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Svoboda V. Pennisi and Dennis McConnell

Variegated Dracaena sanderana plants were grown under 47%, 63%, 80%, and 91% shade cloth. Prior to that, plants were grown under uniform light levels in a greenhouse. Morphological changes which manifested the adaptation to different light levels were not evident until all four leaves present in the apical whorl had expanded. Changes first appeared in a leaf which was 5-15 mm long when plants were placed under the different shade levels. The changes were recognized as alteration in the amount of leaf variegation which gradually changed as new leaves unfolded. After development of four leaves no further morphological changes were apparent. The first `transition' leaf had variegation similar to the preceding leaf and the last `transition' leaf had variegation comparable to the next successive leaf. The amount of variegation was quantified and the changes under different light levels determined. The use of a variegated plant enabled us to readily observe the morphological changes related to light adaptation and showed that a plant is an integrated system which adapts to altered environment over an extended period of time.

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Svoboda V. Pennisi and Dennis B. McConnell

Dracaena sanderana `Ribbon' plants were grown under 47%, 63%, 80%, and 91% shade. After 15 weeks of growth, plants exhibited marked changes in various morphological features. In order to precisely compare leaves of plants grown under different light levels the Plastochron Index (PI) of Erickson and Mickelini (1957) was used. The plastochron was defined in terms of leaf length. Various leaf morphological characteristics were examined and correlated with 1) actual leaf numbers, and 2) with leaf developmental age. A comparison between the two methods 1) and 2) revealed that overall trends displayed by leaves with a Leaf Plastochron Index (LPI) from 12 to 2 were similar to the same trends linked to actual leaf numbers. However, leaves with LPIs lower than 2 showed that under 80% and 91% shade these leaves had higher values for all studied parameters. Comparable leaves of plants in 91% shade had consistently higher values of the leaf parameters compared to plants in other shade treatments. The use of the PI enabled us to accurately compare morphological differences between plants grown under diverse light conditions.

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Svoboda V. Pennisi and Marc W. van Iersel

Interiorscape plants have many documented benefits, but their potential for carbon sequestration is not clear. This study was undertaken to quantify the amount of carbon assimilation under growth chamber conditions designed to mimic the photosynthetic photon flux (PPF) levels and temperatures of typical indoor environments and to quantify the amount of carbon assimilation in situ in a representative interiorscape composed of a variety of plant species and sizes. Quantitative data were obtained in 1) growth chambers with a typical range of PPF levels encountered indoors (≈10, 20, and 30 μmol·m−2·s−1); and 2) in situ conditions in an interiorscape. Under growth chamber conditions, most species exhibited positive dry mass accumulation and carbon sequestration but Sanseveria and Dracaena ‘Janet Craig’ exhibited consistent dry mass loss throughout the 10 weeks under simulated conditions. Carbon content was lower in herbaceous species (e.g., Scindapsus aureus, 38% of dry mass) compared with woody ones (e.g., Ficus benjamina, 43%). PPF-saturated net photosynthetic rates of plants were low, ranging from 3.4 to 7.0 μmol·m−2·s−1, whereas their light compensation points ranged from 8 to 78 μmol·m−2·s−1. In situ, plants exhibited varying dry mass gain, largely dependent on size. In general, a large plant and/or species with a higher amount of woody tissue in their above- or belowground organs (e.g., 4.6 m high arboreal plant) sequestered more carbon than small and/or herbaceous species. This study is the first to provide quantitative data of carbon sequestration in interiorscape environments.

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Svoboda V. Pennisi and Dennis B. McConnell

Detection of cuticular crystals in the 14 species of Dracaena examined indicated that they are probably ubiquitous throughout the genus and may permit rapid separation of dracaenas from plants with similar leaves such as the cordylines (Cordyline sp.). Dracaena species of the dragon tree group deposit the greatest quantity of uniformly small cuticular crystals. However, the distinction between individual species within this grouping, based solely on crystal numbers and size, is not sufficient for taxonomic separation. All other species of Dracaena studied did display species-specific quantities and sizes of cuticular crystals. This, in combination with characteristics of the leaf epidermis, could serve as part of a taxonomic key to the genus.

