Soluble Invertase Activity Research Articles

Residue Analysis and the Effect of Preharvest Forchlorfenuron (CPPU) Application on On-Tree Quality Maintenance of Ripe Fruit in "Feizixiao" Litchi (Litchi chinensis Sonn.).

Litchi is a highly perishable fruit. Ripe litchi fruit loses quality quickly as they hang on tree, giving a very short hanging life and thus harvest period. This study attempted to explore the roles of cytokinin in regulating fruit ripening and senescence of litchi and examine the possibility of applying cytokinin in “on-tree storage” of the fruit. Exogenous cytokinin, forchlorfenuron (CPPU), was applied at 20 mg L−1 7 weeks after full bloom on litchi (Litchi chinensis cv. Feizixiao) fruit clusters. Color parameters, chlorophylls, anthocyanins, fruit and fruit part weights, total soluble solutes (TSSs), soluble sugars, organic acids, non-anthocyanin flavonoids, ethanol, and also CPPU residue in fruit were traced. CPPU residue was higher but decreased faster in the pericarp than in the aril, where it maintained < 10 μg kg−1. CPPU had no significant effect on fruit weight but tended to increase pericarp weight. The treatment suppressed chlorophyll loss and anthocyanin accumulation in the pericarp, increased non-anthocyanin flavonoids in the aril, but had no significant effects on non-anthocyanin flavonoids in the pericarp and total sugar and organic acids in the aril. As the commercially ripe fruit hanged on tree, TSSs, total sugar, and sucrose decreased with ethanol and acetic acid accumulation in the aril. CPPU significantly suppressed the loss of sucrose and total sugar and the accumulation of ethanol and acetic acid in the aril and inhibited malondialdehyde accumulation in the pericarp of the overripe fruit. Soluble invertase, alcohol dehydrogenase, and pyruvate decarboxylase (PDC) activity and gene expression in the aril were downregulated by CPPU. The results suggest that cytokinin partially suppresses the ripening process in litchi and is effective to slow quality loss in the overripe fruit on tree.

Flowering-mediated root-fungus symbiosis loss is related to jasmonate-dependent root soluble sugar deprivation.

The role of flowering in root-fungal symbiosis is not well understood. Because flowering and fungal symbionts are supported by carbohydrates, we hypothesized that flowering modulates root-beneficial fungal associations through alterations in carbohydrate metabolism and transport. We monitored fungal colonization and soluble sugars in the roots of Arabidopsis thaliana following inoculation with a mutualistic fungus Phomopsis liquidambari across different plant developmental stages. Jasmonate signalling of wild-type plants, sugar transport, and root invertase of wild-type and jasmonate-insensitive plants were exploited to assess whether and how jasmonate-dependent sugar dynamics are involved in flowering-mediated fungal colonization alterations. We found that flowering restricts root-fungal colonization and activates root jasmonate signalling upon fungal inoculation. Jasmonates reduce the constitutive and fungus-induced accumulation of root glucose and fructose at the flowering stage. Further experiments with sugar transport and metabolism mutant lines revealed that root glucose and fructose positively influence fungal colonization. Diurnal, jasmonate-dependent inhibitions of sugar transport and soluble invertase activity were identified as likely mechanisms for flowering-mediated root sugar depletion upon fungal inoculation. Collectively, our results reveal that flowering drives root-fungus cooperation loss, which is related to jasmonate-dependent root soluble sugar depletion. Limiting the spread of root-fungal colonization may direct more resources to flower development.

Non-Structural Carbohydrate Metabolism, Growth, and Productivity of Maize by Increasing Plant Density

Increasing plant density seems to improve the productivity of maize crops, and the understanding of how the metabolism of non-structural carbohydrates is affected in plants under high crop density is critical. Thus, with the objective of further clarifying this issue, maize plants were subjected to densities from 30,000 to 90,000 plants ha−1, and the plant growth, soluble sugars and starch contents, invertase and sucrose synthase activities, and plant production were evaluated. We found that the stalk is more sensitive to the increasing plant density than leaves and kernels. The dry weight of the stalk and leaves per single plant decreased more drastically from low to intermediate plant densities, while grain production was reduced linearly in all plant density ranges, leading to higher values of harvest index in intermediate plant densities. The sucrose concentration did not change in leaves, stalk, or kernels of plants subjected to increasing plant densities at the R4 stage. Also, the specific activity of soluble invertase, bound invertase, and sucrose synthase did not change in leaf, stalk, or kernels of plants subjected to increased plant density. The productivity was increased with the increase in plant density, using narrow row (0.45 m) spacing.

