UDP-Glucose: Sterol Glucosyltransferase and a Steryl Glucoside Acyltransferase Activity in Amyloplast Membranes from Potato Tubers

Envelope membranes were isolated from potato tuber amyloplastby a discontinuous sucrose density gradient and high speed centrifugation.These membranes catalyzed the transfer of [¹⁴C]glucose fromUDP-[¹⁴C]glucose to endogenous sterol acceptors and, in turn,catalyzed the esterification of steryl glucosides with fattyacids from an endogenous acyl donor. The synthesis of sterylglucosides was stimulated in the presence of Triton. X-100,while formation of acyl steryl glucosides was inhibited by thedetergent. However, in the presence of an added sterol acceptorand Triton X-100, the inhibition of acyl steryl glucoside synthesiswas overcome by the addition of phosphatidylethanolamine. Theenzyme involved in steryl glucoside formation was solubilizedby treatment of the envelope membranes with 0.3% Triton X-100.The solubilized enzyme had an almost absolute requirement forsterol acceptors. Key words: Solanum tuberosum, Sterol glucosylation, Steryl glucoside acylation, Amyloplast membrane     

Changes of the Protein Synthesis System during the Maturation of Potato Tubers

Respiratory activity, RNA contents and protein synthesis capacity of isolated ribosomes of tubers of Solanum tuberosum, cv. Tonda di Berlino, at progressive stages of development have been determined. In the immature, still growing tubers, respiration steadily decreases with the increase of fresh weight. The entering into dormancy of the tubers collected when immature corresponds to a rapid drop of respiration to the values characteristic of mature tubers. The RNA contents per tuber increase progressively during maturation. A decrease of the RNA contents per tuber (ca. 50 %) is observed in the period between the moment of harvesting and the end of dormancy. The endogenous capacity of isolated ribosomes to carry on amino acid polymerization strongly decreases during tuber development, while the activity supported by polyuridilic acid remains almost unchanged when measured at optimum Mg²⁺ concentrations, and becomes larger for the more mature tubers at superoptimum Mg²⁺ concentrations. These changes of the protein synthesis system during tuber development are compared with those occurring during seed maturation.     

Effect of Arachidonic Acid on Potato Tubers during Storage

Potato (Solanum tuberosumL.) tubers were treated with various concentrations (10^–9to 10^–4M) of biogenic elicitor arachidonic acid during storage (from October to June). The data showed that the resistance-inducing concentration of arachidonic acid was 10^–6M in autumn and 10^–9M in spring. The possible causes of the change in the immunizing concentration of arachidonic acid during storage of potato tubers are discussed.     

Apical Dominance and the Utilization of Carbo-hydrates During Storage of Potato Tubers

Although carbohydrates are metabolized throughout potato tubersduring storage, it would nevertheless appear as if there isenhanced carbohydrate metabolism in the region of the apicalbud. Soluble sugars are higher in this region of the tuber duringthe whole period of storage and growth. In the sprouts themselvesglucose accumulates to extremely high levels. It is postulatedthat this glucose is pooled and is eventually used for the synthesisof starch, especially during the development of ‘littlepotatoes’ which occurs during prolonged storage at lowtemperature in the dark.     

Isolation of Functional RNA from Periderm Tissue of Potato Tubers and Sweet Potato Storage Roots

A reliable and efficient protocol is given for the isolation of mRNA from the periderm of potato tubers and sweet potato storage roots. The method relies on a urea-based lysis buffer and lithium chloride to concentrate total RNA away from most of the cytoplasmic components and to prevent oxidation of phenolic complexes. To enhance the physical separation of the RNA from other macromolecular components, the RNA fraction was incubated in the presence of the cationic surfactant Catrimox-14. Poly(A)⁺ mRNA was separated from total RNA and other contaminants by using Promega's MagneSphere technology. The mRNA was suitable for cDNA library construction and RNA fingerprinting.     

Effects of Storage Temperature and Wounding on Cytokinin Levels in Potato Tubers

The level of butanol-soluble cytokinin in potato tubers (Solanumtuberosum L.) decreased greatly after harvest of the tubers,remained low during rest-period and then began to increase priorto the end of the period. In warm-stored tubers (25?C) the levelrose faster than in cold-stored ones (4?C). On the other hand,the level of water-soluble cytokinin, which was high duringthe rest-period, decreased after the rest was broken. Wounding the tubers caused an increase in butanol-soluble cytokinin.The increase in cytokinin within the first 24 hr after woundingwas smaller in warm-stored tubers than in cold-stored ones andwas decreased with increasing storage time of the tubers. Thelevel of water-soluble cytokinin decreased by wounding. Theseresults suggest that water-soluble cytokinin is a storage formand that the level of butanol-soluble cytokinin is regulatedby an interconversion between the two. (Received February 6, 1982; Accepted May 13, 1982)     

