| Sucrose depletion in harvested asparagus (Asparagus officinalis L.) spear tips is rapid and may trigger senescence. This research focuses on investigating how carbohydrate metabolism in asparagus spear tips, stored at 1{dollar}spcirc{dollar}C, is regulated. The research was divided in two parts. The first portion was an investigation into the effects of low O{dollar}sb2{dollar} and high CO{dollar}sb2{dollar} on respiratory and fermentative metabolism, sucrose-metabolizing and glycolytic enzymes, and phosphate and adenylate levels in spear tips. The second portion was an evaluation of the effects of exogenous cytokinin on sucrose metabolism in harvested asparagus spears.; For this portion of the research, spears were stored with a range of O{dollar}sb2{dollar} partial pressures combined with CO{dollar}sb2{dollar} treatments of 0, 5, 10, and 20 kPa using a system combining modified atmosphere packages in flow-through containers for a period of 6 days. The respiratory quotient increased and ethanol, acetaldehyde, and lactate accumulated below 2 kPa. During 6 days of storage, sucrose declined markedly, relative to harvest. Sucrose content was highest for spears exposed to 5 kPa CO{dollar}sb2.{dollar} SS activity was higher at harvest; however, bound acid invertase activity was the highest after the storage period, indicating that sucrose may be degraded postharvest mostly in the apoplast. 5 kPa CO{dollar}sb2{dollar} reduced sucrose synthase, invertase and hexokinase activities, which may account for the reduction in sucrose utilization. Alcohol dehydrogenase (ADH) and pyruvate decarboxylase activities increased for O{dollar}sb2{dollar} levels below 2 kPa. Lactate dehydrogenase activity was lower than ADH activity; however, it also increased below 2 kPa O{dollar}sb2.{dollar} Visual quality (VQ) was reduced by CO{dollar}sb2{dollar}, but increased as O{dollar}sb2{dollar} increased. VQ was best for spears stored in near-ambient O{dollar}sb2{dollar} and 5 kPa CO{dollar}sb2.{dollar}; Low O{dollar}sb2{dollar} enhanced the interconversion of PEP to PYR and F6P to fructose-1,6-bisphosphate (F1,6P{dollar}sb2{dollar}), indicating a promotion of glycolysis with a resulting loss of carbon in the sugar pool. Low O{dollar}sb2{dollar} caused an increase in pyruvate kinase (PK) activity. However, high CO{dollar}sb2{dollar} besides having an effect on PK, appeared to affect conversion of F6P to F1,6P{dollar}sb2{dollar} at O{dollar}sb2{dollar} levels below 2 kPa.; PPi and ATP decreased below 2 kPa O{dollar}sb2{dollar}, with a concomitant increase in Pi, ADP, and AMP. Low O{dollar}sb2{dollar} also reduced adenylate energy charge (AEC) relative to high O{dollar}sb2.{dollar} Higher CO{dollar}sb2{dollar} reduced AEC for O{dollar}sb2{dollar} levels greater than 2 kPa. Decreases in PPi, ATP, and AEC, and increases in Pi, ADP, and AMP in response to O{dollar}sb2{dollar} deficiency suggest impairment of oxidative phosphorylation and unbalanced cell metabolism, which may limit asparagus spear survival. Below 2 kPa O{dollar}sb2{dollar} the cells were under stress leading to fermentation. Below 1 kPa O{dollar}sb2{dollar} the spear tip tissues were experiencing severely limiting energy availability.; 6-BAP reduced respiration rate of spears with intact tips, slowed changes in fluorescence, and slowed chlorophyll degradation during 31d of storage at 1{dollar}spcirc{dollar}C. 6-BAP also slowed the decline in sucrose content in spears with tips. The visual quality was highest for spears with tips that were treated with 6-BAP. |
PDF Full Text Request