PHOTOSYNTHETIC ACCLIMATION OF PLANTS OF DIVERSE ORIGIN

Plants of 5 species were acclimated for periods of not less than 3 weeks in a desert and subalpine environment. Subsequent measurements of photosynthesis over a range of temperatures indicated both rate modifications and shifts in temperatures of optimal photosynthesis. Plants of all species acclimated in the coldest environment were more efficient in terms of percentage of maximum photosynthetic activity at colder temperatures. Conversely, plants acclimated in the desert environment were more efficient at warmer temperatures.     

DIEL PHASING OF THE CELL-CYCLE IN THE FLORIDA RED TIDE DINOFLAGELLATE, GYMNODINIUM BREVE

The diel cycle is a key regulator of the cell-cycle in many dinoflagellates, but the mechanisms by which the diel cycle entrains the cell-cycle remain poorly understood. In this study, we describe diel phasing of the cell-cycle in the Florida red tide dinoflagellate Gymnodinium breve Davis, determine the diel cue which serves to entrain the cell-cycle, and provide evidence for the presence of cyclin-dependent kinase (CDK), a cell-cycle regulator which may be responsive to this cue. Four laboratory isolates from the West Coast of Florida were compared. When grown on a 16:8 h LD cycle, all isolates displayed phased cell division, with the S-phase beginning 6–8 h into the light phase, and mitosis following 12–14 h later, as determined by flow cytometry. A naturally occurring bloom of G. breve, studied over one diel cycle, displayed diel cell-cycle phasing similar to that in the laboratory cultures, with the S-phase beginning during daylight and the peak of mitosis occurring approximately 4 h after sunset. In the laboratory cultures, the dark/light "dawn" transition was found to provide the diel cue which serves to entrain the G. breve cell-cycle, whereas the light/ dark "dusk" transition did not appear to be involved. Evidence for the presence of CDK in G. breve was obtained using two approaches: (1) identification of a 34-kDa protein, immunoreactive to an antibody against a conserved amino acid sequence (α-PSTAIR) unique to the CDK protein family and (2) inhibition of the cell-cycle by olomoucine, a selective CDK inhibitor. Together, these results provide the basis from which one can begin addressing mechanisms by which the diel cycle regulates the cell-cycle in G. breve.     

RESPONSES OF CERTAIN FRESHWATER PLANKTONIC ALGAE TO FLUORIDE1

The effects of dissolved fluoride supplied as NaF at up to 150 p.p.m. F^? (7.9 mM) on growth, photosynthesis, dark respiration, enolase activity and fluoride uptake were determined for six phytoplankters: Synechococcus leopoliensis (Racib.) Komarek (Cyanophyta), Oscillatoria limnetica Lemmermann (Cyanophyta), Ankistrodesmus braunii Brun (Chlorophyta), Scenedesmus quadricauda (Turp.) Bréb. (Chlorophyta), Cyclotella meneghiniana Kützing (Bacillariophyta) and Stephanodiscus minutus Grun. ex Cleve et Moll (Bacillariophyta). Growth (determined by absorbance at 660 nm or by cell-numbers) was unaffected by fluoride at up to 50 p.p.m. (2.6 mM) in all algae except S. leopoliensis, in which growth ceased transiently followed by resumption of growth at reduced rate. These effects showed a threshold at ca. 25 p.p.m. (1.3 mM) F^? and increased with increasing F^? concentration above this threshold. Photosynthetic O₂ evolution in the chlorophytes was unaffected by F^? at up to 50 p.p.m., whereas in S. leopoliensis F^? above ca. 25 p.p.m. caused a concentration-dependent inhibition of photosynthesis which was most pronounced at saturating irradiance. Dark O₂ uptake was unaffected at up to 50 p.p.m. in chlorophytes but was stimulated in S. leopoliensis. Enolase in clarified cell-extracts of all six algae was inhibited by F^?, with K_i values ranging from 27 to 319 μM. Fluorine (measured by proton-induced gamma-ray emission) could not be detected in chlorophytes exposed during growth to up to 50 p.p. m. F^?, but was detected in S. leopoliensis, O. limnetica and C. meneghiniana. Fluorine associated with cells of these algae increased as the external F^? concentration increased.     

