Apoplastic pH and inorganic ion levels in tomato fruit: A potential means for regulation of cell wall metabolism during ripening

Apoplastic pH and ionic conditions exert strong influence on cell wall metabolism of many plant tissues; however, the nature of the apoplastic environment of ripening fruit has been the subject of relatively few studies. In this report, a pressure-bomb technique was used to extract apoplastic fluid from tomato fruit ( Lycopersicon esculentum Mill.) pericarp at several developmental stages. pH and the levels of K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl⁻ and P were determined and compared with the values for the bulk pericarp and locule tissues. The pH of the apoplastic fluid from pericarp tissue decreased from 6.7 in immature and mature-green fruits to 4.4 in fully-ripe fruit. During the same period, the K⁺ concentration increased from 13 to 37 m M . The levels of Na⁺ and divalent cations did not change, whereas the anions P and Cl⁻ increased in ripe fruit. Ca²⁺ levels remained relatively constant during ripening at 4–5 m M , concentrations that effectively limit pectin solubilization. The electrical conductivity of the apoplastic liquid increased 3-fold during ripening, whereas osmotically active solutes increased 2-fold. Pressure-treated fruit retained the capacity to ripen. The decline in apoplastic pH and increase in ionic strength during tomato fruit ripening may regulate the activity of cell wall hydrolases. The potential role of apoplastic changes in fruit ripening and softening is discussed.     

龙眼果实采后失水果皮褐变与活性氧及酚类代谢的关系

研究了(10±1)℃和50%相对湿度贮藏条件下"福眼"龙眼果实果皮褐变与活性氧和酚类代谢的关系.结果表明,采后失水导致龙眼果实果皮褐变,果皮活性氧清除酶SOD、CAT、APX、GR活性和内源抗氧化物质AsA、GSH含量下降,O-2产生速率和MDA含量增加,细胞膜透性迅速增大;PPO和POD活性增加,总酚和类黄酮含量明显下降.据此认为,果皮褐变可能是细胞的活性氧代谢失调,细胞膜结构破坏,使PPO、POD与酚类物质(含类黄酮)接触、酚类物质氧化的结果.     

Comparative Study of the Carotenoid Composition of the Seeds of Ripening Momordica charantia and Tomatoes

The total carotenoid concentration of the seeds of Momordica charantia rose about 100-fold from the immature to the ripe stage. The massive increase was almost exclusively attributable to lycopene, which accounted for 96% of the carotenoids of the ripe seeds. The carotenoid pattern of the seed was found to be drastically different from that of the pericarp. The seed, which contained fewer carotenoids, had a total concentration 12 times greater than that in the pericarp at the ripe stage. The acyclic lycopene selectively accumulated in the seed, whereas the cyclic carotenoids, cryptoxanthin, zeaxanthin and β-carotene, were the principal pigments of the ripe pericarp. The seed of ripe tomatoes reflected the qualitative pattern of the whole fruit. The total carotenoid concentration was, however, much lower and the lycopene content was particularly low. β-Carotene, having a comparatively high concentration, emerged as the major pigment of the seed.     

Apoplasmic assimilates and grain growth of contrasting rice cultivars differing in grain dry mass and size

Apical dominance in assimilate filling impacts grain growth in basal spikelets of rice panicle. In this study, organic materials of the pericarp, apoplasmic space and endosperm of the apical and basal caryopses, and photosynthesis of the flag leaf were measured during early part of grain development in three types of rice cultivars with similar phenology, but difference in grain weight and size in the dry and wet seasons of 2006 and 2007, respectively. Photosynthetic activity of the flag leaf was consistently low in small-seeded cultivars. Rates of grain filling and cell division of endosperm and concentration of assimilates, starch, proteins and chlorophylls of the caryopsis were lower, but spikelet ethylene production and peroxidase activity were higher in a small-seeded cultivar compared to a big-seeded cultivar. Similar disparities in grain filling and other attributes were noticed for the inferior basal spikelets of the panicle compared to the superior apical spikelets, except the assimilate concentration of the pericarp and endosperm. Temporal fluctuation in assimilate concentration of the organs were similar between the cultivars. Concentration of apoplasmic assimilates mostly exhibited negative correlation with that of pericarp and endosperm. Compared to the apical spikelets, correlation was more negative for the basal spikelets. Conversely, correlation was positive between the concentration of apoplasmic assimilates and endosperm cell number and grain weight of the cultivars. Ethylene released from the spikelets at anthesis affected growth and cell division rates of endosperm and enhanced protein and chlorophyll degradation and peroxidase activity of the caryopsis. It was concluded that variation in spikelet ethylene production may be responsible for differences in size or weight of grains among rice cultivars and spikelets at different locations of the panicle. The concentration of apoplasmic assimilates could be an indicator for grain filling capacity, and ethylene regulated the concentration by affecting pericarp activity for assimilate unloading.     

