Characterization of phosphate esters in the shoots and roots of alfalfa plants susceptible and resistant to bacterial wilt

Acid-soluble phosphate esters were determined in extracts of plant material after a 24 h exposure of the roots of intact alfalfa plants to nutrient media labelled with³²P_i. Similar phosphate ester patterns were found in 2-, 3-, 8-, and 9-week-old plants with the exception of Gra-P which could be detected only in shoot extracts. However, phosphate ester levels differed in the shoots and roots. Whereas Fru-P₂, Glc-6-P, Fru-6-P, and adenine nucleotides were more abundant in the shoots, Grn-P and P-choline levels were higher in the roots. Certain differences in the levels of P-esters were also recorded between plants susceptible and resistant to bacterial wilt.     

The uptake,distribution, and translocation of86Rb in alfalfa plants susceptible and resistant to the bacterial wilt and the effect ofCorynebacterium insidiosum upon these processes

Alfalfa (Medicago sativa; L.) plants susceptible (S) and resistant (R) to the bacterial wilt were fedvia roots with a nutrient solution labelled with⁸⁶Rb⁺, at different times after inoculating them withCorynebacterium insidiosum (McCull.) H. L. Jens. The infection did not influence⁸⁶Rb⁺ uptake per plant in the course of a 14-day-period following inoculation, however it did affect its distribution differentially in the S- and the R-plants.⁸⁶Rb⁺ uptake was significantly decreased due to the infection in the S-plants on the day 49 after the inoculation (a 4-h-exposure to⁸⁶Rb⁺), with the iona also being more slowly translocated to the shoots in diseased S-plants than in diseased R-plants. Likely factors causing these effects and their relationship to alfalfa resistance to the bacterial wilt are discussed.     

The uptake,distribution, leakage,and incorporation of32P into organic compounds in alfalfa plants susceptible and resistant to the bacterial wilt and the effect ofCorynebacterium insidiosum upon these processes

Higher³²P uptake per plant was found in the healthy resistant (R) alfalfa (Medicago saliva L.) plants when compared with the healthy plants susceptible (S) to the bacterial wilt, following the exposure of the roots of intact plants to the radiophosphate solution. The bacterial infection markedly decreased³²P uptake and radioactivity levels per dry matter in most organs of the R-plants on the day 8 and 14 after inoculation withCorynebacterium insidiosum whereas in the S-plants a decrease in³²P uptake was only found on the day 8.³²P leakage rate from the infected R-plant roots to the nonradioactive nutrient solution was higher than from the healthy ones on the day 8. At the same time³²P content in the organic P fraction was somewhat increased due to the infection in the R-plant roots, whereas³²P content in DNA was decreased. After foliar application,³²P distribution pattern was similar in the tissues of both the S- and the R-plants and was not affected due to the infection in the course of the 3rd week after inoculation. However, the bacterial infection markedly increased³²P translocation from the primary leaf to the rest of the R-plant. An erratum to this article is available at .     

Leakage of solutes from leaf discs of alfalfa plants susceptible and resistant to bacterial wilt caused byCorynebacterium michiganense pv.insidiosum

Seven day- and six week-old alfalfa (Medicago sativa L.) plants, susceptible and resistant to bacterial wilt, were inoculated withCorynebacterium michiganense pv.insidiosum (McCulloch) Dye & Kemp. Leakage of solutes absorbing UV light from leaf discs into distilled water was investigated. The bacterial infection did not affect solute leakage rate from unifoliate and trifoliate leaves of either susceptible or resistant plants at an early stage of the disease. This may indicate that cell membrane integrity in alfalfa leaf tissues was not impaired.     

Comparative proteomic analysis of bacterial wilt susceptible and resistant tomato cultivars

To investigate the molecular mechanisms of bacterial resistance in susceptible and resistant cultivars of tomato, a proteomic approach was adopted. Four cultivars of tomato were selected on the basis of their response to bacterial (Pseudomonas solanacearum) inoculation wherein cultivar Roma and Riogarande, and cultivar Pusa Ruby and Pant Bahr were considered as resistant and susceptible cultivars, respectively. Proteins were extracted from leaves of 3-week-old seedlings of the four cultivars and separated by 2-DE. A total of nine proteins were found to be differentially expressed between the susceptible and resistant cultivars. Amino acid sequences of these proteins were determined with a protein sequencer. The identified proteins belongs to the categories of energy, protein destination and storage, and defense. Of these proteins, a 60 kDa chaperonin and an apical membrane antigen were significantly upregulated in resistant cultivars compared with susceptible cultivars. Application of jasmonic acid and salicylic acid resulted in significant changes in levels of apical membrane antigen and protein disulfide-isomerase. Taken together, these results suggest that apical membrane antigen might be involved in bacterial resistance process through salicylic acid induced defense mechanism signaling in tomato plants.     

