Effects of nitrogen and phosphorus deficiencies on levels of carbohydrates, respiratory enzymes and metabolites in seedlings of tobacco and their response to exogenous sucrose

A simple method of growing plants in agar was exploited to investigate the effect of long-term nitrogen (N) and phosphorus (P) deficiencies on respiratory metabolism and growth in shoots and roots of Nicotiana tabacum seedlings, and their interaction with exogenously supplied sucrose. Levels of hexose phosphates and 3-phosphoglyceric acid (3-PGA) were low in P-deficient shoots and roots and high in N-deficient shoots and roots. The ratio of hexose phosphates to 3-PGA and levels of fructose-2,6-bisphosphate were high in P-deficient plants and low in N-deficient plants. These data reflect differences in the way metabolism was perturbed, yet both deficiencies were associated with increased root growth relative to shoot growth, starch accumulation in the shoots, and soluble carbohydrate accumulation, especially hexoses, in the roots. Enzymes for sucrose degradation (sucrose synthase, acid and alkaline invertase) and glycolysis (phosphofructokinase, pyrophosphate-dependent phospho-fructokinase and pyruvate kinase) remained unaltered or declined in the shoots and roots. The accumulation of hexoses in roots of N- and P-deficient plants may result from maintenance of high invertase activities relative to sucrose synthase and glycolytic enzymes in the roots. The possibility that hexose accumulation may drive preferential root growth osmotically in N and P deficiencies is discussed. The addition of sucrose to roots to further investigate the interaction of carbohydrates with growth and allocation in low N and low P produced clear effects even though endogenous levels of soluble carbohydrate were already high in the nutrient-deficient plants. In complete nutrition, growth was stimulated, protein content particularly of the roots was increased and there was a preferential increase in activity of sucrose synthase in roots. At low P, enzyme activities in roots were increased, including sucrose synthase, and protein content increased, particularly in the roots, but there was no increase in growth. In N-deficient plants, exogenous sucrose led to decreased protein, Rubisco and chlorophyll content in shoots, in contrast to the other conditions, and a higher protein content and a general increase of catabolic enzyme activities and growth in the roots.     

Effect of osmo- and hydropriming of chickpea seeds on seedling growth and carbohydrate metabolism under water deficit stress

Seven-day-old seedlings obtained from seeds primed with mannitol (4%)and water showed three to four fold more growth with respect to root and shootlength in comparison with seedlings obtained from non-primed seeds. Seedlingswere grown under water deficit stress conditions created by 15% polyethyleneglycol (PEG) 6000 in the medium. Priming of chickpea seeds with NaCl and PEGwasnot effective in increasing seedling growth under these water deficit stressconditions. The activities of amylase, invertases (acid and alkaline), sucrosesynthase (SS) and sucrose phosphate synthase (SPS) were higher in shoots ofprimed seedlings. An increase in the activities of SS, and both the acid andalkaline invertases was also observed in roots of primed seedlings. The twofoldincrease in specific activity of sucrose phosphate synthase was observed incotyledons of primed seedlings. The higher amylase activity in shoots of primedseedlings enhanced the rapid hydrolysis of transitory starch of the shootleading to more availability of glucose for shoot growth and this was confirmedby the low level of starch in shoots of primed seedlings.     

Exogenous Proline Application Reduces Phytotoxic Effects of Selenium by Minimising Oxidative stress and Improves Growth in Bean (<Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> L.) Seedlings

