Small, repetitive DNAs contribute significantly to the expanded mitochondrial genome of cucumber.
Closely related cucurbit species possess eightfold differences in the sizes of their mitochondrial genomes. We cloned mitochondrial DNA (mtDNA) fragments showing strong hybridization signals to cucumber mtDNA and little or no signal to watermelon mtDNA. The cucumber mtDNA clones carried short (30-53 bp), repetitive DNA motifs that were often degenerate, overlapping, and showed no homology to any sequences currently in the databases. On the basis of dot-blot hybridizations, seven repetitive DNA motifs accounted for >13% (194 kb) of the cucumber mitochondrial genome, equaling >50% of the size of the Arabidopsis mitochondrial genome. Sequence analysis of 136 kb of cucumber mtDNA revealed only 11.2% with significant homology to previously characterized mitochondrial sequences, 2.4% to chloroplast DNA, and 15% to the seven repetitive DNA motifs. The remaining 71.4% of the sequence was unique to the cucumber mitochondrial genome. There was <4% sequence colinearity surrounding the watermelon and cucumber atp9 coding regions, and the much smaller watermelon mitochondrial genome possessed no significant amounts of cucumber repetitive DNAs. Our results demonstrate that the expanded cucumber mitochondrial genome is in part due to extensive duplication of short repetitive sequences, possibly by recombination and/or replication slippage. (+info)
Citrulline, a novel compatible solute in drought-tolerant wild watermelon leaves, is an efficient hydroxyl radical scavenger.
Drought-tolerant wild watermelon accumulates high levels of citrulline in the leaves in response to drought conditions. In this work, the hydroxyl radical-scavenging activity of citrulline was investigated in vitro. The second-order rate constant for the reaction between citrulline and hydroxyl radicals was found to be 3.9x10(9) M(-1) s(-1), demonstrating that citrulline is one of the most efficient scavengers among compatible solutes examined so far. Moreover, citrulline effectively protected DNA and an enzyme from oxidative injuries. Liquid chromatography-mass spectrometry analysis revealed that at least four major products were formed by the reaction between citrulline and hydroxyl radicals. Activities of metabolic enzymes were not inhibited by up to 600 mM citrulline, indicating that citrulline does not interfere with cellular metabolism. We reasoned, from these results, that citrulline contributes to oxidative stress tolerance under drought conditions as a novel hydroxyl radical scavenger. (+info)
Citrulline and DRIP-1 protein (ArgE homologue) in drought tolerance of wild watermelon.
Drought-affected plants experience more than just desiccation of their organs due to water deficit. Plants transpire 1000 times more molecules of water than of CO2 fixed by photosynthesis in full sunlight. One effect of transpiration is to cool the leaves. Accordingly, drought brings about such multi-stresses as high temperatures, excess photoradiation and other factors that affect plant viability. Wild watermelon serves as a suitable model system to study drought responses of C3 plants, since this plant survives drought by maintaining its water content without any wilting of leaves or desiccation even under severe drought conditions. Under drought conditions in the presence of strong light, wild watermelon accumulates high concentrations of citrulline, glutamate and arginine in its leaves. The accumulation of citrulline and arginine may be related to the induction of DRIP-1, a homologue of ArgE in Escherichia coli, where it functions to incorporate the carbon skeleton of glutamate into the urea cycle. Immunogold electron microscopy reveals the enzyme to be confined exclusively to the cytosol. DRIP-1 is also induced by treating wild watermelon with 150 mM NaCl, but is not induced following treatment with 100 microM abscisic acid. The salt treatment causes the accumulation of gamma-aminobutyrate, glutamine and alanine, in addition to a smaller amount of citrulline. Citrulline may function as a potent hydroxyl radical scavenger. (+info)
Molecular characterization of a GA-inducible gene, Cvsus1, in developing watermelon seeds.
To understand the molecular mechanisms that control seed development, we isolated a seed-preferential gene from ESTs of developing watermelon seeds. The gene Cvsus1 encodes a protein that is 86% identical to the Vicia faba sucrose synthase expressed in developing seeds. RNA blot analysis showed that Cvsus1 was preferentially expressed in watermelon seeds. We also investigated gene expression levels both in pollinated seeds and in parthenocarpic seeds, which lack zygotic tissues. Whereas the transcript level of Cvsus1 was rapidly increased during normal seed development, the expression was not significantly increased in the parthenocarpic seeds. However, treating the parthenocarpic fruits with GA3 strongly induced Cvsus1 expression, up to the level accumulated in pollinated seeds. These results suggest that Cvsus1 is induced in maternal tissues via signals from the zygotic tissues, and that GA may be one of those signals. (+info)
Consumption of watermelon juice increases plasma concentrations of lycopene and beta-carotene in humans.
