The effects of exogenous application of abscisic acid and α,α'-dipyridyl on cold acclimation and physical characteristics of Pisum sativum 'Alaska' seedlings
Cold acclimation entails changes in membrane composition, osmotic adjustment, alterations in the cell wall-plasma membrane interface, sugar deposition, and changes in cell wall proteins. There is evidence that a rigid cell wall may be necessary for cold acclimation. Difficulties arise in studying plant material acclimated by exposure to low temperatures, because extraneous changes in the plant material occur that are unrelated to the development of cold tolerance. In order to determine whether cell wall changes are necessary for acclimation, peas were acclimated at warm temperature (26°C) by the application of exogenous ABA, desiccation, light exposure, and an experimental cryoprotectant (GLK 8908). Electrolyte leakage, elastic and plastic bend angles, and stem elongation were used to evaluate freezing injury, cell wall rigidity, and growth, respectively. The role of extensin, a structural hydroxyproline-rich glycoprotein suspected of being involved in cell changes during acclimation, was examined using the hydroxylation inhibitor ⍺,⍺’-dipyridyl. Exogenous ABA application and drought stress decreased freezing injury by approximately a 10% -6°C compared to controls. In one experiment light was found to be more effective than ABA at acclimating peas at warm temperatures. Foliar application of GLK 8908 decreased freezing injury (30% at -6°C). Stem bendability was not correlated with freezing resistance. ABA treated peas grown in the dark had reduced growth rates and increased stem rigidity, but exhibited greater injury at -6°C than untreated dark grown peas. Extensin content was not related to cold hardiness. Although acclimation of ’Alaska’ peas did occur at warm temperatures with various treatments the reductions in freezing injury were minor when compared to plants acclimated by exposure to low temperatures.
GLK 8908 was also evaluated for its effects on ’Alaska’ pea survivability and yield. Peas treated with GLK 8908 (1 and 10% aqueous) and subjected to a -6.7°C freeze were found to have increased survival without significant changes in days to first flower, leaf surface area/plant, and yield/plant.