Sugar accumulation in growing subhooks of etiolated Pisum sativum seedlings - Stimulation of sugar exudation and invertase activity in epicotyls by gibberellic acid

The epicotyl of 5-day-old derooted cuttings of pea ( Pisum sativum L. cv. Alaska) with and without cotyledons exuded sucrose and glucose in the presence of EDTA. The amount of sugars exuded was greatly affected by the position at which the epicotyl was cut. The largest amount of sugars was exuded when the epicotyl was cut 2 mm below the hook, leaving the growing subhook. Gibberellic acid (GA) substantially increased the amount of sugars exuded from the epicotyl in the presence of cotyledons but only slightly in their absence. GA stimulated sugar exudation from the cotyledonary node as well as from the epicotyl. In cuttings with cotyledons, GA enhanced invertase activity in the apoplast, and in the intraceUular soluble and bound fractions in the growing subhook. In decotylized cuttings, GA enhanced only soluble invertase activity. GA did not affect invertase activity in the epicotyl below the subhook. These results suggest that GA stimulates sugar accumulation in the growing subhook by stimulating not only phloem loading of sucrose in the cotyledons but also unloading in the subhook.     

A relationship between irradiation, carbohydrates and rooting in cuttings of Pisum sativum

Rooting ability was studied for cuttings derived from pea plants ( Pisum sativum , L. cv. Alaska) grown in controlled environment rooms. When the cuttings were rooted at 70 μmol m⁻² s⁻, ¹ (photosynthetic photon flux density) or more, a stock plant irradiance at 100 μmol m⁻² s⁻¹ decreased rooting ability in cuttings compared to 5 μmol m⁻², s⁻¹, However, cuttings rooted at 160 μmol m⁻² s⁻¹ formed more roots compared to 5 (μmol m⁻² s⁻¹. Although a high irradiance increased the number of roots formed, it could not overcome a decreased potential for root formation in stock plants grown at high irradiance. Light compensation point and dark respiration of cuttings decreased by 70% during the rooting period, and the final levels were strongly influenced by the irradiance to the cuttings. Respiratory O₂ uptake decreased in the apex and the base of the cutting from day 2 onwards, whereas a constant level was found in the leaves. Only the content of extractable fructose, glucose, sucrose and starch varied during the early part of the rooting period. We conclude that the observed changes in the cuttings are initiated by excision of the root system, and are not involved in the initiation of adventitious roots.     

Factors affecting the relative abundance of two coexisting aphid species on sugar beet

1 The two most common species of aphid colonizing sugar beet Beta vulgaris L. are Myzus persicae (Sulzer) (Hemiptera: Aphididae) and Aphis fabae Scopoli (Hemiptera: Aphididae). 2 M. persicae colonizes sugar beet earlier than A. fabae but the population of the former also declines earlier. Despite similar numbers of each species migrating at the time of colonization, M. persicae is usually less abundant on the crop than A. fabae, suggesting differences between the species in their selection of, and performance on, sugar beet. 3 The intrinsic rate of increase of both species declines as sugar beet matures, however, at any given plant age the intrinsic rate of increase of A. fabae is one and a half times greater than that of M. persicae. This results in more rapid population growth and a later decline of the population. 4 Intraspecific competition appears to result in M. persicae becoming very restless, but there is no evidence for interspecific competition between the two species on this host. 5 A population growth model which takes account of the decline in host quality of sugar beet shows that the M. persicae population peaks 30 days before that of A. fabae, and, excluding differences in emigration rate, the maximum A. fabae population is 14 times greater than the maximum M. persicae population. These results are compared to field data.     

