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.     

Anti-herbivore structures of Paulownia tomentosa: morphology, distribution, chemical constituents and changes during shoot and leaf development

Background and Aims: Recent studies have shown that small structures on plant surfacesserve ecological functions such as resistance against herbivores.The morphology, distribution, chemical composition and changesduring shoot and leaf development of such small structures wereexamined on Paulownia tomentosa. Methods: The morphology and distribution of the structures were studiedunder light microscopy, and their chemical composition was analysedusing thin-layer chromatography and high-performance liquidchromatography. To further investigate the function of thesestructures, several simple field experiments and observationswere also conducted. Key Results: Three types of small structures on P. tomentosa were investigated:bowl-shaped organs, glandular hairs and dendritic trichomes.The bowl-shaped organs were densely aggregated on the leavesnear flower buds and were determined to be extrafloral nectarines(EFNs) that secrete sugar and attract ants. Nectar productionof these organs was increased by artificial damage to the leaves,suggesting an anti-herbivore function through symbiosis withants. Glandular hairs were found on the surfaces of young and/orreproductive organs. Glandular hairs on leaves, stems and flowerssecreted mucilage containing glycerides and trapped small insects.Secretions from glandular hairs on flowers and immature fruitscontained flavonoids, which may provide protection against someherbivores. Yellow dendritic trichomes on the adaxial side ofleaves also contained flavonoids identical to those secretedby the glandular hairs on fruits and flowers. Three specialtypes of leaves, which differed from the standard leaves inshape, size and identity of small structures, developed nearyoung shoot tips or young flower buds. The density of smallstructures on these leaf types was higher than on standard leaves,suggesting that these leaf types may be specialized to protectyoung leaves or reproductive organs. Changes in the small structuresduring leaf development suggested that leaves of P. tomentosaare primarily protected by glandular hairs and dendritic trichomesat young stages and by the EFNs at mature stages. Conclusions: The results indicate that P. tomentosa protects young and/orreproductive organs from herbivores through the distributionand allocation of small structures, the nature of which dependson the developmental stage of leaves and shoots.     

Silica Deposition in Some C3 and C4 Species of Grasses, Sedges and Composites in the USA

We report new information on silica deposition in 15 plant species,including nine grasses, two sedges and four composites. Thesilica depositional patterns found in seven of the grass speciesindicate that they are C₄ plants. However the festucoid grassCortaderia selloana is a C₃ plant with long leaf trichomes andoval silica structures in the leaves. In contrast the panicoidC₄ grasses Chasmathium latifolium, Chasmathium sessiflorum,Imperata cylindrica, Panicum repens, Panicum commutatum andSetaria magna, all produce dumb-bell-shaped silica structuresin the leaves. The chloridoid grasses Spartina patens and Spartinacynosuroides have saddle-shaped structures and no dumb-bellor oval shaped ones. The sedges Rhynchospora plumosa and Scirpuscyperinus were found to have oval phytoliths and may be C₃ plants.Our examination of these and other grasses strongly suggeststhat C₄ grasses tend to produce the same type of silica cells.Grasses and sedges with C₃ type photosynthesis tend to produceoval silica structures. The composite Grindelia squarrosa andsunflowers Helianthus angustifolia, Helianthus atrorubens andHelianthus tuberosus absorb relatively small amounts of siliconand larger amounts of calcium, where both elements deposit inleaf trichomes. We found no clear indicator for the C₃ sunflowersor C₄ types in the Asteraceae. Helianthus tuberosus leaves havemany trichomes on the adaxial surface. These trichomes havea higher concentration of silica than the surrounding leaf surface.Helianthus tuberosus leaves had much higher ash and silica contentsthan those of Helianthus angustifolia and Helianthus atrorubens.The composite Grindelia squarrosa has a usual deposition ofsilica in the basal cells around the guard cells. Silica depositionoften reflects the surface features of a leaf. An exceptionis Scripus cyperinus where the silica structures are deep inthe tissue and do not reflect the surface configurations. Theinforescence of Setaria magna had a 14.64 silica content. Thetufts of white, silky hairs characteristic of Imperata cylindricainflorescence have no silica. C₃ and C₄ plants, silica and ash content, scanning electron microscopy, energy-dispersive X-ray analysis, silicon distribution, spectra of elements in plants, trichomes, silica fibres, phytoliths     

