Despite low respiratory rates in citrus fruit prolonged
Despite low respiratory rates in citrus fruit, prolonged periods of storage may cause significant changes in the levels of organic acids (Echeverria and Valich, 1988). V-ATPase and V-PPase catalyze the electrogenic H+ translocation from the cytosol to the vacuolar lumen to generate an inside-acid pH, and their activity is important in energy recovery during the decline in fruit acidity (Marsh et al., 2001). Here, we have investigated whether changes in Scrambled 10Panx content in juice sacs could be related to differences in V-PPase and V-ATPase gene expression. We observed that the V-PPase transcript level juice sacs showed a down-regulated V-PPase gene expression after HWT as compared to control (except in the damaged fruit HWD 55°C, 2min). Storage of fruit at 2°C for 8 weeks induced V-ATPase gene transcript level in both treatments which was also associated with a lower acid content in the juice (Table 2, Table 5). The finding of an induction of both V-PPase and V-ATPase in fruit damaged by heat treatments (55°C, 2min) is interesting as it may confirm the loss of membrane integrity indicated by a rise in POX level in damaged fruit. A significant induction (5–6-fold) of ATPase and V-PPase occurred and this may be associated with compensation for a loss of tonoplast integrity in fruit treated at 55°C compared to those at 50°C.
Conclusion This study has shown that there is potential for a 2min HWD at 47.4–50°C to reduce CI in mandarins stored at low (2°C) temperature for 8 weeks. There is a narrow range of temperatures that can delay CI development in storage and the suitability of this treatment in different geographic locations and seasons needs to be tested. We also found that V-ATPase and V-PPase transcript levels responded rapidly to heat treatments but were largely recovered after 8 weeks cold storage for successful (non-damaging) heat treatments.
Abnormal vascular smooth muscle cell (VSMC proliferation plays an important pathophysiological role in the development of both major forms of of vascular disease: hypertension and atherosclerosis , . Platelet-derived growth factor-BB (PDGF-BB) and angiotensin II (Ang II) are potent growth factors for VSMCs , , , and are postulated to play an important role in the pathogenesis of cardiovascular disease , . Activation or inhibition of mitogenic signaling pathways are complex biological processes associated with the activation or inhibition of several protein kinases (for review, see ). However, in the past few years interconnections between growth-promoting and growth-inhibitory pathways leading to a balance of cell growth have been recognized. For instance, the activation of the extracellular signal-regulated (ERK) MAP kinase has been recognized as a central mitogenic signaling pathway leading to the expression of the immediate early genes like , . In this context, it has been established that PDGF-BB or Ang II propagate their growth signals in VSMCs binding to the PDGF β-receptors, which are tyrosine kinase receptors , or to G protein-coupled AT1 receptors, respectively, resulting in the activation of the MAP kinases , , expression of c-, and egr-1 mRNA , . In contrast, the stress-activated protein kinase (SAPK) pathway plays an important role in the response to extra- and intracellular stress stimuli and promotes inhibition of cell growth , . Therefore, identification and characterization of several genes encoding for proteins that are involved in the regulation of VSMC growth are essential steps in the understanding of the molecular biological nature of cardiovascular disease. The differential display (DD) approach allows identification and characterization of differentially expressed eukaryotic messenger RNA by means of the polymerase chain reaction (PCR) . In order to identify and characterize genes that may be involved in the growth processes of VSMCs, we compared the differentially expressed genes in control Ang II- or PDGF-BB-stimulated cells.