Plant vascular architecture determines the pattern of herbivore-induced systemic responses in Arabidopsis thaliana.

The induction of systemic responses in plants is associated with the connectivity between damaged and undamaged leaves, as determined by vascular architecture. Despite the widespread appreciation for studying variation in induced plant defense, few studies have characterized spatial variability of induction in the model species, Arabidopsis thaliana. Here we show that plant architecture generates fine scale spatial variation in the systemic induction of invertase and phenolic compounds. We examined whether the arrangement of leaves along the stem (phyllotaxy) produces predictable spatial patterns of cell-wall bound and soluble invertase activities, and downstream phenolic accumulation following feeding by the dietary specialist herbivore, Pieris rapae and the generalist, Spodoptera exigua. Responses were measured in leaves within and outside of the damaged orthostichy (leaves sharing direct vascular connections), and compared to those from plants where source-sink transport was disrupted by source leaf removal and by an insertional mutation in a sucrose transporter gene (suc2-1). Following herbivore damage to a single, middle-aged leaf, induction of cell-wall and soluble invertase was most pronounced in young and old leaves within the damaged orthostichy. The pattern of accumulation of phenolics was also predicted by these vascular connections and was, in part, dependent on the presence of source leaves and intact sucrose transporter function. Induction also occurred in leaves outside of the damaged orthostichy, suggesting that mechanisms may exist to overcome vascular constraints in this system. Our results demonstrate that systemic responses vary widely according to orthostichy, are often herbivore-specific, and partially rely on transport between source and sink leaves. We also provide evidence that patterns of induction are more integrated in A. thaliana than previously described. This work highlights the importance of plant vascular architecture in determining patterns of systemic induction, which is likely to be ecologically important to insect herbivores and plant pathogens.

A novel bud sport from the ‘Benitaka’ table grape cultivar (Vitis vinifera L.) improves sugar and anthocyanin accumulation at the berry ripening stage

Background‘Early-ripening Benitaka’ (Vitis vinifera), a bud sport of ‘Benitaka’ was found in 2008, which ripens earlier than its parental line. Differences in sugar and anthocyanin content and the relevant sucrose and anthocyanin metabolic enzymes for the two cultivars were investigated during fruit ripening. ResultThe mutation made berry size, reducing sugar of pulp and anthocyanin of pericarp increases during fruit ripening. In both ‘Benitaka’ and its mutant, the cell wall invertase activity was similar at the onset of ripening, but it showed markedly higher activity in the mutant at the late stage, which were correspondingly associated with the higher transcript level of cell wall invertase. For soluble invertase, the activity showed no difference between mutant and ‘Benitaka’ during the early stage of berry development, and dropped to the lowest level around the onset of ripening. Interestingly, the mutant had a greater reduction than its parental cultivars in the activity of soluble invertase. In addition, the expression level of the UDP-glucose: flavonoid 3-O-glucosyltransferase (UFGT) gene after veraison was higher in the berry pericarp of the mutant compared with that of the ‘Benitaka’, in agreement with the higher anthocyanin content of the former. ConclusionThe mutation in ‘early-ripening Benitaka’ affected sugar and anthocyanin metabolism, which might be related with accumulation of sugar and anthocyanin and other early-ripening phenotypes.

