Spongy Mesophyll Research Articles

An ultrastructural study ofPseudomonas syringaepv.syringaeinfection of poplar and tobacco foliage

Abstract Necrotic and chlorotic leaf spots observed on nursery grown poplars during moist spring conditions were caused by Pseudomonas syringae pv. syringae. Infected tissue was necrotic, collapsed and desiccated, and contained no viable bacteria at a late stage. Organelles in cells of chlorotic tissue were not moribund and cell wall proliferations were absent. Tissues were negative-imaged and cytoplasm was condensed and granulated. Tobacco leaves infiltrated with >109 cells/ml of P. syringae pv. syringae exhibited ultrastructural changes one hour following infiltration. The plasmalemma invaginated and proliferations formed in cell walls. Vesiculation of boundary and internal membranes occurred in most organelles. After 3 and 6 hours, vesiculation increased, plasma membranes ruptured and organelles degenerated. Small groups of bacteria were observed clustered in depressions in cell walls and in pockets between adjacent cells. Bacteria were covered by a fibrillar network and caused no degradation of the outer wall. Twelve hours following infiltration, most spongy and palisade mesophyll cells had collapsed and intercellular spaces were filled with actively dividing bacteria.

Stereology of the Internal Structures of Leaves in Peperomia obtusifolia, P. camptotricha, and P. scandens

The internal structure of leaves from Peperomia obtusifolia, P. camptotricha, and P. scandens were analyzed with stereology to detect relationships between the internal leaf structure of each species with its diurnal cycles of gas exchange and organic acid fluctuation. In these succulent leaves, the relative volume of leaf occupied by each of three tissues (multiple epidermis and median and spongy mesophyll) varied according to the species and leaf development. In P. obtusifolia, which exhibits light-period gas exchange and little acid fluctuation, 75% of the leaf volume was multiple epidermis. In P. scandens, which exhibits dark-period gas exchange and large acid fluctuation, 77% of the leaf volume was spongy mesophyll. In P. camptotricha, which exhibits increasing dark-period gas exchange and acid fluctuation during leaf development, the multiple epidermis and spongy mesophyll were each about 48% of the leaf volume. In each species the median mesophyll was about 4% of the leaf volume. The area of cell wall exposed to the internal air space of the leaf was dominated by the spongy mesophyll in each species; the area was least in P. obtusifolia, greater in thicker leaves of P. camptotricha, and greatest in P. scandens. The relative volumes of cellular components in P. camptotricha were determined for leaves of different thickness. A high density of chloroplasts in the median mesophyll gave a low ratio of vacuole to cytoplasm, which was similar to the ratio in bundle sheath cells of many plants with C4 metabolism. The vacuole predominated in cells of the multiple epidermis and spongy mesophyll, and the cells were much larger than those in the median mesophyll. However, only the spongy mesophyll contained chloroplasts with the stroma and thylakoid volume more typical of chlorenchyma in plants with Crassulacean acid metabolism. Tissue dimorphism in cell size, chloroplast content, vacuole volume, and cell wall exposed to air space were the structural features most easily associated with the known physiological data of gas exchange and organic acid fluctuation patterns in these species of Peperomia.

Leaf Ultrastructure of Peperomia obtusifolia, P. camptotricha, and P. scandens

Three parenchyma tissues are arranged in separate periclinal layers in the leaves of Peperomia obtusifolia, P. camptotricha, and P. scandens. A transparent, multiple epidermis is situated on the adaxial side of the leaf and has large, tightly packed cells containing mostly starch-filled chloroplasts. A median (palisade) mesophyll, situated between the multiple epidermis and an abaxial spongy mesophyll, has small, moderately packed cells. Chloroplasts occupy a large volume of the median mesophyll cells and contain little starch but extensive thylakoid membranes with numerous, highly stacked grana. A spongy mesophyll is situated on the abaxial side of the leaf and has cells much larger than those in the median mesophyll. The spongy mesophyll chloroplasts contain mostly starch, and the thylakoid membranes have fewer, less stacked grana than those in the median mesophyll. The cellular ultrastructure of each tissue type is similar among these species, indicating a specialized function for each tissue. However,...

