New Plant Growth Regulators Protect Photosynthesis and Enhance Growth Under Drought of Jack Pine Seedlings

To determine whether natural plant growth regulators (PGRs) can enhance drought tolerance and the competitive ability of transplanted seedlings, 1.5-year-old jack pine (Pinus banksana Lamb.) seedlings were treated with homobrassinolide, salicylic acid, and two polyamines, spermine and spermidine, triacontanol, abscisic acid (ABA), and the synthetic antioxidant, Ambiol. PGRs were fed into the xylem for 7 days and plants were droughted by withholding water for 12 days. ABA, Ambiol, spermidine, and spermine at a concentration of 10 μg L⁻¹ stimulated elongation growth under drought, whereas ABA, Ambiol, and spermidine maintained higher photosynthetic rates, higher water use efficiency, and lower Ci/Ca ratio under drought compared with control plants. The damaging effects of drought on membrane leakage was reversed by Ambiol, ABA, triacontanol, spermidine, and spermine. Because ABA, Ambiol, and both polyamines enhanced elongation growth and also reduced membrane damage in jack pine under drought, they show promise as treatments to harden seedlings against environmental stress. The protective action of these compounds on membrane integrity was associated with an inhibition of ethylene evolution, with a reduction in transpiration rate and an enhancement of photosynthesis, which together increased water use efficiency under drought. Although most of the tested compounds acted as antitranspirants, the inhibition in membrane leakage in ABA-, Ambiol-, and polyamine-treated plants appeared more closely related to the antiethylene action. Received December 30, 1998; accepted October 14, 1999     

Effect of Putrescine, 4-PU-30, and Abscisic Acid on Maize Plants Grown under Normal, Drought, and Rewatering Conditions

The experiments were carried out with maize (Zea mays L.) seedlings, hybrid Kneja 530, grown hydroponically in a growth chamber. Twelve-day-old plants were foliar treated with putrescine, N¹-(2-chloro-4-pyridyl)-N²-phenylurea (4-PU-30), and abscisic acid (ABA) at concentrations of 10⁻⁵ m. Twenty-four hours later the plants were subjected to a water deficit program, induced by 15% polyethylene glycol (PEG; molecular weight, 6,000). Three days after drought stress half of the plants were transferred to nutrient solution for the next 3 days. The effects of the water shortage, rewatering, and plant growth regulator (PGR) treatment on the fresh and dry weights, leaf pigment content, proline level, relative water content (RWC), transpiration rate, activities of catalase and guaiacol peroxidase, hydrogen peroxide content, and level of the products of lipid peroxidation were studied. It was established that the application of PGRs alleviated to some extent the plant damage provoked by PEG stress. At the end of the water shortage program the plants treated with these PGRs possessed higher fresh weight than drought-subjected control seedlings. It was found also that putrescine increased the dry weight of plants. Under drought, the RWC and transpiration rate of seedlings declined, but PGR treatment reduced these effects. The accumulation of free proline, malondialdehyde, and hydrogen peroxide was prevented in PGR-treated plants compared with the water stress control. The results provided further information about the influence of putrescine, 4-PU-30, and ABA on maize plants grown under normal, drought, and rewatering conditions. Received September 25, 1997; accepted August 10, 1998     

Phenotypic Adaptation of Tonoplast Fluidity to Growth Temperature in the CAM Plant Kalanchoë daigremontiana Ham. et Per. is Accompanied by Changes in the Membrane Phospholipid and Protein Composition

