Effect of gibberellin and auxin on the synthesis of abscisic acid and ethylyne in buds of dormant and sprouting potato tuber

Gibberellic and beta-indolylacetic acids at concentrations of 10(-7)-10(-5) M were shown to change the hormonal status and duration of dormancy in potato tubers. Gibberellic acid shortened the dormancy and decreased the contents of abscisic acid and ethylene in apical meristems. beta-Indolylacetic acid elongated the dormancy, decreased abscisic acid production, but caused a more than tenfold increase in the production of ethylene by apical tissues. The data suggest that beta-indolylacetic acid and ethylene, as well as gibberellic and abscisic acids, are involved in the regulation of dormancy in potato tubers.     

Effects of gibberellin and auxin on the synthesis of abscisic acid and ethylene in buds of dormant and sprouting potato tubers

Gibberellic and β-indolylacetic acids at concentrations of 10⁻⁷-10⁻⁵ M were shown to change the hormonal status and duration of true dormancy in potato tubers. Gibberellic acid shortened the true dormancy and decreased the contents of abscisic acid and ethylene in the apical meristem. β-Indolylacetic acid elongated the true dormancy and decreased abscisic acid production, but caused a more than tenfold increase in the production of ethylene by apical tissues. The data suggest that β-indolylacetic acid and ethylene, as well as gibberellic and abscisic acids, are involved in the regulation of true dormancy in potato tubers.     

Increased mitochondrial DNA and RNA polymerase activity in ethylene-treated potato tubers

A purified mitochondrial fraction was isolated from potato (Solanum tuberosum L.) tubers respiring normally at 23°C or at an accelerated rate in response to treatment with ethylene (10 microliters per liter).

A pronounced increase in various mitochondrial enzymic activities was observed in response to exposure of the whole tubers to ethylene. Cytochrome c oxidase activity increased more than 50%, DNA polymerase activity increased about 2-fold, and RNA polymerase activity increased 2.5-fold. Moreover, DNA or RNA polymerase activities of mitochondria isolated from tubers not treated with ethylene were not affected by ethylene treatment in vitro. Respiratory control ratios decreased from 2.84 to 1.50 with increasing periods of ethylene treatment from 0 to 15 hours. None of these changes were observed in untreated tubers. It is concluded that the stimulation of respiration by ethylene in potato tubers is accompanied in vivo by an enhancement of mitochondrial enzymic activity of both membrane-associated enzymes which participate in the mitochondrial oxidative electron transport as well as soluble enzymes which are not directly involved in respiration.

     

Effects of ethylene on potato tuber respiration

Treatment of potato tubers (Solanum tuberosum L.) with ethylene gas causes a rapid rise in their respiration rate, reaching 5 to 10 times the rate of untreated tubers over 30 hours of treatment and then falling slowly. The response shows a lag of 8 hours, and more than 24 hours of exposure is required for maximum effect; the temperature optimum is near 25 C. In sensitivity to low concentrations and dependence on temperature, the phenomenon is similar to the effect of ethylene on the respiration of climacteric and nonclimacteric fruits. Treated potato tubers returned to air recover their sensitivity to ethylene more slowly than do nonclimacteric fruits (e.g., mature green oranges). It is proposed that the respiratory rise characteristic of ripening in climacteric fruits and of the wound response in plant tissues is induced by a rise in endogenous tissue ethylene.     

Effects of Oxygen and Respiratory Inhibitors on Induction and Release of Dormancy in Aerial Tubers of Begonia evansiana

Effects of O₂ and some respiratory inhibitors on the induction and release of bud dormancy were examined with the aerial tubers of different ages of Begonia evansiana Andr. Oxygen was needed not only for tuber sprouting but also during the chilling process at 2 to 5 C to break tuber dormancy. If the mature tubers were exposed to blue light during the chilling period, their dormancy was strikingly released even by the chilling given under an O₂ concentration as low as 3%. Blue light pretreatment promoted photo-sprouting of immature tubers only when given under lower O₂ concentrations. On the other hand, red light became effective in inducing dormancy in the immature tubers and in prolonging dormancy in the mature tubers as O₂ tension was increased. This was also the case with the induction of dormancy in the immature tubers by exposing them to a lower temperature (17 C) in the dark. The development of dormancy was suppressed by 2,4-dinitrophenol, p-nitrophenol, and sodium azide.     

