After-effect of Water Stress on Stomatal Opening Potential: I. TECHNIQUES AND MAGNITUDES

The after-effect of a period of water stress upon the light-openingability of stomata was studied in tobacco (Nicotiana tabaccum)and broad bean (Vicia faba). Stomatal opening was always measuredafter floating leaf discs on water under favourable conditionsof light and temperature to obtain maximal opening at full leafturgor. Thus possible interference due to persistence of leaf-waterdeficits in the post-stress leaves was eliminated. Stomatalaperture was accurately estimated using a resistance porometer;values so obtained were substantiated by the direct measurementof aperture. Two to 4 days of wilting of tobacco, producing leaf-water deficitsof 30 to 40 per cent, had a marked after-effect on tobacco stomata.The ability to open in light was depressed and complete recoveryfrom this depression required 2 to 5 days after rewatering.In some cases over-recovery was observed; this was probablyrelated to a physiologically younger condition of leaves ofstressed plants following turgor recovery. In beans similarstresses caused after-effects smaller in magnitude but qualitativelysimilar to those in tobacco. In both tobacco and beans the magnitudeof the after-effect was approximately proportional to the leaf-waterdeficit attained immediately prior to rewatering.     

Ultrastructural Changes in Chloroplasts of Quercus rotundifolia Lam. in Response to Evernic Acid

The amount of total chlorophyll, chlorophylls a and b as wellas the ratio of a to b decreased in chloroplasts isolated fromQuercus rotundifolia leaves, kept for 17 d in a solution of35.5 µM evernic acid in 1 mM Na HCO₃, when compared withthe chloroplasts of control leaves (kept in NaHCO₃). The chloroplastsin the spongy parenchyma were smaller and the amount of starchand plastoglobuli lower. The number of grana per chloroplastsection, the number of thylakoids per grana and the height ofgrana stacks were also less in the chloroplasts of leaves treatedwith evernic acid. Quantitative ultrastructural differenceswere determined by means of electron microscopy and image analysistechniques. Quercus rotundifolia Lam., chloroplasts, ultrastructure, lichens, evernic acid     

A Comparison of the Rate of Maintenance Respiration in Some Crop Legumes and Tobacco Determined by Three Methods

Carbon exchange was measured on whole plants of field bean,lucerne, chick pea, kidney bean, pea and tobacco. The maintenance respiration rate was measured in three ways:(i) by allowing the CO₂ efflux to decay in prolonged darknessto an asymptotic value which was then taken to be the maintenancevalue (the dark decay method); (ii) by plotting the dark CO₂efflux as a function of the net CO₂ uptake over a range of irradiancesand taking maintenance as the dark CO₂ efflux when the net CO₂uptake was zero (the dynamic method); and (iii) by plottingthe total CO₂ uptake as a function of the growth rate and takingmaintenance respiration as the CO₂ efflux when the growth ratewas zero (the zero growth rate method). The range of valuesfor the maintenance coefficient over all species was from 1.6to 2.1 per cent of the dry weight per day, 1.8 to 2.1 per centand 2.7 to 2.9 per cent as determined by these three methodsrespectively. There was a linear relationship, common to allspecies, between the maintenance respiration rate (dark decaymethod) and dry weight, total nitrogen and the organic nitrogencontent. The growth coefficient (0.69±0.01) was the samefor field bean, chick pea and lucerne and was unaffected bythe method of estimation. It was concluded that the dark decay method provided the bestestimate of the minimal maintenance requirements in the plantsstudied. Vicia faba L., Medicago sativa L., Cicer arientinum L., Phaseolus vulgaris L., Pisum sativum L., Nicotiana tobacum L., field bean, lucerne, chick pea, kidney bean, pea, tobacco, respiration, maintenance, growth, nitrogen content     

Cellular Structure and Light Absorbtion in Leaves of Frithia pulchra (Mesembryanthemaceae)