The present study deals with the phenotypic adaptation of tonoplast fluidity in the CAM plant Kalancho? daigremontiana to changes in growth temperature. Tonoplast fluidity was characterized by measuring fluorescence depolarization in membranes labeled with fluorescent fatty acid analogues and by following formation of eximeres in membranes labeled by eximere-forming fluorophores. With both techniques it was found that exposure of the plants to higher growth temperature compared with the control decreased the fluidity of the tonoplast while exposure to lower growth temperature caused the opposite. Three hours of high temperature treatment (raised from 25°C to 35°C; ``heat shock') were sufficient to decrease the tonoplast fluidity to roughly the same extent as growth under high temperature for 30 days. The phenotypic response of tonoplast fluidity to changes in growth temperature was found only in the complete membrane, not however in the lipid matrix deprived of the membrane proteins. Heat treatments of the plants decreased the lipid/protein ratio while exposure to low temperature (for 30 days) increased it. Heat treatments led to a decrease in the percentage of linolenic acid (C18:3) and linoleic acid (C18:2), heat shock and low temperature treatments induced an increase in the percentage of linoleic acid (C18:3), with concomitant decrease in the percentage of linoleic acid (C18:2). However, in the case of heat shock, increase in linolenic acid concerned mainly monogalactosyldiacylglycerol, while with low temperature treatment linoleic acid increased in phosphatidylcholine. Both treatment of the plants with high and low temperature led to a slight decrease in the contribution of phosphatidylcholine and phosphoethanolamine to the total phospholipid content of the tonoplast. High-temperature treatment of the plants not only decreased the phospholipid/protein ratio in the tonoplast, but also led to the occurrence of a 35 kDa polypeptide in the tonoplast which cross-reacted with an antiserum against the tonoplast H⁺-ATPase holoenzyme. The important role of membrane proteins in bringing about the phenotypic rigidization of the tonoplast was mimicked by reconstitution experiments showing that incorporation of the proteins isolated from the tonoplast into phosphatidylcholine vesicles decreased the fluidity of this membrane system. As to be expected from the analyses in the natural membrane, the degree of this effect depended on the phospholipid/protein ratio. Received: 4 March 1998/Revised: 28 July 1998     

Biochemical Changes Associated With Brassica juncea Seed Development. IV. Acid and Alkaline Phosphatases

Changes in acid and alkaline phosphatase activities in cytoplasmic and wall-bound fractions of developing mustard (Brassica juncea) seed were studied. Growth was measured by seed dry weight and water content. Seed dry weight data were fitted to a cubic polynomial equation. Seed water content and dry matter accumulation was significantly correlated. Cytoplasmic acid and alkaline phosphatase activities were substantially less in the cytoplasmic fraction than the wall-bound fraction. Wall-bound acid phosphatase activity was low initially, but high levels were maintained after day 25, indicating a relationship with dry matter accumulation. The results suggest that acid phosphatase plays an important role during mustard seed development. Received February 19, 1998; accepted May 6, 1999     

Hydrophobic and Hydrophilic Radio-Iodination, Crosslinking, and Differential Extraction of Cell Surface Proteins in Paramecium tetraurelia Cells

We combined widely different biochemical methods to analyze proteins of the cell surface of P. tetraurelia since so far one can isolate only a subfraction of cell membrane vesicles enriched in the GPI-anchored surface antigens (``immoblization' or ``i-AGs'). We also found that i-AGs may undergo partial degradation by endogenous proteases. Genuine intrinsic membrane proteins were recognized particularly with lipophilic 5-[¹²⁵I]-iodonaphthalene-1-azide (INA) labeling which reportedly ``sees' integral proteins and cytoplasmic cell membrane-associated proteins. With INA (+DTT), bands of ≤55 kDa were similar as with hydrophilic iodogen (+DTT), but instead of large size bands including i-AGs, a group of 122, 104 and 94 kDa appeared. Several bands of the non i-AG type are compatible with integral (possibly oligomeric) or associated proteins of the cell membrane of established molecular identity, as we discuss. In summary, we can discriminate between i-AGs and some functionally important minor cell membrane components. Our methodical approach might be relevant also for an analysis of some related protozoan parasites. Received: 5 April 1999/Revised: 19 July 1999     

Disease resistance against Magnaporthe grisea is enhanced in transgenic rice with suppression of omega-3 fatty acid desaturases

