Phospholipase D inhibition by hexanal is associated with calcium signal transduction events in raspberry

Abstract

Raspberry (Rubus spp.) is an economically important crop with a restricted growing season and very limited fruit shelf-life due to its extreme tenderness. In order to prolong its shelf life, an aqueous composition containing hexanal as the key active ingredient (HC) was applied as a preharvest spray during fruit development. The effects of HC were assessed using physiological, biochemical and anatomical parameters on the treated fruits and compared with the effects of mock inoculation which lacked hexanal. Sugars and acidity did not show a significant change in response to HC treatment, while the pulling force (the tension required to detach the berry from the receptacle) significantly improved in the HC-treated fruits, compared to control. Scanning electron microscope (SEM) analysis revealed a high correlation between the presence of rigid epidermal hairs and a stronger degree of attachment between berries and their receptacle in the HC treated fruits. Further, electron micrographs also showed abnormal crystalline depositions on the epidermal drupelets of the treated berries. Energy Dispersive X-ray Spectroscopy (EDS) analysis showed those crystals to be largely composed of calcium. HC treatment also resulted in the reduction of transcript level of three phospholipase D genes, as well as altered expression pattern of five members of the annexin gene family, and four calmodulin-binding transcription activators. Quantification of PLD activity showed that hexanal inhibited PLD activity in treated berries. The potential crosstalk between hexanal, phospholipase D activity and calcium and this crosstalk’s role in delaying fruit softening and in prolonging storage life of fruits shelf life is discussed.

Performance of five haskap (Lonicera caerulea L.) cultivars and the effect of hexanal on postharvest quality

“…In mango, a preharvest spray of EFF significantly enhanced the retention of fruit due to inhibition of RNA and protein synthesis in the abscission zone, thereby delaying the onset of abscission and extending the retention of fruit in trees (Anusuya et al 2016). An EFF treatment was also shown to enhance fruit retention of raspberry by strengthening the attachment of the berry to the receptacle through the increased presence of rigid epidermal hairs (El Kayal et al 2017a). Although a preharvest EFF spray was favourable for fruit retention of mango and raspberry, it did not enhance the retention of haskap fruit and appears to have had no effect on the formation of the abscission layer.…”

“…There has been increasing interest into extending the longevity of horticultural produce through the inhibition of PLD, an enzyme involved in fruit deterioration (Paliyath and Subramanian 2008;Sharma et al 2010;Cheema et al 2014;Gill et al 2016;El Kayal et al 2017a, 2017bKumar et al 2018). Phospholipase D activity is strongly inhibited by hexanal, a naturally occurring, volatile C 6 aldehyde (Paliyath et al 1999;Paliyath et al 2003; Tiwari and Paliyath 2011).…”

“…Preharvest spray application of EFF can extend the shelf life of several commercially important fruit crops such as nectarine (Kumar et al 2018), tomato (Cheema et al 2014), guava (Gill et al 2016), sweet cherry (Sharma et al 2010), and strawberry (El Kayal et al 2017b) through the inhibition of PLD. In addition to enhancing shelf life, preharvest sprays of EFF were shown to increase fruit retention of mango (Anusuya et al 2016) and raspberry (El Kayal et al 2017a).…”

Recent Advances in Hormonal Regulation and Cross-Talk during Non-Climacteric Fruit Development and Ripening

“…The loss of membrane integrity during the decline in fruit quality has been associated with 1-phospholipase D (PLD), a phospholipid-degrading enzyme involved in initiating membrane catabolic events that is highly active in berries such as strawberry and raspberry [230,231]. The pre-harvest application of aqueous spray containing hexanal (HC), an enhancer of fruit shelf-life, during fruit development showed significant downregulation of transcript levels of three PLD encoding genes and its associated enzymatic activity, as well as upregulation of the expression of the genes related to calcium-binding protein such as annexin and calmodulin-binding transcription activators [231]. All these changes were associated with the significant increase of the pulling force necessary to detach the berry from the receptacle and abnormal calcium crystalline depositions on the epidermal drupelet [231].…”

“…The pre-harvest application of aqueous spray containing hexanal (HC), an enhancer of fruit shelf-life, during fruit development showed significant downregulation of transcript levels of three PLD encoding genes and its associated enzymatic activity, as well as upregulation of the expression of the genes related to calcium-binding protein such as annexin and calmodulin-binding transcription activators [231]. All these changes were associated with the significant increase of the pulling force necessary to detach the berry from the receptacle and abnormal calcium crystalline depositions on the epidermal drupelet [231]. These antecedents suggest a potential crosstalk between hexanal, phospholipase D activity and calcium in delaying fruit softening and in prolonging the storage life of raspberry.…”