Interactions between hosts and non-hosts of Pinus spp. and Matsucoccus josephi: anatomical responses of stem to infestation

Artificial infestation of seven pine species revealed that Matsucoccus josephi (Homoptera: Margarodidae) completes its development on Pinus brutia , P. eldarica and P. halepersis , whereas only a small number of the scale larvae infesting P. cunariensis and P. pined reached the second instar and none developed to the adult stage. M. josephi crawlers died while trying to feed on P. radiata and P. pinaster. Histological examination of the infested plant sections indicated that necrosis in shoot and stem barks of P. eldarica and P. halepensis occurs just before or after the scale completes its development. Injury reached the cambium, and traumatic resin ducts; parenchyma cells instead of tracheids and curved tracheids were formed. In P. brutia wound periderm was observed in the stem section but not in the shoot cortex following scale development. Wound periderm was also formed in the stem cortex of P. canariensis and P. pinena whereas no pathological changes were detected in the infested cortex of P. pinaster and P. radiata.
Mechanical lesions caused by needle punctures resulted in the production of parenchyma cells instead of tracheids in all four pine species investigated. The response of the pine cortex was non-specific; however several similarities in the response to scale infestation, such as the formation of resin ducts, were observed. We hypothesize that the response of the pine tissue to the scale saliva is a hypersensitive reaction. It is suggested that the development of Matsucoccus species on particular pine species is related to the scale's inability to trigger the defence system of the host while the larvae are feeding.     

Effect of Sink-Source Manipulations on the Photosynthetic Rate and Carbohydrate Content of Cucumber Cotyledons

Mayoral, M. L., Plaut, Z. and Reinhold, L. 1985. Effect of sink-sourcemanipulations on the photosynthetic rate and carbohydrate contentof cucumber cotyledons.-J. exp. Bot. 36 1551–1558. The photosynthetic rate of cucumber cotyledons (Cucumis sativuscv. Dahla) reached a maximum value of 12 mg dm^–2 h^–1,10 d after emergence. In 12-d-old seedlings removal of one cotyledondoubled the CO₂ fixation rate of the other, as observed 3 dafter treatment. When the primary leaf was removed, the photosyntheticrate of the cotyledons was decreased by 33%. At this stage ofgrowth elimination of the roots as a sink for assimilates bygirdling the hypocotyl affected neither the photosynthetic ratenor the carbohydrate content of the cotyledons. By contrast,in 18-d-old seedlings removal of the first leaf brought abouta 42% increase in the photosynthetic rate of the cotyledons.The simultaneous removal of the first leaf and one cotyledondoubled the rate of CO₂ fixation of the remaining cotyledon.Girdling the hypocotyl lowered the photosynthetic rate of thecotyledons by 73%. In both 12- and 18-d-old seedlings a decreaseor increase in the sink-source ratio was correlated with anincrease or a decrease respectively in the carbohydrate contentof the cotyledons. The stomatal resistance of the cotyledonswas not affected by any of the treatments. The effect of sink-sourcemanipulations on photosynthesis and on the level of carbohydratespresent in the cotyledons was more evident in those seedlingsgrowing under high light intensity (580 µE m^–2 s^–1),than in those exposed to 300 µE m^–2 s^–1 Key words: Sink-source relationship, cotyledons, photosynthesis     

Bacterial Symbiote Activation of Insect Parthenogenese Reproduction

ORGANISMS existing in mutualistic interrelationships often show unusual chemical interdependencies; for example, the pupation of the beetle Xyleborus ferrugineus depends on a sterol source provided by its ectosymbiotic fungi^{1, 2}. We now report that bacterial endosymbiotes are transmitted transovarially in this beetle. We also present evidence that natural maturation of the oocytes and haploid parthenogenesis in this insect depend on its bacterial symbiotes.     