Linolenic acid (18:3) is the most abundant fatty acid in plant membrane lipids and is a source for various oxidized metabolites, called oxylipins. 18:3 and oxylipins play important roles in the induction of defense responses to pathogen infection and wound stress in Arabidopsis. However, in rice, endogenous roles for 18:3 and oxylipins in disease resistance have not been confirmed. We generated 18:3-deficient transgenic rice plants (F78Ri) with co-suppression of two omega-3 fatty acid desaturases, OsFAD7 and OsFAD8. that synthesize 18:3. The F78Ri plants showed enhanced resistance to the phytopathogenic fungus Magnaporthe grisea. A typical 18:3-derived oxylipin, jasmonic acid (JA), acts as a signaling molecule in defense responses to fungal infection in Arabidopsis. However, in F78Ri plants, the expression of JA-responsive pathogenesis-related genes, PBZ1 and PR1b, was induced after inoculation with M. grisea, although the JA-mediated wound response was suppressed. Furthermore, the application of JA methyl ester had no significant effect on the enhanced resistance in F78Ri plants. Taken together, our results indicate that, although suppression of fatty acid desaturases involves the concerted action of varied oxylipins via diverse metabolic pathways, 18:3 or 18:3-derived oxylipins, except for JA, may contribute to signaling on defense responses of rice to M. grisea infection.     

Phospholipid synthesis in the squid giant axon: enzymes of phosphatidylinositol metabolism

We examined the properties of several enzymes of phospholipid metabolism in axoplasm extruded from squid giant axons. The following synthetic enzymes, CDP-diglyceride: inositol transferase (EC 2.7.8.11), ATP:diglyceride phosphotransferase, diglyceride kinase (EC 2.7.2.-), and phosphatidylinositol kinase (EC 2.7.1.67), were all present in axoplasm. Phospholipid exchange proteins, which catalyzed the transfer of phosphatidylinositol and phosphatidylcholine between membrane preparations and unilamellar lipid vesicles, were also found. However, we did not find conditions under which the synthesis of CDP-diglyceride, phosphatidylserine, and phosphatidylinositol-4,5-diphosphate could be measured. Subcellular fractionation by differential centrifugation showed that the axoplasmic inositol transferase and phosphatidylinositol kinase activities were largely "microsomal," while the diglyceride kinase and exchange protein activities were primarily "cytosolic."     

Identification of ATP-sensitive Potassium Channel in Frog Ventricular Myocytes

Nuclear magnetic resonance (NMR) microimaging and proton relaxation times were used to monitor differences between the hydration state of the nucleus and cytoplasm in the Rana pipiens oocyte. Individual isolated ovarian oocytes were imaged in a drop of Ringer's solution with an in-plane resolution of 80 μm. Proton spin echo images of oocytes arrested in prophase I indicated a marked difference in contrast between nucleoplasm and cytoplasm with additional intensity gradations between the yolk platelet-rich region of the cytoplasm and regions with little yolk. Neither shortening τ_e (spin echo time) to 9 msec (from 18 msec) nor lengthening τ_r (spin recovery time) to 2 sec (from 0.5 sec) reduced the observed contrast between nucleus and cytoplasm. Water proton T₁ (spin-lattice) relaxation times of oocyte suspensions indicated three water compartments that corresponded to extracellular medium (T₁= 3.0 sec), cytoplasm (T₁= 0.8 sec) and nucleoplasm (T₁= 1.6 sec). The 1.6 sec compartment disappeared at the time of nuclear breakdown. Measurements of plasma and nuclear membrane potentials with KCl-filled glass microelectrodes demonstrated that the prophase I oocyte nucleus was about 25 mV inside positive relative to the extracellular medium. A model for the prophase-arrested oocyte is proposed in which a high concentration of large impermeant ions together with small counter ions set up a Donnan-type equilibrium that results in an increased distribution of water within the nucleus in comparison with the cytosol. This study indicates: (i) a slow exchange between two or more intracellular water compartments on the NMR time-scale, (ii) an increased rotational correlation time for water molecules in both the cytoplasmic and nuclear compartments compared to bulk water, and (iii) a higher water content (per unit dry mass) of the nucleus compared to the cytoplasm, and (iv) the existence of a large (about 75 mV positive) electropotential difference between the nuclear and cytoplasmic compartments. Received: 18 January 1996/Revised: 29 April 1996     