Water relations and growth of tomato fruit pericarp tissue

The water relations of young tomato fruit pericarp tissue were examined and related to tissue expansion. The relationship between bulk turgor pressure and tissue expansion (as change in fresh mass or length of tissue) was determined in slices of pericarp cut from young, growing fruit by incubation in different osmotic concentrations of polyethylene glycol 6000 or mannitol. The bulk turgor of this tissue was low (about 0.2 MPa), even in fruit from plants that were otherwise fully turgid, whether measured psychrometrically or by length change in osmotic solutions. The rate of tissue growth at maximum turgor was less than that at moderate turgor unless calcium was added to the incubation medium. However, added calcium also decreased the rate of growth at lower turgor pressures. Yield turgor was < 0.1 MPa, but it was increased by the addition of calcium ions. Electrolyte leakage from tissue was greatest at maximum turgor pressure but was decreased by the addition of calcium ions or osmoticum. Tissue growth was unaffected by a range of plant growth regulators (IAA, abscisic acid, benzyladenine and GA₃) but was inhibited, particularly at high turgor, by low concentrations of malic or citric acid. The low turgor pressure of pericarp tissue could be due to the presence of apoplastic solutes within the pericarp, and evidence for this is discussed. Thus, fruit tissue may be able to maintain optimal expansion rates only at moderate turgor and low calcium concentration.     

Abscisic Acid levels and seed dormancy

Dormant seeds from Fraxinus species require cold-temperature after-ripening prior to germination. Earlier, we found that abscisic acid (ABA) will inhibit germination of excised nondormant embryos and that this can be reversed with a combination of gibberellic acid and kinetin. Using Milborrow's quantitative “racemate dilution” method the ABA concentration in 3 types of Fraxinus seed and pericarp were determined. While ABA was present in all tissues, the highest concentration was found in the seed and pericarp of dormant F. americana. During the chilling treatment of F. americana the ABA levels decreased 37% in the pericarp and 68% in the seed. The ABA concentration of the seed of the nondormant species, F. ornus, is as low as that found in F. americana seeds after cold treatment. Experiments with exogenously added ABA solutions indicate that it is unlikely that the ABA in the pericarp functions in the regulation of seed dormancy. However, the ABA in the seed does seem to have a regulatory role in germination.     

Differential effects of abscisic acid and ethylene on the fruit maturation of <Emphasis Type="Italic">Litchi chinensis</Emphasis> Sonn.

Two litchi cultivars, a well-coloured ‘Nuomici’ and a poorly coloured ‘Feizixiao’, were used to investigate changes in endogenous abscisic acid (ABA) concentration and ethylene production during fruit maturation and to test the effects of exogenous growth regulators on litchi fruit maturation. Abscisic acid concentration in both the aril and pericarp increased with fruit maturation. Transfusion of ABA into the fruit 3 weeks before harvest accelerated, whereas transfusion of 6-benzyl aminopurine (6-BA) retarded sugar accumulation and pigmentation. The effect of 6-BA was assumed to link with the resultant decrease in ABA. In contrast, 1-aminocyclopropane-1-carboxylic acid (ACC) concentration and ACC oxidase (ACO) activities in the aril remained relatively constant during sugar accumulation. Transfusion of aminooxyacetic acid (AOA) significantly decreased ACC concentration but had no effect on sugar accumulation in the aril. These results suggested that endogenous ABA, but not ethylene, was critical for the sugar accumulation. However, the roles of ABA and ethylene in pericarp pigmentation were rather complicated. Application of exogenous ABA promoted anthocyanin synthesis significantly, but had very little effect on chlorophyll degradation. Ethylene production in litchi fruit decreased with development, but a transient increase of endogenous ethylene production was detected just around the colour break in ‘Nuomici’. Enhanced ACO activity in the pericarp was detected during pigmentation. Ethrel at 400 mg l⁻¹ showed no effect on pericarp coloration, but accelerated chlorophyll degradation and anthocyanin synthesis at a much higher concentration (800 mg l⁻¹). Fruit dipped in ABA solution alone yielded no effect on chlorophyll degradation, but the combined use of ABA and Ethrel at 400 mg l⁻¹ enhanced both chlorophyll degradation and anthocyanin synthesis. These results indicated the possible synergistic action of ethylene and ABA during litchi fruit colouration. ABA is suggested to play a more crucial role in anthocyanin synthesis, while ethylene is more important in chlorophyll degradation. ABA can increase the sensitivity of pericarp tissue to ethylene.     

