Search Results

You are looking at 1 - 10 of 21 items for :

  • Author or Editor: Richard J. Gladon x
  • HortScience x
Clear All Modify Search

Sowing germinated seeds for bedding plant production can decrease the production time and reduce profit losses from sporadically or poorly germinating seeds. Low concentrations of O2 have been used to control radicle length in Impatiens wallerana Hook. F., but only a brief exposure period could be used (12 to 24 h). The effects of prolonged exposures are unknown. Our first objective was to determine if impatiens seedlings could be acclimated to an extreme hypoxic environment by a preliminary exposure to a less severe hypoxic exposure. Our second objective was to determine the effects of longer-duration (greater than 24 h) treatments at low-O2 concentrations on hypocotyl and radicle length, abnormal seedling development, and subsequent plant growth and development. Our third objective was to provide a commercial recommendation of a low-oxygen treatment or treatments that could be used for temporary storage of unused germinated seeds. Germinated seeds were placed in various combinations of 0.5%, 1.0%, and 1.5% O2 for either 4 days (Expt. 1) or 3 days (Expt. 2) followed by 24 h in air to simulate shipping. Germinated seeds were less tolerant of 0.5% O2 than greater O2 concentrations, especially during the first 2 days of treatment, and more abnormal seedlings developed at 0.5% O2. Germinated seeds were more tolerant of 0.5% O2 during Days 3 and 4 of the treatment period or when days at 0.5% O2 were interspersed between days of 1.0% or 1.5% O2. This indicates that germinated impatiens seeds can tolerate extremely low-O2 for longer durations (greater than 24 h) when first acclimated to lower O2 concentrations. Treatment of 1.5% O2 for Days 1 and 2 followed by 0.5% O2 for Day 3 is recommended for commercial use. Hypocotyl and radicle length was controlled to 1 mm without development of abnormal seedlings. Fully grown plants from seedlings that received low-O2 treatments were not different from control plants with regards to hypocotyl and radicle length, percentage abnormal seedlings, and plant growth and quality, ensuring there were no long-term detrimental effects.

Free access

Methionine (MET) is considered the first committed precursor of ethylene (C2H4), and the pathway has been established as MET → S-adenosylmethionine (SAM) → 1-aminocyclopropane-1-carboxylic acid (ACC) → C2H4. It has been suggested that another pathway to C2H4 may exist, and this pathway has been labeled System II. Our objective was to evaluate several compounds as possible precursors of System II C2H4 production. `White Sim' carnations were placed continuously in 20 mM solutions of MET, ACC, δ-aminolevulinic acid, glutamic acid, α-ketoglutarate, or homocysteine. Deionized water was the control. C2H4 production from the entire flower was measured, and ACC in the basal portion of the petals was quantified. Flowers treated with ACC exhibited the greatest C2H4 production and accumulation of ACC. Homocysteine caused greater production of C2H4 and accumulated more ACC than MET and the other possible precursors. These results suggest that homocysteine may be involved in System II C2H4 production in senescing carnation petals.

Free access

Abstract

Evolution of endogenous ethylene (C2H4) increased in seed of apple (Malus domestica Borkh.) in a stepwise manner during 40 days of stratification. C2H4 evolution during culture of isolated embryos depended on the stratification stage. Cultured embryos of seeds stratified 0 to 30 days increased in C2H4 production immediately preceding germination, but embryos stratified 40 days showed a simultaneous rise in C2H4 production with germination. During embryo culture, C2H4 was produced by both embryonic axes and cotyledons. Application of (2-chloroethyl)phosphonic acid (ethephon) to the seed-stratification medium increased embryo germination. Trapping endogenously produced C2H4 with Hg(CIO4)2 during stratification did not affect embryo germination, but trapping it during culture of isolated embryos completely inhibited germination.

Open Access

Abstract

Ficus benjamina L. were subjected to 48 hr of polyethylene glycol (PEG)-induced water stress. Leaf abscission and concentrations of endogenous ethylene (C2H4) in the leaves were monitored. Leaf abscission began 24 to 48 hr after stress initiation, and most abscission occurred within the first 24 hr after water stress was relieved. PEG-stressed plants lost 35% to 47% of their leaves by 120 hr after the experiment was initiated. Older leaves abscised first and remained green throughout the abscission process. Endogenous C2H4 concentrations increased sharply and then declined during the first 6 hr of water stress. Endogenous C2H4 concentrations then increased gradually, and, by the time leaf abscission began, leaves contained 1.50 to 2.25 µl C2H4/liter.

Open Access

The ethylene biosynthetic pathway has been established as methionine (MET) to S-adenosylmethionine to 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene, and this pathway has been labeled System I. Another pathway to ethylene may exist during synthesis of massive amounts of ethylene, and this system has been labeled System II. Our objective was to evaluate the efficacy of several compounds as possible precursors of System II ethylene in ripening tomato fruit tissue. Discs of `Rutgers' tomato pericarp tissue at the mature green, pink, and red ripe stages were incubated continuously in 10, 25, or 40 mm solutions of MET, ACC, 5-aminolevulinic acid (ALA), homocysteine, glutamic acid (GLU), alpha-ketoglutarate, or citrate buffer (control). The ethylene production rate at 8-hour intervals during a 32-hour incubation period and free and conjugated ACC content at the end of the incubation period were quantified. Fruit discs at the mature green stage treated with MET and ACC exhibited increased ethylene production and increased free ACC content. These results confirmed the role of MET and ACC as the predominant precursors of ethylene during the early stages of fruit development in tomato (System I). At the pink stage (System II); however, ALA increased ethylene production by 75% and free ACC content by 46% over the control, and MET increased ethylene by 27% and free ACC content by 57% over the control. At the red ripe stage, ALA caused a 35% increase and GLU caused a 31% increase in ethylene production over the control. These results suggest that ALA and GLU may be metabolized to ethylene via an unknown pathway during tomato fruit ripening (System II).