Bean (Phaseolus vulgaris L.) seedlings were subjected to varying selenium levels (1, 2, 4, and 6 ppm) in a hydroponic culture. The germination reached 100% in 48 h in all Se levels except 6 ppm, where it took 72 h. The root and shoot growth was stimulated at 1 and 2 ppm Se levels that was commensurate with increase in chlorophyll content, leaf water content, and cellular respiration. At 4 and 6 ppm Se levels, the growth was inhibited appreciably, which was associated with increase in stress injury measured as damage to membranes and decrease in cellular respiration, chlorophyll, and leaf water content. The oxidative injury as elevation of lipid peroxidation was larger compared to hydrogen peroxide accompanied by reduced levels of enzymatic (superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase) and non-enzymatic (ascorbic acid and glutathione) antioxidants. Proline content was significantly higher at 1 and 2 ppm Se but diminished considerably at 4 and 6 ppm levels concomitant with the reduced growth. Exogenous application of proline (50 μM) resulted in substantiation of its endogenous levels that antagonised the toxic effects of Se by improving the growth of seedlings. The stress injury was reduced significantly with simultaneous increase in enzymatic and non-enzymatic antioxidants. Especially the components of ascorbate–glutathione cycle showed larger stimulation with proline application. The role of proline in mitigating the toxic effects of Se is discussed.     

Effect of water deficit on carbohydrate status and enzymes of carbohydrate metabolism in seedlings of wheat cultivars

The effect of water deficit on carbohydrate status and enzymes of carbohydrate metabolism (alpha and beta amylases, sucrose phosphate synthase, sucrose synthase, acid and alkaline invertases) in wheat (Triticum aestivum L.) was investigated in the seedlings of drought-sensitive (PBW 343) and drought-tolerant (C 306) cultivars. The water deficit was induced by adding 6% mannitol (water potential -0.815 Mpa) in the growth medium. The water deficit reduced starch content in the shoots of tolerant seedlings as compared to the sensitive ones, but increased sucrose content in the shoots and roots of tolerant seedlings, indicating their protective role during stress conditions. It also decreased the alpha-amylase activity in the endosperm of seedlings of both the cultivars, but increased alpha and beta amylase activities in the shoots of tolerant ones. Sucrose phosphate synthase (SPS) activity showed a significant increase at 6 days of seedling growth (DSG) in the shoots of stressed seedlings of tolerant cultivar. However, SPS activity in the roots of stressed seedlings of sensitive cultivar was very low at 4 DSG and appeared significantly only at day 6. Sucrose synthase (SS) activity was lower in the shoots and roots of stressed seedlings of tolerant cultivar than sensitive ones at early stage of seedling growth. Higher acid invertase activity in the shoots of seedlings of tolerant cultivar appeared to be a unique characteristic of this cultivar for stress tolerance. Alkaline invertase activity, although affected under water deficit conditions, but was too low as compared to acid invertase activity to cause any significant affect on sucrose hydrolysis. In conclusion, higher sucrose content with high SPS and low acid invertase and SS activities in the roots under water deficit conditions could be responsible for drought tolerance of C 306.     

Excess nickel modulates activities of carbohydrate metabolizing enzymes and induces accumulation of sugars by upregulating acid invertase and sucrose synthase in rice seedlings

The effects of increasing concentrations of nickel sulfate, NiSO₄ (200 and 400 μM) in the growth medium on the content of starch and sugars and activity levels of enzymes involved in starch and sugar metabolism were examined in seedlings of the two Indica rice cvs. Malviya-36 and Pant-12. During a 5–20 day growth period of seedlings in sand cultures, with Ni treatment, no definite pattern of alteration in starch level could be observed in the seedlings. In both roots and shoots of the seedlings Ni treatment led to a significant decrease in activities of starch degrading enzymes α-amylase, β-amylase, whereas starch phosphorylase activity increased. The contents of reducing, non-reducing, and total sugars increased in Ni-treated rice seedlings with a concomitant increase in the activities of sucrose degrading enzymes acid invertase and sucrose synthase. However, the activity of sucrose synthesizing enzyme sucrose phosphate synthase declined. These results suggest that Ni toxicity in rice seedlings causes marked perturbation in metabolism of carbohydrates leading to increased accumulation of soluble sugars. Such perturbation could serve as a limiting factor for growth of rice seedlings in Ni polluted environments and accumulating soluble sugars could serve as compatible solutes in the cells under Ni toxicity conditions.     