Changes in growth and in uptake,distribution and translocation of phosphorus in susceptible and resistant alfalfa plants induced byCorynebacterium insidiosum

The weight of alfalfa plants, especially roots of susceptible strain, decreased when inoculated withCorynebacterium insidiosum. At the 6th week after inoculation the³²P uptake per plant and its translocation into the above-ground organs were considerably decreased in susceptible plants. On the other hand, the³²P uptake was increased and the radiophosphorus was accumulated in above-ground organs in resistant plants.     

Changes in phosphorus metabolism in alfalfa plants induced by bacterial wilt

Radioactive phosphate was applied to the roots of intact alfalfa plants (Medicago sativa L.) on the 49th day after inoculation withCorynebacterium insidiosum (Me Culloch) Jensen and the³²P contents in different fractions of phosphoric compounds were determined. In inoculated plants, susceptible to bacterial wilt, the inorganio phosphate contents (³²Pinorg) was increased markedly and the³²P bound in organic compounds soluble in acids (³²Porg) decreased as compared with control. In roots of the same plants the³²P contents in phospholipid fraction and DNA were decreased. In tolerant inoculated plants the³²Pinorg increase and³²Porg decrease as compared with those changes in susceptible plants were less expressive. No expressive changes in determined³²P fractions have been proved in resistant plants without any visible disease symptoms.     

Growth of Pseudomonas phaseolicola in susceptible and in resistant bean plants

Race 1 of Pseudomonas phaseolicola introduced into leaves of susceptible Canadian Wonder bean plants multiplied logarithmically for 3–5 days, reaching final populations about 10⁵–10⁶ times the original. In resistant Red Mexican, Race 1 multiplied less rapidly to give final populations about 10²–10³ times the original. Race 2 behaved in susceptible Red Mexican as did Race 1 in Canadian Wonder. Macroscopic symptoms appeared in leaves when bacterial numbers reached their maxima. When introduced into the cotyledonary node Race 1 moved more rapidly upwards than downwards, and more rapidly and farther in Canadian Wonder than in Red Mexican. But even in Canadian Wonder the bacterium appeared only sporadically above the node of the first compound leaf. It could be isolated only rarely from chlorotic haloes around necrotic areas in leaves, or from chlorotic leaves not carrying lesions. Fewer lesions developed and the bacteria multiplied less in older than in younger leaves. Addition of glucose and casein hydrolysate to inocula of Race 1, separately or together, had little effect on growth in Canadian Wonder or Red Mexican, and the bacterium grew equally well in extracts of susceptible and of resistant plants. Preinoculation of leaves with an avirulent race reduced the number of lesions caused by a virulent race inoculated later, and also reduced growth of this race in leaves of a susceptible variety.     

Variation in the development of stem nematodes, Ditylenchus dipsaci, in susceptible and resistant crop plants

Dicotyledonous plants were reliably inoculated with stem nematodes by placing drops of 1.3% carboxymethylcellulose containing the surface sterilised worms between the cotyledons or in the leaf axils of recently emerged seedlings raised in pots of cool, moist soil. Inoculating onion leaves, bean stems and potato tubers or potato leaves gave variable results and inoculating onion, tulip and narcissus bulbs and lucerne and red clover stems was usually unsuccessful. An attempt to characterise 67 stem nematode populations by the reactions of a number of different plants failed for lack of useful differential hosts. Lucerne was, however, resistant to all but lucerne populations. Multiplication of stem nematode populations varied greatly between cultivars of lucerne or red clover. Some cultivars were resistant to some populations of lucerne or red clover stem nematodes and susceptible to others. These differences could not be ascribed to differences in viability of the nematodes or to differences in success of the inoculations. They indicate the presence of different pathotypes or biotypes in different populations of a so-called ‘host race’ and indicate the need for new resistant cultivars to be tested against a range of populations before they are released for general use. Amongst lucerne cultivars tested, Vertus was resistant to some lucerne stem nematode populations and susceptible to others. The supposedly resistant lucerne cultivars Euver and Lifeuil were as susceptible as was Europe. Amongst red clover cultivars tested, Redhead, Kühn, Changins and Mt Calme were susceptible, Britta, Lucrum and Temara were the least resistant, Renova, Rittinova and Quin were intermediate and susceptible to one or more of the populations tested but Norseman and especially Sabtoron were very resistant.     