Photosynthetic light gradients and spectral régime within leaves of Medicago sativa

By using a fibre-optic probe, light gradients were measured at 450, 550 and 680 nm in sun leaves, 125 µm thick, of Medicago sativa L. cv. Armor. The space irradiances immediately beneath the leaf surface were 1.5-2.0 times greater than the incident light for these wavelengths, indicating that M. sativa leaves are efficient light traps. Although the palisade was only 60 µm thick, each light gradient declined steeply within this layer. More light appeared to be scattered in forward rather than backward directions and the spectral régime of the light fluxes depended upon their direction of travel within the leaf. Spectra for transmitted light were dependent upon depth within the leaf, whereas back-scattered light consisted of mostly green and far-red light at all depths, PAR (photosynthetically active radiation, 400-700 nm) within both the palisade and spongy mesophyll consisted mostly of green and far-red light, and the spongy mesophyll received only 0.11 of the PAR compared with the midregion of the palisade. Anomalous measurements within the palisade were traced to the epidermis, which was found to act as a mosaic of microlenses that focused light within the palisade layer. In M. sativa leaves, the light microenvironment, leaf anatomy and photosynthesis seem to be strongly interrelated.

Leaf anatomy of the Menispermaceae tribe Tiliacoreae Miers

An anatomical study of the leaves of 25 species belonging to 12 of the 19 genera has been made. The anatomical characters found to be of the most use in distinguishing taxa or groups of taxa are: in surface view–stomatal outline, stomatal density and distribution, subsidiary cell or surrounding cell patterns, presence/absence of hairs; in transverse sections–dimensions of adaxial epidermal cells, morphology of spongy mesophyll, midrib outline, number and distribution of vascular bundles, presence/absence of an upper pulvinus, presence/absence of sclereids in the upper pulvinus, presence/absence of secretory sacs, crystal type and distribution.

Microtubule deployment within plant tissues: Fluorescence studies of sheets of intact mesophyll and epidermal cells

Immunofluorescence microscopy of sheets of plant cells has allowed analysis of microtubule arrays across tissues. Examination of multilayer sheets with laser scanning confocal microscopy allows interior cell layers to be observed without interference from out-of-focus fluorescence. Transitory stages in preprophase band formation during stomatal complex development in grass leaves are identified, and preprophase bands are found in the relatively disorganized spongy mesophyll of spinach as well as in more highly organized mesophyll layers.

Regulation of Apoplastic pH in Source Leaves of Vicia faba by Gibberellic Acid

Leaf discs of broad bean (Vicia faba L.), peeled on the spongy mesophyll side, rapidly altered the pH of the surrounding medium (apoplast). Using pH indicator paper appressed against the leaf, immediately after peeling, initial apoplastic pH was estimated to be 4.5. Changes in the apoplastic pH were measured with a microelectrode placed into a 100-microliter drop of an unbuffered solution (2 millimolar KCl, 0.5 millimolar CaCl(2), and 200 millimolar mannitol) on the peeled surface. Discs acidified the medium until the pH stabilized at about 5.0 (about 10 minutes). Acidification was inhibited by 50 micromolar sodium vanadate, an inhibitor of the plasmalemma H(+)-ATPase and attenuated by omitting the osmoticum or potassium ions from the medium. Fusicoccin (10 micromolar) greatly enhanced the rate of acidification. The presence of 0.1 to 1 micromolar gibberellic acid resulted in a slower rate of medium acidification. Gibberellic acid appeared to modulate the activity of the H(+)-translocating ATPase located at the plasma membrane of the mesophyll cells.

Movement of lucifer yellow in leaves of Coleus blumei Benth

Abstract Individual spongy mesophyll cells in green areas of variegated Coleus blumei leaves were injected with the symplast‐mobile dye lucifer yellow and its movement to other cell types was followed with fluorescence microscopy. In 13 trials, the dye remained in the injected cell twice, moved only to other mesophyll cells five times, and moved up to and along minor veins six times. Where extensive movement of the dye occurred, the tissue was fixed with 4% glutaraldehyde, dehydrated, embedded in plastic, sectioned at 3 μm, and examined again with fluorescence microscopy. The dye was found in abaxial bundle‐sheath cells for up to 200 μm or more distant from the site of injection near the minor vein, but no convincing evidence was found for its presence in the vascular tissue itself. It thus appears that superficial whole‐mount views of lucifer yellow movement along leaf minor veins cannot be taken as certain evidence for symplastic transport of the dye into and along the vascular tissues.

