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Biomedical subjects

H K Pratt

Publications and source records attributed to H K Pratt.

At least 19 recordsLinked to original sources
PubMed1974

Dual effects of ethylene on potato dormancy and sprout growth.

Dormant potato tubers (Solanum tuberosum L.) of two cultivars were treated with various concentrations of ethylene gas for various exposure periods. As has been shown by others, ethylene caused a rapid but transient increase in respiration rate, which appeared to be independent of any effects on dormancy. All concentrations tested caused accelerated sprouting, 2 microliters per liter being the most effective. Ethylene exerts a dual effect on potato tubers: it markedly shortens the duration of rest, but it inhibits elongation of the sprouts during extended treatment. Comparing these results with published work on seeds, bulbs, and corms suggests that ethylene must have a significant but as yet unexplained role in rest and dormancy. However, since the most effective ethylene treatment did not equal the response elicited by treatment with ethylene chlorhydrin, other factors must also contribute to termination of rest.

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PubMed1972

Effects of ethylene on potato tuber respiration.

Treatment of potato tubers (Solanum tuberosum L.) with ethylene gas causes a rapid rise in their respiration rate, reaching 5 to 10 times the rate of untreated tubers over 30 hours of treatment and then falling slowly. The response shows a lag of 8 hours, and more than 24 hours of exposure is required for maximum effect; the temperature optimum is near 25 C. In sensitivity to low concentrations and dependence on temperature, the phenomenon is similar to the effect of ethylene on the respiration of climacteric and nonclimacteric fruits. Treated potato tubers returned to air recover their sensitivity to ethylene more slowly than do nonclimacteric fruits (e.g., mature green oranges). It is proposed that the respiratory rise characteristic of ripening in climacteric fruits and of the wound response in plant tissues is induced by a rise in endogenous tissue ethylene.

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PubMed1971

Ethylene biosynthesis in fruit tissues.

Tracer studies with avocado tissues indicate that methionine is converted to ethylene at stages of the climacteric rise and the climacteric peak, but not at the preclimacteric stage. The results suggest that the control of ethylene biosynthesis is at a step after methionine is synthesized. The endogenous content of methionine was found to be so low that methionine must be actively turned over for ethylene biosynthesis during the stages when the rate of ethylene production is high. Oxygen was found to be essential for this conversion, indicating that at least one of the steps in conversion of methionine to ethylene is oxygen-dependent. The ability of methionine and its keto analogue (alpha-keto-gamma-methylthiobutyric acid) to serve as ethylene precursors by apple tissues was compared. Chemical and kinetic evidence support the view that methionine is a closer precursor of ethylene than its keto analogue.

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PubMed1968

Isolation of active mitochondria from tomato fruit.

An improved method for isolating mitochondria from tomato fruit (Lycopersicon esculentum Mill.) is described. The fruit is chilled, and the tissue of the fruit wall cut by hand into very thin slices with a razor blade while immersed in a buffer containing 0.4 m sucrose, 2 mm MgCl(2), 8 mm EDTA, 4 mm cysteine, 10 mm KCl, 0.5 mg per ml bovine serum albumin 50 mm tris-HCl, pH 7.6. The pH is monitored and kept within the range of 7.0 to 7.2 by dropwise addition of 1 n KOH during cutting. The tissue is strained through 8 layers of cheesecloth and centrifuged at 2000 x g for 15 minutes. The supernatant is then centrifuged at 11,000 x g for 20 minutes, and the sediment is washed once with a medium containing 0.4 m sucrose, 10 mm KCl, 1 mm MgCl(2), 10 mm tris-HCl, 10 mm KH(2)PO(4) and bovine serum albumin (0.5 mg per ml), pH 7.2. Electron microscope studies show that this method gives homogeneous, relatively intact mitochondria; they have a higher respiratory control ratio than those reported by other workers. The method was also tested successfully on fruits of cantaloupe and ;Honey Dew' melon.

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PubMed1968

Effect of the kinetin-naphthaleneacetic acid interaction upon total RNA and protein in senescing detached leaves.

