DIFFERENTIAL RESPONSES OF PLANT FOLIAGE TO SIMULATED ACID RAIN

Experiments were performed to show the responses of foliage of several clones of Tradescantia sp., Pteridium aquilinum, Quercus palustris, and Glycine max to simulated acid rain. These experiments were performed to (a) predict the relative sensitivities of foliage of these plants to acid rain, and (b) identify leaf surface and anatomical alterations to simulated acid rain that may be used to diagnose acid rain injury. Plants were exposed to simulated rain at pH levels of 5.7, 3.4, 3.1, 2.9, 2.7, 2.5, and 2.3. Sporophyte leaves of bracken fern {P. aquilinum) were most sensitive to simulated acid rain among the species tested. About 10% of the surface area of older leaves of P. aquilinum was injured after exposure to 10 rainfalls at pH 2.5 (a single 20-min rainfall daily). Foliage of pin oak (Q. palustris) exhibited less than one-percent leaf area injury after exposure to simulated rain at pH 2.5 after 10 rainfalls (one 20-min rainfall daily). The responses of soybeans (G. max) and spiderwort (Tradescantia sp.) were intermediate between these two extremes. Histological observations show that lesion development results in collapsed leaf tissue in all four species. Gall formation that resulted from both cell hypertrophy and hyperplasia occurred in lesions of Tradescantia, and Q. palustris. Limited hyperplastic and hypertrophic reactions occurred in G. max foliage after exposure to simulated acid rain but no leaf galls resulted. Sporophyte foliage of P. aquilinum exhibited a “granular” type abnormality in the cytoplasm prior to the collapse of some epidermal cells injured by simulated rain. Injury occurred most frequently near vascular tissues and trichomes in all four species. In general, plant species that show cell hyperplasia and hypertrophy of leaf tissues after exposure to simulated acid rain are injured less than species that do not show these responses.     

CULTURE OF MATURE ECOTYLEDONOUS EMBRYOS OF PHASEOLUS VULGARIS AND THE NUTRITIONAL ROLE OF COTYLEDONS

Embryos of Phaseolus vulgaris L. were excised from seeds and cultured with cotyledons removed to determine the actions of various cultural conditions upon embryo development. Four media were tested, but ecotyledonized embryos did not grow as rapidly on any of them as did embryos with intact cotyledons on agar-water media. Comparisons of growth of ecotyledonized embryos with embryos bearing fractions of cotyledons indicated ecotyledonized embryos cultured on nutrient media grew about as well as embryos bearing cotyledons from which 97% of the volume had been removed surgically. The final weight of ecotyledonized embryos was greater when detached cotyledons were placed near them and was even greater when extracts of detached and incubated cotyledons were employed in the nutrient medium. Benzyladenine, kinetin, gibberellic acid, indole-acetic acid, presence of sucrose, and light or dark culture failed to enhance the ability of incubated cotyledons to stimulate growth of embryos.     

THE CUTICULAR ANATOMY OF FRENELOPSIS VARIANS FROM THE LOWER CRETACEOUS OF CENTRAL TEXAS

Stem fragments identified as Frenelopsis varions Fontaine have been found in the Lower Cretaceous (Albian) of central Texas. The cuticle is extremely thick and characterized by 5–6 subsidiary cells with papillae overarching the stomatal chamber. Guard cells are deeply sunken below the epidermis. Stomatal complexes are arranged in axial rows extending from the base of an internode to its apex. The rows of stomata continue into the sheathing leaf where the rows curve towards the leaf apex. The epidermis of F. varions was apparently long persistent and underwent prolonged growth. Axial rows of stomata are frequently disrupted resulting in a random pattern of stomata. A single, highly reduced, sheathing leaf is present at each node. The margin of the leaf has numerous unicellular trichomes and extends to form a slightly triangular blade.     