Silica and Ash in Tissues of Some Coastal Plants

Ash and silica contents and their depositional patterns in differenttissues of 44 Mississippi coastal plants were determined. Silicacontent of dried plants varied from no more than a trace inChenopodium album L. leaves to 7.37 per cent in Zizanopsis miliacea(Michx) Doell & Aschers leaves. Ash content varied from2.50 per cent in Lythrum lineare L. stems to 28.24 per centin Borrichia frutescens (L.) DC leaves. Plants in the same familytend to be alike in their ability to absorb or not absorb silica.Poaceae and Cyperaceae had consistently high concentrationsof silica. In contrast, the Asteraceae studied had very lowsilica contents but often had high contents of other minerals.Dicotyledonous plants studied had consistently lower silicacontents than the monocotyledons. Plants growing in salt watercontained considerable sodium chloride. Spectra were obtainedfor major elements in four different plants. Energy-dispersiveX-ray analysis shows that distribution of the element siliconis clearly related to certain epidermal structures such as guardcells, ridges, dumb-bells and balls that appear in electronmicrographs. Silica was deposited differently in each type ofplant studied. In many of the plants silica was deposited inrows of irregular-shaped particles running lengthwise of theleaf and in guard cells. In others, like Zizanopsis miliacea(Michx) Doell & Aschers, the deposit was sheet-like. Zizaniaaquatica L. not only had a sheet-like deposit, but the depositwas ridged and there were rows of dumb-bell-shaped silica cells.Related plants had similar structures. Euchlaena mexicana Schrad.,Tripsacum dactyloides (L.) L and Manisuris rugosa (Nutt.) Kuntzeall had irregular phytoliths similar to those in Zea mays L. coastal plants, marsh plants, ash content, silica deposition, scanning electron microscopy, energy-dispersive X-ray analysis, silicon distribution, X-ray diffraction patterns, spectra of elements in plants     

Effects of Tissue-type and Development on Dark Respiration in Two Herbaceous Perennials

Perennial plants go through a number of developmental stagesduring the growing season. Changes in metabolism during thesephases have been documented in laboratory-grown plants but neverin native plants growing in natural habitats. The purpose ofthis study was to describe the seasonal pattern of dark respirationin the above-ground tissues of two herbaceous perennials, Bistortabistortoides(Pursh) Small and Campanula rotundifolia L., growingin the Rocky Mountains (USA). The effect of biomass accumulationon respiration rate and differences in respiration rate amongtissues were measured. Respiration rate differed significantlyamong the above-ground tissues. Reproductive structures hadthe highest respiration rates, followed by leaves, then stems.Respiration rate decreased by 10–90% over the growingseason in these tissues but was generally not correlated witha decrease in biomass accumulation. The seasonal pattern ofrespiration rate varied significantly among tissues. Total tissuerespiratory flux was calculated at 15 °C for each tissue.In both species, total above-ground respiratory flux was eitherrelatively constant during the growing season with a markeddecrease at seed dispersal or a maximum rate was reached atmid-season. In B. bistortoides, leaves had the highest totalrespiratory fluxes, and the respiratory fluxes of the stem andreproductive structures were similar to one another. In C. rotundifolia,leaf and stem respiratory fluxes were similar, while the respiratoryflux of the reproductive structures was considerably lower thanthat of leaves and stems. This study emphasizes the importanceof developmental processes and tissue-type on respiration rateand highlights the importance of including all plant tissuesin predictive models of plant carbon balance.Copyright 2001Annals of Botany Company Respiration, development, growth, maintenance, tissue, Bistorta bistortoides, Campanula rotundifolia, harebell     

Genetic Control of Leaf Morphology: A Partial View

The partial-shoot theory of the leaf was a controversial hypothesisrevived by Arber and supported by her morphological and anatomicalstudies. This theory highlighted the parallels between leavesand shoots and contrasted with an alternative view that leaves,with their limited growth potential, are completely distinctfrom shoots. Pea morphological mutants with altered growth potentialin their compound leaves are described. The unifoliata mutanthas a limited growth potential relative to wild-type;cochleata,afila and insecatus have extended potentials. Characterizationof theunifoliata mutation and gene expression patterns indicatethat unifoliata is a common factor in pea compound leaf andfloral shoot development, and so provides rudimentary supportfor the idea that some leaves have shoot-like characteristics.Tomato leaves are also considered to lend tentative support.The afila and insecatus leaf forms are described as bipinnateand weakly bipinnate, respectively. These and the tendril-lessmutant are potential phenocopies of legume relatives, an ideabased on Vavilov's law of homologous series of variation. Arberillustrated, but did not articulate in genetical terms, thatmorphological variation in structures within an individual plantcan be interpreted as reiteration of design. Analogous withVavilov's view, this can be considered a consequence of thesame genetic programme in a different location.Copyright 2001Annals of Botany Company Agnes Arber, compound leaf, genetics, knotted1, legume, morphology, mutant, partial-shoot, pea, Pisum sativum, unifoliata, Vavilov     

