Low temperature induction of invertase activity in grapefruit flavedo tissue

Invertase activity increased in the flavedo tissue of ‘Marsh’ grapefruit (Citrus paradisi Macf.) when trees were exposed to cold hardening temperatures and decreased at dehardening temperatures. Invertase activity also increased in the flavedo of detached fruit stored at 5δ. Reducing sugar levels paralleled invertase activity while sucrose levels were inversely related to invertase levels. The mechanism by which low temperatures induce invertase activity in grapefruit flavedo tissue was not determined. However, results indicated that a proteinaceous inhibitor, similar to the one found in potato tubers, is not involved in the regulation of invertase activity in flavedo tissue of grapefruit.     

Girdling affects carbohydrate-related gene expression in leaves,bark and roots of alternate-bearing citrus trees

Effects of girdling on carbohydrate status and carbohydrate-related gene expression in citrus trees were investigated. Alternate-bearing 'Murcott' (a Citrus reticulata hybrid of unknown origin) trees were girdled during autumn (25 Sep. 2001) and examined 10 weeks later. Girdling brought about carbohydrate (soluble sugar and starch) accumulation in leaves and shoot bark above the girdle, in trees during their fruitless, 'off' year. Trees during their heavy fruit load, 'on' year did not accumulate carbohydrates above the girdle due to the high demand for carbohydrates by the developing fruit. Girdling caused a strong decline in soluble sugar and starch concentrations in organs below the girdle (roots), in both 'on' and 'off' trees. Expression of STPH-L and STPH-H (two isoforms of starch phosphorylase), Agps (ADP-glucose pyrophosphorylase, small subunit), AATP (plastidic ADP/ATP transporter), PGM-C (phosphoglucomutase) and CitSuS1 (sucrose synthase), all of which are associated with starch accumulation, was studied. It was found that gene expression is related to starch accumulation in all 'off' tree organs. RNA levels of all the genes examined were high in leaves and bark that accumulated high concentrations of starch, and low in roots with declining starch concentrations. It may be hypothesized that changes in specific sugars signal the up- and down-regulation of genes involved in starch synthesis.     

Frost tolerance and biochemical changes during hardening and dehardening in contrasting white clover populations

Successful winter survival of perennial plants, like white clover, is dependent on proper timing of both hardening and dehardening. The purpose of this study was to investigate the regulation of these processes in two cultivars (AberCrest and AberHerald) and two Norwegian ecotypes (Særheim collected at 58°46′N lat. and Bodø at 67°20′N lat.) of white clover (Trifolium repens L.). For hardening and dehardening, plants were exposed to controlled temperature conditions and frost hardiness of stolons was tested by programmed freezing at the rate of 3°C per hour. In addition, stolons were analysed for starch, soluble sugars and soluble amino acids. Cultivars AberCrest and AberHerald, selected for growth at low temperature and winter hardiness in the United Kingdom, were significantly less hardy than the Norwegian populations. After six weeks of hardening (2 weeks at 6°C and 4 weeks at 0.5°C), estimated LT₅₀ values were ?13.8, ?13.0, ?17.8 and ?20.3°C for AberCrest, AberHerald, Saerheim and Bodø, respectively. The rate of dehardening increased with increasing temperature. At low temperature (6°C), the northern ecotype from Bodø was more resistant to dehardening than AberHerald. However, at 18°C the absolute rate of dehardening (°C day^?1) was twice as high in Bodø as in AberHerald plants. Stolon elongation during dehardening was initiated at lower temperatures in AberHerald than in plants of the Bodø ecotype. The content of total soluble sugars, sucrose and the amino acids proline and arginine were significantly higher in hardy plants of Bodø than in those of AberHerald. Sucrose levels decreased during dehardening and correlations between sucrose content and LT₅₀ during this process were statistically highly significant for both Bodø and AberHerald. The least hardy populations of white clover were characterized by thick stolons, long internodes and large leaves.     

