Activity Of Starch Synthetase Research Articles

Causes of Sterility in Seed Set of Rice under Salinity Stress

The effects of salinity at 50 mM NaCl on floral characteristics, yield components, and biochemical and physiological attributes of the sensitive rice variety IR‐28 were studied under controlled conditions to determine the causes of sterility in seed set under salinity stress. The results showed significant decreases in panicle weight, panicle length, primary branches/panicle, filled seeds/panicle, unfilled seeds/panicle, filled seeds/plant, unfilled seeds/plant, total seeds/panicle, total seed weight/panicle, 1000‐seed weight and total seed weight/plant. The sodium content in different leaves and floral parts increased significantly. In contrast, the potassium content was decreased significantly in leaves and floral parts. A reduction in chlorophyll a and b was also noted in different parts of the leaves. Inhibition of transpiration and photosynthesis was observed in flag leaves at the grain‐filling stage. Soluble carbohydrates in different leaves were reduced significantly in salinized plants but their content in different floral parts was increased, with the exception of primary and secondary branch spikelets. Under salinity stress, total protein concentration in flag, second and third leaves were higher than in control plants. The viability of rice pollen was reduced significantly in salinized plants. It was further observed that starch synthetase activity (α1–4‐glucan glucosyle transferases) in developing rice grains was inhibited very significantly under salinity stress. From these results, it is inferred that sterility and significant reductions in seed set in rice were not merely due to reduction or inhibition of different biochemical constituents and physiological functions, but were mainly due to limitation of soluble carbohydrate translocation in primary and secondary spikelets, accumulation of more sodium and less potassium in all the floral parts, and highly significant inhibition of specific activity of starch synthetase in developing rice grains, thus resulting in failure of seed set.

Effect of Pre‐ and Post‐Kinetin Treatments on Salt Tolerance of Different Potato Cultivars Growing on Saline Soils

AbstractDifferent potato cultivars were subjected to 10 −6M kinetin treatment prior to the transplantation in saline soils (pre‐kinetin treatment) and to the plants already growing on the saline soils (post‐kinetin treatment). The kinetine when applied before the exposure of plants to saline soils showed promotory effects on growth, tuberization and some biochemical parameters of potato at 0.5 % salinity. The degree of inhibition in number of tubers and yield was reduced at 1 % salinity due to pre‐kinetin treatment. The level of proline, reducing sugars and sodium was increased in different plant parts to maintain the osmoregulation. However, kinetin did not play any specific role in reducing down the increase in proline content resulted due to salinity. The level of K+ was found to be higher at low salinity in all the cultivars of potato. Higher concentrations of proteins and enhanced activity of starch synthetase at low level of salinity suggest the salutary effect of Na+ in metabolic functions of plant cells. The nitrate reductase (NR) activity was appeared to be more sensitive than starch synthetase. This could possibly be due to the localization of the enzyme and the cellular concentration of toxic substances increased under stress. Total Glyoalkaloids (TGA) content was reduced at both the salinity levels irrespective of kinetin treatments. On the contrary Na+ content was increased in all the treatments of kinetin at both levels of salinity. During this study cvs. Red Lasoda, Patrones and Atom alue approved to be more tolerant as compare to rest of the cultivars tested. This could be a combined effect of genetic setup, amendments in saline soils and pre‐kinetin treatments of plants exposed to various regimes of salinity. Furthermore it is argued that salt tolerance limit can be extended upto certain level of salinity by pre‐kinetin treatment in potato plants.

Seasonal changes in starch synthetase activity in relation to starch content in kiwifruit.

This paper describes the seasonal changes in starch content of kiwifruit in relation to starch synthetase activity and also examines the properties of this enzyme in the two cultivars, Hayward and Koryoku. The highest activity of starch synthetase was observed in the middle of October for Koryoku and in late October for Hayward. The highest starch contents in Koryoku and Hayward were observed in the middle and late October or early November, respectively. These increases in starch coincided with the highest activities of starch synthetase. Starch content in early-ripening 'Koryoku' peaked around half a month earlier than in late-ripening Hayward. Since the soluble solids content in Koryoku could not be used as a harvest index because suitable firmness was not kept, the highest starch content was selected as the index in a previous paper. Starch synthetase activity followed the pattern of increasing starch content during the maturation and could explain maturity. Starch synthetase activity is a better index of maturity than β-amylase activity, because it supports decreasing starch content during the harvest period of Koryoku.

