Plasma membrane ATPase activity during pepino (Solanum muricatum) ripening

Abstract

Plasma membrane‐enriched samples were extracted from pepino fruit (cv. El Camino) by phase partitioning. H+‐ATPase (EC 3.6.1.35) activity in these samples increased during late fruit development (immediately before the onset of ripening) and western blotting confirmed there was an increase in enzyme abundance at this time. H+‐ATPase activity decreased during early ripening and then increased again in the final phase of ripening. Immunolocalisation showed the plasma membrane H+‐ATPase was most abundant in the outer cell layers of the fruit, which are considered to have a major role in determining fruit texture. Fruit softening was not accelerated by harvest and there was no stimulation of H+‐ATPase activity by harvest. An in vitro tensile test using fruit rings showed tissue softening proceeded faster at low apoplastic pH (4.5) than at pH 6.5; and tissue buffered at pH 6.5 softened less than unbuffered rings. Erythrosin B, an inhibitor of the plasma membrane H+‐ATPase, also retarded softening in vitro. These data suggest that plasma membrane H+‐ATPase activity may contribute to the onset of pepino softening through a reduction in apoplastic pH.

Apoplastic pH and inorganic ion levels in tomato fruit: A potential means for regulation of cell wall metabolism during ripening

“…The mechanism for the change and homeostasis of the apoplastic pH may reside in plasmalemma ATPase activity. ATPase activity has been reported to increase during ripening of several fruits, including the climacteric apple ( Lurie and Ben‐Arie 1983) and pepino ( Heyes et al 1997), and the non‐climacteric strawberry ( Ben‐Arie and Faust 1980).…”

“…The dynamic changes in the cell wall of ripening fruit are anticipated to be under tight control by local pH and ionic conditions; however, relatively few studies have addressed these interactions. Several researchers have proposed a role for apoplastic pH in regulating fruit textural changes ( Knee 1982; Ugalde et al 1988; Huber and O'Donoghue 1993; Heyes et al 1997). Knee (1982) proposed apoplastic acidification as a means for explaining the solubilization of pectins (via calcium displacement) in ripening pome fruits.…”

INFLUÊNCIA DO ETILENO E DA H+-ATPase DURANTE O AMADURECIMENTO DE FRUTOS

“…Foi visto para frutos de mamoeiro, que o pico de etileno parece sinalizar para uma diminuição na atividade da enzima (Azevedo et al, 2008). Heyes et al (1997) verificaram que a bomba de prótons de membrana plasmática tinha sua atividade diminuída durante o início do amadurecimento e com posterior aumento na fase final, até a senescência, em pepino, sugerindo que esta bomba de prótons contribui para o amolecimento destes frutos através da diminuição do pH apoplástico. Domingos e Ruber (1998) também relatam variações no pH do apoplasto para frutos de tomateiro durante o processo de amadurecimento, eles sugerem que a diminuição no pH do apoplasto seja responsável pela degradação de polímeros e ativação de hidrólises alterando a textura do fruto.…”

“…Porém, os dados existentes na literatura sobre a regulação e papel das H + -ATPases no processo de maturação de frutos são controversos. Alguns trabalhos iniciais relataram ativações das H + -ATPases tipo P durante o amadurecimento de frutos (Lurie e Ben-Arie, 1983, Ben-Arie e Faust, 1980, enquanto efeitos inibitórios foram posteriormente relatados (Heyes e Townsend, 1992, Heyes et al, 1997. Em tomate, Amemiya et al (2006), observou um decréscimo da expressão do gene LeVHA-AP1 que codifica a subunidade A da V-ATPase, nos primeiros estádios de maturação, seguido pelo aumento do mesmo no estádio maduro.…”