SEXUAL DIFFERENTIATION OF GRIFFITHSIA (CERAMIALES, RHODOPHYTA): NUCLEAR PLOIDY LEVEL OF MIXED-PHASE PLANTS IN G. JAPONICA1

Mixed-phase plants of Griffithsia japonica Okamura spontaneously occurred in a laboratory culture. Four female plants produced tetrasporangia and spermatangia in addition to their normal female reproductive structures (bisexual/mixed-phase plants), and four male plants produced tetrasporangia as well as spermatangia (male/mixed-phase plants). To determine the nuclear ploidy level of these mixed-phase plants, relative nuclear sizes of male, female, tetrasporangial, and mixed-phase plants were measured using a microscopic image analysis system. Haploid gametophytes could be distinguished from diploid tetrasporophytes by relative nuclear sizes, with the later having nuclei twice the size of the former. Relative nuclear sizes of the mixed-phase plants were similar to those of the haploid plants. Thus, the mixed-phase plants were determined to be haploid. Haploid mixed-phase plants of G. japonica have a potential to produce male, female and tetrasporangial reproductive structures. Sex determination models are discussed to explain "haploid" mixed-phase phenomena in red algae .     

Use of inexpensive pressure transducers for measuring water levels in wells

Frequent measurement of below ground water levels at multiple locations is an important component of many wetland ecosystem studies. These measurements, however, are usually time consuming, labor intensive, and expensive. This paper describes a water-level sensor that is inexpensive and easy to construct. The sensor is placed below the expected low water level in a shallow well and, when connected to a datalogger, uses a pressure transducer to detect groundwater or surface water elevations. Details of pressure transducer theory, sensor construction, calibration, and examples of field installations are presented. Although the transducers must be individually calibrated, the sensors have a linear response to changing water levels (r ² .999). Measurement errors resulting from temperature fluctuations are shown to be about 4 cm over a 35°C temperature range, but are minimal when the sensors are installed in groundwater wells where temperatures are less variable. Greater accuracy may be obtained by incorporating water temperature data into the initial calibration (0.14 cm error over a 35C temperature range). Examples of the utility of these sensors in studies of groundwater/surface water interactions and the effects of water level fluctuations on tree growth are provided.     

Effect of photosynthesis on dark mitochondrial respiration in green cells

Green plant cells can generate ATP in both chloroplasts and mitochondria. Hence the effect of photosynthesis on dark mitochondrial respiration can be considered at a variety of levels. Turnover of ceitric acid cycle dehydrogenases, which is essential for supply of carbon skeletons for amino acid synthesis, seems to be largely unaffected during photosynthesis. The source of carbon for the anaplerotic function of the citric acid cycle in light is however, not known with certainty. NADH generated in these reactions is probably not oxidised via the mitochondrial electron transfer chain coupled to ATP synthesis. However, it may be oxidised by the alternative cyanide-insensitive pathway, exported to the cytosol via the oxaloacetate-malate dicarboxylate shuttle or directly utilised for cytosolic nitrate reduction. Oxidation of succinate via cytochrome oxidase may also be similarly inhibited in light. Whether increase in the cytosolic ATP/ADP ratio in light is responsible for the inhibition of mitochondrial electron transfer to O₂ is not clearly established, because the ATP/ADP ratio is reported to be already quite high in the dark. Effective collaboration between photophosphorylation and oxidative phosphorylation in order to maintain the cytosolic energy charge at a present high level is discussed.     

The role of triiodothyronine in the regulation of synthesis rate and translatable mRNA level of fatty acid synthetase in a preadipocyte cell line

Triiodothyronine (T₃) effects on the activity, rate of synthesis and mRNA content of the key lipogenic enzyme, fatty acid synthetase, were studied in differentiating ob₁₇ preadipocytes cloned from ob/ob mouse epididymal adipose tissue. During differentiation in the presence of insulin, a 6–10-fold increase in both fatty acid synthetase specific activity and synthesis rate were reproducibly observed and occurred concomitantly. The relative synthesis rate exhibited a progressive elevation from 0.5% at confluence to a maximum level of 2% in the presence of insulin. The rate of the enzyme degradation determined by pulse-chase experiments was similar in differentiating cells and insulin-untreated cells of the same age ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, 40–42 h). Furthermore, the increase in the enzyme synthesis rate was preceded by a progressively elevating amount of mRNA encoding for this protein as detected by translation in a reticulocyte lysate cell-free system. It is thus suggested that the increment in total and neosynthesized fatty acid synthetase in essentially due to an increased enzyme synthesis, reflecting an increased relative content of its specific mRNA. T₃ included at a physiological concentration (1.5 nM) in the culture medium enhanced significantly both enzyme synthesis and its specific mRNA. The most important T₃ effect was an acceleration of both processes, a stimulation of the mRNA level being detected as early as day 3 post-confluence and maximum at day 5 when the effect on the synthetase synthesis rate and activity began to be enhanced. This suggests that T₃ would mainly affect fatty acid synthetase as a pretranslational level.     

