Comparative study of the reactivation of oxygen evolution in chloroplasts inhibited by various treatments

Reactivation of photosynthetic oxygen-evolution was investigatedwith chloroplasts inhibited by 0.8 M Tris-, 0.8 M Tris-20% acetone-,0.8 M KCl-, 0.5 M NaClO₄- or 1 mM NH₂OH-washing, and with heat-treatedor aged chloroplasts. These chloroplasts restored oxygen evolvingactivity by two successive treatments; incubation of chloroplastswith reduced DPIP, then with Mn^2$, Ca^2$, dithiothreitol andbovine serum albumin under weak illumination (light-reactivation). Some factors required for light-reactivation could be omitteddepending on the inhibition treatment. For example, Mn^2$, Ca^2$and dithiothreitol were not necessary for (1 mM NH₂OH-STN (pH7.0)-washed)-DPIP-treated chloroplasts, and dithiothreitol for(Tris-acetone (pH 8.4)-washed)-DPIP-treated chloroplasts. Uncouplers, such as atebrin, CCCP, DCCD and NH₄Cl, inhibitedthe lightreactivation. The Mn and Ca contents of the chloroplasts were determined withinhibited and DPIP-treated chloroplasts. The Mn content of thechloroplasts tended to decrease with increasing pH of the washingmedium for inhibition. The Ca content decreased when chloroplastswere washed with 0.8 M KCl. (Received November 22, 1974; )     

Effects of high nitrogen load on growth, photosynthesis and nutrient status of Cryptomeria japonica and Pinus densiflora seedlings

To evaluate the sensitivity of Japanese cedar (Cryptomeria japonica D. Don) and Japanese red pine (Pinus densiflora Sieb. et Zucc.) to high N deposition, 1-year-old seedlings were grown in brown forest soil treated with N as NH₄NO₃ at 0, 25, 50, 100 and 300 mg l^-1 fresh soil volume, equivalent to 0, 28, 57, 113 and 340 kg N ha^-1. Net photosynthetic rate and whole-plant dry mass of C. japonica seedlings were increased by the N treatment, whilst those of P. densiflora seedlings were significantly reduced by the highest N treatment. The reduction in the net photosynthesis of P. densiflora seedlings was mainly due to a depression of carboxylation efficiency accompanied by a decrease in concentration and activity of Rubisco in the needles. In P. densiflora seedlings, needle concentrations of P and Mg were decreased, and the concentrations of N and Mn were increased by the highest N treatment. The reductions in needle protein concentration and Rubisco activity were negatively correlated with the ratios of N/P and Mn/Mg in the needles. These results suggest that nutrient imbalances of these elements may be induced in P. densiflora seedlings grown under high N deposition. We conclude that P. densiflora is more sensitive to high N deposition than C. japonica, and that the relatively high atmospheric N deposition to Japanese forest ecosystems may adversely affect the health of N-sensitive tree species such as P. densiflora.     

锰对植物毒害及植物耐锰机理研究进展

含锰矿渣的排放造成了严重的土壤锰污染。揭示锰毒害和植物的耐锰机制对于污染土壤治理具有重要意义。研究表明, 高浓度的Mn²⁺能够抑制根系Ca²⁺、Fe²⁺和Mg²⁺等元素的吸收及活性, 引起氧化性胁迫导致氧化损伤, 使叶绿素和Rubisco含量下降、叶绿体超微结构破坏和光合速率降低。而锰超累积植物则具有多种解毒或耐性机制, 如区域化、有机酸螯合、外排作用、抗氧化作用和离子交互作用等。根系主要通过有机酸的螯合作用促进植物对Mn²⁺的转运解毒, 同时能够将过量的Mn²⁺区域化在根细胞壁中; 叶片可通过酚类物质或有机酸螯合Mn²⁺, 并将其区域化在叶片表皮细胞和叶肉细胞的液泡中(或通过表皮毛将Mn²⁺排出体外)。其中, 金属转运蛋白在植物对Mn²⁺的吸收、转运、累积和解毒过程中发挥着重要作用。     

