Tuberization in Potato at High Temperatures: Gibberellin Content and Transport from Buds

Warm temperatures (35°C day/30°C night) which inhibittuberization in potato (Solanum tuberosum L., cv. Sebago) increasedgibberellin activity in crude extracts from buds, but not frommature leaves, as determined by the lettuce hypocotyl bioassay.Changes in the growth of tubers and stolons indicate the occurrenceof basipetal movement of GA₃ applied to the terminal bud ora mature leaf. ¹⁴C labelling from GA₃ or mevalonic acid injectedjust below the terminal bud was recovered in the lower shoot,stolons and tubers, but the amount transported was greater atcool temperatures (20/15°C). It is concluded that high temperaturespromote the synthesis of gibberellin in the buds rather thantransport to the stolons. Solanum tuberosum L., potato, tuberization, gibberellin     

Clouds,shadows or twilight? Mayfly nymphs recognise the difference

1. We examined the relative changes in light intensity that initiate night‐time locomotor activity changes in nymphs of the mayfly, Stenonema modestum (Heptageniidae). Tests were carried out in a laboratory stream to examine the hypothesis that nymphs increase their locomotion in response to the large and sustained reductions in relative light intensity that take place during twilight but not to short‐term daytime light fluctuations or a minimum light intensity threshold. Ambient light intensity was reduced over a range of values representative of evening twilight. Light was reduced over the same range of intensities either continuously or in discrete intervals while at the same time nymph activity on unglazed tile substrata was video recorded. 2. Nymphs increased their locomotor activity during darkness in response to large, sustained relative light decreases, but not in response to short‐term, interrupted periods of light decrease. Nymphs did not recognise darkness unless an adequate light stimulus, such as large and sustained relative decrease in light intensity, had taken place. 3. We show that nymphs perceive light change over time and respond only after a lengthy period of accumulation of light stimulus. The response is much lengthier than reported for other aquatic organisms and is highly adaptive to heterogeneous stream environments.     

Effects of stream flooding on the distribution and diversity of groundwater‐dependent vegetation in riparian areas

1. Effects of the frequency and duration of flooding on the structural and functional characteristics of riparian vegetation were studied at four sites (n = 80, 50 × 50 cm, plots) along medium‐sized naturally meandering lowland streams. Special focus was on rich fens, which – due to their high species richness – are of high priority in nature conservation. 2. Reed beds, rich fens and meadows were all regularly flooded during the 20‐year study period, with a higher frequency in reed bed areas than in rich fen and meadow areas. In rich fens, species richness was higher in low frequency flooded areas (≤3 year^?1) than in areas with a high frequency of flooding (>3 year^?1) or no flooding, whereas species richness in reed beds and meadows was unaffected by flood frequency. 3. The percentage of stress‐tolerant species was higher in low intensity flooded rich fen areas than in high intensity and non‐flooded areas, indicating that the higher species richness in low frequency flooded rich fens was caused by competitive release. We found no indication that increased productivity was associated with high flooding frequencies. 4. We conclude that the restoration of morphological features in stream channels to increase the flooding regime can be beneficial for protected vegetation within riparian areas, but also that groundwater discharge thresholds and critical levels for protected vegetation should be identified and considered when introducing stream ecosystem restoration plans.     

Comparative Binding of 125I-and 99mTc-Labeled Native and Glycated Low-Density Lipoprotein to Human Microvascular Endothelial Cells-Potential for Atherosclerosis Imaging?

Native (n), glycated (g), and glycoxidated (go) low-density lipoproteins (LDL) were labeled with ¹²⁵I or ^99mTc, and the labeling efficiency and binding were assessed for potential use of these LDL compounds in imaging analysis of atherosclerotic lesions (PPAR-γ receptors) by determining the number of specific receptors for nLDL, gLDL or goLDL on human microvascular endothelial cells as well as the K_D s using either ¹²⁵I-or ^99mTc-labeled LDLs. The specific activity of labeled gLDL and goLDL was much higher (for goLDL 20 times higher) than that of nLDL. Gel filtration of labeled LDLs revealed, however, that ^99mTc–g/goLDL is significantly degraded by the labeling reaction. No fragmentation was observed for ^99mTc-nLDL and all the ¹²⁵I-labeled LDL forms. Binding studies using both ¹²⁵I-and ^99mTc-nLDL indicated a weak binding affinity (K_D 10^{? 7}mol/L) to human microvascular endothelial cells. The binding affinity of ¹²⁵I-g/goLDL to these cells was significantly higher (K_D 10^{? 9}mol/L) and could be increased further by preactivation of the endothelial cells using TNFα. Incubation with ^99mTc-goLDL, however, did not result in specific binding of the ligand, possibly as a consequence of the fragmentation of the lipoprotein during the labeling. Scatchard transformation of the binding data with ^99mTc-gLDL revealed the presence of only a few binding sites. This was in contrast to the results obtained with ¹²⁵I-labeled gLDL, which revealed a much higher membrane density of scavenger receptors for this ligand. We conclude that for in vitro binding studies as well as for potential in vivo imaging, only ¹²⁵I-labeled goLDL should be used, whereas nLDL may be applied as ¹²⁵I-or ^99mTc-labeled ligand.     

Oxygen uptake in coprophilous beetles (Aphodius, Geotrupes, Sphaeridium) at low oxygen and high carbon dioxide concentrations

Abstract. The rate of O₂ consumption was measured in five coprophilous beetle species (common in Denmark) at O₂ concentrations from 1–21%. With the exception of the mainly soil-living Geotrupes spiniger (Marsham) (Geotrupidae), these beetles are probably exposed to severe hypoxia in fresh cattle pats. Aphodius fossor (Linnaeus), A. contaminatus (Herbst) (Aphodiidae) and Sphaeridium lunatum Fabricius (Hydrophilidae) maintained normal movements and a normal rate of 0₂ uptake (for at least 30 min) at only 1% O₂. There is no evidence, therefore, that the beetles switch to anaerobic metabolism under these conditions. This ability to regulate respiration, and hence to extract 0₂ at very low concentrations, is exceptional even among terrestrial arthropods living in soil or other potentially hypoxic substrates. In A. rufipes (Linnaeus), respiration declined at ambient concentrations below 2% O₂, and in G. spiniger the ability to regulate respiration seemed to fail at even higher concentrations. In four of the species (G. spiniger was not tested), about 11% CO₂ (the level in a dung pat at 2% O₂) did not affect the O₂ uptake at 2% O₂.     

Tuberization in Potato at High Temperatures: Promotion by Disbudding

The role of the terminal and axillary buds, as presumptive organsof gibberellin synthesis, in the control of tuberization inpotato (Solanum tuberosum L., cv. Sebago) at high temperatureswas studied. Decapitation alone strongly promoted the outgrowthof axillary buds, but did not promote tubenzation. When growthof the axillary buds was suppressed by the use of chemical pruningagents (MH, TIBA or 1-decanol), tuberization was promoted. Manualremoval of the buds promoted tuberization to a similar extent.The results are consistent with the hypothesis that the budsare major sites of gibberellin synthesis in the potato, andthat high temperatures stimulate the synthesis of gibberellinsand their export to the stolons, where they inhibit tuber formation. Solarium tuberosum L., potato, tuberization, temperature, disbudding, chemical pruning, gibberellins