外源激素对褐飞虱翅型分化的影响

该文报道外源蜕皮激素(ED)和保幼激素类似物(JHA)对褐飞虱Nilaparvata lugens (Stal)翅型分化及体内酯酶活性、可溶性糖和游离氨基酸含量等的影响。褐飞虱在3、4龄若虫期经JHA处理后,所羽化出的成虫短翅型比例明显升高;而在5龄若虫期处理,所羽化出成虫的短翅型比例无明显变化。ED处理能增加3、4龄若虫体内酯酶活性、可溶性糖及游离氨基酸含量,而JHA处理则能有效地抑制ED的这些生物活性,这可能是JHA处理后褐飞虱成虫短翅型比例提高的生理生化基础。     

螺旋藻对糖尿病大鼠的疗效观察

以糖尿病大鼠为试验对象,做喂饲螺旋藻对糖尿病的疗效试验。结果证明：螺旋藻可明显改善糖尿病大鼠的症状,表现为糖尿病大鼠血清胰岛素水平升高,血糖降低,体重增加,毛色光亮及死亡率降低,其中尤以螺旋藻配以中药试验组的效果更为明显。     

STORAGE OF PHOSPHORUS IN NITROGEN-FIXING ANABAENA FLOS-AQUAE (CYANOPHYCEAE)1

P accumulation and metabolic pathway in N₂-fixing Anabaena flos-aquae (Lyngb.) Bréb were investigated in P-sufficient (20 μMP) and P-limited (2 μMP) turbidostats in combined N-free medium. The cyanobacterium grew at its maximum rate (μ_max, 1.13 d^?1) at the high P concentration and at 65% of μ_max under P limitation, with total cell P concentrations (Q_P) at steady states of 12.0 and 5.2 fmol·cell^?1, respectively. At steady state, polyphosphates (PP_i) accounted for only 3% of Q_P (0.4 fmol·cell^?1) in P-rich cells. Its concentration in P-limited cells was 5.8% (0.3 fmol·cell^?1). On the other hand, sugar P was very high at 22% of Q_P in P-rich cells and was undetectable in P-limited cells. Pulse chase experiments with ³²P showed that P-rich cells initially incorporated the labeled P into the acid-soluble PP_i fraction within the first few minutes and to a lesser extent into nucleotide P. Radioactivity in the PP_i then declined rapidly with concomitant increases in sugar P and nucleotide P fractions. In contrast, in P-limited cells, no radiolabel was detected in acid-soluble PP_i, and ³²P was initially incorporated into nucleotide P, sugar P, and ortho P fractions. The latter two fractions then subsequently declined. Therefore, under N₂-fixing conditions the cyanobacteria appeared to store P as sugar P and also utilize P through different pathways under P-rich and -limited conditions. When nitrate was supplied as the N source under P-sufficient conditions, PP_i accounted for about 15% of steady-state Q_P, but no sugar P was detected. Therefore, the same organism stored P in different cell P fractions depending on its N sources.     

Effects of base cation fertilization on the nutrient status,free amino acids and some carbon fractions of the leaves of sugar maple (Acer saccharum Marsh.)

A study was conducted in the Lower Laurentians of southern Quebec to test the hypothesis that base cation fertilization would improve the nutrient status of declining sugar maples (Acer saccharum Marsh.) and alter the partitioning of leaf C and N. Six 40×40 m plots were delineated in an 80 year old stand of sugar maple. Three plots received a mixture of fertilizer and liming materials (500 kg ha^–1 of K₂SO₄, 250 kg ha^–1 of CaCO₃ and 250 kg ha^–1 of CaMg(CO₂)₂) in the spring of 1989. Leaves from mid crown of dominant or co-dominant maples were sampled monthly during the 1990 growing season. Trees were cored in 1992 to measure their response in diameter growth. Fertilization increased diameter growth and foliar K concentration of trees but reduced foliar Ca concentration. Fertilization resulted in lower starch concentrations and higher ratios of soluble sugars to starch in June and September, and in higher free amino acid concentrations but lower ratio of total non-structural carbohydrates to free amino acids in September. Leaf proline concentration was correlated with leaf starch concentration (r=0.39). The results suggest that amelioration of K deficiencies in sugar maple through fertilization with a mixture of base cations can increase tree growth and affect the seasonal dynamics of foliar C and N pools.Abbreviations FAA free amino acids - TNC total non-structural carbohydrates     

