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C.P. Sharma and Sandhya Singh

When grown in refined sand with one-twentieth normal K supply, cauliflower (Brassica oleracea L. var. botrytis L. cv. Pusi) had lower dry matter and tissue concentration of K than the controls and developed visible symptoms characteristic of K deficiency. In K-deficient plants, the specific leaf weight, diffusive resistance, and proline concentration in leaves were significantly higher and relative water content (RWC), leaf water otential (ψ), stomatal aperture, stomatal density, and transpiration rate were significantly lower than in control plants. When K-deficient plants were supplied additional Na to the extent K was deficient, Na concentration in the plants increased and the plants recovered from the K deficiency effect on free proline concentration, RWC, leaf water potential, stomatal aperture, stomatal density, specific leaf weight, diffusive resistance, and transpiration.

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R.L. Green, S.I. Sifers, C.E. Atkins, and J.B. Beard

We compared evapotranspiration (ET) rates for 11 Zoysia genotypes, encompassing two species and their hybrid, maintained at nonlimiting soil moisture under field conditions and in an environmental chamber of high evaporative potential. ET rate relationships to leaf area [leaf extension rate (LER)], canopy resistance [shoot density (SHD)], and internal resistance [abaxial (AB) and adaxial (AD) leaf blade stomatal densities] characteristics were determined. Three-year ET rate means were not significantly different among genotypes in the field study, but ET rates among genotypes differed significantly under the higher evaporative potential of an environmental-chamber study. ET rate was not significantly correlated with LER for either the data from the field or the chamber. ET rates of both types of tests also were not significantly correlated with SHD or AB or AD leaf blade stomatal density. Data from field and environmental-chamber research suggest that differences of individual morphological traits among the 11 zoysiagrasses do not influence the ET rate when measured from minilysimeters maintained at nonlimiting soil moisture.

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Paul W. Foote, J. Scott Cameron, and Stephen F. Klauer

Leaf-area based CO2 assimilation rate (ALA as an Indicator of genotypic differences in photosynthetic capacity is questioned on the basis of correlations found between ALA and specific leaf weight and small leaf size. To address this question of photosynthetic apparatus concentration In F. chiloensis genotypes differing significantly in ALA, visual image analysis software was used to quantify a number of leaf anatomy parameters. In 1991 and 1992, after gas exchange measurements in the field, leaf tissue was prepared In cross-sections and leaf clearings for light microscopy. Cross-sections were used to measure internal anatomical parameters and clearings for vein and stomatal densities.

Analysis of variance of 1991\92 measurements showed significant genotypic variation for leaf veination, leaf thickness, palisade cell length, cross-sectional area In mesophyll tissue and internal air space. Differences in stomatal density were observed in 1991. None of the anatomical parameters measured were correlated with ALA. This suggests that the concentration of physical apparatus Is not the major source of variation In ALA among these eight genotypes.

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Madhulika Sagaram, Leonardo Lombardini, and Larry Grauke

An assessment of anatomical traits of pecan cultivars (`Pawnee', `Mohawk', and `Starking hardy giant') collected from three locations (Tifton, Ga.; Chetopa, Kans.; and Stillwater, Okla.) was conducted at Texas A&M University. The objective of the study was to provide an understanding of patterns of geographic variation within the natural range for anatomical (stomatal density, stomatal index, and epidermal cell density) traits. Microscopy using acetate casts was used as the means to investigate the patterns of variation in the epidermal characteristics of pecan leaf. `Starking hardy giant' had the greatest number of stomates/cm2 (46,229, 47,807, and 45,990 at Tifton, Chetopa, and Stillwater, respectively) while `Mohawk' had the least (37,397, 36,217, and 35,305). `Pawnee' had the greatest number of epidermal cells/cm2 (251,806, 250,098 and 254,883 at Tifton, Chetopa, and Stillwater, respectively) while `Starking hardy giant' had the least (141,699, 138,405, and 142,155). Differences in stomatal index were observed between the three cultivars at Tifton and Stillwater. No differences in stomatal index were observed between `Pawnee' and `Mohawk' at Chetopa. The study showed that stomatal density as well as epidermal cell density of all the tested cultivars were significantly different (P < 0.05) at a particular location but no differences were observed in a given cultivar grown at different locations.