Increased disease resistance and enzyme activity induced by ethylene and ethylene production of black rot infected sweet potato tissue

Exposure of root tissue from a susceptible variety of sweet potato to low concentrations of ethylene induced a resistance to infection by Ceratocystis fimbriata and an increase in the activity of peroxidase and polyphenoloxidase in the tissue. Susceptible tissue that was inoculated with a pathogenic strain of C. fimbriata or a nonpathogenic strain that can induce resistance liberated more ethylene into closed chambers than tissue inoculated with strains that did not induce resistance. It is suggested that ethylene may be a stimulus that diffuses from infected areas into adjoining tissue to initiate metabolic changes which may lead to disease resistance. Polyphenol oxidase but not peroxidase activity was increased in slices of potato tubers and parsnip roots treated with ethylene. The activity of these enzymes in root tissue of carrot, radish or turnip was not altered by ethylene treatment.     

Bactericidal activity of some plant essential oils against Ralstonia solanacearum infection

Potato plants and their tubers in Egypt are affected by one of the most renowned soil-borne pathogen, Ralstonia solanacearum, that caused brown rot in potato tubers and wilt in plants. There is no efficient therapeutic bactericide so; control of bacterial wilt is very rough.The study investigated three different concentrations of seven essential plant oils under in vitro and in vivo conditions as a result of their effects on Ralstonia solanacearum growth and their possibility use as potato seed pieces dressing for controlling bacterial wilt disease incidence. In vitro, anise oil at the three tested different concentrations (0.04, 0.07, and 0.14% vol/vol) was the most effective one inhibiting the growth of T4 and W9 isolates of Ralstonia solanacearum then pursued by thyme, lemongrass, and clove oils. On the other hand, rocket oil at the tested concentration was the least effective one followed by fennel oil. However, wheat germ oil was not completely effective. In vivo, experiment revealed that anise oil at the three concentrations significantly reduced disease incidence and severity in sponta and hermes potato cultivars and their effect was associated with increase of peroxidase, polyphenoloxidase, phenols and the foliar fresh weight of treated plants as well as the weight of tubers/plant followed by thyme and lemongrass oils compared to the infected untreated control.Morphological differences in bacterial cell structure have been observed using a transmission electron microscope (TEM). Anise oil at higher concentration caused of cell wall rupture and degraded cellular components.     

Detection of Potato Viruses Y and A in Tubers by Enzyme-Linked Immunosorbent Assay after Natural and Artificial Break of Dormancy

The effects of natural and artificial break of dormancy on the detection of potato viruses Y (PVY) and A (PVA) in tubers of field-grown potato cultivars with primary and secondary infections were studied by enzyme-linked immunosorbent assay (ELISA). Both viruses were at low concentration and unevenly distributed in dormant -tubers. Four to six weeks after treatment with Rindite, maximum concentrations of PVY and PVA were detected at both tuber ends with generally higher values at the rose end than at the heel end. Slower and smaller virus increase and a retarded and/or limited virus translocation were observed in treated tubers of resistant cultivars. Consequently, detectability of PVY and PVA was higher in tubers of susceptible cultivars than in those of the resistant ones. Detection of both viruses was very difficult and unreliable in tubers after natural break of dormancy. The very low concentration of PVY and PVA in dormant tubers and their drastic multiplication in Rindite- treated tubers appear to be characteristic of potyviruses and are unique among the major potato viruses.     

Effect of ethylene on the endogenous cytokinin and gibberellin levels in tuberizing potatoes

High concentrations of 2-chloroethylphosphonic acid inhibited tuberization on aged potato tubers (Solanum tuberosum) that had been predisposed to the little tuber disorder. As a result of this treatment sprouts developed which contained relatively high levels of endogenous gibberellins and which elongated normally. The endogenous cytokinin levels in the different treatments did not change appreciably. It is suggested that tuberization is prevented by ethylene either as a direct inhibition of cell division or that it prevents the endogenous cytokinins from functioning. Irrespective of the mode of action of ethylene, cell division apparently is the primary process affected, the result being that storage tissue required for the accumulation of starch is not formed.     