Biosynthesis of Starch in Proplastids of Germinating Ricinus communis Endosperm Tissue

Electron photomicrographs of endosperm tissue from germinating seed of Ricinus communis L. cv. Hale show proplastids which contain prominent starch grains. The content of starch in endosperm tissue increased from 500 micrograms per seed, in imbibed seed, to 1,100 micrograms per seed in 5-day-old seedlings. The maximum net rate of starch deposition was 1.1 nanomoles glucose incorporated per minute per seed. About 200 micrograms of starch remained in the endosperm 9 days after imbibition. Starch content followed the same developmental pattern as the content of sucrose, free reducing sugars, and other metabolic processes found in this tissue. Two key enzymes of starch synthesis, adenosine diphosphoglucose (ADPG) pyrophosphorylase and ADPG-starch glucosyl transferase (starch synthetase) exhibited maximum activities at 4 and 5 days after germination, respectively. The maximum activity of ADPG pyrophosphorylase was 8.17 nanomoles ADPG formed per minute per seed, whereas starch synthetase exhibited an activity of 125 nanomoles glucose incorporated per minute per seed. These levels of enzyme activity are sufficient to account for the starch synthesis observed. Other enzymes which may be involved in starch synthesis include 3-phosphoglycerate kinase which showed an activity of 8.76 units per seed, triose-P isomerase (2.56 units per seed), fructose-1,6-bisphosphate aldolase (0.99 units per seed), fructose-1,6-bisphosphatase (0.23 units per seed), phosphoglucose isomerase (12.6 units per seed), and phosphoglucomutase (9.72 units per seed). The activities of these enzymes were similar to previously reported values.Starch synthetase was found in association with the fraction containing proplastids isolated from endosperm tissue. Of the total starch synthetase activity in the endosperm, 38% was particulate. Forty-four% of the total particulate activity of starch synthetase placed on sucrose gradients was associated with the band containing proplastids. The proplastids contained 98% of the ribulose 1,5-bisphosphate carboxylase carboxylase activity placed on the gradient.

Studies on the Carbon Dioxide Promotion and Ethylene Inhibition of Tuberization in Potato Explants Cultured in Vitro

Ethylene inhibited the tuberization of etiolated potato (Solanum tuberosum L. var. Red La Soda) sprout sections cultured in vitro. Carbon dioxide did not overcome the C(2)H(4) inhibition but it was required for normal tuberization. Ethylene totally prevented root formation and development. It inhibited stolon elongation, and caused thickening and diageotropical growth of the stolon. In addition, C(2)H(4) prevented the accumulation of both starch and red anthocyanin which are always present in a tuber. Ethylene also inhibited the kinetin-increased tuberization of sprout sections.Three to five days of exposure to CO(2) were required to obtain promotion of tuberization of stolons cultured in vitro. Bicarbonate ion did not affect starch synthetase activity isolated from potato tubers in vitro. The evidence presented suggests that CO(2) gas rather than HCO(-) (3) or CO(2-) (3) ions in equilibrium with dissolved CO(2) was probably responsible for the stimulation. Morphological changes elicited by CO(2) and C(2)H(4) are described and the mechanism of action of both on tuberization is discussed.