Response to Temperature in a Stand of Pearl Millet: 10. PARTITION OF ASSIMILATE

Effects of temperature on partition of assimilate between leaves,stems and panicles of pearl millet are analysed in terms ofa duration (t_w) over which a structure increased in weight,and a partition factor (p)—the fraction of new dry matterallocated to the structure during t_w. The value of tw was, forall structures, inversely proportional to temperature abovea base of 10 °C and below an optimum of 28 to 30 °C.For stems and panicles, the value of p was, with one exception,little affected by temperature. The dry weight of these structureswas, therefore, proportional to t_w, and decreased with risein temperature. (The exception was panicles at the lowest temperature,19 °C, for which p was reduced by 40% because few grainswere set.) For leaves, however, p increased with rise in temperature,counteracting the effect on t_w, such that dry weight changedlittle with temperature. The optimum temperature for reproductiveyield was 22 °C, but the proportion of the total dry matterallocated to reproductive structures changed little between22 °C and 31 °C. Key words: Pearl millet, temperature, thermal time, partitioning     

Leaf Characteristics and Net Gas Exchange of Diploid and Autotetraploid Citrus

The effect of tetraploidy on leaf characteristics and net gasexchange was studied in diploid (2x ) and autotetraploid (4x) ‘Valencia’ sweet orange (Citrus sinensis (L.)Osb.) and ‘Femminello’ lemon (Citrus limon (L.)Burm. f.) leaves. Comparisons between ploidy levels were madeunder high irradiance (I) in a growth chamber or low total Iin a glasshouse. Tetraploids of both species had thicker leaves,larger mesophyll cell volume and lower light transmittance thandiploids regardless of growth I. Mesophyll surface area perunit leaf area of 2x leaves was 5–15% greater than on4x leaves. Leaf thickness and mesophyll cell volume were greaterin high I leaves than low I leaves. In high I, average leafarea was similar for 2x and 4x leaves, whereas in low I it was30% greater in 4x than in 2x leaves. Nitrogen and chlorophyllconcentration per cell increased with ploidy level in both growthconditions. The ratio of chlorophyll a:b was 25% greater in2x than in 4x leaves. When net CO₂assimilation rate (A_CO2) wasbased on leaf area, 4x orange leaves had 24–35% lowerA_CO2than their diploids. There were no significant differencesin A_CO2between 2x and 4x orange or lemon leaves when expressedon a per cell basis. Overall, lower A_CO2per unit leaf area oftetraploids was related to increase in leaf thickness, largermesophyll cell volume, the decrease in mesophyll area exposedto internal air spaces, and the lower ratio between cell surfaceto cell volume. Such changes probably increased the resistanceto CO₂diffusion to the site of carboyxlation in the chloroplasts. Cell volume; chlorophyll; irradiance; leaf thickness; nitrogen; photosynthesis; ploidy; Citrus limon ; C. sinensis ; ‘Valencia’ sweet orange; ‘Femminello’ lemon     

Ultrastructure and Development of the Laticifers of Ficus carica L

Laticifers of Ficus caricaL. are of the branched, non-articulatedtype. They occur in the cortex and pith of the plant axis andpenetrate leaves and inflorescences. Observations were madeon laticifers located in shoot apices. Growing regions of laticifers undergo a sequence of ultrastructuralchanges. These are: (a) a pronounced increase in the vacuolarspace which divides the cytoplasm into separated masses; (b)a development of numerous vesicular structures in the cytoplasm.The vesicular structures are released into the vacuolar space.The whole process is accompanied by disintegration of cytoplasm.Apparently isolated masses of cytoplasm occur in the luminaof laticifer tips in sections taken from dormant apices. Itis assumed that these masses have a role in the initiation ofnew laticifer regions in the next growing season. Ficus caricaL., laticifers, ultrastructure, development differentiation     

A New Histochemical Method for Localization of the Site of Monoterpene Phenol Accumulation in Plant Secretory Structures