Activities of sucrose-metabolizing enzymes in grains of two wheat (Triticum aestivum L.) cultivars subjected to water stress during grain filling

Developmental changes in the starch and soluble sugars content of grains and the activities of sucrose metabolism enzymes in drought-tolerant (Triticum aestivum L. cv. Zagros) and drought-sensitive with high yielding potential under favorable conditions (cv. Marvdasht) wheat genotypes were investigated under controlled water deficit during grain filling. The two cultivars were grown in pots under well-watered (WW) and water-stressed (WS) starting from anthesis until maturity. Water stress caused a marked reduction in glucose, fructose and sucrose content of grains of sensitive cultivar. These changes were paralleled by sharp decline in the activities of cell wall invertase and soluble invertase in the grains of sensitive cultivar. Whereas in tolerant cultivar as the surge in invertase activity faded; in grains it was replaced by a substantial increase in sucrose synthase activity as seed development proceeds. Notwithstanding the increase in sucrose synthase activity in grains of sensitive cultivar; however, this little raise could not be sufficient to compensate for decreased levels of invertases and might restrict transport efficiency of storage material, and together with insufficient photosynthate may be the main reasons for dramatical reduction in the number of kernel and subsequent grain yield under WS treatment in Marvdasht. Key words: Invertase activity, sucrose metabolism, sucrose synthase, water stress, wheat (Triticum aestivum L.).

Comparison of the Drought Stress Responses of Tolerant and Sensitive Wheat Cultivars during Grain Filling: Impact of Invertase Activity on Carbon Metabolism during Kernel Development

Developmental changes in the starch and soluble sugars content of flag leaves and grains and the activities enzymes of sucrose metabolism in drought-tolerant (Triticum aestivumL. cv. Zagros) and drought-sensitive with high yielding potential under favorable conditions (cv. Marvdasht) wheat genotypes investigated under controlled water deficit during grain filling. Cultivars were grown in pots and treated with either well-watered (WW) or water-stressed (WS) from anthesis to maturity. WS caused a marked reduction in glucose, fructose and sucrose content of flag leaves and grains of sensitive cultivar. These changes were paralleled by sharp decline in the activity of cell wall invertase and soluble invertase at the both flag leaves and grains of sensitive cultivar. Whereas a transient surge in the activity invertases of flag leaves was found in tolerant cultivar. As the surge in invertase activity faded, in leaves and grains of tolerant cultivar it was replaced by a substantial increase in sucrose synthase activity as seed development proceeds. Notwithstanding increase in sucrose synthase activity in leaves and grains of sensitive cultivar, however this little raises could not be sufficiently active to compensate for decreased levels of invertases and might restrict sucrose export, and together with a concomitant repression in young ovaries, may limit sucrose transport and use and result in partial zygote abortion that led to dramatically reduction in number of kernel and subsequent grain yield under WS treatment in Marvdasht.

Variability in Activities of Sucrose Metabolizing Enzymes in Relation to Sucrose Accumulation Among Parents and Their Progenies of Sugarcane

Variability studies on sucrose metabolizing enzymes in relation to sucrose accumulation have been done in stem tissues of parents and a set of ten progenies of the cross Co 89003 (early maturing) × Co Se 92423 (late maturing) during sugarcane development. Sucrose content increased from stem elongation stage to maturity stage in both parents and progenies. Sucrose concentrations of the progenies were intermediate between those of the parents at stem elongation stage. Reducing sugars content, i.e., glucose plus fructose continuously decreased with advancement of the growth of the stem in all the genotypes. Specific activities of sucrose synthase (SS) and sucrose phosphate synthase (SPS) peaked at ripening stage and declined thereafter in each of the parents and their progenies. Specific activity of soluble acid invertase (SAI) in stem was found highest at stem elongation stage and declined thereafter in all the genotypes. Unlike SAI, soluble neutral invertase (SNI) activity increased with cane maturation. No significant overall relationship was found between the specific activities of SS/SPS/SNI and sucrose accumulation. However, a significant nonlinear negative relationship (R 2 = 0.643) between SAI and sucrose accumulation did exist over all genotypes. The difference in specific activities of SPS and SAI (SPS–SAI) and sucrose concentration were significantly positively correlated, showing a near hyperbolic relationship (R 2 = 0.495). Hence, this study may assist the sugarcane breeders in the selection of genotypes having higher capacity for sucrose accumulation and their maturity behavior under subtropical conditions.