Propagation,growth, and carbohydrates of <Emphasis Type="Italic">Dendrobium</Emphasis> Second Love (Orchidaceae) <Emphasis Type="Italic">in vitro</Emphasis> as affected by sucrose,light, and dark

In general, plant material grown in vitro has low photosynthetic ability to achieve positive carbon balances. Therefore, a continuous supply of carbohydrates from the culture medium is required, and sucrose has been the most commonly used carbon source. In this paper, we investigate the effects of different sucrose concentrations and the presence and absence of light on the endogenous levels of soluble carbohydrates and starch as well as on the proliferation and growth of Dendrobium Second Love (Orchidaceae) in vitro. The possibility of using etiolated stem segments as a means for micropropagating this hybrid was also verified. The results obtained indicated that the presence and absence of light and the sucrose concentrations used influenced the amounts of soluble carbohydrates and starch and the proliferation of D. Second Love shoots and roots. An increase in sucrose concentration caused a progressive increase in the amounts of total carbohydrates and starch. Under both light conditions, sucrose was the main sugar found in the shoots followed by glucose and fructose. The addition of sucrose to the culture medium up to 2% and 4% was advantageous to the number of shoots produced per explant and the root longitudinal growth in the presence and absence of light, respectively. Shoot and root dry matter and the number of roots formed per explant increased as sucrose concentration was raised up to 6% in both light treatments. The use of dark-grown shoot segments proved to be a useful and reliable alternative for the micropropagation of this hybrid.     

硒对三裂叶野葛毛状根生长及抗氧化酶活性的影响

本文研究硒(Se)对三裂叶野葛毛状根生长及抗氧化酶活性的影响。结果表明,低浓度亚硒酸钠(0~0.5 mg/L)可促进毛状根生长及异黄酮的生物合成,而高浓度亚硒酸钠抑制其生长和异黄酮的积累,且浓度愈高抑制作用愈强。此外,硒可促进可溶性蛋白的生物合成,亚硒酸钠浓度愈高促进作用愈明显;硒还可降低毛状根中SOD活性,提高POD活性,降低MDA含量。说明硒对三裂叶野葛毛状根生长和抗氧化酶活性有重要的调节作用。     

Growth and shoot formation in protoplast-derived calli of Brassica oleracea ssp. acephala and ssp. capitata

The effect of media components and environmental factors on growth and organogenesis of protoplast-derived calli of curly kale and cabbage were tested. Optimal growth (fresh weight increase of calli, shoots and roots) was found at 60 mM sucrose. Lower sucrose concentrations (3–30 mM) were favourable for shoot formation. Nitrate concentrations from 23 to 100 mM in combination with 8 or 21 mM ammonium were optimal for shoot formation. However, growth was reduced by high (100 mM) nitrate concentration. The effects of various organic nitrogen compounds at 0.5 and 2 mM were tested. Glutamine did not influence shoot formation and barely growth. Proline at 0.5 mM stimulated growth of cabbage calli but decreased growth of curly kale calli, and at 2 mM, proline also inhibited shoot production. Adenine sulphate decreased growth of cabbage calli at 0.5 mM, and at 2 mM shoot production was also reduced. Spermidine and spermine inhibited both growth and differentiation. Putrescine resulted in about 50% higher fresh weights, and also increased the number of calli producing shoots by about 35%. More calli produced shoots in white light than in blue or red light or in darkness. The length of the photoperiod or intensity of light was not critical for shoot production.     

