Comparative Enzymic Studies of Sucrose Metabolism in the Taproots and Fibrous Roots of Beta vulgaris L

Comparative enzymic studies of sugar beet (Beta vulgaris L.) taproots and fibrous roots revealed differences in invertase (EC 3.2.1.26) and sucrose synthetase (EC 2.4.1.13) activity. Invertase activity of the two root forms differs with respect to specific activity, pH optimum, and enzyme solubility. Acid invertase (pH 4.5) in the taproot was restricted to the peripheral meristematic tissue which produces cells for both taproot and fibrous root growth. This finding supports the hypothesis that the enzyme regulates sucrose partitioning between the taproot and fibrous roots. A distinct alkaline invertase (pH 8.0) was detected in sucrose storage tissues of the taproot.     

Colonization and Sex Ratios of Pratylenchus alleni in Soybean Roots under Two Soil Moisture Regimes

Population size and sex ratios of Pratylenchus alleni in soybeans were studied trader two different moisture regimes in Hagener loamy fine sand. Soil moisture was maintained from field capacity to 50% below field capacity in the dry regime and from field capacity to 25% above field capacity in the wet regime. The initial peak of colonization of soybeans by P. alleni was in the top 5-cm of taproot 14 days after seeding. There were more P. alleni per unit length of taproot in the dry than in the wet regime during the first 7 days, and this trend continued in the top 5-cm of the taproot for 21 days. Nematode density was greater in taproots than in fibrous roots. The ratio of males to females recovered from roots was significantly higher in the dry than in the wet regime.     

Growth regulator effects on storage root development in carrot

The major carbohydrates stored in carrots are sucrose, glucose and fructose. The ratio of sucrose to reducing sugars varies between cultivars, with early forcing types generally having a higher level of reducing sugars while storage types have a greater proportion of sucrose.In an early forcing cultivar, Super Sprite, high acid invertase activity was correlated with low levels of stored sucrose. As acid invertase activity decreased, the levels of reducing and non-reducing sugars appeared to be related to a balance between alkaline invertase and sucrose synthetase activities.Foliar applications of gibberellic acid at 35 and 42 days after sowing reduced the root/shoot ratio while similar applications of chlormequat chloride marginally increased the ratio. Both growth regulators temporarily increased sucrose stograge, but only gibberellic acid consistently reduced hexose accumulation.Gibberellic acid reduced acid invertase activity following both applications while only reducing the activities of sucrose synthetase after the first application and alkaline invertase after the second application, respectively. Chloremequat chloride increased acid invertase activity after the first application but otherwise has no effect on the activities of the enzymes studied. The significance of changes in assimilate partitioning are discussed in relation to published schemes on carbohydrate storage in root vegetables.     

Nucleoside Diphosphate Levels in Taproots and Fibrous Roots of Beta vulgaris L. : Implifications for Control of Sucrose Allocation between Two Sinks

Sucrose synthase (EC 2.4.1.13) of sugarbeet (Beta vulgaris L.) fibrous roots has a distinctly different order of preference for nucleoside diphosphate substrates than that of the taproot enzyme (Silvius, Snyder 1979 Plant Physiol 64: 1070-1073). Separation and quantitation of UDP, ADP, and GDP in root extracts by high-pressure liquid chromatography revealed that UDP levels in taproot tissue were 5 to 10 times greater than those of fibrous root tissues. The lower fibrous root UDP levels were associated with significantly higher ADP and GDP levels in these roots as compared to the taproot. These differences are consistent with differences in the substrate affinity of sucrose synthase and suggest a regulatory role of the enzyme in the control of sucrose cleavage and utilization between the two root types.     