Papaya (Carica papaya) Lysozyme Is a Member of the Family 19 (Basic, Class II) Chitinases

The most comprehensive studies on a plant lysozyme (EC 3.2.1.17) are those on the enzyme from papaya (Carica papaya) latex, published in 1967 and 1969. However, the N-terminal amino acid sequence of five amino acid sequence of this enzyme, determined by manual Edman degradation, did not allow assignment to any of the much later-classified families of glycosyl hydrolases. N-Terminal sequence analysis of 22 residues of papaya lysozyme now shows unambiguously that the enzyme belongs to the family 19 chitinases. It has properties similar to those of basic class I chitinases with lysozyme activity, such as cleavage specificity at the C-1 of N-acetylmuramic acid with inversion of configuration, but as it lacks an N-terminal hevein domain, it should be classified as a class II chitinase. Received: 3 February 1999 / Accepted 25 July 1999     

Effect of drought on sorbitol and sucrose metabolism in sinks and sources of peach

In peach (Prunus persica [L.] Batsch.), sorbitol and sucrose are the two main forms of photosynthetic and translocated carbon and may have different functions depending on the organ of utilization and its developmental stage. The role and interaction of sorbitol and sucrose metabolism was studied in mature leaves (source) and shoot tips (sinks) of ‘Nemaguard’ peach under drought stress. Plants were irrigated daily at rates of 100, 67, and 33% of evapotranspiration (ET). The relative elongation rate (RER) of growing shoots was measured daily. In mature leaves, water potential (Ψ_w), osmotic potential (Ψ_s), sorbitol‐6‐phosphate dehydrogenase (S6PDH, EC 1.1.1.200), and sucrose‐phosphate synthase (SPS, EC 2.4.1.14) activities were measured weekly. Measurements of Ψ_s, sorbitol dehydrogenase (SDH, 1.1.1.14), sucrose synthase (SS, EC 2.4.1.13), acid invertase (AI, EC 3.2.1.26), and neutral invertase (NI, EC 3.2.1.27) activities were taken weekly in shoot tips. Drought stress reduced RER and Ψ_w of plants in proportion to water supply. Osmotic adjustment was detected by the second week of treatment in mature leaves and by the third week in shoot tips. Both SDH and S6PDH activities were reduced by drought stress within 4 days of treatment and positively correlated with overall Ψ_w levels. However, only SDH activity was correlated with Ψ_s. Among the sucrose enzymes, only SS was affected by drought, being reduced after 3 weeks. Sorbitol accumulation in both mature leaves and shoot tips of stressed plants was observed starting from the second week of treatment and reached up to 80% of total solutes involved in osmotic adjustment. Sucrose content was up to 8‐fold lower than sorbitol content and accumulated only occasionally. We conclude that a loss of SDH activity in sinks leads to osmotic adjustment via sorbitol accumulation in peach. We propose an adaptive role of sorbitol metabolism versus a maintenance role of sucrose metabolism in peach under drought stress.     

Resistivity of Red Blood Cells Against High-Intensity, Short-Duration Electric Field Pulses Induced by Chelating Agents

The interaction of human red blood cells (RBCs) with diethylenetriamine-pentaacetic acid (DTPA) or its Gd-complex (Magnevist, a widely used clinical magnetic resonance contrast agent containing free DTPA ligands) led to the following, obviously interrelated phenomena. (i) Both compounds protected erythrocytes against electrohemolysis in isotonic solutions caused by a high-intensity DC electric field pulse. (ii) The inhibition of electrohemolysis was observed only when cells were electropulsed in low-conductivity solutions. (iii) The uptake of Gd-DTPA by electropulsed RBCs was relatively low. (iv) (Gd-) DTPA reduced markedly deformability of erythrocytes, as revealed by the electrodeformation experiments using high-frequency electric fields. Taken together, the results indicate that (Gd-) DTPA produce stiffer erythrocytes that are more resistant to electric field exposure. The observed effects of the chelating agents on the mechanical properties and the electropermeabilization of RBCs must have an origin in molecular changes of the bilayer or membrane-coupled cytoskeleton, which, in turn, appear to result from an alteration of the ionic equilibrium (e.g., Ca²⁺ sequestration) in the vicinity of the cell membrane. Received: 19 January 1999/Revised: 1 April 1999     

