Beta Vulgaris Var Research Articles

Efficacy of Chinaberry tree (Meliaceae) aqueous extracts and certain insecticides against the pea leafminer (Diptera: Agromyzidae)

Aqueous extracts of fruits and leaves of the Chinaberry tree, Melia azedarach L. were tested for their efficacy versus other biotic and synthetic insecticides against the pea leafminer, Liriomyza huidobrensis (Blanchard). The study included field experiments on naturally infested swiss chard, Beta vulgaris var. Cicla L., and greenhouse experiments on artificially infested cucumber, Cucumis sativus L. that were conducted in 1995–96. The other treatments included azadirachtin (0·25%), ultrafine mineral oil, abamectin, cyromazine, imidacloprid, pyrazophos and control. Results of field experiments indicated that Melia fruit extract and the other insecticides significantly lowered the number of larvae per swiss chard plant as compared to the control, at 5 days sampling after second spray or 15 days after first spray, when two consecutive sprays were performed. However, at 10 days after second spray, the fruit extract did not differ significantly from the control, but it was comparable in its effect to the insecticides, except abamectin and cyromazine. In greenhouse experiments, the pea leafminer larvae were found at higher densities on cucumber leaves located at the lower plant part (10–60 cm) compared to other leaf positions. The Melia fruit extract and the other pesticides significantly decreased the number of live larvae per cucumber leaf compared to the control, 10 days after each spray. The fruit extract, abamectin, cyromazine, imidacloprid and pyrazophos lowered the leafminer population significantly compared to the control, throughout the period of the experiments. However, the fruit extract was significantly less effective than these insecticides at the final count, 20 days after second spray. Abamectin and cyromazine consistently showed a significant decrease in number of larvae, in both field and greenhouse experiments. At certain periods of the experiments, Melia extracts were comparable in their efficacy to the tested commercial biorational and synthetic pesticides. Thus, they have a good potential to be used in the management of the pea leafminer. This is the first report for use of M. azedarach against L. huidobrensis.

Effect of Blanching and Drying Methods on β -Carotene, Ascorbic acid and Chlorophyll Retention of Leafy Vegetables

Leaves of savoy beet (Beta vulgaris var bengalensis), amaranth (Amaranthus tricolor) and fenugreek (Trigonella foenum graecum) were subjected to different blanching and drying treatments to establish the retention of β -carotene, ascorbic acid and chlorophyll. The vegetables were blanched at 95±3 °C in (i) water, (ii) water followed by potassium metabisulphite (KMS) dip, (iii) salt solution, (iv) salt solution followed by KMS dip, and (v) mixture of sodium bicarbonate, magnesium oxide and KMS and dried in (a) sun, (b) shade, (c) solar drier, (d) cabinet drier, and (e) low temperature drier. Method (ii) was found most suitable for blanching and selected for subsequent drying and method (e) had least drastic effect on β -carotene, ascorbic acid and chlorophyll content of the processed product.

The effect of red beet (Beta vulgaris var. rubra) fiber on alimentary hypercholesterolemia and chemically induced colon carcinogenesis in rats.

The effect of diet supplemented with 5% and 15% cellulose or with 15% fiber isolated from red beet (Beta vulgaris var. rubra) on the development of alimentary hypercholesterolemia and chemically induced colon carcinoma was studied in male Wistar rats. Hypercholesterolemia was induced by a diet containing 0.3% of cholesterol and colon carcinoma was induced by treatment with dimethylhydrazine (20 mg/kg, 12 doses applied s.c. in one-week intervals). Fibrous matter isolated from red beet contained 89% fiber, of which 9% was in water soluble form. Animals were killed 14 weeks after the application of dimethylhydrazine (i.e. 26 weeks after starting on the diets). Red beet fiber diet (and not the increased cellulose intake) caused a reduction of serum cholesterol and triacylglycerol levels (by 30 and 40%, respectively) and a significant increase in the fraction of cholesterol carried in HDL. This diet induced also a significant decrease (almost by 30%) of cholesterol content in aorta. Higher cellulose content in the diet and even more so the administration of red beet fiber caused a significant reduction of conjugated dienes content in plasma, erythrocytes and in liver. Also observed were increases in the activities of superoxide dismutase and catalase in erythrocytes and in colon and activities of glutathione peroxidase and glutathione-S-transferase in liver. The presence of both higher cellulose content and red beet fiber in the diet significantly reduced the incidence of precancerous lesions--aberrant crypt foci--in the colon. The diet containing red beet fiber did not affect significantly the incidence of colon tumours although the number of animals bearing tumours was reduced by 30%.

