Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

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PHOSPHOLIPASE D, MEMBRANE DETERIORATION, AND SENESCENCE 207 9.3.2.3 Activation of PLD by calcium Stimulation of PLD by calcium may arise through more than one mechanism. Two possibilities are calcium-dependent membrane association, which increases enzyme substrate interactions and substrate availability, and direct activation of the enzyme by calcium. PLD activity in strawberry fruit membranes was also stimulated by calcium (Fig. 9.8, top panel). Both microsomal and mitochondrial PLD were maximally stimulated (sixfold stimulation for microsomal membranes, threefold stimulation for mitochondrial membranes) between 1 and 3-mM added calcium. The assay mixture contained 0.2-mM ethylene glycol-bis-βaminoethyl ether, N,N,N ′ ,N ′ tetra-acetic acid (EGTA) that acts as a calcium-buffering agent and provides precise levels of free calcium, especially at low levels of added calcium. Microsomal membranes showed nearly fourfold stimulation between 0.15- and 0.25-mM added Choline released (nmol/mg protein) 70.00 60.00 50.00 40.00 30.00 20.00 10.00 0.00 0 1 2 3 4 5 6 7 8 9 10 11 CaCl 2 (mM) Mitochondrial membrane Microsomal membrane Choline released (nmol/mg protein) 70.00 60.00 50.00 40.00 30.00 20.00 10.00 Mitochondrial membrane Microsomal membrane 0.00 0 0.2 0.4 0.6 0.8 1 1.2 CaCl 2 (mM) Fig. 9.8 Effect of increasing calcium on PLD activity in mitochondrial and microsomal membrane of strawberry fruit. Precise levels of free calcium levels were obtained by including 0.2-mM EGTA in the assay mixture. Under these conditions, free calcium concentrations for 100, 150, 200, and 250 μM added calcium ranged from ≤1, 1, 15, and 40 μM, respectively. PLD activity was measured by the release of radiolabeled choline from 16:0/16:0 phosphatidylcholine (L 3 -phosphatidyl (N-methyl- 3 H) choline, 1,2-dipalmitoyl) in a 1-mL reaction mixture resulting from a 15-min reaction period. The lower panel is an expansion of lower concentrations of calcium shown in the top panel. The values are mean ±SE from three separate experiments. (Reproduced with permission from Yuan et al., 2005.)
208 POSTHARVEST BIOLOGY & TECHNOLOGY OF FRUITS, VEGETABLES, & FLOWERS calcium (Fig. 9.8, bottom panel), which provides free calcium in the range of ≤1to40μM. Nearly threefold stimulation in PLD activity is observed at free calcium in the range of 1 μM (0.2-mM added calcium and 0.2-mM EGTA), which is in the range of physiologically activated levels of calcium (Felle, 1988; Yuan et al., 2006b). Thus, microsomal PLD is stimulated at low micromolar levels of calcium, implying a potential role in signal transduction processes. By contrast, mitochondrial PLD activity did not show any significant promotion at these levels of calcium (Fig. 9.8). Maximal stimulation of mitochondrial PLD was observed between 1 and 3 mM free calcium. 9.4 Subcellular localization of phospholipase D PLD is a soluble enzyme. However, analysis of PLD activity in subcellular fractions revealed the presence of PLD activity in mitochondrial, endoplasmic reticulum, and plasma membrane fractions. Membrane-associated PLD activity increases during ripening and after wounding. PLD was localized by immunoelectron microscopy in germinating castor bean tissue, and was shown to be associated with the plasma membrane and the vacuole (Xu et al., 1996). After wounding of castor bean leaves, lipolysis by PLD increased sharply following calcium-mediated translocation from the cytoplasm to microsomal membranes (Ryu and Wang, 1996). In rice, PLD was localized in cell walls, membranes, and chloroplasts (McGee et al., 2003), and was recruited to the plasma membrane at the point of adhesion of a bacterial pathogen (Young et al., 1996). In tomato fruits, PLD was localized in cytoplasm, plasma membrane, endoplasmic reticulum, mitochondria, and nuclear membrane (Pinhero et al., 2003). During early stages of development, PLD was primarily localized in the cytoplasm. As development progressed, a relatively large number of PLD polypeptides were observed in the endoplasmic reticulum (Fig. 9.9). In ripened strawberry fruit, a large number of PLD molecules were localized in the cell wall space (Yuan et al., 2006a). This may represent an advanced stage where cell permeability is compromised and the PLD molecules have leaked out of the cell or possibly were transported by exocytosis. 9.5 Characteristics of phospholipase D PLD (EC 3.1.4.4) is a key enzyme that catalyzes the hydrolysis of membrane phospholipids yielding PA and a hydrophilic head group (Galliard, 1980). PLD in plants was originally proposed to be important in phospholipid catabolism, initiating a lipolytic cascade in membrane deterioration during senescence and stress (Paliyath and Droillard, 1992). PLD could also be involved in phospholipid turnover that maintains cell viability and homeostasis (Dawidowicz, 1987). Recent studies in plants indicate that PLD action plays an important role in transmembrane signaling and cellular regulation (Wang, 2002, 2005). Activation of PLD generates lipid messengers, most importantly PA, which mediate an array of physiological responses (Wang, 2005; Bargmann and Munnik, 2006; Wang et al., 2006). The role of phospholipase D in the initiation of membrane deterioration during ripening and senescence has been well recognized (Paliyath and Droillard, 1992). About 15–25% loss of total phospholipids occurs during full ripening of tomato fruit pericarp tissue, with a coincident increase in PA, suggesting that PLD is involved in membrane degradation (Güçlü et al., 1989; Whitaker, 1994). Moreover, all the enzyme activities involved in the senescence cascade, including PLD, have been demonstrated in tomato fruit microsomal
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Postharvest Biology and Technology
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Edition first published 2008 c○ 2
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vi CONTENTS 9 Structural Deteriorat
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Contributors Ishan Adyanthaya Depar
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x CONTRIBUTORS Gopinadhan Paliyath
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xii PREFACE difficult to find a boo
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Chapter 1 Postharvest Biology and T
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POSTHARVEST BIOLOGY AND TECHNOLOGY
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COMMON FRUITS, VEGETABLES, FLOWERS,
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Chapter 3 Biochemistry of Fruits Go
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BIOCHEMISTRY OF FRUITS 21 et al., 2
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BIOCHEMISTRY OF FRUITS 23 3.2.2 Lip
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BIOCHEMISTRY OF FRUITS 25 exposure
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BIOCHEMISTRY OF FRUITS 27 isoform o
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BIOCHEMISTRY OF FRUITS 29 Maltose
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BIOCHEMISTRY OF FRUITS 31 content i
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BIOCHEMISTRY OF FRUITS 33 control.
