Cell-wall lysing enzymes and products of cell-wall digestion elicit ethylene in citrus

Ethylene production was induced in Valencia oranges [ Citrus sinensis (L.) Osbcck] by injection of the fungal enzyme mixture Pectolyase ( Aspergillus japonicus ) which contains pectolytic enzymes into the peel. The mixture also stimulated production of 1-aminocyclopropane-1-carboxylic acid (ACC). Cycloheximide partially inhibited the Pectolyase-induced ethylene response. Pectin fragments, resulting from partial acid hydrolysis or Pectolyase digestion, caused an increase in ethylene production when injected into the peel of intact orange fruits. Pectic fragments produced by fungal enzymes are known to be elicitors of phytoalexins and in this study are shown to elicit ethylene in citurs.     

Physiological effects of temperature and growth regulators on foliar chlorophyll,soluble protein,and cold hardiness in citrus

Leaf chlorophyll (Chl, A, B) and total soluble protein were assayed in greenhouse-grown 1.5-year-old trees of 2 citrus types, trifoliate orange (Poncirus trifoliata (L.) Raf.) and sour orange (Citrus aurantium L.) exposed to 12 h (day/night) photoperiods in growth chambers under high (30°/21°C, day/night; noncold-hardening) and low (16°/5°C; cold-hardening) temperature regimes. Trees were sprayed 2 × per week for 5 weeks with one of the following solutions at 100 M: napthaleneacetic acid (NAA), paclobutrazol (2RS, 3RS)-1-(4-chlorophenyl-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol) (PPP333), benzyl-adenine (BA), abscisic acid (ABA), gibberellic acid (GA₃), minerals only (N, P, K, S, Ca, Mg) and BA (+) minerals. NAA, PP333, ABA and GA₃ decreased Chl A, B and soluble protein in both citrus types under cold-hardening conditions in contrast to increases with the use of BA and BA (+) minerals especially in trifoliate orange. Both BA and GA₃ increased Chl A, B and protein synthesis under high temperature in both citrus types. Under noncold-hardening temperatures, GA₃ enhanced Chl A, B but sharply reduced foliar protein concentration. Dieback of both cultivars following exposure to temperatures down to –6.7°C was decreased 7% by NAA sprays during noncold-hardening temperatures. Cold tolerance of noncoldhardened trifoliate orange trees was also improved with ABA and PP333. Foliar sprays of NAA (sour orange) and PP333 and BA (+) minerals (trifoliate) increased cold tolerance of cold-hardened trees by 8%. Results indicate that spray applications of growth regulators influence physiological factors associated with foliar functioning and cold tolerance in citrus during different temperature regimes.Summary Growth promoters (BA) and inhibitors (NAA) have the potential to promote cold hardines through either a strong stimulatory effect on foliar physiology or a marked inhibition of growth in general. This suggests that each growth regulator may possess an independent role in the cold-hardiness phenomenon and may also interact with physiological processes other than soluble protein and chlorophyll metabolism. The relationship between soluble protein levels in citrus foliage and the degree of cold hardiness remains uncertain and is essentially unresolved pending more specific qualitative research.University of Florida Agricultural Experiment Station Series No. 7446.This paper reports the results of research only. Mention of a trademark of a proprietary product does not constitute a recommendation for use by the U.S. Department of Agriculture to the exclusion of other products that may also be suitable.     

Citrus replant problem in Iraq II. Possible role of allelopathy

The role of allelopathy in citrus replant problems was investigated in Iraq. The failure of citrus seedlings to grow normally in old citrus orchards was not caused by differences between old and non-citrus soils in electrical conductivity, pH, organic matter, soil texture and those minerals tested. Extracts of soil collected from old citrus orchards significantly reduced the growth of sour orange seedlings. Extracts and decaying sour orange roots reduced the growth of sour orange seedlings as did extracts of non-senescent sour orange leaves and decaying senescent leaves. Thus it appears that allelopathy is at least partly involved in the citrus replant problem.     