Photosynthesis in Flaveria brownii, a C4-Like Species

Light microscopic examination of leaf cross-sections showed that Flaveria brownii A. M. Powell exhibits Kranz anatomy, in which distinct, chloroplast-containing bundle sheath cells are surrounded by two types of mesophyll cells. Smaller mesophyll cells containing many chloroplasts are arranged around the bundle sheath cells. Larger, spongy mesophyll cells, having fewer chloroplasts, are located between the smaller mesophyll cells and the epidermis. F. brownii has very low CO(2) compensation points at different O(2) levels, which is typical of C(4) plants, yet it does show about 4% inhibition of net photosynthesis by 21% O(2) at 30 degrees C. Protoplasts of the three photosynthetic leaf cell types were isolated according to relative differences in their buoyant densities. On a chlorophyll basis, the activities of phosphoenolpyruvate carboxylase and pyruvate, Pi dikinase (carboxylation phase of C(4) pathway) were highest in the larger mesophyll protoplasts, intermediate in the smaller mesophyll protoplasts, and lowest, but still present, in the bundle sheath protoplasts. In contrast, activities of ribulose 1,5-bisphosphate carboxylase, other C(3) cycle enzymes, and NADP-malic enzyme showed a reverse gradation, although there were significant activities of these enzymes in mesophyll cells. As indicated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the banding pattern of certain polypeptides of the total soluble proteins from the three cell types also supported the distribution pattern obtained by activity assays of these enzymes. Analysis of initial (14)C products in whole leaves and extrapolation of pulse-labeling curves to zero time indicated that about 80% of the CO(2) is fixed into C(4) acids (malate and aspartate), whereas about 20% of the CO(2) directly enters the C(3) cycle. This is consistent with the high activity of enzymes for CO(2) fixation by the C(4) pathway and the substantial activity of enzymes of the C(3) cycle in the mesophyll cells. Therefore, F. brownii appears to have some capacity for C(3) photosynthesis in the mesophyll cells and should be considered a C(4)-like species.

Light and chlorophyll gradients within Cucurbita cotyledons

Abstract. Measurement of light within 10–14‐d‐old green and etiolated Cucurbita pepo cotyledons were made with fibre‐optic microprobes to assess the influence of chlorophyll distribution and anatomical variations in mesophyll cell type (spongy versus palisade) on internal light pattern. More than 50% of the pigment in green cotyledons occurred in the upper (adaxial) 300 μm and this gradient strongly influenced the internal propagation of 680 nm light. When the upper (adaxial) surface was irradiated with 680 nm light, almost complete absorption occurred within the first 400 μm (palisade) of approximately 1200‐μm‐thick cotyledons. In contrast, when lower (abaxial) surfaces were irradiated with 680 nm light, penetration extended throughout the spongy mesophyll to about the 700 μm depth. Measurements of collimaled and scattered light gradients at 550, 680 and 750 nm indicated that collimaled light was rapidly scattered by mesophyll cells. In cotyledons irradiated on the upper surface, spongy mesophyll cells received only scattered light. Furthermore, comparisons of scattered light gradients obtained from cotyledons irradiated on upper and lower surfaces suggested that spongy mesophyll cells scatter light more effectively than palisade cells, probably due to the greater proportion of intercellular air spaces in spongy mesophyll tissue. These data also indicate that both the spectral quality and quantity of light incident on palisade versus spongy mesophyll cells differs, perhaps contributing to developmental and physiological differences between these two mesophyll cell types.

Manipulating carnation petal senescence. I. The interaction and transport of benzyladenine and indoleacetic acid

Indoleacetic acid (IAA) promotes carnation petal senescence with the petals irreversibly wilting, whilst benzyladenine (BA) delays petal senescence so that they eventually “burn” or become necrotic at the petal perimeter. An anatomical study showed that with irreversible wilting the spongy mesophyll in the flag region becomes loosely packed. The rate and type of petal senescence was used as an indicator to measure the interaction of BA and IAA and, in relation to this parameter, each hormone was found to alter the physiological expression of senescence by the other. Although BA did alter IAA transport, it was concluded that the change in senescence pattern when these hormones were added together was not entirely due to differences in their transport.

Measurement of light within thin plant tissues with fiber optic microprobes

Vogelmann, T. C., Knapp, A. K., McClean, T. M. and Smith, W. K. 1988. Measurement of light within thin plant tissues with fiber optic microprobes. ‐ Physiol. Plant. 72: 623–630.The measurement of light with fiber optic microprobes has been extended to thin (200–300 μm) plant tissue samples. To test the method, light measurements were made in thin aqueous films and paradermal sections from 10‐day‐old etiolated Cucurbita pepo L. cv. Fordhook cotyledons. The measurements obtained were highly reproducible. Paradermal sections of spongy mesophyll that were irradiated with collimated light scattered light more effectively than the palisade layer of intact cotyledons. These results demonstrate that different plant tissues have different light scattering characteristics. The successful extension of the fiber optic microprobe technique to thin systems makes it possible to examine the optical properties of different cell layers within leaves and other plant organs.

