2013 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. Project has been classified as "Exempt" by the rating Institutional Biosafety Committee, ltr dated 5-26-2010.
Continuing studies initiated last year, the expression of the family of cytokinin oxidase genes in potato tuber meristems was determined for a second harvest/storage season. Analysis of cytokinin content in wounded tuber tissues has been completed and results have demonstrated a significant increase in hormone content during the initial stages of tuber wound-healing. Using the novel mass-spectrometric method of analysis developed last year, the effects of storage duration and dormancy status on the endogenous contents of polyamines has been determined. Results from these initial studies have indicated that an increase in polyamine content accompanies the resumption of bud growth following the termination of tuber dormancy. The effects of high temperatures on the ABA content of developing tubers was determined and ABA content was found to decline significantly following the imposition of high temperatures. Analysis of GA content and expression of GA metabolic genes following imposition of high temperature stress during tuber formation has been initiated and the tuber tissues harvested and frozen. Due to the sequestration, analysis of GA content by a contract lab has been delayed pending acquisition of sufficient funding. Freshly harvested field-grown tubers exhibiting pink eye symptoms were collected from cooperating producers, wounded in the laboratory and the time courses of wound-induced changes in water vapor loss, and ABA/JA contents were determined. Results gathered to date suggest only limited impact of pink eye on the time course of tuber wound-healing processes. Tubers of the cultivar Russian Banana, previously posited to readily develop pink eye under controlled conditions, were grown in a controlled environment chamber in soil taken from commercial fields with a history of pink eye expression. Tubers were generated under conditions considered optimum for pink eye development, harvested, and evaluated for the disorder. No pink eye development was noted in repeated independent trials.
Identifying biological processes reducing potato skinning injury. Potato tuber skinning injury at harvest results in costly defects, blemishes and increased susceptibility to infection. The only available approach to enhance resistance to skinning injury (skin-set) is pre-harvest vine-killing and there is no objective method to determine the extent of skin-set development. Little is known about the expression profile of genes and associated biological processes that may regulate or mark skin-set development. Previously, ARS scientists in Fargo, ND determined that skin-set development was dependent upon phellogen cell wall strengthening after cessation of meristematic activity within the native periderm. Continuing these studies, ARS scientists in Fargo, ND and a North Dakota State University geneticist demonstrated that tuber skin thickness does not increase during tuber growth or during periderm maturation and consequently does not affect susceptibility to harvest related skinning injury. Results further suggest that reduced expression of genes controlling cell wall formation and cell division is important for the initiation of periderm maturation and the development of resistance to skinning injury. These results are important in the development of modern agricultural technologies that are needed to improve resistance to tuber skinning injury at harvest.
Neubauer, J., Lulai, E.C., Thompson, A.L., Suttle, J.C., Bolton, M.D., Campbell, L.G. 2013. Molecular and Cytological aspects of native periderm maturation in potato tubers. Journal of Plant Physiology. 170:413-423.
Suttle, J.C., Lulai, E.C., Huckle, L.L., Neubauer, J. 2013. Wounding of potato tubers induces increases in ABA biosynthesis and catabolism and alters expression of ABA metabolic genes. Journal of Plant Physiology. 170:560-566.
Chao, W.S., Serpe, M., Suttle, J.C., Jia, Y. 2013. Increase in ACC oxidase levels and activities during paradormancy release of leafy spurge (Euphorbia esula) buds. Planta. 238:205-215.
Suttle, J.C., Abrams, S.R., De Stefano-Beltran, L., Huckle, L.L. 2012. Chemical inhibition of potato ABA 8'-hydroxylase activity alters in vitro and in vivo ABA metabolism and endogenous ABA levels but does not affect potato microtuber dormancy duration. Journal of Experimental Botany. 63(15):5717-5725.