Tylenchulus graminis n. sp. and T. palustris n. sp. (Tylenchulidae), from Native Flora of Florida,with Notes on T. semipenetrans and T. furcus

Tylenchulus graminis n. sp. and T. palustris n. sp. are described and illustrated from broomsedge (Andropogon virginicus L.) and pop ash (Fraxinus caroliniana Mill.), respectively. T. graminis resembles T. furcus in having a distinct anus, but T. graminis second-stage juveniles (J2) do not have a bifid tail. T. semipenetrans does not have a perceptible anus. The mature female of T. graminis has a mucronate pointed terminus while T. semipenetrans has a smooth and round terminus. T. graminis males have wider stylet knobs and basal bulb and a longer tail than T. semipenetrans males. T. graminis J2 have a longer posterior body portion (without large fat globules) than T. semipenetrans J2. T. palustris resembles T. semipenetrans in having an undetectable anus but differs by the short and conoid mature female postvulval section. The male of T. palustris has larger stylet knobs and basal bulb than those of T. semipenetrans and a bluntly rounded tail terminus, which is tapered in T. semipenetrans. T. palustris differs from T. furcus and T. graminis in having an undetectable anus, by the conoid postvulval section of mature females, by the shorter and rounded tail of males, and the shorter J2 posterior body section without large fat globules. T. graminis and T. palustris are parasites of indigenous flora of Florida.     

Three further naphthoquinones produced by Fusarium solani

Three naphthoquinone pigments are described which were produced by Fusarium solani. They are 2,3-dihydro-5,8-dihydroxy-6-methoxy-2-hydroxymethyl-3-(2-hydroxypropyl)-1,4-naphthalenedione, 2,3-dihydro-5-hydroxy-4-hydroxymethyl-8-methoxy-naphtho[1,2-b]furan-6,9-dione and 5,8-dihydroxy-2-methoxy-6-hydroxymethyl-7-(2-hydroxypropyl)-1,4-naphthalenedione. One of these pigments was shown to be the precursor of the other two.     

Stylet penetration by the bayberry whitefly, as affected by leaf age in lemon, Citrus limon

Bayberry whitefly (Parabemisia myricae [Kuwana]) crawlers were placed on young and mature lemon leaves and were allowed 7–9 days to settle. Afterwards, the nymphs were fixed and sectioned in situ on the leaves and the area of leaf under each whitefly was examined at 1 000 x for stylet penetration. Both stylets and stylet tracks were readily visible in the sections. The path of penetration was mostly intercellular and the objective appeared to be the phloem. Passage of the stylets through the plant tissue did not cause detectable damage to most cells; however, damaged plant cells occasionally were noticed. Nymphs that had moulted during the 7–9 day settling period reached the phloem significantly more often than those that were still in their first instar. In each of the three replicates, penetration in the mature leaf occurred significantly less often than penetration in the young leaf (4% vs. 72%, p<0.01, ²). Penetration appears to be inhibited in the mature leaf either by the leaf cuticle or by factors detected by the nymphs after very shallow penetration into the leaf. The cuticle of mature leaves was much thicker than the cuticle of young leaves and may have been a barrier to stylet penetration.

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Résumé Des larves de premier stade (avant la fixation) de l'aleurode, Parabemisia myricae (Kuwana), ont été placées, pour qu'elles se fixent, pendánt 2 à 9 jours, sur des feuilles jeunes ou mûres de citronnier. Des morceaux de feuilles avec des larves fixées ont été trempés dans 2% d'agar; ce procédé a permis de maintenir les larves à leurs sites de fixation finale. Des pièces d'agar contenant les morceaux de feuilles avec les larves ont ensuite été trempées dans de la paraffine, et sectionnées en séries de 10 . Il était nécessaire de maintenir une basse température pendant l'opération afin d'obtenir de bonnes sections des feuilles mûres durcies. Les stylets et leurs traces étaient faciles à voir dans les sections teintées aux safranins, et fast green. Presque toutes les traces des stylets étaient intercellulaires et leur destination semblaient être de phloème. En général, la plupart des cellules ne semblaient pas endommagées, les larves qui avaient mué pendant la période de 7 à 9 jours de fixation avaient atteint significantivement plus le phloeme que les larves du premier stade. Dans trois essais, la pénétration des feuilles mûres était significativement moins fréquente que celle des feuilles jeunes (p<0.01, ²).La pénétration dans des feuilles mûres semble être empêchée par la cuticule ou par des facteurs perçus par les nymphes après une pénétration superficielle. La cuticule des feuilles mûres était beaucoup plus épaisse que la cuticule des jeunes feuilles et pourrait donc représenter une barrière à la pénétration des stylets.

