Rangil Singh

Sucrose metabolism in sugar cane grown under varying climatic conditions: Synthesis and storage of sucrose in relation to the activities of sucrose synthase, sucrose-phosphate synthase and invertase

Abstract The contents of sucrose and hexoses in relation to the activities of sucrose synthase, sucrose-phosphate synthase and soluble invertase in leaf blade and of soluble and wall-bound invertase in stem tissues of sugar cane growing under naturally varying weather conditions were determined. In leaf blades, sucrose synthase, sucrose-phosphate synthase and soluble invertase were most active at tillering. Sucrose synthase was relatively more active than sucrose-phosphate synthase throughout the growth of the cane. In stem tissues the activity of soluble acid invertase was highest at the stem elongation stage and then declined, whereas the activities of soluble neutral invertase and wall-bound acid invertase increased with age. With the ageing of the cane, sucrose accumulation in the stem gradually increased with a concomitant fall in hexose content. A narrow ratio ofsucrose in the basal to top portion of the cane relates to maturity of the cane. On feeding uniformly labelled sucrose and hexoses to storage tissue for 4 hr. ca 85–90 % of the 14C in intracellular sugars was present in sucrose. Synthesis of sucrose from glucose in leaf disks was stimulated by Mg2+ and Mn2+.

Phytohormone-mediated transformation of sugars to starch in relation to the activities of amylases, sucrose-metabolising enzymes in sorghum grain

Indole-acetic acid (IAA) and abscisic acid (ABA) were fed throughcomplete liquid medium (containing 2, 4, 8% sucrose) to detached earheads of sorghum. The effect of these phytohormones on interconvertion ofsugarsand their transformation to starch in relation to the activities ofα-, β-amylases, sucrose-synthase (synthesis), sucrose-phosphatesynthase and soluble invertases was studied in the grain. This effect on theuptake of (U-14C) sucrose by detached ear heads and incorporation of14C into free sugars and starch of grain and into free sugars ofinflorescence parts was also studied. At concentrations of up to 4%sucrose in the culture medium, IAA increased the content of total free sugarsinthe grain. However, accumulation of starch and activities of α- andβ-amylases increased when lAA was present even beyond the 4%sucroseconcentration in the culture medium. At all sucrose concentrations, the effectsof ABA and IAA were opposite. With 4% sucrose, both phytohormones causedmaximum accumulation of starch in the grain. ABA enhanced the relativeproportion of sucrose in the sugar pool with a concomitant reduction in theactivities of soluble acid (pH 4.8) and neutral (pH 7.5) invertases. Incontrast, IAA decreased the sucrose proportion of grain sugars with asimultaneous elevation and reduction in the activities of invertases andsucrose-phosphate synthase, respectively. Irrespective of sucrose concentrationin the culture medium, the activity of sucrose synthase (synthesis) wasenhancedwith IAA as well as ABA at their 10 μM concentration. IAA alsoenhanced incorporation of 14C from (U-14C) sucrose intothe EtOH extract (principally constituted by free sugars) and starch of thegrain, but ABA caused the reverse effect. Based on the results, it is suggestedthat IAA and ABA have contrasting effects on the transformation of sucrose tostarch in sorghum grain where its capacity to synthesise starch is modulatedpositively by IAA and negatively by ABA.

Fructosan metabolism in Cichorium intybus roots

Abstract Incorporation of [ 14 C]sucrose into difructosyl glucose (F 2 G), trifructosyl glucose (F 3 G) and tetrafructosyl glucose (F 4 G) in the presence of various nucleoside triphosphates revealed that formation of F 4 G and F 3 G is retarded in the presence of ATP, and formation of F 3 G and F 2 G is significantly enhanced in the presence of CTP, whereas UTP has no effect on the synthesis of these oligosaccharides. Different fructosyl transferases seem to be responsible for the different fructosylation steps and self transfer seems to be the major pathway for fructosan synthesis. Utilization of added glucose, which is formed by sucrose sucrose fructosyl transferase action in vivo , is completely inhibited in acetate buffer whereas in phosphate, citrate and citrate-phosphate buffers glucose is actively utilized. In the presence of fluoride ions both glucose utilization and its conversion to CO 2 is inhibited by ca 50%. CO 2 production from [ 14 C]glucose is completely inhibited in acetate ions. No evidence for the incorporation of 14 C from [ 14 C]glucose into [ 14 C]sucrose is observed. The ratio of bound fructose to bound glucose is the same in the entire length of the root indicating that there is no preferential zone for fructosan synthesis.