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Robert M. Welker, Richard P. Marini, and Douglas G. Pfeiffer

White apple leafhopper (WALH; Typhlocyba pomaria McAtee) feeding damage on apple (Malus domestica Borkh.) leaves was examined with scanning and transmission electron microscopy. WALH created feeding holes in the (lower) abaxial epidermis, with no visible exterior evidence of cell injury to the adaxial (upper) epidermis. Feeding holes were located in areas of the leaf with high stomatal density and were near stomata. Groups of cells in the palisade layers were empty or contained coagulated cell contents. Adjacent, apparently noninjured, palisade cells contained an abundance of starch granules, possibly indicating that photoassimilate export was impaired. Spongy mesophyll cells abaxial to the feeding area were left intact as were the epidermal cells adaxial to the feeding area. External views of either epidermis and internal leaf views of injured cells indicated no cell wall collapse.

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Coye A. Balok and Rolston St. Hilaire

Identification of tree taxa that can thrive on reduced moisture regimes mandated by xeriscape programs of the southwest United States could be facilitated if responses to drought of those taxa are determined. Leaf water relations, plant development, and cuticular wax content of seven taxa maintained as well-irrigated controls or exposed to drought and irrigated based on evapotranspiration were studied. Leaf water potential of drought-stressed Fraxinus velutina Torr. (Arizona ash), Koelreuteria paniculata Laxm. (golden rain tree), Quercus macrocarpa Michx. (bur oak), and Quercus muehlenbergii Engelm. (chinkapin oak) were lower at predawn than the controls. Drought-stressed plants of F. velutina, K. paniculata, and Quercus lobata Née (California white oak) had more negative midday water potential than the control plants. Drought reduced stomatal conductance to as little as 17%, 23%, and 45% of controls in F. velutina, K. paniculata, and Q. macrocarpa, respectively. Drought-stressed plants of F. velutina, K. paniculata, Q. macrocarpa, and Q. muehlenbergii had reduced transpiration rates. Fraxinus velutina had both the highest net assimilation rate (NAR) and relative growth rate (RGR) regardless of irrigation treatment. Mean specific leaf weight (dry weight (DW) of a 1-cm2 leaf disc divided by the weight), trichome density, stomatal density, leaf thickness, and cuticular wax content varied among species but not between irrigation treatments. Leaves of Q. buckleyi Buckl. (Texas red oak) had one of the highest stomatal densities, and also had leaves which were among the waxiest, most dense, and thickest. Abaxial leaf surfaces of F. velutina were the most pubescent. Across species, drought led to lower ratios of leaf surface area to root DW, and leaf DW to root DW. Quercus buckleyi plants subjected to drought had the highest root to shoot DW ratio (3.1). The low relative growth rate of Q. buckleyi might limit widespread landscape use. However, Q. buckleyi may merit increased use in landscapes on a reduced moisture budget because of foliar traits, carbon allocation patterns, and the relative lack of impact of drought on plant tissue water relations.

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Susan L. Steinberg, Jayne M. Zajicek, and Marshall J. McFarland

Growth of potted hibiscus (Hibiscus rosa-sinensis L.) was limited either by pruning or by a soil drench of `uniconazole at 3.0 mg a.i. per pot. Both treatments changed the water use of hibiscus. Five days after treatment with uniconazole, plants showed reduced water use, an effect that became more pronounced with time. Water use of pruned plants was reduced immediately after pruning, but soon returned to the level of the control due to the rapid regeneration of leaf area. Pruned or chemically treated plants used 6% and 33% less water, respectively, than the control. Chemically treated plants had a smaller leaf area, and individual leaves had lower stomatal density, conductance, and transpiration rate than control plants. Under well-watered conditions, the sap flow rate in the main trunk of control or pruned plants was 120 to 160 g·h-1·m-2, nearly three times higher than the 40 to 70 g·h-1·m-2 measured in chemically treated plants. Liquid flow conductance through the main trunk or stem was slightly higher in chemically treated plants due to higher values of leaf water potential for a given sap flow rate. The capacitance per unit volume of individual leaves appeared to be lower in chemically treated than in control plants. There was also a trend toward lower water-use efficiency in uniconazole-treated plants. Chemical name used: (E)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-l-yl)-1-penten-3-ol (uniconazole).