SHORT-TERM RESPONSES OF NUTRIENT-DEFICIENT ALGAE TO NUTRIENT ADDITION1

Changes in net photosynthesis, dark respiration, ATP content, and some other aspects of composition were measured following phosphate or ammonium addition to cultures of the green alga Scenedesmus quadricauda (Turp.) Bréb. deficient in phosphorus or nitrogen. The deficient nutrient was rapidly taken up. Light-saturated net photosynthesis was depressed below the pre-addition rate during nutrient uptake and did not increase markedly above that rate until several hours after uptake was complete. Dark respiration, on the other hand, was markedly stimulated during uptake of the deficient nutrient and to a lesser extent after uptake was complete. Phosphate addition to P-deficient cells caused a large increase in the ATP content within 2–4 h of addition, whereas ammonium addition to N-deficient cells caused much less or no increase in ATP content. Short-term enrichment experiments to detect nutrient limitations are evaluated in the light of these and similar results taken from the literature. The available evidence shows that photosynthetic responses cannot reliably be used in short-term enrichments but changes in respiration or ATP content may be useful in certain circumstances.     

GENETICS OF RESISTANCE OF SALIX SERICEA TO A DIVERSE COMMUNITY OF HERBIVORES

We measured resistance of Salix sericea, the silky willow, to a diverse assemblage of 12 herbivores. We investigated the potential for multispecies coevolution among these herbivores by measuring genetic correlations between pairs of herbivores interacting within the component community. After measuring herbivore attack on half-sib families of potted S. sericea during three years, we found significant narrow-sense heritabilities of resistance to Phyllonorycter salicifoliella and Phyllocnistis sp. in 1991. Thus, there is the potential for selection on resistance to these two herbivores. Despite the many significant phenotypic correlations between herbivore abundances within a year, most genetic correlations between herbivore abundances within a year were not significant. The genetic and phenotypic correlation structure varied from year to year in this three-year study. Thus, it appears that there is the potential for evolution of resistance to the two herbivores for which we found significant heritabilities, but multispecies coevolution seems unlikely.     

Characterization of a Gibberellin-Insensitive Dwarf Wheat, D6899 : EVIDENCE FOR A REGULATORY STEP COMMON TO MANY DIVERSE RESPONSES TO GIBBERELLINS

The effects of gibberellin in two wheat varieties, Nainari 60 and D6899, have been studied. D6899 is a dwarf wheat having a single locus mutation, the Rht 3 gene (“Tom Thumb” gene), which is located on chromosome 4A. When compared with the standard height wheat variety, Nainari 60, D6899 does not have a slowdown in cellular metabolism such as respiration rate, protein content, rate of protein synthesis, and uptake of amino acids. The content of ATP is even higher in D6899. However, all of the gibberellin-mediated physiological processes that we have studied, including leaf elongation, synthesis and release of hydrolytic enzymes, and secretion of phosphate ions and reducing sugars in aleurone layers, are retarded in D6899. D6899 and Nainari 60 have essentially the same uptake and metabolism of gibberellin and their levels of endogenous inhibitors such as abscisic acid do not differ drastically. The dosage-response curve of the gibberellin-mediated α-amylase production indicates that a rate-limiting step, which is common to many of the diverse gibberellin responses, is partially blocked in D6899 wheat.     

EFFECTS OF TURBULENCE ON THE MARINE DINOFLAGELLATE GYMNODINIUM NELSONII1

Laboratory experiments were conducted to study the effects of agitation on growth, cell division, and nucleic acid dynamics of the dinoflagellate Gymnodinium nelsonii Martin. When cultures were placed on an orbital shaker at 100 rpm, cell division was prevented, cellular volume increased up to 1.5 times that of the nonperturbed cells, the form and location of the cell nucleus were modified, and the RNA and DNA concentrations per cell increased up to 10 times those of the controls. When shaking was stopped after 10 days, cells divided immediately at about 2/3 of the division rate of the unshaken populations, and all the altered parameters were restored. If the agitation continued for more than 20 days, total cell death and disintegration occurred. Several cellular types differing in size and shape were observed in the control and shaken cultures. One possible hypothesis for these results is that failure of the cell to divide results from physical disturbance of the microtubule assemblage associated with chromosome separation during mitosis. My study suggests that small-scale oceanic turbulence of sufficient intensity may inhibit growth of individual dinoflagellate cells, but immediate development of the population may continue when calm weather follows the active mixing period.     