Transfer of 238U, 226Ra and 210Pb from slag-contaminated soils to vegetables under field conditions

The uptake of 238U, 226Ra and 210Pb by beans (dwarf bean Modus), kohlrabi ( brassica oleracea var. gongylodes), mangold ( beta vulgaris var. macrorhiza), lettuce (American gathering brown), carrots (Rotin, Sperlings's), celery, and radish from a control soil and from soil/slag mixtures was investigated in field experiments. The observed concentration ratios (CR) suggest that 226Ra in the slag/soil mixtures is less available for root uptake than 226Ra in the control soil. This is especially evident for beans, mangold and carrots, and less conspicuous for lettuce. A similar behaviour was observed for the uptake of 238U by celery and radish, but not in the case of lettuce. In this latter case, the CR was even higher when this vegetable was grown on a coal slag contaminated soil when compared to the pure control soil. It is shown that the root uptake of a natural radionuclide from a slag contaminated soil in excess to that from an uncontaminated soil can be characterized best by defining a fractional concentration ratio (CR fr). In this way, all above results are quantified with respect to the root uptake of the radionuclides from the slag fraction in the soils. Because CR fr is not affected by atmospheric contributions to the plant activity, this quantity can be also used to obtain the root uptake of 210Pb by vegetation which results only from the slag fraction in the soil. By comparing the CR fr-values observed for different radionuclides, it is shown that e.g. the amount of 210Pb root-uptake by lettuce from the slags is similar to that of 238U and 226Ra.

Characterization of six bacteriophages of serratia liquefaciens CP6 isolated from the sugar beet phytosphere

Six phages (PhiCP6-1 to PhiCP6-6) that are commonly found in the phytosphere of sugar beet (Beta vulgaris var. Amethyst) were investigated, and their relative impacts on their host (Serratia liquefaciens CP6) were compared. There were fundamental differences between the two most abundant predators of CP6 (PhiCP6-1 and PhiCP6-4). Like PhiCP6-2 and PhiCP6-5, PhiCP6-1 belonged to the family Siphoviridae, while PhiCP6-4 exhibited the morphology of the family Podoviridae. The other phages were members of the family Myoviridae. DNA-DNA cross-hybridization revealed that PhiCP6-1 and PhiCP6-4 had little common DNA, although all of the other phages exhibited some genetic similarity. Like PhiCP6-2, PhiCP6-3, and PhiCP6-5, PhiCP6-1 was capable of forming a lysogenic association with its host, while PhiCP6-4 and PhiCP6-6 appeared to be entirely virulent. Single-step growth curve experiments revealed that PhiCP6-4 had a much shorter latent period and a smaller burst size than PhiCP6-1. Also, PhiCP6-1 could transduce a number of host chromosomal markers with transfer frequencies of 2.9 x 10(-9) to 3.9 x 10(-7), whereas PhiCP6-4 could not transduce S. liquefaciens CP6 genes. When viewed in the context of the strikingly different temporal niches of these phages, our data provide an insight into how bacteriophage interactions with their hosts might reflect the natural ecology of bacteriophages. Our data also illustrate how the potential for gene transfer changes over time in an environment that supports several different phages.

In situ population dynamics of bacterial viruses in a terrestrial environment

Predation by bacteriophages is thought to control bacterial numbers and facilitate gene transfer among bacteria in the biosphere. A thorough understanding of phage population dynamics is therefore necessary if their significance in natural environments is to be fully appreciated. Here we describe the in situ population dynamics of three separate phage populations predating on separate bacterial species, living on the surface of field-grown sugar beet (Beta vulgaris var. Amethyst), as recorded over a 9-month period. The distributions of the three phage populations were different and fluctuated temporally in 1996 (peak density, approximately 10(3) PFU g-1). One of these populations, predating on the indigenous phytosphere bacterium Serratia liquefaciens CP6, consisted of six genetically distinct DNA phages that varied in relative abundance to the extent that an apparent temporal succession was observed between the two most abundant phages, PhiCP6-1 and PhiCP6-4.

