Speculations on carbon dioxide starvation, Late Tertiary evolution of stomatal regulation and floristic modernization

Ambient atmospheric CO₂ concentration ([CO₂]_a) has apparently declined from values above 200μmol mol⁻¹ to values below 200μmol mol⁻¹ within the last several million years. The lower end of this range is marginal for C₃ plants. I hypothesize that: (1) declining [CO₂]_a imposed a physiological strain on plants, and plant taxa evolving under declining [CO₂]_a tended to develop compensating mechanisms, including increased stomatal efficiency; (2) angiosperms were better able to adjust to declining [CO₂]_a than were gymnosperms and pteridophytes; and (3) angiosperm adjustment has been uneven. Fast-evolving taxa (e.g. grasses and herbs) have been better able to adapt to CO₂ starvation. If these propositions are true, stomatal adjustment mechanisms should show patterned variation, and a single pattern of stomatal regulation cannot be assumed.     

Adaptation of Escherichia coli to high osmolarity environments: Osmoregulation of the high-affinity glycine betaine transport system ProU

Abstract: A sudden increase in the osmolarity of the environment is highly detrimental to the growth and survival of Fscherichia coli and Salmonella typhimurium since it triggers a rapid efflux of water from the cell, resulting in a decreased turgor. Changes in the external osmolarity must therefore be sensed by the microorganisms and this information must be converted into an adaptation process that aims at the restoration of turgor. The physiological reaction of the cell to the changing environmental condition is a highly coordinated process. Loss of turgor triggers a rapid influx of K⁺ ions into the cell via specific transporters and the concomitant synthesis of counterions, such as glutamate. The increased intracellular concentration of K⁺-glutamate allows the adaptation of the cell to environments of moderately high osmolarities. At high osmolarity, K⁺-glutamate is insufficient to ensure cell growth, and the bacteria therefore replace the accumulated K⁺ ions with compounds that are less d eleterious for the cell's physiology. These compatible solutes include polyoles such as trehalose, amino acids such as proline, and methyl-amines such as glycine betaine. One of the most important compatible solutes for bacteria is glycine betaine. This potent osmoprotectant is widespread in nature, and its intracellular accumulation is achieved through uptake from the environment or synthesis from its precursor choline. In this overview, we discuss the properties of the high-affinity glycine betaine transport system ProU and the osmotic regulation of its structural genes.     

The glycinin box: a soybean embryo factor binding motif within the quantitative regulatory region of the 11S seed storage globulin promoter

The soybean embryo factor binding sequence in the glycinin A₂B_1a gene promoter was delimited to an A/T-rich 9 bp sequence, 5-TAATAATTT-3, designated as the glycinin box, by DNA footprinting and gel mobility shift assay using synthetic oligonucleotides. It was shown that the interaction with the factor takes place at a defined DNA sequence rather than at random A/T-rich sequence blocks in the glycinin 5 flanking region. There are four glycinin boxes in the quantitative regulatory region between positions – 545 and – 378 of the glycinin A₂B_1a promoter. Multiple nonamer motifs similar to the glycinin box were also found in the equivalent regions of other glycinin and legumin promoters, suggesting that they must be conserved as a binding site for the embryo factor that activates the differential and stage-specific expression of seed 11S globulin genes in leguminous plants.     

Genetic manipulation of 6-phosphofructokinase in potato tubers

The aim of this work was to discover whether genetic manipulation of 6-phosphofructokinase [EC 2.7.1.11; PFK(ATP)] influenced the rate of respiration of tuber tissue of Solanum tuberosum L. Transgenic plants were produced that contained the coding sequence of the Escherichia coli pfkA gene linked to a patatin promoter. Expression of this chimaeric gene in tubers resulted in a 14to 21-fold increase in the maximum catalytic activity of PFK(ATP) without affecting the activities of the other glycolytic enzymes. Tubers, and aged disks of tuber tissue, from transformed plants showed no more than a 30% fall in the content of hexose 6-monophosphates; the other intermediates of glycolysis increased threeto eightfold. Fructose-2,6-bisphosphate was barely detectable in aged disks of transformed tubers. The relative rates of ¹⁴CO₂ production from [1-¹⁴C]-and [6-¹⁴C]-glucose supplied to disks of transformed and control tubers were similar. Oxygen uptake and CO₂ production by aged disks of transformed tubers did not differ significantly from those from control tubers. The same was true of CO₂ production, in air, and in nitrogen, for tuber tissue. It is concluded that PFK(ATP) does not dominate the control of respiration in potato tubers.Abbreviations Fru2,6bisP fructose-2,6-bisphosphate - FW freshweight - GUS -glucuronidase - PFK(ATP) 6-phosphofructokinase - PFK(PPi) pyrophosphate: fructose-6-phosphate 1-phosphotransferase     

Sleep and cortical temperature in the Djungarian hamster under baseline conditions and after sleep deprivation

The Djungarian hamster (Phodopus sungorus) is a markedly photoperiodic rodent which exhibits daily torpor under short photoperiod. Normative data were obtained on vigilance states, electroencephalogram (EEG) power spectra (0.25–25.0 Hz), and cortical temperature (T_CRT) under a 168 h light-dark schedule, in 7 Djungarian hamsters for 2 baseline days, 4 h sleep deprivation (SD) and 20 h recovery.During the baseline days total sleep time amounted to 59% of recording time, 67% in the light period and 43% in the dark period. The 4 h SD induced a small increase in the amount of non-rapid eye movement (NREM) sleep and a marked increase in EEG slow-wave activity (SWA; mean power density 0.75–4.0 Hz) within NREM sleep in the first hours of recovery. T_CRT was lower in the light period than in the dark period. It decreased at transitions from either waking or rapid eye movement (REM) sleep to NREM sleep, and increased at the transition from NREM sleep to waking or REM sleep. After SD, T_CRT was lower in all vigilance states.In conclusion, the sleep-wake pattern, EEG spectrum, and time course of T_CRT in the Djungarian hamster are similar to other nocturnal rodents. Also in the Djungarian hamster the time course of SWA seems to reflect a homeostatically regulated process as was formulated in the two-process model of sleep regulation.Abbreviations EEG electroencephalogram - EMG electromyogram - N NREM sleep - NREM non-rapid eye movement - R REM sleep - REM rapid eye movement - SD sleep deprivation - SWA slow-wave activity - T_CRT cortical temperature - TST total sleep time - VS vigilance state - W waking