RESPONSES OF FRESHWATER ALGAE TO INHIBITORY VANADIUM CONCENTRATIONS: THE ROLE OF PHOSPHORUS1

We found that species-specific differences exist among a variety of freshwater algae and cyanobacteria in the extent to which growth and photosynthesis are inhibited by vanadium. A major factor controlling the degree of inhibition by vanadium was the phosphorus state (P-sufficient vs. P-deficient) of the organisms. In P-sufficient cultures, vanadium was inhibitory when the vanadium concentration exceeded the phosphate concentration. In P-deficient cultures, the depression of photosynthesis by vanadium increased with increasing phosphorus deficiency. Our conclusion that vanadium competed with phosphate for uptake sites was supported by the following three observations: 1) the decreased influx of ³²P-PO ₄ into P-deficient cells in the presence of vanadium, 2) the amelioration of vanadium inhibition of photosynthesis by the addition of phosphate, and 3) the accumulation of vanadium by cells. At vanadium concentrations that severely inhibited growth, the cells of Scenedesmus obliquus (Turp.) Kruger were larger than normal and contained more vacuoles, lipid, and starch bodies than normal cells. Four-celled coenobia were replaced by unicells. Scenedesmus acutusf: alternans Hortobagyi cells from vanadium-inhibited cultures had 7.5 times more vanadium per cell than control cultures and contained numerous granules that did not stain for polyphosphate and may be composed of condensed vanadate molecules. The cellular P quota and turnover time of PO₄in the medium are important regulators of the extent of inhibition by vanadium.     

RESPONSES OF LEAF SPECTRAL REFLECTANCE TO PLANT STRESS

Leaf spectral reflectances were measured to determine whether leaf reflectance responses to plant stress may differ according to the agent of stress and species. As a result of decreased absorption by pigments, reflectance at visible wavelengths increased consistently in stressed leaves for eight stress agents and among six vascular plant species. Visible reflectance was most sensitive to stress in the 535–640-nm and 685–700-nm wavelength ranges. A sensitivity minimum occurred consistently near 670 nm. Infrared reflectance was comparatively unresponsive to stress, but increased at 1,400–2,500 nm with severe leaf dehydration and the accompanying decreased absorption by water. Thus, visible rather than infrared reflectance was the most reliable indicator of plant stress. Visible reflectance responses to stress were spectrally similar among agents of stress and species.     

CELL SURVIVAL CHARACTERISTICS AND MOLECULAR RESPONSES OF ANTARCTIC PHYTOPLANKTON TO ULTRAVIOLET-B RADIATION1

Twelve species of Antarctic diatoms were studied to assess UV sensitivity in relation to cellular and molecular aspects of DNA damage and repair. Responses of cell survival, induction of DNA damage, and DNA repair capacity were determined. There was a wide range of interspecific UV-sensitivity among diatoms. D₃₇ values (average fluence to kill one cell) ranged from 681 J · m^?2 (most sensitive) to 25,338 J · m^?2 (most resistant). Molecular analysis (by radioimmunoassay) of UV-induced DNA damage [induction of cys-syn cyclobutane dimers and pyrimidine (6-4) pyrimidone photoproducts] also revealed considerable variability among species [0.98–84 lesions · (10⁸ daltons DNA)^?1 induced by exposure to 2500 J · m^?2]. Repair of DNA damage ranged from 0.18 to 2.72 lesions removed · (10⁸ daltons DNA)^?1 in 6 h; removal represented 0.72–73.5% of initial damage. Comparison of cellular responses associated with photoenhanced repair and nucleotide excision (“dark”) repair indicated that light-mediated correction of UV damage was an important factor in cell survival. There was a relationship between the number of photoproducts induced and cell survival, but not between repair efficiency and survival. The data also indicate a general dependence of photoproduct induction and D₃₇ values on cell size and shape (expressed as the surface area: volume ratio which ranged from 0.07 to 0.66 between species) and suggest that these factors are indicators of UV sensitivity. Smaller cells with greater surface area: volume ratios sustained more damage per unit of DNA, had lower D₃₇ values, and were more sensitive to UV exposure. The wide species variations observed in molecular and cellular responses to UV exposure emphasize the ecological implications of changes in natural UV regimes. These changes can act as determinants of cell size and taxonomic structure within phytoplankton communities and have as yet unknown effects on trophic interactions within the Antarctic ecosystem.     

强啡肽对纹状体内D_1多巴胺受体反应的调节

用6-羟多巴胺破坏黑质纹状体通路,使大鼠多巴胺耗竭后,应用原位杂交组织化学方法测量D1多巴胺受体对即早基因c－fos和zif268诱导反应,分析强啡肽对突触前、后调节作用。先用D1多巴胺受体激动剂SKF－38393反复处理动物,促进纹状体内强啡肽表达,在伏隔核强啡肽表达增加,同时伴随着即早基因c-fos和zif268的减少．在纹状体的背部和两侧,强啡肽表达虽大量增加,而D1多巴胺受体反应仍然维持原水平．在中央纹状体区,即早基因的表达处于中间水平。结果提示,纹状体内强啡肽起着调节多巴胺输入到纹状体黑质神经元的作用,包括突触前、后位置;并且调节作用在纹状体的腹、背侧区是不同的     

植物个体对全球变化响应的敏感度分析

建立了基于生理学机制的植物个体生长发育系统动力学模型。建模中考虑了ＣＯ２增加有 引起的气候变化的综合作用对植物的重要生理过程,如光合、呼吸等,及生物量季节动态的影响。