Osmoregulation and nutritional relationships between Orobanche foetida and faba bean

The present study aims at comparing the phloem composition of the tolerant XBJ90.03-16-1-1-1 and the susceptible Bachaar genotypes and the impact of the faba bean genotype on the levels of the major solutes and invertase activities in the parasite Orobanche foetida. In comparison to Bachaar, the XBJ90.03-16-1-1-1 genotype limited the growth of orobanche tubercles under in vitro conditions. The limited growth was due to low soluble invertase activity, low osmotic potential of the infected roots and the organic nitrogen deficiency of the host phloem sap. The faba bean genotype did not affect the osmoregulation process of O. foetida. Among the organic solutes, stachyose, hexoses, starch and free amino acids, mainly asparagine and aspartate were highly accumulated in orobanche. However, asparagine/aspartate, glutamine/glutamate, alanine, serine, gamma amino butyric acid, stachyose, sucrose were identified as the main organic components in the host phloem exudates. The key role of the enzymes α-galactosidase, asparagine synthetase and aspartate oxaloglutarate aminotransferase in the utilization of the host solutes is proposed in O. foetida parasitizing faba bean.

Nitrogen and carbon relationships between the parasitic weed Orobanche foetida and susceptible and tolerant faba bean lines

The parasitic weed Orobanche foetida (Poiret) is an emergent agronomical problem on faba bean in Tunisia. The Tunisian breeding programs for faba bean resistance to O. foetida have produced several tolerant lines including the line XBJ90.03-16-1-1-1, which limits both parasite attachments to the host roots and growth of the attached parasites. The present study aims to provide a better understanding of the nutritional relationships between the parasite and this tolerant line in comparison with the susceptible Bachaar genotype. Phloem saps of faba bean were harvested using phloem exudation experiments. The major organic compounds potentially transferred from both faba bean genotypes to the parasite were identified as sucrose, raffinose, stachyose, citrate, malate, asparagine (ASN), aspartate (ASP), glutamine, glutamate, serine, alanine and GABA. However, the phloem exudates of the tolerant line were highly deficient in nitrogen when compared to that of the susceptible line. When attached to roots of the tolerant line, the parasite displayed limited activities of soluble invertases in tubercles, and especially in shoots, suggesting that the low performance of the broomrapes attached to the tolerant line resulted from a reduced capacity to utilize the host-derived carbohydrates. On the other hand, the mechanisms involved in the osmotic adjustment and primary metabolism of the parasite did not differ significantly according to the host genotype: mineral cations, especially potassium and calcium, predominated as the major osmotically-active compounds in both tubercles and shoots; shoots accumulated preferentially hexoses as organic solutes although tubercles accumulated preferentially starch and soluble amino acids, especially ASP and ASN. This suggests an important role for a glutamine-dependent asparagine synthetase (EC 6.3.5.4) in the N metabolism of the parasite.

Internodal soluble invertase isoenzymes in relation to sucrose storage and maturity behaviour in sugarcane cultivars

Changes in activities of internodal soluble invertases in relation to sucrose storage in two sugarcane cultivars viz. Co 89003 (early maturing) and Co 1148 (late maturing) have been studied at different physiological stages of cane development. The higher rate of decline in the activity of soluble acid invertase with ageing of the cane coupled with rapid rise in sucrose/reducing sugars ratio indicated better sink strength and higher sucrose storage in Co 89003. Six isoenzymes of soluble acid invertase in Co 89003 and five isoforms of this enzyme in Co 1148 were identified at internodal elongation stage. However, no neutral invertase isoenzyme was detected in either cultivar at this stage. At maturity stage, three isoenzymes of neutral and four isoenzymes of acid invertase were identified in Co 89003 whereas five isoenzymes of neutral and two isoenzymes of acid invertase were identified in Co 1148. These internodal soluble invertase isoenzymes differed with respect to their catalytic efficiencies for sucrose mobilization in storage tissue. Relative to Co 1148, soluble acid invertase isoenzymes of Co 89003 were less efficient catalytically because of their low Vmax/Km values. Marked differences were also observed in the inhibitory action of Mn++ on various isoenzymes of invertase.

