiting (“off”) trees of healthy, severely alternate bearing ‘Nadorcott’ mandarin (Citrus reticulata Blanco) trees in commercial orchards in South Africa, whereas leaves of heavily-fruiting (“on”) trees maintain a healthy green colour. This study investigated the role of fruit load and leaf carbohydrate content on the development of leaf chlorosis in “off” trees under a broad spectrum of source/sink relationships. Leaf chlorosis in “off” trees was mediated by low sink activity, and leaf total chlorophyll content strongly correlated with leaf starch content [r2=(−)0.74 (P<0.001)]. A decrease in leaf total chlorophyll content in “off” trees coincided with a peak in leaf starch content during winter, after activity of all the major sinks reached a minimum. In “on” trees, leaf starch content was significantly lower compared to “off” trees, the major carbohydrate component was sugars, and leaves maintained a healthy green colour. Summer de-fruiting of “on” trees instantly resulted in accumulation of leaf starch, but loss in leaf total chlorophyll content was delayed until autumn. Lower leaf nitrogen (N) and lower leaf sugar content do not appear to be the cause of leaf chlorosis in “off” trees, but rather a response to the disruptive effect of fruit-load-induced starch accumulation on the leaf chloroplasts. Results can be used to prevent unnecessary winter N applications in “off” ‘Nadorcott’ mandarin trees. This phenomenon was previously artificially induced at the branch-level, but this is the first report of fruit-load-induced citrus leaf chlorosis on a whole-tree level.

Sucrose transporters and plasmodesmal regulation in passive phloem loading.

An essential step for the distribution of carbon throughout the whole plant is the loading of sugars into the phloem in source organs. In many plants, accumulation of sugars in the sieve element-companion cell (SE-CC) complex is mediated and regulated by active processes. However, for poplar and many other tree species, a passive symplasmic mechanism of phloem loading has been proposed, characterized by symplasmic continuity along the pre-phloem pathway and the absence of active sugar accumulation in the SE-CC complex. A high overall leaf sugar concentration is thought to enable diffusion of sucrose into the phloem. In this review, we critically evaluate current evidence regarding the mechanism of passive symplasmic phloem loading, with a focus on the potential influence of active sugar transport and plasmodesmal regulation. The limited experimental data, combined with theoretical considerations, suggest that a concomitant operation of passive symplasmic and active phloem loading in the same minor vein is unlikely. However, active sugar transport could well play an important role in how passively loading plants might modulate the rate of sugar export from leaves. Insights into the operation of this mechanism has direct implications for our understanding of how these plants utilize assimilated carbon.

Experimental branch cooling increases foliar sugar and anthocyanin concentrations in sugar maple at the end of the growing season

Autumnal leaf anthocyanin expression is enhanced following exposure to a variety of environmental stresses and may represent an adaptive benefit of protecting leaves from those stresses, thereby allowing for prolonged sugar and nutrient resorption. Past work has shown that experimentally induced sugar accumulations following branch girdling triggers anthocyanin biosynthesis. We hypothesized that reduced phloem transport at low autumnal temperatures may increase leaf sugar concentrations that stimulate anthocyanin production, resulting in enhanced tree- and landscape-scale color change. We used refrigerant-filled tubing to cool individual branches in a mature sugar maple (Acer saccharum Marsh.) tree to test whether phloem cooling would trigger foliar sugar accumulations and enhance anthocyanin biosynthesis. Cooling increased foliar sucrose, glucose, and fructose concentrations 2- to nearly 10-fold (depending on the specific sugar and sampling date) relative to controls and increased anthocyanin concentrations by approximately the same amount. Correlation analyses indicated a strong and steady positive relationship between anthocyanin and sugar concentrations, which was consistent with a mechanistic link between cooling-induced changes in these constituents. Tested here at the branch level, we propose that low temperature induced reductions in phloem transport may be responsible for increases in foliar sugars that trigger anthocyanin displays at grander scales.

The influence of soybean new blade’s sugar content variation to its apparent growth

To a certain extent, leaf sugar content shows the plant growth status. At the beginning of the rapid growth of the seedlings of soybean, internal physiological indexes, such as the correlation between sugar content and external apparent growth is not very clear. This experiment measured the soybean seedling stage in different gradient of the soluble sugar content and the correlation of the apparent growth indicators, including leaf weight, leaf width, leaf length, root length, number of radicle, etc. The correlation between soluble sugar content and the apparent growth studies to preliminary discussion on this issue is analyzed. The data shows that in the seedling stage, leaf soluble sugar content increase quickly, and the apparent growth has different correlation with indicators. The weight of leaf has a intimate relativity with soluble sugar content, but leaf width and length have weaker correlation with it. And the root length and number of young root show little correlation with soluble sugar content. Experiment results indicate that in soybean seedling stage, internal physiological indexes do have a specific relationship with external growth index in some degree.

A steady-state stomatal model of balanced leaf gas exchange, hydraulics and maximal source-sink flux.

Trees must simultaneously balance their CO2 uptake rate via stomata, photosynthesis, the transport rate of sugars and rate of sugar utilization in sinks while maintaining a favourable water and carbon balance. We demonstrate using a numerical model that it is possible to understand stomatal functioning from the viewpoint of maximizing the simultaneous photosynthetic production, phloem transport and sink sugar utilization rate under the limitation that the transpiration-driven hydrostatic pressure gradient sets for those processes. A key feature in our model is that non-stomatal limitations to photosynthesis increase with decreasing leaf water potential and/or increasing leaf sugar concentration and are thus coupled to stomatal conductance. Maximizing the photosynthetic production rate using a numerical steady-state model leads to stomatal behaviour that is able to reproduce the well-known trends of stomatal behaviour in response to, e.g., light, vapour concentration difference, ambient CO2 concentration, soil water status, sink strength and xylem and phloem hydraulic conductance. We show that our results for stomatal behaviour are very similar to the solutions given by the earlier models of stomatal conductance derived solely from gas exchange considerations. Our modelling results also demonstrate how the 'marginal cost of water' in the unified stomatal conductance model and the optimal stomatal model could be related to plant structural and physiological traits, most importantly, the soil-to-leaf hydraulic conductance and soil moisture.