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Steven A. Altman and Theophanes Solomos

Treating `Elliott's White' cut carnations with 50 or 100 mm aminotriazole for 4 days inhibits the respiratory climacteric and significantly extends vase life. Aminotriazole induced time- and concentration-dependent inhibition of ethylene evolution and onset of the ethylene climacteric by inhibiting ACC synthase activity. Flowers treated with 50 or 100 mm aminotriazole for 2 days exhibited concentration-dependent increases in ethylene evolution, respiratory activity, ACC synthase activity, and petal ACC content in response to the application of exogenous ethylene at 10 μl·liter-1. Senescence-associated morphological changes, increased ACC synthase activity, ACC content, and ethylene evolution were completely inhibited in flowers treated for 4 days with 100 mm aminotriazole. Although treatment with 50 mm aminotriazole for 4 days did not completely inhibit components of the ethylene biosynthetic pathway, no morphological or respiratory responses to the application of exogenous ethylene at 10 μl·liter-1 were observed, a result indicating that prolonged aminotriazole treatment inhibited ethylene action. Chemical names used: 3-1H-amino-1,2,4-triazole-1-yl (aminotriazole), 1-aminocyclopropane-1-carboxylic acid (ACC).

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Charmara Illeperuma, Donald Schlimme and Theophanes Solomos

Potato tubers (Solanum tuberosum `Russet Burbank') were stored at 1 °C in air for 28 days and then transferred to 10 °C in either air or 2.53 kPa O2. During cold storage there was an increase in sucrose, glucose, and fructose. The activities of extractable sucrose phosphate synthase (SPS) and invertase increased by 2.2- and 7.7-fold, respectively, during 28 days at 1 °C. The activity of sucrose synthase (SS) remained constant at 1 °C and was similar to that found in tubers kept continuously at 10 °C. With the transfer of tubers from 1 to 10 °C, there was an initial sharp rise in respiration which peaked at ≈7 days, followed by a gradual decline. Sucrose declined rapidly during reconditioning, while glucose and fructose declined more slowly. With the transfer of tubers from 1 to 10 °C, the activity of SS increased sharply after 7 days at 10 °C, to be followed by a decline to the levels found in control tubers. The activities of both extractable SPS and invertase decreased during reconditioning, reaching the values of the control tubers within ≈15 days. Low O2 inhibited the decrease in sugars and suppressed the rise in SS activity, but it did not alter the decrease in SPS and invertase. Western blot analysis showed that the amount of SPS protein remained unchanged at 1 and 10 °C. These results indicate that the activity of SPS is regulated by factors other than the amount of its protein. The activities of the above three enzymes showed no changes in tubers kept at 10 °C continuously. In control tubers SPS showed the highest activity, followed by SS and invertase.

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Aref A. Abdul-Baki and Theophanes Solomos

The diffusion coefficient of CO2 in `Russet Burbank' potato (Solanum tuberosum L.) tubers was determined under steady-state conditions at 10 and 27C. The data showed that the skin is the main barrier to gas diffusion, with an average diffusion coefficient of 6.57 × 10-7 and 7.61 × 10-7 cm·s-1 at 10 and 27C, respectively. The flesh also presents an appreciable barrier to gas diffusion. The average diffusion coefficient of CO2 in the flesh was 2.00 × 10-4 and 2.24 × 10-4 cm·s-1 at 10 and 27C, respectively. Under regular storage conditions, the tuber is well aerated and the concentration of O2 at the center of the tuber is sufficient to maintain aerobic respiration.

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MADIS PIHLAK, STEVEN ALTMAN, THEOPHANES SOLOMOS and DAVID JONES

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Mehar Asif, Prabodh Trivedi, Theophanes Solomos and Autar Mattoo

We have studied the effects of MCP and low O2, applied singly and in combination, on apple fruit ripening at 1, 7, and 18 °C. The single application of 2 ppm MCP is more effective in delaying the onset of the C2H4 climacteric than is 1% O2. However, the combined application has a much larger effect than the single applications of either MCP or 1% O2. For instance, at 7 °C, the onset of the C2H4 climacteric occurs at 15, 50, and 90–95 days for the controls, 1% O2 and 2 ppm MCP, respectively, whereas the combined application of 2 ppm MCP and 1% O2 suppressed the initiation of the C2H4 climacteric for 200 days, the duration of the experiment. The retardation of the climacteric onset by the treatments is associated with the suppression of ACC-synthase (ACS1) and the putative receptor ERS1. The accumulation of their transcripts is critically dependent on the rate of C2H4 evolution. As expected, the combined application of MCP and 1% O2 completely suppressed the expression of both genes. Yet when the fruits were transferred to 18 °C in air, they ripened normally. A similar pattern of inhibition in response to the above treatments was also observed with a C2H4-dependent MAPK. The expression of ETR1, ETR2 and ACC-oxidase was not affected by the treatments. The nature of this strong effect of the combined application of MCP and low O2 is not clear. It should be pointed out that MCP does not inhibit the induction of hypoxic proteins such as ADH.