QTLs for enzyme activities and soluble carbohydrates involved in starch accumulation during grain filling in maize

ADPglucose, the essential substrate for starch synthesis, is synthesized in maize by a pathway involving at least invertases, sucrose synthase, and ADPglucose pyrophosphorylase, as shown by the starch-deficient mutants, mn1, sh1, and bt2 or sh2, respectively. To improve understanding of the relationship between early grain-filling traits and carbohydrate composition in mature grain, QTLs linked to soluble invertase, sucrose synthase, and ADPglucose pyrophosphorylase activities and to starch, sucrose, fructose, and glucose concentrations were investigated. In order to take into account the specific time-course of each enzyme activity during grain filling, sampling was carried out at three periods (15, 25, and 35 d after pollination) on 100 lines from a recombinant inbred family, grown in the field. The MQTL method associated with QTL interaction analysis revealed numerous QTLs for all traits, but only one QTL was consistently observed at the three sampling periods. Some chromosome zones were heavily labelled, forming clusters of QTLs. Numerous possible candidate genes of the starch synthetic pathway co-located with QTLs. Four QTLs were found close to the locus Sh1 (bin 9.01) coding for the sucrose synthase. In order to confirm the importance of this locus, the CAPS polymorphism of the Sh1 gene was analysed in 45 genetically unrelated maize lines from various geographical origins. The DNA polymorphism was significantly associated with phenotypic traits related to grain filling (starch and amylose content, grain matter, and ADPglucose pyrophosphorylase activity at 35 DAP). Thus, the Sh1 locus could provide a physiologically pertinent marker for maize selection.

BIOCHEMICAL RESPONSES OF CHESTNUT OAK TO A GALLING CYNIPID

We characterized the distribution of nutritional and defensive biochemical traits in galls elicited on chestnut oak (Quercus prinus L.) by the gall wasp Andricus petiolicolus Basse (Cynipidae) in comparison with gypsy moth-wounded and unwounded leaves. Gall cortex and epidermis exhibited elevated soluble peroxidase (POX) and soluble invertase activities, and greater condensed tannin concentrations than did nutritive tissues or leaves. Nutritive tissue, on which the insect feeds, contained few polyphenols, and lower POX and invertase activities compared with other gall tissues and leaves. Elevated total POX activity arose from a complex pattern of enhanced and suppressed isoform activities in galls. Invertase enzyme activity decreased in all tissues over the course of the 7-d study, although gypsy moth wounding suppressed this decline slightly in ungalled leaves. Our results indicate that the distribution of biochemical defenses in this typical cynipid gall differs significantly from the leaf tissue from which it is formed and support a role for invertases in establishing the gall as a sink. A. petiolicolus larvae do not induce, and may suppress, plant defense responses in nutritive tissue, while enzymatic activity and phenolic accumulation are enhanced in gall tissues surrounding feeding sites. These patterns suggest that the gall is manipulated by the insect to enhance its food and protective value.

Carbohydrate metabolism during tuber initiation in potato: A transient surge in invertase activity marks the stolon to tuber transition

The relationship between carbohydrate metabolism and tuber initiation in potato was determined by monitoring changes in the amount of starch and sugars along with the activities of sugar metabolizing enzymes upon transfer of plants to tuber-inducing conditions (TI; short days, cold nights) from non-inducing conditions (NTI: long days, warm nights). Switch to TI conditions caused an immediate slow-down in plant growth and triggered swelling of stolon tips, which went on to develop into tubers. Leaves of plants moved to TI conditions accumulated less starch and sugar while their stolon tips showed a sudden upsurge in starch content and a sharp decline in sugars even before any tip swelling was detectable. These changes were paralleled by a transient surge in the activity of cell wall invertase (74%) and soluble invertase (30%) in stolon tips of plants transferred to TI conditions in two unrelated cultivars under different experimental conditions. As the surge in invertase activity faded, it was replaced by a substantial increase in sucrose synthase activity as the tuber enlargement proceeded. The transient increase in invertase activity just prior to tuber initiation appears to mark a turning point in the transition of stolon tip to tuber.