Enzymes of Carbohydrate Metabolism in the Developing Rice Grain

The levels of reducing and nonreducing sugars, starch, soluble protein, and selected enzymes involved in the metabolism of sucrose, glucose-1-P, and glucose nucleotides were assayed in dehulled developing rice grains (Oryza sativa L. line IR1541-76-3) during the first 3 weeks after flowering. The level of reducing sugars in the grain was highest 5 to 6 days after flowering. The level of nonreducing sugars and the rate of starch accumulation were maximum 11 to 12 days after flowering, when the level of soluble protein was also the highest. The activities of bound and free invertase, sucrose-UDP and sucrose-ADP glucosyltransferases, hexokinase, phosphoglucomutase, nucleoside diphosphokinase, and UDP-glucose and ADP-glucose pyrophosphorylases were high throughout starch deposition, and were maximum, except for nucleoside diphosphokinase which did not increase in activity, between 8 and 18 days after flowering. Soluble primed phosphorylase and ADP glucose-alpha-glucosyltransferase (starch synthetase) were both present during starch accumulation. Phosphorylase activity was at least 2-fold that of soluble starch synthetase but the synthetase followed more closely the rate of starch accumulation in the grain. The activity of starch synthetase bound to the starch granule also increased progressively with increased starch content of the grain.

Evidence for lipid-enzyme interaction in starch synthesis in chilling-sensitive plants

Soluble and starch grain-bound forms of ADPglucose: α-1,4-glucan α-4-glucosyltransferase (starch synthetase) from maize, avocado and sweet potato show a discontinuity (change in slope) in Arrhenius plots at about 12°. In contrast, enzymes from potato have a constant energy of activation from 23° to 3°. t-Butanol, but not Triton X-100 or phospholipase A, abolishes the discontinuity in the plot of grain-bound starch synthetase activity of the chilling-sensitive plants. The previously found association of starch synthetase and the lipid lysolecithin with amylose molecules suggests that the discontinuous Arrhenius plot in chilling-sensitive plants reflects a phase change in the lipid at a critical temperature as has been reported for membrane-bound enzymes in these species. t-Butanol in high concentration probably acts by entering the amylose helix and perturbs the usual lipid-enzyme interaction.

Starch synthetase: Comparison of UDPG and ADPG as glucosyl donors in immature barley endosperm

The activity of starch synthetase in developing barley endosperm was measured in amyloplasts and in the soluble endosperm fraction by incorporation of radioactively labelled glucose into starch. Both uridine diphosphate glucose (UDPG) and adenosine diphophate glucose (ADPG) were used as glucosyl donors. Enzyme activity was initially located in the soluble fraction, but increasing activity could be detected in the amyloplast fraction during endosperm maturation.

Physical properties of starch granules of tobacco leaves during maturity stage

Abstract Although there are many studies concerning starch accumulation pattern of tobacco leaves during maturity stage (1, 2, 3, 4, 5), much less attention has been paid to physical properties of starch granules of tobacco leaves. Matheson et al. (6) reported in their study of starch changes in developing and senescing tobacco leaves, that the viscosities and iodine affinities of isolated starch granules increased with increasing age of the leaf, the β-amylosis limits of the whole starch and chain length of the amylopectins Were constant through the growth of the leaf and that the average granule size increased as the leaf matured and decreased as the starch conent decreased. One of the cl1aracteristics of maturity is to accumulated a large amount of starch after topping, but they used non topped f1ants, therefore the starch content was rather low. In our previous work (7) it has been demonstrated by using starch granules isolated rom tobacco leaves of topped plants, that the granule size and the ratio of amylopectin to amylose increased with the leaf maturity, a large alllount of calcium oxalate was found in the granules, and that the activity of starch synthetase bound with starch granules decreased with time after topping.

Starch synthetase in developing barley amyloplasts

The activity of starch synthetase in amyloplasts from barley endosperm was measured. The relative effectiveness of UDPG and ADPG as glucosyl donors was determined, and correlated with amyloplast age. Only UDPG linked synthesis could be detected up to about 12 days after anthesis. After this time ADPG was the main glucosyl donor.

Changes of Starch Synthetase Activity of Cucumber Leaves during Ammonium Toxicity

AbstractThe changes of granule bound starch synthetase activity in cucumber leaves (Cucumis sativus L. cv. Suisei No. 2) were investigated during ammonium toxicity. Generally speaking the quantity of starch granules of injured plants were less than that of normal plants. ADPG is a more effective glucose donor to starch synthesis than UDPG. It was found that the starch synthetase activity of injured plants was decreased compared to the normal plants. This variation of enzyme activity was higher when UDPG was used as glucose donor. The addition of K+ and NH4+ generally inhibited the enzyme activity when UDPG was used as glucose donor, but stimulated it when ADPG was used. This stimulation was found to be more effective in enzymes prepared from injured plants than from normal plants. The level of potassium bound to starch granules was not changed markedly between normal and injured plants.