EFFECTS OF SIMULATED ACID RAIN ON PHASEOLUS VULGARIS L. (FABACEAE)

Experiments were performed to determine the effects of simulated acid rain on Phaseolus vulgaris L. At pH values below 3, plants exhibited a failure to attain normal height, had necrotic and wrinkled leaves, excessive and adventitious budding, and premature abscission of primary leaves. Histologically, leaves had smaller cells, less intercellular space, and smaller starch granules within the chloroplasts. Respiration rates of the treated plants increased only slightly at low pH values. Apparent rates of photosynthesis, however, increased dramatically. Both carbohydrate production and root biomass were reduced by low pH treatments, and application of Congo red indicator to the acid-treated leaf tissue showed that the cell contents were acidified to a pH of below 4.0.     

EFFECTS OF RED AND FAR-RED RADIATION ON CELL DIVISION AND ELONGATION IN THE STEM OF PINTO BEAN SEEDLINGS

Nine-day-old Pinto bean seedlings, Phaseolus vulgaris L., were treated daily for 12 days with supplementary red or far-red radiation following daily exposure to 8 hr of daylight. Stem elongation was nearly exponential from the 4th to the 12th day of treatment and was about 2.9 times greater under far-red radiation. Cell division and cell elongation were promoted essentially equally by far-red radiation. There was virtually no difference in either the rate of leaf initiation or the duration of growth of internodes under the supplementary radiation.     

Artichoke Leaf Morphology and Surface Features in Different Micropropagation Stages

Artichoke (Cynara scolymus L.) leaf size and shape, glandular and covering trichomes, stomatal density, stomata shape, pore area and epicuticular waxes during micropropagation stages were studied by scanning electron microscopy (SEM) and morphometric analysis with the aim to improve the survival rate after transfer to greenhouse conditions. Leaves from in vitro shoots at the proliferation stage showed a spatular shape, ring-shaped stomata, a large number of glandular trichomes and juvenile covering hairs, but failed to show any epicuticular waxes. Leaves from in vitro plants at the root elongation stage showed a lanceolated elliptic shape with a serrated border, elliptical stomata, decreased pore area percentage, stomatal density, and mature covering trichomes. One week after transfer to ex vitro conditions, epicuticular waxes appeared on the leaf surface and stomata and pore area were smaller as compared to in vitro plants. Artichoke acclimatization may be improved by hormonal stimulation of root development, since useful morphological changes on leaves occurred during root elongation.     

ECOLOGICAL ADAPTATIONS OF SALT MARSH GRASS,DISTICHLIS SPICATA (GRAMINEAE), AND ENVIRONMENTAL FACTORS AFFECTING ITS GROWTH AND DISTRIBUTION

Salt grass is an important pioneer plant in early stages of succession. The sharp-pointed rhizomes with numerous epidermal silica cells, and the aerenchymatous network of the rhizome, leaf sheath, and roots facilitate development of the plant in heavy clays, shales, and inundated soils. In salt marshes of southern Utah, salt grass contributes to a hummock-building process that favors localized removal of salts by capillary action and evaporation. This process provides a narrow strip of soil that is favorable for the rooting of extended rhizomes. In laboratory experiments, maximum growth for Distichlis spicata, a perennial salt marsh grass, was obtained at 15,000 ppm soluble salts in nutrient solution cultures. Comparable concentrations of salts occurred in soils of the habitat from which plants were taken. Nearly equal concentrations of sodium and potassium were found in the plant tissue where the growth of the plants was optimal; such a ratio was maintained in the plants during most of the growing season. In the field the greatest amount of growth of salt grass takes place when temperatures are cool and soil moisture is quite high during the early spring. During mid-summer as air temperatures rise, crude protein in the plant decreases. During periods of high salt and water stress, morphological and anatomical adaptations of the stomata, salt glands, and trichomes of salt grass are important for survival. Stomata on exposed ridges of vascular bundles, where desiccation is greatest, usually are covered by four epidermal cells. In contrast, stomata found in the grooves between vascular bundles tend to be uncovered. The salt gland is composed of a large basal cell and a cap cell and actively excretes (in a diurnal rhythm) excess sodium, potassium, and chloride ions. A mechanism for salt excretion from this gland is postulated. The silica-containing trichomes on the leaves may play a role in cooling the leaf under conditions of high solar radiation and also serve to protect the plant against attack by herbivores.     

