Location: Sugarbeet and Potato Research
2017 Annual Report
Objectives
Objective 1: Delineate and integrate the molecular processes that control cytokinin content and their biological activities during tuber dormancy progression and wound-healing.
Sub-Objective 1-1: Determine changes in tuber meristem cytokinin content and expression of genes encoding cytokinin biosynthetic enzymes during dormancy progression.
Sub-Objective 1-2: Determine changes in the expression of cytokinin-responsive histidine kinase genes and the acquisition of cytokinin sensitivity during tuber dormancy progression.
Sub-Objective 1.3: Determine changes in cytokinin content and the expression of genes encoding key cytokinin metabolic enzymes in tuber tissues following mechanical wounding.
Objective 2: Quantify nitric oxide release during potato storage and handling and determine nitric oxide involvement in tuber dormancy progression and wound-healing.
Sub-Objective 2.1: Determine the release and role of NO in potato tuber dormancy exit.
Sub-Objective 2.2: Determine the release and role of NO in the potato tuber wound-healing response.
Objectives 1 and 2 build upon research findings secured during the previous project cycle and address current knowledge gaps in the regulatory processes controlling tuber dormancy progression and wound healing.
Approach
Worldwide, the potato ranks fourth among the major food crops. Global potato production exceeds 364 million metric tons (FAOSTAT, March, 2013) and U.S. production exceeds 437 million cwt (USDA-NASS, January, 2013) of which over 400 million cwt worth an estimated $2.01 billion are harvested in the fall. Over 70% of the fall potato crop is placed into storage for year-round use. Unlike other major food crops, potatoes are stored in a fully hydrated and highly perishable form. Postharvest losses routinely approach 10% of the stored crop and occur through both physiological and disease-related processes. Two of the most important physiological processes affecting potato storage and market quality are dormancy/sprouting and wound-healing. Despite the severity of these losses, management strategies and technologies employed to combat these problems were empirically derived, are several decades old and do not effectively meet today’s consumer or industry demands to control damage, minimize physiological deteriorations, and reduce disease problems. Further improvements in postharvest storage technologies are hindered by ignorance of the biological mechanisms underlying these physiological processes. The goals of this project are to identify critical molecular, biochemical and physiological mechanisms controlling tuber dormancy/sprout growth and wound-healing and, ultimately, to genetically, chemically, or physically manipulate these rate-limiting processes to develop improved methods to maintain potato nutritional and processing quality during storage. Specific goals are: 1) Identify the cognate processes that control cytokinin content and activity during postharvest storage/wound-healing, and 2) Determine the involvement of nitric oxide in tuber dormancy progression and wound-healing.
Progress Report
The biosynthesis and release of nitric oxide (NO) are important plant wound-responses which appear to be critical in modulating tuber wound-healing (WH) and reducing associated costly rot, defects and nutritional losses of potatoes damaged at harvest/handling into storage and at seed cutting. Methods are being developed to determine the time-course and amount of nitric oxide and nitric oxide synthase (the enzyme producing NO) induced in response to tuber wounding. The efficacy of an electronic probe that specifically detects and quantifies the ephemeral presence of nitric oxide and two additional probes that are quantitatively specific to the presence of the stable nitic oxide breakdown products (nitrate and nitrite) are being used to determine if they possess the necessary stability and sensitivity to measure production of nitric oxide in wound-responding potato tuber tissue and NO synthase. Initial results show that nitric oxide and resulting nitrate/nitrite products are detected at one point early in the wound-healing time course, but at levels near the threshold of probe sensitivity. Nitric oxide donors (sodium nitroprusside, S-nitroso-N-acetyl-penicillamine, and S-nitrosoglutathione) and inhibitors/scavengers (NG-nitro-L-arginine methyl ester, NG-nitro-L-arginine, carboxy-2-phenyl-4,4,5,5-tetramethylimidazolinone-3-oxyl) are being included in these studies to formulate environments that are: 1) artificially supplemented with nitric oxide, and 2) blocked of nitric oxide accumulation. These environments (supplemented and blocked of nitric oxide) will be used to determine the time-course for release and optimum concentration of nitric oxide in tuber wound-healing. Results from this project will be used in the development of new approaches to safely treat freshly stored potatoes to enhance wound-healing and reduce costly rot and nutritional losses (> $330 m/yr.). Objective 2; sub-objective 2.2.
Accomplishments
1. Polyamine metabolism (peroxidation) is required for potato tuber wound healing (WH). The lack of biological information needed for development of technologies to induce rapid WH (suberization) in tubers damaged during harvest, handling and seed cutting results in infection, defect development and nutritional losses that exceed $330 m/yr. ARS scientists in Fargo, North Dakota determined the involvement of a relatively obscure biological pathway (polyamine (PA) synthesis and metabolism) in potato WH by applying inhibitors of these PA processes and determining the effect on suberin formation. Results showed that inhibition of a specific step in PA metabolism virtually halted the WH processes (suberin biosynthesis) indicating that this metabolic step was the source of cellular hydrogen peroxide required for suberin biosynthesis and the associated barriers to infections. These results indicate that this specific step in PA metabolism is essential in tuber wound healing and suggest that enhancement of hydrogen peroxide production from this biological process has potential in the development of approaches to improve WH and reduce wound-related losses for the industry and consumer. Objective 2; subobjective 2.2.
