A new family and a new genus for two taxa previously assigned to Apodachlyella completa (J. E. Humphrey) H. Indoh (Peronosporomycetidae: Leptomitales)

DICK, M. VV., 1986. A new family and a new genus for two taxa previously assigned to Apodachlyella completa (J. E. Humphrey) H. Indoh (Peronosporomycetidae: Leptomitales) . At present two distinct taxa are referrable to Apodachlyella completa. New genus and species names (I'lerogone helodes M. W. Dick genus & sp. nov.) are necessary for the taxon reported from the British Isles. Confirmation of the unique wall membranes in the antheridia and oogonia is used to justify the placement of A. completa in a new, monotypic family of the Leptomitales (Apodachlyellaceae M. W. Dick fam. nova). Plerogone is placed provisionally in the Leptomitaceae.     

Aerenchyma (Gas-space) Formation in Adventitious Roots of Rice (Oryza sativa L.) is not Controlled by Ethylene or Small Partial Pressures of Oxygen

Jackson, M. B., Fenning, T. M., and Jenkins, W. 1985 Aerenchyma(gas-space) formation in adventitious roots of rice (Oryza sativaL.) is not controlled by ethylene or small partial pressuresof oxygen.—J. exp. Bot. 36: 1566–1572. The extent of gas-filled voids (aerenchyma) within the cortexof adventitious roots of vegetative rice plants (Oryza sativaL. cv. RB3) was estimated microscopically from transverse sectionswith the aid of a computer-linked digitizer drawing board. Gas-spacewas detectable in 1-d-old tissue and increased in extent withage. After 7 d, approximately 70% of the cortex had degeneratedto form aerenchyma. The extent of the voids in 1-4-d-old tissuewas not increased by stagnant, poorly-aerated external environmentscharacterized by sub-ambient oxygen partial pressures and accumulationsof carbon dioxide and ethylene. Treatment with small oxygenpartial pressures, or with carbon dioxide or ethylene appliedin vigorously stirred nutrient solution also failed to promotethe formation of cortical gas-space. Furthermore, ethylene productionby rice roots was slowed by small oxygen partial pressures typicalof stagnant conditions. Silver nitrate, an inhibitor of ethylene action, did not retardgas-space formation; similarly when endogenous ethylene productionwas inhibited by the application of aminoethoxyvinylglycine(A VG), aerenchyma development continued unabated. Cobalt chloride,another presumed inhibitor of ethylene biosynthesis, did notimpair formation of the gas in rice roots nor did it decreasethe extent of aerenchyma even if A VG was supplied simultaneously.These results contrast with those obtained earlier using rootsof Zea mays L. We conclude that in rice, aerenchyma forms speedily even inwell-aerated environments as an integral part of ordinary rootdevelopment There seems to be little or no requirement for ethyleneas a stimulus in stagnant root-environments where aerenchymais likely to increase the probability of survival. Key words: Rice (Oryza sativa L.), ethylene, flooding, aeration, aerenchyma, environmental stress     

Effects of Drought on Partitioning of Nitrogen in Two Wheat Varieties Differing in Drought-tolerance

A model was constructed to describe the translocation and partitioningof nitrogen on the seventh day after anthesis for well-wateredand droughted plants of two wheat varieties (Triticum aestivumL. cv. Warigal and Condor). The glasshouse-grown plants weredetillered so that a simplified model could be derived for themain stem. A 9-d drought treatment was imposed just after anthesisand this coincided with the period of endosperm cell divisionin the grains. Warigal, which had a higher grain yield thanCondor under drought, absorbed up to 15-times more nitrogenand translocated 1.5-fold more nitrogen to the shoot via thexylem. In both varieties, nitrogen redistributed from vegetativeorgans accounted for more than 60 per cent in control and 70per cent in droughted plants of the nitrogen needed for eargrowth. The net loss of nitrogen increased by 4-3 per cent inthe leaves, but decreased by 60 per cent in the stem under drought.Stem and roots appeared to play an important role in the nitrogeneconomy of droughted plants: less nitrogen was translocateddirectly to the grains from the senescing leaves and 40–60per cent more nitrogen was translocated to the roots. Nearlyall the nitrogen reaching the roots in the phloem was reloadedinto the xylem stream and translocated back to the shoot. Thetransfer of nitrogen through the stem was reduced under droughtand this resulted in a constant C:N ratio of the grains whichmay be important in the regulation of endosperm cell division. Triticum aestivum L., wheat, drought, nitrogen, senescence, translocation     

Detection of the Microtubule Cytoskeleton of the Coccidian Toxoplasma gondii and the Hemoflagellate Leishmania donovani by Monoclonal Antibodies Specific for β-Tubulin1

Seven monoclonal antibodies specific for mammalian β-tubulin demonstrate the microtubule cytoskeleton of Toxoplasma gondii and Leishmania donovani by indirect immunofluorescence microscopy. Immunoblots of T. gondii and L. donovani proteins separated by SDS polyacrylamide gel electrophoresis confirm the specificity of the monoclonal antibodies for tubulin. Differential staining of flagellar and subpellicular microtubule populations was not seen in L. donovani with these antibodies. All seven antibodies also detected the subpellicular microtubules of T. gondii, but the polar ring and conoid of this organism was not visualized by any of them. This technique provides a rapid and specific way to assess microtubular organization in whole organisms.     

