Effect of nitrogen deficiency on photosynthesis and the partitioning of 14C-labelled leaf assimilate in unshaded and partially shaded plants of Lolium temulentum

The effect of a deficiency of applied nitrogen on the rate of leaf photosynthesis, and on the subsequent partitioning of ¹⁴C-labelled leaf assimilate between new leaf, stem, tillers and root, was investigated in single plants of Lolium temulentum L., grown normally in controlled environments, or grown with collars shading the base of the plant. The nitrogen deficiency reduced the rate of leaf photosynthesis, increased the retention of assimilate in the leaf, suppressed the export of assimilate to tillers, and generally increased the export of assimilate to roots and to new leaves. Shading the base of the plant generally had little effect on the rate of leaf photosynthesis, reduced the export of assimilate to roots, and increased the export of assimilate to new leaf and to the stem, which elongated when shading was imposed.     

Evolution of the tetrapod ear: an analysis and reinterpretation

The dominant view of tetrapod otic evolution–the “standard view”–holds that the tympanum developed very early in tetrapod history and is homologous in all tetrapods and that the opercular process of the rhipidistian hyomandibula is homologous to the tympanic process of the stapes in lower tetrapods. Under that view, the labyrinthodont amphibians of the Paleozoic are usually considered ancestral to reptiles, and thus the “otic notch” of labyrinthodonts and the tympanum it presumably contained form the starting-point for middle ear evolution in reptiles. Four problems have classically been identified with the standard view: the differing relationships of the internal mandibular branch of N. VII (chorda tympani) to the processes of the stapes in amniotes and anurans; the differing orientations of the stapes in key fossil and living groups; the location of the tympanum in early fossil reptiles; and the transferral of the tympanum, during the origin of mammals, from the stapes to the articular bone of the lower jaw. An examination of these problems and of the solutions proposed under the standard view reveals the ad hoc, and therefore unsatisfactory, nature of the proposed solutions. To organize and review alternative hypotheses of otic evolution an analytical table is constructed, using three characters (tympanic process, Nerve VII, tympanum), each with two possible states. A total of eight hypotheses about middle ear evolution are possible under this system, one of which is the standard view. The seven “non-standard” hypotheses, only five of which have been argued in the literature, are briefly examined. Six of the “non-standard” hypotheses appear unattractive for various reasons, including reliance on ad hoc arguments. The seventh was first proposed by Gaupp in 1898. It is today almost universally ignored but apparently largely for historical rather than scientific reasons. This hypothesis, her called the “alternative view”, appears to rest on assumptions equally as plausible as those of the standard view. Moreover, it offers a solution of the problems associated with the standard view without, apparently, raising any similarly serious problems. This paper compares the standard and alternative views of middle ear evolution in detail. Comparison proceeds on two levels. On one level, they are compared in terms of the hypotheses of phyletic tetrapod relationships each promotes and how strongly each supports its hypothesis. Both views promote the same hypothesis of tetrapod relationships. The alternative view is the more parsimonious, but the difference is not considered sufficient to provide a choice. On another level, the two views are compared in terms of their implications for: (1) the evolution of relative and absolute auditory perceptive ability; (2) the origin of reptiles; (3) the evolution of the suspensorium and cranial kinesis; and (4) the origin and evolution of recent amphibians. The nature of the data required for a test of the implications of the two views is specified in each case. Where data are available. the alternative view is consistent and the standard view is inconsistent with these data. We conclude that the alternative view is the preferable hypothesis of middle-ear evolution. This conclusion implies the following: the tympanic membranes and the tympanic processes of the stapes in recent mammals, reptiles + birds. and frogs. are not homologous; the evolution of “special periotic systems” in the ancestors of amphibians and amniotes were independent events and preceded the evolution of tympanic membranes; the amphibian tympanic membrane. probably including that of labyrinthodonts. is not ancestral to that of amniotes. and that labyiinthodonts with an otic notch are not suitable as amniote ancestors; the stapes of early reptiles functioned primarily as part of the jaw suspension rather than in hearing; the mechanisms and abilities of sound perception in recent tetrapods are likely to be diverse rather than forming parts of a cline; and the lack of a tympanum in Gymnophiona and Caudata may be a retention of a primitive condition.     

The Influence of Testa Condition on the Imbibition and Vigour of Pea Seeds

Seed lots of peas with high rates of water uptake which containeda large proportion of seeds with at least one crack in the testaand were low in vigour, as indicated by electrolyte leakageand poor field emergence. Comparisons of the tetrazolium chloridestaining of the cotyledons after imbibition in water and polyethyleneglycol of two seed lots both with and without scarificationshowed that cracks in the testa could cause cell death by increasingthe rate of water uptake. Although the major cause of poor seedvigour appeared to be the incidence of cracks in the testa whichresulted in rapid water uptake, cell death, and solute leakage,the condition of the embryo also influenced the response towater uptake. The practical significance of these observationsto the problems of field emergence and seed production in peasis discussed.     