Host plant acceptance by the phytophagous mite Tetranychus kanzawai Kishida is affected by the availability of a refuge on the leaf surface

We used 11 wild plants to experimentally test the effects of leaf trichomes and leaf quality on host plant acceptance by a phytophagous spider mite, Tetranychus kanzawai, in the absence of predators. There was a positive correlation between leaf hair traits (height/density) and host plant acceptance. We used two model plants (Phaseolus vulgaris and Phaseolus lunatus; the former had higher and denser leaf hairs than the latter) to examine the effects of leaf hairs on the dispersal and fecundity of T. kanzawai in the presence of a predatory mite, Neoseiulus womersleyi. In the presence of N. womersleyi, significantly fewer T. kanzawai females dispersed from a P. vulgaris leaf than from a P. lunatus leaf. Moreover, in the presence of the predator the fecundity of T. kanzawai females on P. lunatus was significantly lower than on P. vulgaris, although in terms of host quality the two plants were equivalent. In the presence of N. womersleyi, T. kanzawai females on P. vulgaris spent more time on webs than those on P. lunatus. Moreover, webs seemed to be less accessible than leaf surfaces to the predator. These results suggest that leaf hairs provide a refuge for T. kanzawai adult females.     

EFFECTS OF SINGLE AND MULTIPLE EXPOSURES OF FERULIC ACID ON THE VEGETATIVE AND REPRODUCTIVE GROWTH OF PHASEOLUS VULGARIS BBL-290

Phaseolus vulgaris BBL-290 plants were grown in growth chambers in the Southeastern Plant Environment Laboratory and exposed to either single (at seedling, flower, or podfill) or multiple (biweekly or weekly) treatments of ferulic acid (FA). In the first experiment, plants were harvested one week after FA treatment (0, 1.0, 2.0 mM) and at final harvest (56 days old). FA delayed leaf expansion during the seedling and flowering stages. The total plant leaf area and the plant dry weight of plants treated with 1.0 and 2.0 mM FA as seedlings were reduced one week after treatment by 38–48%. The total plant leaf area and the plant dry weight of plants treated at flowering with 2.0 mM FA were reduced by 25% one week after treatment. Treatment with 2.0 mM FA at podfill caused the senescence and abscission of older leaves and reduced total plant leaf area, plant dry weight and mean pod dry weight by 54, 40, and 48%, respectively, one week after treatment. The plants treated at the seedling and flowering stages recovered by final harvest. In a subsequent experiment, FA (0, 0.50, 1.0, 1.5 mM) reduced total plant leaf area at the seedling and flowering stages but not at podfill. The youngest expanding leaves were most sensitive to FA at flowering. The leaf area of these leaves was reduced by 35 and 25%, one and two weeks after treatment, respectively. Their absolute growth rates were reduced from 31 to 56% one week after treatment at flowering. Their relative growth rates were reduced by 50% one week after treatment. Growth rates then recovered within two weeks after treatment. In the final experiment, biweekly exposures of FA (0.25, 0.50, 0.75, 1.0) reduced total plant leaf area but did not affect any other growth parameters. Weekly exposures of FA (0.25, 0.50, 0.75, 1.0) reduced total plant leaf area up to 34%, absolute growth rate up to 58%, leaf number up to 31% and pod number up to 58%. As the frequency of exposure to FA increased, the concentration necessary to affect bean plant growth and development decreased.     

Leaf epidermal characters related with plant's passive resistance to pathogens vary among accessions of wild beans Phaseolus vulgaris var. aborigineus (Leguminosae–Phaseoleae)

We report here whether accessions of Phaseolus vulgaris var. aborigineus, collected from the southernmost part of the Andean domestication center of common bean, presented differences among leaf epidermal characters. Epidermal microcharacters such as deposition of wax crystalloids, cuticle thickness, trichome types, size and density, stomata types and size, stomatal density and index were examined on the surface of 66 leaves of 11 accessions of P. vulgaris var. aborigineus by means of light and scanning electron microscopy. Unlike the leaves of cultivated beans, those of P. vulgaris var. aborigineus were hypostomatous. Among epidermal characters only the stomatal density, stomatal index, and the number of trichomes on the abaxial leaf epidermis were different between bean accessions. The stomatal density and index of the accessions were inversely related to the altitude of the area of the wild bean collection. This is the first report describing the presence of diversity among epidermal characters (e.g. hypostomatous leaves) in P. vulgaris var. aborigineus that might contribute to plant resistance to pathogens.     

