Submitted to: Journal of Food Agriculture and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 22, 2013
Publication Date: January 31, 2013
Citation: Malik, N.S., Perez, J.L., Kunta, M. 2013. Changes in free amino acid levels in sour orange leaves in response to cold stress and during recovery from cold stress. Journal of Food, Agriculture & Environment. 11(1):1086-1088. Interpretive Summary: Citrus greening disease, also known as Huanglongbing (HLB), is a devastating disease that has caused serious damage to citrus industry in Florida, USA, and other places in the world. The disease causing bacteria (Candidatus Liberibacter spp.) is transmitted by Asian citrus psyllid (ACP), Diaphorina citri (Kuwayama). Since there is no cure for the disease as yet, the problem is managed through controlling the insect vector; primarily by spraying insecticides throughout the year. We have, therefore, started studies on interactions between ACP and the host plant. Previously, we reported that plants recovering from cold stress attracted more ACP than the control plants continuously kept under warm condition. In parallel studies, cold treated plants were shown to have relatively increased amounts of ninhydrin positive material, at least during 5-24h recovery period from cold stress; changes in various polyphenols and polyamines were are also observed . One reason for increased attractiveness of a host plant for herbivores is increased nutrient levels (e.g., amino acids) providing greater feeding opportunities. In fact, out breaks of herbivore insects have been attributed to changes in amino acid levels in host plant facilitating feeding and fecundity of insect pests. This study was therefore conducted to extend our previous studies on interactions between ACP and cold stressed plants by looking at changes in free amino acid levels in sour orange leaves when subjected to the cold stress and during recovery period when greater attractiveness to ACP was observed.
Technical Abstract: In a previous study, we reported that potted sour orange trees recovering from cold stress attracted more Asian citrus psyllid than the control plants continuously kept under warm condition. In parallel studies, cold treated plants were shown to have relatively increased amounts of ninhydrin positive material during 5-24h recovery period from cold stress. Here we report on changes in free amino acid levels in sour orange leaves in the 24 h recovery period following the termination of the chilling treatment. Proline was most abundant amino acid and increased in response to chilling treatment; it remained at higher than initial levels during the first 5 h recovery period and then declining to initial levels after 24 h. In addition, amino acids such as serine, glutamic acid, glycine, lysine, isoleucine, tyrosine, arginine, and histidine increased due to cold treatment and/or during recovery after cold treatment, while asparagine, phenylalanine, leucine alanine, or threonine either decreased or remained unchanged in response to cold stress and during immediate recovery period. The special pattern with which levels of different free amino acids change in response to cold stress might have important implications on interactions between Asian citrus psyllids and citrus host plants.