Effect of temperature on soluble invertase activity, and glucose, fructose and sucrose status of onion bulbs (Allium cepa) in store

The activity of soluble invertase, and the variation in glucose, fructose and sucrose contents in onion bulbs (Allium cepa) during long-term storage at 10°C and 20°C were investigated. Invertase activity increased progressively after 8 weeks to 0.084 and 0.092 nkat/g fresh weight (FW), then sharply to 0.29 and 0.35 nkat/g FW at 20°C and 10°C, respectively, and remained high during 5 weeks. Then, activity decreased abruptly to 0.039 and 0.041 nkat/g, and remained low during the last 8 weeks and close to that observed initially. Glucose increased to 17.73 and 14.62 mg/g FW after 4 weeks at 20°C and 10°C, respectively, then decreased sharply between week 5 and week 7 to 4.13 and 4.91 mg/g FW, respectively, and remained rather stable ranging from 9 and 10 mg/g FW at both temperatures. Fructose showed a similar pattern and was 14.8 and 21.68 mg/g FW at 20°C and 10°C, respectively. Between week 10 and week 24, fructose ranged from 5 and 6 mg/g FW, and from 6 and 7 mg/g FW at 20°C and 10°C, respectively. Sucrose increased to 19.63 and 14.43 mg/g FW at 20°C and 10°C, respectively, decreased during 3 weeks, and then increased randomly from 5.69 to 9.42 mg/g FW at 20°C, but remained in a steady state at 10°C ranging 5.03±0.78 mg/g FW. During the last 6 weeks, the sucrose content was higher at 20°C than at 10°C. The fructose–glucose ratio varied during the first 8 weeks but remained at a steady level during the last 16 weeks. The (glucose+fructose)/sucrose ratio increased randomly at 10°C, whereas at 20°C the ratio increased during 10 weeks then decreased progressively during the final 14 weeks.

Drought stress effect on carbohydrate concentration in soybean leaves and pods during early reproductive development: its implication in altering pod set

To advance our understanding of the physiological mechanisms by which pod abortion is regulated in soybean ( Glycine max L. Merr.), leaf photosynthetic rates, carbohydrate concentrations and soluble invertase activities in leaves, flowers and pods were determined in plants subjected to drought stress during early reproductive development. Soybeans were grown in pots in an environmentally controlled glasshouse. Drought stress was imposed from −11 to 10 days after anthesis (DAA). Drought decreased photosynthetic rates and water potentials in leaves, flowers and pods. Drought decreased leaf sucrose and starch concentrations but increased hexose (glucose+fructose) concentrations. Drought did not affect the activity of soluble invertase in leaves. In flowers and pods, sucrose concentrations were higher under drought as compared with well-watered controls. Hexose and starch concentrations of flowers and pods were also higher under drought until 7 and 3 DAA, respectively; thereafter they were significantly lower than those of the well-watered controls. Soluble invertase activity was decreased by drought in pods 5–10 DAA. Although the concentrations of non-structural carbohydrate (sucrose+hexose+starch) were higher in droughted flowers and pods, the total amount of non-structural carbohydrate accumulated in pods during the sampling periods was substantially reduced by drought. Pod growth was decreased by drought 3–5 DAA, which coincided with a decrease in hexose to sucrose ratio, when a significant reduction of pod set was occurred. Collectively, the results indicate that both source and sink restrictions are involved in regulating pod set in drought-stressed soybeans. It is suggested that a low availability of current and reverse photosynthate in leaves coupled with an impaired ability to utilize the incoming sucrose by pods resulted in a decreased carbohydrate flux from leaves to pods, together with a decreased hexose to sucrose ratio in pods are potential factors contributing to pod abortion in drought-stressed soybeans.

Response of potato tuber cell division and growth to shade and elevated CO2.

Plants adjust their sink-organ growth rates, development and distribution of dry matter in response to whole-plant photosynthate status. To advance understanding of these processes, potato (Solanum tuberosum L.) plants were subjected to CO(2) and light flux treatments, and early tuber growth was assessed. Atmospheric CO(2) (700 or 350 micro mol mol(-1)) and light flux (shade and control illumination) treatments were imposed at two growth stages: tuber initiation (TI) and tuber bulking (TB). Elevated CO(2) increased accumulation of total net biomass when imposed at both stages, and increased tuber growth rate by about 36 %, but did not increase the number of tubers. Elevated CO(2) increased the number of cells in tubers at both TI and TB stages, whereas shade substantially decreased the number of cells at both stages. Generally, treatments did not affect cell volume or the proportion of nuclei endoreduplicating (repeated nuclear DNA replication in the absence of cell division), but the shade treatment led to a decrease in cell volume at TB and a decrease in endoreduplication at TI. Elevated CO(2) increased, and shade decreased, glucose concentration and soluble invertase activity in the cambial zones at both TI and TB, whereas sucrose concentration and activities of glucokinase, fructokinase, cell-wall-bound invertase and thymidine kinase were unaffected. Modulation of tuber cell division was responsible for much of the growth response to whole-plant photosynthate status, and treatments affected cambial-zone glucose and soluble invertase in a pattern suggesting involvement of a glucose signalling pathway.