Partitioning of shoot and root dry matter and carbohydrates in bean plants suffering from phosphorus, potassium and magnesium deficiency

The influence of varied supply of phosphorus (10 and 250 mmolP m^–3) potassium (50 and 2010 mmol K m^–3) and magnesium(20 and 1000 mmol Mg m^–3) on the partitioning of dry matterand carbohydrates (reducing sugars, sucrose and starch) betweenshoots and roots was studied in bean (Phaseolus vulgaris) plantsgrown in nutrient solution over a 12 d period. Shoot and rootgrowth were quite differently affected by low supply of P, K,and Mg. The shoot/root dry weight ratios were 4.9 in the control(sufficient plants), 1.8 in P-deficient, 6.9 in K-deficientand 10.2 in Mg-deficient plants. In primary (source) leaves,but not in trifoliate leaves, concentrations of reducing sugars,sucrose and starch were also differently affected by low nutrientsupply. In primary leaves under K deficiency and, particularlyMg deficiency, the concentrations of sucrose and reducing sugarswere much higher than in control and P-deficient plants. Magnesiumdeficiency also distinctly increased the starch concentrationin the primary leaves. In contrast, in roots, the lowest concenfrationsof sucrose, reducing sugars and starch were found in Mg-deficientplants, whereas the concentrations of sucrose and starch wereparticularly high in P-deficient plants. There was a close relationshipbetween shoot/root dry weight ratios and relative distributionof total carbohydrates (sugars and starch) in shoot and roots.Of the total amounts of carbohyd rates per plant, the followingproportions were parti tioned to the roots: 22.7% in P-deficient,15.7% in control, 3.4% in K-deficient and 0.8% in Mg-deficientplants. The results indicate a distinct role of Mg and K in the exportof photosynthates from leaves to roots and suggest that alterationin photosynthate partitioning plays a major role in the differencesin dry matter distribution between shoots and roots of plantssuffering from mineral nutrient deficiency. Key words: Bean, carbohydrates, magnesium nutrition, phosphorus nutrition, potassium nutrition, shoot/root growth     

Copper-induced alteration in sucrose partitioning and its relationship to the root growth of two Elsholtzia haichowensis Sun populations

Hydroponic culture was used to comparatively investigate the copper (Cu)-induced alteration to sucrose metabolism and biomass allocation in two Elsholtzia haichowensis Sun populations with one from a Cu-contaminated site (CS) and the other from a non-contaminated site (NCS). Experimental results revealed that biomass allocation preferred roots over shoots in CS population, and shoots over roots in NCS population under Cu exposure. The difference in biomass allocation was correlated with the difference in sucrose partitioning between the two populations. Cu treatment (45 μM) significantly decreased leaf sucrose content and increased root sucrose content in CS population as a result of the increased activities of leaf sucrose synthesis enzymes (sucrose phosphate synthetase and sucrose synthase) and root sucrose cleavage enzyme (vacuolar invertase), which led to increased sucrose transport from leaves to roots. In contrast, higher Cu treatment increased sucrose content in leaves and decreased sucrose content in roots in NCS population as a result of the decreased activities of root sucrose cleavage enzymes (vacuolar and cell wall invertases) that led to less sucrose transport from leaves to roots. These results provide important insights into carbon resource partitioning and biomass allocation strategies in metallophytes and are beneficial for the implementation of phytoremediation techniques.     

Etiolated Growth as Measure of Non-structural Biomass in Lucerne Taproots

Enzymatic hydrolysis of starch in lucerne (Medicago sativa L.)taproots is the conventional method used to determine the quantityof carbohydrates allocated to regrowth. Etiolated growth froma taproot could be used to quantify total root biomass allocatedto regrowth. This study compared concentrations of non-structuralcarbohydrates, as measured by -amylase hydrolysis of starchto glucose, to concentrations of non-structural biomass, asmeasured by etiolated growth from lucerne taproots placed inan incubator and plants in situ. The concentration of starchfrom enzymatically assayed taproots was 325 g kg^-1 expressedas glucose equivalents. Etiolated growth and weight loss byrespiration from plants grown in the incubator accounted for524 g of actual biomass per kg of root. There was 46·2g kg^-1 of N, 3·1 of P, and 33·1 of K in the etiolatedgrowth. An 88% increase in etiolated growth dry weight was observedfrom plants in situ compared to taproots placed in the incubator.Accurate quantification on non-structural biomass should notbe limited to sampling just the taproot, but must included theentire root system. Compared to determining non-structural carbohydratesby enzymatic hydrolysis of starch, the procedure used in determiningnon-structural biomass by etiolate growth gave results in unitsrelative to the plant. The use of etiolate growth also providedinformation on mineral nutrient partitioning from root to shoots,was less technically demanding, and could be applied to theentire root system.Copyright 1993, 1999 Academic Press Medicago sativa, root carbohydrates, etiolated growth, taproot     

