Carrot Transcript Profile Responds to Growth and Chilling Exposure.

Alternative oxidase (AOX) is a key enzyme of the alternative respiration, known to be involved in plant development and in response to various stresses. To verify the role of and genes in carrot tap root growth and in response to cold stress, their expression was analyzed in two experiments: during root growth for 13 weeks and in response to a cold challenge trial of 7 days, in both cases using different carrot cultivars. Carrot root growth is initially characterized by an increase in length, followed by a strong increase in weight. presented the highest expression levels during the initial stages of root growth for all cultivars, but showed no particular trend in expression. Cold stress had a negative impact on root growth, and generally up-regulated with no consistent effect on . The identification of cis-acting regulatory elements (CAREs) located at the promoters of both genes showed putative sequences involved in cold stress responsiveness, as well as growth. However, promoter presented more CAREs related to hormonal pathways, including abscisic acid and gibberellins synthesis, than . These results point to a dual role of on carrot tap root secondary growth and cold stress response.