Effects of manganese, calcium, dithiothreitol and bovine serum albumin on the light-reactivation of Tris-acetone-washed chloroplasts

Oxygen-evolution activity of spinach chloroplasts was investigatedby washing chloroplasts with 0.8M Tris buffer containing 20%acetone. This inactivitation was easily removed by two successivetreatments, dark- and light-reactivations. The first treatmentwas dark-reactivation step, rewashing inactivated chloroplastswith reduced DPIP (DPIP treatment). The second one was a light-reactivatedchloroplasts with incubating chloroplasts with Mn²⁺, Ca²⁺, dithiothreitoland bovine serum albumin under ilumination. Both light- and dark-reactivation treatments were required toregain oxygen-evolution activity of Tris-acetone-washed chloroplasts,which is characteristic of such chloroplasts. However, in Tris-washedchloroplasts considerable activity was recovered by dark-reactivationalone. Manganese and calcium contents of Tris-acetone-washed chloroplastswere compared with those of chloroplasts obtained by other preparations. Tris-acetone washing was presumed to inhibit the oxygen-evolutionsite of Photo-systetm II by affecting Mn, Ca and other substancesin chloroplasts. The inhibition site was estimated from a changein fluorescence yield of chlorophyll and the effect of artificialelectron donor specific for Photosystem II on NADP photoreductionactivity. (Received August 20, 1973; )     

Uptake and distribution of 65Zn and 54Mn in wheat grownat sufficient and deficient levels of Zn and Mn: I. During vegetative growth

The uptake and distribution of ⁶⁵Zn and ⁵⁴Mn by wheat (Triticumaestivum cv. Aroona) was investigated. Plantswere grown in achelate-buffered nutrient solution with either sufficient Znand Mn, low Zn or low Mn. A single representative seminal rootfrom 14-d-old and 42-d-old plants was dual-labelled with ⁶⁵Znand ⁵⁴Mn. The 14-d-old plants were harvested every 10 min from10–140 min of labelling, whilst the 42-d-old plants wereharvested after 2 h of labelling. At harvest, each plant wasseparated into leaves, main stem, unexposedroots, and tillers.In addition, the crown was separatedfrom the stem in the 14-d-oldplants In the control plants labelled at 14 d, ⁶⁵Zn was firstdetectedand accumulated in the crown of the roots after 40–60min. Labelled Zn was then detected in the stem, followed bythe leaves. The oldest and youngest leaves received less ⁶⁵Znthan the second and third oldest leaves. The plants grown underlow Zn conditions accumulated more ⁶⁵Zn in their older leavesand transferred ⁶³Zn to the unexposed roots. Distribution of⁵⁴Mn was similar in the controls to that of ⁶⁵Zn, except theolder leaves received no HMn, At the second harvest, a similardistribution pattern of ⁶⁵Zn and ⁵⁴Mn was observed with regardto leaf age. Large amounts of ⁶⁵Zn and ⁵⁴Mn were detected withinthe unexposed roots of all treatments. It is suggested thatthe distribution of root-supplied Zn and Mn may be determinedby micronutrient status and its relationship with leaf transpirationrates. Key words: Distribution, manganese, vegetative growth, wheat, zinc     

Short-Term Nitrate Effects on Hydroponically-Grown Soybean cv. Bragg and its Supernodulating Mutant: I. CARBON, NITROGEN AND MINERAL ELEMENT DISTRIBUTION, RESPIRATION AND THE EFFECT OF NITRATE ON NITROGENASE ACTIVITY

