Phosphorus translocation in salt-stressed cotton

The effect of salinity on plants has usually been studied at high inorganic P concentration ([Pi]) in the nutrient solution, and salinity × Pi interactions have been examined at much higher [Pi] than found in soil solutions. Short-term ³²Pi experiments were carried out to study the effect of salinity (150 m M NaCl) on phosphorus translocation in cotton plants ( Gossypium hirsutum L. cv. Acala SJ-2) grown in nutrient solutions containing 10 μ M [Pi]. The effect of additional Ca to a concentration of 10 μ M was also tested. Salinity inhibited ³²P translocation from root to shoot. This inhibition was more evident at higher [Pi] in the root medium. Increasing [Pi] 33-fold in the solution resulted in a 4.3-fold increase in [³²P] in the root under saline conditions, but only in a 1,8-fold increase in the shoot. In older shoot tissues total [P] was elevated in the salinized plants. In the young tissues, however, total P concentration was higher in control plants. Inhibition of ³²P translocation by salinity was greater from root to young leaves than to mature shoot tissues. Salinity also decreased ³²P recirculation from the cotyledons to the young leaf. Inhibition by salinity of both ³²P translocation and recirculation to young leaves was fully reversed by increasing Ca supply from 1 to 10     

Genotype and medium affect shoot regeneration of melon

The effects of basal media, growth regulators and gelling agents on the morphogenetic response of eleven Cucumis melo L. var. reticulatus and inodorus genotypes were examined. Regeneration was achieved from cultured cotyledons of all genotypes and the morphogenic response was affected by the genetic background. Among the combination of factors tested, MS basal medium supplemented with 2.8 M 6-benzyladenine (BA) and 1.0 M abscisic acid (ABA) solidified with agar gave the highest frequency of shoot regeneration.Abbreviations ABA abscisic acid - BA 6-benzyladenine - TDZ thidiazuron     

Effect of in vitro and in vivo colchicine treatments on pollen production and fruit set of melon plants obtained by pollination with irradiated pollen

Haploid/doubled haploid (DH) technology can aid plant breeding programs by accelerating production of homozygous lines, provided enough viable DH progeny can be obtained from diverse haploid genotypes. In cases where there is a low frequency of spontaneous doubling, chromosome doubling procedures are required to achieve fecundity. We produced 63 parthenogenetic melon plantlets via pollination with γ-irradiated pollen, cloned them by nodal cuttings, and tested the effects of in vitro and in vivo colchicine treatment on survival, ploidy, pollen production, and fruit recovery. The most effective procedure was in vitro exposure of 3 cm shoot tip explants to 500 mg/l colchicine for 3 h. This treatment gave 83% survival of explants and 26% conversion to diploidy. Fruit recovery rate was 60% among plants with good pollen production. In vivo exposure of the tops of young plants to 5000 mg/l for 2 and 4 h yielded some fruits but also resulted in less survival and more morphological abnormalities. Strategies for recovery of progeny from parthenogenetic melon plants are recommended. To our knowledge, this study represents the first comprehensive study of recovery of fruits and viable seeds from parthenogenetic melon plants.     

The inheritance of organogenic response in melon

Previous studies have demonstrated variation in organogenic competence among plants within a population ofCucumis melo. In order to determine if leaf explant response is under genetic control, we investigated the distribution of the shoot regeneration frequency in F₁ and F₂ generations from parents representing extreme values forin vitro organogenic response. Results suggest a genetic model with two genes, partial dominance, independent segregation and similar effects for both genes.     