In order to quantify the structural differences between celltypes of leaves from a ‘ window’ plant, an ultrastructuralmorphometric analysis was made of the epidermal, window andchlorenchyma tissues of Frithia pulchra. Epidermal cells arethe largest cells found in Frithia leaves and are characterizedby the presence of a thick outer tangential cell wall and numerousvacuolar inclusions. Epidermal tissue has an optical densityof 0.30. The transparent window tissue (i.e. optical density= 0.08) has a uniform ultrastructure throughout the length ofthe leaf. The vacuome comprises aproximately 97 per cent ofthe protoplasmic volume of window cells. Chlorenchyma cellspossess thin cell walls and are surrounded by numerous intercellularspaces. Cells of the apical chlorenchyma tissue possess approximately30 plastids per cell. These chloroplasts have an average individualvolume of 220 µm². Cells of the basal chlorenchyma tissuecontain chloroplasts that are five to six times smaller andmore numerous than those in cells of the apical chlorenchyma.The increased volume of chloroplasts in the apical comparedwith basal chlorenchyma cells (i.e. 31.4 and 20.2 per cent ofthe protoplasm, respectively) is positively correlated withtheir optical densities of 1.46 and 0.97, respectively. Frithia pulchra, stereology, leaf, light absorption, window plant     

The Development of Desiccation-tolerance and Maximum Seed Quality During Seed Maturation in Six Grain Legumes

‘Physiological maturity’, i.e. the time when seedsreach their maximum dry weight during development, occurredwhen maturation drying on the parent plant in the field hadreduced seed moisture content to approximately 60 per cent infaba bean (Vicia faba L.), lentil (Lens culinaris Medic.), chickpea(Cicer arietinum L.), white lupin (Lupinus albus L.), soya bean(Glycine max [L.] Merr.) and pea (Pisum sativum L.) The onsetof desiccation-tolerance, i.e. the ability of seeds to germinatefollowing harvest and rapid artificial drying, coincided withphysiological maturity, except in pea where it occurred a littleearlier at about 70 per cent moisture content. Maximum seedquality as determined by maximum viability, minimum seedlingabnormalities and maximum seedling size occurred in pea, chickpeaand lupin when seeds were harvested for rapid drying at physiologicalmaturity; but for maximum seed quality in the other speciesmaturation drying had to proceed further - to about 45 per centmoisture content in soya bean and to about 30 per cent moisturecontent in lentil and faba bean seed crops. Much of this variationamongst the six species, however, was due to differences inthe variation in maturity within each seed crop. Results forindividual pods showed that peak maturity, i.e. maximum seedquality following harvest and rapid artificial drying, was achievedin all six species once maturation drying had reduced the moisturecontent of the seeds to 45–50 per cent. In pea, faba beanand soya bean there was a substantial decline in viability andan increase in seedling abnormalities when harvest was delayedbeyond the optimal moisture content for harvest.     

Translocation of Photoassimilates Between Sister Ramets in Two Rhizomatous Forest Herbs

Autoradiography and liquid scintillation techniques were usedto trace the pattern of photoassimilate translocation in twoperennial forest herbs, Aster acuminatus Michx. and Clintoniaborealis (Ait.) Raf. Vegetative shoots of C. borealis emergeearly each spring from the growing apices of a long-lived rhizomesystem. Vegetative shoots of A. acuminatus emerge in late springfrom rhizomes that decay within 2 years. In both species rametssurvive for only one growing season. Any connected plants aresisters. Mature leaves of these two species were exposed for1 h periods to ¹⁴CO₂ during spring and summer. Radioactivitycould subsequently be detected in exposed leaves (16–84per cent, depending on the season), adjacent above ground plantparts (0.7–23 per cent), roots and rhizomes (4.9–84per cent) and, when present, flowers (4–8.5 per cent).Old rhizomes of C. borealis are prominent storage sites forphotosynthate. In A. acuminatus, no significant translocationbetween sister ramets (i.e. above ground shoots connected bya common rhizome) was observed. In C. borealis, there was small,but consistent translocation between sister ramets (0.2–4per cent). Disturbance of unexposed sister ramets by defoliation,shading or herbivory increased the flow of photoassimilatesto disturbed parts in C. borealis, but not in A. acuminatus.Based on the absence of translocation flow, ramets of A. acuminatusmay be regarded as physiologically independent. Connected rametsof C. borealis show physiological integration. These resultsare correlated with ecological differences between the two species. Aster acuminatus, Clintonia borealis, translocation, ramet, vegetative reproduction, forest herb     