花铃期干旱和渍水对棉铃碳水化合物含量的影响及其与棉铃生物量累积的关系

在池栽条件下,以美棉33B为材料,研究花铃期干旱、渍水7 d和渍水14 d处理对棉铃碳水化合物含量的影响及其与生物量累积的关系.结果表明: 干旱处理对下部果枝棉铃铃壳碳水化合物含量的影响较小,降低了中部铃壳碳水化合物含量;干旱处理上部铃壳和渍水处理铃壳可溶性糖、淀粉含量增加,蔗糖含量先降后增,且随渍水持续期延长变幅增大,蔗糖外运受阻加重.与铃壳相比,花铃期干旱和渍水处理对棉籽碳水化合物含量的影响较小.干旱和渍水7 d处理中部果枝棉铃生物量快速增长起始期提前但历时短,下部和上部棉铃生物量累积最大增长速率降低;渍水14 d处理不同果枝部位棉铃生物量累积最大增长速率均降低.相关分析表明,棉铃生物量及其最大增长速率与铃壳可溶性糖和蔗糖含量关系密切.因此,花铃期干旱和渍水影响棉铃蔗糖外运,改变棉铃生物量累积特性,是棉铃生物量降低的原因.
     

Sucrose-metabolizing enzymes in transport tissues and adjacent sink structures in developing citrus fruit

Juice tissues of citrus lack phloem; therefore, photosynthates enroute to juice sacs exit the vascular system on the surface of each segment. Areas of extensive phloem unloading and transport (vascular bundles + segment epidermis) can thus be separated from those of assimilate storage (juice sacs) and adjacent tissues where both processes occur (peel). Sugar composition, dry weight accumulation, and activities of four sucrose-metabolizing enzymes (soluble and cell-wall-bound acid invertase, alkaline invertase, sucrose synthase, and sucrose phosphate synthase) were measured in these transport and sink tissues of grapefruit (Citrus paradisi Macf.) to determine more clearly whether a given enzyme appeared to be more directly associated with assimilate transport versus deposition or utilization. Results were compared at three developmental stages. Activity of sucrose (per gram fresh weight and per milligram protein) extracted from zones of extensive phloem unloading and transport was significantly greater than from adjacent sink tissues during the stages (II and III) when juice sacs grow most rapidly. In stage II fruit, activity of sucrose synthase also significantly surpassed that of all other sucrose-metabolizing enzymes in extracts from the transport tissues (vascular bundles + segment epidermis). In contrast, sucrose phosphate synthase and alkaline invertase at this stage of growth were the most active enzymes from adjacent, rapidly growing, phloem-free sink tissues (juice sacs). Activity of these two enzymes in extracts from juice sacs was significantly greater than that form the transport tissues (vascular bundles + segment epidermis). Soluble acid invertase was the most active enzyme in extracts from all tissues of very young fruit (stage I), including nonvascular regions, but nearly disappeared prior to the onset of juice sac sugar accumulation. The physiological function of high sucrose synthase activity in the transport tissues during rapid sucrose import remains to be determined.     

Low night temperatures inhibit galactinol synthase gene expression and phloem loading in melon leaves during fruit development

Low night temperatures seriously affect plant growth and fruit quality. To investigate the effect of low night temperatures on the expression of galactinol synthase genes (GOLS) and phloem loading of raffinose family oligosaccharides, particular stachyose and raffinose (RFO represents stachyose and raffinose in this paper) and to gain a better understanding of the relationship between the phloem loading of RFO and fruit development, melon (Cucumis melo L.) plants at the fruit development stage were treated with temperatures of 28/12°C or 28/9°C (day/night) with 28/15°C as the control. Both the CmGOLS1 and CmGOLS2 gene expression and the activity of galactinol synthase were clearly repressed after treatments with 9 and 12°C at night, and the effect of 9°C was more obvious. Furthermore, low night temperatures inhibited photosynthesis and caused the lower amounts of sucrose to supply the RFO synthesis. However, the total soluble sugar, RFO, and sucrose contents were increased in leaves subjected to low night temperatures. It is supposed that low night temperature blocked symplastic phloem loading, which led to the accumulation of RFO in the leaf cells. With increasing content of RFO in the leaves, the expression of GOLS genes was inhibited according to the principle of feedback, and therefore the decreased expression of GOLS limited RFO synthesis and was indirectly harmful to phloem loading, thereby affecting fruit development.     

