Relationships between macroalgal functional form groups and substrata stability in a subtropical rocky-intertidal system

The general hypothesis that morphological, physiological, and ecological adaptations of macro algal functional-form groups can be related to the level of disturbance encountered in a natural environment was examined. Two articulated calcareous coralline algae (Amphiroa van-bosseae Lemoine, 24% cover and Corallina frondescens Post. & Rupr. 20%) and one non-articulated coralline alga (Lithophyllum sp., 16%), all late-successional predation-tolerant strategists, comprise most of the community cover on stable bedrock substrata at Punta Las Cuevitas, Sonora, Mexico. Conversely, Ulva rigida C. ag. (26% cover) and a ralfsioid crust (23%), shows to be early-successional opportunistic strategists, cover more of the disturbed boulder habitat. Porolithon sonorense Daws., a stress-tolerant strategist, is uniquely abundant on both substratum types (13% cover on boulders, 10% on bedrock). The sheet-like and filamentous algae, prevalent in the temporally unstable habitat, generally show greater productivity (>2×) than the thicker and calcareous forms conspicuous in the more constant environment. It appears that selection for delicate thalli with high productivities, as well as selection for tougher morphologies having lower photosynthetic rates due to greater proportions of structural tissues, are widespread, divergent evolutionary forces among marine algae. Experiments with captive sea urchins (Echinometra vanbrunti Agassiz), in conjunction with fish-preference data published for some of the same algae studied here, offer strong support for the functional-form model. Parrotfishes, rudderfishes, surgeonfishes, damselfishes and E. vanbrunti, in the Gulf of California, preferentially feed on delicate, early-successional, sheet-like, and filamentous algae, while rejecting or ignoring the more structured, late-successional and calcareous algae. There is no significant (P > 0.05) gradation in calorific content between the first four of the six functional groups (i.e., Sheet-, Filamentous-, Coarsely Branched- and Thick Leathery-Groups), but the mean value for these fleshy forms (2.6 kcal · g ash-free dry wt^?1) is significantly greater than that for the last two groups (0.3 kcal, Jointed Calcareous- and Crustose-Groups). The approach used in this study demonstrates a realistic technique for predicting macrophyte community composition from knowledge of the disturbance levels in a given habitat or the reverse. The form group-disturbance relationship has important implications for future biological monitoring of rocky-inter-tidal and subtidal systems.     

光呼吸代谢物乙醇酸、乙醛酸和草酸对烟草叶片硝酸还原的影响

乙醇酸、乙醛酸和草酸能明显促进烟草(Nicotiana rustica)叶片在黑暗中的硝酸还原,光呼吸抑制剂a-羟基吡啶甲烷磺酸能消除前二者的促进作用而不能完全消除草酸的作用。草酸+NAD~+能显著促进离体的硝酸还原。烟叶提取液加入草酸和NAD~+后生成NADH和CO_2认为活体内由乙醛酸氧化生成的草酸是经脱氢生成NADH供硝酸还原之用。未能证明在烟叶内存在乙醇酸脱氨酶,因此排除由乙醇酸直接脱氢以还原硝酸的可能。     

Nitrate reductase is not accumulated in chloroplast-ribosome-deficient mutants of higher plants

The activities of nitrite reductase (EC 1.7.7.1) are 60–70% of wild-type activity in pigment-deficient leaves of the chloroplast-ribosomedeficient mutants albostrians (Hordeum vulgare) and iojap (Zea mays). The activity and apoprotein of nitrate reductase (EC 1.6.6.1.) are lacking in the barley mutant. Only very low activities of nitrate reductase can be extracted from leaves of the maize mutant. The molybdenum cofactor of nitrate reductase and xanthine dehydrogenase (EC 1.2.3.2) is present in maize and barley mutant plants. However, it is not inducible by nitrate in pigment-deficient leaves of albostrians. From these results we conclude: (i) Nitrite reductase (a chloroplast enzyme) is synthesized in the cytoplasm and does not need the presence of nitrate reductase for the induction and maintenance if its activity. (ii) The loss or low activity of nitrate reductase is a consequence of the inability of the mutants to accumulate the apoprotein of this enzyme. (iii) The chloroplasts influence the accumulation (i.e. most probably the synthesis) of the nonchloroplast enzyme, nitrate reductase. The accumulation of nitrate reductase needs a chloroplast factor which is not provided by mutant plastids blocked at an early stage of their development.Abbreviations CRM cross-reacting material - Mo-co molybdenum cofactor - NiR nitrite reductase - NR nitrate reductase     