     

NaCl effects on 4-desmethylsterol composition of plasma-membrane-enriched preparations from citrus roots

Abstract The free 4-desmethylsterol composition of plasma-membrane-enriched preparations from white fibrous roots of Rangpur lime (Citrus reticulata var. austera hybrid?), Kharna khatta (C. kharna Raf.) and Etrog citron (C. medica L.) seedlings grown in the presence of 0, 50, or 100 mol m^?3 NaCl for 28 d was quantitated by gas chromatography (GC) on analytical capillary (SE-54 fused silica) columns and the sterols were identified by combined gas chromatography-mass spectrometry (GC-MS). Only three 4-desmethylsterols were positively identified by GC-MS, viz. campesterol, stigmasterol and sitosterol. Cholesterol could not be positively identified in any of the membrane preparations. Campesterol levels were generally similar for all treatments and for all three genotypes, approximating 30% of the total free 4-desmethylsterol content of the plasma membranes. At all levels of salinity (0, 50 or 100 mol m^?3 NaCl) sitosterol levels decreased in the order Rangpur lime > Kharna khatta > Etrog citron and stigmasterol levels decreased in the reverse order. The ratio of sitosterol to stigmasterol was highest in Rangpur lime and lowest in Etrog citron at each level of salinity and was reduced by salt treatment in all three genotypes. Salt-induced reductions in the ratio of ‘more planar’ to ‘less planar’ sterols correlated inversely with the accumulation of Cl^? in the leaves of the three genotypes suggesting a role for plasma membrane sterols in the Cl^? exclusion mechanism. A model relating sterol structure, membrane sterol composition and membrane permeability to Cl^? exclusion ability in citrus is presented.     

Growth and carbon partitioning in compatible and incompatible peach/plum grafts

The shoot growth of compatible ( Prunus persica L. Batsch cv. Springtime grafted on Prunus cerasifera L. Ehrh cv. Myrobolan P2032) and incompatible ( Prunus persica L. Batsch cv. Springtime grafted on Prunus cerasifera L. Ehrh cv. Myrobolan P18) peach/plum grafts was observed over a period of 100 days after grafting under controlled conditions. Leaf and root activities were determined by studying carbon assimilation and partitioning, leaf mineral contents and water relations. Shoot length and leaf number were not significantly affected in the incompatible combination during the first 55 days after grafting, but then, shoot growth rate was significantly reduced. Final total dry weights of the shoot were similar in both graft combinations. The incompatible combination did not show any water stress. Soluble sugar and starch contents increased in the leaves of the incompatible combination, accounting for about 36% of the increase of leaf dry weight per unit area. Photosynthesis was affected by the compatibility of the grafts. Leaf nitrogen content (% dry weight) fell in the incompatible graft combination 65 days after grafting. However, nitrogen content on an area basis was not affected. The possibility of nitrogen stress is discussed.     

Effects of natural complex carbohydrate (citrus pectin) on murine melanoma cell properties related to galectin-3 functions

Citrus pectin (CP) and pH-modified citrus pectin (MCP) are highly branched and non-branched complex polysaccharides, respectively, rich in galactoside residues, capable of combining with the carbohydrate-binding domain of galectin-3. We reported previously that intravenous injection of B16-F1 murine melanoma cells with CP or MCP into syngeneic mice resulted in a significant increase or decrease of lung colonization, respectively (Platt D, Raz A (1992)J Natl Cancer Inst 84:438–42). Here we studied the effects of these polysaccharides on cell-cell and cell-matrix interactions mediated by carbohydrate-recognition. MCP, but not CP, inhibited B16-F1 melanoma cells adhesion to laminin and asialofetuin-induced homotypic aggregation. Both polysaccharides inhibited anchorage-independent growth of B16-F1 cells in semisolid medium, i.e. agarose. These results indicate that carbohydrate-recognition by cell surface galectin-3 may be involved in cell-extracellular matrix interaction and play a role in anchorage-independent growth as well as thein vivo embolization of tumour cells.Abbreviations CP natural citrus pectin - MCP pH-modified CP - EHS Englebreth-Holm Swarm - CMF-PBS Ca²⁺-and Mg²⁺-free phosphate-buffered saline, pH 7.2 - HRP horseradish peroxidase - ABTS 2,2-azino-di(3-ethylbenzthiazoline sulfonic acid - DMEM Dulbecco's modified Eagle's minimal essential medium - BSA bovine serum albumin     

中国优质水果资源的分布与适宜生态环境

根据农业部在80年代两次组织评选出的全国189个优质水果产地的生态环境资料,用微型电子计算机系统建立数据库,统计分析柑桔、苹果和梨优质产品的构成比例、产区分布地域及其适宜的环境指标和主栽品种的生态适应性,为果树良种区域化栽培与选育提供依据。