Ontogeny of Stomata on the Foliar and Floral Or{dot}gans of some Species of Crotalaria L.

The structure and development of stomata in eight species ofCrotalaria belonging to the family Papilionaceae are described.The study is mostly confined to the leaves but it has also beenmade on the floral organs of C. mysorensis, C. retusa, C. sericea,and C. triquetra. The stomata may be paracytic, anisocytic,anomocytic, diacytic, or with one subsidiary cell. The differenttypes occur individually or they are placed side by side evenon the same surface of an organ. In general the paracytic typeis by far the commonest, followed by anisocytic and anomocyticones. Diacytic stomata and those with one subsidiary cell arerelatively rare. Different types of stomata in various organsof the same plant develop mesogenously. The present investigationalso indicates that the inconstancy of stomata in the familyis due to (a) their diversity and (b) an increase in the numberof subsidiary cells either by their division or by the neighbouringperigenes becoming subsidiary cell-like.     

The Ultrastructure of Protophloem Sieve Elements in Leaves of Aegilops comosa var. thessalica

The differentiation and obliteration of protophloem sieve elementsin leaves of the grass Aegilops comosa var. thessalica havebeen studied by electron microscopy. These elements differentiatesimilarly to metaphloem sieve elements of the same plant andother monocotyledons. Plasmalemma, smooth endoplasmic reticulum(ER), mitochondria, P-type plastids and sometimes nuclear remnantsconstitute the protoplasmic components at maturity, all areperipherally distributed. The differentiation of end walls intosieve plates and the presence of sieve areas on the lateralwalls indicate that protophloem sieve elements are componentsof sieve-tube. They may be functional for a brief period butsoon after their maturation they are compressed and finallyobliterated by the stretching of actively-growing surroundingcells. The protoplasmic components of mature elements degenerateand are destroyed during obliteration of the sieve elements. Aegilops comosa var. thessalica, protophloem, sieve elements, differentiation, ultrastructure     

Structure and Development of Stomata on the Vegetative and Floral Organs of Some Amaryllidaceae

The structure and development of stomata in 10 Amaryllidaceousmembers are described. The study is made on the leaves and floralorgans of Amaryllis belladona, Crinum asiaticum, C. bulbispermum,C. latifolium, C. pratense, Pancratium sp., Polianthes tuberosa,and Zephyranthes atamsco, and on leaves of Agave sp. and Curculigoorchioides. In most of the organs of the different plants studiedmore than one type of stoma occur, even on the same surface.However, the stomata are largely anomocytic in Amaryllis, Crinum,Pancratium, Polianthes, and Zephyranthes, but they are tetracyticin Agave and Curculigo. An increase in the number of subsidiarycells in teracytic, tricytic, paracytic, and stomata with onesubsidiary cell has been noted. It may be due to wall formationin the subsidiary cells or by the neighbouring perigenes assumingtheir form. The range of variation in different types of stomatain each organ has been studied. Abnormal features such as juxtaposedor superimposed contiguous stomata, connections between guardcells of nearby stomata, transformation of meristemoids intoepidermal cells are observed. The development of different typesof stomata in different organs of the same plant is perigenous.The systematic position of different genera is discussed inlight of the present findings. A method of preparing epidermalimprints by the use of Depex, a mounting medium, and white ofan egg is also described.     

Influence of Acid and Salt Sprays on Furanocoumarin Concentrations on the Ruta graveolens Leaf Surface

Ruta graveotens subshrubs, known to contain a large fractionof their furanocoumarins on the leaf surface, were used forinvestigation of salt and acid rain effects on the plant surfaceand substances occurring there. Groups of shoots on each plantcovered by plastic bags were sprayed with either sulphuric acid,pII 2.5, saturated sodium chloride solution, or a distilledwater control. Uncovered shoots, an additional control, hadthe highest concentrations of furanocoumarins both on the surfaceand in the whole leaf. The upper leaves contained less furanocoumarinsin absolute amounts but were similar to the lower leaves ona percentage basis. Spraying caused a decrease in total furanocoumarinconcentrations, slight in the case of distilled water and greaterfor acid and salt, but the percentage on the surface after sprayingincreased. The upper and lower leaves reacted differently tosalt than to sulphuric acid and water: with salt, the percentagesof furanocoumarins on the surface of both kinds of leaves showedsimilar increases; with the other two sprays, upper leaves showeda similar increase, but the lower leaves had a much higher percentageon the surface owing to a high rate of extrusion. Simulated acid rain, salt sprays, plant surface, furanocoumarins, Ruta graveolens     