Cytokinin‐cytokinin‐Induced tuber formation Tuber Formation on Stolons of Solanum tuberosum

AbstractKinetin‐induced tuberization of isolated stolons was investigated with regard to accumulation of labelled kinetin, starch, protein and nucleic acid synthesis. Using kinetin‐8‐14C, it was found that more labelled meterial appeared at the locus of tyber formation that in other parts of the stolon. Substantial accumulation was evident before visible signs of tuber formation. The basal portion of the stolon also accumulated substantial amounts of labelled material.Kinetin‐treated stolons showed extensive starch accumulation which was not evident in gibberellic acid‐treated or untreated stolons. Starch accumulation occurred before any visible sign of tuber formation. There was no marked differences in the ability of the apical 0.5 cm of kinetin‐treated and untrated stolons to incorporate 14 C uridine into RNA and 14C leucine into TCA precipitable protein. From these results it was concluded that kinetin‐induced tuber formation may not involve the synthesis of new proteins. It is suggested that kinetin may be regulating tuber formation by suppressing starch hydrolase activity and stimulating starch synthetase activity whereas gibberellic acid inhibits tuber formation by promoting starch hydrolase activity or by suppressing starch synthesizing enzymes.

Effects of Univalent Cations on the Activity of Particulate Starch Synthetase

An investigation was made to determine the univalent cation requirements of starch synthetase from a variety of plant species of economic importance. The particulate enzyme from sweet corn was shown to have an absolute requirement for potassium, with the optimum activation occurring at 0.05 M KCl. Rubidium, cesium, and ammonium were 80% as effective as potassium while sodium and lithium were respectively 21% and 8% as effective as potassium. The K(A) for potassium was determined to be 6 mM. In the case of the particulate starch synthetase from wheat, bush beans, field corn, soybeans, peas, or potatoes, considerable stimulation of enzyme activity was obtained by the addition of potassium to the reaction mixture. In these studies, low enzyme activity was observed in the absence of added potassium, but the content of endogenous univalent cations in the reactions may be sufficient to account for the activities observed. Anions of various types had no effect on starch synthetase activity. Divalent cations produced slight activation in the presence or absence of potassium. All efforts to show a potassium requirement for glycogen synthetase from rat liver have been negative.

Enzymic mechanism of starch synthesis in sweet potato roots: II. Enhancement of the starch synthetase activity by maltooligosaccharides

The effect of maltooligosaccharides on the transglucosylation reaction catalyzed by the granules-bound starch synthetase of sweet potato roots was studied. The stimulatory effect of oligosaccharides on the incorporation of 14C-glucose into starch granules (starch synthesis) was found to be novel, and not due to the mere adherence of the radioactive oligosaccharides formed by the transglucosylation reaction (oligosaccharide synthesis). The stimulatory effect of K + and oligosaccharide on the enzyme reaction proved to be additive, if ADPG was used as the glucose donor. However, there exists an optimal level of K + for the enzymic transglucosylation reaction, if UDPG was used as the glucose donor. At high levels of K +, oligosaccharide did not exhibit any stimulatory effect. Over the entire range of added K +, the rate of oligosaccharide synthesis appeared to exceed that of the starch-synthesizing reaction. The addition of glucose was found to suppress the starch-synthesizing reaction using both ADPG and UDPG as the glucose donors. The mutual interaction of glucose with K + and with maltooligosaccharide in the starch synthesizing reaction was studied.