Growth of grana from "primary" thylakoids in Phaseolus vulgaris

The plastids of young dark-grown bean leaves, exposed to periodiclight are agranal, devoid of chlorophyll b and contain primarythylakoids and chlorophyll a. Transfer of these plants to continuousillumination results in synthesis of new chlorophyll a, chlorophyllb and grana. This study was done in order to study whether andhow the grana are formed from preexisting primary thylakoids.¹⁴C--aminolevulinic acid was used to label the chlorophyll aof the primary thylakoids, and its fate was studied after transferof the plants to continuous light. It was found that chlorophyll b and grana become ¹⁴C-labelled.The total radioactivity of chlorophyll b per bean increasedwith the parallel decrease of that of chlorophyll a. All subchloroplastfractions, obtained after digitonin disruption of chloroplasts,contained chlorophyll a of equal specific radioactivity. Thespecific radioactivity of chlorophyll b was lower than thatof chlorophyll a, and, in addition, it was lower in the granathan in the stroma lamellae fraction. The data suggest that chlorophyll b is formed from chlorophylla; the grana are formed by stacking of preexisting primary thylakoids;chlorophyll b is synthesized faster in the grana than the stromalamellae; the newly formed chlorophyll a molecules are distributedat random throughout the developing photosynthetic membraneand not on specific growing sites. (Received April 24, 1976; )     

Dynamics of Carbon Photosynthetically Assimilated in Nodulated Soya Bean Plants under Steady-state Conditions 1. Development and Application of 13CO2 Assimilation System at a Constant 13C Abundance

A long-term, steady-state ¹³CO₂ assimilation system at a constantCO₂ concentration with a constant ¹³C abundance was designedand applied to quantitative investigations on the allocationof photoassimilated carbon in nodulated soya bean (Glycine maxL.) plants. The CO₂ concentration in the assimilation chamberand its ¹³C abundance were maintained constant with relativevariances of less than ±0.5 per cent during an 8-h assimilationperiod. At the termination of 8-h ¹³CO₂ assimilation by plantsat early flowering stage, the currently assimilated carbon relativeto total tissue carbon (measured by the degree of isotopic saturation)were for young leaves (including flower buds), 13.9 per cent;mature leaves, 15.7 per cent; stems+petioles, 5.9 per cent;roots, 5.4 per cent and nodules, 6.9 per cent, 48 h after theend of the ¹³CO₂ assimilation period, they were 12.3, 7.5, 7.4,6.8 and 6.1 per cent, respectively. The treatment with a highconcentration of nitrate in the nutrient media significantlydecreased the allocation of ¹³C into nodules. Experiments on¹³CO₂ assimilation by plants at the pod-filling stage were alsoconducted. Labelling by ¹³C was weaker than at the early floweringstage, but an intense accumulation of ¹³C into reproductiveorgans was observed. Glycine max L., nodulated soya bean plants, ¹³CO₂ assimilation, carbon dynamics     

Changes in chloroplast DNA during development in tobacco, Medicago truncatula, pea, and maize

We examined the DNA from chloroplasts obtained from young and fully expanded leaves of tobacco (Nicotiana tabacum L.), Medicago truncatula, pea (Pisum sativum L.), and maize (Zea mays L.). The changes in plastid DNA content and structure were monitored by four independent methods: 4′,6-diamidino-2-phenylindole (DAPI) staining with intact chloroplasts, in situ DAPI staining of cytological sections, ethidium bromide staining at the single-molecule level after exhaustive deproteinization of lysed chloroplasts, and pulsed-field gel electrophoresis. During leaf development, we found a decline of chloroplast DNA (cpDNA) in all four plants. For tobacco, for which plants can readily be regenerated from somatic cells, cpDNA persisted longer than in the other three plants. We also found a striking progression from complex multigenomic DNA molecules to simple subgenomic molecules during plastid development. Although the decrease in molecular size and complexity paralleled the decrease in DNA content per plastid, 6% of the chloroplasts in a fully expanded tobacco leaf still contained DNA in complex branched structure, whereas no such complex structures were found in mature leaves for the hard-to-regenerate maize.     