Studies in seed dormancy

Summary ABA has been identified by GLC-MS and routinely determined by GLC as one of several inhibitory substances in the testa and pericarp of hazel nuts. Its concentration in newly harvested nuts, which had not developed embryo dormancy, was 19.0 nmoles/g dry weight for the testa, 1.4 nmoles/g for the pericarp and 0.09 nmoles/g for the embryo. Dry storage of the nuts resulted in the development of embryo dormancy together with a slight loss of ABA. On imbibition of dormant nuts at 5° C and 20° C there was a 61% loss of ABA from the testa and pericarp in both cases. However the 5° C imbibition resulted in the breaking of seed dormancy while the 20° C imbibition had no effect on the dormancy. The ABA of the testa and pericarp seems to be concerned with the maintenance of seed dormancy prior to the onset of embryo dormancy. Subsequent to the onset of embryo dormancy, ABA seems to show little effect on either the maintenance or breaking of seed dormancy.Abbreviations ABA abscisic acid - GLC gas-liquid chromatography - MS mass spectrometry     

Pericarp strength of sunflower and its value for plant defense against the sunflower moth,Homoeosoma electellum

Sunflower pericarps provide a barrier against seed feeding by larvae of the sunflower moth, Homoeosoma electellum. Pericarp hardening is thought to be accelerated by a phytomelanin layer beneath the hypodermis, but among germplasm with phytomelanin, broad variation in sunflower pericarp strength exists. To facilitate the use of pericarp strength in sunflower breeding, resistance to mechanical puncture was assessed for diverse sunflower germplasm, and feeding tests were used to evaluate whether differences in pericarp strength prevent H. electellum larvae from penetrating achenes. Test on field-grown sunflowers indicates that public restorer lines have lower pericarp strengths compared with maintainer lines and commercial hybrids at 14 days after the start of anthesis. Interspecific crosses or plant introduction (PI) accessions believed to be resistant to H. electellum, including PI 170415, comprised a group with exceptionally high pericarp strength relative to other germplasm. In subsequent tests on greenhouse-grown sunflowers, overall results were similar, but using field-grown plants provided greater statistical power. In choice tests with achenes that differed in pericarp strength, 7- to 9-day-old sunflower moth larvae fed more often on seed protected by a weaker pericarp, at a more than 5-to-1 ratio, while 10-day-old larvae fed indiscriminately. Pericarp strength data contradict previous published results for individual entries and heterotic groups, but support the generalization that improved physical resistance to the sunflower moth is possible. To use pericarp strength in PI 170415 or similar sources, the inheritance of high pericarp strength and potential trade-offs between pericarp strength and other agronomic traits need to be understood.     

不同浓度氧贮藏荔枝的几种酶活性变化

在空气和高浓度氧下贮藏荔枝1至2天,果皮和果肉脂氧合酶活性增高;而在低浓度氧下则无此酶活增高。3天后酶活降低,5天后果实酶活很低。三种浓度氧下3天,果皮过氧化物酶活增至最大值,随后则略有降低。在高浓度氧和空气下,果皮多酚氧化酶活性增高,酶活性较低浓度氧的高。在高浓度氧下,黄嘌呤氧化酶活性鞍空气和低浓度氧下的高。几种酶活性增高,可能导致氧化和过氧化作用加剧和引起果皮褐变。     

Solute Accumulation by Grape Pericarp Cells: V. RELATIONSHIP TO BERRY SIZE AND THE EFFECTS OF DEFOLIATION

