Chilling Tolerance Of Seedlings Research Articles

Photosynthesis, chilling acclimation and the response of antioxidant enzymes to chilling stress in mulberry seedlings

This study investigates the effects of cold-acclimation in conferring chilling tolerance in seedlings of the mulberry (Morus alba) variety ‘Qiuyu’. Changes in photosynthesis and antioxidant enzymes in chilling acclimatized (CA), and non-acclimatized (NA) seedlings were recorded during chilling stress (3 °C) and a recovery period (25 °C) each for 3 days. The results showed that CA plants had higher net photosynthetic rates (Pn), stomatal conductance (Gs), and maximum photochemical efficiency of photosystem II (Fv/Fm) in response to chilling stress compared to NA. The seedlings maintained the same trends during the recovery stage. The responses of QA reduction degree $$(1 - {\text{q}}_{\text{P}} )$$ and prime electronic transfer rates (Fo) were lower in acclimatized than in non-acclimatized seedlings. Low-temperature acclimation and chilling stress also caused an increase in leaf proline and soluble sugar contents. Leaf malondialdehyde levels were significantly lower while ascorbate peroxidase (APX) activity was significantly higher in acclimatized seedlings, suggesting that elevated osmolytes and APX confer resistance to chilling temperatures. In this study on the response of mulberry seedlings to chilling stress, we also looked at the recovery process. The response to chilling determines whether mulberry leaves can survive under cold temperatures, while the recovery process determines whether photosynthesis can recover as soon as possible to avoid any secondary damage.

Salicylic acid improves chilling tolerance by affecting antioxidant enzymes and osmoregulators in sacha inchi (Plukenetia volubilis)

The effects of pretreatment of 0–5 mM salicylic acid (SA) on the sacha inchi (Plukenetia volubilis) seedlings during chilling stress were investigated. The stress induced damage to seedlings, and SA pretreatment decreased the level of damage. Lipid peroxidation, measured in terms of malondialdehyde content, increased significantly by stress, and SA pretreatment prevented the increase because SA decreased the production rate of superoxide anion (O 2 ·― ) and H2O2 content. SA pretreatment increased the activities of antioxidant enzymes including superoxide dismutase, catalase, guaiacol peroxidase, ascorbate peroxidase, and glutathione reductase and decreased activity of dehydroascorbate reductase. In addition, SA pretreatment increased the content of proline and soluble sugar. Results suggested that the pretreatment of sacha inchi seedlings with SA may induce antioxidant enzymes which lead to increased chilling tolerance. The best protection appeared to be obtained from seedlings that were sprayed with SA at 0.5 and 1 mM. Induction of chilling tolerance in seedlings by exogenous application of SA may have a significant practical application in sacha inchi plantation.

Involvement of polyamines in the interacting effects of low temperature and mineral supply on Pringlea antiscorbutica (Kerguelen cabbage) seedlings.

Pringlea antiscorbutica, which is the sole endemic crucifer in the subantarctic zone, undergoes seedling development in a harsh and cold environment. Since, at the mature stage, this species exhibits several adaptations linked to cold tolerance such as high polyamine levels, potential adaptations and polyamine response were investigated in seedlings. In order to assess the specificity of responses, P. antiscorbutica was compared with Arabidopsis thaliana, which is characterized by a life cycle preventing cold exposure at seedling stage. P. antiscorbutica and A. thaliana seedlings were found to have strikingly contrasted responses to temperature changes and to mineral nutrition. Whereas A. thaliana seedlings showed the typical growth arrest of chilling-sensitive plants, P. antiscorbutica seedlings showed optimal root growth at low temperature (5/10 degrees C) and temperate conditions caused the early arrest of root growth. Cold tolerance was associated with increased levels of polyamines or with maintenance of high levels of polyamines. Comparison of both species showed that polyamine levels could be a significant marker of chilling tolerance in seedlings. Treatments with varying mineral supply showed a positive relationship between root growth rate and variations of agmatine and putrescine endogenous contents in roots of P. antiscorbutica. This may be the first demonstration that, even under conditions of accumulation induced by environmental stress, polyamine levels can still be correlated with developmental processes. Com parison of mineral supply and temperature effects strongly indicated a trade-off of polyamine involvement between development and response to stress.

