Occurrence of sucrose and sucrose metabolizing enzymes in achlorophyllous algae

The presence of sucrose and the enzymes related to sucrose metabolism, i.e. sucrose synthase (SS) (UDP-glucose: D-fructose-2-glucosyl transferase, EC 2.4.1.13), sucrose phosphate synthase (SPS) (UDP-glucose: D-fructose-6-phosphate-2-glucosyl transferase, EC 2.4.1.14) and invertase (β-D-fructofuranoside fructohydrolase, EC 3.2.1.26) was demonstrated in Prototheca zopfii, a colorless alga. The levels of enzyme activities were lower than those obtained in Chlorella vulgaris, which is generally considered the photosynthetic counterpart of P. zopfii. Whem enzyme activities were measured in bleached cells of C. vulgaris, the levels were of the same order than those found in P. zopfii. These results would indicate that the sucrose metabolizing enzymes are not related to the algae ability to carry on photosynthesis.     

In vitro and in vivo inhibition of sucrose synthesis by sucrose

The inhibitory effects of sucrose on rates of sucrose synthesis by sucrose phosphate synthase (SPS) from the maize scutellum and on net rates of sucrose production in maize scutellum slices from added glucose or fructose were studied. Scutellum extracts were prepared by freezing and thawing scutellum slices in buffer. The extracts contained SPS and sucrose phosphate phosphatase, but were free of sucrose synthase. SPS activity was calculated from measurement of UDP formation in the presence of UDPG, fructose-6-P and sucrose. The ranges of metabolite concentrations used were those estimated to be in scutellum slices after incubation in water or fructose for periods up to 5 hr. UDPG and fructose-6-P also were added at concentrations that saturated SPS. At saturating substrate levels, sucrose inhibition of SPS was less than that when tissue levels of substrates were used. With tissue levels of substrates and sucrose concentrations up to ca 166 mM, sucrose inhibitions of sucrose synthesis in vitro by SPS were similar to those observed in vivo. However, as the sucrose concentration rose above 166 mM, SPS activity was not inhibited further, whereas there was a further sharp decline in sucrose production by the slices. It is concluded that sucrose synthesis in vivo is controlled by sucrose inhibition of SPS over a considerable range of internal sucrose concentrations.     

Increase of sucrose synthase activity in wheat plants after a chilling shock

Plants of wheat (Triticum aestivum) were grown at 23°C. After 17 days they were suddenly transferred to 4°C under the same light conditions. The change in temperature produced an increase in the level of sucrose and fructans. Following the chilling shock, enzymes related to sucrose metabolism were measured. The activities of fructose 1,6-biphosphatase, UDPGlc pyrophosphorylase, sucrose phosphate synthase (SPS), UDPase and invertase were not modified even after 8 days at 4°C. On the contrary, the activity of sucrose synthase (SS) (UDP-glucose: D-fructose-2-glucosyl transferase, EC 2.4.1.13) rose continuously, immediately after the chilling shock.     

Conservation and reservation of non-vascular plants in Tasmania,with special reference to lichens

Conservation management of the Tasmanian flora is now focusing on non-vascular plants. Major problems include the low level of information on the composition of the flora and the low number of competent specialists available to deal with the plants. Collation of information from literature and from collections in herbaria is required to establish exactly which data are available and their reliability. An environmental domain analysis covering all ecosystems would indicate which environments were under-represented or absent from current reserves and where needs for conservation lie. Within practical time-frames, this process is probably the best method of capturing unknown components of the flora whilst also catering for widespread species and those closely associated with particular environments. It also incorporates regional variability. Minor habitats, which are often floristically rich, and very rare species are best dealt with on an individual basis. Basic research into taxonomy and ecology is paramount. Reservation and conservation management must be based on well-established and maintained databases which are in turn based on a coherent taxonomy and sound biogoographical information. It is only by pursuing an active research programme that the necessary accurate information can be obtained and the success of the management procedures can be gauged.     

