Sugar regulation of plastid reversion in citrus epicarp is mediated through organic acid metabolism.
The inhibition by sucrose of chromoplast reversion to chloroplast in citrus epicarp was studied by observing the effects of several sugars, sugar metabolites and 1-iodoacetate on chlorophyll reaccumulation in cultured Citrus paradisi Macf. pericarp segments. Pericarp segments of 1 cm in diameter were cut from yellow fruits and cultured on modified medium plus the indicated metabolites and kept under continuous fluorescent light. Accumulation of chlorophyll in the segments was measured with a spectrophotometer fitted with sphere reflectometer. Respiration was determined via., an infrared gas analyzer. Inhibition of regreening was not specific to a particular sugar. The organic acids malate, citrate, succinate, 2-oxoglutarate and especially malonate elicited effects similar to sucrose, but at much lower concentrations. However, malonate inhibition of chlorophyll accumulation was overcome by increased concentrations of glutamine. At concentrations that usually inhibited chlorophyll, malonate did not reduce CO2 production in the presence of glutamine or KNO3. Sucrose effects on regreening were reduced by 1-iodoacetate. These results indicate that sugar regulation of plastid reversion during regreening in citrus epicarp is not directly due to sugars, but is instead mediated through metabolism of sugars to organic acids, especially malonic acid.
Ahmed
Omer Khidir
OK
Department of Horticulture, University of Khartoum, Khartoum North, Sudan.
D002241:Carbohydrates / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry / Q000378:metabolism*; D019069:Cell Respiration / Q000502:physiology; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism*; D002957:Citrus / Q000033:anatomy & histology / Q000502:physiology; D005638:Fruit / Q000033:anatomy & histology / Q000737:chemistry / Q000378:metabolism; D018087:Plastids / Q000378:metabolism*; D012621:Seasons
D002241:Carbohydrates; D002264:Carboxylic Acids; D002734:Chlorophyll