Ammoniacal silver staining of proteins: mechanism of glutaraldehyde enhancement

When the conditions for detecting proteins by ammoniacal silver staining (B. R. Oakley, D. R. Kirsch, and N. R. Morris (1980) Anal. Biochem. 105, 361-363.) following gel electrophoresis were varied, it was noted that glutaraldehyde pretreatment was necessary for maximal staining, which could not be explained simply as the result of "fixation." Further studies indicated that glutaraldehyde enhancement of protein staining with this silver reagent was probably due to oxidation of the aldehyde groups by silver ions, resulting in metallic silver depositions within the gel which act as nucleation sites for additional metallic silver localization in the protein bands upon the addition of formaldehyde developer. This proposed mechanism is consistent with the Tollen's reaction, as well as some aspects of the photographic process. Consistent with this notion, silver-staining intensities are directly related to mole percentage lysine of various standard proteins.     

Increase in nitrate reductase activity in the presence of sucrose in bean leaf segments

The supply of sucrose to leaf segments from light-grown bean seedlings caused a substantial increase in substrate inducibility of in vivo and in vitro nitrate reductase activity but only a small increase in total protein. Cycloheximide and chloramphenicol inhibited the increase in enzyme activity by nitrate and sucrose. The in vivo decline in enzyme activity in nitrate-induced leaf segments in light and dark was protected by sucrose and nitrate. The supply of NADH also protected the decline in enzyme activity, but only in the light. In vitro stability of the extracted enzyme was, however, unaffected by sucrose. The size of the metabolic nitrate pool was also enhanced by sucrose. The experiments demonstrate that sucrose has a stimulatory effect on activity or in vivo stability ' of nitrate reductase in bean leaf segments, which is perhaps mediated through increased NADH level and/or mobilization of nitrate to the metabolic pool.     

Possible roles of calcium and ammonium in the development of bitter pit in apple

Apple trees ( Malus pumila Mill . var. domestica Fuji/ Malus prunifolia rootstock) showed a high susceptibility to bitter pit when supplyed with ammonium salt instead of nitrate (control) in the nutrient solution. When apple fruit was affected by bitter pit, a lower calcium as well as a higher nitrogen and ammonium-nitrogen contents was observed in the fruit flesh near the calyx end. The activity of the mitochondrial Ca²⁺-uptake of the fruit flesh near the calyx end was higher when the tree was grown with ammonium salt than when grown with nitrate. Both the activities of succinate: cytochrome c oxidoreductase and the mitochondrial Ca²⁺-uptake per g of tissue were higher in affected fruit than in healthy fruit. Each of chlorpromazine, N-(6-aminohexyl)-5-chloro-l-napthalenesulfonamide (W-7) and N-(6-aminohexyl)-l-naphthalenesulfonamide (W-5), calmodulin antagonists, was infiltrated into the fruit for 20 min under reduced pressure (about 1 × 10⁴ Pa). Few days later, numerous bitter pit-like spots were observed in both fruit treated with W-7 and chlorpromazine, while only a few spots were observed after the infiltration with W-5, a less potent calmodulin antagonist. A possible mechanism for the occurrence of bitter pit is discussed.     

Characteristics of structural proteins of infectious flacherie virus from the silkworm, Bombyx mori

Structural proteins and the characteristics of infectious flacherie virus (IFV) purified from the silkworm, Bombyx mori, are described. The purified IFV had four major structural proteins, which were detected only in high concentration gels of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and a few minor ones. Molecular weights of the major proteins were 35,200 (VP 1), 33,000 (VP 2), 31,200 (VP 3), and 11,600 (VP 4), and numbers per virion were 62, 57, 54, and 31, respectively. Amino acid compositions of VP 1, VP 2, and VP 3 were similar to each other but that of VP 4 was somewhat different. By isoelectric focusing and two-dimensional electrophoresis, high resolution of the structural proteins was obtained with silver staining. The isoelectric points of the four major proteins were determined as 7.7(VP 1), 6.7(VP 2), 4.8(VP 3), and 5.5(VP 4). This work is the first report on insect picornaviruses that presents some discriminative properties of each viral protein that was compared to those of mammalian picornaviruses.     

