Development Of Wound Periderm Research Articles

Abscisic acid mediates wound-healing in harvested tomato fruit

The development of wound periderm is vital to prevent water vapor loss and pathogen invasion in wounded fruit. The effect of abscisic acid (ABA) on wound-healing in harvested tomato fruit was evaluated in this study. Wounded tomato fruit were treated with ABA or fluridone (FLD, an inhibitor of ABA biosynthesis), respectively, and allowed to wound-heal at 20°C in darkness for 4days. Weight loss of tomato fruit reflected the intuitionistic effects of different treatments during wound-healing. Autofluorescence and histochemical staining demonstrated the development of suberized wound periderm in harvested tomato fruit at 3–4day after wounding. Alkanoic acids, n-alkanes, unsaturated fatty acids and pentacosane represented the major components in the suberin. ABA-treated fruit showed enhanced autofluorescence, histochemical intensity and suberin deposition along with increased activities of phenylalanine ammonia-lyase (PAL) and peroxidase (POD). FLD treatment, however, alleviated the features of suberization and enzyme activities during wound-healing. The results suggest that ABA is involved in the stimulation of wound-induced suberization in harvested tomato fruit.

Wounding induces changes in cytokinin and auxin content in potato tuber, but does not induce formation of gibberellins

Cytokinin, auxin and gibberellin contents in resting and wound-responding potato tubers have not been fully determined and coordinated with wound-healing processes. Using a well-defined wound-healing model system, hormone content and expression of genes associated with hormone turnover were determined in tubers following wounding. Changes in hormone content were coordinated with: (I) formation and completion of the wound closing layer (0–5/6 days), and (II) initiation of phellogen and wound periderm formation (∼7 days). Quantifiable amounts of biologically active cytokinins (Z, DZ and IP) were not detected in resting or wound-responding tubers. However, the precursor IPA and catabolic product c-ZOG were found in small amounts in resting and wound-responding tubers. Wound-induced activation of cytokinin biosynthesis was suggested by an increase in t-ZR and c-ZR content at 0.5 days and large increases in IPA and c-ZR content by 3 days and throughout 7 days after wounding suggesting roles in II, but little or no role in I. Expression of key genes involved in cytokinin metabolism followed similar profiles with transcripts decreasing through 3 days and then increasing at 5–7 days after wounding. Both free IAA and IAA-Asp were present in resting tubers. While IAA-Asp was no longer present by 3 days after wounding, IAA content nearly doubled by 5 days and was more than 4-fold greater at 7 days compared to that in resting tuber (0 day) suggesting roles in II, but little or no role in I. Gibberellins were not present in quantifiable amounts in resting or wound-responding tubers. These results suggest that bio-active cytokinins are wound-induced, but their residency is temporal and highly regulated. The transient presence of active cytokinins and corresponding increases in IAA content strongly suggest their involvement in the regulation of wound periderm development. The absence of gibberellins indicates that they are not a regulatory component of wound-healing processes.

Kinetics and localization of wound-induced DNA biosynthesis in potato tuber

Tuber wounding induces a cascade of biological responses that are involved in processes required to heal and protect surviving plant tissues. Little is known about the coordination of these processes, including essential wound-induced DNA synthesis, yet they play critical roles in maintaining marketability of the harvested crop and tubers cut for seed. A sensitive “Click-iT EdU Assay” employing incorporation of the thymidine analog, 5-ethynyl-2′-deoxyuridine (EdU), in conjunction with 4′,6-diamindino-2-phenylindole (DAPI) counter labeling, was employed to objectively identify and determine the time course and spatial distribution of tuber nuclei that were wound-induced to enter S-phase of the cell cycle. Both labeling procedures are rapid and sensitive in situ. Following wounding, EdU incorporation (indicating DNA synthesis) was not detectable until after 12h, rapidly reached a maximum at about 18h and then declined to near zero at 48h. About 28% of the nuclei were EdU labeled at 18h reflecting the proportion of cells in S-phase of the cell cycle. During the ∼30h in which induced cells were progressing through S-phase, de novo DNA synthesis extended 7–8 cell layers below the wound surface. Cessation of nuclear DNA synthesis occurred about 4 d prior to completion of wound closing layer formation. Initiation of wound periderm development followed at 7 d, i.e. about 5 d after cessation of nuclear DNA biosynthesis; at this time the phellogen developed and meristematic activity was detected via the production of new phellem cells. Collectively, these results provide new insight into the coordination of wound-induced nucleic acid synthesis with associated tuber wound-healing processes.

