Production of ethylene by gravistimulation: a potential problem with the interpretation of data from some experimental techniques

Abstract. Gravistimulation was investigated as a potential and unwanted component in the interpretation of physiological investigations on plants. Using both seedlings and mature sunflower plants, two situations are described where gravistimulation contributes significantly to the outcome of an experiment not initially designed to include this parameter. The number of adventitious roots formed in derooted seedings decreased when the tops of the plants were allowed to bend over under their own weight, and the effect correlated positively with the rate of ethylene production by non-vertical stems. In droughted mature plants, and increase in leaf and stem ethylene caused by water stress was supplemented by additional ethylene produced in the lower halves of stems. Drought had caused these stem tissues to wilt, become gravistimulated, and thus produce more ethylene. Other situations in which gravistimulated ethylene production and its physiological consequences are likely to be complicating factors in experiments are discussed. It is concluded that procedures that unnecessarily place experimental material in non-vertical orientations should be avoided.     

Temporal response of stream benthic macroinvertebrate communities to the synergistic effects of anthropogenic acidification and natural drought events

1. We evaluated whether the surprisingly weak biological recovery associated with declines in acid deposition were related to drought‐induced re‐acidification of streams. We used test site analysis (TSA) to characterise temporal changes (1995–2003) in the degree and nature of impairments to stream benthic macroinvertebrate (BMI) communities influenced by acid deposition and drought. 2. The BMI communities in four historically impacted test streams were compared with communities in 30 minimally impacted reference streams. Six multivariate (e.g. ordination axes scores) and four traditional (e.g. % Diptera) summary metrics were used to describe BMI communities. Using all metrics simultaneously (i.e. Mahalanobis or generalised distance), the TSA provided a single probability that a test community was impaired. If a test community was significantly impaired, a further analysis was done to identify the metric(s) important in distinguishing the test community from reference condition. 3. Results of the TSAs indicated that the generalised distances between test communities and the reference condition were inversely related to stream water pH (n = 36). The TSAs also indicated ordination metrics based on BMI abundance were important in distinguishing significantly impaired communities from reference conditions. Temporal trends indicated that there has been short‐term recovery of these BMI communities, but that overall improvements have been hampered by acid or metal toxicity associated with drought‐induced re‐acidification of the streams. 4. Our use of a variety of summary metrics to obtain a single statistical test of significance within the context of the reference‐condition approach provided a simple and unambiguous framework for evaluating the biological condition of test sites.     

Forest–flood relation still tenuous – comment on 'Global evidence that deforestation amplifies flood risk and severity in the developing world' by C. J. A. Bradshaw, N.S. Sodi, K. S.-H. Peh and B.W. Brook

In a recent paper in this journal, Bradshaw and colleagues analyse country statistics on flood characteristics, land cover and land cover change, and conclude that deforestation amplifies flood risk and severity in the developing world. The study addresses an important and long-standing question, but we identify important flaws. Principal among these are difficulties in interpreting country statistics and the correlation between population and floods. We review current knowledge, which suggests that the removal of trees does not affect large flood events, although associated landscape changes can under some circumstances. Reanalysis of the data analysed by Bradshaw and colleagues shows that population density alone already explains up to 83% of the variation in reported flood occurrences, considerably more than forest cover or deforestation (<10%). Feasible explanations for this statistical finding – whether spurious or causative – are not difficult to conceive. We, therefore, consider the conclusion of Bradshaw and colleagues to be unsupported. However, their study is a valuable first step to show how these or similar flood data might be used to further explore the relationship between land cover and flooding.     

Regulation of Electrogenic Pumping in Barley by pH and ATP

The relationship of the electrogenic pump to the ATP concentrationin barley roots was examined. Excision, salt accumulation andchanges in temperature produced changes in the ATP concentrationwhich did not correlate with changes in membrane potential (_m).Illumination of seedlings prior to excision of the root elevatedthe ATP level and caused _m to hyperpolarize. Metabolic inhibitionby sodium azide resulted in a fall in ATP concentration andmembrane depolarization. With treatment in azide for longerthan 10 min there was a linear relationship between ATP concentrationand _m. Time-courses of the effects of azide and carbon monoxideshowed that this relationship did not hold at short treatmenttimes because the ATP concentration fell more rapidly than thedecay of _m. Application of butyrate or fusicoccin produced littleor no change in the ATP concentration but both caused significantchanges in _m. The effects on _m of butyrate, fusicoccin, external pH and metabolicinhibitors were considered to be consistent with regulationof electrogenic pumping by cytoplasmic pH. Key words: Cytoplasmic pH, Electrogenic pumping, Fusicoccin, Butyrate     