Anatomische Untersuchungen an der Blattspreite bei Allium L. (Alliaceae) I. Arten mit einer einfachen Leitbündelreihe

Summary Most of the species of this group are distinguished by a character’s syndrom (named here “typ 1”): subepidermal lactifers, palisade mesophyll absent (or if present it seems to be secondarily evolved from spongy mesophyll), and a spongy mesophyll of various cell forms which could have been derived from ancestral many- and short-armed, long cells. All analyzed species of the American sections of subg. Amerallium sensu T raub 1968 belong to this group and represent a rather derived evolutionary line, whereas the Eurasian sections Molium, Xanthoprason, Chamaeprason, Narkissoprason, and Briseis are mostly less differentiated. But sect. Arctoprasum (A. ursinum) and genus (or sect., subg.) Nectaroscordum seem to represent rather isolated evolutionary sub-lines. The analyzed species of subg. Bromatorrhiza belong partly to “typ 1” (A.fasciculatum, A. hookeri). The other species A. cyathophorum var. farreri, A. mairei, and A. amabile possess a true palisade mesophyll and intraparenchy-matic lactifers. That combination of characters is named “typ 2” and seems to be the ancestral one from which the evolution could have been gone to the “type 1” syndrome as well as to the other groups of genus Allium having a circle or two opposedly orientated rows of vascular bundles in the leaf blade.

The distribution of calcium and magnesium in developing tobacco leaves as measured by low-temperature X-ray microanalysis

The processes of leaf maturation and senescence are linked closely to the redirection of ions and organic nutrients between leaves and other part of the plant. It is known from work on whole leaves, that Ca2+ and Mg2+ play an important role in leaf development, although no studies have been made of changes at the cell and tissue level. This present study follows the cellular changes in Ca2+ and Mg2+ in the epidermal and photosynthetic tissues by X-ray microanalysis of frozen hydrated leaves.Full details of sample preparation, instrumentation, and the basis of the quantitative procedures have been reported elsewhere. Flat, frozen hydrated fracture faces of upper and lower epidermis; palisade and spongy mesophyll cells were analysed for Ca2+ and Mg2+. Data was collected from each of the four cell types in 20 different leaves at each of the following five stages of growth. Juvenile (10 weeks from seed); Mature (13 weeks), Ripe (16 weeks), Senescent (19 weeks) and Old (21 weeks). Cells containing obvious calcium oxalate crystals were avoided.

Physiological and anatomical features of the silvering disorder ofCucurbita

SummaryLeaf silvering is a physiological disorder of marrows, Cucurbita pepo, exacerbated by drought. Silvered leaves had spaces between the upper epidermis and the mesophyll cells and within the mesophyll. The palisade cells were smaller and spongy mesophyll cells fewer. Completely silvered leaves contained 14% less chlorophyll per unit leaf blade area than green leaves. The rate of photosynthesis decreased as severity of silvering increased. The rate of photosynthesis was about 30% lower in the completely silvered than in the green leaves at saturating and above-saturating light and CO2. The results suggest that in silvered plants the CO2 absorption mechanism has been affected.

Crassulacean acid metabolism in tropical dicotyledonous trees of the genusClusia

The performance of crassulacean acid metabolism (CAM) by dicotyledonous trees of the genusClusia sampled at three sites in the state of Falcon in northern Venezuela is characterized.Clusia leaves have a somewhat succulent appearance. Unlike leaves of many other CAM plants, which are uniformly built up of very large isodiametric cells, there are distinct layers of palisade and spongy mesophyll, with individual cells being smaller. There is no specialized water storage tissue. δ13C values indicate thatC. multiflora in the elfin-cloud forest on top of Cerro Santa Ana, at ∼800 m altitude, performs C3 photosynthesis (δ13 −27.1‰). However,C. rosea in the tall cloud forest on Cerro Santa Ana (∼600m altitude), andC. rosea andC. alata in the dry forest on Serrania San Luis (∼900 m altitude) perform CAM (δ13C −14.1 to −19.2‰). InC. alta andC. rosea there were large day-night changes in the levels of malic and citric acids ranging from 63 to 240 mmol 1−1 for malid acid and from 35 to 112 mmol 1−1 for citric acid. The sum of the changes in malate and citrate levels accounts for the changes of titratable protons measured. With a day-night change of titratable protons of 768 mmol 1−1 in one of the analyses,C. rosea showed the highest value yet encountered in a CAM plant. Oscillations of free sugars (fructose, glucose, sucrose) and of starch were also analysed in the CAM performingClusia species. Carbon skeletons of the precursors involved in nocturnal malate and citrate synthesis largely derive from free sugars and not from polyglucan. Unlike some other CAM plants, there is no clear and quantitative correlation between day-night changes of organic acid levels and cell sap osmolality.