A comparison between two hydroponically-grown soybean genotypes(Glycine max [L.] Merr.) cv. Bragg and the supernodulating mutantnts 1007 was made in terms of dry matter accumulation, carbon,nitrogen, and mineral element distribution, ¹⁵N natural abundanceand the effect of short-term treatment with 4·0 mol m^–3KNO₃ on nitrogenase activity and respiration. Differences weremost pronounced in nodule dry weight and plant nitrogen content,both of which were recorded to be substantially elevated inthe mutant. Mineral element concentrations in different plantparts proved to be rather similar with the exception of Ca,found to be lower in leaves of the mutant, and Mn concentrationswhich were twice as high in roots of nts 1007. The values of¹⁵N natural abundance showed that both genotypes were equallydependent on nitrogen fixation when nitrate was absent. Theresults of the acetylene reduction assays indicated similarspecific nodule activity, while on a per plant basis nitrogenaseactivity of the mutant proved to be more than twice the amountof Bragg. This effect was also reflected in higher nodule respirationwhile root respiration remained below that of Bragg. Nitrate induced a substantial reduction in nitrogenase activitynot only in Bragg, but also in nts 1007. Nodule respiratoryactivity of Bragg was reduced by nitrate from 1·27 to0·34 mg C h^–1 plant^–1. In nts 1007 correspondingvalues were 2·70 to 1·52 mg C h^–1 plant^–1.Starch concentration in nodules was decreased in both genotypes,but nevertheless remained higher in nts 1007. Values for solublesugars in nodules even increased in the mutant in response tonitrate while the same treatment caused a reduction in Bragg.The data indicate that nitrogenase activities of Bragg and nts1007 are equally sensitive to short-term application of nitrate. Key words: Glycine max, C and N distribution, nitrate, root respiration, ¹⁵N natural abundance     

Involvement of Carboxyl Groups of the PSII Reaction Center Proteins in Photoactivation of the Apo-Water-Oxidizing Complex

Involvement of residues of acidic amino acids in photo-ligationof manganese into the apo-water-oxidizing complex was investigatedby use of l-ethyl-3-[3-(dimethylami-no)propyl]carbodiimide (EDC),a water-soluble carboxyl modifier. Treatment of Mn-depletedPSII membranes by EDC in the presence of nucleophiles induceda loss of photoactivation capability in the Mn complex and partialloss of capability of photooxidation of Mn²⁺, but little decreasein the DCIP photoreduction supported by diphen-ylcarbazide.The inhibition of diphenylcarbazide-photo-oxidation by submicromolarMn²⁺, indicative of the intactness of high-affinity Mn-bindingsites, was apparently abolished by EDC treatment. From aminoacid quantitation analysis of Dl and D2 proteins and CP47 ofthe chemically-modified membranes, approximately three carboxylgroups of the D1 protein were found to be chemically-modifiedwith EDC after removal of the functional Mn. These results suggestthat acidic amino acids on the D1 protein are involved in photoactivationof the apo-water-oxidizing complex and probably in ligationof Mn to the water-oxidizing complex. (Received October 21, 1996; Accepted March 3, 1997)     

The Translocation and Redistribution of Manganese in Avena

⁵⁴Mn present in the first two leaves of oat seedlings subsequentlydeprived of manganese was later redistributed to leaves 4 and5. ⁵⁴Mn was found in leaves 3 and 4 even when the roots of seedlingswere excised immediately after exposure to ⁵⁴Mn, but more wasdetected if the roots were left intact. ⁵⁴Mn applied as a drop to the 4th leaf of manganese-deficientoat plants was concentrated in the stem and translocated primarilyto the youngest developing leaf or to the grain if present.⁵⁴Mn was readily detected in the roots but almost none was translocatedto the first three leaves. More ⁵⁴Mn was translocated in 96hrs. than 24, but little or no more was translocated in 192hrs. Plants which were given 0.5 p.p.m. stable manganese until theyreached the 4th leaf stage, and were then exposed to ⁵⁴Mn, showeda fairly uniform distribution of ⁵⁴Mn throughout the plant.There was relatively slight concentration at active growth centres. It is concluded that physiologically significant redistributionof manganese occurs in the oat plant.     