Comparison between Aging of Slices and Ethylene Treatment of Whole White Potato Tubers

Cyanide-resistant O(2) consumption can be stimulated by either treating whole white potato tubers (Norchip) with ethylene, in the presence of 100% O(2), or aging slices obtained from untreated potato tubers. A comparison of alternative pathway activity elicited by either treatment was undertaken. The proportion of electrons flowing through the alternative path in the presence of intermediate concentrations of KCN and at various concentrations of salicylhydroxamic acid was identical in both cases. However, the respiration of slices from ethylene-treated tubers was in every case stimulated by KCN, whereas the aged slices never exhibited this phenomenon. Furthermore, the metabolism of d-[U-(14)C]glucose was several hundred times greater in aged slices than in fresh slices from C(2)H(4)-treated tubers. These results, along with the respiratory kinetics of aged slices from ethylene-treated tubers, suggest that aged slices and fresh slices from ethylene-treated tubers are biochemically dissimilar.     

Involvement of endogenous gibberellins in potato tuber dormancy and early sprout growth: a critical assessment

The role of endogenous gibberellins (GAs) in the regulation of potato (Solanum tuberosum) tuber dormancy was examined by determining: 1. changes in endogenous GA levels during natural dormancy progression, 2. the effects of GA biosynthesis inhibitors on tuber dormancy duration and 3. the dormancy status and tuber GA levels in a dwarf mutant of potato. The tubers (cv. Russet Burbank) used in these studies were still completely dormant after 98 days of storage. Between 98 and 134 days of storage, dormancy began to end and tubers exhibited limited (< 2 mm) sprout growth. Tuber dormancy weakened with further storage and tubers exhibited greater rates of sprout growth after 187 days of storage. Tubers stored for 212 days or longer were completely non-dormant and exhibited vigorous sprout growth. Immediately after harvest, the endogenous contents of GA19, GA20, and GA1 were relatively high (0.48-0.62 ng g fresh weight(-1)). The content of these GAs declined between 33 and 93 days of storage. Internal levels of GA19, GA20, and GA, rose slightly between 93 and 135 days of storage reaching levels comparable to those found in highly dormant tubers immediately after harvest. Levels of GA19, GA20, and GA1 continued to increase as sprout growth became more vigorous. Neither GA4 nor GA8 was detected in any tuber sample regardless of dormancy status. Dormant tubers exhibited a time-dependent increase in apparent GA sensitivity. Freshly harvested tubers were completely insensitive to exogenous GAs. As postharvest storage continued, exogenous GAs promoted premature dormancy release with GA1 and GA20 eliciting the greatest response. Injection of up to 5 microg tuber(-1) of kaurene, GA12, GA19 or GA8 had no effect on dormancy release. Sprout growth from non-dormant tubers was also promoted by exogenous GA in the following sequence of activity: GA1 = GA20 > GA19. Kaurene, GA12, and GA8 were inactive. Continuous exposure of developing tubers to inhibitors of GA biosynthesis (AMO-1618, ancymidol, or tetcyclasis) did not extend tuber dormancy but rather hastened dormancy release. Comparison of tuber dormancy and GA1 content in tubers of a wild-type and dwarf mutant of S. tuberosum ssp. andigena revealed a near-identical pattern of dormancy progression in spite of the absence of detectable levels of GA1 in tubers of the dwarf sibling at any time during dormancy progression. Collectively, these results do not support a role for endogenous GA in potato tuber dormancy release but are consistent with a role for GAs in the regulation of subsequent sprout growth.     

Changes in the levels of free IAA and cytokinins in potato tubers during dormancy and sprouting

Changes in the levels of free indol-3-ylacetic acid (IAA) and free cytokinins were determined in the course of dormancy and sprouting period in potato tubers(Solanum tuberosum L., cv. Nevskii) stored at 4 °C. The same analyses were performed in potato tubers after Ethrel application, which prolongs dormancy. No significant changes were found in free IAA level during dormancy followed by a rapid decrease during sprouting. After Ethrel application a significant lower IAA level was found 3 weeks after application, but further on no changes in free IAA level between treated and non-treated tubers were detected. Cytokinin level was relatively low and constant till sprouting and increases then by about 55 %, mainly due to an increase in the level of zeatin riboside and isopentenyladenosine. Ethrel application decreased cytokinin level during dormancy slightly, but postpones the increase coupled with sprouting by about 1 month. Thus, IAA does not seem to have a significant effect on tuber dormancy, while cytokinins are probably necessary for sprouting initiation.     