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Svoboda V. Pennisi and Dennis B. McConnell

The effect of 0, 3, and 7 mm Ca2+ on the allocation and deposition of Ca2+ into intracellular and sub-cuticular periplasmic calcium oxalate (CO) crystals was examined in leaf primordia of rooted cuttings of Dracaena sanderiana Hort. Sander ex M.T. Mast. Crystal development was monitored in two types of cuttings, those rooted in deionized water for 18 months and those rooted in Metro Mix 500 for 6 weeks. Response differed remarkably depending on the type of cutting. Cuttings rooted in deionized water deposited sub-cuticular crystals at the expense of intracellular crystals (raphides). The number of sub-cuticular crystals in leaf primordia of cuttings rooted in deionized water grown in solutions supplemented with either 0, 3, or 7 mm Ca2+ was similar, but crystals were considerably smaller in plants grown in 0 mm Ca2+. Sub-cuticular crystals appeared developmentally earlier in leaf primordia of all cuttings grown in either 3 mm or 7 mm Ca2+ than in cuttings rooted in deionized water grown in 0 mm Ca2+. This finding supports the premise that deposition of sub-cuticular crystals is modulated by Ca2+ levels and could be induced at an earlier ontogenetical stage by raising rhizospheric Ca2+ levels or delayed by lowering rhizospheric Ca2+ levels. The total number of sub-cuticular crystals per epidermal cell did not differ significantly between treatments implying that crystal nucleation sites are predetermined and finite in number. In contrast, the formation of intracellular raphides was highly variable and depended on Ca2+ concentrations. In terms of Ca2+ prioritization, sub-cuticular CO crystals took precedence over intracellular CO raphides.

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Dennis B. McConnell, Jennifer C. Bradley and Svoboda V. Pennisi

In 1975, the Environmental Horticulture Dept. initiated a work experience program. Students who work full time for an environmental firm of institution may register for ORH 4941 Practical Work Experience. Although ORH 4941 was not required, 241 students participated in the program during the 22 years when it was an elective course. In 1998, the departmental education committee changed the status of ORH 4941 from an elective to a required course. The objectives of this study were to determine if any differences have occurred since the status of the course has changed. The following were examined: 1) selected student characteristics (GPA, gender, age, etc.), 2) employing firms participating in the work experience program, and 3) required administrative procedures.

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Amy L. Burton, Svoboda V. Pennisi and Marc W. van Iersel

Excessive internode elongation and leaf senescence are common problems with foliage plants transferred to interiorscapes. The authors’ objective was to determine whether plant growth regulators applied late in the production cycle could control growth during production and improve interiorscape performance. In addition, the authors wanted to quantify the effect of irradiance on growth and morphology during the production phase and in the interiorscape. Geogenanthus undatus C. Koch & Linden ‘Inca’ plants were grown under one of two photosynthetic photon fluxes (PPF; 50 or 130 μmol·m−2·s−1), and were treated with either α−(methylethyl)-α-[4-(trifluoromethoxy)phenyl]-5-pyrimidinemethanol (flurprimidol) or α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidinemethanol (ancymidol) during the week 12 production, at 0.5, 1.0, or 1.5 mg/pot of active ingredient. The high PPF resulted in significantly higher leaf, stem, root, and total dry weight, and leaf area, but lower leaf area ratio (leaf area divided by total plant dry weight) compared with the low PPF. After production, plants were placed in a simulated interior environment for 4 months under a PPF of 15 μmol·m−2·s−1 and a photoperiod of 12 hours/day. Production PPF did not affect most growth parameters after 4 months in the interior environment, except for the root-to-shoot ratio. Under low-production PPF, root-to-shoot ratios were lower than under high-production PPF. For both growth regulators, the height and growth indexes were lower than for control plants, but flurprimidol offered greater control than ancymidol. Flurprimidol-treated plants had lower root dry weight and root-to-shoot ratios compared with ancymidol-treated and control plants. Applications of ancymidol or flurprimidol administered to G. undatus C. Koch & Linden ‘Inca’ late during the production cycle resulted in significant growth control and, therefore, superior plant performance throughout the postharvest period.