Stimulation of Na,K-ATPase by low potassium requires reactive oxygen species

The signaling pathway that transduces the stimulatory effect of low K⁺ on the biosynthesis of Na,K-ATPase remains largely unknown. The present study was undertaken to examine whether reactive oxygen species (ROS) mediated the effect of low K⁺ in Madin-Darby canine kidney (MDCK) cells. Low K⁺ increased ROS activity in a time- and dose-dependent manner, and this effect was abrogated by catalase and N-acetylcysteine (NAC). To determine the role of ROS in low-K⁺-induced gene expression, the cells were first stably transfected with expression constructs in which the reporter gene chloramphenicol acetyl transferase (CAT) was under the control of the avian Na,K-ATPase -subunit 1.9 kb and 900-bp 5'-flanking regions that have a negative regulatory element. Low K⁺ increased the CAT expression in both constructs. Catalase or NAC inhibited the effect of low K⁺. To determine whether the increased CAT activity was mediated through releasing the repressive effect or a direct stimulation of the promoter, the cells were transfected with a CAT expression construct directed by a 96-bp promoter fragment that has no negative regulatory element. Low K⁺ also augmented the CAT activity expressed by this construct. More importantly, both catalase and NAC abolished the effect of low K⁺. Moreover, catalase and NAC also inhibited low-K⁺-induced increases in the Na,K-ATPase ₁- and ₁-subunit protein abundance and ouabain binding sites. The antioxidants had no significant effect on the basal levels of CAT activity, protein abundance, or ouabain binding sites. In conclusion, low K⁺ enhances the Na,K-ATPase gene expression by a direct stimulation of the promoter activity, and ROS mediate this stimulation and also low-K⁺-induced increases in the Na,K-ATPase protein contents and cell surface molecules. Madin-Darby canine kidney cells; N-acetylcysteine; catalase     

Ontogeny, Phytogeny, and Cellular Cooperation

The capacity of adult newt (Triturus viridescens) spleen cellsto secrete antibody at 4 C allows simultaneous visualizationand quantification of non-secretory (S^–) and secretory(S⁺) rosette forming cells (RFC). Visualization of mammalianS⁺ RFC requires 37 C, a temperature at which S^– RFC appearto be fragile. RFC can be distinguished as S^– or S⁺ dueto whether one or more layers of erythrocytes adhere to thesurface of sensitized spleen cells. Different doses of horseerythrocytes (HRBC) affect newt S^– RFC and S⁺ RFC differentially.By varying the time between injections of different concentrationsof chicken erythrocytes (CRBC, the "carrier") and a constantdosage of CRBC-TNP (trinitrophenyl, the hapten) it is possibleto measure "helper" activity that correlates with the populationof S^– RFC and is both dose and time dependent. By varyingassay time after "helper" activity has been maximized, one candetermine the cytodynamics of anti-TNP antibody producing cell(APC) activity. For the first time these morphologically separableRFC can be related to their suspected physiologic behavior.A shift from S^– RFC to S⁺ RFC takes place during the immuneresponse. That similar dose-dependent response curves can beshown in adultRana pipiens suggests that the newt responsesrepresent a fundamental vertebrate pattern.     

Surface alkaline phosphatase activities of macroalgae on coral reefs of the central Great Barrier Reef, Australia

Inshore reefs of the Great Barrier Reef (GBR) are subject to episodic nutrient supply, mainly by flood events, whereas midshelf reefs have a more consistent low nutrient availability. Alkaline phosphatase activity (APA) enables macroalgae to increase their phosphorus (P) supply by using organic P. APA was high (~4.0 to 15.5 µmol PO₄^3- g DW^-1 h^-1) in species colonising predominantly inshore reefs and low (<2 µmol PO₄^3- g DW^-1 h^-1) in species with a cross-shelf distribution. However, APA values of GBR algae in this study were much lower than data reported from other coral reef systems. In experiments with two Sargassum species tissue P levels were correlated negatively, and N:P ratios were positively correlated with APA. High APA can compensate for a relative P-limitation of macroalgae in coral reef systems that are subject to significant N-inputs, such as the GBR inshore reefs. APA and other mechanisms to acquire a range of nutrient species allow inshore species to thrive in habitats with episodic nutrient supply. These species also are likely to benefit from an increased nutrient supply caused by human activity, which currently is a global problem.     