Putrescine uptake and translocation in higher plants

Putrescine uptake and translocation were studied by feeding [³H] putrescine to roots of tomato seedlings ( Lycopersicon esculentum Miller, cv. Earlypak 7) at the stage of expanded cotyledons, of maize seedlings ( Zea mais L.) at the coleoptile stage, and of one year old pines ( Pinus pinea L.). Putrescine translocation was rapid as radioactivity appeared in the upper part of the seedlings within 30 min, continuing to increase up to 24 h, while it decreased in roots. The putrescine supplied was partly metabolized to spermidine and spermine in the course of 24 h. The transport was temperature-dependent as it increased with increasing temperature from 4°C to 30°C. In plants kept in 100% relative humidity the transport decreased by 27% compared to controls kept in 50% relative humidity. The existence of basipetal transport was assessed by feeding labeled putrescine to cotyledons or to a primary leaf of tomato plants at different stages of growth. The influence of ringing at the hypocotyl level on polyamine translocation in pine plants was studied in order to exclude cortical parenchyma and phloem from transport. Radioactivity decreased in the hypocotyl just above the ring and in the upper parts (epicotyls with needles), but long-distance transport was low affected indicating xylem transport. It is suggested that polyamine transport is not polar, and that it occurs mainly through xylem vessels.     

Root-pressure driven xylem sap flow in greenhouse melon (Cucumis melo L.): diurnal change and the effects of shading, growth stage, rootstock and fruit number

Grafted and ungrafted greenhouse melon were used to investigate the effect of diurnal change, shading, growth stage, rootstock and fruit numbers on melon xylem sap flow rate. A clear diurnal change was observed in xylem sap flow rate. Shading of the plant on the previous day decreased the sap flow rate. An increase in the number of fruit on a plant decreased the sap flow rate, but, grafting to squash plant lessened the effect of fruit number. Consideration of timing and environmental factors is necessary when the xylem sap is collected for root study.     

Genetic difference in somatic embryogenesis from seeds in melon (Cucumis melo L.)

Significant differences in somatic embryogenesis from melon seeds were observed among 18 cultivars; especially, cultivars Earl's Favorite and Barnett which produced a large number of somatic embryos. F₁ seeds were obtained by reciprocal crosses between cultivars. Some lines produced a large number of somatic embryos whereas others showed no or poor embryogenic response. Most of the F₁ seeds formed somatic embryos. The frequency of somatic embryogenesis decreased as compared to the parents with the highest potential. Transfer of the frequency of somatic embryogenesis from superior responding cultivars to inferior cultivars was proved. It was difficult to determine the mode of inheritance of somatic embryogenesis because there was a large variation in the range of somatic embryogenesis from F₂ seeds, and cytoplasmic effect was recognized in certain combinations.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - BAP 6-benzylaminopurine     

Protoplast regeneration and fusion in Cucumis: melon × cucumber

The aim of this investigation was to develop a protocol to be used in asymmetric protoplast fusions with breeding material of melon and cucumber. Efficient methods for plant regeneration from unfused protoplasts of commercial melon lines were established and are reported. Ploidy levels of explant material and plants, regenerated from protoplasts were analyzed. Electrofusion was carried out between melon protoplasts and irradiated and non-irradiated donor protoplasts of cucumber. Although initial plating efficiencies of heterokaryons were high, development stopped after a few divisions. In control experiments, shoots were regenerated at high frequencies. In only two fusion experiments, development continued to the callus stage, but further development was not observed. When analyzed with PCR using arbitrary primers, the majority of these calli DNA were identical to the melon DNA. However, a few of the examined calli, although being mainly homologous to melon, were observed to have new bands corresponding to bands specific for cucumber. Due to sexual incompatibility, successful hybridization between cucumber and melon was never obtained by sexual crosses. We suggest that the failure to regenerate plants in our fused material could be explained partially by an analogous somatic incompatibility reaction.Abbreviations BA benzyl adenine - 2,4-d 2,4-dichlorophenoxyacetic acid - FDA fluorescein diacetate - FITC fluorescein isothiocyanate - IAA indoleacetic acid - MS Murashige & Skoog - NAA naphtalene acetic acid - PEG polyethylene glycol - PE plating efficiency - RAPD random amplified polymorphic DNA     

A comparison of mineral uptake and translocation by above-ground and below-ground root systems ofSalix syringiana