The dispersal and establishment of pseudomonad populations in the phyllosphere of sugar beet by phytophagous caterpillars

The role of phytophagous insects in the dispersal of phyllosphere bacterial populations has been investigated. Following seed inoculation, a leaf colonising population of Pseudomonas fluorescens SBW25EeZY6KX ( lacZY and aph- xylE) was established in field grown sugar beet ( Beta vulgaris var. amethyst). Third instar, Mamestra brassicae (Lepidoptera: Noctuidae) larvae were placed onto the emerging leaves of mature plants and the dispersal of the marked strain (ca. 5×10 5 cfu/g leaf) to untreated plants monitored. Forty-two days after caterpillar introduction, approximately twenty days after pupation of the larvae, an established population of transferred bacteria was detected at densities similar to those determined for seed inoculated plants of the same age. Under appropriate conditions phylloplane colonising pseudomonads can be dispersed by invertebrates and establish viable populations on the leaves of recipient plants.

Ferulic Acid Dehydrodimers in the Cell Walls ofBeta vulgaris and their Possible Role in Texture

Sugarbeet, a form of Beta vulgaris var vulgaris, fails to soften completely after heating at 100°C for several hours. This is due to thermal stability of the cell–wall polymers involved in cell–cell adhesion. In contrast, beetroot softens within 25–30 min due to a relatively rapid increase in the ability of the cells to separate. Information concerning the cell–wall polymers responsible for cell–cell adhesion was obtained by subjecting sugarbeet and beetroot tissues to a range of chemical and biochemical treatments designed to cleave cell–wall chemical bonds selectively. Treatment of sugarbeet tissues with chelating agents, weak base (Na2CO3, 0·05 M) or a purified, specific endoxylanase did not facilitate vortex-induced cell separation. However, this could be induced after extraction in dilute, cold alkali (0·05–0·1 M KOH) or dilute, hot acid (0·1 M TFA, 100°C). Tissues from beetroot behaved similarly. Furthermore, the cell walls of sugarbeet and beetroot were similar in yield and neutral carbohydrate composition; the cell–wall-galacturonic acid content of beetroot was 50% higher as compared with sugarbeet. They were also rich in ferulic acid (FA) and its derivatives (6–7 mg g-1 CWM), and exhibited pH-dependent autofluorescence which disappeared during alkali-induced cell separation. In sugarbeet, over 20% of the FA was in dimer form. In beetroot, however, the value was only 10%. The main FA dimers were 8-O-4′DiFA and 8,5′DiFA (benzofuran form). The results indicate that the degree of thermal stability of cell–cell adhesion and, therefore, texture in Beta vulgaris tissues is related to the degree of FA-cross linking between pectic polysaccharides. © 1997 SCI.

The acquisition of indigenous plasmids by a genetically marked pseudomonad population colonizing the sugar beet phytosphere is related to local environmental conditions

The transfer of naturally occurring conjugative plasmids from the indigenous microflora to a genetically modified population of bacteria colonizing the phytospheres of plants has been observed. The marked strain (Pseudomonas fluorescens SBW25EeZY6KX) was introduced as a seed dressing to sugar beets (Beta vulgaris var. Amethyst) as part of a field experiment to assess the ecology and genetic stability of deliberately released bacterial inocula. The sustained populations of the introduced strain, which colonized the phytosphere, were assessed throughout the growing season for the acquisition of plasmids conferring mercury resistance (Hg(supr)). Transconjugants were isolated only from root and leaf samples collected within a narrow temporal window coincident with the midseason maturation of the crop. Conjugal-transfer events were recorded during this defined period in two separate field release experiments conducted over consecutive years. On one occasion seven of nine individual plants sampled supported transconjugant P. fluorescens SBW25EeZY6KX, demonstrating that conjugative gene transfer between bacterial populations in the phytosphere may be a common event under specific environmental conditions. The plasmids acquired in situ by the colonizing inocula were identified as natural variants of restriction digest pattern group I, III, or IV plasmids from five genetically distinct groups of large, conjugative mercury resistance plasmids known to persist in the phytospheres of sugar beets at the field site. These data demonstrate not only that gene transfer may be a common event but also that the genetic and phenotypic stability of inocula released into the natural environment cannot be predicted.