Prolonged Flooding Effects on Anatomy of Highbush Blueberry

Abstract Roots of flooded highbush blueberry (Vaccinium corymbosum L.) plants examined by light and scanning electron microscopy exhibited enlarged epidermal cells, compressed cortical cells, and disrupted vascular tissue. The stems of flooded plants showed disrupted epidermal tissue, condensed outer cortical cells, and large aerenchyma-like mid-cortical tissue. Leaves from flooded plants showed an increase in intercellular spaces in the spongy mesophyll and a disrupted palisade layer. There were no apparent differences in inflorescence bud anatomy, although inflorescences were small and delayed in development.

Carbon Flow and Metabolic Specialization in the Tissue Layers of the Crassulacean Acid Metabolism Plant, Peperomia camptotricha

Leaves of Peperomia camptotricha contain three distinct upper tissue layers and a one-cell thick lower epidermis. Light and dark CO(2) fixation rates and the activity of ribulose bisphosphate carboxylase/oxygenase and several C(4) enzymes were determined in the three distinct tissue layers. The majority of the C(4) enzyme activity and dark CO(2) fixation was associated with the spongy mesophyll, including the lower epidermis; and the least activity was found in the median palisade mesophyll. In contrast, the majority of the C(3) activity, that is ribulose bisphosphate carboxylase/oxygenase and light CO(2) fixation, was located in the palisade mesophyll. In addition, the diurnal flux in titratable acidity was greatest in the spongy mesophyll and lowest in the palisade mesophyll. The spatial separation of the C(3) and C(4) phases of carbon fixation in P. camptotricha suggests that this Crassulacean acid metabolism plant may have low photorespiratory rates when it exhibits daytime gas exchange (that is, when it is well watered). The results also indicate that this plant may be on an evolutionary path between a true Crassulacean acid metabolism plant and a true C(4) plant.

Effects of silverleaf infection on ultrastructure of foliage ofPrunus,Rosa, andPopulus

Abstract Foliage of peach, rose, and poplar, silvered as a result of stem infection Chondrostereum purpureum, was examined by both light and electron microscopy. Silvered leaves had fewer palisade cells which were more loosely arranged than in healthy leaves. Also, the epidermis became detached from palisade cells. Both palisade and spongy mesophyll cells were highly vacuolate, and moribund chloroplasts were packed with starch granules. Cells micro-organelles showed little ultrastructural change apart from the chloroplasts which become more electron dense, and the thylakoids and intergranal lamellae which became disorganised. Leaf area, transpiration, and stomatal conductance decreased significantly as the intensity of leaf-silvering increased. Stomata of severely-silvered leaves remained closed. Affected foliage possibly died of starvation as a result of severe water stress arising from physical occlusion of vessels in conjunction with possible toxin action in the leaves.

A Mosaic Disease of Wax Myrtle Associated with a New Species of Eriophyid Mite

Abstract A mosaic disease of wax myrtle (Myrica cerifera L.) occurring in Florida is described. Affected plants had small, distorted leaves that displayed a virus-like mosaic pattern characterized by pale green blistered areas interspersed with dark green, normal-colored tissues. Affected epidermal, palisade, and spongy mesophyll cells were disorganized, distorted, and frequently contained fewer definable chloroplasts than healthy leaves. Standard virus indexing techniques yielded no evidence of a viral etiology; however, a new species of eriophyid mite, Calepitrimerus ceriferaphagus Cromroy, was recovered from symptomatic tissue. Symptomatic plants produced symptomless new growth after treatment with the systemic acaricide oxamyl, suggesting an association of the mite with the mosaic disease. Chemical name used: methyl 2-(dimethyl-amino)-N-[[methylamino)carbonyl]oxy]-2-oxoethanimidothioate(oxamyl).