Leaf Heteroblasty in Pseudopanax crassifolius: Functional Significance of Leaf Morphology and Anatomy

Pseudopanax crassifolius (A. Cunn.) C. Koch. is a strongly heteroblastictree indigenous to New Zealand. Changes in the morphology andanatomy of leaves are described for seedling, juvenile, transitionaland adult phases of development. Seedlings produce five leaftypes; all are relatively small, thin, anthocyanic, have a lowspecific weight, and are anatomically comparable to the leavesof many shade plants. Juvenile leaves are long, linear, deflexed,coriaceous and sharply-toothed. They have a high specific weight,a thick, ornamented cuticle, a multiseriate hypodermis composedof collenchyma, well developed palisade and many spongy mesophylllayers. Juvenile leaves are strong relative to adult leavesand to the leaves of other species. Leaf strength is providedby fibres associated with the midrib. Adult leaves are shorter,broader and less massive than juvenile leaves, and are orientedhorizontally. Transitional leaves are morphologically intermediatebetween juvenile and adult leaves. The anatomy of juvenile,transitional and adult leaves is similar. The heteroblasticseries may be associated with changes in leaf construction costs,light interception and heat dissipation.Copyright 1993, 1999Academic Press Lancewood, Pseudopanax crassifolius (A. Cunn.) C. Koch., leaf heteroblasty, anatomy, morphology, structural adaptations     

The Effects of Oil-based Fungicides on Water Loss of Coleus blumei Leaves and Pelargonium Hybrid Petals

Effects of oil-based fungicides on plant surfaces were studiedby assessing water loss from excised sprayed leaves or petalsand by microscopy. Two fungicides (Turbair Zineb Fungicide andTurbair Copper Fungicide) were sprayed, using a Potter tower,onto the adaxial surfaces of excised leaves or petals, and weightloss was determined as a measure of water loss. Doses of approximately4–9 g m^–2 significantly increased water loss fromPelargonium hybrid petals and leaves of Coleus blumei Benth.The fungicides, their supernatants and the carrier oil increasedwater loss from the petals but effects of the supernatants andthe carrier oil on C. blumei leaves were less conclusive. LowTemperature Scanning Electron Microscopy (LTSEM) did not revealany scoring or marked erosion of the adaxial surface of leavesor petals 24 h after application of the fungicides. Coleus blumei Benth., Pelargonium hybrid, cuticle, fungicides, oils, LTSEM, water loss     

Flag Leaf Anatomy of Triticum and Aegilops Species in Relation to Photosynthetic Rate

Quantitative anatomical and other measurements were made onfully expanded flag leaves of a series of diploid, tetraploidand hexaploid Triticum and Aegilops species, and photosyntheticrates per unit leaf area were measured at light saturation (P_max). Diploids had the highest P_max, hexaploids the lowest with tetraploidsbeing intermediate. The anatomical features of tetraploids andhexaploids were generally similar, but different from the diploids.The diploids had thinner leaves with less dry matter and chlorophyllper unit area. The surface area of the mesophyll cells per unitvolume of mesophyll tissue was similar for all ploidy levels,as was the ratio mesophyil cell surface area per unit leaf area.It is argued that while these anatomical features are unlikelyto account for the observed variation in Pmax, it is possiblethat other structural factors with which they are correlatedmay causally influence P_max. One such feature is the averagediffusion path length from the plasmalemma at the cell surfaceto the sites of carboxylation. Anatomy, photosynthesis, mesophyll, cell size, Triticum, Aegilops, polyploidy     

Formation of Pseudowhorls inPeperomia verticillata(L.) A. Dietr. Shoots Exhibiting Various Phyllotactic Patterns