Photosynthesis and Osmotic Adjustment of Two Sugarbeet Cultivars Grown under Saline Conditions1

The response of photosynthesis in two sugarbeet cultivars exposedto 180 mol m^–3 NaCl was investigated. An increase in photosynthesis was found in both cultivars duringthe initial 4 d after exposure to salinity. With longer timeperiods, CO₂ fixation in one cultivar, Monriac, was not affected,while under the same conditions, photosynthesis of the othercultivar, Kawemegapoly, was significantly reduced. Full osmoticadjustment was obtained in both cultivars, and the sensitivityof Kawemegapoly to salinity was not due to loss of turgor. Thepossible mechanisms responsible for this phenomenon are discussed.Rubisco activity responded to salinity as CO₂ fixation ratein both cultivars. Key words: Photosynthesis, osmotic adjustment, salinity     

Genetic diversity for drought resistance in wild emmer wheat and its ecogeographical associations

Wild emmer wheat (Triticum turgidum spp. dicoccoides (Körn.) Thell.), the tetraploid progenitor of cultivated wheat, is a potential source for various agronomical traits, including drought resistance. The objectives of this study were to characterize (1) the genetic diversity for drought resistance in wild emmer wheat, and (2) the relationship between drought responses of the wild emmer germplasm and the ecogeographical parameters of its collection sites. A total of 110 wild emmer accessions consisting of 25 populations and three control durum wheat cultivars were examined under two irrigation regimes, well-watered (’wet’) and water-limited (’dry’). Wide genetic diversity was found both between and within the wild emmer populations in most variables under each treatment. A considerable number of the wild emmer accessions exhibited an advantage in productivity (spike and total dry matter) over their cultivated counterparts. Most wild emmer wheat accessions exhibited a greater carbon isotope ratio (δ¹³C, indicating higher water-use efficiency) under the dry treatment and higher plasticity of δ¹³C relative to the cultivated controls, which may have contributed to the drought adaptations in the former. The most outstanding drought-tolerance capacity (in term of productivity under the dry treatment and susceptibility indices) was detected in wild emmer populations originated from hot dry locations. The results suggest that wild emmer has the potential to improve drought resistance in cultivated wheat.     

Similar patterns of local barn owl adaptation in the Middle East and Europe with respect to melanic coloration

The maintenance of phenotypic variation is a central question in evolutionary biology. A commonly suggested mechanism is that of local adaptation, whereby different phenotypes are adapted to alternative environmental conditions. A recent study in the European barn owl (Tyto alba) has shown that natural selection maintains a strong clinal variation in reddish pheomelanin‐based coloration. Studies in the region where phenotypic variation in this owl is the highest in Europe have further demonstrated that dark‐reddish and pale‐reddish owls exploit open and wooded habitats, predate voles and wood mice, and are long‐tailed and short‐tailed, respectively. However, it remains unclear as to whether these traits evolved as a consequence of allopatric evolution of dark colour in northern Europe and white colour in southern Europe, during which owls could have also evolved different morphologies and foraging behaviour. This scenario implies that covariation between coloration and foraging behaviour could be a specificity of the European continent, which is not found in other worldwide‐distributed populations. To investigate this issue, we studied a barn owl population in the Middle East. The results obtained show that, as in Central Europe, dark‐reddish female owls breed more often in the open landscape than their pale‐reddish female conspecifics, their offspring are fed with more voles than Muridae, and they are longer‐winged and longer‐tailed. These findings indicate that, in the barn owl, the association in females between pheomelanin‐based coloration and foraging behaviour and morphology is not restricted to the European continent but may well evolve in sympatry in many barn owl populations worldwide. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 447–454.     