The Effect of Osmotic and Ionic Stress on the Primary Processes of Photosynthesis in Dunaliella tertiolecta

Cells of the euryhaline unicellular green alga Dunaliella tertiolectawere exposed to a range of osmotic potentials imposed by theaddition of NaCl, KCl, sucrose or ethylene glycol to the algalsuspending medium. The alga synthesized glycerol in responseto increased concentrations of NaCl, KCl or sucrose, but notto increased concentrations of ethylene glycol. The overallprocess of photosynthesis was inhibited by all four treatmentsduring the first 100 min, but especially by NaCl and KCl. Theinduction of chlorophyll fluorescence indicated that photosystemIl was inhibited by such treatment although to a lesser extentthan the overall process. The size and half-time of decay ofthe flash-induced field-indicating absorption change at 519nm were decreased by NaCl and KCl but the effect of sucroseand ethylene glycol on the absorption change was much less.Therefore, the photosynthetic processes in intact Dunaliellacells are more markedly inhibited by the combined osmotic andionic stresses due to NaCl and KCl than by osmotic stress alone.In most cases some recovery of the inhibition of photosynthesiswas seen concomitant with the synthesis of intracellular glycerol,suggesting that the alga has the ability to overcome osmoticand ionic stresses. Key words: Dunaliella, Photosynthesis, Osmotic stress     

Factors affecting aphid acquisition and transmission of soybean mosaic virus

Myzus persicae transmitted soybean mosaic virus (SMV) most efficiently following 30 or 60 s acquisition probes on infected plants. There were no differences in susceptibility to SMV infection of soybean plants 1 to 12 wk old, but symptoms were more severe in plants inoculated when young than when old. Soybeans inoculated between developmental stages R3 and R6 only showed yellowish-brown blotching on one or more leaves. There were no observable differences in the time of appearance or type of symptoms shown by soybean seedlings inoculated either by sap or by aphids; infected plants became acquisition hosts for aphids 5–6 days after inoculation. There was no change in the efficiency with which M. persicae transmitted SMV from source plants up to 18 wk after inoculation. M. persicae transmitted SMV from leaves of field-grown soybeans when plants were inoculated at developmental stages V6, R2, and R3 and tested as sources 57–74 days after inoculation but not from plants inoculated at R5 and tested as sources 14 to 32 days after inoculation. M. persicae acquired SMV from soybean buds, flowers, green bean pods, and unifoliolate, trifoliolate, and senescent leaves. Middle-aged and deformed leaves were better sources of the virus than buds, unfolding and old symptomless leaves. The results are being incorporated into a computer model of SMV epidemiology.     

Positive and Negative Messages from Roots Induce Foliar Desiccation and Stomatal Closure in Flooded Pea Plants

Flooding the soil for 5–7 d caused partial desiccationin leaves of pea plants (Pisum sativum. L. cv. ‘Sprite’).The injury was associated with anaerobiosis in the soil, a largeincrease in the permeability of leaf tissue to electrolytesand other substances, a low leaf water content and an increasedwater saturation deficit (WSD). Desiccating leaves also lackedthe capacity to rehydrate in humid atmospheres, a disabilityexpressed as a water resaturation deficit (WRSD). This irreversibleinjury was preceded during the first 4–5 d of floodingby closure of stomata within 24 h, decreased transpiration,an unusually large leaf water content and small WSD. Leaf waterpotentials were higher than those in well-drained controls.Also, there was no appreciable WRSD. Leaflets detached fromflooded plants during this early phase retained their watermore effectively than those from controls when left exposedto the atmosphere for 5 min. Stomatal closure and the associated increase in leaf hydrationcould be simulated by excising leaves and incubating them withtheir petioles in open vials of water. Thus, such changes inflooded plants possibly represented a response to a deficiencyin the supply of substances that would usually be transportedfrom roots to leaves in healthy plants (negative message). Ionleakage and the associated loss of leaf hydration that occurswhen flooding is extended for more than 5 d could not be simulatedby isolating the leaves from the roots. Appearance of this symptomdepended on leaves remaining attached to flooded root systems,implying that the damage is caused by injurious substances passingupwards (positive message). Both ethylene and ethanol have beeneliminated as likely causes, but flooding increased phosphorusin the leaves to concentrations that may be toxic. Key words: Pisum sativum, Flooding, Foliar desiccation, Stomata, Ethylene     

Nucleoside diphosphate kinase from lily pollen

Nucleoside diphosphate kinase was a predominantly soluble enzymein lily pollen (Lilium longiflorum, var. Ace), and very littleenzyme activity was associated with the mitochondrial fraction.GTP was the preferred substrate when ADP was the second substrate.The enzyme was purified 18-fold to a specific activity of 7µmoles/min/mg protein. ¹This study was supported by grant GB-8764 from the U.S. NationalScience Foundation. (Received October 5, 1970; )     

The Structure of Calf Liver Cytochrome <Emphasis Type="Italic">b</Emphasis><Subscript>5</Subscript> at 2.8 Å Resolution

CYTOCHROME b₅ is a haem-containing protein in the microsomes of liver tissue. It interacts specifically with a flavo-protein, cytochrome b₅ reductase, which catalyses the transfer of electrons from NADH to the haem iron of the cytochrome¹. The microsomal cytochrome b₅ system has been implicated in fatty acid desaturation reactions² and a similar system in erythrocytes may catalyse the reduction of methaemoglobin³. Calf liver cytochrome b₅, solubilized by pancreatic lipase, has a molecular weight of 11,000 and consists of ninety-three amino-acids in the sequence shown in Fig. 1 (refs. 4 and 5). The haem group is non-covalently bound to the protein and can be removed reversibly by acid acetone treatment⁶.     

Synthesis of Substance P

SUBSTANCE P has been synthesized by the solid-phase procedure of Merrifield^1,2 according to the sequence H-Arg-Pro-LysPro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH₂ reported in the previous letter.