Photosynthesis in Panicum milioides, a Species with Reduced Photorespiration

The capacity for C₄ photosynthesis in Panicum milioides, a specieshaving reduced levels of photorespiration, was investigatedby examining the activity of certain key enzymes of the C₄ pathwayand by pulse-chase experiments with ¹⁴CO₂. The ATP$P₁ dependentactivity of pyruvate,P₁ dikinase in the species was extremelylow (0.14–0.18 µmol mg chlorophyll^–1 min^–1).Low activity of the enzyme was also found in Panicum decipiensand Panicum hians (related species with reduced photorespiration)and in Panicum laxum (a C₃ species). The antibody to pyruvate,P₁dikinase caused about 70% inhibition of the ATP$P₁ dependentactivity of the enzyme in P. milioides. The activity of NAD-malicenzyme and NADP-malic enzyme in ^P. ^milioides was equally low(approximately 0.1–0.2 µmol mg chlorophyll^–1min^–1) and similar to the activity in P. decipiens, P.hians and P. laxum. Photosynthetic pulse-chase experiments underatmospheric conditions showed a typical C₃-like pattern of carbonassimilation including the labelling of glycine and serine asexpected during photorespiration. During the pulse with ¹⁴CO₂only about 1% of the labelled products appeared in malate and2–3% in aspartate. During a chase in atmospheric levelsof CO₂ for up to 6 min there was a slight increase in labellingin the C₄ acids. The amount of label in carbon 4 of aspartatedid not change during the chase, indicating little or no turnoverof the C₄ acid via decarboxylation. The results indicate thatunder atmospheric conditions P. milioides assimilates carbondirectly through the C₃ pathway. Photorespiration as indicatedby the CO₂ compensation point may be repressed in the speciesby a more efficient recycling of photorespired CO₂. (Received June 8, 1982; Accepted July 22, 1982)     

Response to Waterlogging and Differing Sensitivity to Divalent Iron and Manganese in Clones of Dactylis glomerata L. derived from Well-drained and Poorly-drained Soils

Clonally propagated plants of Dactylis glomerata derived froma well-drained, heavily grazed cliff habitat (clone L) and froman undergrazed poorly-drained soil (clone A) were tested forwaterlogging tolerance in soil-culture. Water-logging did notaffect the two clones differentially, a result, which contrastedstrongly with that of a previous experiment in which simulatedgrazing (clipping to 20 cm) unexpectedly caused clone A to beless tolerant of waterlogging than clone L. Maximum leaf andleaf sheath length was reduced more by water-logging in cloneL than in clone A (P < 0.05). In solution-culture when providedwith factorial combinations of 0.5, 5 and 50 mg dm^–2 ofFe²⁺ and Mn²⁺ the shoot dry weight yield of the dry-soil clonewas reduced more than that of the wet-soil clone by 50 mg Fedm^–3 irrespective of Mn²⁺ concentration (P < 0.01)but the reduction of growth was less at higher Mn²⁺ concentrations.Fifty milligrams of Mn²⁺ dm^–3 reduced the growth of thedry soil clone but increased the growth of the wet soil clonewith Fe²⁺ at 5 mg dm^–2 (P < 0.05). Iron at 0.5 mg dm^–2was suboptimal for shoot growth of both clones at any levelof Mn²⁺ and caused more severe leaf chlorosis in the wet soilclone. Leaf tissue of clone L contained more iron than thatof clone A after waterlogging (P < 0.01) but in solutionculture, though increasing iron from 0.5 to 50 mg dm^–3almost doubled leaf iron content (P < 0.001), the interactionClones x Mn x Fe just failed to reach significance at P <0.05. The manganese content of leaf tissue from the two clonesvaried differently in response to solution manganese (Clonesx Mn P < 0.01), clone A showing a slightly greater increaseof manganese content at high solution concentration. Iron at50 mg dm^–3 suppressed Mn uptake (Mn x Fe, P < 0.001)in both clones. The two clones thus show marked environmentaladaptation to the chemistry of wet and dry soils. Dactylis glomerata, Cocksfoot grass, Orchard grass, waterlogging, iron, manganese, toxicity, deficiency, ecotypes     