The Apical Membrane Glycocalyx of MDCK Cells

The microenvironment near the apical membrane of MDCK cells was studied by quantitation of the fluorescence of wheat germ agglutin attached to fluorescein (WGA). WGA was shown to bind to sialic acid residues attached to galactose at the α-2,3 position in the glycocalyx on the apical membrane. Young MDCK cells (5–8 days after splitting) showed a patchy distribution of WGA at stable sites that returned to the same locations after removal of sialic acid residues by neuraminidase treatment. Other lectins also showed stable binding to patches on the apical membrane of young cells. The ratio of WGA fluorescence emission at two excitation wavelengths was used to measure near-membrane pH. The near-membrane pH was markedly acidic to the pH 7.4 bathing solution in both young and older cells (13–21 days after splitting). Patches on the apical membrane of young cells exhibited a range of near-membrane pH values with a mean ±sem of 6.86 ± 0.04 (n= 121) while the near-membrane pH of older cells was 6.61 ± 0.04 (n= 120) with a uniform WGA distribution. We conclude that the distribution of lectin binding sites in young cells reflects the underlying nonrandom location of membrane proteins in the apical membrane and that nonuniformities in the pH of patches may indicate regional differences in membrane acid-base transport as well as in the location of charged sugars in the glycocalyx. Received: 15 December 1999/Revised: 16 March 2000     

New Glycoprotein-Associated Amino Acid Transporters

The L-type amino acid transporter LAT1 has recently been identified as being a disulfide-linked ``light chain' of the ubiquitously expressed glycoprotein 4F2hc/CD98. Several LAT1-related transporters have been identified, which share the same putative 12-transmembrane segment topology and also associate with the single transmembrane domain 4F2hc protein. They display differing amino acid substrate specificities, transport kinetics and localizations such as, for instance, y⁺LAT1 which is localized at the basolateral membrane of transporting epithelia, and the defect of which causes lysinuric protein intolerance. The b^0,+AT transporter which associates with the 4F2hc-related rBAT protein to form the luminal high-affinity diamino acid transporter defective in cystinuria, belongs to the same family of glycoprotein-associated amino acid transporters (gpaATs). These glycoprotein-associated transporters function as amino acid exchangers. They extend the specificity range of vectorial amino acid transport when located in the same membrane as carriers that unidirectionally transport one of the exchanged substrates. gpaATs belong to a phylogenetic cluster within the amino acid/polyamine/choline (APC) superfamily of transporters. This cluster, which we designate the LAT family (named after its first vertebrate member), includes some members from nematodes, yeast and bacteria. The latter of these proteins presumably lack association with a second subunit. In this review, we focus on the animal members of the LAT cluster that form, together with some of the nematode members, the family of glycoprotein-associated amino acid transporters (gpaAT family). Received: 20 July 1999/Revised: 7 September 1999     

Effect of Trace Levels of Nigericin on Intracellular pH and Acid-Base Transport in Rat Renal Mesangial Cells

Nigericin is an ionophore commonly used at the end of experiments to calibrate intracellularly trapped pH-sensitive dyes. In the present study, we explore the possibility that residual nigericin from dye calibration in one experiment might interfere with intracellular pH (pH _i ) changes in the next. Using the pH-sensitive fluorescent dye 2′,7′-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF), we measured pH _i in cultured rat renal mesangial cells. Nigericin contamination caused: (i) an increase in acid loading during the pH _i decrease elicited by removing extracellular Na⁺, (ii) an increase in acid extrusion during the pH _i increase caused by elevating extracellular [K⁺], and (iii) an acid shift in the pH _i dependence of the background intracellular acid loading unmasked by inhibiting Na-H exchange with ethylisopropylamiloride (EIPA). However, contamination had no effect on the pH _i dependence of Na-H exchange, computed by adding the pH _i dependencies of total acid extrusion and background acid loading. Nigericin contamination can be conveniently minimized by using a separate line to deliver nigericin to the cells, and by briefly washing the tubing with ethanol and water after each experiment. Received: 14 October 1998/Revised: 2 March 1999     