Seasonal changes of the different components of the inhibitor β complex in potato tubers

Seasonal changes of the inhibiting substances in the inhibitor β complex were studied in diethyl ether and methanol extracts of peelings from potato tubers, cv. Majestic, prepared during dormancy and cessation of dormancy. In both extracts the acidic ether soluble substances were investigated. From the methanol extracts also non-ether soluble but butanol soluble substances were studied. At each extraction time experiments were performed to determine the stage of rest in the tubers. Four different inhibitory zones were found with the Avena straight growth test of thin layer chromatograms. One of these was probably an artefact formed during chromatography. The level of all these substances decreased when rest ceased. – Thin layer chromatograms of the butanol fraction of methanol extracts, which should have contained the bound forms of the inhibitors, showed the same inhibitory zones as the ether fractions. This probably resulted from hydrolysis of the bound inhibitors when the extracts were chromatographed in an alkaline solvent system during purification.     

Effects of single and mixed inoculation with two arbuscular mycorrhizal fungi in two different levels of phosphorus supply on β-carotene concentrations in sweet potato (Ipomoea batatas L.) tubers

Aims

This study aimed to determine the effect of arbuscular mycorrhizal (AM) fungi and phosphorus (P) supply levels on β-carotene concentrations in sweet potato (Ipomoea batatas L.) tubers.

Methods

Two commercial AM fungal isolates of Glomus intraradices (IFP Glintra) and Glomus mosseae (IFP Glm) which differ in their life cycles were used. Sweet potato plants were grown in a horizontal split-root system that consisted of two root compartments. A root-free fungal compartment that allowed the quantification of mycelial development was inserted into each root compartment. The two root compartments were inoculated either with the same or with different AM isolates, or remained free of mycorrhizal propagules. Each fungal treatment was carried out in two P supply levels.

Results

In the low P supply level, mycorrhizal colonization significantly increased β-carotene concentrations in sweet potato tubers compared with the non-mycorrhizal plants. Glomus intraradices appeared to be more efficient in increasing β-carotene concentrations than G. mosseae. Dual inoculation of the root system with the two mycorrhizal fungi did not result in a higher increase in tuber β-carotene concentrations than inoculation with the single isolates. Improved P nutrition led to higher plant tuber biomass but was not associated with increased β-carotene concentrations.

Conclusions

The results indicate a remarkable potential of mycorrhizal fungi to improve β-carotene concentrations in sweet potato tubers in low P fertilized soils. These results also suggest that β-carotene metabolism in sweet potato tubers might be specifically activated by root mycorrhizal colonization.     

Quantitative detection of induced systemic resistance genes of potato roots upon ethylene treatment and cyst nematode,Globodera rostochiensis,infection during plant–nematode interactions

Potato cyst nematodes caused by Globodera rostochiensis, are quarantine-restricted pests causing significant yield losses to potato growers. The phytohormone ethylene play significant roles in various plant-pathogen interactions, however, the molecular knowledge of how ethylene influences potato–nematode interaction is still lacking. Precise detection of potato-induced genes is essential for recognizing plant-induced systemic resistance (ISR). Candidate genes or PR- proteins with putative functions in modulating the response to potato cyst nematode stress were selected and functionally characterized. Using real-time polymerase chain reaction (RT-PCR), we measured the quantified expression of four pathogenesis-related (PR) genes, PR2, PR3, peroxidase, and polyphenol oxidase. The activation of these genes is intermediate during the ISR signaling in the root tissues. Using different ethylene concentrations could detect and induce defense genes in infected potato roots compared to the control treatment. The observed differences in the gene expression of treated infected plants are because of different concentrations of ethylene treatment and pathogenicity. Besides, the overexpressed or suppressed of defense- related genes during developmental stages and pathogen infection. We concluded that ethylene treatments positively affected potato defensive genes expression levels against cyst nematode infection. The results emphasize the necessity of studying molecular signaling pathways controlling biotic stress responses. Understanding such mechanisms will be critical for the development of broad-spectrum and stress-tolerant crops in the future.     

