Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/1996
Publication Date: N/A
Interpretive Summary: For a finite period of time following harvest, potatoes will not sprout and are physiologically dormant. Dormancy is gradually lost during postharvest storage and the resultant sprouting is detrimental to the nutritional and processing qualities of potatoes. Because of this, sprouting results in sever financial loss to producers. Currently, sprouting is controlled through the use of synthetic sprout inhibitors. The research being conducted in this lab is directed towards 1.) identifying key physiological processes that naturally regulate tuber dormancy and, ultimately, 2.) modifying these processes genetically thereby eliminating the need for artificial sprout suppression. In this paper, the cellular bases for dormancy-induced growth arrest in potato buds (eyes) was determined. Using a combination of computer based & laser-driven techniques together with more classical methods, we found that dormant potato buds are arrested at the very earliest stage of cell division prior to DNA replication. In further studies using molecular cloning techniques, the gene coding for a key enzyme controlling bud growth was isolated, cloned (copied) and examined in potato tissues. These results demonstrated that the absence of growth in dormant potato buds was not a result of a deficiency in this critical enzyme and, therefore, must result from another biochemical block.
Technical Abstract: Potato (Solanum tuberosum L.cv. Russet Burbank) tubers undergo a period of endodormancy that is characterized by cell division arrest. At the time of harvest, the tubers used in this study were completely endodormant (i.e. 0% sprouting). After 120 days of storage at 3C, tubers transferred to 20C had begun to exit endodormancy and exhibited ca 50% sprouting. After 223 days of 3C storage, tubers transferred to 20C were completely nondormant and exhibited 100% sprouting. Based on flow cytometry, about 70% of nuclei isolated from endodormant meristems are arrested in the G1/G0 phase of the cell cycle. Storage of tubers at 3C did not alter the cell cycle position nor did transfer of tubers from 3 to 20C for 7 days prior to analysis unless tubers had been stored for at least 223 days. After 223 days of cold (3C) storage, tubers transferred to 20C for 7 days showed sprout growth in excess of 5mm and an increase in the percentage of nuclei in the G2 phase of the cell cycle. Uptake and incorporation of 3H-thymidine into DNA was low in all tubers up until 120 days postharvest. After that time only tubers incubated at 20C for 7 days prior to analysis exhibited an increase in 3H-thymidine incorporation. This increase coincided with visible sprout growth, demonstrating that cell cycle shifts in tuber meristems relate directly to sprout growth and not the breakage of the endodormancy per se. Using degenerate primers, a portion of a p34 homolog was amplified from RNA isolated from log-phase potato suspension culture cells by polymerase chain reaction. Northern analysis with this probe demonstrated that mRNA levels for two p34 homologs were present throughout the endodormant period.