Betaxanthin pattern of hairy roots from Beta vulgaris var. lutea and its alteration by feeding of amino acids

Betaxanthins from hairy root cultures of Beta vulgaris var. lutea showed two predominating substances, portulaxanthin II and vulgaxanthin I, and several minor components in HPLC profiles. The presence of muscaaurin VII, indicaxanthin, dopaxanthin, vulgaxanthin II, III and IV were suggested, the latter two as new natural compounds. Administration of nine l-amino acids to individual hairy root strains led to an increase in concentration or the appearance of one betaxanthin in each case. These betaxanthins structurally corresponded to the substances applied, except of that from glutamic acid. It was vulgaxanthin I instead of vulgaxanthin II and might be formed due to the function of glutamine synthetase. Also, the d-isomers of amino acids were incorporated into corresponding betaxanthins not only by hairy root cultures but also by seedlings of B. vulgaris var. lutea. The feeding experiments substantiate arguments for a spontaneous condensation of betalamic acid with an amino acid or amine in the course of betaxanthin biosynthesis.

Dietary fiber and pectin fractions of Beta vulgaris var. conditiva

The alcohol-insoluble substance (AIS) from red beet (Beta vulgaris var. conditiva Alef.) (3.31% of the edible substance) was extracted sequentially with water, ammonium oxalate, 0.05 N HCl and 0.05 N NaOH. Accordingly 3.93 g, about 0.8 g, 2.96 g resp. 3.80 g galacturonan/100 g AIS were extracted with this procedure. These pectin extracts were purified as Cu2 +-salts and fractionated into a water-soluble and a water-insoluble part. The composition of neutral monosaccharide units was estimated in the fractions. Gal, Ara and Glc dominated; Xyl, Rha and Man were also present but in smaller amounts. A higher GalA content was found in the soluble fractions (with the exception of the alkali extract). Pectins from red beet are middle- or low-esterified and partially acetylated. The composition of the AIS and of the residue after pectin extraction (RE) was determined (14.6 resp. 9.5% pectin; 10,6 resp. 17.6% protein; 58.7 resp. 64.9% total polysaccharides). In the AIS 23.3% soluble and 54.7% insoluble dietary fiber were estimated, whereas in RE 15.3 resp. 54.7% were found (enzymatic method). Following dietary fiber fractions were determined by the detergent method for both preparations: 39.0 resp. 52.7% NDF; 6.3 resp. 4.5% NDF filtrate; 23.6 resp. 41.8% ADF; 1.2 resp. 1.8% lignin. The water binding capacity decreased from 19.85 g water (AIS) to 11. 53 g water (RE) related to 1 g AUS. From these just 50% were found in the NDF fractions and about 13% in the ADF fractions. Alterations of the grown biological structures during pectin extraction and dietary fiber analysis (detergent method) were investigated by scanning electron microscopy.

Protection Afforded by Crude Spinach-Beet Leaf Extract and Equivalent Amounts of Chlorophyll and Chlorophyllin Against Clastogenic Effects of Potassium Dichromate in Mice In Vivo

The comparative efficacy of crude extract of spinach-beet leaves (Beta vulgaris var. benghalensis Hort. Chenopodiaceae) and equivalent amounts of chlorophyll and chlorophyllin in reducing clastogenic activity of a hexavalent chromium compound, potassium dichromate (K 2 Cr 2 O 7 ), was tested in mouse bone marrow cells in vivo. The endpoints monitored were chromosomal aberrations (CA). Mice were fed the crude leaf extract by gavage for 7 consecutive days and then treated with the metallic salt on day 7. In separate sets, chlorophyll extracted from the spinach-beet leaves and a synthetic compound chlorophyllin were administered simultaneously with, before, or after exposure to the chromium compound. Chromosomes were studied from bone marrow cells 24 h after the treatment. Crude leaf extract and chlorophyllin did not induce chromosomal aberrations when given alone. Priming with the crude extract reduced the clastogenic effects of potassium dichromate to the control level. Similar protection was afforded by chlorophyllin when given simultaneously. Chlorophyll, on the other hand, induced significantly higher number of chromosomal aberrations when given alone as compared to distilled water and did not reduce the clastogenic activity of the metal when administered in combination.