Wound-induced suberization genes are differentially expressed, spatially and temporally, during closing layer and wound periderm formation

Potato tuber (Solanum tuberosum L.) wounds incurred at harvest and upon seed cutting require rapid suberization as a major part of the healing process to prevent infection and desiccation. However, little is known about the induction and expression of genes that are essential for these processes and in particular to the two major stages of wound-induced suberization, i.e. closing layer formation and wound periderm formation. The objectives of this research were to address these needs by determining the effects of wounding on the induction and expression profiles of specific genes involved in wound-induced suberization in potato tuber (S. tuberosum L.) during the initiation and completion of closing layer formation and wound periderm formation. Although both stages critically involve suberization, there are significant differences between the two processes. Closing layer development requires rapid suberization of existing parenchyma cells bordering the wound surface to provide the initial protective barrier for the wound. Wound periderm development occurs later, i.e. after completion of closing layer formation, and requires development of a wound phellogen layer which mediates the formation of highly organized files of suberized wound-phellem cells that provide a more durable protective barrier for the tuber. The processes delineating these two separate stages of wound-induced suberization are poorly understood. This research shows that, unlike some wound responding genes such as phenylalanine ammonia lyase (StPAL-1) and anionic peroxidase (StPrx), certain genes that are specifically involved in both of these processes do not remain uniformly up-regulated during the two stages of healing (i.e. StTHT encoding Hydroxycinnamoyl-CoA:tyramine N-(hydroxycinnamoyl)transferase, StFHT encoding a fatty ω-hydroxyacid/fatty alcohol hydroxycinnamoyl transferase, StKCS6 encoding a 3-ketoacyl-CoA synthase, StFAOH encoding a fatty acid ω-hydroxylase and StGPAT5 encoding a protein with acyl-CoA:glycerol-3-phosphate acyltransferase). Instead, they are up-regulated during closing layer formation; i.e. starting by ca. 1d after wounding, but then slightly down-regulated or pause near completion of the closing layer (ca. 5–6d) and then again up-regulated as wound periderm development is fully initiated (ca. 7d) and down-regulated near completion (ca. 28d after wounding). This differential in the expression profile, i.e. decrease between stages, was not anticipated and may be the first demonstration of measurable changes of any sort of biological flux as wound induced suberization transitions from closing layer to wound periderm development. Results were repeated using minitubers from two different crop years and demonstrate that these processes are separate, but coupled in some yet to be determined fashion. The biology of this differential expression is important because of the roles closing layer and wound periderm development play in protecting the tuber from disease and other challenges.

Wounding coordinately induces cell wall protein, cell cycle and pectin methyl esterase genes involved in tuber closing layer and wound periderm development

Little is known about the coordinate induction of genes that may be involved in agriculturally important wound-healing events. In this study, wound-healing events were determined together with wound-induced expression profiles of selected cell cycle, cell wall protein, and pectin methyl esterase genes using two diverse potato genotypes and two harvests (NDTX4271-5R and Russet Burbank tubers; 2008 and 2009 harvests). By 5d after wounding, the closing layer and a nascent phellogen had formed. Phellogen cell divisions generated phellem layers until cessation of cell division at 28d after wounding for both genotypes and harvests. Cell cycle genes encoding epidermal growth factor binding protein (StEBP), cyclin-dependent kinase B (StCDKB) and cyclin-dependent kinase regulatory subunit (StCKS1At) were induced by 1d after wounding; these expressions coordinated with related phellogen formation and the induction and cessation of phellem cell formation. Genes encoding the structural cell wall proteins extensin (StExt1) and extensin-like (StExtlk) were dramatically up-regulated by 1–5d after wounding, suggesting involvement with closing layer and later phellem cell layer formation. Wounding up-regulated pectin methyl esterase genes (StPME and StPrePME); StPME expression increased during closing layer and phellem cell formation, whereas maximum expression of StPrePME occurred at 5–14d after wounding, implicating involvement in later modifications for closing layer and phellem cell formation. The coordinate induction and expression profile of StTLRP, a gene encoding a cell wall strengthening “tyrosine-and lysine-rich protein,” suggested a role in the formation of the closing layer followed by phellem cell generation and maturation. Collectively, the genes monitored were wound-inducible and their expression profiles markedly coordinated with closing layer formation and the index for phellogen layer meristematic activity during wound periderm development; results were more influenced by harvest than genotype. Importantly, StTLRP was the only gene examined that may be involved in phellogen cell wall thickening after cessation of phellogen cell division.