Suppressive effect of H2O2 on increase in activities of acid invertases in rye roots

Although various effects of H2O2 on plant cellular functions have been reported, the effects of H2O2 on glycolytic enzymes remain unknown. It was shown that H2O2 has a suppressive effect on increase in activities of soluble and insoluble acid invertases among a number of glycolytic enzymes during a growth stage of rye roots.

The role of invertases and hexose transporters in controlling sugar ratios in maternal and filial tissues of barley caryopses during early development.

To analyse carbohydrate metabolism and its role during early seed development of barley we characterised genes encoding two cell wall-bound invertases (HvCWINV1 and HvCWINV2) and two putative hexose transporter-like genes (HvSTP1 and HvSTP2). No typical vacuolar invertase gene could be identified. Instead, a gene encoding sucrose:fructan 6-fructosyltransferase (HvSF6FT1), an enzyme with soluble acid invertase activity, was isolated and characterised. Furthermore, enzyme activities and sugar levels were measured. HvSF6FT1-mRNA levels and acid soluble invertase activity are highest in the maternal pericarp 1-2 days after flowering (DAF). HvSF6FT1 is strongly expressed in regions flanking the main vascular bundle and to a lower extent in filial endospermal transfer cells, which persist until maturity and never accumulate starch. In contrast, cell wall-bound invertase HvCWINV2 is expressed early in development mainly in the style region and later on in pericarp areas which transiently accumulate starch and undergo degradation later in development. The hexose transporter HvSTP2 shows a temporal and spatial expression pattern similar to HvCWINV2. Transcripts of HvCWINV1 have been localised within the first row of endospermal cells and in the outermost area of the nucellar projection as well as in endospermal transfer cells before starch filling; the same regions of the endosperm are labelled with a hexose transporter HvSTP1-probe. HvSTP1 is expressed at very low levels within the pericarp but much higher in the syncytial endosperm at 3 DAF and in endospermal transfer cells 7 DAF. The temporal and spatial association of HvCWINV1 and HvSTP1 expression indicates that hexoses liberated by the invertase within the endospermal cavity are taken up by the transporter to be delivered into the central uncellularised space of the endosperm to supply mitotically active endosperm cells with hexoses. The results are discussed and compared with published data on the role of soluble sugars as signal molecules in seed developmental processes.

Sucrose‐phosphate synthase activity in mature rice leaves following changes in growth CO2 is unrelated to sucrose pool size

Summary • Photosynthetic acclimation of C3 plants to elevated atmospheric [CO2] is often attributed to soluble carbohydrate accumulation. We report the effects of modifying the carbohydrate source–sink balance on carbohydrate metabolism in mature leaves and partitioning in vegetative tissues of rice (Oryza sativa). • Plants were grown under ambient atmospheric [CO2] in outdoor, sunlit, environment-controlled chambers. During late vegetative development treatments were changed to high or low [CO2]. • Within 1 d of changing to low [CO2], sucrose-phosphate synthase (SPS) activation was significantly reduced in mature leaves, while soluble invertase activity decreased. Plants switched to high [CO2] showed increases in SPS substrate-saturated and substrate-limited activities and a decline in invertase activity. The changes in SPS activity did not correlate with leaf sucrose pool size. By 9 d after the change from ambient to high [CO2], nonstructural carbohydrates in stems and leaf sheaths increased significantly; > 70% of this increase was due to sucrose accumulation, indicating that excess assimilate was being rapidly exported to vegetative sinks. • Results indicate that immediately following source–sink modification, regulatory adjustments in key enzymes controlling carbohydrate metabolism were linked to feedforward, rather than feedback, processes.