Search Results

You are looking at 1 - 5 of 5 items for

  • Author or Editor: Eleazar Reyes x
  • All content x
Clear All Modify Search
Free access

Eleazar Reyes and Paul H. Jennings

Roots of `Golden Girl' squash (Cucurbita pepo var. melopepo) and `Encore' cucumber (Cucumis sativus L.), 4- and 3-days-old, respectively, were exposed to 2, 6, 10, and 15C for 24, 48, 96, 144, and 192 hours to compare the sensitivity to chilling temperatures and the subsequent recovery at more favorable temperatures. Seedlings were more sensitive to chilling at 2 and 6C when measured by their ability to resume growth when returned to 26C. Root growth decreased after 48 hours of chilling. Seedlings stressed at 10 and 15C were able to continue root growth at these temperatures and when returned to 26C. However, seedlings at 10C exhibited root-tip browning in both crop species, suggesting disfunction in metabolic pathways that were repressed in seedlings growing at 2C where those symptoms were not present. Effects on root dry weight occurred in the first 24 hours at all temperatures studied. After 96 hours of treatment, seedlings grown at 2 and 6C were irreversibly damaged, as evidenced by their inability to resume growth when returned to 26C. Leakage of electrolytes from squash and cucumber roots increased after 48 hours at 2C. Potassium, Na+, and PO4 -2 were lost in greater amounts than Mg+2, Cl-, and SO4 -2. No difference in ionic leakage occurred at 10 and 15C, and Ca+2 leakage was not detected at any chilling stress temperature.

Free access

Eleazar Reyes and Paul H. Jennings

The effects of chilling stress on respiration and induction of the alternative pathway (AP) were investigated with roots of 3-day-old cucumber seedlings (Cucumis sativus L.) grown at 26 °C and then chilled at 2, 10, or 15 °C for 24, 48, 96, 144, or 192 hours. Oxygen uptake by roots exposed to 2 °C was significantly lower than by 10 or 15 °C-treated roots, and the inhibition of oxygen uptake in the presence of SHAM (salicylhydroxamic acid) increased from 29% in unchilled tissue to 60% after 96 hours of treatment. At 10 and 15 °C, the capacity of the AP was nearly double that of the unchilled control and the 2 °C-treated seedlings. A 24 hours, postchilling treatment at 26 °C resulted in greater oxygen uptake at all temperatures as treatment time increased up to 96 hours. At 2 °C, the capacity of the AP was significantly reduced below the level of the 10 and 15 °C-treated tissue and the untreated control. The activity of the AP became fully activated by 96 hours in roots chilled at 2 °C. Results suggest that the capacity of the AP can be affected by low-temperature treatments, and exposure to 2 °C for up to 96 hours leads to a significant loss in capacity of the AP.

Free access

Eleazar Reyes and Paul H. Jennings

The effect of chilling stress on induction of the cyanide-resistant pathway was investigated using roots of 3-day-old cucumber (Cucumis sativus L.) and 5-day-old pea (Pisum sativum L.) grown at 26°C, and then chilled at 2°C for 48 or 96 hours for cucumber, and 72 or 192 hours for pea. A 24-hour post-chilling treatment at 26°C was imposed on different sets of chilled roots from both crops. Carbohydrate status was determined by gas chromatography with an autosampler using a 12.5-m cross-linked methyl silicone capillary column (0.1 mm). Exposing seedlings to 2°C, as well as to a postchilling treatment, induced differential responses in the activity of the cyanide-resistant pathway. Cucumber seedling roots exhibited an accumulation of fructose, glucose and sucrose during chilling, with a rapid decline observed during the post-chilling treatment at 26°C. Pea seedling roots maintained a constant level of carbohydrates throughout the chilling period, and exhibited a slight decrease by the end of 192 hours at 2°C. There was an increase in carbohydrate levels during the post-chilling treatment. The involvement of the cyanide resistant pathway and carbohydrate changes will be discussed.

Free access

Eleazar Reyes and Paul H. Jennings

The effect of chilling stress on induction of the cyanide-resistant pathway was investigated using roots of 3-day-old cucumber (Cucumis sativus L.) grown at 26C and then chilled at 2C, 10C, or 15C for 24, 48, 72, and 96 h. A 24-h post-chilling treatment was imposed on different sets of chilled cucumber roots at 26C. Exposing seedlings to 2C, 10C, and 15C, as well as to a post-chilling treatment, induced differential responses in the activity of the cyanide-resistant pathway. Cucumber seedling roots exhibited an increase in the cyanide-resistant pathway after a 96-h chilling treatment at 2C. The involvement of the cyanide-resistant pathway in the chilling stress response will be discussed.

Free access

Eleazar Reyes and Paul H. Jennings

The effect of chilling stress on respiration and induction of the cyanide-resistant pathway was investigated using roots of cucumber and pea grown at 26°C and 23°C and exposed to 2°C,. 10°C or 15°C for either 24 or 96h. Oxygen uptake of 2°C treated cucumber roots decreased between 24 and 96 h of chilling and then dramatically increased between 96 and 192h. The cyanide-resistant pathway did not change in cucumber roots at 10°C or 15°C for 24h or 96h, nor after a 24h recovery period at 26°C. At 2°C, cyanide resistant O2 uptake increased during the 24h recovery period following a 24h chilling but not after 96h chilling. Cyanide resistant oxygen uptake in pea roots was unaffected by 10°C and 15°C for 24h or 96h and a 24h recovery at 23°C. At 2°C, no effect in cyanide resistant O2 uptake was observed by 24h chilling but a significant increase occurred after 96h which returned to pre-stress levels with a 24h recovery at 23°C.