Survival, Colonization and Dispersal of Genetically Modified Pseudomonas fluorescens SBW25 in the Phytosphere of Field Grown Sugar Beet

A genetically modified microorganism (GMM), Pseudomonas fluorescens SBW25 (lacZY and kanr-xylE), derived from a strain taken from the leaves of mature sugar beet (Beta vulgaris var. Amethyst), was released as a seed inoculum (ca 1×107 cfu/seed) to field-grown sugar beet in 1993 and 1994. The inoculum successfully colonized the roots and leaves of developing plants and survived in the phytosphere throughout the growing season, (270 days post release). Variation in the population dynamics of the GMM colonizing the immature leaf habitat was observed over two consecutive seasons. In 1993, the GMM represented a minor component of the pseudomonad community in emerging seedlings (<6%), (4×104 cfu g−1, coefficient of variation, CV=7%) whereas, in 1994, plants of similar size were colonized by significantly greater numbers of the GMM (1.1 × 106 cfu g−1, CV=10%) (81% of the total pseudomon-ads) reaching maximum densities 102 days after release. Limited dispersal of the GMM from sugar beet to other plants species was recorded. Although GMMs could not be detected in soil (<1 cfu g−1) or on overwintering plant tissue (<20 cfu g−1) GMMs persisted and colonised plants grown the following season. No transfer of the marker genes to other indigenous microorganisms was recorded.

Anisotropic swelling of cell walls of sugar beet tissue: Influence of ion‐exchange and sucrose

AbstractCell walls of sugar beet tissue (Beta vulgaris var altissima Döll), the cell and vacuolar membrane of which were destroyed by heat or the action of lipophilic substances, were observed by transmission electron microscopy. The average thickness of secondary walls (SW) and the region composed of the middle lamella and two primary walls (PW) was statistically evaluated and compared with the swelling of the entire denaturated tissue. By introducing different counter‐ions with water as solvent, the extension along the wall E2 increased in the order H+ &lt; K+ ∼ Ca2+ &lt; La3+, and the extension across the wall (SW plus PW) E2 increased in the order Ca2+ ∼ K+ &lt; La3+ &lt; H+. Replacement of the swelling medium by sucrose solution (0.5 M) caused either an increase of the wall thickness (K+, Ca2+, La3+) or a contraction (H‐form); the anisotropy E2E3 was either negative (H+, Ca2+, La3+) or positive (K+). Comparison of the PW with the SW region mostly yielded a ratio of Ezpw/Ezxm between 1 and 2. The ion‐exchange K+→Ca2+ was predominantly manifested in a change of the PW region, while the influence of sucrose on the K+‐treated wall seemed to be confined to the SW region. Specimens in the H‐form in water showed a further increase of the wall thickness (SW and PW) when the pH was reduced from 7 to 3. (At pH 3 the carboxyl groups inside the wall must exist nearly completely in the non‐dissociated state.) All the changes of swelling observed may be explained by a superposition of electrostatic and anisotropic hydrophobic interactions between the matrix polysaccharides.

Comparison of the effects of crude extract of spinach‐beet leaves and equivalent amounts of chlorophyll and chlorophyllin in modifying the clastogenic activity of chromium (VI) oxide in mice in vivo

AbstractThe anticlastogenic activities of a crude extract of leaves of spinach‐beet (Beta vulgaris var. benghalensis Hort.) and equivalent amounts of chlorophyll extracted from the leaves and of synthetic chlorophyllin in reducing cytotoxicity were compared following exposure of mice in vivo to a known clastogen chromium (VI) oxide. Male Swiss albino mice were administered orally the vegetable extract for 7 consecutive days and then exposed to the clastogen by gavage (20 mg/kg b wt). For comparison, equivalent amounts of extracted chlorophyll and synthetic chlorophyllin were administered to the mice, 2 h before exposure to the same dose of the metal. Chromosomes were studied from bone marrow cells 24 h after exposure, following colchicine‐hypotonic‐fixative‐flame drying‐Giemsa staining schedule. Chlorophyllin and the crude extract, when given alone, did not induce chromosomal aberrations and reduced the clastogenic effects induced by chromium (VI) oxide to a statistically significant level, indicating a protective action. Chlorophyll, however, produced a significant increase of chromosomal aberrations compared with control, when administered alone and was not able to reduce the clastogenicity of the metallic salt to a significant level.

Isolation ofCryptococcus neoformans var.neoformans from bird droppings, fruits and vegetables in Mexico City

The presence of Cryptococcus neoformans in various natural sources, such as bird droppings, fruits and vegetables, was investigated. A total of 711 samples were analyzed; C. neoformans var. neoformans was isolated from seven out of 74 bird droppings (9.5%), with parrots as one of the most significant sources. Fruits were positive in 9.5% of the 169 samples studied, specially citrus fruits, particularly grapefruit, in which the highest frequency was found. From the 468 vegetable samples, only 20 were positive (4.2%). It is emphasized that five of the positive vegetables species are autochthonous to Mexico: avocado (Nectandra salicifolia), beet (Beta vulgaris var. quinopodiace), chayote (Sechium edule), stringbean (Cassia sp), and nopal (Opuntia ficus-indica).