We have studied the accumulation of water, dry matter (DM) andglucose and fructose (G + F) in selected grape berries cv. Dolcettoof varying initial size growing on leafed and defoliated vines.The first measurements at 2 d after veraison were obtained non-destructivelyfrom correlations with linear dimensions and deformability;the final measurements were made when the berries were harvested13 d later. The increments in DM and G + F per pericarp increased with initialberry size thus discounting an hypothesis of an equal amountof solutes supplied to all berries. The increments in weightof DM and G + F per increment of pericarp volume were constantin berries of different size, supporting an hypothesis of acontrol determined by concentration in the solution availablefor accumulation in all berries. Defoliation reduced the incrementsper pericarp and per g fr. wt. by about the same proportionand its effects were consistent with the above interpretations. Key words: Grape pericarp, sugar accumulation, phloem unloading, Vitis vinifera.     

Acorn Pericarp Removal as a Cache Management Strategy of the Siberian Chipmunk,Tamias sibiricus

Numerous recent studies have revealed a variety of behavioral adaptations of rodents for maximizing returns from cached seeds. Herein we report on a novel behavior by the Siberian chipmunk (Tamias sibiricus) in northeastern China, by which they consistently remove the pericarp (shell) of Quercus mongolica acorns before dispersing and caching these nuts. We investigated the effects of pericarp removal on acorn germination, tannin concentrations, cache pilferage, and insect damage, to determine if and how pericarp removal facilitates cache management by Siberian chipmunks and whether or not such behavior influences seed fates. Chipmunks cached acorns only after the pericarps were removed. Chipmunks preferred pericarp‐removed acorns over intact acorns when removing them from seed stations for both consumption and caching. Pericarp removal did not affect germination or tannin concentration of cached Q. mongolica acorns, suggesting that the behavior is not an adaptation for long‐term storage and tannin decomposition. Acetone treatments of the pericarp and artificial pericarp removal failed to alter pilferage rates by Siberian chipmunks and wood mice (Apodemus peninsulae). Since damage of acorns by weevils often leads to cache losses, we also tested the effects of weevil infestation on cache decision following pericarp removal. Siberian chipmunks removed pericarps and then scatter hoarded significantly more sound than weevil‐infested acorns, strongly suggesting that pericarp removal is used to discriminate between the infested and non‐infested acorns. Thus, we argue that the primary function of this behavior is to ensure successful storage of sound acorns, at least for short‐term storage. Future studies should consider the potential impact of pericarp removal on weevil populations and long‐term patterns of seed survival and establishment from the Siberian chipmunk’s caches.     

Characterization and inheritance of the Anthocyanin fruit (Aft) tomato

Tomato (Lycopersicon esculentum) accession LA1996 with the Anthocyanin fruit (Aft) gene has dark green foliage, elevated anthocyanin expression in the hypocotyls of seedlings, and anthocyanin in the skin and outer pericarp tissues of the fruit. Interest in the health benefits and antioxidant capacity of anthocyanins led to this study of the genetic potential for increased levels of this important class of phytonutrients in tomato fruit. In order to conform to tomato gene nomenclature rules, we propose changing the symbol Af for Anthocyanin fruit to Aft. Segregation ratios of anthocyanin expression in F(2) and BC(1) populations of a cross between the processing tomato UC82B and LA1996 were consistent with a single dominant gene hypothesis. Anthocyanin expression was reduced in backcross populations compared to F(2 )populations. Anthocyanin concentration, as measured by the pH differential method, of pigment-rich pericarp and skin tissues from LA1996 was estimated to be 20.6 mg/100 g and 66.5 mg/100 g, respectively. Anthocyanidin composition was characterized by high-performance liquid chromatography (HPLC). Fruit of accession LA1996 contained predominantly petunidin, followed by malvidin and delphinidinin. Lycopene, beta-carotene, phytoene, and phytofluene levels were similar to those of normal tomatoes and lower than those found in high pigment tomatoes.     