Genomic dissection of drought resistance in durum wheat × wild emmer wheat recombinant inbreed line population

Drought is the major factor limiting wheat productivity worldwide. The gene pool of wild emmer wheat, Triticum turgidum ssp. dicoccoides , harbours a rich allelic repertoire for morpho-physiological traits conferring drought resistance. The genetic and physiological bases of drought responses were studied here in a tetraploid wheat population of 152 recombinant inbreed lines (RILs), derived from a cross between durum wheat (cv. Langdon) and wild emmer (acc# G18-16), under contrasting water availabilities. Wide genetic variation was found among RILs for all studied traits. A total of 110 quantitative trait loci (QTLs) were mapped for 11 traits, with LOD score range of 3.0–35.4. Several QTLs showed environmental specificity, accounting for productivity and related traits under water-limited (20 QTLs) or well-watered conditions (15 QTLs), and in terms of drought susceptibility index (22 QTLs). Major genomic regions controlling productivity and related traits were identified on chromosomes 2B, 4A, 5A and 7B. QTLs for productivity were associated with QTLs for drought-adaptive traits, suggesting the involvement of several strategies in wheat adaptation to drought stress. Fifteen pairs of QTLs for the same trait were mapped to seemingly homoeologous positions, reflecting synteny between the A and B genomes. The identified QTLs may facilitate the use of wild alleles for improvement of drought resistance in elite wheat cultivars.     

Unseasonable Latewood and Incrusted Pits are the Cause of Drying in Pinus halepensis and P. eldaricaInfested with Matsucoccus josephi

Mendel, Z. and Liphschitz, N. 1988. Unseasonable latewood andincrusted pits are the cause of drying in Pinus halepensis andP.eldarica infested with Matsucoccus josephi.—J. exp. Bot.39: 951–959. A study was made of the effects of Matsucoccus josephi (Insecta:Homoptcra: Margarodidae) on (a) water transport in Pinus halepensis,using a basic fuchsin solution and (b) the structural changesof the xylem of Pinus halepensis, P. brutia andP. eldarica usinga scanning electron microscope.Examinations were carried outin artificially and naturally infested plants. Transport ofthe fuchsin dye was arrested below the affected zone of heavilyinfested shoots, but reached the shoot apex through sparselyinfested segments or via segments heavily infested with thefirst larval stage. Heavily infested stem sections of P. halepensisand P.eldarica were characterized by narrow pits and incrustedpit membranes. In non-infested shoots and those infested withfirst or early second-scale larvae in both these species andheavily infested P. brutia shoots, there were typical earlywoodpits with wide pit apertures and thin membranes. It is suggestedthat blocking of water ascent in P. halepensis and P. eldaricastarts when female second-instar larvae complete their developmentand only when population density is relatively high. Therefore,it is considered that the accelerated drying of the growth ofP. halepensis and P. brutia is directly related to the narrowingof the pit apertures, which resembled those of latewood pitsalthough produced early in the season. The absence of changesin the xylem of heavily infested P brutia may explain why thisspecies tolerates a high density of M. josephi. The structuralmodification of the xylem caused by the scale may be relatedto imbalance in plant growth hormones which are either transmittedwith the insect saliva or formed in the plant by salivary enzymes. Key words: Xylem, Matsucoccus, Pinus     

Nitrate Reductase Activity of Wheat Seedlings during Exposure to and Recovery from Water Stress and Salinity

Nitrate reductase activity was inhibited as a result of reduced soil moisture potentials or application of NaCI to nutrient solutions. The decrease in enzyme activity of wheat seedlings exposed to salinity, was found 24 hours after exposure to stress. The effect of stress on nitrate reductase was found in cell-free extracts as well as in riro in assays of intact leaf sections. A recovery in enzyme activity was found after irrigation or after removal of seedlings from salinity. While relative water content of the leaves was restored within 3 hours after removal of stress, full recovery of enzyme activity occurred only after 24 hours. Cycloheximide and chloramphenicol suppressed the activity of nitrate reductase in non-stressed seedlings, but had no effect on the activity of plants exposed to salinity. However, during removal of stress, cycloheximide prevented completely the recovery of nitrate reductase, while chloramphenicol did not interfere with the recovery of the inhibited enzyme activity. It is concluded that a fraction of nitrate reductase may be located in the cytoplasm and lost activity during stress, probably due to inhibited protein synthesis. Another fraction which may be associated with chloroplasts, was inhibited by stress due to conformational changes or partial denaturation.