Cloning, expression, and characterization of the trout cardiac Na+/Ca2+ exchanger

Isoform 1 of the cardiacNa⁺/Ca²⁺exchanger (NCX1) is an important regulator of cytosolicCa²⁺ concentration in contractionand relaxation. Studies with trout heart sarcolemmal vesicles haveshown NCX to have a high level of activity at 7°C, and this uniqueproperty is likely due to differences in protein structure. In thisstudy, we describe the cloning of an NCX (NCX-TR1) from a Lambda ZAPII cDNA library constructed from rainbow trout(Oncorhynchus mykiss) heart RNA. TheNCX-TR1 cDNA has an open reading frame that codes for a protein of 968 amino acids with a deduced molecular mass of 108 kDa. A hydropathy plotindicates the protein contains 12 hydrophobic segments (of which thefirst is predicted to be a cleaved leader peptide) and a largecytoplasmic loop. By analogy to NCX1, NCX-TR1 is predicted to have ninetransmembrane segments. The sequences demonstrated to be the exchangerinhibitory peptide site and the regulatoryCa²⁺ binding site in thecytoplasmic loop of mammalian NCX1 are almost completely conserved inNCX-TR1. NCX-TR1 cRNA was injected into Xenopus oocytes, and after 3-4days currents were measured by the giant excised patch technique.NCX-TR1 currents measured at ~23°C demonstratedNa⁺-dependent inactivation andCa²⁺-dependent activation in amanner qualitatively similar to that for NCX1 currents.

     

Cerebral vascular endothelial heme oxygenase: expression, localization, and activation by glutamate

Endogenous carbon monoxide (CO)contributes to vasodilator responses of cerebral microvessels innewborn pigs. We investigated the expression, intracellularlocalization, and activity of heme oxygenase (HO), the key enzyme in COproduction, in quiescent cerebral microvascular endothelial cells(CMVEC) from newborn pigs. HO-1 and HO-2 isoforms were detected byRT-PCR, immunoblotting, and immunofluorescence. HO-1 and HO-2 aremembrane-bound proteins that have a strong preference for the nuclearenvelope and perinuclear area of the cytoplasm. Betamethasone(10⁶ to 10⁴ M for 48 h) was associatedwith upregulation of HO-2 protein by ~50% and inhibition of Cox-2but did not alter HO-1 or endothelial nitric oxide synthase expressionin CMVEC. In vivo betamethasone treatment of newborn pigs (0.2 and 5.0 mg/kg im for 48 h) upregulated HO-2 in cerebral microvessels by30-60%. HO activity as ¹⁴CO production from[¹⁴C]glycine-labeled endogenous heme was inhibited bychromium mesoporphyrin (10⁶ to 10⁴ M).L-Glutamate (0.3-1.0 mM) stimulated HO activity1.5-fold. High-affinity specific binding sites forL-[³H]glutamate suggestive of the glutamatereceptors were detected in CMVEC. Altogether, these data suggest that,in cerebral circulation of newborn pigs, endothelium-derived CO maycontribute to basal vascular tone and to responses that involveglutamate receptor activation.