Comparisons of the Respiratory Effluxes of Nodules and Roots in Six Temperate Legumes

The specific respiration rates of nodulated root systems, ofnodules and of roots were determined during active nitrogenfixation in soya bean, navy bean, pea, lucerne, red clover andwhite clover, by measurements on whole plants before and afterthe removal of nodule populations. Similar measurements weremade on comparable populations of the six legumes, lacking nodulesbut receiving abundant nitrate-nitrogen, to determine the specificrespiration of their roots. All plants were grown in a controlled-environmentclimate which fostered rapid growth. The specific respiration rates of nodulated root systems ofthe three grain and three forage legumes during a 7–14-dayperiod of vegetative growth varied between 10 and 17 mg CO₂g^–1 (dry weight) h^–1. This mean value consistedof two components: a specific root respiration rate of 6–9mg CO₂ g^–1 h^–1 and a specific nodule respirationrate of 22–46 mg CO₂ g^–1 h^–1. Nodule respirationaccounted for 42–70 per cent of nodulated root respiration;nodule weight accounted for 12–40 per cent of nodulatedroot weight. The specific respiration rates of roots lackingnodules and utilizing nitrate nitrogen were generally 20–30per cent greater than the equivalent rates of roots from nodulatedplants. The measured respiratory effluxes are discussed in thecontext of nitrogen nitrogen fixation, nitrate assimilation. Glycine max, Phaseolus vulgaris, Pisum sativum, Medicago sativa, Trifolium pratense, Trifolium repens, soya bean, navy bean, pea, lucerne, red clover, white clover, nodule respiration, root respiration, fixation, nitrate assimilation     

Cocaine and Cinnamoylcocaine Content of Erythroxylum Species

The dried leaves of 31 species and two varieties of the genusErythroxylum were quantitatively analysed for cocaine and bothcis- and trans-cinnamoylocaine, using a stable-isotope dilutionmethod and gas chromatography-mass spectrometry selected-ionmonitoring. Both cocaine and cinnamoylcocaine were detectedin all four varieties of cultivated coca (E. coca var. coca,E. coca var. ipadu, E. novogranatense var. novogranatense andE. novogranatense var.truxillense). Cinnamoylcocaines (cis andtrans) were found in much higher concentrations in both varietiesof E. novogranatense than in either variety of E. coca. Amazoniancoca (E. coca var. ipadu) contained consistently lower cocainelevels than the montane variety (E. coca var. coca). Twenty-ninewild species of Erythroxylum, selected to represent morphological,ecological and taxonomic diversity, were analysed for the samealkaloids; cocaine was detected in 13 neotropical species, representingfive sections of the genus. No cocaine was detected in the OldWorld species. Two wild species from Venezuela, E. recurrensand E. steyermarkii, contained cocaine levels comparable tothose found in the commercially cultivated species. Erythroxylaceae, Erythroxylum, coca, cocaine, cinnamoylcocaine, alkaloids, chemotaxonomy     

PHOTOOXIDATION REACTIONS BY CHLOROPLASTS SOLUBILIZED WITH SURFACE-ACTIVE AGENTS

1. Solubilization of chioroplasts with a mixture of 1 per centDuponol C and 1 per cent Span 80 (3: 1) caused a destructionof activity in the HILL reaction, but the treatment broughtabout an increase by about 60 per cent in the rate of ascorbatephotooxidation in the presence of DPIP. Heating the broken chloroplastscaused a marked decrease in the photooxidation activity. Byadding surface- active agents to the boiled preparation, theactivity was restored up to almost 80 per cent of the originallevel.
2. With colloidal suspensions of isolated chiorophylls,ascorbatewas only slightly photooxidized in the presence ofDPIP. Byaddi tion of the surface-active agents, the activitywas greatlyenhanced.
3. Dependency of the photooxidation bywhole and solubilized chloroplastsand isolated chlorophylla on the presence of DPIP was examined.DPIP can serve as anintermediate electron carrier in solubilizedchloroplasts aswell as in whole chloroplasts.
4. Effect of o-phenanthrolineon ascorbate photooxidation by thesethree preparations wastested. With solubilized chloroplastsand isolated chlorophylls,the addition of the inhibitor hadno influence on their ascorbatephotooxidation either in thepresence or absence of DPIP.
5. Treatmentof whole chloroplasts with the surface-active agentsinducedan activity of photooxidation of cytochrome c. The electron-flowpattern for the photooxidation of ascorbate by whole and solubilizedchloroplasts was briefly discussed.