Nutrient uptake and translocation by above-ground adventitious roots and below-ground roots of woodySalix syringiana saplings were studied with gamma spectrometry. Each of four radionuclides (⁷⁵Se,¹³⁸Cs,⁵⁴Mn, and⁶⁵Zn) administered to adventitious and belowground roots were detected in stems and leaves within one month. Nuclides tended to be immobilized in the leaves and branches closest to the adventitious roots that absorbed them, while nuclides absorbed from below-ground sources were distributed more evenly throughout the plant. The capacity of adventitious roots to acquire nutrients from above-ground sources suggests they function as a potential auxiliary pathway of nutrient uptake and might enhance plant nutrient status where below-ground root uptake it hindered by adverse soil conditions.     

Ploidy of somatic embryos and the ability to regenerate plantlets in melon (Cucumis melo L.)

Summary The number of chromosomes in cells of callus, somatic embryos and regenerated plantlets during somatic embryogenesis were examined in two cultivars of melon (Cucumis melo L.). Somatic embryos were diploid (50.0%/32.1%), tetraploid (38.5%/57.5%) and octoploid (11.5%/10.4%) whereas in callus cells diploidy (41.9%/43.3%), tetraploidy (27.9%/25.8%), octoploidy (11.6%/15.5%) and a low frequency of other types of ploidy and aneuploidy were observed. Mixoploid somatic embryos were not observed. These results suggest that the somatic embryos were selectively differentiated from diploid, tetraploid and octoploid cells, and that endopolyploidization of cultured cells occurred before the start of cell division leading to somatic embryogenesis. The ratio of diploid to tetraploid (1.30/0.55) in somatic embryos was less than that in callus cells (1.50/1.68) while ratios of diploid to octoploid (4.35/3.09) and tetraploid to octoploid (3.35/5.52) in somatic embryos were greater than those in callus cells (3.61/2.80 and 2.40/1.67). Therefore, it appears that the ability of callus cell to differentiate into somatic embryos increases in the following order: octoploid < diploid < tetraploid. Regenerated plantlets were diploid (65.5%/55.1%) and tetraploid (34.5%/44.9%). No octoploid plantlets were observed. The ratio of diploid to tetraploid in regenerated plantlets (1.72/1.23) was greater than that in somatic embryos. Therefore, it appears that the ability of somatic embryos to develop into plantlets increases in the following order: octoploid < tetraploid < diploid.     

Ammonia and O2 uptake in relation to proton translocation in cells of Nitrosomonas europaea

The uptake of ammonia and O₂ by washed cells of Nitrosomonas has been followed simultaneously and continuously using electrode techniques. The stoichiometry of NH ₄ ⁺ oxidation, O₂ uptake and NO ₂ ^- production was 1 : 1.5 : 1.0 and for NH₂OH oxidation a ratio of 1 for O₂ : NO ₂ ^- . A variety of inhibitors of electron transport and metals as well as uncouplers restricted ammonia uptake more markedly than O₂ utilization. There is good evidence for the involvement of copper in the NH ₄ ⁺ uptake process.A quinacrine fluorescence technique has been used to study the proton extrusion by washed cells on adding NH₄Cl and NH₂OH respectively as substrates. The uptake of NH ₄ ⁺ was followed by the extrusion of H⁺ and this process was depressed by those inhibitors which were also effective in the electrode experiments. A requirement for copper is also established for the translocation of protons into the medium, resulting from the uptake of NH ₄ ⁺ by cells.Abbreviations mCCCP carbonyl cyanide m-chlorophenylhydrazone - DBP 2,4 dibromophenol - DCCD N-N-dicyclohexylcarbodimide - DIECA Sodium diethyldithiocarbamate - DNP 2,4 dinitrophenol - HOQNO 2-heptyl-4-hydroxyquinoline-N-oxide - NBD chloride 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole - N-serve 2-chloro-6-trichloromethyl-pyridine - PCP pentachlorophenol - 2-TMP 2-trichloromethyl-pyridine - TPB tetraphenylboron - TTFA 1-[thenoyl-(2)]-3,3,3-trifluoracetone - KSCN Potassium thiocyanate     