Fructose and inulinase production from waste Cichorium intybus roots

Abstract The roots of Cichorium intybus collected at seed maturation stage have no economic utility and are, therefore, discarded. However, these roots contain a considerable amount of free and bound fructose. Fusarium oxysporum when grown on aqueous extract of these roots produces extracellular inulinase which can be used for production of fructose from inulin.

Invertase-mediated Interconversion of Sucrose and Hexoses During Their Translocation in Growing Pearl Millet Plant

Metabolism of free sugars, particularly sucrose, in various plant tissues enroute from leaf sheaths to grains in growing pearl millet was studied. With the enhancement in growth, the levels of both reducing and non-reducing sugars declined in middle and basal leaf sheaths but increased in flag leaf sheath towards plant maturity. In sheath, wall-bound invertase was more active than soluble invertases and the activities of all these enzymes rose towards maturity. Besides hexoses and sucrose, some fructose polymers were also detected in the internodes. In contrast with internodes, where the levels of total free sugars declined till around anthesis, in penultimate node their levels continuously increased, but attained peak values at 65 CAS in middle- and basal nodes. In both these tissues, arriving sucrose encounters invertases but in nodes wall-bound invertase appears to be the pivotal one. On feeding (U-14C)-sucrose to the detached ear-heads a large proportion of 14C was incorporated into hexoses alone in peduncle and rachis. PCMBS and HgCl2 inhibited the metabolism of sucrose supplied to peduncle and rachis pointing to the involvement of invertases in sucrose cleavage in these organs. Through the regulated operation of invertase(s), the nodes seem to maintain a controlled flow of free sugars from source to sink tissue.

Synthesis and Storage of Sucrose in Relation to Activities of Its Metabolizing Enzymes in Sugarcane Cultivars Differing in Maturity

Metabolic changes in the contents of sucrose and hexoses in relation to the activities of invertase, sucrose synthase and sucrose-phosphate synthase in early (CoJ 64) and late (Co 1148) maturing cultivars of sugarcane have been studied. During early stages of cane growth, lower activities of sucrose synthase and sucrose-phosphate synthase in leaf blade In CoJ 64 over Co 1148 were observed. However, sucrose content in sheath/blade was higher in CoJ 64 than in Co 1148. With the advancing age, the activity of soluble acid invertase (pH 5.4) in stem declined more rapidly in CoJ 64. This resulted in building up of high ratio of sucroselinvert sugars in stem tissue of this cultivar. Feeding uniformly-labelled sucrose and glucose to the cut discs of leaf sheath resulted in higher uptake of 14C in CoJ 64 than in Co 1148. Uptake by stem tissue discs of 14C from sucrose was less than that from hexoses. Based on these results, it is suggested that (i) the rapid fall in the activity of soluble acid invertase in stem concomitant with fast accumulation of sucrose in this tissue is an index of early maturity of the cane, and (ii) high content of sucrose in sheath is a reflection of an efficient translocation of this sugar in early maturing cultivars.