The interaction between kinetin and naphthaleneacetic acid in the regulation of senescence of excised tissue of mature broccoli leaves has been used to examine the extent of synchrony between changes in chlorophyll, RNA, and protein. Kinetin increased the net uptake of (14)C-labeled orotic acid and leucine. Naphthaleneacetic acid decreased the effect of kinetin on net uptake after long treatment, but in short-time treatments the auxin increased the effect of kinetin on net uptake. Results of long (24 hr) treatments indicated a general synchrony between the loss of RNA, protein, and chlorophyll. Naphthaleneacetic acid reduced the stabilizing effect of kinetin upon chlorophyll content and upon the content and synthesis of RNA. In short-time experiments, however, RNA content and synthesis were transiently increased by kinetin, and further increased by kinetin plus naphthaleneacetic acid, while chlorophyll content decreased in the presence of kinetin and decreased further in the presence of kinetin plus naphthaleneacetic acid. Actinomycin-D accelerated the loss of chlorophyll, RNA and protein and strongly depressed the rate of RNA synthesis. In the presence of actinomycin-D the stabilizing effect of kinetin upon RNA was substantially reduced. In contrast, the chlorophyll and protein contents remained higher than in the control. Actinomycin-D did not nullify the basal incorporation of orotic acid into RNA, nor did it negate the effect of kinetin upon incorporation. The failure of synchrony between changes in chlorophyll and RNA does not substantiate the proposal that kinetin regulates senescence by a direct effect upon DNA-dependent RNA synthesis.

Naphthaleneacetic Acids↗
PubMed1967

An effect of light on the production of ethylene and the growth of the plumular portion of etiolated pea seedlings.

The production of ethylene by etiolated pea epicotyls (Pisum sativum L., cv. Alaska) is confined to the plumule and plumular hook portion of the epicotyl, and occurs at a rate of about 6 mul.kg(-1).hr(-1). Such a rate is sufficient to give physiologically active concentrations of ethylene within the tissue. Exposure of etiolated seedlings to a single dose of red light caused a transient decrease in ethylene production and a corresponding increase in plumular expansion. Far-red irradiation following the red light treatment decreased the red effect to the level achieved by the far-red alone, suggesting that the ethylene production mechanism is controlled by phytochrome and thus that the ethylene intervenes as a regulator in the phytochrome control of plumular expansion.

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PubMed1966

Ethylene as a factor regulating the growth of pea epicotyls subjected to physical stress.

Pea epicotyls (Pisum sativum, cv. Alaska) were enclosed in chambers in which their elongation was restricted by means of a foam neoprene stopper or by a medium of glass beads. These treatments increased evolution of ethylene and resulted in reduced length and increased diameter of both the internodes and the cells of the internodes. These responses increased with increasing degrees of restriction. A time-sequence study of the emergence of epicotyls through 90 mm of glass beads showed that an accelerated evolution of ethylene preceded a reduction in elongation. As the epicotyls elongated through the glass bead medium and less resistance was encountered, evolution of ethylene declined and rapid elongation was resumed. The morphological and anatomical effects of a 120-mm column of glass beads were duplicated by applied ethylene concentrations of 0.2 ppm or less. Evolution of CO(2) was inhibited slightly by the ethylene treatments. The data indicate that production of ethylene by pea epicotyls is increased by nonwounding physical stress, and that the ethylene acts as an endogenous growth regulator, decreasing elongation and increasing diameter in response to increasing increments of stress.

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PubMed1966

Interaction of naphthaleneacetic Acid and kinetin in the senescence of detached leaves.

Kinetin and naphthaleneacetic acid were applied separately and in combination to excised leaf disks, localized areas of laminae, and petioles of detached leaves of broccoli (Brassica oleracea L., var. italica) and Xanthium (Xanthium pensylvanicum Wallr.). Senscence (measured as loss of chlorophyll) was strongly retarded by kinetin, but very slightly influenced by naphthaleneacetic acid. When the 2 substances were applied concurrently, the effect of kinetin was markedly reduced by naphthalene acetic acid. Neither interference with uptake nor transport of kinetin appeared to cause the reduction.In broccoli, the response to kinetin was as great in young leaves as in old leaves, and the reduction of the kinetin effect by naphthaleneacetic acid was greater in young leaves than in old leaves. Results indicate that the prevention of loss of critical material may be more significantly related to the delay of senescence by kinetin than is directed transport and accumulation (mobilization). Kinetin may control 2 or more events which contribute independently to the delay of senescence in detached leaves, and naphthaleneacetic acid may possibly interfere with only 1 of them.

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