Location: Sugarbeet and Potato Research2011 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 discorders adversely affecting tuber wound healing.
3. Progress Report
A series of primer sets were designed to specifically amplify individual members of the five- member gene family of cytokinin oxidase. Each primer set was tested and found to amplify a single family member. Using these primers, the expression patterns for each family member was determined in both aerial and tuber potato tissues. Efforts will now shift to determining expression patterns during natural and chemically forced dormancy termination. Methods for cytokinin analysis and Brdu labeling have been established in wounded tuber tissues. Preliminary experiments have demonstrated an increase in cytokinin content within 24 hours of wounding. Preliminary studies have focused on developing a single-node model system to examine the effects of high temperature treatment on the hormone content of developing tubers. These studies have established optimum greenhouse and growth chamber conditions to generate suitable plant material and induce premature sprouting with elevated temperatures. Field tubers exhibiting mild PE symptoms were obtained from a local producer, transported to the laboratory, systematically wounded, and a time-course series of tissues samples was harvested and frozen for analysis. Extraction and analytical methods for ABA/JA analysis using LC-MS and internal standards have been established in wounded tuber tissues. Seed tubers of cv. Russian Banana tubers have been obtained from Colorado and the plant material has been multiplied in the greenhouse. Studies will now turn to determining the sensitivity of this cultivar to PE-inducing environmental conditions.
1. Identifying regulatory mechanisms controlling tuber wound healing. Incomplete wound healing of harvested and stored potatoes results in disease and quality defects that cost the industry hundreds of millions of dollars annually. Research is needed to identify the internal factors regulating the wound healing process to develop new methods to reduce wound-related tuber damage and consequent economic losses. A hormone in plants called jasmonic acid has been shown to control aspects of wound-healing in several plant tissues, but its role in tuber wound repair was unknown. ARS scientists in Fargo, ND determined the effects of wounding on jasmonic acid accumulation, the expression of genes encoding its biosynthetic enzymes, and its role in wound-healing of potato tubers. They determined that jasmonic acid increased substantially within 4 hours of wounding as did expression of genes encoding three key biosynthetic enzymes. Neither jasmonic acid treatment nor inhibition of its accumulation by washing the tuber affected the time course or extent of deposition of an important wound-induced polymer involved in the wound healing. These results demonstrated that jasmonic acid is not required for the induction of processes essential to wound-induced tissue repair and that treatment of tubers with jasmonic acid or its analogs would likely have no beneficial effects on the wound-induced reduction of postharvest quality and storage life.
Lulai, E.C., Huckle, L.L., Neubauer, J., Suttle, J.C. 2011. Coordinate expression of AOS genes and JA accumulation: JA is not required for initiation of closing layer in wound healing tubers. Journal of Plant Physiology. 168:976-982.