2012 Annual Report
1a.Objectives (from AD-416):
To determine the normal and molecular processes that control the initiation, maintenance and termination of potato bud dormancy and regulate early sprout growth and tuber wound healing. The specific objectives are as follows:
Objective 1: Determine role and metabolic control of cytokinin content and activity during dormancy progression and wound-healing. Sub-Objective 1-1: Clone and characterize genes encoding cytokinin dehydrogenase/oxidase in potato tubers and determine changes in transcript abundances during tuber dormancy. Sub-Objective 1-2: Determine changes in cytokinin content during wound-healing of potato tubers in relation to wound-induced cell division.
Objective 2: Determine role of polyamines in tuber dormancy and wound-healing. Sub-Objective 2.1: Quantify changes in free polyamine content and polyamine biosynthetic gene abundances in tuber meristems during dormancy progression and determine physiological significance of these changes in dormancy exit. Sub-Objective 2.2: Quantify changes in polyamine content in tuber parenchyma tissues during wound-healing and determine the role of endogenous polyamines in tuber wound-healing.
Objective 3: Determine the effects of heat-sprouting on endogenous hormone levels in tuber meristems. Sub-Objective 3.1: Quantify changes in ABA content and expression of genes encoding key ABA metabolic enzymes in tuber meristems during heat-induced sprouting. Sub-Objective 3.2: Determine changes in gibberellin (GA) content and transcription of GA biosynthetic genes during heat-induced sprouting.
Objective 4: Determine effects of pink-eye syndrome on tuber wound-healing and endogenous contents of wound-related hormones. Sub-Objective 4.1: Quantify formation of wound-induced suberin components in tubers developing pink-eye and those that are fully afflicted in relation to non-afflicted tubers. Sub-Objective 4.2: Quantify tuber ABA and JA content in the periderm and cortical parenchyma of tubers developing the pink-eye syndrome in relation to non-afflicted tubers. Sub-objective 4.3: Develop a greenhouse/growth chamber protocol to artificially induce the PE syndrome in a susceptible potato genotype.
1b.Approach (from AD-416):
Identify physiological/biochemical mechanisms that control potato tuber dormancy/sprout growth and wound-healing/skin set. Determine the roles of endogenous hormones in tuber dormancy progression and identify the biochemical and molecular mechanisms governing hormone homeostasis in tubers as related to dormancy. Identify and characterize genes controlling tuber dormancy/sprout growth and wound-healing/skin set. Identify hormones and endogenous elicitor systems initiating and regulating wound-healing in harvest-damaged and cut-seed tubers. Identify physiological processes and disorders adversely affecting tuber wound healing.
Using the primers sets developed and validated last year, the expression of five cytokinin oxidase genes during natural dormancy progression was determined during a complete storage season. Preliminary analyses of the effects of wounding on the endogenous contents of hormones have been completed. Initial results suggest that wounding affects several classes of hormones including the cytokinins. A novel method for polyamine analysis in plant samples using LC-MS is being optimized for use with potato tuber tissues. This method offers several improvements over current protocols including simultaneous determination of quantity coupled with unequivocal identification. Attempts to develop a single-node model system to examine the effects of heat stress on tuber re-growth are continuing. Incomplete tuberization of the cuttings has been a persistent problem and construction of a new misting chamber to facilitate these studies is underway and should greatly aid in these studies. Primer sets for genes encoding three regulatory steps in gibberellin biosynthesis and metabolism have been designed and validated. Field samples from pink eye afflicted fields have been collected and initial analyses have been completed. The lack of excess rainfall has significantly reduced the incidence of pink eye in commercial fields thus far. The cultivar Russian Banana has been multiplied and greenhouse and growth chamber studies have been initiated to determine the suitability of this model system for manipulating pink eye development under controlled conditions.
Manipulating hormone metabolism in potato tubers to prevent sprouting. Uncontrolled potato tuber sprouting in storage results in the deterioration of market and nutritional qualities that cost the potato industry hundreds of millions of dollars annually. Currently, sprouting is controlled through the use of synthetic inhibitors and there is great interest in developing novel more benign sprout inhibitors. The plant hormone abscisic acid (ABA) has been demonstrated to play an essential role in tuber dormancy and has been suggested as a possible natural sprout control agent. To determine the feasibility of this hypothesis, ARS scientists in Fargo, ND examined a series of compounds to identify candidates which inhibited the metabolism of ABA thereby increasing its concentration in potato tubers. Two compounds were found to be potent inhibitors of ABA metabolism but only one of these elevated the ABA content of tubers. Treatment of dormant tubers with this inhibitor doubled the ABA content of tubers but had no effect on the length of tuber dormancy. These results suggested that increasing the content of ABA (either genetically or chemically) would have no effect on the length of tuber dormancy and therefore would be of little commercial value.
Neubauer, J., Lulai, E.C., Thompson, A.L., Suttle, J.C., Bolton, M.D. 2012. Wounding coordinately induces cell wall protein, cell cycle and pectin methyl esterase genes involved in tuber closing layer and wound periderm development. Journal of Plant Physiology. 169:584-595.
Qiu, Y., Xi, J., Du, L., Suttle, J.C., Poovaiah, B.W. 2012. Coupling calcium/calmodulin-mediated signaling and herbivore-induced plant response calmodulin-binding transcription factor AtSR1/CAMTA3. Plant Molecular Biology. 79:89-99.
Gu, X.-Y., Foley, M.E., Horvath, D.P., Anderson, J.V., Feng, J., Zhang, L., Mowry, C.R., Ye, H., Suttle, J.C., Kadowaki, K., Chen, Z. 2011. Association between seed dormancy and pericarp color is controlled by a pleiotropic gene that regulates abscisic acid and flavonoid synthesis in weedy red rice. Genetics. 189:1515-1524.