Effects of Fertilization and Irrigation on the Seasonal Changes of Carbohydrate Reserves in Different Age-Classes of Needle on 20-Year-Old Scots Pine Trees (Pinus silvestris)

The effects of fertilization, irrigation or both on the seasonal changes of starch and soluble carbohydrates (glucose, fructose, myo-inositol, pinitol and sucrose) in needles of 20-year-old Scots pine trees (Pinus silvestris L.) were studied during three consecutive years. The starch content of the mature needles increased during spring and early summer to about 25% of dry weight. Neither fertilization nor irrigation affected the general pattern of starch accumulation during the spring. The starch reserves were mobilized when the shoot started to grow. Starch content decreased more rapidly in needles from fertilized than in those from unfertilized trees. The current needles from the control trees accumulated starch while they were still growing. The current needles of the fertilized trees did so to a lesser extent. The amount of starch was closely correlated to the air temperature and to the growth rate. Large amounts were found at low temperatures and low growth rates. The concentrations of soluble carbohydrates showed the well-known seasonal variation, with the highest value during the winter. The levels of sugars were nearly similar, irrespective of fertilization. An exception was sucrose, which was found in small quantities in needles from fertilized plots. Small amounts of sucrose were also found in growing current needles. The results are discussed in relation to growth limitation by assimilate availability and indicate that the ‘sink demand’ is the limiting factor.     

Sucrose metabolism in grape (Vitis vinifera L.) branches under low temperature during overwintering covered with soil

The effect of low temperature on sugar content and activities of key enzymes related to sucrose metabolism in grape (Vitis vinifera L.) branches during overwintering covered with soil was investigated. We measured the contents of soluble sugar and the activities of sucrose-phosphate synthase (SPS), sucrose synthase (SS), acid invertase (AI) and neutral invertase (NI) of three grape varieties with different freezing tolerance, Beta, Vidal and Merlot, in October, 2011, January, 2012 and March, 2012. The result showed that: total soluble sugar had the significant negative correlation, ?0.988, with temperature during overwintering covered with soil. The content of hexose was about twofold content of sucrose in January, while sucrose increased and the hexose decreased to a very low level in March, the ratios between hexose and sucrose declined to 0.26, 0.15 and 0.18. Sucrose was more important than hexose in protecting grape branches from cold injury under low temperature, but non-freezing. The accumulation of sucrose was mostly due to the elevation of the SPS activity, whereas the increase of hexose was due to the enhanced AI activity. Three grape varieties responded to low temperature positively as reflected by the variations of physiological and biochemical characteristics, such as superoxide dismutase, catalase and proline. Besides, by the principal components analysis and combined with cultivation practices, among twelve characteristics, the sugar metabolism mainly contributed to the difference of the cold resistance. The results indicated that sucrose metabolism regulation played an important role during overwintering covered with soil, and it was the key factor to explain the difference of cold resistance.     

猕猴桃果实采后成熟过程中糖代谢及其调节

20℃下采后猕猴桃果实中淀粉酶活性快速上升于果实软化启动阶段,随着果实进入快速软化阶段,淀粉迅速水解,葡萄糖和果糖快速积累,SPS活性增加,酸性转化酶活性下降,蔗糖积累;至果实软化后期,SPS活性降低,蔗糖含量下降.AsA和低温可抑制淀粉酶活性、己糖积累、SPS活性上升和酸性转化酶活性下降,延缓蔗糖积累,相反,乙烯则可促进淀粉酶活性,加速淀粉降解和己糖积累进而直接或间接增加SPS活性,促使蔗糖积累.采后猕猴桃果实的SPS活性变化中有己糖激活效应和蔗糖反馈抑制效应.AsA、低温和乙烯等对糖代谢的调节主要是通过对SPS活性的影响而实现的.     