Antisense repression of vacuolar and cell wall invertase in transgenic carrot alters early plant development and sucrose partitioning.

To unravel the functions of cell wall and vacuolar invertases in carrot, we used an antisense technique to generate transgenic carrot plants with reduced enzyme activity. Phenotypic alterations appeared at very early stages of development; indeed, the morphology of cotyledon-stage embryos was markedly changed. At the stage at which control plantlets had two to three leaves and one primary root, shoots of transgenic plantlets did not separate into individual leaves but consisted of stunted, interconnected green structures. When transgenic plantlets were grown on media containing a mixture of sucrose, glucose, and fructose rather than sucrose alone, the malformation was alleviated, and plantlets looked normal. Plantlets from hexose-containing media produced mature plants when transferred to soil. Plants expressing antisense mRNA for cell wall invertase had a bushy appearance due to the development of extra leaves, which accumulated elevated levels of sucrose and starch. Simultaneously, tap root development was markedly reduced, and the resulting smaller organs contained lower levels of carbohydrates. Compared with control plants, the dry weight leaf-to-root ratio of cell wall invertase antisense plants was shifted from 1:3 to 17:1. Plants expressing antisense mRNA for vacuolar invertase also had more leaves than did control plants, but tap roots developed normally, although they were smaller, and the leaf-to-root ratio was 1.5:1. Again, the carbohydrate content of leaves was elevated, and that of roots was reduced. Our data suggest that acid invertases play an important role in early plant development, most likely via control of sugar composition and metabolic fluxes. Later in plant development, both isoenzymes seem to have important functions in sucrose partitioning.     

川滇高山栎灌丛萌生过程中的营养元素供应动态

萌生更新是森林更新的重要方式, 是硬叶栎林受到干扰后植被恢复的主要机制。以位于青藏高原东南缘的川西折多山东坡川滇高山栎(Quercus aquifoliodes)灌丛为研究对象, 调查分析了砍伐后灌丛萌生过程中基株根系和萌株生物量动态、营养元素含量, 以及基株根系和土壤对萌株生长过程中的营养元素供应动态。结果表明, 川滇高山栎灌丛平均地上和地下生物量分别为(11.25 ± 0.92) t·hm^-2和(34.85 ± 2.02) t·hm^-2, 具有较大的根冠比(3.10:1); 萌生过程中, 萌株生物量呈线性增加趋势, 以灌丛活细根生物量变化为最大, 其次是活中根和活粗根, 树桩和根蔸生物量变化最小; 萌生过程中, 灌丛细根和中根N、P含量表现为先增加、后降低的变化趋势, 萌生初期树桩、粗根和根蔸中N和K的含量明显下降, 根蔸中Ca含量略有下降, 而P没有明显下降, 根系Mg含量变化幅度较大, 灌丛地下根系储存了较多的营养元素; 土壤、树桩、粗根和根蔸是川滇高山栎灌丛砍伐后0-120天萌生生长的主要营养来源, 砍伐后60天, 萌株生长所需的营养除K元素主要来源于根系外, 其余营养元素主要来源于土壤; 在砍伐后60-120天, 基株根系对萌株生长所需的N、K和Ca贡献较大, 而对P和Mg的贡献较小; 在砍伐后120-180天, 根系除K元素对萌生生长还保持较大的贡献外, 对其余营养元素的贡献均较小。高山栎林管理要注重加强地下根系的保护。     