Products Released from Enzymically Active Cell Wall Stimulate Ethylene Production and Ripening in Preclimacteric Tomato (Lycopersicon esculentum Mill.) Fruit

Enzymically active cell wall from ripe tomato (Lycopersicon esculentum Mill.) fruit pericarp release uronic acids through the action of wall-bound polygalacturonase. The potential involvement of products of wall hydrolysis in the induction of ethylene synthesis during tomato ripening was investigated by vacuum infiltrating preclimacteric (green) fruit with solutions containing pectin fragments enzymically released from cell wall from ripe fruit. Ripening initiation was accelerated in pectin-infiltrated fruit compared to control (buffer-infiltrated) fruit as measured by initiation of climacteric CO₂ and ethylene production and appearance of red color. The response to infiltration was maximum at a concentration of 25 micrograms pectin per fruit; higher concentrations (up to 125 micrograms per fruit) had no additional effect. When products released from isolated cell wall from ripe pericarp were separated on Bio-Gel P-2 and specific size classes infiltrated into preclimacteric fruit, ripening-promotive activity was found only in the larger (degree of polymerization >8) fragments. Products released from pectin derived from preclimacteric pericarp upon treatment with polygalacturonase from ripe pericarp did not stimulate ripening when infiltrated into preclimacteric fruit.     

Differential expression of litchi XET genes in relation to fruit growth

Xyloglucan endotransglycosylase (XET) catalyses the transglycosylation of xyloglucan, the major hemicellulose polymer, which has been thought to mediate the cross-linking of cellulose microfibrils in cellular walls and proposed to be involved in the control of cell wall relaxation. To understand the relationship between litchi fruit cracking and gene expression patterns, three XET genes from litchi fruit were identified and then examined for their expression profiles in pericarp and aril tissues at different development stages, using a cracking-resistant cultivar, 'Huaizhi', and a cracking-susceptible cultivar, 'Nuomici'. Three full-length cDNAs of 1267, 1095 and 1156 bp encoding XETs, named LcXET1, LcXET2 and LcXET3, respectively, were isolated from expanding fruit using RT-PCR and RACE-PCR (rapid amplification of cDNA ends) methods. Northern blotting analysis showed that LcXET1 mRNA accumulation occurred much earlier in aril tissues at 59 days after anthesis (DAA) than in pericarp tissues at 73 DAA in 'Nuomici'. However, it appeared at almost the same time (66 DAA) in pericarp and aril tissues in 'Huaizhi', which suggested that differential accumulation of LcXET1 in pericarp and aril tissues in 'Nuomici' and 'Huaizhi' was closely associated with fruit cracking. LcXET2 mRNA accumulation could be detected in pericarp and aril tissues throughout fruit development but exhibited a differential accumulation pattern between pericarp and aril tissues. In the aril of 'Nuomici', intensive signal bands were detectable at 59-73 DAA in rapidly expanding fruits of 'Nuomici' but only weak bands could be found in the pericarp tissues. In contrast, moderate signal bands were detectable both in pericarp and aril tissues of 'Huaizhi' fruits. Furthermore, LcXET3 showed constitutive expression in both pericarp and aril tissues of developing 'Nuomici' and 'Huaizhi' litchi fruit. In addition, differential expression patterns of three XETs genes were observed in different tissues of litchi, with only LcXET1 being fruit-specific. To further address the role of LcXET in fruit cracking, alpha-naphthalene acetic acid (NAA) was used to treat 'Nuomoci' to reduce fruit cracking. Enhanced LcXET1 mRNA accumulation appeared in pericarp while LcXET2 and LcXET3 mRNA accumulation enhanced in aril tissues in the NAA-treated fruits. Thus, LcXET1 is more likely to play a role in reducing litchi fruit cracking than LcXET2 and LcXET3.     

Optimized ultra-high-pressure-assisted extraction of procyanidins from lychee pericarp improves the antioxidant activity of extracts

To establish optimal ultra-high-pressure (UHP)-assisted extraction conditions for procyanidins from lychee pericarp, a response surface analysis method with four factors and three levels was adopted. The optimum conditions were as follows: 295 MPa pressure, 13 min pressure holding time, 16.0 mL/g liquid-to-solid ratio, and 70% ethanol concentration. Compared with conventional ethanol extraction and ultrasonic-assisted extraction methods, the yields of the total procyanidins, flavonoids, and phenolics extracted using the UHP process were significantly increased; consequently, the oxygen radical absorbance capacity and cellular antioxidant activity of UHP-assisted lychee pericarp extracts were substantially enhanced. LC-MS/MS and high-performance liquid chromatography quantification results for individual phenolic compounds revealed that the yield of procyanidin compounds, including epicatechin, procyanidin A2, and procyanidin B2, from lychee pericarp could be significantly improved by the UHP-assisted extraction process. This UHP-assisted extraction process is thus a practical method for the extraction of procyanidins from lychee pericarp.