Abstract
The freezing tolerance of 69 accessions of field-grown, common wheat (Triticum aestivum) was assessed in three consecutive winters. To measure freezing tolerance directly, field-grown plants were subjected to a range of freezing temperatures in a controlled environment and plant regrowth was subsequently assessed. Indirect assessments of freezing tolerance, as measured by chlorophyll fluorescence transient measurements followed by a JIP-test (an in vivo measurement of the adaptive behavior of the photosynthetic apparatus), were performed on detached leaves frozen at the same time as whole plants. Both direct and indirect tests were also used on plants cold acclimated in the laboratory. These results were compared with results of a field survival study performed at seven experimental sites. An analysis of the data indicated that only some of the JIP-test parameters were suitable for the prediction of freezing tolerance and winter survival. Estimates of cold hardiness were very similar, regardless of the experimental year, but were dependent on the method of cold acclimation and time of sampling. Indirect measurements of cold hardiness were more in line with the field survival data for field-cold-acclimated plants sampled in mid-winter than for plants that were either sampled earlier or cold acclimated in the laboratory. Indirect measurements taken on leaves that had not frozen failed to provide accurate estimates of cold hardiness. Our observations, together with previously reported findings, indicate that cold acclimation under natural field conditions activates a greater array of freezing tolerance mechanisms than cold acclimation performed in under controlled environmental conditions in a laboratory.
Highlights
Advances in our understanding of plant cold hardiness has increased greatly during the last decade and was recently summarized by Gusta and Wisniewski (2013)
As measured by plant survival for plants cold acclimated in the field and subjected to controlled freezing in the laboratory, cold acclimated in the laboratory and subjected to controlled freezing, and by assessing survival in the field after the winter
Freezing tolerance was estimated by measuring various chlorophyll fluorescence parameters on detached leaves after they had been subjected to the same level of freezing as in the other assessment methods
Summary
Advances in our understanding of plant cold hardiness has increased greatly during the last decade and was recently summarized by Gusta and Wisniewski (2013). A thorough analysis of methods utilized to assess the freezing tolerance of plants cold acclimated under controlled environmental conditions in comparison to various field conditions, together with explanations for the basis of any observed differences, is crucial for predicting the effects of climate change on plant biodiversity Such an assessment is necessary for successful breeding of plants that are more winter hardy given predicted changes in climate (Rapacz et al 2014). Chlorophyll fluorescence induction transient analysis (JIP-test) provides a useful approach for researchers to obtain indirect information regarding the structure and function of the photosynthetic apparatus. By using a JIP-test, it is possible to characterize the equilibrium between the inflow and outflow of the entire energy flux within PSII and estimate the possible fate of the absorbed light-energy
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