A new method is reported for the histochemical localizationof monoterpene phenols in essential oil secretory structures.The method was adapted from a spot test originally devised forin vitro detection of phenolic compounds in organic analyses.Plant subjects were the Lamiaceae species Thymus vulgaris L.,Oreganum vulgare L. and Mentha x piperita L., which accumulateessential oil in glandular trichomes. A reagent consisting of4-nitrosophenol in conc. H₂SO₄was applied to sample leaves ofeach species. A positive test for phenol was indicated by theproduction of coloured indophenols. Using this method, monoterpenephenols were identified in the trichomes of T. vulgaris(thymol)and O. vulgare(carvacrol), indicated by colour changes to redand green respectively. No phenol was detected in trichomesof M. x piperita. Results were confirmed by GC-MS analysis ofleaf volatile extracts from each species, and in vitro testswith thymol and carvacrol. The method could be used in fieldsurveys for rapid identification of potential medicinal plantsand bioactive compounds. Copyright 2001 Annals of Botany Company Histochemistry, secretory structures, glandular trichomes, Lamiaceae, Thymus vulgaris, Oreganum vulgare, Mentha x piperita, essential oil, aromatic monoterpenes     

Simultaneous CO2- and 16O2/18O2-gas exchange and fluorescence measurements indicate differences in light energy dissipation between the wild type and the phytochrome-deficient aurea mutant of tomato during water stress

The CO₂-, H₂O- and ¹⁶O₂/¹⁸O₂ isotopic-gas exchange and the fluorescencequenching by attached leaves of the wild-type and of the phytochrome-deficienttomato aurea mutant was compared in relation to water stressand the photon fluence rate. The chlorophyll content of aurealeaves was reduced and the ultra-structure of the chloroplastswas altered. Nevertheless, the maximum rate of net CO₂ uptakein air by the yellow-green leaves of the aurea mutant was similarto that by the dark-green wild-type leaves. However, less O₂was produced by the leaves of the aurea mutant than by leavesof the wild-type. This result indicates a reduced rate of photosyntheticelectron flux in aurea mutant leaves. No difference in bothphotochemical and non-photochemical fluorescence quenching wasfound between wild-type and aurea mutant leaves. Water stresswas correlated with a reversible decrease in the rates of bothnet CO₂ uptake and transpiration by wild-type and aurea mutantleaves. The rate of gross ¹⁶O₂ evolution by both wild-type andaurea mutant leaves was fairly unaffected by water stress. Thisresult shows that in both wild-type and aurea leaves, the photochemicalprocesses are highly resistant to water stress. The rate ofgross ¹⁸O₂ uptake by wild-type leaves increased during waterstress when the photon fluence rate was high. Under the sameconditions, the rate of gross ¹⁸O₂ uptake by ^aurea mutant leavesremained unchanged. The physiological significane of this differencewith respect to the (presumed) importance of oxygen reductionin photoprotection is discussed. Key words: Water stress, gas exchange, fluorescence quenching, Lycopersicon esculentum, mutant (tomato, aurea), energy dissipation     

Nitrate Supply and the Biophysics of Leaf Growth in Salix viminalis

The influence of nitrogen on leaf area development and the biophysicsof leaf growth was studied using clonal plants of the shrubwillow, Salix viminalis grown with either optimal (High N) orsub-optimal (Low N) supplies of nitrate. Leaf growth rate andfinal leaf size were reduced in the sub-optimal treatment andthe data suggest that in young rapidly growing leaves, thiswas primarily due to changes in cell wall properties, sincecell wall extensibility (% plasticity) was reduced in the LowN plants. The biophysical regulation of leaf cell expansion also differedwith nitrogen treatment as leaves aged. In the High N leaves,leaf cell turgor pressure (P) increased with age whilst in theLow N leaves P declined with age, again suggesting that foryoung leaves, cell wall plasticity limited expansion in theLow N plants. Measurements of cell wall properties showed thatcell wall elasticity (%E) was not influenced by nitrogen treatmentand remained constant regardless of leaf age. Key words: Salix, cell wall extensibility, nitrogen nutrition, biophysics of leaf growth     

A Comparison of Tomato Fruit Chloroplast and Chromoplast DNAs as Analyzed with Restriction Endonucleases