A third cryptic virus in beet (Beta vulgaris)

Japanese leaf beet Beta vulgaris var. cicla cv. Fudanso plants were found to contain four double‐stranded RNA (dsRNA) components in apparently healthy beet plants. Two were identified as from beet cryptic virus 1 (BCV1), but the other two showed different mobilities on gel electrophoresis and were transcribed into complementary DNA (cDNA) and cloned. Hybridization analysis showed no significant sequence homology between these two dsRNAs and the dsRNA components of BCV1 or the other known cryptic virus of beet, BCV2. Slot‐ and dot‐blot hybridization were used with cDNA clones as probes to identify plants containing these two dsRNA components. Virus particles were purified from these plants and were shown to contain the two new dsRNA components, thus demonstrating the existence of a new beet cryptic virus, which we have called BCV3.

The effect of chloride and nitrogen on nitrate accumulation and yield in beetroot (Beta vulgaris var. conditiva)

A pot and a field experiment were conducted to evaluate the effects of different nitrogen and chloride fertilizer levels on the nitrate content of beetroot. The yield and dry matter content were also determined. Sulphate fertilization was used as a control to chloride fertilization. There was a considerable decrease in the nitrate content of beetroots during the growing season. High nitrogen fertilization caused nitrate accumulation in both experiments. Chloride had a significant decreasing effect on the nitrate accumulation towards the middle of the growing period in the pot experiment. In the field experiment, chloride also decreased nitrate accumulation towards the middle of the growing period, soon after additional application of ammonium nitrate limestone (13.8 % NH4-N; 13.7 % NO3-N). Chloride tends to decrease nitrate accumulation only at an early stage of root development when nitrate is not the only source of nitrogen in the soil. The yield was higher on high nitrogen supply, in the pot experiment also on chloride application. Nitrogen decreased the dry matter content, but chloride had this effect only in the field experiment.

Comparison of chloroplast and mitochondrial DNA from five morphologically distinct Beta vulgaris cultivars: sugar beet, fodder beet, beet root, foliage beet, and Swiss chard

Two cytoplasms, N and S, are used in the breeding of sugar beet, Beta vulgaris var. altissima. These cytoplasms can be distinguished by their mitochondrial DNA. In an attempt to detect new cytoplasms, we compared the restriction profiles of chloroplast and mitochondrial DNA from five different cultivars of Beta vulgaris. All restriction patterns of chloroplast DNA were identical. With the exception of sugar beet with S-cytoplasm, all cultivars studied showed the same restriction profile of mitochondrial DNA, indicating that these cultivars all contain the N-cytoplasm. These results are discussed with regard to the large morphological differences of the cultivars and the cytoplasmic variability found in natural populations of the wild beet, Beta maritima.

Localization of glyoxylate-cycle marker enzymes in peroxisomes of senescent leaves and green cotyledons

Crude particulate homogenates from leaves of barley (Hordeum vulgare L.), rice (Oryza sativa L.), leaf-beet (Beta vulgaris var. cicla L.) and pumpkin (Cucurbita pepo L.) cotyledons were separated on sucrose density gradients. The peroxisomal fractions appeared at a buoyant density of 1.25 g·cm(-3) and contained most of the activities of catalase (EC 1.11.1.6), and hydroxypyruvate reductase (EC 1.1.1.81) on the gradients. In peroxisomal fractions from detached leaves and green cotyledons incubated in permanent darkness we detected the presence of isocitrate lyase (EC 4.1.3.1) and malate synthase (EC 4.1.3.2), key enzymes of the glyoxylate cycle, and β-oxidation activity (except in pumpkin). As proposed by H. Gut and P. Matile (1988, Planta 176, 548-550) the glyoxylate cycle may be functional during leaf senescence, and the presence of two key enzymes indicates a transition from leaf peroxisome to glyoxysome; for pumpkin cotyledons in particular a double transition occurs (glyoxysome to leaf peroxisome during greening, and leaf peroxisome to glyoxysome during senescence).