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Open access

James R. Carpenter and Cary A. Mitchell

Abstract

Effects of cyanide (as KCN) and/or salicylhydroxamic acid (SHAM) on respiratory rates (QO2) of excised tree roots were evaluated before and after flooding intact plants. CN, an inhibitor of cytochrome oxidase, stimulated QO2 in flood-intolerant sugar maple (Acer saccharum Marsh.) and Japanese yew (Taxus cuspidata Sieb. and Zucc.), but not in flood-tolerant red maple (Acer rub rum L.), and inhibited QO2 in very flood-tolerant baldcypress (Taxodium distichum (L.) Rich). Eight days of flooding eliminated CN-stimulation of QO2 in sugar maple. SHAM, an inhibitor of the alternative oxidase, had little effect on QO2 of any species when used alone, but greatly inhibited QO2 of all species when combined with KCN, indicating the presence of substantial amounts of both respiratory pathways in flood-tolerant and intolerant species, as well as the ability of electrons to flow from one pathway to another when one is blocked by a specific inhibitor. Flooding reduced root respiration capacity in all species, affecting intolerant species the most and tolerant the least. The exception was QO2 of dormant Taxus roots, which was not inhibited by flooding. CN-sensitive QO2 was lost from roots of intolerant species in particular, and to a lesser extent from more tolerant species. A limiting leveL of O2 (0.5%) suppressed SHAM-sensitive QO2 more than CN-sensitive QO2 indicating a greater affinity for O2 by the CN-sensitive path-way. The evidence is consistent with a model for relative flood tolerance based upon differential damage to the aerobic respiratory mechanism.

Free access

Manijeh Mohammadi-Dehcheshmeh, Ahmad Khalighi, Esmaeil Ebrahimie, Manoochehr Sardari, and Rohangiz Naderi

Wild populations of Fritillaria sp. have dramatically decreased in Iran because of pest overflow and continual grazing. Previous studies have shown that Fritillaria cannot rapidly and efficiently propagate by traditional methods. In vitro tissue culture techniques have shown high potential for micropropagation of endangered plants. The use of bulb-scale pieces for tissue culture can result in the destruction of the endangered parent plant. Fritillaria is a heterozygous plant in which the genetic content of each embryo is different from others, even on the same plant. In this study, mature embryos of F. imperialis and F. persica were used as explant for the first time. Embryos were extracted from seeds and cultured on B5 medium supplemented with various combinations of BAP (0, 0.1, 1 mg/L), NAA (0, 0.4, 4 mg/L), and IAA (0, 0.4, 4 mg/L). Embryo explant showed low genotype dependency between different heterogenous and heterozygote populations of both F. imperialis and F. persica. The best response of bulblet regeneration in both F. imperialis and F. persica was obtained from 1 mg/L BAP + 0.4 mg/L NAA+4 mg/L IAA and direct organogenesis pathway, with 15 bulblets per explant for F. imperialia and 20 for F. persica. Because of the large number of embryos in a plant and their different genetic contents, established in vitro propagation by using embryo explant in this study can provide broad genetic resources and variations. As explained above, in vitro protocols can play a major role in rescuing F. imperialis and F. persica from extinction.

Free access

Gary W. Stutte

The use of light-emitting diodes (LEDs) to support plant growth is a radical departure from use of gas-discharge lamps, which were developed in mid-19th and widely adopted by the industry during the 20th century. Initial investigation by the National Aeronautics and Space Administration (NASA) in the late 1980s on the use of LEDs to grow plant in space is resulting in an industry-wide transition from gas discharge to solid-state lighting systems. This global transformation is given urgency by national policies to reduce energy consumption and being facilitated by ready access to information on LEDs. The combination of research, government policy, and information technology has resulted in an exponential increase in research into the use and application of LED technology in horticulture. Commercial horticulture has identified the opportunities provided by LEDs to optimize light spectra to promote growth, regulate morphology, increase nutrient content, and reduce operating costs. LED-light technology is enabling the development of innovative lighting systems, and is being incorporated into large-scale plant factories for the production of edible, ornamental, and medicinal plants. An overview of prevalence of readily accessible information on LEDs and implications for future adoption in horticulture is discussed.

Free access

Hirofumi Terai, Hironobu Tsuchida, and Masashi Mizuno

Green fruits of normal ripening type of tomatoes (Lycopersicon esculentum Mill) were picked 13-39 days after anthesis and stored at 20°C. Although more days were required for the ripening of the fruits if the stage of picking was earlier, all fruits became red and soft during storage. This result shows that considerably immature fruits have the ability of ripening. Green tomato fruits at three stages (18. 29 and 38 days after anthesis) were treated with ethylene for one day. The activity of ethylene forming enzyme (EFE) and the conversion of applied 1-aminocyclopropane-1-carboxylic acid (ACC) to N-malonyl-ACC (MACC) in the three stages of tomato fruits were accelerated by exogenous ethylene, though endogenous ethylene production was hardly observed. When the green tomato fruits (31-34 days after anthesis) were treated with ethylene for one day and then transferred to air. the activity of EFE and the conversion of applied ACC to MACC were depressed. The activity of ACC synthase was not accelerated by ethylene treatment of only one day, but was accelerated by a longer term treatment, followed by increased ethylene production and the onset of ripening.