Effect of Source of Nitrogen on the Growth of Fiskeby Soya Bean: the Carbon Economy of Whole Plants

Fiskeby V soya bean was grown from seed germination to seedmaturation with two contrasting patterns of nitrogen metabolism:either wholly dependent on dinitrogen fixation, or with an abundantsupply of nitrate nitrogen, but lacking root nodules. The carbonand nitrogen economies of the plants were assessed at frequentintervals by measurements of photosynthesis, shoot and rootrespiration, and organic and inorganic nitrogen contents. Plantsfixing atmospheric nitrogen assimilated only 25–30 percent as much nitrogen as equivalent plants given nitrate nitrogen:c. 40 per cent of the nitrogen of ‘nitrate’ plantswas assimilated after dinitrogen fixation had ceased in ‘nodulated’plants. The rates of photosynthesis and respiration of the shootsof soya bean were not markedly affected by source of nitrogen;in contrast, the roots of ‘nodulated’ plants respiredtwice as rapidly during intense dinitrogen fixation as thoseof ‘nitrate’ plants. The magnitude of this respiratoryburden was calculated to increase the daily whole-plant respiratory loss of assimilate by 10–15 per cent over thatof plants receiving abundant nitrate. It is concluded that ‘nodulated’plants grew more slowly than ‘nitrate’ plants inthese experiments for at least two reasons: firstly, the symbioticassociation fixed insufficient nitrogen for optimum growth and,secondly, the assimila tion of the nitrogen which was fixedin the root nodules was more energy-demanding in terms of assimilatethan that of plants which assimilated nitrogen by reducing nitratein their leaves.     

Genetic differences among mainland and insular forms of the Citril Finch Serinus citrinella

The Citril Finch Serinus citrinella breeds in several mountains of central and southern Europe and on Corsica, Sardinia and Tuscany islands. Several studies have emphasized differences in phenotype and vocalization, and some authors consider mainland and insular forms to be two distinct species. A genetic approach based on the sequences of a mitochondrial DNA fragment was used to estimate genetic distance separating several populations. Individuals from the Alps and the Pyrenees belong to one group and the individuals from Corsica to the second. These results, discussed together with data on ecology, biometrics and vocalization, suggest keeping only one polytypic species which includes two distinct forms.     

Variability in response of potato cultivars to micropropagation.: In vitro performance

The variation in response of 23 cultivars to temperature and sucrose level was investigated for in vitro shoot cultures of potato. It was found that both temperature and sucrose level had a significant effect but in terms of the interactions with cultivars that temperature was the more important. The means and components of variation for the different treatments were examined to reveal the potential for selecting a treatment combination giving optimal expression of the characters measured to assess growth of the micropropagated plantlets. In the case of rapid multiplication systems, a high mean response for number of usable nodes combined with a low cultivar component of variation (i.e. a high response uniformly over cultivars) would be desirable. This combination of character expressions was generally achieved, in the present study, when cultures were raised at 20°C with 3% sucrose in the medium.     

Effects of gamma irradiation on the life stages of yellow flower thrips, Frankliniella schultzei (Trybom) (Thysanoptera: Thripidae)

Irradiation at a minimum absorbed dose of 250 Grays (Gy) has been approved by the USDA as a quarantine treatment for certain fruits in Hawaii to control four species of tephritid fruit flies. Subsequent research must determine whether this dose is sufficient to control other quarantine pests, such as mealybugs, thrips, mites, beetles, moths, and scale insects, on other commodities with export potential that are approved for irradiation treatment for fruit flies. This study demonstrated that irradiation at 250 Gy caused non‐emergence of eggs and pupae, failure of larval development, and sterility of adults of yellow flower thrips, Frankliniella schultzei (Trybom). Adults were the most resistant stage tested, with 100% mortality at 57, 36 and 30 days post‐treatment for the 250, 350 and 400 Gy treatments, respectively. Untreated adults survived up to 66 days. After receiving an irradiation dose of 250 Gy, no one‐ to two‐day old eggs hatched successfully, while 3–4‐day old eggs hatched but did not develop beyond the larval stage. Of the controls, 96.0% of 1–2‐day old eggs and 75.9% of the 3–4‐day old eggs hatched and survived through pupation. No first or second instar larvae treated with a target dose of 250 Gy were able to pupate. When pupae were irradiated at 250 Gy, 37% emerged as adults and all were sterile compared to 88.3% emergence of controls.