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BIOCHEMISTRY OF FRUITS 35 range fro
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BIOCHEMISTRY OF FRUITS 37 six (gluc
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BIOCHEMISTRY OF FRUITS 39 Ethylene
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BIOCHEMISTRY OF FRUITS 41 3.3.3 Pro
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BIOCHEMISTRY OF FRUITS 43 component
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Phenylalanine Phenylalanine ammonia
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BIOCHEMISTRY OF FRUITS 47 coloratio
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BIOCHEMISTRY OF FRUITS 49 Fluhr, R.
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Chapter 4 Biochemistry of Flower Se
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BIOCHEMISTRY OF FLOWER SENESCENCE 5
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PROGRAMMED CELL DEATH DURING PLANT
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(a) (a′) (b) (b′) (c) (d) Fig.
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Chapter 6 Ethylene Perception and G
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ETHYLENE PERCEPTION AND GENE EXPRES
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Chapter 7 Enhancing Postharvest She
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ENHANCING POSTHARVEST SHELF LIFE AN
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HEAT TREATMENT FOR ENHANCING POSTHA
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HEAT TREATMENT FOR ENHANCING POSTHA
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THE ROLE OF POLYPHENOLS 261 mainly
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THE ROLE OF POLYPHENOLS 263 Table 1
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THE ROLE OF POLYPHENOLS 265 Pentose
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THE ROLE OF POLYPHENOLS 267 Phenyla
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THE ROLE OF POLYPHENOLS 269 3' OH H
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THE ROLE OF POLYPHENOLS 271 OH OH O
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THE ROLE OF POLYPHENOLS 273 compoun
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THE ROLE OF POLYPHENOLS 275 washing
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THE ROLE OF POLYPHENOLS 277 (Fujita
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THE ROLE OF POLYPHENOLS 279 Boyer,
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THE ROLE OF POLYPHENOLS 281 Peschel
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ISOPRENOID BIOSYNTHESIS IN FRUITS A
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Chapter 14 Postharvest Treatments A
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POSTHARVEST TREATMENTS AFFECTING SE
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Chapter 15 Polyamines and Regulatio
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POLYAMINES AND REGULATION OF RIPENI
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Chapter 16 Postharvest Enhancement
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POSTHARVEST ENHANCEMENT OF PHENOLIC
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RHIZOSPHERE MICROORGANISMS 361 the
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RHIZOSPHERE MICROORGANISMS 363 Rese
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RHIZOSPHERE MICROORGANISMS 365 Tabl
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RHIZOSPHERE MICROORGANISMS 367 Toma
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RHIZOSPHERE MICROORGANISMS 369 Such
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RHIZOSPHERE MICROORGANISMS 371 Gian
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Chapter 18 Biotechnological Approac
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BIOTECHNOLOGICAL APPROACHES 375 tec
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BIOTECHNOLOGICAL APPROACHES 381 Fla
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BIOTECHNOLOGICAL APPROACHES 383 adm
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BIOTECHNOLOGICAL APPROACHES 389 Kik
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BIOTECHNOLOGICAL APPROACHES 391 Tat
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POSTHARVEST FACTORS AFFECTING POTAT
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BIOSENSOR-BASED TECHNOLOGIES 419 20
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BIOSENSOR-BASED TECHNOLOGIES 421 Ta
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BIOSENSOR-BASED TECHNOLOGIES 425 Li
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BIOSENSOR-BASED TECHNOLOGIES 427 So
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BIOSENSOR-BASED TECHNOLOGIES 429 Pr
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BIOSENSOR-BASED TECHNOLOGIES 431 e
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BIOSENSOR-BASED TECHNOLOGIES 435 st
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Cl O O O OH Cl O OH Cl Cl Cl 2,4-Di
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BIOSENSOR-BASED TECHNOLOGIES 441 Le
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Chapter 21 Changes in Nutritional Q
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CHANGES IN NUTRITIONAL QUALITY OF F
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Index Abscisic acid (ABA), 65, 210,
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INDEX 469 Biosensor-based technolog
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INDEX 471 Cryptochlorogenic acid (4
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INDEX 473 French bean, 95 Fresh-cut
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INDEX 475 LePLDα3 (AY013253), 213-
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INDEX 477 Pectin methylesterase (PM
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INDEX 479 PSY1 expression, 289 PSY1
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INDEX 481 Sugars, biosynthesis of,
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