Flavonoids in the leaves of Thymus: a chemotaxonomic survey

The flavonoid aglycone analysis of 20 Thymus taxa (most Iberic or Balearic endemics) shows the presence of luteolin, apigenin, acacetin, genkwanin, 6-hydroxyluteolin, xanthomicrol, cirsimaritin; four partially identified flavones, of which three are 6-OR-substituted and one flavonol. The differences observed between T. capitatus (L.) Hoffmanns. et Link (subgenus Coridothymus (Reichenb. fil.) Borbás) and the other species belonging to the subgenus Thymus (L.) Jalas, seem enough to maintain the separation of the two groups, but within the same genus, as proposed in Flora Europaea.     

Direct screening for high-level expression of an introduced α-amylase gene in plants

A method is described for obtaining transgenic plants with a high level of expression of the introduced gene. Tobacco protoplasts were transformed with an expression construct containing a translational fusion between mature -amylase from Bacillus licheniformis and the signal peptide of the tobacco PR-S protein. A total number of 5200 transformed protoplasts was cultured to microcalli and screened for -amylase expression by incubation on media containing starch followed by staining with iodine. The calli were divided into four classes, based on the resulting halo sizes on the plates. The halo sizes were found to correlated with the expression levels in transgenic plants regenerated from the calli. The expression levels varied between 0 and 0.5% of soluble leaf protein in the regenerated transgenic plants. Wider implications of this method are discussed.     

The periodic change in adenosine 3′,5′-monophosphate concentration in sea-urchin eggs

The level of adenosine 3′,5′-monophosphate (cyclic AMP) in the eggs of the sea urchin, Anthocidaris crassispina, was found to change periodically after fertilization. The minimum and maximum levels of cyclic AMP were 1.0·10^?7 M and 1.5·10^?6 M, respectively. The activity of adenylate cyclase in a 105 000 × g precipitate reached a plateau at 20 min after fertilization and stayed constant for at least 2 h. It was also found that 1.0 mM CaCl₂ increased the activity of adenylate cyclase in the same precipitate from unfertilized eggs. In contrast, phosphodiesterase activity changed periodically and correlated with cyclic AMP levels in the eggs. Up to a concentration of 1.5·10^?6 M cyclic AMP, phosphodiesterase activity was low, but it became activated when the level of cyclic AMP rose beyond this level. These results indicate that the change in the intracellular level of cyclic AMP is regulated mainly by the change in phosphodiesterase activity.     

Light-dependent quenching of chlorophyll fluorescence in pea chloroplasts induced by adenosine 5′-triphosphate

Addition of ATP to chloroplasts causes a reversible 25–30% decrease in chlorophyll fluorescence. This quenching is light-dependent, uncoupler insensitive but inhibited by DCMU and electron acceptors and has a half-time of 3 minutes. Electron donors to Photosystem I can not overcome the inhibitory effect of DCMU, suggesting that light activation depends on the reduced state of plastoquinone. Fluorescence emission spectra recorded at ?196°C indicate that ATP treatment increases the amount of excitation energy transferred to Photosystem I. Examination of fluorescence induction curves indicate that ATP treatment decreases both the initial (F_o) and variable (F_v) fluorescence such that the ratio of F_v to the maximum (F_m) yield is unchanged. The initial sigmoidal phase of induction is slowed down by ATP treatment and is quenched 3-fold more than the exponential slow phase, the rate of which is unchanged. A plot of F_v against area above the induction curve was identical plus or minus ATP. Thus ATP treatment can alter quantal distribution between Photosystems II and I without altering Photosystem II-Photosystem II interaction. The effect of ATP strongly resembles in its properties the phosphorylation of the light-harvesting complex by a light activated, ATP-dependent protein kinase found in chloroplast membranes and could be the basis of physiological mechanisms which contribute to slow fluorescence quenching in vivo and regulate excitation energy distribution between Photosystem I and II. It is suggested that the sensor for this regulation is the redox state of plastoquinone.