Antisense suppression of phospholipase D alpha retards abscisic acid- and ethylene-promoted senescence of postharvest Arabidopsis leaves.

Abstract

Membrane disruption has been proposed to be a key event in plant senescence, and phospholipase D (PLD; EC 3.1.4.4) has been thought to play an important role in membrane deterioration. We recently cloned and biochemically characterized three different PLDs from Arabidopsis. In this study, we investigated the role of the most prevalent phospholipidhydrolyzing enzyme, PLDa, in membrane degradation and senescence in Arabidopsis. The expression of PLDa was suppressed by introducing a PLDa antisense cDNA fragment into Arabidopsis. When incubated with abscisic acid and ethylene, leaves detached from the PLDa-deficient transgenic plants showed a slower rate of senescence than did those from wild-type and transgenic control plants. The retardation of senescence was demonstrated by delayed leaf yellowing, lower ion leakage, greater photosynthetic activity, and higher content of chlorophyll and phospholipids in the PLDa antisense leaves than in those of the wild type. Treatment of detached leaves with abscisic acid and ethylene stimulated PLDa expression, as indicated by increases in PLDa mRNA, protein, and activity. In the absence of abscisic acid and ethylene, however, detached leaves from the PLDa-deficient and wild-type plants showed a similar rate of senescence. In addition, the suppression of PLDa did not alter natural plant growth and development. These data suggest that PLDa is an important mediator in phytohormone-promoted senescence in detached leaves but is n o t a direct promoter of natural senescence. The physiological relevance of these findings is discussed. INTRODUCTIONSenescence in plants is characterized by degradation of cellular components, leading to the loss of cellular compartmentalization and tissue structure and ultimately to plant death. Disruption of membrane integrity has been hypothesized to be a major contributing factor to senescence (Beutelman and Kender, 1977; Thompson, 1988; Paliyath and Droilard, 1992; Borochov et al., 1997). One of the most characteristic features in membrane deterioration is a progressive decline of phospholipid levels with a relative enrichment of free fatty acids and sterols in the membranes (Draper, 1969;Liljenberg and Kates, 1985;Manoharan et al., 1990; Paliyath and Droilard, 1992). The change in lipid composition may cause the localized transformation of a membrane lipid bilayer into destabilized bilayer and nonbilayer structures, such as gel, micellar, and hexagonal phases (Lafleur et al., 1990), leading to the loss of membrane integrity and functions of membrane-associated proteins during senescence.How does the loss of membrane phospholipids occur during senescence? One model suggests that the breakdown of phospholipids results from a membrane lipid degradation pathway (Thompson, 1988;Paliyath and Droillard, 1992; Both authors contributed equally to this work. 'To whom correspondence should be addressed. E-mail wangs@ ksu.edu; fax 785-532-7278. Samama and Pearce, 1993;Voisine et al., 1993). In this process, phospholipase D (PLD) initiates the first reacti...

The role of phospholipase D in plant stress responses

“…The generated PA could be broken down further by phosphatases, acylhydrolases and lipoxygenases into soluble molecules, which could subsequently be absorbed and recycled. PLD in plants has been proposed function in this way in processes such as senescence (Fan et al, 1997) and wounding (discussed in section 4.2).…”

“…Indeed, knock-down or knock-out of specific PLD isoforms has been shown to have distinct effects. AtPLDα1-silenced Arabidopsis plants have an altered response to wounding , induction of senescence (Fan et al, 1997), water loss (Sang et al, 2001a), superoxide generation (Sang et al, 2001b) and freezing . Arabidopsis AtPLDδ knock-out lines are more sensitive to H 2 O 2 and freezing .…”

Large‐scale identification of leaf senescence‐associated genes

“…The hexokinase-mediated sugar signaling pathway has been suggested to regulate the initiation of senescence (Dai et al, 1999). Lipid degradation also accompanies the other characteristic catabolic processes of leaf senescence (Thompson et al, 1998), and is re¯ected by an increase in the expression of a lipase (At2g42690) and Phospholipase Da (Fan et al, 1997). It is most likely that lipid degradation is not just a symptom of the senescence process but may also act in regulating the progression of age-dependent senescence .…”

Overexpression of AtSZF2 from Arabidopsis Showed Enhanced Tolerance to Salt Stress in Soybean

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