Interconversion and translocation of free sugars during galactomannan utilization in germinating guar (Cyamopsis tetragonoloba) seed

Abstract With the onset of the degradation of galactomannan, the galactose and mannose levels increased in the endosperm. The hydrolysis of galactomannan was more or less complete within the first 3 days of germination. In the cotyledons, sucrose was the predominant free sugar during the period of rapid galactomannan hydrolysis and reducing sugars (glucose + fructose) were present in only 10–20% proportion. The level of soluble acid invertase activity was in the order of embryonic axis > endosperm > cotyledons. On the basis of (a) absence of galactose and mannose, (b) high proportion of sucrose, (c) very fast conversion of [14C]glucose and [14C]mannose to [14C]sucrose and (d) very low levels of both soluble and bound invertases in cotyledons, we conclude that there is an active synthesis of sucrose in this tissue where disaccharide seems to be least hydrolysed during the period of galactomannan mobilization. A rapid hydrolysis of galactomannan in endosperm during early germination resulted in the synthesis of some starch, as a temporary reserve, in cotyledons. When the cotyledons entered the phase of first leaf formation, cotyledonary sucrose was hydrolysed giving rise to invert sugars. In the embryonic axis, the increase in the ratio of reducing sugars to sucrose coupled with a higher level of invertase, compared with sucrose-UDP glucosyl transferase, indicated that free sugars from the cotyledons are translocated to the embryonic axis as sucrose.

Profiles of enzymes of sucrose metabolism in the leaves of chicory (Cichorium intybus) during development

Abstract The activity of sucrose phosphate synthase (SPS) was evenly distributed between the lamina and petiole at all stages of development of Cichorium intybus. As compared to sucrose synthase (SS), the activitie ofSPS in lamina and petiole at both the early (February) and mid-stages (April) of growth were higher . Activities of these enzymes in the lamina and petiole at the mid-stage of development were 3–10 times higher as compared to the early and late (July) stages and coincidedwith the maximum rate of fructan synthesis and dry weight accumulation in roots (sink). The supply of photosynthates to the roots, as revealed by 14CO2 fixation and its transportation at this stage, was much more when compared to that at late stage. It appeared that at mid-development leaves made use of enhanced activity of SS in addition to SPS activity for meeting the photosynthate requirement of the sink region. Acid invertase remained the major form of invertase during growth. At the early and mid-stages, petioles showed two acid invertase whereas lamina, in addition to two acid invertases, contained an additional low molecular weight alkaline invertase at the late stage. Leaves of the erect stem at the time of flowering contained only one form of acid invertase.

Accumulation of starch, protein and activities of sucrose-cleaving, transaminating enzymes in chickpea pods raised through liquid culture

Abstract Using liquid culturing of detached inflorescences of chickpea ( Cicer arietinum ), manipulations with respect to sugars and amino nitrogen were done on the feeding sap entering the developing pods. The effects of such manipulations on the accumulation of biomass in seed, starch and protein in cotyledons and the activities of soluble acid and neutral invertase (EC 3.2.1.26), sucrose synthase (cleavage, EC 2.4.1.13), glutamate oxaloacetate transaminase (EC 2.6.1.1) and glutamate pyruvate transaminase (EC 2.6.1.2) in pod tissues were investigated. Compared with supplied hexoses, addition of sucrose in the culture medium resulted in higher accumulation of biomass in seed and decapitation of detached inflorescence did not affect this biomass accumulation. Appearance in seed tissues of over 70 % of 14 C in extracted sugars for sucrose alone indicated entry into seed of translocated sucrose as such and/or its reconstitution in these tissues. Comparative effect of exogenously-fed cold sugars on incorporation of 14 C from sucrose into EtOH-soluble products of seed tissues indicated that a minimum level of sucrose in transport stream is essential for an effective unloading of this sugar into seeds. Whereas in pod wall and seed coat, the cleavage of sucrose is principally catalysed by soluble neutral invertase, in cotyledons both soluble neutral invertase and sucrose synthase (cleavage) are involved. The accumulation of proteins in cotyledons was significantly higher with amides, compared with inorganic nitrogen, added to the culture medium. In pod wall and seed tissues, the activity of glutamate oxaloacetate transaminase was much higher than that of glutamate pyruvate transaminase. Increased supply of glutamine at an adequate fixed level of sucrose resulted in diversion of sucrose from starch to protein synthesis with concurrent increase in the activities of both transaminases in cotyledons.

Inulin is a better inducer of acid invertase than sucrose

Abstract Inulin has been found to be a better inducer of invertase than sucrose and this led to an increased secretion of invertase in the medium on using inuli