Codon Usage in Plastid Genes Is Correlated with Context, Position Within the Gene, and Amino Acid Content

Highly expressed plastid genes display codon adaptation, which is defined as a bias toward a set of codons which are complementary to abundant tRNAs. This type of adaptation is similar to what is observed in highly expressed Escherichia coli genes and is probably the result of selection to increase translation efficiency. In the current work, the codon adaptation of plastid genes is studied with regard to three specific features that have been observed in E. coli and which may influence translation efficiency. These features are (1) a relatively low codon adaptation at the 5′ end of highly expressed genes, (2) an influence of neighboring codons on codon usage at a particular site (codon context), and (3) a correlation between the level of codon adaptation of a gene and its amino acid content. All three features are found in plastid genes. First, highly expressed plastid genes have a noticeable decrease in codon adaptation over the first 10–20 codons. Second, for the twofold degenerate NNY codon groups, highly expressed genes have an overall bias toward the NNC codon, but this is not observed when the 3′ neighboring base is a G. At these sites highly expressed genes are biased toward NNT instead of NNC. Third, plastid genes that have higher codon adaptations also tend to have an increased usage of amino acids with a high G + C content at the first two codon positions and GNN codons in particular. The correlation between codon adaptation and amino acid content exists separately for both cytosolic and membrane proteins and is not related to any obvious functional property. It is suggested that at certain sites selection discriminates between nonsynonymous codons based on translational, not functional, differences, with the result that the amino acid sequence of highly expressed proteins is partially influenced by selection for increased translation efficiency. Received: 21 July 1999 / Accepted: 5 November 1999     

Senescence of Flag Leaves and Ears of Wheat Hastened by Methyl Jasmonate

Treatment of flag leaves and ears of wheat plants with MJ (jasmonic acid methylester) (10⁻⁵ and 10⁻⁴ m) did not increase ethylene production, but it did accelerate senescence as indicated by the loss of chlorophyll. MJ also caused the closure of stomata, and consequently the rates of transpiration and photosynthesis decreased. Early maturity shortened the grain filling period, so the thousand grain weight was lower. Although ethylene elicited the same physiologic effects, the syndrome of senescence by MJ is independent of the former. We conclude that senescence and death in wheat are far from being elucidated; however, MJ and ethylene seem to participate in the phenomenon. Received July 10, 1997; accepted January 5, 1998     

F-actin at Newly Invaginated Membrane in Neurons: Implications for Surface Area Regulation

Neuronal shape and volume changes require accompanying cell surface adjustments. In response to osmotic perturbations, neurons show evidence of surface area regulation; shrinking neurons invaginate membrane at the substratum, pinch off vacuoles, and lower their membrane capacitance. F-actin is implicated in reprocessing newly invaginated membrane because cytochalasin causes the transient shrinking-induced invaginations, vacuole-like dilations (VLDs), to persist indefinitely instead of undergoing recovery. To help determine if cortical F-actin indeed contributes to cell surface area regulation, we test, here, the following hypothesis: invaginating VLD membrane rapidly establishes an association with F-actin and this association contributes to VLD recovery. Cultured molluscan (Lymnaea) neurons, whose large size facilitates three-dimensional imaging, were used. In fixed neurons, fluorescent F-actin stains were imaged. In live neurons, VLD membrane was monitored by brightfield microscopies and actin was monitored via a fluorescent tag. VLD formation (unlike VLD recovery) is cytochalasin insensitive and consistent with this, VLDs formed readily in cytochalasin-treated neurons but showed no association with F-actin. Normally, however (i.e., no cytochalasin), VLDs were foci for rapid reorganization of F-actin. At earliest detection (1–2 min), nascent VLDs were entirely coated with F-actin and by 5 min, VLD mouths (i.e., at the substratum) had become annuli of F-actin-rich motile leading edge. Time lapse images from live neurons showed these rings to be motile filopodia and lamellipodia. The retrieval of VLD membrane (vacuolization) occurred via actin-associated constriction of VLD mouths. The interplay of surface membrane and cortical cytoskeleton in osmotically perturbed neurons suggests that cell surface area and volume adjustments are coordinated in part via mechanosensitive F-actin dynamics. Received: 25 March 1999/Revised: 15 June 1999     