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Svoboda V. Pennisi, Dennis B. McConnell and Michael E. Kane

We induced preferential allocation of Ca to two calcium oxalate (CO) sinks in immature leaf tissues of D. sanderiana: subepidermal extracellular deposits and intracellular raphides. Allocation was affected by exogenous Ca levels. Two groups of rooted cuttings were termed Ca-deficient and non-deficient. The first group consisted of cuttings that had been deprived of Ca for 18 months, and, the second, cuttings rooted under standard horticultural conditions. All plants were grown in liquid medium supplemented with 100 ppm of potassium nitrate and subjected to 0, 3, or 7mm Ca from calcium acetate. The most striking feature of Ca-deficient plants grown in 0 mm Ca was the absence of intracellular raphides in the leaf primordia. The largest number of intracellular raphides developed in Ca-deficient plants grown in 7 mm Ca. The number of extracellular crystals in Ca-deficient plants grown in Ca-supplemented solutions versus non-supplemented were similar, but crystals were considerably smaller in non-supplemented plants. Total number of extracellular crystals per epidermal cell did not differ significantly between plants in all treatments. This implies that nucleation sites are pre-determined and finite in number. In contrast, the number of intracellular raphides was highly variable. In terms of Ca prioritization, the extracellular crystals took precedence over intracellular raphides, and this was most obvious in Ca-deficient plants. The significance of this research is that the extracellular crystals represent Ca sinks with limited induction capacity compared to intracellular Ca sinks. Plants with genetic predisposition for intracellular CO crystal formation may be able to respond favorably to root environments with low Ca levels compared to species with limited capacity for intracellular CO deposition. Intracellular CO crystals, therefore, play an integral role in plant nutrition as Ca storage sinks.

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Svoboda V. Pennisi, Marc W. van Iersel and Stephanie E. Burnett

The growth of three english ivy cultivars in ebb-and-flow subirrigation systems was examined under three photosynthetic photon flux (PPF) treatments (low, medium, or high, corresponding to an average daily PPF of 3.2, 5.4, or 8.5 mol·m–2·d–1, respectively) and four fertilizer concentrations (0, 100, 200, or 300 mg·L–1 N) geared toward production of acclimatized foliage plants. Marketable quality english ivy can be subirrigated with 100 mg·L–1 N. Although 8.5 mol.m–2.d–1 produced the maximum shoot dry weight (SDW), good quality plants also were produced under 5.4 mol·m–2·d–1. `Gold Child', `Gold Dust', and `Gold Heart' english ivy produced with low fertility and low light may be better acclimatized and show superior performance in interior environments. Under light levels lower than 8.5 mol·m–2·d–1, `Gold Heart' had less variegation (12% or 21% for ivy grown under 3.2 or 5.4 mol·m–2·d–1, respectively). `Gold Dust' and `Gold Child' had 65% and 22% variegated leaf area, respectively, when grown under 5.4 mol·m–2·d–1 PPF. Under 5.4 mol·m–2·d–1 PPF, `Gold Dust' retains attractive foliage with overall perception of increased lighter-green coloration.

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Svoboda V. Pennisi, Dennis B. McConnell and Richard W. Henley

Detailed anatomical observations of the dorsal gland and its development in Ficus benjamina L. (Weeping Fig) leaves are reported. The dark spot on the abaxial surface of Ficus benjamina leaves is a normal morphological feature of the species. It is a highly specialized modified epidermal layer. An investigation of six commercially available cultivars revealed all possessed a glandular dorsal epidermis but not all developed a pigmented gland. The variability in gland thickness suggests that differences exist between cultivars. Based on histochemical tests, we propose that the term “phenolic gland” be substituted for the term “wax gland” found in the literature, as all tests indicated the presence of polyphenols in the glandular epithelium of F. benjamina leaves.