Construction of a fosmid library of cucumber (Cucumis sativus) and comparative analyses of the eIF4E and eIF(iso)4E regions from cucumber and melon (Cucumis melo)

A fosmid library of cucumber was synthesized as an unrestricted resource for researchers and used for comparative sequence analyses to assess synteny between the cucumber and melon genomes, both members of the genus Cucumis and the two most economically important plants in the family Cucurbitaceae. End sequencing of random fosmids produced over 680 kilobases of cucumber genomic sequence, of which 25% was similar to ribosomal DNAs, 25% to satellite sequences, 20% to coding regions in other plants, 4% to transposable elements, 13% to mitochondrial and chloroplast sequences, and 13% showed no hits to the databases. The relatively high frequencies of ribosomal and satellite DNAs are consistent with previous analyses of cucumber DNA. Cucumber fosmids were selected and sequenced that carried eukaryotic initiation factors (eIF) 4E and iso(4E), genes associated with recessively inherited resistances to potyviruses in a number of plants. Indels near eIF4E and eIF(iso)4E mapped independently of the zym, a recessive locus conditioning resistance to Zucchini yellow mosaic virus, establishing that these candidate genes are not zym. Cucumber sequences were compared with melon BACs carrying eIF4E and eIF(iso)4E and revealed extensive sequence conservation and synteny between cucumber and melon across these two independent genomic regions. This high degree of microsynteny will aid in the cloning of orthologous genes from both species, as well as allow for genomic resources developed for one Cucumis species to be used for analyses in other species. Names are necessary to report factually on available data; however, the US Department of Agriculture (USDA) neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable.     

A genetic map of melon (Cucumis melo L.) with RFLP, RAPD, isozyme, disease resistance and morphological markers

One hundred and ten markers were analysed for linkage in 218 F₂ plants derived from two divergent cultivars (Védrantais and Songwhan Charmi) of Cucumis melo (L.). Thirty-four RFLPs, 64 RAPDs, one isozyme, four disease resistance markers and one morphological marker were used to construct a genetic map spanning 14 linkage groups covering 1390 cM of the melon genome. RAPD and RFLP markers detected similar polymorphism levels. RFLPs were largely due to base substitutions rather than insertion/deletions. Twelve percent of markers showed distorted segregation. Phenotypic markers consisted of two resistance genes against Fusarium wilt (Fom-1 and Fom-2), one gene (nsv) controlling the resistance to melon necrotic spot virus, one gene (Vat) conferring resistance to Aphis gossypii, and a recessive gene for carpel numbers (3 vs 5 carpels: p).     

Selenium uptake,translocation, assimilation and metabolic fate in plants

The chemical and physical resemblance between selenium (Se) and sulfur (S) establishes that both these elements share common metabolic pathways in plants. The presence of isologous Se and S compounds indicates that these elements compete in biochemical processes that affect uptake, translocation and assimilation throughout plant development. Yet, minor but crucial differences in reactivity and other metabolic interactions infer that some biochemical processes involving Se may be excluded from those relating to S. This review examines the current understanding of physiological and biochemical relationships between S and Se metabolism by highlighting their similarities and differences in relation to uptake, transport and assimilation pathways as observed in Se hyperaccumulator and non-accumulator plant species. The exploitation of genetic resources used in bioengineering strategies of plants is illuminating the function of sulfate transporters and key enzymes of the S assimilatory pathway in relation to Se accumulation and final metabolic fate. These strategies are providing the basic framework by which to resolve questions relating to the essentiality of Se in plants and the mechanisms utilized by Se hyperaccumulators to circumvent toxicity. In addition, such approaches may assist in the future application of genetically engineered Se accumulating plants for environmental renewal and human health objectives.     