Seasonal Changes of the Metabolites in the Leaves, Bark and Xylem Tissues of Olive Tree (Olea europaea. L) II. Carbohydrates

Seasonal changes of starch and soluble carbohydrates in leaves,bark and xylem tissues of olive tree were examined during acomplete annual cycle. Leaf starch and soluble carbohydrateswere detected at high levels during the spring and autumn metabolicallyactive periods. The low level of leaf starch in combinationwith the drastic reduction of soluble carbohydrates and mannitol,defined the summer period of the low metabolic state of thetree. The low leaf starch level in conjunction with the risensoluble carbohydrate levels in leaves in winter were associatedwith cold acclimation processes. The bark and xylem tissueswere performing as starch deposition sites, and differencesin the extent of starch accumulation in these tissues were detectedduring the seasons. The starch fluctuations in bark and xylemwere discussed in relation to the translocation of metabolitesand other physiological processes. Mannitol, the most abundantleaf carbohydrate, was examined in relation to the reducingsugars exported to the bark. The bark mannitol was examinedin conjunction with the sucrose, glucose and starch levels inthe maturing bark tissues and was correlated to the low wintertemperatures. During the winter there was a drastic reductionof mannitol circulation from the bark to xylem. Olive tree, Olea europaea, L, carbohydrates     

Sucrose accumulation in developing peach fruit

Uptake of ¹⁴C-sugars and activities of sucrose metabolizing enzymes were determined in order to study the mechanism(s) of sucrose accumulation in developing peach fruit. Mesocarp of young peach fruit contained glucose and fructose but little sucrose. Starting 88 days after anthesis (DAA) the sucrose concentration increased greatly. The mechanism of sucrose accumulation was studied by measuring ¹⁴C-sucrose and ¹⁴C-glucose uptake rates at three different stages of fruit development, and by assaying weekly the activity of enzymes involved in the hydrolysis and/or synthesis of the soluble sugars. Uptake of 0.5–100 m M ¹⁴C-sucrose and ¹⁴C-glucose by mesocarp tissue slices showed a complex pattern at the first stage of fruit development (62 DAA). During the subsequent growth stages the pattern of sugar uptake changed and was approximately monophasic at the third stage of fruit development.
At 10 m M , glucose was taken up more rapidly than sucrose at the first and second stage of fruit development. Uptake was partially inhibited by the uncoupler carbonylcyanide m -chlorophenylhydrazone (CCCP) at 25 μ M. These results, together with the presence of a putative extracellular invertase, suggest an apoplastic route for sucrose uptake which is dependent, at least in part, on energy supply.
Activities of sucrose hydrolyzing enzymes (insoluble acid invertase, soluble acid invertase, neutral invertase, sucrose synthase) were high in young fruits and declined sharply with fruit development concomitantly with accumulation of sucrose. The storage of the sugar was not accompanied by a rise in synthetic activities (sucrose synthase, sucrose phosphate synthase), suggesting that sucrose could, at least in part enter the carbohydrate pool directly.     

Carbohydrate Metabolism and Frost Hardiness in Pine and Spruce Seedlings Grown at Different Photoperiods and Thermoperiods

Large changes occur in carbohydrate contents of pine (Pinus silvestris L.) and spruce (Picea abies (L.) Karst.) seedlings cold-hardened by photoperiod or by combined photo- and thermo-period. The largest change is in sucrose content, which is almost doubled after six weeks short-day (6/18 h) treatment; and more than doubled (spruce) or more than tripled (pine), when also temperature is lowered (10/5°C). Development of frost hardiness is strongly correlated with the change in carbohydrate contents. At dehardening, the carbohydrate content decreases rapidly, especially in pine, and the raffinose formed during the rest period disappears within 2–4 weeks. Frost hardiness decreases in parallel. The content of soluble carbohydrates may thus play a role in frost hardiness, although it is not the only factor. Bud formation at cold acclimation is not directly correlated with the changes in carbohydrate content and hardiness.     