Suboptimal temperature favors reserve formation in biennial carrot (Daucus carota) plants

In response to suboptimal temperatures, temperate annual plants often increase root:shoot ratios, build-up carbohydrates and display typical morphological and anatomical changes. We know less about the responses of biennials such as carrot. As a model plant, carrot has the additional feature of two functionally and morphologically distinct root parts: the taproot, which stores carbohydrate and other compounds, and the fibrous root system involved in acquisition of water and nutrients. Here, we analyze the effects of temperature (12 vs 25°C) on growth, carbohydrate accumulation and whole-plant morphology in two carrot cultivars. Our working hypothesis is that suboptimal temperature favors active formation of reserve structures, rather than passive accumulation of storage carbohydrates. In comparison with plants grown at 25°C, plants grown at 12°C had: (1) higher fibrous root:shoot ratio (13%) , (2) thicker (10–15%) and smaller (up to two- to three-fold) leaves, (3) lower leaf cuticular permeance (two- to four-fold), (4) higher taproot:shoot ratio (two-fold), (5) higher phloem:xylem ratios in taproot (two- to six-fold), (6) unchanged percentage dry matter content (%DMC) in leaves, petioles or fibrous roots and (7) higher %DMC in taproot (20%). However, %DMC of individual taproot tissues (phloem and xylem) was unaffected by temperatures and was consistently higher in the phloem (up to 30%). Therefore, the higher %DMC of whole taproots at 12°C was attributed solely to the increased development of phloem tissue. Carrot, therefore, shares many of the most conspicuous elements of temperate plant responses to low temperatures. Consistently with our hypothesis, however, carrots grown at suboptimal temperature promoted reserve structures, rather than the increase in carbohydrate concentration typical of most temperate annual species and woody perennials.     

Partitioning of Carbohydrates in Annual and Perennial Cotton (Gossypium hirsutum L.)

An analysis of the partitioning of carbohydrates in annual andperennial cotton was made to ascertain the distribution of assimilatesand constitution of reserves. Root/shoot dry matter ratio ishigh in perennial cotton and this plant shows a preferentialaccumulation of dry matter in roots corresponding to its adaptationto drought. Starch content is also higher in perennial cottonroots than in annual. It can be said that the earlier maturingthe cultivar, the lower the root/shoot ratio and the lower thestarch content. Nevertheless, at the whole plant level in annualcotton the starch content is highest in leaves where it is accumulatedbefore migration, and stem wood, and lowest in root and bark.While starch content in roots of annuals declines after 3 months,it is still increasing in perennials. Accumulation of carbohydratesas reserve material can be modified by selection and such selectionis accompanied by an increase in the activities of ß-amylasein exporting organs: leaves, woody tissue of the stem, and barkbut not in roots. Invertase activities were highest in leavesbut did not respond to selection. Non-irrigated cotton had ahigher activity of ß-amylase in leaves and stem woodcorresponding to the mobilization of reserve assimilates. Smallerincreases were observed in the activity of invertase. High yieldingannual cottons show a higher activity of ß-amylaseand invertase in leaves corresponding to a higher capacity ofassimilate transfer. Also a comparison was made from emergenceto 4 months of the partitioning of carbohydrates between leaf,stem and roots in annual and perennial cotton. In conclusionperennial cotton apparently owes its drought resistance to apartitioning of assimilates that favours the growth of the rootsystem and the accumulation of starch reserves in roots. Key words: Gossypium hirsutum L, carbohydrates, partitioning     

Photosynthate partitioning and nodule formation in soybean plants that received red or far-red light at the end of the photosynthetic period