Pyrophosphorylases in Solanum tuberosum: I. Changes in ADP-Glucose and UDP-Glucose Pyrophosphorylase Activities Associated with Starch Biosynthesis during Tuberization, Maturation, and Storage of Potatoes

Changes in ADP-glucose and UDP-glucose pyrophosphorylase activities were followed during tuber development of Solanum tuberosum and prolonged storage at 4 and 11 C. Potato tuberization was accompanied by a sharp increase in starch synthesis simultaneous with a marked rise in ADP-glucose pyrophosphorylase activity. When tubers reached an average diameter of 1 centimeter (0.5 gram average tuber weight) and had already established 58% starch on a dry weight basis, ADP-glucose pyrophosphorylase increased 16- to 24-fold over its activity seen in low starch containing stolon tissue. During this same period UDP-glucose pyrophosphorylase increased approximately 2- to 3-fold. Although participation of UDP-glucose in starch formation can not be neglected, it is suggested that the onset of rapid non-photosynthetic potato tuber starch biosynthesis may be closely related to the simultaneous increase in ADP-glucose pyrophosphorylase activity.     

The Effect of Gamma-Irradiation on the Sucrose Content in Sweet Potato Roots and Potato Tubers

The sucrose content in both potato tubers and sweet potato roots was considerably increased by gamma-irradiation. The maximum increase was achieved by an irradiation dose of 3 to 4 kGy for potatoes and 0.8 to 2 kGy for sweet potatoes. Cooling treatment (15°C, 2 weeks) for sweet potato roots also enhanced the sucrose content (almost 2 times) but was not additive to the irradiation treatment; the maximum sucrose content in irradiated sweet potato roots was in the range of 7 to 12% irrespective of the cooling treatment, depending on the variety of sweet potatoes. Irradiation made the sucrose content in the roots 2 to 4 times higher.     

The Control and Branch Growth on Potato Tubers: I. ANATOMY OF BUDS IN RELATION TO DORMANCY AND CORRELATIVE INHIBITION

A study was made of the morphology of potato buds during thedormant period and of the anatomy of dormant, growing, and correlativelyinhibited buds. Lateral buds showed a progressive increase indevelopment with increasing number of nodes measured basipetally,and some further development in association with second-growthof the tuber. In dormant buds, or buds which had not grown afterthe end of the rest period, the cytoplasm of cells in the meristematicdome stained only lightly with Heidenhain's iron-hematoxylin,whereas cells of buds which had grown had densely staining cytoplasm.The xylem vessels leading to dormant buds were filled with tannin-likesubstances for a short distance below the bud. Buds which hadgrown after the end of the rest period had both old obstructedxylem vessels and new open vessels. The end of the dormant period was not reflected in the internalbud anatomy unless buds also commenced to grow. Thus, whiledormant buds had distinctive anatomical features, none of thestructures appeared to be primarily associated with dormancy.Correlatively inhibited buds showed the features either of dormantor of growing buds depending on whether or not they had grownat the end of the dormant period.     

Effect of Storage in Darkness and in Light on the Content of Membrane Lipids of Potato Tubers

The lipid composition of tubers from the potato varieties Bintje and Desirée was investigated during storage. Storage in total dark ness after harvest gave only small changes in the amounts of triglycerides. monogalactosyl diglycerides and digalactosyl digtycerides. Storage in light resulted in changes in these lipids and in their fatty acid composition. The absolute amount and the relative content of linolenic acid in the galactolipids increased. A simultaneous and equivalent decrease in the percentage of linoleic acid took place without any marked percentage changes in the other major fatty acids. The light induced changes of the lipids, which occur simultaneously with greening of the tuber, are discussed and related to the development of thylakoid membrane systems in the plastids.     

Changes in Levels of Butanol- and Water-Soluble Cytokinins during the Life Cycle of Potato Tubers

The nature of the water-soluble cytokinin in potato tubers (Solanumtuberosum L.) and the changes in the levels of both butanol-and water-soluble cytokinins during their life cycle were examined.The main cytokinin detected in the water-soluble fraction hadthe same chromatographic behavior and susceptibility to enzymesas zeatin ribotide. The level of butanol-soluble cytokinin inelongating stolon tips was low, while that of water-solublecytokinin was extremely high. Upon swelling of the stolon tips,the former increased greatly as the latter decreased. The resultssuggest that the increased butanol-soluble cytokinin is responsiblefor the subsequent vigorous thickening growth of the stolonsto form tubers and that the water-soluble cytokinin is a temporarystorage form. (Received February 6, 1982; Accepted May 13, 1982)     