The response of resistant kiwifruit (Actinidia chinensis) to armoured scale insect (Diaspididae) feeding

The responses of five experimental genotypes and one commercial variety of kiwifruit (Actinidia chinensis) to attack by two polyphagous, congeneric armoured scale insect pests (Hemiberlesia rapax and H. lataniae) are described. H. lataniae feeding elicits a response in the bark and fruit of all but one of the experimental genotypes, leading to the development of wound periderm over a 4–5 week period, and death of the insect. The response, which differs slightly between tissue types and genotypes, consists of wound periderm formation in a bowl shape beneath and around the insect, preventing its stylet from reaching normal unmodified parenchyma tissue. Wound periderm cell walls become suberised and cells beneath the insect become filled with phenolic compounds. In some cases, cells beneath the insect become hypertrophic or undergo lysis, exhibiting characteristics of a hypersensitive-like response. The remaining genotype showed no physical change in tissue structure in response to H. lataniae feeding, and the insects survived but were substantially reduced in size. These results suggest that both physical and chemical plant resistance responses are involved. In contrast, H. rapax elicited no observable histological response from any of the genotypes and the insects developed normally on bark and fruit. Both insect species developed normally on leaf petioles and these exhibit only slight cell wall thickening in response to their feeding. This unusual plant defensive response to a sucking insect has similarities to simple types of gall formation in response to insect and pathogen attack and has characteristics of resistance gene-mediated models of plant defence.

Wound healing and induced resistance in potato tubers

It was demonstrated that biogenic elicitors, arachidonic acid and chitosan, locally and systemically stimulated wound healing in potato tuber tissues by increasing the number of wound periderm layers, accelerating the development of cork cambium (phellogen), and inducing proteinase inhibitors. The signal molecules, jasmonic and salicylic acids, had different effects on the development of wound periderm: jasmonic acid locally and systemically stimulated potato wound healing and elevated the level of proteinase inhibitors, whereas salicylic acid did not have any effect on wound healing and even blocked the formation of proteinase inhibitors.

Methyl jasmonate induces changes mimicking anatomical defenses in diverse members of the Pinaceae

Conifers have defenses such as the production of phenolic compounds and resins that can be induced by bark beetles and other invading organisms, but the signaling agents involved are unknown. The anatomical effects of methyl jasmonate (MJ), a potent inducer of certain plant defenses, were compared with wounding of the bark of 12-15-year-old trees of five conifer species. Wounding in all species resulted in tissue necrosis and wound periderm development immediately around the wound site. One cm from the wound, swelling of phloem polyphenolic parenchyma cells and phenolic accumulation were observed in Pseudotsuga menziesii (Mirb.) Franco, Picea pungens Engelman, Larix occidentalis Nutt. and Pinus monticola Douglas ex D. Don, but not in Taxus brevifolia Nutt. Traumatic resin ducts were formed in response to wounding in three species of Pinaceae, but not in P. monticola, which formed irregular clusters of cells rather than ducts. Taxus brevifolia did not form resin ducts in response to either wounding or MJ treatment. In the Pinaceae species studied, surface application of 100 mM MJ caused similar anatomical changes to those observed in response to wounding, including phenolic accumulation, cell swelling and traumatic resin duct formation, but it did not induce a wound periderm. Traumatic resin ducts differed in size among the study species, ranging from small in L. occidentalis to very large in P. menziesii. In P. menziesii, P. pungens and L. occidentalis, traumatic resin ducts were more abundant after MJ treatment than after wounding. We conclude that the octadecanoid pathway is likely involved in defense responses in stems of the Pinaceae, but not necessarily in other taxa.

Formation of the ligno‐suberized barrier zone and wound periderm in four species of European broad‐leaved trees

SummaryThe development of wound periderm after mechanical wounding was examined in the barks of Acer pseudoplatanus, Betula pendula, Fagus sylvatica and Sorbus aucuparia. Following the initial necrosis of cells immediately surrounding the wounds, development of the ligno‐suberized barrier zone was detected within 7 days. Suberin deposition was observed in this tissue in A. pseudoplatanus, S. aucuparia and B. pendula 7 days after wounding, but not in F. sylvatica until day 14. By 28 days after wounding, extensive thickening of the walls of these cells had occurred. Differentiation of the wound periderm was detected immediately abutting the ligno‐suberized barrier‐zone tissues in all species, with extensive development by 28 days. Fifty‐six days after wounding, the wound periderm was fully formed and completely confluent with the original periderm. Development of the wound response was similar in all species, with differences only in the timing of first detection of suberin.