Salinity Induces Accumulation of Soluble Sugars and Alters the Activity of Sugar Metabolising Enzymes in Rice Plants

Changes in the starch and sucrose contents, and the sucrose phosphate synthase, acid invertase, and starch phosphorylase activities were studied in the seedlings of salt sensitive and salt tolerant rice cultivars growing under two NaCl concentrations (7 and 14 dS m^-1) for 20 d. Under salinity, the starch content in roots declined more in salt sensitive cvs. Ratna and Jaya than in salt tolerant cvs. CSR-1 and CSR-3 and was unchanged in shoots. The contents of reducing and non-reducing sugars, and the activity of sucrose phosphate synthase was increased more in the sensitive than in the tolerant cultivars. Acid invertase activity decreased in shoots of the salt tolerant cultivars, whereas increased in salt sensitive cultivars. Starch phosphorylase activity decreased in all cultivars. This revised version was published online in July 2006 with corrections to the Cover Date.     

Selenium improves the antioxidant ability against aluminium-induced oxidative stress in ryegrass roots

We investigated the role of selenium (Se) against aluminium (Al) stress in ryegrass by evaluating the growth responses and the antioxidant properties of plants cultured hydroponically with Al (0 or 0.2 mM) and selenite (0–10 µM Se). Al addition significantly reduced the yield and length of shoots and roots, and most Al was accumulated in the roots. Al also enhanced lipid peroxidation and activated the peroxidase (POD), ascorbate peroxidase (APX) and superoxide dismutase (SOD) enzymes in the roots. Se application up to 2 µM improved root growth and steadily decreased thiobarbituric acid reactive substances (TBARS) accumulation in plants treated with 0 and 0.2 mM Al. However, above 2 µM, Se induced stress in plants grown with or without Al. Significant changes in antioxidant enzymes activities were also found as a result of the added Se. At low Se addition levels POD was activated, whereas APX activity decreased irrespective of added Al. Furthermore, Se supplied up to 2 µM greatly decreased root SOD activity in Al-stressed plants. Our study provides evidence that Se alleviated the Al-induced oxidative stress in ryegrass roots through the enhancement of the spontaneous dismutation of superoxide radicals and the subsequent activation of POD enzyme.     

Indole acetic acid mimics the effect of salt stress in relation to enzymes of carbohydrate metabolism in chickpea seedlings

The effect of addition of indole acetic acid (3 M) andNaCl (75 mM) on growth and enzymes of carbohydrate metabolism inchickpea seedlings was compared. In comparison with control seedlings, theseedlings growing in the presence of indole acetic acid (IAA) had reducedamylase activity in cotyledons and enhanced sucrose synthase (SS) and sucrosephosphate synthase (SPS) activities in cotyledons and shoots at all days ofseedling growth. Compared with control seedlings, sucrose content was higher incotyledons, shoots and roots and reducing sugar content was lower in shoots ofIAA treated seedlings. A low invertase (acid and alkaline) activity in shoots ofIAA treated seedlings could lead to reduced sink strength and hence decreasedgrowth of seedlings. Effects of NaCl stress on growth and activities of amylase,SS and SPS in cotyledons and invertase, SS and SPS in shoots were similar tothose observed with addition of IAA.     

Calcium-mediated conversion of sucrose to starch in relation to the activities of amylases and sucrose-metabolizing enzymes in sorghum grains raised through liquid culture

Detached ears of sorghum (Sorghum vulgare) were cultured in complete liquid medium containing Ca2+(0, 3, 10 and 30 mM) and effect of this ion on the conversion of sucrose to starch with respect to the activities of amylases, sucrose synthase, sucrose phosphate synthase and soluble invertases were studied in developing grains. Presence of 3 mM Ca2+ in culture medium enhanced both accumulation of starch and activity of alpha-amylase in grain but without having any influence on the activity of beta-amylase. However, with 10 and 30 mM Ca2+, the accumulation of starch and activities of both amylases decreased and with advancement in culturing period, starch accumulation was further decreased. Irrespective of its concentration, Ca2+ enhanced the activities of sucrose synthase (synthesis), sucrose-phosphate synthase, soluble acid invertase and soluble-neutral invertase. Increase in the concentration of Ca2+ in culture medium was concomitant with an elevation in relative proportion of sucrose in the grain reflecting a net balance in per cent increase with Ca2+ in the activities of sucrose-synthesizing enzymes over sucrose-hydrolysing ones. Based on the results, it is suggested that assimilation of Ca2+ by grain is essential for maintaining high activity of alpha-amylase to generate starch primers required for the conversion of sucrose to starch during grain filling in sorghum.     