Proportions and function of the limbs of glyptodonts

Vizcaíno, S.F., Blanco, R.E., Bender, J.B. & Milne, N. 2010: Proportions and function of the limbs of glyptodonts. Lethaia, Vol. 44, pp. 93–101. This study examines the limb bone proportions and strength of glyptodonts (Xenarthra, Cingulata). Two methods are used to estimate the body mass and location of the centre of gravity of the articulated specimens. These estimates, together with measurements of the femur and humerus, are used to calculate strength indicators (SI). The other long bones of the limbs are used to calculate limb proportion indices that give an indication of digging ability, speed, and limb dominance in armadillos, the glyptodonts’ living closest relatives. The results show that regardless of how the body mass and centre of gravity are calculated, the majority of the glyptodont’s weight is borne by the hindlimbs. The SI calculations show that femora are sturdy enough to bear these loads. The fact that the femora have higher SI than the humerii indicates that sometimes the hindlimbs are required to bear an even greater proportion of the body weight, possibly when rising to a bipedal posture or pivoting on their hindlimbs to deliver a blow with their armoured tail. The analysis of limb proportions indicates that both the hindlimb and the forelimb have proportions that correlate strongly with body mass. This outcome supports the other results, but also shows that forelimbs must be also involved in manoeuvring the glyptodont body. □Glyptodonts, Mammalia, Xenarthra, limbs, strength indicators.     

Coevolution of mistletoes and frugivorous birds?*

Small frugivorous birds that feed largely on the fruits of stem-parasitic mistletoes have independently evolved in various parts of the world. Local populations of mistletoes may be dispersed almost exclusively by these birds. Four attributes of mistletoe dispersal systems may have enhanced the evolution of reciprocal dependence between mistletoes and specialized dispersers: (1) Safe sites for mistletoe seeds (i.e. the young branches of a compatible host) are precisely defined in space and time. (2) The viscidity of mistletoe seeds induces smaller dispersers to deposit seeds in safe sites. (3) Frugivores differ markedly in the efficiency with which they disperse mistletoe seeds to safe sites. (4) Relatively large viscid fruits and adaptive fruiting displays exclude or deter most members of the potential disperser guild. Some birds have anatomical adaptations as a result of dietary specialization on mistletoe fruit, and some mistletoes have fruiting displays that target specialized birds or a narrow disperser spectrum. Coevolution between guilds of mistletoes and specialized dispersers is therefore probable. The uncoupled selective pressures that might have driven their coevolution are the mistletoes’ provision of fruit crops that are unavailable to more generalized frugivores, in return for seed dispersal to the small stems most suitable for infection. As in other mutualistic seed dispersal systems, phylogenetic, ecological and life history factors constrain the evolution of monophyletic interdependence, resulting in varying degrees and patterns of reciprocal specificity between mistletoes and dispersers.     

Phytosterols and Other Lipids as Survival Factors for Tetrahymena at 0–5 C

SYNOPSIS. Tetrahymena pyriformis syngen 1, mating type II, (optimal growth temperature ∼ 37 C) ordinarily dies out in 5-14 days at 0-5 C. Dying cells were lumpy, suggesting membrane damage. By supplying crude soy lecithin, survival at 0-5 C was prolonged (after growth in peptone-yeast-dextrin) to at least 22 weeks. Crude soy sterols or sitosterol or stigmasterol, and antioxidant, e.g., Ionox 330 or ascorbylpalmitate, permitted survival of cells in suspension or in growth media for at least 16-22 weeks. These sterols are known to protect against triparanol toxicity, which suggested that triparanol, which blocks cholesterol synthesis in higher animals, might enhance cold-induced injury. Triparanol was more toxic at 0–5 than at 28 C for cell suspensions and cells in growth medium; this toxicity was annulled by crude soy lecithin or β-sitosterol, the only phytosterol tested. The synthetic medium intended as a control on the crude media became toxic at 0–5 C. Protection against cold damage is discussed as a means of elucidating the role of sterols—especially phytosterols—and other lipids in maintaining the integrity of the ciliate cell membrane.     

A review of ploidy in the genus Prosopis (Leguminosae)

The genus Prosopis contains 44 species of trees and shrubs, the majority of which originate in the Americas. Most species are reported to be diploid, with a somatic chromosome number of 2 n  = 28. There are rare reports of polyploidy, although it is thought that these may represent polysomaty in root tissues. However, flow cytometry has recently indicated that P. juliflora is entirely tetraploid with a somatic chromosome number of 2 n  = 56. In order to clarify the situation, an extensive review of ploidy in Prosopis was undertaken, the first of its kind. The ploidy levels of 124 samples of Prosopis from 21 countries, including both the natural and introduced ranges, were analysed using flow cytometry. In addition, a comprehensive literature review was carried out, examining 305 published ploidy values and covering 32 of the 44 species of Prosopis . Flow cytometry analysis suggests that P. juliflora is the only tetraploid species, with a somatic chromosome number of 2 n  = 4 x  = 56, whilst the remainder of the species analysed are diploid with 2 n  = 2 x  = 28, including the first report for P. articulata (2 n  = 28). A critical review of published ploidy values shows that all species of Prosopis are reported to be entirely diploid, except P. glandulosa , P. juliflora , and P. koelziana , for which both diploid and tetraploid values have been recorded. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 425–438.