Physiological correlates of the morphology of early vascular plants

RAVEN, J. A., 1984. Physiological correlates of the morphology of early vascular plants. The early evolution of vascular land plants is considered in relation to the physiological problems of life on land. The universal characteristics of vascular plants (xylem, cuticle, stomata, intercellular air spaces, long-distance symplastic transport and alternation of generations) are discussed in terms of the essential properties of a homoiohydric phototroph. Likely precursors of vascular plants, and the physico-chemical and biotic environment in which they occurred, are outlined prior to a discussion of the selective forces acting on the evolution of vascular plants in the Upper Silurian and Lower Devonian. Emphasis is placed on biochemical and structural 'pre-adaptations' which may have occurred in the precursors of vascular plants and on which natural selection could have acted with lignified xylem, stomata, etc., as the end-products. Guiding principles in the analysis include the physiology of extant plants, physico-chemical constraints, and compatibility with the fossil record. It is concluded that the likely sequence of acquisition of vascular plant characteristics was: heteromorphic alternation of generations with an erect sporophyte; cuticularization of sporophyte; evolution of xylem; occurrence of intercellular air spaces with pores in the epidermis; stomatal activity of the pores. Endodermis and phloem-type long-distance transport probably originated around stages (3)-(5).     

Starch-producing Polytoma uvella lacks sucrose and sucrose-metabolizing enzymes

The absence of sucrose, sucrose synthetase and sucrose phosphate synthetase has been demonstrated by chromatographic, enzymatic and radioisotopic metho     

The distribution of flavonoids in chloroplasts of twenty five species of vascular plants

A survey was made of the major flavonoids in whole leaf extracts and in chloroplast preparations from twenty five species of vascular plants including Anthophyta (20), Coniferophyta (1), Ginkophyta (1), Pterophyta (2), and Arthrophyta (1). The chloroplasts variously contained derivatives of flavones, C-glycosylflavones, flavonols, flavanones, isoflavones, 3-deoxyanthocyanidins, and anthocyanins. Twenty three species contain one or more flavonoids in isolated chloroplast, usually in a pattern quite similar to that found in whole-leaf extracts but occasionally showing enrichment of one or more flavonoids in the chloroplasts. Flavonoids are apparently absent from chloroplasts of Phaseolus aureus and Morus alba although whole-leaf extracts of these species are rich in quercetin derivatives.     

Fragmentary non-vascular plant microfossils from the late Silurian of Wales

A wide variety of cuticles and tubular elements is described from a late Silurian (Ludlow Series) locality in Wales which has already yielded a macroflora containing Cooksonia Lang, Steganotheca Edwards and vascularized axes. These microfossils are compared with Lang's Downtonian .Nematothallus complex and Silurian assemblages of similar composition from north America. It is concluded that the majority of these microfossils derive from non-vascular plants of uncertain affinity which lived on land.     

Distribution in excised Lycopersicum esculentum roots of the principal enzymes involved in sucrose metabolism

Sucrose synthetase and sucrose phosphate synthetase could not be detected in 7-day-old excised tomato roots grown in sucrose. These roots, however, possessed a highly active acid invertase and a neutral invertase of low activity. The distribution of the cell wall-located acid invertase along the root axis appeared to be related to growth. This was not the case for the soluble enzyme. The possible functions of these two enzymes are discussed.     

Measurement of enzymes related to sucrose metabolism in permeabilized Chlorella vulgaris cells

Sucrose phosphate synthase (UDP-glucose: D-fructose-6-phosphate-2-glucosyl transferase, EC 2.4.1.14), sucrose synthase (UDP-glucose: D-fructose-2-glucosyl transferase, EC 2.4.1.13) and invertase (β-D-fructofuranoside fructohydrolase, EC 3.2.1.26) were measured in toluene permeabilized cells of Chlorella vulgaris Beijerinck. All three activities were detected at all stages of the growth curve; sucrose synthase and sucrose phosphate synthase showed a zone of maximum activity, while invertase increased with time of growth. Sucrose phosphate synthase and sucrose synthase (sucrose synthesis direction) were stimulated by divalent cations and inhibited by UDP. This inhibition could be reversed by Mg²⁺ or Mn²⁺. Sucrose phosphate synthase activity was inhibited by inorganic phosphate and was enhanced by glucose-6-phosphate, but was insensitive to sucrose. Arbutine decreased sucrose synthase activity in both directions. Sucrose cleavage was inhibited by divalent cations and by pyrophosphate. The effects on the enzyme activities of the presence of 2,4-dichlorophenoxyacetic acid (2,4-D), gibberellic acid, abscisic acid and kinetin in the growth medium were investigated. Sucrose synthase activity was practically unaffected by all plant hormones tested, except for the presence of kinetin which stimulated the activity. Sucrose phosphate synthase activity was increased by both kinetin and abscisic acid. The effect of the latter was partially reversed by the presence of gibberellic acid. 2,4-D and kinetin were potent stimulators of invertase activity.     