Effect of aluminium on metabolism of starch and sugars in growing rice seedlings

The effect of increasing concentrations of Al₂(SO₄)₃ in situ on the content of starch, sugars and activity behaviour of enzymes related to their metabolism were studied in growing seedlings of two rice cvs. Malviya-36 and Pant-12 in sand cultures. Al₂(SO₄)₃ levels of 80 and 160 μM in the growth medium caused an increase in the contents of starch, total sugars as well as reducing sugars in roots as well as shoots of the rice seedlings during a 5–20 days growth period. The activities of the enzymes of starch hydrolysis α-amylase, β-amylase and starch phosphorylase declined in Al-exposed seedlings, whereas the activities of sucrose hydrolyzing enzymes sucrose synthase and acid invertase increased in the seedlings due to Al³⁺ treatment. The enzyme of sucrose synthesis, sucrose phosphate synthase showed decreased activity in Al³⁺ treated seedlings compared to controls. Results suggest that Al³⁺ toxicity in rice seedlings impairs the metabolism of starch and sugars and favours the accumulation of hexoses by enhancing the activities of sucrose hydrolyzing enzymes.     

Activities of starch hydrolytic enzymes and starch mobilization in roots of <Emphasis Type="Italic">Caragana korshinskii</Emphasis> following above-ground partial shoot removal

In many resprouting plants, carbohydrates are stored as starch in roots and will be mobilized to support above-ground tissue regrowth after shoot damage. Our objective was to determine how activities of starch hydrolytic enzymes change damage-induced starch mobilization in Caragana korshinskii roots after above-ground tissue loss. Zero percent (control), 30% (30% RSL), 60% (60% RSL) of main shoot length, and 25% (25% RSN), 50% (50% RSN), and 100% (100% RSN) of main shoot number were removed. Compared with control plants, clipping accelerated the reduction of starch in the roots, increased sucrose flux per flower per hour and nectar production per flower per day in 30% RSL, 60% RSL, 25% RSN, and 50% RSN treatments, and improved vegetative growth in 100% RSN treatment. All treatments had similar total nonstructural carbohydrate (TNC) concentrations in leaves, shoots, and stems with the exception of 100% RSN with higher TNC concentration in shoots. Both α-, and β-amylase activities were enhanced by clipping, the former being more strongly correlated with starch degradation in the roots than the latter. The other two possible starch-breaking enzymes, α-glucosidase, and starch phosphorylase showed no significant differences in the activities between treatments. The results suggest that starch degradation in the roots of C. korshinskii was regulated by α-amylase activity and more mobilized starch was used to support vegetative growth in 100% RSN treatment and support sexual reproduction followed by other clipping treatments.     

Effects of abscisic acid (ABA) on grain filling processes in wheat

The effect of in situ water stress on the endogenous abscisic acid (ABA) content of the endosperm and the in vitro application of ABA on some important yield regulating processes in wheat have been studied. Water stress resulted in a marked increase in the ABA content of the endosperm at the time close to cessation of growth. Application of ABA to the culture medium of detached ears reduced grain weight. Exogenously applied ABA, at the highest concentration (0.1 mM) reduced transport of sucrose into the grains and lowered the starch synthesis ability of intact grains. In vitro sucrose uptake and conversion by isolated grains was stimulated by low ABA concentrations (0.001 mM) in the medium but was inhibited by higher concentrations. ABA application had no effect on sucrose synthase (SS) and uridine diphosphate glucose pyrophosphorylase (UDP-Gppase) activities, whereas adenosine diphosphate glucose pyrophosphorylase (ADP-Gppase), soluble starch synthase (SSS), and granule-bound starch synthase (GBSS) activities were reduced. These results raise the possibility that water stress-induced elevated levels of endogenous ABA contribute to reduced grain growth.     