Ascorbate peroxidase activity in resistant and susceptible plants of Lycopersicon esculentum.

Activity of redox-enzymes of AA system and of catalase was measured in two near-isogenic tomato lines, respectively resistant and susceptible to Tobacco Mosaic Virus infection. AFR reductase, DHA reductase and catalase showed quite similar activities in both lines, whereas AA peroxidase activity in resistant plants was 75% higher than in susceptible ones, with Km values about 4-fold lower. These data suggest that hydrogen peroxide scavenging operated by AA peroxidase could play an important role in the development of biological defence mechanisms against pathogens.     

Determination of the levels of abscisic acid-glucose ester in plants

Abscisic acid-β-D-glucopyranosyl ester (ABAGE) has been measured in several plant species using ²H-labelled ABAGE as an internal standard. The effects of water stress on the levels of ABAGE and its possible physiological role are discussed. Some chemical properties of ABAGE are described.     

Physiological changes in, and phosphate uptake by potato plants during development of, and recovery from phosphate deficiency

The development of phosphate deficiency (P-stress) was observed in rooted sprouts of Solanum tuberosum L. cv. Desiree growing in solutions without phosphate. Shoot growth was inhibited by P-stress within 3 to 5 days of terminating the phosphate supply, while significant effects on root growth were not recorded until 7 to 9 days. Thus, the shoot:root dry weight ratio decreased from 4.3 to 2.6 over a 10-day period. Growth in the absence of an exogenous phosphate supply progressively diluted the phosphorus in the plant. The proportional decrease in concentration was similar in roots and shoots over a 7-day period, even though the former were growing more quickly. The potential for phosphate uptake per unit weight of root increased rapidly during the first 3 days of P-stress. When the plants were provided subsequently with a labelled, 1 mol m^?3 phosphate solution, the absorption rate was 3 to 4-fold greater than that of control plants which had received a continuous phosphate supply. The increased rate of uptake by P-stressed plants was accounted for by an increase (3-fold) in the V_max of system 1 for phosphate transport and by a marked increase in the affinity of the system for phosphate (decrease in K_m). In the early stages of P-stress, before marked changes in growth were measured, the proportion of labelled phosphate translocated to the shoots increased slightly relative to the controls when a phosphate supply was restored. In the later stages of stress a greater proportion was retained in the root system of P-stressed plants than in that of controls. In plants with roots divided between solutions containing or lacking a phosphate supply, the increased absorption rate was determined by the general demand for phosphate in the plant and not by the P-status of the particular root where uptake was measured. By contrast, the poportion translocated was strongly dependent on the P-status of the root. The restoration of a phosphate supply to P-stressed plants was marked by a rapid increase in the P concentration in snoots and roots which returned to levels similar to unstressed controls within 24 h. The enhanced uptake rate persisted for at least 5 days, resulting in supra-normal concentrations of P in both shoots and roots, and in the formation of extensive necrotic areas between the veins of mature leaves. Autoradiographs showed accumulations of ³²P in these lesions and at the points where guttation droplets formed on leaves.     

Biochemical responses of glyphosate resistant and susceptible soybean plants exposed to glyphosate