The influence of row orientation on spectral distribution of light received by growing soybean [ Glycine max (L.) Merr. (cv. Coker 338)] plants was measured under field conditions, and light spectrum effects on photosynthate partitioning were studied under controlled environments. Light received by leaves under field conditions differed among those grown in north-south vs east-west oriented rows. In morning and late afternoon, the far-red/ red ratio received by leaves at the surface of the canopy differed about 3-fold from the east to west sides of north-south rows, but only 1.3-fold from the south to north sides of east-west rows.
In controlled environments, brief exposures to red or far-red light at the end of the photosynthetic period influenced partitioning of photosynthate among leaves, stems and roots. The top/root ratios differed significantly between the red and far-red treated plants. Red treated plants partitioned less photosynthate to stems and more to roots than did those treated with far-red. Also, plants with larger root systems developed more nodules. Phytochrome effects on photosynthate partitioning between tops and roots may influence yield of soybean plants grown in soils with low water-holding capacity.     

Decreased energy synthesis is partially compensated by a switch to sucrose synthase pathway of sucrose degradation in restricted root of tomato plants

Tomato (Solanum lycopersium L.) plants were grown hydroponically to investigate the changes of energy metabolism and adaptive mechanism in response to root restriction. Root restriction resulted in a significant increase in root lipid peroxidation and reduction in leaf net CO₂ assimilation rate, which was accompanied by increase of alcohol dehydrogenase (ADH; EC 1.1.1.1) and lactate dehydrogenase (LDH; EC 1.1.1.27) activities. Total, cytochrome pathway, and alternative pathway respirations were all decreased in the roots after 15 days of root restriction treatment. Accompanied with the decrease of ATP content, ratio of invertase/sucrose synthase activity was increased in the restricted roots together with a decrease in glucose content and an increase in fructose content. We concluded that the decreased energy synthesis under root restriction condition was partially compensated by the energy-conserving sucrose synthase pathway of sucrose metabolism.     

Sink development, sucrose metabolising enzymes and carbohydrate status in turnip (Brassica rapa L.)

Accumulation of 60–70 % of biomass in turnip root takes place between 49–56 days after sowing. To understand the phenomenon of rapid sink filling, the activities of sucrose metabolising enzymes and carbohydrate composition in leaf blades, petiole and root of turnip from 42–66 days of growth were determined. An increase (2–3 folds) in glucose and fructose contents of roots accompanied by an increase in activities of acid and alkaline invertases was observed during rapid biomass accumulating phase of roots. The observed decrease in the activities of acid and alkaline invertases along with sucrose synthase (cleavage) in petiole during this period could facilitate unrestricted transport of sucrose from leaves to the roots. During active root filling period, a decrease in sucrose synthase (cleavage) and alkaline invertase activities was also observed in leaf blades. A rapid decline in the starch content of leaf blades was observed during the phase of rapid sink filling. These metabolic changes in the turnip plant led to increase in hexose content (35–37 %) of total dry biomass of roots at maturity. High hexose content of the roots appears to be due to high acid invertase activity of the root.     

Short-term control of root: shoot partitioning

We present data showing that the fraction of the available photosynthatepartitioned between the root and the shoot of a barley seedlingis affected by the supply of photosynthate from the source leaf:an increased fraction of the exported photosynthate goes tothe shoot when supply is reduced. Also, if the roots are cooleda short time before reducing the supply of photosynthate, thenthe effect of a reduced supply upon partitioning is reversedwith an increased fraction then going to the root. We concludethat the distribution of available photosynthate between competingsinks is influenced by source supply as well as sink function.The reported source-sink interactions are consistant with thepredictions of a recently pro posed model of source-sink interaction(Minchin et al., 1993). The concept of marginal partitioningis introduced to describe the distribution, between all of thesinks, of a small change in photosynthate supply. Key words: Carbohydrate partitioning, shoot : root ratio, source-sink interactions     

Localization of sucrose synthase in wheat roots: increased in situ activity of sucrose synthase correlates with cell wall thickening by cellulose deposition under hypoxia