Comparison of tuber and shoot formation from in vitro cultured potato explants

The development of axillary buds of potato (Solanum tuberosum L.) plants, cultured in vitro, was analyzed. Depending on the composition of the culture medium, the buds developed into either tubers (medium with 8% sucrose), shoots (1% sucrose), or stolons (8% sucrose and 0.5 μM gibberellin). Endogenous sugar and starch levels, and key-enzymes involved in the conversion of sucrose to starch were determined at different stages of development. Moreover, the spatial distribution of sugar levels and enzyme activities were determined within the developing structures. Glucose and fructose decreased upon tuber formation, most noticeably in the swelling parts, where also starch accumulated. The activities of sucrose synthase, fructokinase and ADP-glucose pyrophosphorylase were highest under tuber-inducing conditions, the increase being confined to the tubers, and absent in the subtending stolons. It is concluded that changes in the measured parameters, observed under tuberizing conditions, are specifically related to the formation of the tuber, and are confined to the swelling part only. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of Kinetin on Starch and Sucrose Metabolising Enzymes in Salt Stressed Chickpea Seedlings

Higher amylase activity in cotyledons of kinetin treated salt stressed (75 mM NaCl) chickpea (Cicer arietinum L. cv. PBG-1) seedlings, as compared to salt stressed seedlings was observed during a growth period of 7 d. The activities of acid and alkaline invertases were maximum in shoots and minimum in cotyledons under all conditions. The reduced shoot invertase activities under salt stress were enhanced by kinetin with a simultaneous increase in reducing sugar content. Kinetin increased the activities of sucrose synthase (SS) and sucrose phosphate synthase (SPS) in both the cotyledons and shoots of stressed seedlings. Kinetin appears to increase the turnover of sucrose in the shoots of stressed seedlings.     

Lead effects in the chick during selenium deficiency

1. Growing chicks (Gallus domesticus) were fed a selenium-deficient diet supplemented with 0 or 2000 ppm lead (Pb) and 0 or 0.1 ppm selenium (Se). 2. Selenium addition stimulated growth at 0 but not at 2000 ppm Pb, while Pb depressed growth at both levels of Se. 3. Selenium addition stimulated Se-dependent glutathione peroxidase (GSH-Px) activity in liver, but Pb was without effect on GSH-Px activity. 4. Lead addition increased non-protein sulfhydryl (NPSH) concentrations in liver, kidney and thigh muscle. NPSH levels were not altered by Se. 5. The reported antagonism between Pb and Se does not appear to be mediated through effects on GSH-Px or NPSH metabolism.     

Characterisation of the wheat phospholipid fraction in the presence of nickel and/or selenium

The influence of nickel (Ni) and/or selenium (Se) on phospholipid composition was studied in shoots and roots of wheat seedlings. Phospholipid differences between samples were analysed using liquid chromatography/electrospray ionization–MS coupled. A total of 39 lipid species were identified. Individual phospholipids were then quantified using a multiple reaction monitoring method. In the roots, Ni toxicity was associated with an elevated level of phosphatidic acid species. In the shoots, the phosphatidylcholine/phosphatidylethanolamine ratio was about fivefold higher than in roots and decreased in Ni-treated samples. Additionally, the concentrations of phospholipid species containing C 18:3 fatty acid were reduced. Lipidome data were then analyzed using principal component analysis, which confirmed the compositional changes in phospholipids in response to Ni and Ni + Se. In contrast, the phospholipid profiles of wheat seedlings exposed to Se alone showed more similarities with the control. Together, our results suggested that the presence of Se, despite a considerable improvement of growth of Ni-treated wheat, did not counterbalance negative effect of Ni on the phospholipid composition in wheat roots and shoots.