Heat-shock-induced Chilling Tolerance in Malvaceous Seedlings

Crops indigenous to the tropics and subtropics and some temperate crops suffer physiological injury when exposed to temperatures <12°C. Heat shock has induced chilling tolerance in a number of sensitive species (e.g., corn, cucumber, and tomato), but not in okra. To study this anomaly, we investigated the chilling sensitivity and heat shock response of a variety of Malvaceous species (i.e., cotton, hibiscus, kenaf, and okra). Seedlings with 8- to 12-mm long radicles were exposed to heat shock temperatures of 40 to 45°C for 2 to 12 minutes. Heat shocks were applied by two methods, floating the seeds in petri dishes on heated water and immersing the seeds in the heated water. The seedlings were held at 20°C for 2 hours after the heat treatments and then chilled at 2.5°C for 3 days. After chilling, seedlings were placed at 25°C for 3 additional days. The growth at 25°C was used as an assessment of chilling injury. Although there was a great deal of variability among the seedlings, a significant number of the okra and kenaf seedlings were more tolerant to chilling after heat shock: (i.e., more growth subsequent to chilling) compared to nonheat-shocked controls. More chilling tolerance was induced by the floating method than the immersion method. The response of cotton seedlings to heat-shock was variable, and the seedlings appeared damaged by even slight heat treatments (i.e., 4 minutes at 40°C). The variability in the capacity of heat-shocks to induce chilling tolerance in seedlings of Malvaceous species will be discussed.

Induction of chilling tolerance in cucumber (Cucumis sativus) seedlings by endogenous and applied ethanol

Five‐day‐old etiolated cucumber (Cucumis sativus L.) seedlings cv. Marketmore held at 2°C for 72 h developed chilling injury, resulting in desiccation and collapse of the hypocotyl tissue and eventual plant death. Hypoxia‐induced accumulation of ethanol and acetaldehyde led to tolerance of subsequent chilling, as evidenced by continued hypocotyl growth and freedom from injury. Attenuated accumulation of volatiles by applied bisulfite reduced the development of hypoxia‐induced chilling tolerance in seedlings. In seedlings held in normoxia cold tolerance was induced by applied ethanol vapors, whereas acetaldehyde had a marginal effect, suggesting that hypoxia‐induced cold tolerance may arise from the accumulation and activity of ethanol. Cold tolerance was also induced by exposure of seedlings to volatile anesthetics including n‐propanol, n‐butanol, chloroform and halothane, suggesting that ethanol activity may result from fluidization of membrane lipids. This view is consistent with results which showed that ethanol activity was not associated with lipid metabolism. However, development of cold tolerance in ethanol‐enriched tissues was time dependent, indicating that ethanol activity probably also entails biosynthetic event(s).

INDUCTION OF CHILLING-TOLERANCE IN CUCUMBER (CUCUMIS SATIVUS L.) SEEDLINGS BY ENDOGENOUS AND APPLIED ETHANOL

Five-day-old etiolated cucumber (Cucumis sativus L. cv. Marketmore) seedlings held at 2C for 72 hours develop chilling injury resulting in desiccation and collapse of the hypocotyl tissues and eventual plant death. Hypoxia-induced accumulation of ethanol and acetaldehyde led to tolerance to subsequent chilling as evidenced by continued hypocotyl growth and freedom from injury. Arrest of volatile accumulation by applied bisulfite negated the development of hypoxia-induced chilling tolerance in seedlings. In seedlings held in normoxia, cold tolerance was induced by applied ethanol vapors, whereas acetaldehyde had a marginal effect, suggesting that hypoxia-induced cold tolerance may arise from the accumulation and activity of ethanol. Cold tolerance was induced by exposure to gaseous n-propanol and n-butanol vapors and other volatile anesthetics, including chloroform and halothane, indicating that ethanol activity may stem in part from an anesthetic effect that causes disorder of membrane lipids. However, development of cold tolerance in ethanol-enriched tissues was time-dependent, suggesting an association with biosynthetic event(s). Ethanol did not change the fatty acid composition in cucumber hypocotyl membranes.