Magnesium deficiency in expanding leaves of Phaseolus vulgaris-gas exchange and nutrient concentrations

Phaseolus vulgaris was cultured either with or without magnesium in an aerated nutrient solution in growth chambers from 21 days after germination. Five days after transfer to Mg-deficient nutrient solution, terminal leaflets of first trifoliate leaves stopped expansion. From the fifth day after transfer, the net assimilation rate, the transpiration rate and the leaf water vapour conductance of first trifoliate leaves of the deficient plants declined. Following resupply of Mg on the seventh day after transfer to the Mg-deficient solution, the assimilation rate increased to 93% by the 12th day, the transpiration rate to 76% and the leaf water vapour conductance to 50% of the control plants.     

COMPARATIVE ANATOMY OF SOME PARENTS AND HYBRIDS OF THE HAWAIIAN MADIINAE (ASTERACEAE)

Comparative leaf morphology and anatomy was examined in five species and four hybrids involving three genera of Hawaiian Madiinae (Asteraceae). The comparisons included Argyroxiphium grayanum, Dubautia ciliolata subsp. ciliolata, D. knudsenii subsp. knudsenii, D. scabra subsp. leiophylla, D. scabra subsp. scabra, and Wilkesia gymnoxiphium, and the hybrids A. grayanum × D. scabra subsp. leiophylla, D. ciliolata subsp. ciliolata × D. scabra subsp. scabra, D. knudsenii subsp. knudsenii × D. scabra subsp. leiophylla, and W. gymnoxiphium × D. scabra subsp. leiophylla. Foliar morphology, leaf tissue organization, and various characters of stomata and trichomes were compared, using epidermal peels, cross and paradermal sections, and clearings of leaves. Pronounced anatomical differences among these closely related taxa were characterized, and effects of hybridization on the expression of anatomical features were documented. Most comparisons of parents and hybrids revealed statistically significant differences in leaf size, distribution of adaxial and abaxial stomata, and marginal and surface trichomes. In most instances hybrids demonstrated intermediate status in their foliar characters, indicating that these features are inherited from both parents. However, differences in foliar characters were usually of sufficient magnitude to allow recognition of hybrids as well as parents.     

Stomatal Diffusion Resistance of Snap Beans. II. Effect of Light

The effect of light on the stomatal resistance of abaxial and adaxial leaf surfaces of snap beans (Phaseolus vulgaris L.) was studied in the growth chamber and in the field. The adaxial stomata required more light to open than the abaxial stomata; the abaxial stomatal apertures were still about 50% open at 1% full sunlight and light-induced closure was never observed under daytime field conditions. A given value of abaxial stomatal resistance was obtained at a given illumination of the abaxial guard cells whether illumination was adaxial or abaxial.     

Einfluss von Chlorcholinchlorid und Ethrel auf Zellteilung und Zellstreckung bei Primärblättern von Weizenkeimpflanzen

Both chlorcholinchloride and ethrel are used as growth retardants in cereal cultivation. Wheat seedlings were cultivated in nutrient solutions containing 10^-3M CCC, CEPA or 5 × 10^-4M CCC and CEPA, respectively. The epidermis of full-grown primary leaves was analysed. CCC relatively equally decreases the length of leaves and long epidermal cells, whereas CEPA mainly inhibits cell division. Leaf growth is always a little more inhibited than the number of stomata and trichomes is reduced by CCC or CEPA. This results in an increased frequency of stomata and trichomes by about 14 to 16 per cent. This means that retardants can strongly influence the length of leaves and the length or number of long epidermal cells but, due to the mechanism of programmed determination, the frequency of stomata and trichomes is kept constant within relatively narrow limits. Furthermore it can be concluded that long epidermal cells function as pace-makers in the growth of leaves of monocotyledonous plants.      