Free access

Thomas H. Boyle

Allotetraploid Z. angustifolia × Z. elegans hybrids (2 n =46) were reciprocally backcrossed to Z. angustifolia (2 n = 22 or 44) and Z. elegans (2 n = 24 or 48). Pollen germination and pollen tube penetration of the stigmatic surface were observed for all 8 cross combinations. At 14 days after pollination, the percentage of florets with embryos ranged from 0 to 69%, and some hybrid embryos exhibited developmental abnormalities. Seed-propagated backcross (BC1) populations were generated with Z. angustifolia (2 n =44)as ♀ or ♂, and Z. elegans (2 n =48) as ♀ BC1 progeny from these 3 crosses demonstrated low to high levels of resistance to bacterial leaf and flower spot (incited by Xanthomonas campestris pv. zinniae) and high levels of resistance to powdery mildew (incited by Erysiphe cichoracearum). BC1 hybrids derived from crossing allotetraploid hybrids as ♀ and Z. elegans (2 n =48) lines have commercial potential as disease-resistant, flowering annuals.

Open access

Patricia Tolson Tomlinson and Carol J. Lovatt

Abstract

Changes in the capacity of ‘Washington’ navel orange [Citrus sinensis (L.) Osbeck] fruit to synthesize (de novo or by salvage) pyrimidine nucleotides, but not purine nucleotides, appears to be related to the stage of fruit development. De novo pyrimidine synthesis in whole-fruit tissue increased 6-fold during Stage I of development (cell division phase), from 10 nmol [14C]bicarbonate incorporated into uridine nucleotides during 5 hr per g dry weight whole-fruit tissue from ovaries harvested at flower petal drop to 57 nmol for 2-month-old fruit. Capacity of peel tissue to synthesize pyrimidine nucleotides de novo decreased following completion of Stage I, from 43 nmol [14C]bicarbonate incorporated into uridine nucleotides during 5 hr per g dry weight of peel tissue from 2-month-old fruit to 11 nmol for 5-month-old (Stage II) fruit. This decrease was not offset by increased salvage of uridine. Capacity of whole-fruit tissue to synthesize purines de novo increased 3-fold during Stage I. Synthetic capacity of peel tissue from Stage I fruit was half that observed for whole-fruit tissue and did not decrease significantly during Stages II (cell enlargement phase) and III (maturation phase). These observations suggest purine synthetic capacity may not be related to stage of development. Changes in protein or glucose contents, or respiratory activity of peel tissue, could not account for the observed reduction in pyrimidine synthetic capacity. Thus, the reduction observed in synthetic activity was specific for pyrimidine nucleotides. The capacity of fast-growing, 1-month-old fruit (high potential to set) to synthesize or catabolize either pyrimidine or purine nucleotides did not differ from that of slow-growing fruit (low potential to set), suggesting that nucleotide synthesis is not limiting to growth.

Open access

Jack W. Buxton and L. P. Stoltz

Abstract

A method is described for determining glucose metabolism by the C-6/C-1 ratio. After an initial lag period to allow for equilibration of labelled glucose, an increase of accumulated 14CO2 in rose petals was linear with time. By taking the limit of the ratio of the C-1 and C-6 lines, one can arrive at the C-6/C-1 ratio as a ratio of the slopes of the lines. The slope of each of the lines can be calculated with 2 determinations within a relatively short time period. This method reduces metabolic recycling of the glucose and other problems associated with the traditional method of determining the C-6/C-1 ratio.

Free access

D. Gerasopoulos and D.G. Richardson

Mature `Anjou' pears (Pyrus communis L.) continuously stored at 20 °C or -1 °C before transfer to 20 °C exhibited differences in the sequence of ripening events up to 100 days. Pears continuously held at 20 °C showed little change in ripening characteristics (chlorophyll, firmness, titratable acidity) for 14 to 28 days, then these characteristics decreased at a daily rate of 1.4% thereafter. A 40% increase in soluble polyuronides paralleled the firmness loss, while ACC did not exceed 0.5 nmol·g-1 until the 84th day, and internal ethylene did not exceed 0.2 μL·L-1 until after 90 days, whereas ACC oxidase activity (and total protein) peaked after 63 days. `Anjou' pears stored at -1 °C showed no changes in chlorophyll, firmness, protein, or total polyuronides for at least 84 d. Despite essentially no change in firmness during -1 °C storage, there was a slow but steady increase (≈15 %) in soluble polyuronides. ACC oxidase activity, expressed as ethylene production, rose to 71 nL·g-1·h-1 and the ACC content increased to almost 1.0 nmol·g-1 by the 84th day. Internal ethylene slowly increased and levelled to 1 μL·L-1 by the 56th day. Satisfaction of a chilling requirement thus appears to favor the development of ethylene synthesis capacity, which on transfer from cold storage to higher temperatures results in enough internal ethylene to rapidly drive the associated ripening mechanisms. Fruit for which the chilling requirement (≥70 days at -1 °C) was met softened in response to accelerated internal ethylene production on transfer to 20 °C for 7 days. However, pears that were not chilled or partially chilled did not sustain the increased ACC levels or ACC oxidase activity. Chemical name used: 1-aminocyclopropane-1-carboxylate (ACC).