Taste receptor activity and feeding behaviour reveal mechanisms of white spruce natural resistance to Eastern spruce budworm Choristoneura fumiferana

The pattern of feeding of Eastern spruce budworm Choristoneura fumiferana (Clem.) (Lepidoptera, Tortricidae) is compared on foliage from white spruce Picea glauca (Moench) Voss. (Pinaceae) trees previously determined to be susceptible and resistant to defoliation by budworm. No differences are observed in electrophysiological responses from taste sensilla to aqueous extracts of the two foliage types, nor is there a preference for either extract type in a choice test. Acetone extracts from the two foliage types are both preferred to a control sucrose solution, although neither elicits a preference relative to the other. These results suggest that there is no difference in phagostimulatory power of internal leaf contents of the two foliage types. Longer‐term observation of feeding behaviour in a no‐choice situation shows no difference in meal duration, confirming the lack of difference in phagostimulatory power. However, on average, intermeal intervals are twice as long on the resistant foliage, leading to an overall lower food consumption during the assay. This result suggests an anti‐digestive or toxic effect of the resistant foliage that slows behaviour and limits food intake. Previous research has shown that waxes of the resistant foliage deter initiation of feeding by the spruce budworm and that this foliage contains higher levels of tannins and monoterpenes. The data suggest that the resistant foliage contains a post‐ingestive second line of defence against the spruce budworm.     

The Significance of the Obturator in the Control of Pollen Tube Entry into the Ovary in Peach (Prunus persica)

Changes in the obturator of the peach (Prunus persica) havebeen investigated and related to pollen tube growth in thisregion. At anthesis, the cells of the obturator are active andrich in starch reserves. Twelve days after anthesis these cellsproduce a secretion that stains for carbohydrates and for proteins.As the secretion is produced, starch vanishes from these cellsand they degenerate and collapse as callose is accumulated.Secretion is independent of pollination as it takes place ina similar fashion both in pollinated and in unpollinated flowers. Pollen tube growth along the obturator surface depends on thissecretion for, although pollen tubes reach the base of the styleseven days after pollination, they cannot grow on the obturatoruntil five days later, when the secretion is produced. Thisdiscontinuous secretion taking place at the obturator may providea mechanism that controls the entrance of pollen tubes intothe ovary in the peach. Prunus persica, peach, obturator, pollen tube     

Generative Cell Division and Sperm Cell Association in the Pollen Grain of Sambucus nigra

Generative cell division in tricellular pollen grains of Sambucusnigra L. (Caprifoliaceae) has been examined with light and electronmicroscopy. During division the generative cell is located inthe centre of the pollen grain, near to the nucleus of a surroundingvegetative cell. Conventional mitosis of the generative cellis followed by cytokinesis through centrifugal cell plate formation.Two sister sperm cells remain in spatial contact with each otherand are surrounded, as formerly their progenitor cell was, bythe vegetative cell. From the changes of shape of the generativecell during division and of the sperm cells it may be assumedthat the space between these cells and the vegetative one containsa labile, non-rigid, wall material. No plastids have been observedin the generative cell and its mitochondria appear to be unequallydistributed between the two future sperm cells during division. Sambucus nigra L., generative cell division, pollen, sperm cell association     

