Response to CMNP is under hormonal control and involves phospholipid signaling

• Published in: Acta horticulturae no. 965; pp. 101 - 103
• Main Authors: Alferez, F, Burns, J.K
• Format: Journal Article
• Language: English
• Published: International Society for Horticultural Science 01-01-2012
• Subjects: abscisic acid; abscission; Citrus; gene expression; hormonal regulation; hormones; indole acetic acid; mechanical harvesting; oranges; phospholipase A2; phospholipases; phospholipids; trees
• ISSN: 0567-7572; 2406-6168
• DOI: 10.17660/actahortic.2012.965.11

Control of abscission is a main goal for citriculture to ensure success of mechanical harvesting. Adoption of mechanical harvesting will accelerate when an abscission agent is available that specifically causes mature fruit to abscise, increases fruit removal and improves economic efficiency of machines. The abscission agent CMNP has been extensively evaluated, and it's use with processed orange harvesting improves machine efficiency and removes an average of 12% more mature fruit when compared to untreated controls. Our research focuses on mechanisms that control abscission, overcoming developmental barriers and improving response to CMNP throughout the harvest season. The simultaneous presence of young developing fruitlets and mature fruit on 'Valencia' sweet orange trees is associated with variable efficacy to CMNP; such variability can reduce the benefits of abscission agent application. A main factor controlling abscission is the endogenous balance between the hormones auxin (IAA) and abscissic acid (ABA). In some model systems, both hormones interact with a group of enzymes called phospholipases and control several developmental processes and responses to environmental cues. We followed IAA and ABA content and phospholipase A2 (CssPLA2) gene expression during the time when fruitlets and mature fruit were present simultaneously in 'Valencia'. Our results show that an elevated level of IAA originating from young developing fruit was correlated with a period of less responsiveness to abscission agents. By inhibiting IAA transport from fruitlets to mature fruit, we demonstrated that CssPLA2 gene expression was reduced and mature fruit loosening improved. ABA content accumulated as fruit developmentally matured and emerged from the period of less responsiveness. The results highlight hormonal interaction and the potential for lipid signals to control abscission in citrus.