¹ Contribution No. 130 from the Department of Biology, Facultyof Science, Kyushu University. Aided in part by Grant-in-Aidfor Fundamental Scientific Research from the Ministry of Education. (Received August 23, 1962; )     

Silica and Ash in Tissues of Some Plants Growing in the Coastal Area of Mississippi, USA

Ash and silica contents and their depositional patterns in differenttissues of 27 plants growing in the Ocean Springs area of Mississippi(many grow elsewhere), were determined. Silica content of driedplant parts varied from no more than 0 per cent in Borrichiafrutescens (L.) D.C. stems to 18.76 per cent in Arundinariagigantea (Walt.) Muhl. leaves. Ash content varied from 0·73per cent in Cliftonia monophylla (Lam.) Britt. ex Sarg. stemsto 44·02 per cent in Batis maritima L. leaves. Plantssuch as Batis maritima L., Borrichia frutescens (L.) D.C., Salicorniabigelovii Torr. and Salicornia virginica L. which grew in salinemarshes had high ash contents due NaCl in their tissues. Morusrubra L. leaves had a high silica content for a dicotyledonousplant (3·12 per cent). Energy-dispersive X-ray analysisshows that the distribution of the element silicon is clearlyrelated to certain epidermal structures such as ridges, cellwalls, rows of irregular shaped structures lengthwise of theleaf, dumb-bell shaped ones and especially in trichomes. Therewas a high concentration of silica containing trichomes alongthe veins on the underside of Morus rubra L. leaves and thiswould protect them from insects. The outer parts of the inflorescencesof Ctenium aromaticum (Walt.) Wood, Elymus virginicus L., Juncuspolycephalus Michx. and phragmites communis Trin. were highlysilicified. This should give the seed some protection from insects.The sharp particles would be irritating to oesophageal tissuesand might be implicated in such a cancer.     

Cytosolic Ascorbate Peroxidase in Seedlings and Leaves of Maize (Zea mays)

Ascorbate peroxidase (APX) was purified to homogeneity frommaize (Zea mays L. cv.) coleoptiles. APX was a monomer witha molecular mass of 28 kDa, as determined by gel nitration andSDS-polyacrylamide gel electrophoresis. It contained one protohememoiety per molecule, with the oxidized form giving a Soret peakat 403 nm with small peaks at 502 and 638 nm, and the reducedform giving peaks at 435 and 556 nm. The enzyme was not inactivatedby depletion of ascorbate. Cell fractionation and immunohistochemicalstudies using polyclonal antibodies raised against maize APXrevealed that the enzyme was not located in the chloroplastsof green leaves. It was abundant in the cytoplasm but not inthe vacuoles of cells in the coleoptile, mesocotyl and youngleaves of seedlings. In mature green leaves, small amounts ofthe enzyme were distributed in vascular systems, in particularin the companion cells. The N-terminal amino acid sequence ofmaize APX exhibited high homology to pea cytosolic APX, spinachAPX and Arabidopsis APX, but not to APX from tea chloroplasts. (Received February 15, 1993; Accepted May 6, 1993)     

Patterns of 14C-labelled Assimilate Partitioning in Red and White Clover During Vegetative Growth

A quantitative analysis of the ¹⁴C-labelled assimilate suppliedby the expanded leaves on the primary shoot to growing leaves,stem, lateral shoots (branches or stolons) and roots in redand white clover was conducted during vegetative growth. Stem growth of the primary shoot was inhibited in both cloversand utilized no energy resources. The growing leaves at theprimary shoot apex of white clover imported 4 per cent of theshoot's assimilate compared with 10 per cent in red clover.At the basal end of the primary shoot, the tap root of whiteclover imported 16 per cent of the shoot's assimilate comparedwith 22 per cent in red clover. Branches in red clover and stolonsin white clover were by far the largest sinks for primary shootassimilate, importing 39 per cent and 63 per cent of the labelledassimilate, respectively. Analyses of the translocation of assimilate from individualprimary shoot leaves demonstrated that in both clovers olderleaves exported more of their assimilate to branches or stolons,whereas younger leaves exported more of their assimilate toroots, and possibly in white clover, to growing leaves at thetip of the shoot. Of the labelled assimilate exported to branchesor stolons, each primary shoot leaf exported preferentiallyto the branch or stolon in its own axil, but in addition exportedsubstantial quantities of assimilate to all other axillary shoots,particularly those arising from basal axils where the subtendingleaf had died. Trifolium repens, Trifolium pratense, red clover, white clover, assimilate partitioning, perennation     