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H. Biesinger, W.F. Campbell, T. Strickland, F.B. Salisbury, P.S. Hole, L. Gillespie, M. Levinskikh, and I. Ivanova

The objectives of this research were to mimic the gradient irradiances to which wheat (Triticum aestivum L. cv. SuperDwarf) plants were exposed aboard the Russian space station Mir, and to determine whether these irradiances inhibit growth and floral development. SuperDwarf wheat plants were exposed to irradiances of 20–40, 60–80, 100–120, and 140–180 (PPF = μmol·cm–2·s–1) and grown to maturity. Twenty plants were randomly selected from each irradiance level and chlorophyll, total leaf area, shoot biomass, and total soluble leaf and plasma membrane (PM) proteins were recorded. Irradiance at increasing levels of intensity increased the fresh biomass, leaf area, chlorophyll content, and the total soluble PM and leaf proteins of wheat tissue. There were significant differences between the abaxial and adaxial sides of the wheat leaves in stomatal density, stomatal index, stomatal length and width, and number of stomata along 1-mm length of leaf. These data may be uniquely valuable for further studies of relationships between chlorophyll content, photosynthetic rate, and productivity of wheat grown aboard the Russian space station Mir, space missions of long duration, or future manned space stations to generate oxygen, purify water, remove carbon dioxide, produce food and recycle waste materials. (Supported by NASA Grant NCC 2-831 and the Utah Agr. Expt. Station.)

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Nihal C. Rajapakse and John W. Kelly

Transpiration rates of chrysanthemum [Dendranthema ×grandiflorum (Ramat.) Kitamura] plants grown under spectral filters were evaluated as part of an investigation on using light quality to regulate plant growth. The 6% CuSO4·5H2O spectral filter reduced photosynthetic photon flux density in red (R) and far red (FR) wavelengths and increased the R: FR and blue (B): R ratios (B = 400 to 500 nm; R = 600 to 700 nm; FR = 700 to 800 nm) of transmitted light relative to the water (control) filter. After 28 days, cumulative water use of plants grown under CuSO4 filters was ≈37% less than that of control plants. Transpiration rates were similar among plants grown under CuSO4 and control filters when expressed as leaf area, a result suggesting that the reduced cumulative water loss was a result of smaller plant size. Plants grown under CuSO4 filters had slightly lower (10%) stomatal density than control plants. Light transmitted through CuSO4 filters did not alter the size of individual stomata; however, total number of stomata and total stomatal pore area per plant was ≈50% less in plants grown under CuSO4 filters than in those grown under control filters due to less leaf area. The results suggest that altering light quality may help reduce water use and fertilizer demands while controlling growth during greenhouse production.

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Thomas E. Marler, Bruce Schaffer, and Jonathan H. Crane

Growth and leaf physiology responses of container-grown `Arkin' carambola (Averrhoa carambola L.) trees to long-term exposure of ≈25%, ≈50%, or 100% sunlight were studied in four experiments in Guam and Florida. Shading increased rachis length and leaflet area, and decreased leaflet thickness. Shaded trees also had a more horizontal branch orientation. Shading reduced dark respiration (Rd) and light compensation and saturation points but increased chlorophyll concentration and N-use efficiency. Light-saturated net CO2 assimilation (A) was not affected by developmental light level. Trees in full sun had smaller total leaf area, canopy diameter, and shoot: root ratio and exhibited leaflet movement to avoid direct solar radiation. Also, trees grown in 100% sunlight had a more vertical branch orientation and greater stomatal density than shaded trees. The ratio of variable to maximum fluorescence (Fv/Fm) declined during midday in 100% sunlight trees. This pattern was accompanied by a midday suppression of A in 100% sunlight-grown trees in Guam. `Arkin' carambola trees exposed to ≈25%, ≈50%, or 100% sunlight for up to 39 weeks exhibited physiological and morphological adaptations that resulted in similar growth. These results indicate that carambola efficiently adapts to different developmental light intensities.