Pseudowhorls are composed of leaves attached at almost equallevels and separated by single fully elongated internodes. InPeperomiaverticillata, pseudowhorls form regularly in shoots exhibitingboth spiral and truly whorled patterns of phyllotaxis. In spiralsystems, they are composed of successive leaves positioned onthe ontogenetic helix. In whorled phyllotaxis, leaves of twoadjacent whorls occur at almost the same level and this wayform a pseudowhorl. The number of leaves per pseudowhorl dependson the type of phyllotactic pattern and also the system of primordiapacking. In all the shoots, regardless of the type of phyllotaxis,the number of leaves per pseudowhorl equals the number of leafprimordia in physical contact with the apical dome. It is thesame as the higher number in contact parastichy pairs in spiralpatterns or the number of orthostichies in whorled phyllotaxis.The pseudowhorled pattern is already manifested in the arrangementof leaf primordia. In spiral and whorled phyllotaxis the plastochronratio calculated for primordia or whorls belonging to adjacentpseudowhorls is always higher than that calculated for membersof one pseudowhorl. Moreover, angular distances between primordiaof one pseudowhorl in spiral patterns are more uniform thanexpected in Fibonacci phyllotaxis. These observations were madeon plants both growing in pots and culturedin vitro. 6-Benzylaminopurine,a synthetic cytokinin, added to the medium increases the meannumber of leaves per pseudowhorl. It seems that this effectis indirect: phyllotaxis changes first rather than the destinyof a particular internode in a process of selective elongation.Copyright1999 Annals of Botany Company Peperomia verticillata, pseudowhorls, phyllotaxis, shoot apex.     

Leaf Nucleic Acids:: II. METABOLISM DURING SENESCENCE AND THE EFFECT OF KINETIN

The nucleic acids in the green and in the senescent leaves ofthree types of plant have been studied. High and low molecularweight RNA of the chloroplast is not present in senescent leavesof Xanthium pensylvanicum, but both cytoplasmic and chloroplasticfractions are found in yellow leaves of Vicia faba and Nicotianatabacum. RNA is more rapidly degraded than DNA in the leavesof these plants when they are detached, and kinetin treatmenttemporarily arrests the loss of chlorophyll and nucleic acid.Once X. pensylvanicum leaves are yellow and senescent they cannotbe re-greened, whereas those of Nicotiana spp., and to someextent those of V. faba, can be rejuvenated. We suggest thatthe retention of chloroplast RNA in yellow leaves may be a majorfactor determining their ability to re-green and that the patternof organelle senescence prior to the first stages of leaf autolysisand dehydration is species-specific.     

Stomata of Micropropagated DelphiniumPlants Respond to ABA, CO2, Light and Water Potential, but Fail to Close Fully

Morphological and physiological characteristics of micropropagatedplants of Delphinium cv. Princess Caroline were studied. Leavesproduced in vitro showed poor control of water loss which appearsto result from restricted responses by stomata and not frompoor cuticular development. Stomata of leaves produced in vitrowere larger and more frequent than those produced during acclimatization.Despite the fact that stomata from isolated epidermis of leavesproduced in vitro reduced their apertures when exposed to turgor-reducingtreatments, they did not close fully. This, together with highstomatal frequencies might explain the poor control of waterloss shown by intact leaves produced in culture when exposedto dry air. While leaves from acclimatized plants showed almostcomplete closure with ABA, low water potentials, darkness andCO₂, stomata from leaves produced in vitro reduced their apertureswhen exposed to those factors, but only to a limit. Therefore,stomata from leaves cultured in vitro seem to be partially functional,but some physiological or anatomical alteration prevents themfrom closing fully. Stomata from leaves produced in vitro wereparticularly insensitive to ABA which appears to be partly associatedwith the high cytokinin concentration in the culture medium.In the long-term, this stomatal insensitivity to ABA might contributeto plant losses when micropropagated plantlets are transferredto soil. Key words: Micropropagation, stomatal physiology, dehydration, PEG, ABA, BAP, darkness, CO₂, Delphinium     

Electrical Currents at the Leaf Surface of Commelina communis and their Relationship to Stomatal Activity