     

Properties, development and cellular-localization of cinnamic acid 4-hydroxylase in cut-injured sweet potato

In sweet potato root tissue, cinnamic acid 4-hydroxylase activityincreased markedly in response to cut injury, and reached amaximum after 1 day of incubation. The patterns of developmentand successive decline were similar to those for phenylalanineammonia-lyase activity. The development of both enzyme activitieswas inhibited by cycloheximide. The activity was strictly dependenton pH of the homogenizing and reaction media. The optimum pHof the reaction was 8.0. The respective Km values for trans-cinnamicacid and NADPH were 2.6?10^-5 and 1.8?10^-6M. The activity wasnot affected by ß-mercaptoethanol and the intermediatesand product of the polyphenol biosynthetic pathway. Carbon monoxideinhibited strongly the activity and its inhibition was partiallyprevented by light. Thus, the enzyme may be involved in thecytochrome P-450 mediated electron transport system. Studiesusing differential centrifugation and sucrose density gradientcentrifugation, showed that the intracellular distribution of4-hydroxylase activity differed distinctly from that of themitochondrial marker enzyme and was not in accord with thatof NADPH-cytochrome c reductase activity. ¹This paper constitutes part 114 of the Phytopathological Chemistryof Sweet Potato with Black Rot and Injury. ²Present address: Laboratory of Biochemistry, Faculty of Agriculture,Nagoya University, Chikusa, Nagoya 464, Japan. (Received May 20, 1974; )     

The Effect of Triacontanol on Peroxidase, IAA, and Plant Growth in Pisum sativum var.'Alaska' and 'Little Marvel'

The present study investigates the effects of triacontanol (CH₃(CH₂)₂₈CH₂OH),on plant growth (root and stem), peroxidase activity (apicalmeristem tissue), and auxin destruction (apical meristem tissue)in ‘Little Marvel’ dwarf (LM) and ‘Alaska’peas (AP). Triacontanol inhibited root growth in LM comparedto untreated controls. However, root growth in AP tissue wasenhanced by 1.0 mg I^–1 triacontanol and inhibited by allother treatments, in comparison to untreated controls. Wateruptake in triacontanol-treated AP plants was greater than inuntreated controls, with the converse being the case for LM.Triacontanol treatment caused an increase in peroxidase activityin both LM and AP plants compared to untreated controls. Interms of (1–¹⁴C)IAA destruction, GA₃ + 0.01 mg 1^–1triacontanol caused appreciable auxin breakdown (40%) in LMtissue, with GA₃ + 0.1 mg 1^–1 triacontanol giving a 43%decrease compared to untreated controls. In AP tissue, 10 µMGA3 increased auxin destruction by 188% whereas 0.1 mg I^–1triacontanol caused a 20% decrease compared to untreated controls.The effects of triacontanol on root and stem growth, peroxidaseactivity, and auxin destruction appear to be cultivar-specific,with respect to LM and AP varieties of peas.     

Allocation of Photosynthate to Individual Tubers of Solanum tuberosum L.: II. RELATIONSHIP BETWEEN GROWTH RATE, CARBOHYDRATE CONCENTRATION AND 14C-PARTITIONING WITHIN TUBERS