Genetic mapping of a fusarium wilt resistance gene (Fom-2) in melon (Cucumis melo L.)

Fusarium wilt caused by Fusarium oxysporum f.sp. melonis is one of the most devastating diseases in melon production worldwide. The most effective control measure available is the use of resistant varieties. Identifying molecular markers linked to resistance genes can serve as a valuable tool for the selection of resistant genotypes. Bulked segregant analysis was used to identify markers linked to the Fom-2 genes, which confers resistance to races 0 and 1 of the fungal pathogen. Pooled DNA from homozygous resistant or homozygous susceptible progeny of F₂ cross between MR-1 and AY was screened using 240 PstI/MseI and 200 EcoRI/MseI primer combinations to identify AFLP markers linked to Fom-2. Fifteen markers potentially linked to Fom-2 were identified, all with EcoRI/MseI primer pairs. These were mapped relative to Fom-2 in a backcross (BC) population of 60 progeny derived from MR-1 × AY with AY as recurrent parent. Two AFLP markers (ACT/CAT1 and AAC/CAT1) flanked the gene at 1.7 and 3.3 cM, respectively. Moreover, AFLP marker AGG/CCC and the previously identified RAPD marker 596-1 cosegregated with Fom-2. These two dominant markers were converted to co-dominant markers by designing specific PCR primers that produced product length polymorphisms between the parents. A survey of 45 melon genotypes from diverse geographic origins with the co-dominant markers demonstrated a high correlation between fragment size and the resistance phenotype. These markers may therefore be useful in marker-assisted breeding programs.     

Phosphorus and pH relationships in an andic soil with surface and incorporated organic amendments

Muskmelon seedlings were grown hydroponically in a greenhouse and starved of nitrogen and/or phosphorus for 4 weeks. They were then transferred to an optimal N and P regime or to the opposite stress for an additional 3-week period. Nitrogen stress reduced markedly N, Ca, and chlorophyll contents of leaves and stems, but increased P content. Phosphorus stress reduced significantly P and K concentrations in stems and leaves but did not affect markedly chlorophyll content and did not result in N accumulation. Both stresses reduced significantly the area of the first leaf mainly by adversely affecting cell division. Repair of N and P concentrations in deficient seedlings by transfer to the optimal nutrition regime was more rapid in N- than in P-stressed seedlings.Contribution from the Agricultural Research Organization. The Volcani Center, Bet Dagan, Israel, No. 2351-E, 1988 series, Pl. Soil.     

有机酸类化感物质对甜瓜的化感效应

以甜瓜种质“新银辉”为材料,用苹果酸、柠檬酸、对羟基苯甲酸、肉桂酸、阿魏酸、水杨酸和香豆酸等7种有机酸类化感物质处理甜瓜种子和幼苗,探讨其对甜瓜的化感效应及作用机理.结果表明:苹果酸可以促进甜瓜种子发芽和幼苗胚根生长,抑制植株鲜重增加和胚轴生长;柠檬酸促进发芽,对羟基苯甲酸和肉桂酸抑制发芽,但三者均抑制胚根生长,且对鲜重和胚轴生长表现为低促高抑效应,高浓度肉桂酸对种子发芽和胚轴生长的抑制效应最强,可能是甜瓜重要的化感物质;阿魏酸和香豆酸对发芽表现为低促高抑效应,抑制鲜重、胚根和胚轴生长;水杨酸对发芽和胚轴生长表现为低促高抑效应、抑制鲜重和胚根生长.7种有机酸处理后过氧化物酶活性均增强,有机酸类物质对甜瓜的化感效应可能和其体内的过氧化氢水平有较高的相关性;苹果酸、肉桂酸、对羟基苯甲酸和水杨酸处理后甜瓜幼苗体内超氧化物歧化酶的活性基本呈下降趋势,柠檬酸、阿魏酸和香豆酸则表现为低促高抑效应;过氧化物酶活性变化较复杂,但基本随处理浓度升高而上升;丙二醛含量大多低于对照.