A vibrating probe was used to detect and measure electricalcurrents at the surface of excised leaves and isolated leafepidermis from Commelina commnunis. Currents of up to 4.0 µAcm^–2 moving out from the leaf surface were observed whenthe stomata were open. When the stomata were almost closed nocurrent was detected and when they were fully closed a smallinwardly directed current was observed. There appeared to bea linear relationship between current and stomatal aperture.The current was stimulated by fusicoccin and eliminated by increasingthe external pH suggesting that it was brought about by a flowof H⁺ from the leaf surface. Key words: Electrical currents, leaves, stomata, vibrating probe     

The Structure of the Mesophyll of Flag Leaves in Three Triticum Species

Flag leaves of Triticum urartu, T. monococcum and T. aestivumcv. Professeur Marchal were examined by light and electron microscopyand by separating cells to determine whether differences inleaf anatomy could be related to known differences in theirlight-saturated rates of photosynthesis. Mesophyll cells fromthe three species were lobed and orientated with their longaxis parallel to the veins. The longest, most-lobed cells flankedthe sclerenchyma associated with the veins. Mean cell dimensionswere greatest in Professeur Marchal, but there was no significantdifference in the ratio of the mesophyll cell surface area tocell volume amongst the three species. Flag leaves of T. urartushowed the highest rates of photosynthesis and were also thethickest, with closely-spaced veins from which many of the mesophyllcells radiated. These flag leaves also had significantly more(21.9 per cent) air-filled space, and the highest ratio (15.2)of mesophyll cell surface exposed to this air-filled space perunit leaf area. Ways in which these anatomical characteristicsmay contribute to the higher rate of photosynthesis are discussed. Triticum urartu, Triticum monococcum, Triticum aestivum, flag leaves, morphology, mesophyll     

Stomata and Structure of Tetraploid Apple Leaves cultured in Vitro

Leaves of anther-derived tetraploid apple (Malus pumila Mill.)shoots were examined by low-temperature scanning electron microscopy(LT-SEM). Leaves were serrate and wide with an undulating adaxialsurface due to convex epidermal cells, apparently without crystallineepicuticular wax. Stomata were absent from the adaxial surface,except for the marginal teeth which exhibited 40-60 stomataper leaf; they probably originated from residual mitotic activity.One third of abaxial stomata was occluded by the residual cuticleof the mother guard cell across the stomatal pore which rupturedwhen the stomata became functional. The stomatal index was 7·2(± 1·6) with 60-75 stomata mm^-2, i.e. abaxialstomata of tetraploid leaves expanded in vitro were less frequentthan those in triploid leaves either cultured in vitro (475-575stomata mm^-2) or grown on the tree (320-390 stomata mm^-2) wherethe stomatal index was 21 (± 4). Freeze-fracture transsectionsshowed that the tetraploid in vitro leaves were composed ofa layer of adaxial epidermal cells, followed by a single layerof palisade cells and four to five layers of spongy mesophyllcells and the abaxial layer of epidermal cells, in contrastto juvenile seedling-grown apple leaves in which the two layersof palisade cells comprised the majority (52-60%) of the leafvolume. The same morphological features, such as wide and lesspointed leaves, reduced stomatal density and stomatal index,and increased stomatal size that were previously reported fortree-grown tetraploid leaves were also expressed in vitro. Thus,causes of the stomatal deformation in tissue-cultured Rosaceaeare interpreted to be in part genetic and not purely environmental.Copyright1994, 1999 Academic Press Malus pumila Mill., apple, biotechnology, breeding, cryo-preservation, CO₂, juvenile, low temperature-scanning electron microscopy (LT-SEM), micropropagation, ploidy, stomata, tissue-culture, transpiration     

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     

Heterophylly in Ranunculus flabellaris Raf.: The Effect of Abscisic Acid

Ranunculus flabellaris Raf., the Yellow Water-Crowfoot, is aheterophyllous semi-aquatic dicotyledonous plant, showing strikingmorphological and anatomical differences between terrestrialleaves and those formed underwater. After plants are submergedin a 25 µM solution of abscisic acid, leaves are producedat a normal rate but they exhibit many of the characteristicsof terrestrial leaves. Ranunculus flabellaris Raf., Yellow Water-Crowfoot, heterophylly, abscisic acid     

Giant Stomata

The presence of abnormally large stomata on leaves of Mangiferaindica L. and Limoma acidissima L. is reported. Apart from theirsize, these stomata are indistinguishable from normal stomatapresent on these leaves, and it is likely that they functionin a similar way.     