Changes in histone H3 and H4 multi-acetylation during natural and forced dormancy break in potato tubers

The effects of post-harvest storage and dormancy progression on histone acetylation patterns were examined in potato ( Solanum tuberosum L. cv. Russet Burbank) tubers. Storage of field-grown tubers at 3°C in the dark resulted in the progressive loss of tuber meristem dormancy, defined as measurable growth after transfer to 20°C for 7 days. Dormancy emergence was concomitant with sustained increases in histone H3.1 and H3.2 multi-acetylation, and with transient increases in H4 multi-acetylation that peaked 4–5 months post-harvest. Treatment of dormant tubers with bromoethane (BE) resulted in rapid loss of dormancy over 9 days. Similar to cold-stored field-grown tubers, dormancy break in BE-treated tubers occurred at the same time as transient rises in H4 and H3.1/3.2 multi-acetylation, peaking at days 1 and 4, respectively. BE treatment also resulted in small increases in RNA synthesis at day 6, and a three-fold, sustained activation of DNA synthesis thereafter. A defined sequence of epigenetic events, beginning with previously characterized transient cytosine demethylation, followed by increased H3 and H4 histone acetylation and ultimately, tuber meristem re-activation, may thus exist in potatoes during dormancy exit and resumption of rapid growth.     

Control of potato tuber dormancy and sprouting by expression of sense and antisense genes of pyrophosphatase in potato

Inorganic pyrophosphate (PPi) is an enzyme involved in sugar metabolism in potato tubers. In our previous study, we isolated an inorganic pyrophosphatase (PPase) gene from potato and obtained the transgenic potato plants transformed with the sense and antisense PPase genes respectively. In the present experiment, the physiological indexes, tuber dormancy, and sprouting characteristics of the transgenic potatoes were analyzed and evaluated. The result showed that the PPase activity and the inorganic phosphate content of tubers were lower in the antisense transgenic plant lines but were higher in the sense transgenic plant lines, compared with wild-type tubers. Soluble sugars, such as glucose, fructose and sucrose increased in transgenic plants that had overexpression of the sense PPase gene, but decreased in the antisense transgenic plant lines, compared with wild-type tubers. Tuber sprouting time of the antisense transgenic plants were delayed for 2 and 3 weeks and reached the 100 % sprouting rate only after 14 and 16 weeks storage compared with the wild-type when tubers are stored under 25 and 4 °C, respectively. In contrast, tuber sprouting time of the sense transgenic plants was earlier by approximately 2 weeks than that of wild-type tubers under these storage temperatures.     

Quantitative detection of induced systemic resistance genes of potato roots upon ethylene treatment and cyst nematode,Globodera rostochiensis,infection during plant–nematode interactions

Potato cyst nematodes caused by Globodera rostochiensis, are quarantine-restricted pests causing significant yield losses to potato growers. The phytohormone ethylene play significant roles in various plant-pathogen interactions, however, the molecular knowledge of how ethylene influences potato–nematode interaction is still lacking. Precise detection of potato-induced genes is essential for recognizing plant-induced systemic resistance (ISR). Candidate genes or PR- proteins with putative functions in modulating the response to potato cyst nematode stress were selected and functionally characterized. Using real-time polymerase chain reaction (RT-PCR), we measured the quantified expression of four pathogenesis-related (PR) genes, PR2, PR3, peroxidase, and polyphenol oxidase. The activation of these genes is intermediate during the ISR signaling in the root tissues. Using different ethylene concentrations could detect and induce defense genes in infected potato roots compared to the control treatment. The observed differences in the gene expression of treated infected plants are because of different concentrations of ethylene treatment and pathogenicity. Besides, the overexpressed or suppressed of defense- related genes during developmental stages and pathogen infection. We concluded that ethylene treatments positively affected potato defensive genes expression levels against cyst nematode infection. The results emphasize the necessity of studying molecular signaling pathways controlling biotic stress responses. Understanding such mechanisms will be critical for the development of broad-spectrum and stress-tolerant crops in the future.