An inexpensive photosynthetic irradiance sensor for ecological field studies

The design and characteristics of inexpensive and simply constructed equal-energy response photosynthetic irradiance sensors is described for use particularly where several cells are required in comparative ecological studies either above or below water. The dimensions of the sensors can be changed proportionally to suit different applications or components. The response of the sensor to irradiance at varying angles corresponds very closely to that required by the cosine law. The sensor is comparatively insensitive to other environmental variables in field use and gave a stable output; the long term drift was proportional to electrical output but in continuous use, drift is regular and could reach -0.08 year^-1 of the total. The spectral range and cosine response is discussed in comparison to other more expensive (x 5–10) commercially available, sensors and to local standards.     

Sperm cell surface characteristics of Plumbago zeylanica L. in relation to transport in the embryo sac

Myosin associated with the male germ cells of angiosperms interacts with actin, promoting transport of the non-motile generative and later sperm cells in the pollen tube. Myosin localizing on the sperm cell plasma membrane seems negligible in Plumbago, as reflected by the absence of: (i) anti-myosin labeling using immunoelectron microscopy, (ii) sperm motility on actin matrices, and (iii) electrophoretic movement changes after addition of antibody. Sperm cells injected directly into actively streaming Nitella internodal cells, however, follow actin bundles and their movement is sensitive to ATP and Mg²⁺. This may be based on simple charge binding since negatively charged latex beads also migrate on actin, whereas neutral or positively-charged latex beads do not. Sperm cells are negatively charged according to capillary microelectrophoresis, whereas killed sperm cells, which are positively charged do not migrate. The sperm cell that normally fertilizes the egg has a higher calculated charge (8.277 × 10³ esu/cm²) compared with the sperm cell that fuses with the central cell (6.120 × 10³ esu/cm²). Received: 15 December 1998 / Accepted: 21 January 1999     

The potential utility of postnatalskeletal developmental patterns in squamate phylogenetics

Postnatal patterns of skeletal development, includingthe sequence of appearance of ossification centres and the distributionof sesamoids, appear to be highly conserved species-level phenomenain squamates. As such, they are a potential source of charactersfor phylogenetic inquiry. These patterns, from 21 species representing14 crown squamate clades, form the basis for two analyses. In thefirst, the sequence of postnatal skeletal events is coded as charactersusing the sequence unit approach. This analysis reveals that thesequence of postnatal skeletal events might be useful for determiningrelationships at or above the level of crown clades, but not amongthem. The second analysis utilizes discrete data from postnatalskeletal development, such as the presence/absence of sesamoidsand the number of secondary centres in epiphyseal cartilages. Thesediscrete data appear capable of recovering the deeper divergenceswithin Squamata, but evolve too slowly to be informative at thelevel of crown clades. Thus, patterns of postnatal skeletal developmenthave the potential to help illuminate relationships throughout thesquamate tree. Further progress in this area will require the examinationof additional squamate species, the exploration of alternative codingschemes for developmental sequences, and comparable postnatal datafor Sphenodon .  © 2002 The Linnean Societyof London, Zoological Journal of the Linnean Society, 2002, 136 ,277−313.     

Measurement of mass flow of water in the stems of herbaceous plants

Abstract. Heat balance methods of stem flow measurement offer the opportunity to measure directly the mass flow rate of water in plants. We have tested one such approach; the constant power heat balance method of Sakuratani (1981). The results supported his statement of an approximate accuracy of 10% when measuring the transpiration rate of herbaceous plants. The response to sudden changes in stem flow rate is not instantaneous, but investigation of the time constant shows that it decreases as stem flow increases, to the extent that, at flow rates typical of daytime conditions the system is capable of accurately tracking changes in stem flow within 5 min or less.
We describe a new gauge design that is relatively rugged, simple to use with an appropriate digital datalogger and suitable for field use over prolonged periods of time. It does not injure or penetrate the stem, is amenable to continuous and direct recording of the mass flow rate of water in the stem and requires no calibration. A further refinement, which should improve both the accuracy and the dynamic response of the system, is proposed.     