Glyphosate is a wide spectrum, non-selective, post-emergence herbicide. It acts on the shikimic acid pathway inhibiting 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), thus obstructing the synthesis of tryptophan, phenylalanine, tyrosine and other secondary products, leading to plant death. Transgenic glyphosate-resistant (GR) soybean [Glycine max (L.)] expressing an glyphosate-insensitive EPSPS enzyme has provided new opportunities for weed control in soybean production. The effect of glyphosate application on chlorophyll level, lipid peroxidation, catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GOPX) and superoxide dismutase (SOD) activities, soluble amino acid levels and protein profile, in leaves and roots, was examined in two conventional (non-GR) and two transgenic (GR) soybean. Glyphosate treatment had no significant impact on lipid peroxidation, whilst the chlorophyll content decreased in only one non-GR cultivar. However, there was a significant increase in the levels of soluble amino acid in roots and leaves, more so in non-GR than in GR soybean cultivars. Root CAT activity increased in non-GR cultivars and was not altered in GR cultivars. In leaves, CAT activity was inhibited in one non-GR and one GR cultivar. GOPX activity increased in one GR cultivar and in both non-GR cultivars. Root APX activity increased in one GR cultivar. The soluble protein profiles as assessed by 1-D gel electrophoresis of selected non-GR and GR soybean lines were unaffected by glyphosate treatment. Neither was formation of new isoenzymes of SOD and CAT observed when these lines were treated by glyphosate. The slight oxidative stress generated by glyphosate has no relevance to plant mortality. The potential antioxidant action of soluble amino acids may be responsible for the lack of lipid peroxidation observed. CAT activity in the roots and soluble amino acids in the leaves can be used as indicators of glyphosate resistance.     

Plant growth and nutrient uptake characteristics of Fe-deficiency chlorosis susceptible and resistant subclovers

The objective of this study was to evaluate the growth and nutrient-uptake characteristics of Fe-deficiency resistant and susceptible subclover (Trifolium subterraneum L., T. yanninicum Katzn. and Morley, T. brachcalycinum Katzn. and Morley) cultivars on a calcareous soil. Ten subclover cultivars showing varying susceptibilities to Fe-deficiency chlorosis (Karridale, Nangeela, Geraldton, Mt. Barker, Woogenellup, Larisa, Trikkala, Rosedale, Koala and Clare) were grown on a low-Fe, calcareous soil (Petrocalcic Paleustoll) under moist (18% water content, 85% of water holding capacity) and water-saturated conditions using a Cone-tainer^® culture system. Chlorosis and its correlation with growth traits and mineral nutrition of the 10 cultivars were examined. The Fe-deficiency susceptibilities of the 10 cultivars decreased in the above order under the moist condition, but in slightly different order under the saturated condition. Shoot and root dry weights, total dry weight, and root-to-shoot ratio were each negatively correlated with chlorosis under both soil-moisture conditions, as was total shoot content of P, Ca, Fe, Mn and Zn. Shoot P and Fe concentrations were each positively correlated with chlorosis under the moist soil condition. Iron and Cu utilization efficiencies (biomass per unit weight of nutrient) in the shoot were each negatively correlated with chlorosis under the moist soil condition. These results suggest that there may be several characteristics of Fe-deficiency chlorosis resistance in subclovers, such as a more effective soil-Fe mobilizing mechanism(s), more balanced nutrition, lower required Fe concentration in the shoot, higher shoot-Fe utilization efficiency, and higher root/shoot ratio under Fe-deficiency stress conditions.     

Genetic and sexual separation between insect resistant and susceptible Barbarea vulgaris plants in Denmark

Co‐evolution between herbivores and plants is believed to be one of the processes creating Earth’s biodiversity. However, it is difficult to disentangle to what extent diversification is really driven by herbivores or by other historical‐geographical processes like allopatric isolation. In the cruciferous plant Barbarea vulgaris, some Danish individuals are resistant to herbivory by flea beetles (Phyllotreta nemorum), whereas others are not. The flea beetles are, in parallel, either resistant or susceptible to the plants defenses. To understand the historical‐evolutionary framework of these interactions, we tested how genetically divergent resistant and susceptible plants are, using microsatellite markers. To test whether they are reproductively fully compatible, resistant and susceptible plants were grown intermixed in an outdoor experiment, and the paternity of open‐pollinated offspring was determined by analysis of molecular markers. Resistant and susceptible Danish plants were genetically strongly differentiated and produced significantly fewer hybrids than expected from random mating or nearest neighbour mating. Our results suggest that the two types belong to different evolutionary lineages that have been (partly) isolated at some time, during which genetic and reproductive divergence evolved. A parsimonious scenario could be that the two plant types were isolated in different refugia during the previous ice age, from which they migrated into and met in Denmark and possibly neighbouring regions. If so, resistance and susceptibility has for unknown reasons become associated with the different evolutionary lineages.