Carbohydrate content and glycosidase activities following cold hardening in two grass species

The freezing resistance of the grass species Phleum pratense L. (timothy) and Phalaris arundinaces L. increases significantly after cold hardening. The content and composition of soluble carbohydrates were determined in the plants after short day treatment, cold hardening and dehardening. The amounts of mono-, di- and trisaccharides were reduced during the short day treatment, increased during cold hardening and decreased again during dehardening. The total amounts of soluble carbohydrates (mono-, di-, tri- and polysaccharides) were the same in hardened and dehardened plants, indicating that during hardening soluble polysaccharides (fructose polymers, fructans) were converted to mono- and oligosaccharides. Sucrose increased most after hardening conditions and, in P. arundinacea , a significant increase in 1-F-fructosylsucrose (isokestose) was also observed.
Invertase (β-fructofuranosidase. EC 3.2.1.26) activity increased following cold hardening and decreased following dehardening, while the α-galactosidase (EC 3.2.1.22) activity seemed to increase after dehardening. The glycosidases are probably involved in the mobilisation of polysaccharides during cold hardening.     

The importance of hardening and winter temperature for growth in mountain birch populations

Seedlings of five mountain birch populations (Betula pubescens Ehrh. ssp. czerepanovii) from Fennoscandia and Iceland were raised and grown at natural daylengths at Tromsø, Norway (69°N) and different temperatures during late summer and fall season, followed by winter temperature treatment at ambient and +4 °C above ambient temperatures at Bergen, Norway (60°N). The experiment took place during two seasons (2000/01 and 2001/02). The following summer shoot and biomass growth were reduced as a result of winter warming and subsequent premature dehardening in early flushing provenances and treatments. Biomass increased in plants grown at low hardening temperature when compared with high temperature treatment. As a conclusion, increased winter temperatures would tend to increase the risk of spring frost damage and reduce growth in birch seedlings, because the differences between the frost hardening and ambient temperatures are decreasing, and because the time from budbreak to dehardening is shortened. The results are discussed in relation to simultaneous experiments with frost hardiness in the same populations and treatments.     

The effect of abiotic stresses on carbohydrate status of olive shoots (Olea europaea L.) under in vitro conditions

Olive plants produce both sucrose and mannitol as major photosynthetic products. Contrary to previously studied celery [Vítová et al., Mannitol utilisation by celery (Apium graveolens) plants grown under different conditions in vitro. Plant Sci 2002; 163: 907-16], in vitro these carbohydrates were found to be able to sustain growth of olive shoots roughly to the same extent at all tested concentrations (1-9% w/v). We studied the involvement of the particular components of the endogenous carbohydrate spectrum in response to different abiotic stresses (osmotic stress, salinity, low temperature) in vitro. Salinity (100mM NaCl) caused a decrease of total soluble carbohydrates, while an increase was observed during low-temperature treatment (0 and 4 degrees C). Mannitol accumulated primarily under salinity (up to 40% of total soluble carbohydrates compared to 10-20% in controls). Only a small (two-fold) increase of proline content in salinity stressed plants indicates proline does not play a significant role in olive stress response. Low temperature led to an increase of the raffinose family oligosaccharides (RFO) proportion in total carbohydrates. We conclude that olive plants exploit the high diversity of the carbohydrate spectrum in specific response to different stresses.     

Kernel Abortion in Maize : II. Distribution of C among Kernel Carbohydrates

This study was designed to compare the uptake and distribution of ¹⁴C among fructose, glucose, sucrose, and starch in the cob, pedicel, and endosperm tissues of maize (Zea mays L.) kernels induced to abort by high temperature with those that develop normally. Kernels cultured in vitro at 30 and 35°C were transferred to [¹⁴C]sucrose media 10 days after pollination. Kernels cultured at 35°C aborted prior to the onset of linear dry matter accumulation. Significant uptake into the cob, pedicel, and endosperm of radioactivity associated with the soluble and starch fractions of the tissues was detected after 24 hours in culture on labeled media. After 8 days in culture on [¹⁴C]sucrose media, 48 and 40% of the radioactivity associated with the cob carbohydrates was found in the reducing sugars at 30 and 35°C, respectively. This indicates that some of the sucrose taken up by the cob tissue was cleaved to fructose and glucose in the cob. Of the total carbohydrates, a higher percentage of label was associated with sucrose and a lower percentage with fructose and glucose in pedicel tissue of kernels cultured at 35°C compared to kernels cultured at 30°C. These results indicate that sucrose was not cleaved to fructose and glucose as rapidly during the unloading process in the pedicel of kernels induced to abort by high temperature. Kernels cultured at 35°C had a much lower proportion of label associated with endosperm starch (29%) than did kernels cultured at 30°C (89%). Kernels cultured at 35°C had a correspondingly higher proportion of ¹⁴C in endosperm fructose, glucose, and sucrose. These results indicate that starch synthesis in the endosperm is strongly inhibited in kernels induced to abort by high temperature even though there is an adequate supply of sugar.     