Mineral Depletion and Leaf Senescence in Soya Bean as Influenced by Foliar Nutrient Application During Seed Filling

Senescence, as judged by the time courses of leaf lamina photosynthesis,soluble protein and chlorophyll contents, was studied in relationto mineral redistribution in field-grown soya beans [Glycinemax (L.) Merr] to investigate the hypothesis that the depletionof nutrients m the leaves by the developing seeds is the causeof soya bean senescence. A mineral nutrient solution was appliedto the canopy during the seed-filling period, and the effectson senescence and mineral depletion of the leaves were determinedin three cultivars, at two leaf positions, weekly from beginningof seed filling through physiological maturity. The onset of senescence occurred shortly after the beginningof rapid seed filling Photosynthetic rate declined about 60per cent within 3 weeks. Protein dropped by 52 per cent andchlorophyll by 48 per cent over the same period. Foliar nutrient application, at a rate previously shown to givesignificant yield increases in soya beans, increased the concentrationsof N, P and K in the leaf laminae, but tended only to delaytheir decline and failed to either delay the onset or alterthe course of senescence. The results of this experiment seem to indicate that, undernormal growth conditions, the events of senescence in the soyabean are not causally related to the N, P or K concentrationsof the leaf laminae Glycme max (L.) Merr., soya bean, nitrogen, phosphorus, potassium, leaf protein, chlorophyll, photosynthesis, foliar nutrient application, mineral depletion, leaf senescence     

Microclimate, Photosynthesis and Growth of Lucerne (Medicago sativa L.). II. Canopy Structure and Growth

The growth of lucerne var. Europe was examined in the fieldduring 1976. The annual dry matter production of unirrigatedlucerne during 1976, with no nitrogen fertilizer application,was 82.5 per cent greater than unirrigated S.24 perennial ryegrass,with a nitrogen application of 384 kg ha^–1. The mean aboveground growth rate of lucerne was 7.3 g DM m^–2 day^–1between March and early June, of which stem material contributeda maximum of 76.5 per cent. Significant losses of leaves andstems occurred from the end of April, indicating a loss of potentialforage material. Nitrogen analyses of the above ground crop suggested that in56 days lucerne yielded 10.7 per cent more nitrogen than didS.24 annually with a nitrogen fertilizer addition of 280 kgha^–1. Between 13 and 57 per cent of the daily photosynthate is translocatedbelow ground. Medicago sativaL, lucerne, dry matter production, canopy structure, nitrogen analyses     

Compartmentation of Aldolase Isoforms in Maize Leaves

The leaves of maize seedlings contain two principal isozymesof fructose 1,6-bisphosphate aldolase (E.C. 4.1.2.13 [EC] ), one chloroplasticand one cytosolic (Gasperini and Pupillo, 1982). Mesophyll protoplastswere separated from bundle sheath (BS) strands of both light-grownand dark-grown maize leaves. Aldolase isozymes were separatedfrom extracts of chloroplasts, etioplasts, protoplasts and BSstrands by column isoelectric focusing. The major isozyme ofgreen leaves (pI 4.2) was exclusively in BS chloroplasts, andthere was no evidence of other isozymes occurring in BS tissue.The cytosolic isozyme (pI 6.7) was present in protoplasts ofmesophyll cells, where it may limit the synthesis of hexose-phosphates(estimated activity of 9.4 µmol h^–1 g^–1 fr.wt.) together with lower activities of an acidic form (pI 4.6).Etiolated leaves contained significant amounts of the pI 6.7isozyme in both mesophyll and BS cells, but also minor activitiesof one or more acidic forms with pI values of 4.4–4.7(average pI 4.6) which appear to be located partly in BS etioplasts.The main developmental events for maize leaf aldolase afterillumination were a moderate decrease of cytosolic isozyme (pI6.7) which disappears from the BS within hours and a large,gradual increase of the BS plastid isozyme (pI 4.2). The isoformwith a pI 4.6 also increased rapidly to a low, steady activityin greening mesophyll protoplasts. Key words: C₄, fructose 1,6-bisphosphate, aldolase, Zea mays