Developmental Patterns of Phytohormone Content in the Cortex and Pith of Potato Tubers as Related to Their Growth and Starch Content

The contents of ABA, IAA, and cytokinins (zeatin + zeatin riboside) were determined in the cortex and pith of medium-sized (25 g) and large (120 g) tubers of potato (Solanum tuberosum L., cv. Malakhit) at the end of the flowering phase (48 days after sprouting) and related to plant growth (cell division and enlargement) and starch biosynthesis and deposition. The patterns of phytohormone distribution were different in the cortex and pith. In the latter, with most cells at the enlargement phase, the IAA content increased, as well as the ratios IAA/ABA and IAA/cytokinins. In the cortex dominated by the dividing cells, the ABA content declined, and the ratio cytokinins/ABA exceeded that in the pith. The enhancement of starch synthesis and accumulation in the pith and the retardation of these processes in the cortex followed the changes in the ABA content providing indirect support to the previously made observation that the exogenous ABA promoted starch biosynthesis. The data obtained are discussed in the context of the hormonal control of carbohydrate metabolism and starch deposition in growing tubers.     

The Control of Branch Growth on Potato Tubers: III. THE BASIS OF CORRELATIVE INHIBITION

Correlatively inhibited lateral buds on potato tubers were suppliedwith various nutrient solution through the surfaces of leafprimorida. The media, which also supported the growth of isolatedbuds in tissue culture, stimulated the growth of the dominant(growing) sprotus but the inhibition was not due to a shortageof nutrients. The neutral fraction of the ether extract frompotato tubers bearning inhibited sprotus contained a substancesor substances capable, at physiological concentrations, of inhibitingthe growth of buds both in situ and when isolated. Buds on-eyepieceswere not inhibited when supplied with a tissue-culture mediumas well as the neutral fraction. The latter contained both growth-inhibitingand growth-promoting substances. The inhabitor complex was partiallypurified. It was soluble in water and ether and was most unstable.When treated with fluorescein followed by bromine it gave acharacteristic reddish-brown fluorescence. Attempts to establishits chemical nature were unsuccessful. The available evidenceindicated that the substance(s) was effective in preventingthe extension of potato buds at concentrations approximatingto those found in situ and that it disappeared from tuber tissuewithin 24 h of removing the growing sprouts. It is suggestedthat this complex, which is rapidly metabloized in tissue, isthe prime component involved in apical dominance. Nutrient supplydoes not appear to be directly involved although a ready supplyof nutrients can partially offset the effect of the inhibitor.     

The Control of Branch Growth on Potato Tubers: II. THE PATTERN OF SPROUT GROWTH

Following the end of dormancy or after desprouting, many budson a potato tuber start to grow. However, if the storage temperaturefavours rapid growth, a number may remain inhibited. After atime, the smaller sprouts stop growing. This inhibition affectsonly those sprouts below a certain length, which is proportionalto the length of the longest sprout. This critical length isrelatively greater for small tubers than for large ones (i.e.longer sprouts are inhibited); it is also greater for tubersstored under dry conditions than for those under moist conditions.The results are interpreted in terms of a correlative inhibitior,continuously produced under the influence of growing buds andcontinuously destroyed as it moves up into all stems. It issuggested that in the terminal bud of the stem there is a sensitiveregion which controls the growth of the other stem tissues andon which the inhibitor acts. It stems longer than the criticallength the inhibitor is possibly inactivated before it reachesthis sensitive tissue; in shorter stems the inhibitor acts onthe tissue and hence inhibits stem elongation.     

Translucent Tissue Defects in Solanum tuberosum L: I. Alterations in Amyloplast Membrane Integrity, Enzyme Activities, Sugars, and Starch Content

Kennebec (cv) potatoes randomly developed translucent areas in their centrally located pith-parenchymal cells during storage. These defective areas were characterized as having reduced starch concentration and increased levels of free sugars (i. e. sucrose and glucose) and inorganic phosphate. Electron micrographs of potato tubers stored at 10° ± 1°C for 8 months indicated that the amyloplast membrane was still intact and continuous around starch granules in both normal and prematurely sweetened tissue. The total activities of phosphorylase and sucrose-6-P synthase were elevated 5.4- and 3.8-fold, respectively, in the defective tissue compared to healthy nonsweetened tubers while there were no significant differences in the levels of sucrose synthase, UDPglucose pyrophosphorylase, invertase, or α-amylase. Total and specific activities of acid phosphatase were only slightly elevated in translucent tissue but their increase was significant (P < 0.05, t test) over that seen in healthy tubers. The premature sweetening in storage may have been indirectly triggered by moisture and heat stress experienced during development. Translucency eventually led to physical deterioration of the tissue.