Patterns of leaf surface wetness for montane and subalpine plants

The frequency and duration of water on leaf surfaces have important consequences for plant growth and photosynthetic gas exchange. The objective of the present study was to compare the frequency and duration of leaf wetness under natural field conditions among species and to identify variation in structural features of leaves that may reduce surface wetness. During June–September 1992 in the central Rocky Mountains (USA), natural leaf wetting due to rain and dewfall was observed on 79 of 89 nights in open meadow habitats compared to only 29 of 89 nights in the understorey. Dew formation occurred at relative humidities that were often well below 100% because of radiational heat exchange with cold night skies and low wind speeds (< 0.5 m s^?1). A survey of 50 subalpine/montane species showed that structural characteristics associated with the occurrence and duration of leaf surface wetness differed among species and habitats. Both adaxial and abaxial surfaces accumulated moisture during rain and dewfall events. Leaf surfaces of open-meadow species were less wettable (P= 0.008), and had lower droplet retention (P= 0.015) and more stomata P= 0.017) than adjacent understorey species. Also, leaf trichomes reduced the area of leaf surface covered by moisture. Ecophysiological importance is suggested by the high frequency of leaf wetting events in open microsites, influences on growth and gas exchange, and correspondence between leaf surface wettability and habitat.     

Comparative leaf anatomy of Salix species and hybrids

Epidermal features, mesophyll differentiation and calcium oxalate characteristics of 19 species and 12 hybrids of Salix are described. The species and hybrids can be distinguished by the presence or absence of the following epidermal features: striated cuticle; stomata; covering trichomes; beaded anticlinal walls, and diosmin-like njstals. In or near marginal teeth, glandular trichomes are present in all cases. The leaf veins of all specimens examined have calcium oxalate prism sheaths and, with the exception of S. herbacea , cluster crystals in some cells of the mesophyll. Most sprcies studied in the subgenus Salix show: both adaxial and abaxial stomata; striated cuticle metopllyll of palisade cells, with little or no spongy mesophyll, but with a well-defined hypodermis, and absence of thick-walled, sinuous trichomes. Characteristic features of the subgenus Caprisalix are: abaxial stomata only; epidermal crystals; smooth cuticle; mesophyll diflerentiated into palisade cells and spongy mesophyll and without a hypodermis, and trichomes more numerous and varied than those of the subgenus Salix . Leaves of the two species of the subgenus Chaemelia examined and those of S. lapponum , have predominantly anomocytic stomata, whereas all the other leaves studied have predominantly paracytic stomata. The anatomical features described, in conjunction with the morphologiral characters, enable the species and hybrids of Salix studied to be autheenticated.     

Differences in histological and physiological traits of ozone sensitive and resistant bean strains

An examination of possible histological causes of differences in ozone sensitivity between ozone sensitive (R123) and resistant (S156) Phaseolus vulgaris strains was carried out. A distinction between the causes and effects of ozone sensitivity was also performed. We studied several morphological and histological traits, which included stomata number and size and also looked at different cell characteristics, such as stomatal index; leaf tissue thickness, fraction and gaseous conductance of intercellular air spaces. Together with this, we made gas-exchange measurements and found inner CO₂ levels to be higher in the ozone sensitive strain. We also found several quantitative morphological parameters between the two strains to be initially different, however, these differences changed after exposure to summer climate and ozone. Stomatal function between the two strains was also differently altered by the pollutant, which was apparent from differences in stomatal openness when investigated in summer. According to our histological data, epidermal cells of the ozone sensitive strain grew larger on leaves that developed after exposure to cumulative considerable phytotoxic ozone doses; moderately decreasing the number of stomata and epidermal cells per mm² epidermal area despite the originally higher number of epidermal cells in sensitive plants. Cross sections of injured sensitive leaves revealed disorganisation of mesophyllum tissues.     