Potato plants (Solanum tuberosum L.) were grown in water culturein a controlled environment. The growth rates of individualtubers were closely reflected by their ¹⁴C-content 20 h after¹⁴CO₂ had been applied to the aerial parts of the shoot for4 h. The ¹⁴C-content of the tuber (sink strength) was significantlycorrelated to the ¹⁴C-concentration of the tuber tissue (¹⁴Cg^–1 fr. wt.=sink activity). The sink activity, which differedbetween individual tubers by up to a factor of 10, was alsoclosely related to the conversion rates of ¹⁴C into the starchand the remainder as well as to the ¹⁴C-content in the ethanolsoluble fraction. This indicates the simultaneous use of photosynthatefor growth and storage in the growing tubers. No preferenceof photosynthate utilization for either of these processes couldbe detected in relation to the sink activity of the tubers.Tubers with high sink activity imported ¹⁴C-labelled photosynthateat higher rates although their tissue contained higher concentrationsof reducing sugars and sucrose than the tissue of tubers withlow sink activity. Despite the close relationship between sinkactivity and the rate of starch synthesis (¹⁴C-conversion intostarch), no significant correlation was found between sink activityand the actual starch concentration of the tissue. The applicationof zeatin riboside directly onto individual tubers increasedtheir growth rates in comparison to non-treated tubers of thesame plant. The results indicate the importance of both growthand storage processes for the regulation of sink activity inyoung potato tubers. Key words: Potato tuber, ¹⁴C-photosynthate partitioning, zeatin riboside application     

Ageing of Cucumber and Onion Seeds: Phospholipase D, Lipoxygenase Activity and Changes in Phospholipid Content

Cucumber (Cucumis sativus L. cv. Mesa) and onion (Allium cepaL. cv. Rijnsburger Heldis) seeds were rapidly aged at 40 °Cand 74% relative humidity. Onion seeds were also slowly agedat 40 °C with 15% relative humidity for 11 months and onemore month at 28% relative humidity. Significant loss of totaland individual phospholipids was an early event during bothstorage treatments. With slow ageing of onion, loss of phosphatidylcholineoccurred several months before loss of viability and vigourwas detected. Phosphatidic acid, the lipid product of phospholipaseD action, increased during rapid ageing of both cucumber andonion. Phosphatidic acid was present in onion seeds before theageing treatments and its content remained unchanged in theslowly aged seeds. There was 1600 (cucumber) and 2000 (onion)times more phospholipase D activity (6 x 10⁵ and 2·9x 10⁵ nmol g^–1 d^–1 in cucumber and onion, respectively)in crude extracts from non-aged seeds than was required to accountfor the fastest fall in phospholipids (72, 372 and 144 nmolg^–1 d^–1 for cotyledons and radicles of cucumberand onion, respectively, over the first 9 d [cucumber] or 1d [onion] of ageing) and fastest increase in phosphatidic acid(7, 162 and 37 nmol g^–1 d^–1). How accurate a guidethe in vitro activity of phospholipase D was to the in vivoactivity was unclear. However, the considerable excess activityseen with the formation of phosphatidic acid supports the proposalthat hydrolysis of phospholipids by phospholipase D is a firststep in deterioration during ageing. Substantial lipoxygenaseactivity was also detected (58 x 10³ and 54 x 10³ nmol g^–1d^–1 respectively, for non-aged cucumber and onion seeds).However, the increase in conjugated dienes (an early productof peroxidation) in ageing cucumber seeds was comparativelysmall (90 nmol g^–1 d^–1 over 21 d ageing), and increasein malondialdehyde could not be detected, indicating that peroxidationmay not have been a major factor in cucumber. The increase inconjugated dienes during rapid ageing of onion seeds was larger(1·5 x 10³ nmol g^–1 d^–1 over days 0–2of rapid ageing), much greater than the decrease in phospholipidacyl groups (260 nmol g^–1 d^–1 over days 0–2of rapid ageing) indicating the occurrence of peroxidation offatty acids released from reserve as well as from membrane lipids.This higher level of conjugated dienes during onion ageing wasthe main difference between cucumber and onion, indicating thatthe level of peroxidation could be an important difference betweenfast and slow ageing seeds. However, peroxidation is not theonly possible deleterious process since hydrolysis of the normalmembrane phospholipids to phosphatidic acid increased the contentof non-bilayer-forming lipids and this too could be a directmembrane-destabilizing consequence of phospholipase D actionduring ageing. Key words: Cucumis sativus L. (cucumber), Allium cepa L. (onion), seed ageing, phospholipase D, lipoxygenase, phospholipids