|KUNTA, MADHURABABU - Texas A&M University|
|Patt, Joseph - Joe|
Submitted to: Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2014
Publication Date: 2/14/2014
Citation: Malik, N.S., Perez, J.L., Kunta, M., Patt, J.M., Mangan, R.L. 2014. Changes in free amino acids and polyamine levels in Satsuma leaves in response to Asian citrus psyllid infestation and water stress. Insect Science. DOI:10.1111/1744-7917.12075/full.
Interpretive Summary: Asian citrus psyllid (ACP), Diaphorina citri (Kuwayama), is the main vector of the bacteria (Candidatus Liberibacter spp.) that causes citrus greening disease, also known as Huanglongbing (HLB), which has been responsible for serious damage to citrus crop in Florida and other parts of the world. Since the disease is managed primarily through controlling the vector it is important to have good understanding of host/ACP relationship at physiological and biochemical levels. This study was conducted as part of a larger program to elucidate biochemical aspects of ACP interactions with the host plant. Among a plethora of metabolic changes that may occur during plant-insect interactions, changes in profiles of free amino acids are generally distinctly noticeable and often related to the increased infestation; perhaps, as increased availability of specific nutrients. In fact, it has also been shown that different species of insects differ in their preferences for specific amino acids. Thus, amino acid changes induced by one herbivore could deter or attract another insect herbivore. Both, biotic stress, from herbivore, and abiotic stress, such as water deficit, can produce common and/or different changes in amino acid profiles that may in turn promote or deter feeding by specific insect species. Therefore, in this study we have looked at changes in free amino acid profiles in Satsuma (Owari cultivar) leaves in response to ACP feeding on leaves and also when the plants were subjected to water stress. Changes in amino acid levels could also affect levels of polyamines because in metabolic chain some amino acids (e.g. arginine) act as precursors for the synthesis of polyamines in plants. Polyamines have also been implicated in plant defenses. Putrescine has been reported to directly affect insect growth and metamorphosis such as induction of diapause and post diapause development. In addition, they could also promote the production of volatiles that may attract predators. Thus data on changes in the levels of polyamines in Satsuma leaves in response to ACP feeding and water stress are also included in this study.
Technical Abstract: The effects of biotic and abiotic stresses on changes in amino acids and polyamine levels in Satsuma orange (Citrus unshiu; cultivar Owari) leaves were investigated. Asian citrus psyllids (Diaphorina citri (Kuwayama) (ACP) infestation was used to induce biotic stress while a water deficit was imposed to induce abiotic stress. Potted trees were infested by placing 50 psyllids on 3 citrus leaves enclosed in nylon mesh bags for five days. A parallel set of potted plants were kept water stressed by maintaining the soil at 20% water holding capacity for five days. Levels of total free amino acids were higher in water stressed and ACP infested leaves. The level of the polyamine putrescine increased in infested leaves but not in water stressed leaves. Proline was the most abundant amino acid and its levels significantly increased by both biotic and abiotic stresses. Proline levels in infested leaves were significantly higher than the water stressed leaves. Histidine, methionine, asparagine, arginine, serine, and Leucine levels also increased significantly in infested leaves, but in water stressed leaves only leucine, methionine, and threonine increased. Levels of amino acids, such as tyrosine, isoleucine, phenylalanine, glutamic acid, and alanine declined in infested leaves and under water stress asparagine, phenylalanine, serine, and histidine also declined compared to controls. This indicates that while proteolysis occurred under both stresses, metabolic conversion of amino acids was different under the two stresses. In ACP infested leaves some amino acids may be used as feeding material and/or converted into secondary metabolites for defense.