Comparative morphology of the leaf epidermis in the genera Codonanthe (Martius) Hanstein and Nematanthus Schrader (Gesneriaceae)*

The leaf epidermis of 14 species ofCodonanthe and 10 species of Nematanthus has been examined. Species of Codonanthe section Codonanthe are geographically restricted to south-eastern Brazil, and are diploid. They possess multicellular-uniseriate nonglandular trichomes, glandular trichomes with a four-celled head and a short body, anisocytic stomata and lack extrafloral nectaries. Species of Codonanthe section Spathuliformae and Codonanthe subgenus Codonanthella are distributed from southern Mexico through Central America to north-western South America and are tetraploid. They possess unicellular non-glandular trichomes (except C. caribaea), glandular trichomes with a two-celled head (except C. caribaea) and a short body, anisocytic stomata and extrafloral nectaries (except C. caribaea). All Nematanthus species are distributed in south-eastern Brazil and are diploid (N=8). Six species of Nematanthus consistently have multicellular-uniseriate nonglandular trichomes, glandular trichomes with a four-celled head and a short (unicellular) or long (multicellular) body, anisocytic stomata and lack extrafloral nectaries. Four species of Nematanthus have multicellular-uniseriate non-glandular trichomes, glandular trichomes with a head of more than four cells and a short body, anisocytic and helicocytic stomata and lack extrafloral nectaries.     

Proton excretion and cell expansion in bean leaves

Light-induced expansion of Phaseolus vulgaris L. leaf cells is accompanied by increased cell-wall plasticity. The possibility that leaf-cell walls are loosened by excreted protons has been investigated. First, light causes acidification, detected at the leaf surface, within 5–15 min. Growth starts 10–20 min after exposure to light. Second, exogenous acid induces loosening of isolated leaf cell walls. Third, infiltration of the tissue with a neutral buffer inhibits light-induced growth. Fourth, fusicoccin stimulates growth of as well as H⁺ excretion by bean leaf cells, without light. These findings show that the acid-growth theory is applicable to light-induced growth of leaf cells, and indicate that light-induced proton excretion initiates cell enlargement in leaves.Abbreviations FC fusicoccin - RL red light - WEx wall extensibility - WL white light     

Changes in mesophyll anatomy and sink–source relationships during leaf development in Quercus glauca, an evergreen tree showing delayed leaf greening

Changes in mesophyll anatomy, gas exchange, and the amounts of nitrogen and cell wall constituents including cellulose, hemicellulose and lignin during leaf development were studied in an evergreen broad‐leaved tree, Quercus glauca, and in an annual herb, Phaseolus vulgaris. The number of chloroplasts per whole leaf in P. vulgaris increased and attained the maximal level around 10 d before full leaf area expansion (FLE), whereas it continued to increase even after FLE in Q. glauca. The increase in the number of palisade tissue cells per whole leaf continued until a few days before FLE in Q. glauca, but it had almost ceased by 10 d before FLE in P. vulgaris. The radius and height of palisade tissue cells in Q. glauca, attained their maximal levels at around FLE whereas the thickness of the mesophyll cell wall and concentrations of the cell wall constituents increased markedly after FLE. These results clearly indicated that, in Q. glauca, chloroplast development proceeded in parallel with the cell wall thickening well after completion of the mesophyll cell division and cell enlargement. The sink–source transition, defined to be the time when the increase in daily carbon exchange rate exceeds the daily increase in leaf carbon content, occurred before FLE in P. vulgaris but after FLE in Q. glauca. During leaf area expansion, the maximum daily increase in nitrogen content on a whole leaf basis (the maximum leaf areas were corrected to be identical for these species) in Q. glauca was similar to that in P. vulgaris. In Q. glauca, however, more than 70% of nitrogen in the mature leaf was invested during its sink phase, whereas in P. vulgaris it was 50%. These results suggest that Q. glauca invests nitrogen for cell division for a considerable period and for chloroplast development during the later stages. We conclude that the competition for nitrogen between cell division and chloroplast development in the area of expanding leaves can explain different greening patterns among plant species.