Free access

Abstract

Once-over harvested bud-cut chrysanthemums, Chrysanthemum morifolium Ramat., were opened in solutions of 8-hydroxyquinoline citrate (8-HQC) and/or sucrose. Flowers opened in solutions containing 2 or 4% sucrose and 200 ppm 8-HQC were comparable to or better than control flowers which matured in the greenhouse. Flower shape was influenced by the length of time in solution and solution constituents. Flowers harvested at a minimum of 50 mm diameter developed to 125 mm in 5 to 7 days while the greatest increase in inflorescence height took place between days 7 and 14. Flowers opened in solution did not have a longer vase life than control flowers allowed to develop in the greenhouse.

Open Access

Abstract

Methods of chloroplast pigment extraction and sample preparation previously established for leaves do not apply for fruits and other organs of several horticultural crops. Methods presented in this report overcome these difficulties, and results presented show this procedure can be used for several diverse horticultural crops. A high performance liquid chromatography (HPLC) run time of 25 minutes in the isocratic mode gave baseline separation of chlorophyll a (chl a), chlorophyll b (chl b), and β-carotene while neoxanthin, violaxanthin, and lutein eluted as partially resolved peaks. A run time of 48 minutes in the linear gradient mode gives baseline separation of all 6 major chloroplast pigments.

Open Access

Our recent research has focused on the control of genes and enzymes involved with the synthesis of chlorophyll, especially as it relates to tomato fruit development and ripening. Glutamate-1-semialdehyde-2,1-aminomutase (GSAAM) is one of the first committed enzymes in the chlorophyll biosynthetic pathway, and it is one of three enzymes that catalyze the conversion of glutamate into 5-aminolevulinic acid. We have isolated a full-length cDNA clone of GSAAM from a tomato fruit library. The tomato primary sequence shows extensive homology to GSAAM sequences found in other plant species. The primary structure also predicts a 46.7-kDa, 437-amino acid, mature protein and a transit peptide of 44 amino acids. Southern analysis indicated that GSAAM was present as a single copy. Northern blot analysis showed that GSAAM was expressed differentially in various tomato organs and that GSAAM transcripts decreased with increased fruit age. Immunoblot analysis also indicated that GSAAM protein decreased dramatically with increased fruit age. These results show that there is developmental regulation of the expression of GSAAM in tomato fruits.

Free access

Due to apparent participation of plant lipoxygenases (LOXs) in the biosynthetic pathways for jasmonic acid, methyl jasmonate, traumatin, and several C-6 volatile compounds, LOXs are believed to have a role in senescence, plant growth and development, and wound- and pathogen-induced defense responses. Multiple functions that are ascribed to this enzyme family are in accordance with the heterogeneity of LOX isozyme forms. It is possible that different LOX isoforms may be involved in different physiological processes. In our search for a gene that encodes a LOX isozyme form specifically involved in potato defense responses against pests and pathogens, we have screened an abscisic acid-induced potato leaf cDNA library, and we have isolated, sequenced, and characterized a cDNA clone that we have designated POTLX-3. The high sequence homology of our cDNA clone to other reported plant LOX genes provided evidence that POTLX-3 is a lipoxygenase. This cDNA clone represents a novel potato LOX gene in that it shares the least nucleotide and amino acid sequence homology to other isolated potato LOX genes. Northern analysis indicated that POTLX-3 transcripts did not accumulate in untreated potato leaves, but it was highly induced by treatment with physiological levels of ethylene. Northern analysis also was performed to study whether the POTLX-3 mRNA accumulation could be induced by other plant hormones that affect expression of the other plant LOX and defense-related genes. Treatment of potato leaves with methyl jasmonate, abscisic acid, gibberellic acid, auxin (NAA), and cytokinin (BA) did not induce POTLX-3 gene expression. Because the pattern of POTLX-3 gene expression is similar to that of pathogenesis-related (PR) proteins, especially the PR-1 and PR-5 groups, we suspect that POTLX-3 may be involved specifically in ethylene-induced defense responses against pathogens.

Free access

Plant lipoxygenases (LOXs) (linoleate:oxygen oxidoreductase, EC 1.13.11.12) catalyze the oxygenation of polyunsaturated fatty acids such as linolenic and linoleic acids. Some of the final products of LOX-catalyzed reactions are traumatin, jasmonic acid (JA), methyl jasmonate (MJ), and C-6 volatile compounds, and they serve hormone-like regulatory and defense-related roles in plants. Recently, it has been proposed that LOXs play a role in potato tuberization processes because JA, MJ, and structurally similar tuberonic acid and tuberonic acid glycoside have been shown to be tuber-inducing substances. In order to study possible lipoxygenase involvement in potato tuberization, we have isolated, sequenced, and characterized the expression pattern of two cDNA clones, designated POTLX-1 and POTLX-2, that represent similar, but distinct, LOX genes. Within the scope of our experiments, northern hybridization studies with mRNA extracted from various organs of `Superior' potato plants indicated that the expression of these two genes is restricted to developing tubers and roots only. Moreover, there is a positive correlation between POTLX-1 and POTLX-2 mRNA accumulation and the stage of potato tuber development, and this implicates LOX in tuberization processes. Accumulation of their transcripts was not detected in leaves, flowers, stems, shoot tips, or axillary buds. These results indicate that the isozyme forms encoded by these two genes are tuber-specific, and they are good candidates to study LOX involvement in potato tuberization processes. Treatment of potato leaves with abscisic acid, MJ, gibberellic acid, auxin (NAA), and cytokinin (BA) did not trigger transcriptional activation of either of these genes.

Free access