Pre- and post-harvest hormonal changes of carrots

Sprouting and rooting are the most important measures of postharvest quality for carrots. Changes within the carrot in the content profiles of the plant hormones affecting rooting and sprouting, namely auxins, gibberellins, cytokinins, ethylene and abscisic acid, were studied during growth, development and cold storage at 0 and 5 degrees C of the carrot. Rooting and sprouting ratio and morphological differentiation within the roots were also investigated as part of the evaluation of quality. Auxin level increased up to harvest time, and decreased during harvest, while ABA and GA(3) levels were low at the beginning of the growth and development period, and then increased until harvest. The levels of these hormones were higher in leaf tissues than root samples. Ethylene production decreased in leaf tissues and increased in roots during the growth and development period. Cytokinins accumulated in root tissues during this period, then decreased at harvest maturity; this contrasted with levels of cytokinins seen in leaves during these periods. During cold storage at 0 and 5 degrees C, auxin levels were seen to increase while ABA and GA3 levels decreased with rooting and sprouting occurring during this period. Ethylene levels increased at the beginning of the storage period and then declined. Cytokinin levels showed a general decrease after reaching to a peak value during cold storage at 5 degrees C and constantly increased at 0 degrees C. These hormonal changes and post-harvest growth indicate that there is a short dormancy period after harvest due to preharvest hormonal accumulation. The dormancy period ends with a decrease in ABA, ethylene and GA(3) levels and with an increase in levels of cytokinin and auxin during the storage period. Morphological differentiation showed that it is possible to determine adventitious root formation before it is apparent.