Watermelon is a rich natural source of lycopene, a carotenoid of great interest because of its antioxidant capacity and potential health benefits. Assessment of bioavailability of lycopene from foods has been limited to tomato products, in which heat processing promotes lycopene bioavailability. We examined the bioavailability of lycopene from fresh-frozen watermelon juice in a 19-wk crossover study. Healthy, nonsmoking adults (36-69 y) completed three 3-wk treatment periods, each with a controlled, weight-maintenance diet. Treatment periods were preceded by "washout" periods of 2-4 wk during which lycopene-rich foods were restricted. All 23 subjects consumed the W-20 (20.1 mg/d lycopene, 2.5 mg/d beta-carotene from watermelon juice) and C-0 treatments (controlled diet, no juice). As a third treatment, subjects consumed either the W-40 (40.2 mg/d lycopene, 5.0 mg/d beta-carotene from watermelon juice, n = 12) or T-20 treatment (18.4 mg/d lycopene, 0.6 mg/d beta-carotene from tomato juice, n = 10). After 3 wk of treatment, plasma lycopene concentrations for the W-20, W-40, T-20 and C-0 treatments were (least squares means +/- SEM) 1078 +/- 106, 1183 +/- 139, 960 +/- 117 and 272 +/- 27 nmol/L, respectively. Plasma concentrations of beta-carotene were significantly greater after W-20 (574 +/- 49 nmol/L) and W-40 (694 +/- 73 nmol/L) treatments than after the C-0 treatment (313 +/- 27 nmol/L). Plasma lycopene concentrations did not differ at wk 3 after W-20, W-40 and T-20 treatments, indicating that lycopene was bioavailable from both fresh-frozen watermelon juice and canned tomato juice, and that a dose-response effect was not apparent in plasma when the watermelon dose was doubled. (+info)
Variability and genetic structure of the population of watermelon mosaic virus infecting melon in Spain.
The genetic structure of the population of Watermelon mosaic virus (WMV) in Spain was analysed by the biological and molecular characterisation of isolates sampled from its main host plant, melon. The population was a highly homogeneous one, built of a single pathotype, and comprising isolates closely related genetically. There was indication of temporal replacement of genotypes, but not of spatial structure of the population. Analyses of nucleotide sequences in three genomic regions, that is, in the cistrons for the P1, cylindrical inclusion (CI) and capsid (CP) proteins, showed lower similar values of nucleotide diversity for the P1 than for the CI or CP cistrons. The CI protein and the CP were under tighter evolutionary constraints than the P1 protein. Also, for the CI and CP cistrons, but not for the P1 cistron, two groups of sequences, defining two genetic strains, were apparent. Thus, different genomic regions of WMV show different evolutionary dynamics. Interestingly, for the CI and CP cistrons, sequences were clustered into two regions of the sequence space, defining the two strains above, and no intermediary sequences were identified. Recombinant isolates were found, accounting for at least 7% of the population. These recombinants presented two interesting features: (i) crossover points were detected between the analysed regions in the CI and CP cistrons, but not between those in the P1 and CI cistrons, (ii) crossover points were not observed within the analysed coding regions for the P1, CI or CP proteins. This indicates strong selection against isolates with recombinant proteins, even when originated from closely related strains. Hence, data indicate that genotypes of WMV, generated by mutation or recombination, outside of acceptable, discrete, regions in the evolutionary space, are eliminated from the virus population by negative selection. (+info)
Inheritance of egusi seed type in watermelon.
An unusual seed mutant in watermelon (Citrullus lanatus var. lanatus) has seeds with a fleshy pericarp, commonly called egusi seeds. The origin of the phenotype is unknown, but it is widely cultivated in Nigeria for the high protein and carbohydrate content of the edible seeds. Egusi seeds have a thick, fleshy pericarp that appears during the second to third week of fruit development. We studied the inheritance of this phenotype in crosses of normal seeded Charleston Gray and Calhoun Gray with two plant introduction accessions, PI 490383w and PI 560006, having the egusi seed type. We found that the egusi seed type is controlled by a single recessive gene, and the symbol eg was assigned. (+info)
Stabilization of cucurbitacin E-glycoside, a feeding stimulant for diabroticite beetles, extracted from bitter Hawkesbury watermelon.
Cucurbitacins are feeding stimulants for diabroticite beetles, including corn rootworms and cucumber beetles, which can be added to a bait containing an insecticide thereby reducing the levels of other insecticide treatments needed to control these pests. One of them, cucurbitacin E-glycoside, is water soluble and easily processed from mutant bitter Hawkesbury watermelons (BHW) that express elevated levels of cucurbitacin. Storage of BHW extract at room temperature resulted in a 92% reduction of cucurbitacin E-glycoside over two months, while refrigeration or freezing resulted in a 60% loss of the active ingredient during this time. The loss of the active ingredient was correlated with an increase in BHW extract pH from 5 to greater than 9. The increase in pH of the BHW extracts at room temperature appeared to be due to the growth of certain bacteria, especially Bacillusspp. In refrigerated extracts, the pH remained relatively constant, and bacterial growth was dominated by bacteria such as Lactobacilli. An alternative to refrigeration is concentration of BHW extract. One means of concentration is spray drying, but the high sugar content of the BHW extract (20mg/ml glucose, 40mg/ml fructose) makes this technique impractical. Fermentation of the BHW extract by the yeast, Saccharomyces boulardii, eliminated the sugars and did not raise the pH nor alter the cucurbitacin E-glycoside content of the extract. Elimination of the sugars by fermentation produced an extract that could be successfully spray dried. BHW extract fermented by S. boulardii produced a higher level of feeding stimulation for spotted cucumber beetles in laboratory choice tests. When applied to cucumbers, there was no difference in control of spotted and striped cucumber beetles between baits of fresh or fermented juices combined with the same insecticide. (+info)