Chromoplast DNA was isolated from ripe-red tomato fruits, andits structure compared with that of chloroplast DNAs from maturegreen fruits and leaves. There was a good correspondence betweenthe structures analyzed by BamHI or EcoRI digestion and by hybridizationwith a probe for the gene of the ribulose 1,5-bisphosphate carboxylase/oxygenaselarge subunit. ¹ Present address: Koryo International College, Nisshin, Aichi470-01, Japan. (Received November 5, 1984; Accepted February 6, 1985)     

Effect of Removal of Flower Buds, Open Flowers, Young Pods and Shoot Apex on Growth and Pod Set in Soybean

The complete removal of the reproductive structures once andshoot apices of soybeans (Glycine max L. Merrill) during earlyanthesis but before the rapid seed development stage significantlyincreased flowering and pod set in greenhouse and field grownplants. The treated plants had darker green leaves, shorterstems and petioles and retained their chlorophyll content longerthan control plants. Pod maturation was also delayed. Althoughdecapitation and the removal of reproductive structures increasedthe number of 3- or more-seeded pods in all varieties tested,seed weight per plant was not consistently increased. The possibleinvolvement of endogenous hormones in pod set and multi-loculepod production in soybeans is discussed. Key words: Glycine max (L.) Merr, Reproductive structures, Shoot apex, Growth, Flowering, Pod set, Multi-locule pods     

Biomechanical Attributes of the Leaves of Pine Species

The flexural stiffness EI, elastic modulus E, second momentof area I, length L, and weight Wt of foliage leaves from 26species of pine were measured to determine the manner in whichEI is scaled to leaf size (L or Wt, or both) and to determineif the biomechanical attributes of foliage leaves could be juxtaposedwith the systematic affiliations of species within Pinus Biomechamcaland morphometric data were explored based on a model from engineeringtheory that predicts the relationships among EI, Wt and L providedthat the maximum tip-deflection _max of an untapered cantileveredbeam sustaining its own weight is maintained as the beam eitherincreases in length or weight, or both, I e _max = Wt L²/8EIThe data show that EI disproportionately increased as eitherWt or L, or both increased The allometry of leaves did not conformto that predicted by the model Rather, EI was proportional tothe product of Wt and L raised to an exponent slightly greaterthan one Thus, Omax was predicted not to be maintained as eitherWt or L, or both, increased, as verified by observations Therelationship between El and Wt(L) differed for species typicallyproducing two leaves per fascicle and those bearing more thantwo leaves per fascicle Also, El is geometrically constrainedby the number of leaves produced per fascicle, principally interms of the effects of the number of leaves per fascicle onI Pinus, pine, leaves, biomechanics, Young's modulus     

Modification of Leaf Formation by Cytokinin and Chlormequat (CCC) in Vitis

Application of the cytokinin, 6-(benzylamino)-9-(2-tetrahydropyrany1)-9H-purine(PBA, 1mM) and 2-chloroethyl trimethyl ammonium chloride (chlormequat;3 mM), a growth retardant, to grapevines induced the formationof fused leaves (two laminae and two petioles) and double leaves(two separate petioles each with a single lamina). Double leaveswere found in Vitis vinifera L. seedlings, in Vitis ripariaand in Muscadinia (Vitis) rotundifolia. In some of the treatedvines, leaves arose with opposite phyllotaxy. Other anomaliesincluded production of two opposite axillary buds in axils ofopposite leaves and production of two tendrils per node. Sometendrils grew into shoots. In Muscat of Alexandria, applicationof GA₃ (3 µM, 15 µM), followed by an applicationof chlormequat (0.4 mM, 1.2 mM), led to a marked reduction inthe extension growth of axillary shoots. Vitis vinifera L., Vitis riparia, Muscadinia (Vitis) rotundifolia, grapevines, leaf formation, cytokinin, chloromequat     

Transpiration Stream of Desert Species: Resistances and Capacitances for a C3, a C4, and a CAM Plant

Transpiration rates and water potentials of three sympatricdesert perennials, a C3 subshrub (Encelia farinosa), a C₄ bunchgrass(Hilaria rigida), and a CAM succulent (Agave deserti), wereanalysed using an electrical circuit analogue that includedresistances and capacitances for the leaves, stems, and roots.The water storage capability of the organs differed considerably,capacitance ranging over 1000-fold from the thin leaves of H,rigida to the massive leaves of A. deserti, although the capacitanceper unit volume varied only 1.9-fold. The diurnal changes inwater storage could support maximum transpiration rates of H.rigida for 4 min, E. farinosa for 7 min, and A. deserti for16 h. The time constant for equilibration of water from storageto the xylem ranged from 29 s for roots of H. rigida to 52 minfor leaves of A. deserti. Resistances for such movement wererelatively low for the succulent leaves of A. deserti and wereup to about 50-fold higher for the three organs of E. farinosa.Xylem resistances calculated using the Hagen-Poiseuille lawand measured xylem dimensions were 2.1- to 2.1-fold lower thanresistances estimated from observed water potential drops, adiscrepancy which is in agreement with other published data.Contrary to data on other plants, the xylem resistances in theroots and leaves of E. farinosa and H. rigida averaged only15% of the stem xylem resistance. Key words: Capacitance, Xylem resistance, Transpiration stream, Desert     