Sucrose synthase (SuSy; EC 2.4.1.13) plays a prominent role in O(2) deficiency and functions at a branch point, partitioning sucrose between cell wall biosynthesis and glycolysis. The cleavage of sucrose by SuSy was localized in wheat ( Triticum aestivum L. cv. Alcedo) roots subjected to 4 days of hypoxia. Increased SuSy activity was observed by in situ activity staining in the tip region and in the stele of root axes. The pattern of cellulose deposition correlated with regions of high SuSy activity. Cellulose accounted for more than 30% of root dry weight and the cellulose content increased substantially under hypoxia. The strongest accumulation of cellulose occurred in the base and mid-regions of the roots where the content rose to 163% and 182% of controls, respectively. In the root axis, cellulose deposition occurred in the endodermis and walls of pith cells. In root tips, cellulose was primarily deposited in developing xylem and phloem. The marker enzyme for O(2) shortage, pyruvate decarboxylase (EC 4.1.1.17), exhibited a 14-fold increase in the root apex, whereas in basal root tissues, which contained more aerenchyma, pyruvate decarboxylase activity was only doubled. The root apex also contained the highest concentration of sucrose and hexoses. The elevated sugar content in all root zones was partially used to synthesize cellulose for secondary wall thickening.     

Sucrose Utilization via Invertase and Sucrose Synthase with Respect to Accumulation of Cellulose and Callose Synthesis in Wheat Roots under Oxygen Deficiency

The sucrose cleavage by sucrose synthase (SuSy) and neutral invertase was studied in wheat roots (Triticum aestivum L.) subjected to hypoxia or anoxia for 4 days. By in situ activity staining, increased SuSy activity was observed in the tip region and stele of root axes while the activity of invertase decreased. Cellulose content significantly increased in hypoxically treated roots. The cellulose deposition was correlated with regions of high SuSy activity, being mainly located in the pericycle and endodermis. Invertase activity was distributed along the root without clear difference between cortex and stele. Under root hypoxia, a significant increase in the structural carbohydrates, callose and especially cellulose, was shown. Increasing levels of soluble carbohydrates were partially used to synthesize cellulose for secondary wall thickening and callose to counteract the tissue injury following low-oxygen stress. Under strict anoxia, the roots were much more injured but sustained a high level of cellulose and callose while the soluble carbohydrates almost disappeared.     

Sulla carnosa modulates root invertase activity in response to the inhibition of long‐distance sucrose transport under magnesium deficiency

• Being the principal product of photosynthesis, sucrose is involved in many metabolic processes in plants. As magnesium (Mg) is phloem mobile, an inverse relationship between Mg shortage and sugar accumulation in leaves is often observed.
• Mg deficiency effects on carbohydrate contents and invertase activities were determined in Sulla carnosa Desf. Plants were grown hydroponically at different Mg concentrations (0.00, 0.01, 0.05 and 1.50 mM Mg) for one month.
• Mineral analysis showed that Mg contents were drastically diminished in shoots and roots mainly at 0.01 and 0.00 mM Mg. This decline was adversely associated with a significant increase of sucrose, fructose and mainly glucose in shoots of plants exposed to severe deficiency. By contrast, sugar contents were severely reduced in roots of these plants indicating an alteration of carbohydrate partitioning between shoots and roots of Mg‐deficient plants. Cell wall invertase activity was highly enhanced in roots of Mg‐deficient plants, while the vacuolar invertase activity was reduced at 0.00 mM Mg. This decrease of vacuolar invertase activity may indicate the sensibility of roots to Mg starvation resulting from sucrose transport inhibition. ¹⁴CO₂ labeling experiments were in accordance with these findings showing an inhibition of sucrose transport from source leaves to sink tissues (roots) under Mg depletion.
• The obtained results confirm previous findings about Mg involvement in photosynthate loading into phloem and add new insights into mechanisms evolved by S. carnosa to cope with Mg shortage in particular the increase of the activity of cell wall invertase.