Sucrose phosphate synthase and other sucrose metabolizing enzymes in fruits of various species

Recent reports have suggested that sucrose phosphate synthase (EC 2.4.1.14), a key enzyme in sucrose biosynthesis in photosynthetic “source” tissues, may also be important in some sucrose accumulating “sink” tissues. These experiments were conducted to determine if sucrose phosphate synthase is involved in sucrose accumulation in fruits of several species. Peach (Prunus persica NCT 516) and strawberry (Fragaria x ananassa cv. Chandler) fruits were harvested directly from the plant at various stages of fruit development. Kiwi (Actinidia chinensis), papaya (Carica papaya), pineapple (Ananas comosus) and mango (Mangifera indica) were sampled in postharvest storage over a period of several days. Carbohydrate concentrations and activities of sucrose phosphate synthase, sucrose synthase (EC 2.4.1.13), and acid and neutral invertases (EC 3.2.1.26) were measured. All fruits contained significant activities of sucrose phosphate synthase. Moreover, in fruits from all species except pineapple and papaya, there was an increase in sucrose phosphate synthase activity associated with the accumulation of sucrose in situ. The increase in sucrose concentration in peaches was also associated with an increase in sucrose synthase activity and, in strawberries, with increased activity of both sucrose synthase and neutral invertase. The hexose pools in all fruits were comprised of equimolar concentrations of fructose and glucose, except in the mango. In mango, the fructose to glucose ratio increased from 2 to 41 during ripening as sucrose concentration more than doubled. The results of this study indicate that activities of the sucrose metabolizing enzymes, including sucrose phosphate synthase, within the fruit itself, are important in determining the soluble sugar content of fruits of many species. This appears to be true for fruits which sweeten from a starch reserve and in fruits from sorbitol translocating species, raffinose saccharide translocating species, and sucrose translocating species.     

Differences in sucrose metabolism relative to accumulation of bird-deterrent sucrose levels in fruits of wild and domestic Vaccinium species

We examined variability in sucrose levels and metabolism in ripe fruits of wild and domestic Vaccinium species and in developing fruits of cultivated blueberry (V. ashei and V. corymbosum). The objective was to determine if sufficient variability for fruit sucrose accumulation was present in existing populations to warrant attempts to breed for high-sucrose fruit, which potentially would be less subject to bird predation. Threefold differences in fruit sucrose concentration were found among Vaccinium species, ranging from 19 to 24 mg (g fresh weight)^?1 in V. stamineum and V. arboreum to approximately 7 mg (g fresh weight)^?1 in cultivated blueberry (V. ashei and V. corymbosum) and V. darrowi. Hexose levels were similar among species, ranging from 90 to 110 mg (g fresh weight)^–1, and glucose and fructose were present in equal amounts. Soluble acid invertase (EC 3.2.1.26) activity was negatively correlated with fruit sucrose concentration. There was no apparent correlation between fruit sugar concentration and either sucrose synthase (EC 2.4.1.13) or sucrose phosphate synthase (EC 2.4.1.14) activities, both of which were low for all species studied. Developmental increases in fruit sugar levels of cultivated blueberry followed a pattern similar to that observed in fruit fresh weight accumulation. Hexose concentrations ranged from 6 to 30 mg (g fresh weight)^?1 during the first 60 days after anthesis. Between 60 days and fruit ripening (80 days), hexose levels rose from 30 to 80 mg (g fresh weight)^?1. Sucrose was not detected in fruits until ripening, when low levels were found. Insoluble acid invertase activity was relatively high early in fruit development, decreasing as soluble acid invertase activity increased. Between 60 days and fruit ripening, soluble acid invertase activity increased from 3 to 55 μmol (g fresh weight)^–1 h^–1. Both sucrose synthase and sucrose phosphate synthase activities were low throughout development. The extent of sucrose accumulation in fruits and the degree of variability for this trait among Vaccinium species support the feasibility of developing high sucrose fruits, which would be a potentially valuable addition to current strategies of minimizing crop losses to birds.     