Acclimation of Respiratory Properties of Leaves of Spinacia oleracea L., a Sun Species, and of Alocasia macrorrhiza (L.) G. Don., a Shade Species, to Changes in Growth Irradiance

To clarify the way in which the light available for growth affectsrespiration in leaves of sun and shade plants, we examined therespiratory properties of mature leaves of Spinacia oleraceaL., a sun species, and of Alocasia macrorrhiza (L.) G. Don.,a shade species, that had been grown at various irradiances.In leaves of S. oleracea, the respiratory rates, on a dry massbasis, decreased with time during the night, and the higherwas the growth irradiance during the day, the higher was therespiratory rate. The marked decreases in the respiratory rateduring the night were accompanied by decreases in the concentrationof carbohydrates in the leaves. By contrast, the respiratoryrates of leaves of A. macrorrhiza were virtually constant throughoutthe night and the absolute rates were lower than those of S.oleracea even though the absolute value of the concentrationof carbohydrates and its decrease at night resembled to thosein S. oleracea. The maximum activities of respiratory enzymeswere also similar to those in S. oleracea. However, the leavesof A. macrorrhiza contained less soluble protein than thoseof S. oleracea. These results suggest that, in S. oleracea,the concentration of carbohydrates might determine the respiratoryrate while such is not the case in A. macrorrhiza. The lowerrespiratory rates in A. macrorrhiza might be due to a lowerdemand for ATP. (Received November 29, 1995; Accepted February 15, 1996)     

Polyphenoloxidase and the Respiration of Ivy Leaves

1. Polyphenoloxidase is present in ivy leaves but not in thoseof Aucuba or Euonymus.
2. Respiration of intact ivy leaves wasmarkedly stimulated bycatechol (R.Q. approximately=I), gallicacid, caffeic acid,and dihydroxyphenylalanine. The stimulationwas not relatedto injury as far as could be detected and wasnot followed byinhibition. The extra oxygen consumption representsa many timesrepeated oxidation of the amount of catechol supplied.
3. The effect of catechol on the respiration of Aucuba and Euonymusleaves was very small.
4. Cupferron and phenylthiourea, whichinhibit polyphenoloxidasein vitro, nevertheless increased respirationwhen administeredto leaves through the petiole. On the otherhand, when appliedby infiltration, cupferron did cause inhibition,but in Aucubaand Euonymus as much as in ivy.

     

EMF Genes Interact with Late-Flowering Genes to Regulate Arabidopsis Shoot Development

To investigate the genetic mechanisms regulating the transitionfrom vegetative to reproductive phase in Arabidopsis, doublemutants between two embryonic flower (emf) and 12 differentlate-flowering mutants were constructed and analyzed. Doublemutants in all combinations displayed the emf phenotypes withoutforming rosettes during early development; however, clear variationsbetween different double mutants were observed during late development,fwa significantly enhanced the vegetative property of both emfmutants by producing a high number of sessile leaves withoutany further reproductive growth in emf1 fwa double mutants.It also produced numerous leaf-like flower structures similarto those in leafy ap1 double mutant in emf1 fwa double mutants.Nine late-flowering mutants, ft, fca, ld, fd, fpa, fe, fy, fha,and fve, caused different degrees of increase in the numberof sessile leaves, the size of inflorescence, and the numberof flowers only in weak emf1 and emf2 mutant alleles background.Two late-flowering mutants, co and gi, however, had no effecton either emf1 and emf2 mutant alleles in double mutants. Ourresults suggest that FWA function in distinct pathways fromboth EMF genes to regulate flower competence by activating geneswhich specify floral meristem identity. CO and GI negativelyregulate both EMF genes, whereas the other nine late-floweringgenes may interact with EMF genes directly or indirectly toregulate shoot maturation in Arabidopsis. ¹ To whom correspondence should be addressed.