Unusual conformation of a 3′-thioformacetal linkage in a DNA duplex

Summary The DNA·DNA duplex ·d(GCGCAAAACGCG) (designated duplex III) containing a 3-thioformacetal (3-TFMA) linkage in the center of the sequence was characterized in detail by two- and three-dimensional homonuclear NMR spectroscopy. The NMR results were analyzed and compared with those of two duplexes of the same sequence: One is an unmodified reference sequence and the other contains a formacetal (OCH₂O) linkage at the central T^T step (designated duplex I and duplex II, respectively). In general, the NMR spectra of duplex III closely resemble those of the analogous duplexes I and II, suggesting an overall B-type structure adopted by the 3-TFMA-modified duplex III. Nonetheless, the detection of several distinct spectral features originating from the protons at the modification site is indicative of a local conformation that is clearly different from the corresponding region in duplexes I and II. The 3-thioformacetal linker, in contrast to the formacetal (FMA) linkage, cannot be accommodated in a conformation usually found in natural nucleic acid duplexes. As a consequence, the 3-TFMA-modified T6 sugar adopts an O4-endo form (an intermediate structure between the usual C2-endo and C3-endo forms). This change is accompanied by a change in the (C4–C3–S3–CH₂) dihedral angle and by subsequent adjustments of other torsion angles along the backbone. Notably, this conformational readjustment at the T6–T7 backbone linkage is localized; its collective result has negligible effect on base-base stacking of the T6 and T7 residues. A close examination of the COSY data in all three duplexes reveals a subtle variation in sugar geometry, with more S-type character adopted by the modified duplexes II and III. The results of this study illustrate that, although the difference between FMA and 3-TFMA linkages is merely in the substitution of the T6(O3) in the former by a sulfur atom in the latter, the stereoelectronic difference in a single atom can induce significant local structural distortion in an otherwise well-structured oligonucleotide duplex.Supplementary material available from the authors: One table containing J₁₂, J₁₂ and J₃₄ of duplexes I, II and III.     

Binding of carbohydrates to solid supports part 2: reaction of sugar hydrazones with isothiocyanate-substituted polystyrene

The binding of sugars to a polymer support as thiosemicarbazones has been investigated as a means of immobilizing glycans. Hydrazones of glucose andN-acetylglucosamine were prepared by reaction with hydrazine hydrate, and successfully reacted with isothiocyanate-substituted polystyrene by incubation at room temperature and neutral pH. The binding was efficient and stable in aqueous buffers over a range of pH conditions. The bound sugars were recovered in moderate yield by treatment of the beads with hydrazine hydrate, benzaldehyde or acetone. Direct binding of reducing sugars to thiosemicarbazide-substituted polystyrene was not successful because of the unfavourable thermodynamics.     

Spittlebug indicators of nitrogen-fixing plants

Abstract.

• 1 Spittlebugs (Homoptera: Cercopoidea) are preferentially associated with nitrogen-fixing angiosperms. Generally, the Aphrophoridae associate with legumes, the Clastopteridae with actinorhizal plants, and the Cercopidae with associative nitrogen-fixing grasses. This is the first reported insect—host association specific to nitrogen-fixing plants.
• 2 It is probable that spittlebugs are attracted to nitrogen-fixing plants because these hosts provide a relatively rich, reliable source of organic nitrogen compounds for xylem-sucking insects.
• 3 Many spittlebugs live on plants that do not fix nitrogen, and ecological, mechanical or chemical factors may bar some spittlebugs from otherwise suitable nitrogen-fixing plants.
• 4 Among nitrogen-fixing hosts, spittlebugs appear to prefer plants that transport fixed nitrogen as amino acids and amides to plants that transport fixed nitrogen as ureides.