Standard dimensions forcis N-methyl peptide unit and flexibility ofcis peptide units

The mean dimensions of thecis N-methyl peptide unit have been arrived at by analysing the crystal structure data on compounds containing such units. These dimensions can be used as standard in conformational studies on cyclic peptides. While the bonds meeting at C are almost coplanar, those meeting at N show a slight pyramidal disposition. A comparison of the dimensions of the normal and N-methylatedcis peptide units show that there are perceptible differences in the parameters connected with N. In addition, the flexibility of thecis peptide unit has been analysed by studying the distribution of the parameters in different classes of compounds such as cyclic di, tri and higher peptides. The salient features are: (i) The angle C^αCN in cyclic dipeptide and the angle C^δNC^α in higher peptides tend to be lower, when the peptide unit is associated with a prolyl residue; (ii) in cyclic tripeptides the internal anglesviz., C^αCN and CNC^α are significantly larger thereby increasing the intra-annular space; (iii) the bond C^α-C is distinctly shorter when it occurs in cyclic dipeptides. The results lead to the conclusion that thecis peptide unit takes up aneed-based flexibility in its dimension.     

Environmental factors influencing the occurrence of juvenile fish in the mangroves of Pagbilao,Philippines

128 fish species belonging to 54 families were collected from the mangroves of Pagbilao. Ambassis kopsi (Ambassidae) was the most abundant species.Fourteen environmental factors were correlated to the catch per unit time for some species. The occurrence of A. kopsi was positively correlated to nitrate in the water, carbon in the sediments and litter fall. Out of the 8 species investigated, 6 were positively correlated to litter fall. Three species showed positive correlation to phosphate in the water, two to organic carbon in the sediments, nitrate, silicate and pH, and one to salinity and carotenoids in water. The biomass of the total catch was correlated to carbon in the sediments and litter fall.     

A 31P NMR study of the internal pH of yeast peroxisomes

The internal pH of peroxisomes in the yeasts Hansenula polymorpha, Candida utilis and Trichosporon cutaneum X4 was estimated by ³¹P nuclear magnetic resonance (NMR) spectroscopy. ³¹P NMR spectra of suspensions of intact cells of these yeasts, grown under conditions of extensive peroxisomal proliferation, displayed two prominent P_i-peaks at different chemical shift positions. In control cells grown on glucose, which contain very few peroxisomes, only a single peak was observed. This latter peak, which was detected under all growth conditions, was assigned to cytosolic P_i at pH 7.1. The additional peak present in spectra of peroxisome-containing cells, reflected P_i at a considerably lower pH of approximately 5.8–6.0. Experiments with the protonophore carbonyl cyanide m-chlorophenylhydrazon (CCCP) and the ionophores valinomycin and nigericin revealed that separation of the two P_i-peaks was caused by a pH-gradient across a membrane separating the two pools. Experiments with chloroquine confirmed the acidic nature of one of these pools. In a number of transfer experiments with the yeast H. polymorpha it was shown that the relative intensity of the P_i-signal at the low pH-position was correlated to the peroxisomal volume fraction. These results strongly suggest that this peak has to be assigned to P_i in peroxisomes, which therefore are acidic in nature. The presence of peroxisome-associated P_i was confirmed cytochemically.Abbreviations CCCP Carbonyl cyanide m-chlorophenylhydrazon - DCCD N,N-dicyclohexylcarbodiimide     

猫颈动脉区压力和化学感受性刺激对巨细胞旁外侧核单位放电的影响

在31只氯醛糖和氨基甲酸乙酯麻醉的猫,观察了选择性激活颈动脉压力和化学感受器对巨细胞旁外侧核(PGL)单位放电的影响。136个PGL自发放电单位中,有84个在激活颈动脉压力感受器(BA)(新福林,1—2μg/kg,iv)和/或激活颈动脉化学感受器(CA)(nicotine 5—20μg,溶于0.25—0.5ml生理盐水中,注入甲状腺动脉)时,放电频率有变化。在这些有反应的单位中,16个仅对CA起反应(11个兴奋、5个抑制);54个以各种组合方式对CA和BA都起反应,其中以CA引起兴奋反应而BA引起抑制反应的占比例最大;14个仅对BA起反应(7个兴奋,7个抑制)。在定位分布上,那些只对CA起反应的单位多位于PGL的腹侧部份;仅对BA起反应的单位则位于对CA起反应单位的较背侧;对BA和CA均起反应的单位介于上述两者之间或在较深区域。这些结果表明,颈动脉区压力和化学感受器活动传入到PGL,并会聚在其中一些神经元上。 在PGL内全部有反应的单位中,68个对激活颈动脉压力感受器起反应,其中兴奋的29个,抑制的39个(P>0.05);70个对激活颈动脉化学感受器起反应,其中48个兴奋,22个抑制(P<0.005)。这些结果提示,BA对PGL神经元引起兴奋和抑制两种效应,而CA则诱发兴奋为主的反应。