Synergistic effect of 1-aminocyclopropane-1-carboxylic acid and ethylene during senescence of isolated carnation petals

The effects of ethylene (C₂H₄), (2-chloroethyl)phosphonic acid (ethefon) and 1-aminocyclopropane-1-carboxylic acid (ACC) on senescence of isolated intact petals and of upper petal parts of carnation flowers ( Dianthus caryophyllus L. cv. White Sim) were investigated.
Isolated upper petal parts did not respond to treatment with ethefon or ACC. These tissues did, however, show severe wilting in intact petals that were treated with ethefon or ACC. When isolated upper petal parts were simultaneously treated with ACC and ethefon or ACC and ethylene, a marked synergistic effect on senescence was found. Treatment of isolated petals with radiolabeled ACC led to the accumulation of radiolabeled ACC and N-malonyl-ACC (MACC) in the upper parts. The formation of ethylene and the malonylation of ACC were inhibited by pretreatment of the flower with the inhibitor of ethylene action, silver thiosulphate (STS), which indicates that both were induced by endogenously produced ethylene. Treatment of isolated upper parts with ACC slightly increased their ethylene production. However, when these petal parts were simultaneously treated with ethylene and ACC, the conversion of ACC to ethylene was markedly stimulated.
The results indicate that, in intact petals, ethylene may be translocated from the basal to the upper part where it stimulates the activity of the ethylene-forming enzyme (EFE), thereby making the tissue receptive to ACC.
In addition, it was found that upon incubation of petal portions in radiolabeled ACC, both the petal tissue and the incubation solutions produced radiolabeled carbon dioxide. This was shown to be due to microorganisms that were able to metabolize the carbon atoms in the 2 and 3 position of ACC into carbon dioxide.     

Agrobacterium-mediated gene delivery and the biology of hostrange limitations

Insertion of foreign DNA into Ti plasmid-derived vectors in Agrobacterium tumefaciens is currently the most frequently used strategy for generating transgenic plants in a wide variety of species. Limitations of the host range of Agrobacterium restrict its usefulness in many cases, particularly when dealing with monocotyledonous plants. The objective of this presentation is to briefly discuss the efficiency of the transformation process utilized by Agrobacterium tumefaciens , potential barriers to efficient transformation by Agrobacterium that result in limitation of its useful host range, and how an understanding of the successful Agrobacterium /plant cell interaction might lead to advances in a variety of DNA delivery methodologies.     

Root distribution in relation to soil nitrogen availability in field-grown tomatoes

Tomato root growth and distribution were related to inorganic nitrogen (N) availability and turnover to determine 1) if roots were located in soil zones where N supply was highest, and 2) whether roots effectively depleted soil N so that losses of inorganic N were minimized. Tomatoes were direct-seeded in an unfertilized field in Central California. A trench profile/monolith sampling method was used. Concentrations of nitrate (NO₃ ^-) exceeded those of ammonium (NH₄ ⁺) several fold, and differences were greater at the soil surface (0–15 cm) than at lower depths (45–60 cm or 90–120 cm). Ammonium and NO₃ ^- levels peaked in April before planting, as did mineralizable N and nitrification potential. Soon afterwards, NO₃ ^- concentrations decreased, especially in the lower part of the profile, most likely as a result of leaching after application of irrigation water. Nitrogen pool sizes and rates of microbial processes declined gradually through the summer.Tomato plants utilized only a small percentage of the inorganic N available in the large volume of soil explored by their deep root systems; maximum daily uptake was approximately 3% of the soil pool. Root distribution, except for the zone around the taproot, was uniformly sparse (ca. 0.15 mg dry wt g^-1 soil or 0.5 cm g^-1 soil) throughout the soil profile regardless of depth, distance from the plant stem, or distance from the irrigation furrow. It bore no relation to N availability. Poor root development, especially in the N-rich top layer of soil, could explain low fertilizer N use by tomatoes.