Enzymic mechanism of starch synthesis in sweet potato roots: I. Requirement of potassium ions for starch synthetase

The effect of K + on the starch synthesis catalyzed by the granules-bound ADPG 2 2 Abbreviations used are: ADPG, adenosine diphosphate glucose; UDPG, uridine diphosphate glucose. - and UDPG-starch transglucosylase (starch synthetase) prepared from sweet potato roots, rice grains, white potato roots, and taro roots was examined. The magnitude of the stimulation was most marked by the sweet potato root ADPG-starch transglucosylase and was least by the taro and rice enzyme. From the results of kinetic experiment using sweet potato root enzyme, it was found that the addition of 0.1 m K + increases the enzyme activity about 7-fold, and KA value was determined to be 1.3 × 10 −2 m. The level of K + giving the maximum starch synthetase activity was found to be about 0.05–0.1 m, roughly equivalent to the cellular concentration of K + in the sweet potato roots. However, both K m (ADPG) and K i (ADP) values were not affected by the addition of K + to the reaction system. Pretreatment of the sweet potato enzyme with K + caused an appreciable protective effect against the heat-inactivation of enzyme (60 ° for 30 min), while the nearly complete loss of the enzyme activity occurred without K +-treatment. Some physiological implications have been made concerning the dynamic role of K + in regulating the starch synthesizing reaction in the sweet potato roots.

Biochemical Aspects of Parasitism by the Angiosperm Parasites: Starch Accumulation

AbstractThe investigation dealt with starch accumulation in four species of Cuscuta (Cuscuta campestris, C. indecora, C. planiflora and C. reflexa), a leafy mistletoe (Dendrophthoe falcata) and a chlorophyll‐lacking root parasite (Orobanche aegyptiaca). The highest content of starch occurred In O. aegyptiaca, with a maximum of 45 per cent of dry weight Starch in Cuscuta filaments and mistletoe leaves showed a maximum of about 10 per cent of dry weight. The starch content varied along the length of the Cuscuta vine, with a maximum in the apical region. Orobanche had a higher starch content when it was still submerged than it was fully developed. Cuscuta vines did not show any marked diurnal alteration in the starch content. The content of ethanol‐soluble carbohydrate was only a tenth of the starch in Orobanche, but was relatively higher in the other parasites. the neutral sugars in Cuscuta filaments were sucrose and glucose, whereas fructose was also present in mistletoe and Orobanche. Raffinose and stachyose were absent or present only ill traces in parasite tissue. Starch granules from Cuscuta and Orobanche bad ADPG/UDPG‐starch synthetase activity and homogenates starch phosphorylase activity. The former enzyme appeared to be responsible for synthesis of starch and the latter for utilization. The four different species of Cuscnta, growing on alfalfa, had more or less the same activity of starch synthetase and also of phosphorylase activity. Hosts infected by Cuscuta had significantly less starch per plant than the controls. A characteristic feature of invasion by Cuscuta and Orobanche was increased phosphorylase activity in the host tissues. The protein content of the tissues of Cuscuta and Orobanche was of a lower level than that of the host shoot system or foliage, indicating that the parasite differed from the host in having a higher carbon (of starch) to nitrogen (of protein) ratio.

Enzymic mechanism of starch synthesis in ripening rice grains: V. Iodoacetate inhibition of granular starch synthetase activity

Granular starch synthetase activity of rice seeds was inhibited by SH-blocking agents, e.g., iodoacetate, p-chloromercuribenzoate, and N-ethylmaleimide. However, pretreatment of starch granules with adenine nucleotides protected the enzyme from iodoacetate inhibition. The rate of protecting effect was ATP = ADP > AMP > ADP-glucose. Although UTP and UDP had a similar protecting action, it was much less compared with that of adenine nucleotides. Evidence for the masking of active SH-groups in the enzyme molecule with adenine nucleotide was the alkylation of the starch granules with iodoacetate-1- 14C, which was inhibited by ADP but not UDP. Ready association of starch granule with ATP-8- 14C was demonstrated, and could be prevented to some extent by co-incubation with iodoacetate. The effect of ADP-glucose was partly thought to be the effect of ADP liberation during the course of the starch synthesis reaction. However, kinetic analyses showed that ADP-glucose perse has an intrinsic role in association with the granular enzyme.

The intracellular distribution of uridine diphosphate glucose starch synthetase in potato tubers

Fractionation of subcellular particles from potato tubers in sucrose-citratte media has shown very high levels of uridine diphosphate glucose starch synthetase activity to be associated with the starch granules. No activity has been detected in other fractions. The starch granules prepared in this medium show minimal damage.