Mobilizable carbon reserves in young peach trees as evidenced by trunk girdling experiments

The seasonal patterns in concentrations of both soluble (NSC-S)and insoluble (NSC-I) non-structural carbohydrates, in 3-year-oldpeach trees (Prunus persica L. Batsch) grown in sand cultureare described. The ability of trees to mobilize their carbohydratereserves in response to scion-trunk girdling, which preventsphotosynthate transport toward the roots, was tested at fourphenological stages. Girdling induces a NSC-I depletion in rootsand rootstock-trunk bark and a NSC-I accumulation in leavesand shoots. On the contrary, the NSC-S concentrations of theorgans located both above and below girdling were not significantlyaffected by the treatment. Consequently, when phloem transportbreaks down, trees, whatever their growing stage, mobilize carbohydratereserves below the girdle to maintain the soluble sugar contentsat the same level as in control trees. Key words: Girdling, non-structural carbohydrates, Prunus persica L., carbon reserves, seasonal patterns     

Translocation of 14C, carbohydrate content and activity of the enzymes of sucrose metabolism in rose petals temperatures

Both export of ¹⁴C from the source leaves of roses (Rosa × hybrida cv. Golden Times) and import of ¹⁴C to the petals were reduced by plant exposure to low night temperature. However, the import was affected to a greater extent than the export. During all stages of flower bud development the concentration of reducing sugars in petals of roses grown at reduced night temperature was lower than in petals of plants grown at higher night temperature. There was no significant difference in starch content in response to the night temperature, and the content of starch decreased toward complete flower bud opening. The concentration of sucrose in flowers at the low night temperature remained low during all stages of flower bud development, while at the high night temperature the concentration of sucrose increased during flower bud development, reaching a peak at the stage when petals start to unfold. At both temperatures the concentration of sucrose declined at complete flower opening. The activity of sucrose synthase (EC 2.4.1.14) was inhibited by low temperature in young rose shoots more than in the petals, while the activity of acid invertase (EC 3.2.1.26) was affected similarly in both tissues by the temperature treatments.     

Carbohydrate availability affects growth and metabolism in peach fruit

Along with sucrose, sorbitol represents the main photosynthetic product and form of translocated carbon in peach. This study aimed at determining whether peach fruit carbohydrate metabolism is affected by changes in source–sink balance , and specifically whether sorbitol or sucrose availability regulates fruit enzyme activities and growth. In various trials, different levels of assimilate availability to growing fruits were induced in vivo by varying crop load of entire trees, leaf : fruit ratio (L:F) of fruiting shoots, or by interrupting the phloem stream (girdling) to individual fruits. In vitro, fruit tissue was incubated in presence/absence of sorbitol and sucrose. Relative growth rate (RGR), enzyme activities and carbohydrates were measured at different fruit growth stages of various peach cultivars in different years. At stage III, high crop load induced higher acid invertase (AI, EC 3.2.1.26) activities and hexose : sucrose ratios. Both sorbitol and sucrose contents were proportional to L:F, while sorbitol dehydrogenase (SDH, EC 1.1.1.14) activity was the only enzyme activity directly related to L:F in both fruit growth stages. Girdling reduced fruit RGR and all major carbohydrates after 4 days and SDH activity already after 48 h, but it did not affect sucrose synthase (SS, EC 2.4.1.13), AI and neutral invertase (NI, EC 3.2.1.27). Fruit incubation in sorbitol for 24 h induced higher SDH activities than in buffer alone. In general, assimilate availability affected both sorbitol and sucrose metabolism in peach fruit, and sorbitol may function as a signal for modulating SDH activity. Under highly competitive conditions, AI activity may be enhanced by assimilate depletion, providing a mechanism to increase fruit sink strength by increasing hexose concentrations.