Sunflower (Helianthus annuus) Leaves Contain Compounds that Reduce Nuclear Propidium Iodide Fluorescence

Sunflower leaves have unidentified compounds that interferewith propidium iodide (PI) intercalation and/or fluorescence.Independently prepared pea leaf nuclei show greater PI fluorescencethan nuclei from pea leaves simultaneously processed (co-chopped)with sunflower leaves. Differences in fluorescence persist aftermixing the PI-stained pea and the co-chopped pea/sunflower samples,i.e. PI staining protects the nuclei from the effects of theinhibitor. The current results are significant to practicalflow cytometric determination of plant nuclear DNA content.They show: (1) simultaneous processing of nuclear samples fromthe target and the standard species is necessary to obtain reliableDNA estimates; (2) a test for the presence of inhibitors shouldbe conducted; and (3) when inhibitors are present caution shouldbe taken in interpreting differences in estimated DNA content.The previously reported environmentally-induced variation inDNA content in sunflower populations is most simply explainedby variation in the amount of environmentally-induced inhibitorthat interferes with intercalation and/or fluorescence of PI.Intraspecific variation of DNA content for Helianthus annuusneeds to be re-evaluated using best practice techniques comparingphysiologically uniform tissues that are free of inhibitors.The best estimate for 2C DNA content of H. annuus used in thisstudy is 7.3 pg. Copyright 2000 Annals of Botany Company Helianthus annuus, DNA content, flow cytometry, propidium iodide, endogenous inhibitors     

Nitrate Assimilation in Higher Plants with Special Reference to the Cocklebur (Xanthium pennsylvanicum Wallr.)

A soluble NADH-dependent nitrate reductase is described forthe shoot system of Xanthium. Young leaves and immature stemtissues contain high levels of the enzyme. They are relativelyrich in free amino acids and amides but store little free nitrate.The specific activity of the enzyme is lower in fully expandedleaves, although these leaves exhibit higher rates of fixationof carbon in photosynthesis than do younger leaves. Neithernitrate nor free amino acids accumulate in the mesophyll ofthe leaf. Older parts of the stem axis accumulate large amountsof soluble nitrogen, almost entirely as free nitrate. Reservesof nitrate in the shoot and root are rapidly depleted if nitrateis removed from the external medium. Nitrate reductase is apparently absent from roots of Xanthium.This finding is supported by analyses of bleeding sap from nitrate-fedplants which show that 95 per cent of the nitrogen exportedfrom roots is present as free nitrate. However, roots are capableof synthesizing and exporting large amounts of amino nitrogenif supplied with reduced nitrogen such as urea or ammonium. A scheme is presented summarizing the main features of the metabolismof nitrate in Xanthium and this is compared with the situationin nitrate-fed plants of the field pea (Pisum arvense L.), aspecies previously shown to be capable of reducing nitrate inits root system.     

Leaf Structural Peculiarities in Sarcopoterium spinosum, a Seasonally Dimorphic Subshrub

Extensive investigations on the anatomy of the two leaf typesin a seasonally dimorphic subshrub revealed interesting variationsbetween summer and winter leaves. Summer leaves of Sarcopoteriumspinosum possess a thick epidermis composed of tannin-containingcells and large amounts of mucilage secreted through the innerpericlinal walls towards the mesophyll. A thick cuticle is alsopresent on the surface of the leaf. In winter leaves the epidermalcells produce no mucilage while phenolics are accumulated ingranular form only. Besides these, some other variations betweensummer and winter leaves are also discussed in respect of theability of the plant to withstand the unfavourable Mediterraneanconditions. Seasonal dimorphism, leaf anatomy, Sarcopoterium spinosum