Sheep Erythrocyte Membrane Binding and Transfer of Long-Chain Fatty Acids

We have studied binding and membrane transfer rates of unsaturated long-chain fatty acids in sheep red cells, as previously done for human red cells, in order to elucidate the transport mechanism. Observed differences must be assigned to the different composition of the membrane in the two species. Equal surface areas of the membranes of the two species have similar binding capacities and affinities for palmitic-, linoleic-, oleic- and arachidonic acid at 37°C. The competitive bindings of linoleic- and arachidonic acid as well as the distribution of bound arachidonic acid on the two sides of the membrane are not different in the two species. However, the rate constants for membrane transfer in sheep are less than half of those measured previously for human ghosts. This finding is confirmed by the exchange efflux kinetics of ghosts containing albumin-bound fatty acid. Studies of sheep ghost membranes with oleic-, arachidonic- and linoleic acid reveal a proportionality between the membrane transfer rate constants and the number of fatty acid double bonds, as found previously for human ghost membrane, and the effect of double bonds is in harmony with a large negative activation entropy for diffusion through the membrane. The established replacement of lecithin by sphingomyelin with a low unsaturation fatty acid index in sheep membranes probably causes a lower transversal lipid phase fluidity. Double bonds diminish the flexibility of hydrocarbon chains and thus the large negative activation entropy of diffusion across the membrane. The smaller transfer rate constants of the three unsaturated fatty acids in sheep membranes support the hypothesis that the transfer is diffusion in protein defined annular lipid domains and not carrier mediated. Received: 24 February 1999/Revised: 10 June 1999     

Drought Stress Syndrome in Wheat Is Provoked by Ethylene Evolution Imbalance and Reversed by Rewatering, Aminoethoxyvinylglycine, or Sodium Benzoate

In this work we present evidence that the drought stress syndrome in the flag leaves and ears of wheat plants, provoked by the production of ethylene (shortening the grain filling period and lowering the grain weight) is reversed by the application of a free radical scavenger, sodium benzoate or the ethylene synthesis inhibitor, aminoethoxyvinylglycine. Rehydration by watering also attenuated the detrimental effect of the water deficit. Consequently, the grain filling period was longer, the grain weight increased, and the total protein content was higher than that in plants watered regularly. Received June 11, 1998; accepted March 10, 1999     

Uptake, Distribution, and Metabolism of 1-Naphthaleneacetic Acid and Indole-3-Acetic Acid During Callus Initiation From Actinidia deliciosa Tissues

1-Naphthaleneacetic acid (NAA) and 6-benzyladenine (BA) were required for in vitro callus formation at the basal edge of kiwifruit (Actinidia deliciosa [A. Chev] Liang and Ferguson, cv. Hayward) petioles. The uptake, metabolism, and concentration of NAA and indole-3-acetic acid (IAA) content were examined in the explants during the callus initiation period. After 1, 6, 12, 24, 48, and 96 h of culture in the presence of [H³]NAA, petioles were divided into apical, middle, and basal portions and analyzed. Except for a high IAA level measured at 12 h, IAA content decreased in tissues during a culture period of 96 h. NAA uptake was higher in petiolar edges than in the middle portion, and NAA was rapidly conjugated with sugars and aspartic acid inside the tissues. The amide conjugation was triggered in apical and basal portions from 12 h and in the middle part from 48 h, with α-naphthylacetylaspartic acid being the major metabolite. Free-NAA concentration in cultured petioles achieved an equilibrium with the exogenously applied NAA (0.27 μm) from 12 h, and it remained constant thereafter. The relationships between the role attributed to NAA and BA in the initiation and the maintenance of disorganized growth of callus in kiwifruit cultures are discussed. Received December 21, 1998; accepted July 20, 1999