The Role of DNA Synthesis During Hypocotyl Elongation in Light and Dark

Fluorodeoxyuridine, an inhibitor of DNA synthesis, did not affectgermination and post-germinative growth in the aerial part oflettuce and Haplopappus gracilis seedlings when grown in thelight. In the dark, however, elongation of the hypocotyl wasinhibited by fluorodeoxyuridine, strikingly in lettuce and onlyslightly in Haplopappus gracilis. This could imply that thecontrolling mechanism of hypocotyl elongation is in some casesrelated to DNA synthesis, either because mitotic processes (oftenlittle taken into account in considering hypocotyl growth) areinvolved in the elongation of hypocotyls only when they aregrown in the dark, or because DNA synthesis affects cell elongationdirectly, or through the production of a greater number of endopolyploidcells in the dark. Using mainly autoradiographic and cytofluorimetricmethods, these possibilities were tested. Besides lettuce (Lactucasativa L. var. Great Lakes) and H. gracilis (Nutt.) Gray, radish(Raphanus sativus L. var. Tondo rosso quarantino) and soybean(Soya hyspida Sieb. and Zucc. var. Tokyo) seedlings were alsostudied. Fluorodeoxyuridine drastically inhibits cell elongation onlywhen it is preceded or accompanied by mitotic or endomitoticevents. Need for DNA synthesis during hypocotyl elongation,as well as during early post-germinative growth, seems to beof particular importance when endomitotic processes are involved. DNA synthesis, elongation, endoreduplication, fluorodeoxyuridine, Haplopappus gracilis (Nutt.) Gray, Lactuca sativa L., Raphanus sativus L., Soya hyspida Sieb and Zucc     

Transmission Electron Microscopical Observations on Stomatogenesis during Metamorphosis of Eufolliculina uhligi (Ciliophora: Heterotrichida)1

Stomatogenesis during metamorphosis of the marine loricate ciliate, Eufolliculina uhligi, was observed by transmission electron microscopy. Kinetosome proliferation in the stomatogenic territory leads to the formation of an anarchic field. This separates into the left adoral and the right paroral primordia. Both primordia consist of pairs of kinetosomes. One kinetosome of a pair is associated with one transverse and two postciliary microtubules; the other has one transverse microtubule. The postciliary microtubules of the adoral kinetosomes become divergent; those of the paroral kinetosomes become convergent. The adoral kinetosomes arrange in promembranelles. Then a third row of kinetosomes is produced anteriorly to each promembranelle. This third row is short at the peristome but longer in the buccal area. The paroral kinetosomes form a stichodyad. The buccal part of the paroral primordium is resorbed during formation of the buccal cavity. Stomatogenesis ends with the development of a functioning cytostome. During this process, the postciliary microtubules of the buccal adoral membranelles elongate and become associated with cytopharyngeal vesicles. Fusion of these vesicles with the cytostome has been observed some time after the completion of the oral structures.     

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     

Preliminary Studies on the Photosynthetic Structures of Trifolium alpinum L. as Related to Productivity

Trifolium alpinum L. is a high-quality alpine forage plant growingspontaneously from 1900 to 2800 m above sea level and is widelydistributed in Piedmont and the Valle d'Aosta (Italy), whereit can reach population frequencies of 90 per cent. Yields weredetermined on forage harvested in the Valle dell'Orco (Piedmont)and were comparable to cultivated clovers from higher latitudes;yields decreased progressively as the elevation increased. Thechemical and nutritional characteristics of the forage, thoughcomparable to clovers cultivated in the Po valley (Italy), were,however, more constant. The structure of the leaf lamina asrelated to elevation was investigated using light microscopy,TEM and SEM. This is complemented by data on chlorophyll concentration,succulence, specific leaf weight and area. At all elevationsT. alpinum lacks, apart from bundle sheath cell chloroplastsin a centrifugal arrangement, the structural characteristicsof C₄ plants. The chlorophyll a:b ratio (less than four) istypical of a C₂ plant. Succulence indices (S and S_m) were verylow, making CAM pathway photosynthesis unlikely. Unusual anddifficult to interpret structures included: small functionalchloroplasts in both the epidermises, stomata present almostexclusively in the upper epidermis and mitochondria enveloped(or enclosed) by chloroplasts. It was observed that, as theelevation increases, populations are selected which are well-adaptedfor gas exchange (increase in specific leaf area, stomatal densityand intercellular spaces) and characterized by a decrease inthe grana thylacoid:integrana thylacoid ratio (consistent withthe increase in the chlorophyll a:b ratio), the per cent water,S_m and the specific leaf weight. Trifolium alpinum L., alpine trefoil, leaf structures, photosynthesis, yield, elevation, C₂, C₄