Interspecies differences in the preference of ammonium and nitrate in vascular plants

Three solution experiments were performed to test the importance of NH ₄ ⁺ versus NO ₃ ^- +NH ₄ ⁺ to growth of 23 wild-forest and open-land species, using field-relevant soil solution concentrations at pH 4.5. At N concentrations of 1–200 M growth increased with increasing N supply in Carex pilulifera, Deschampsia flexuosa, Elymus caninus and Bromus benekenii. Geum urbanum was the most N demanding species and had little growth below 200 M. The preference for NH ₄ ⁺ or NO ₃ ^- +NH ₄ ⁺ was tested also at pH 4.0; no antagonism was found between NH ₄ ⁺ and H⁺, as indicated by similar relative growth in both of the N treatments at both pH levels. Growth in solution with NH ₄ ⁺ relative to NO ₃ ^- +NH ₄ ⁺ , 200 M, was negatively related to the mean pH of the field occurrence of the species tested; acid-tolerant species grew equally well with only NH ₄ ⁺ as with NO ₃ ^- +NH ₄ ⁺ (Oxalis acetosella, Carex pilulifera, Festuca gigantea, Poa nemoralis, Deschampsia flexuosa, Stellaria holostea, Rumex acetosella), while species of less acid soils were favoured by NO ₃ ^- +NH ₄ ⁺ (Urtica dioica, Ficaria verna, Melandrium rubrum, Aegopodium podagraria, Geum urbanum, Bromus benekenii, Sanguisorba minor, Melica ciliata, Silene rupestris, Viscaria vulgaris, Plantago lanceolata). Intermediate species were Convallaria majalis, Elymus caninus, Hordelymus europaeus and Milium effusum. No antagonism between NH ₄ ⁺ and Ca²⁺, Mg²⁺ and K⁺ was indicated by the total uptake of the elements during the experiment.     

菊芋蔗糖代谢相关产物与关键酶基因对高温的响应

蔗糖是一类重要的碳水化合物,其代谢与植物生长发育及抵抗胁迫等有密切的关系。蔗糖合成酶(SUS)、蔗糖磷酸合成酶(SPS)与蔗糖转化酶(INV)是参与蔗糖代谢的三类关键酶。本研究依据转录组测序数据,从能源植物菊芋中鉴定了2个SUS、2个SPS和7个INV基因(GenBank No:MK386943-53)。生物信息学分析表明,菊芋SUS、SPS和INV的氨基酸序列与其他物种具有较高的相似性,均属于亲水性蛋白。在25、30°C处理10、15、20 d的菊芋幼苗叶片中,这三种基因家族成员呈现不同的表达模式;除可溶性总糖含量减少外,果糖、蔗糖、蔗果三糖等含量没有发生明显变化。表明高温下幼苗蔗糖代谢关键酶基因发生了响应,蔗糖代谢处于平衡状态,显示了菊芋对高温的良好耐受性。     

Regulation of sucrose storage by amino acid arginine in sugarcane cell suspension cultures

Sugarcane cell cultures were obtained from callus formed on explants derived from young expanding leaves of two early maturing sugarcane varieties viz “CoJ83” and “CoJ86”. The cell cultures were varied with different arginine concentrations in the culture medium. For each cultivar, sucrose content with 20 μM arginine in the culture medium decreased from 3 to 5 days and then increased to 10 days after subculturing. Higher concentration of arginine in the culture medium (60 μM) decreased the sucrose content at different days after subculturing and thus significantly stimulated sucrose mobilization. The activity of sucrose synthase and sucrose phosphate synthase reached maximum while the activity of acid and neutral invertase was minimal in the culture medium with 20 μM arginine. Thus arginine at low concentration (20 μM) enables the cells to accumulate the higher level of sucrose. The optimum level of amino acids can be utilized to regulate the in vivo activity of sucrose synthase, sucrose phosphate synthase and invertase to achieve maximum sucrose accumulation in sugarcane storage tissue.     

Effect of sucrose accumulation on zein synthesis in maize starch-deficient mutants

Starch-deficient maize (Zea mays) mutants, brittle-2 (bt2), brittle-1 (bt), and shrunken-2 (sh2), which accumulated large quantities of sucrose, had less than normal amounts of zein (the major storage protein) in the endosperm. Reduction of zein synthesis in the starch-deficient mutants was negatively correlated with the accumulation of sucrose and low osmotic potential in the developing endosperms. When radioactive amino acids were injected into the shank below ears that segregated for the starch-deficient mutant and normal kernels at 28 days post-pollination, mutant kernels absorbed only ca 22–36% of the labelled amino acids found in their normal controls. Thus, a low osmotic potential in the mutant endosperm may favour water movement but reduce solute movement. The inability of amino acids to move into the mutant endosperms, therefore, in part explains the reduction of zein accumulation in starch-deficient mutant endosperms.