Wound Periderm Development in Red Mangrove, Rhizophora mangle L.

The response of red mangrove, Rhizophora mangle L., to wounding was studied Young mangrove seedling hypocotyls were wounded. Wound periderm development was documented with both light microscopy and scanning electron microscopy. The separation of necrotic tissue from the living tissue by a closing layer occurred in 17 d, and the development of wound periderm enclosing the wound was observed in 52 d. Brachysclereids developed in the wound periderm, and vascular tissue proliferated near the wound. Wound periderm development compartmentalized wounds and thus may prevent the spread of pathogens from the wounded tissues to the adjacent living tissues.

The effect of temperature and relative humidity on wound healing and infection of potato tubers byAlternaria solani

Under environmental conditions favorable for wound healing, potato tubers became significantly (P = 0.05) more resistant toA. solani infection during a two-day interval between wounding and inoculation. This period coincided with the time required for wounded tubers to completely seal wounded surfaces by suberization at 15.6°C/98% RH. Suberization of the wounded surfaces provided tubers significant (P = 0.05) protection againstA. solani invasion but wound periderm development was also essential for total exclusion of the pathogen. Wound healing takes place faster at high temperatures and relative humidities. The effect of temperature is more critical in the wound healing process.

EFFECT OF GROWTH REGULATORS AND HERBICIDES ON NORMAL AND WOUND PERIDERM ONTOGENY IN FRAXINUS PENNSYLVANICA SEEDLINGS*

Summary. IAA, GA, kinetin, 2,4‐D and naptalam were applied at 100 or 1000 ppm in lanolin to wounds made at the top of the hypocotyl of Fraxinus pennsylvanica Marsh. seedlings. Formation of normal periderm was prevented in the hypocotyl below the wounded tissue by 1000 ppm IAA or naptalam and 100 or 1000 ppm 2,4‐D. IAA or naptalam at 100 ppm and GA or kinetin at 100 or 1000 ppm retarded normal periderm development. Wound periderm development was prevented only by 1000 ppm 2,4‐D. Wound‐stimulated development of normal periderm in tissues near the wound was prevented by 1000 ppm kinetin and 100 or 1000 ppm 2,4‐D. Anomalous growths which appeared morphologically similar to nascent roots developed in the wounded hypocotyl section of seedlings treated with 1000 ppm naptalam and 100 or 1000 ppm 2,4‐D. Identical growths were found in unwounded portions of the hypocotyl of seedlings treated with 100 or 1000 ppm 2,4‐D. The data emphasize differences in physiological control of normal and wound periderm development. Effets de substances de croissance et d'herbicides sur l'onlogénie du pérderme normal ou blessé dans des plantules de Fraxinus pennsylvanica.

Effect of Phytophthora infestans Infection on Wound Periderm Formation in Cut Potato Tuber Tissue

Observations were made on the processes of (1) wound periderm formation, (2) lignification (with phloroglucine-HCl), and (3) suberification (with Sudan III) of cut tuber surfaces of the highly resistant potato cv. Rishiri (R1) either inoculated with race 0 (incompatible) or race 1 (compatible) of Phytophthora infestans or non-inoculated. All experiments were conducted at 19-20°C. With cut tissue (control, noninoculated), renewed cell division first appeared on the surface two days after cutting, with subsequent cell division progressing toward inner tissue. Cell division occurring in a few cells located in succession from the cut surface toward the inner tissue resulted in the formation of a periderm. When the cut surface was inoculated with an incompatible race just after cutting, cell division was delayed, and the thickness of the periderm was reduced. In tissue inoculated with a dilute zoospore suspension, cell division first occurred in the cell directly adjacent to the browned cell, thereafter progressing toward the inner tissue. When inoculated with a concentrated zoospore suspension, cell division first occurred in the third cell away from the browned cell. Usually no cell division occurred in the second cell (the cells directly adjacent to the browned cell). The rapidity and extent of lignification and suberification also were reduced by infection with an incompatible race. Infection by a compatible race strongly inhibited the development of wound periderm structure.Evidence was presented that the infection by the incompatible race itself can cause the formation of the periderm.With aged tubers, the brown lesion progressed inward more deeply. The formation of the periderm was delayed and its extent also was reduced, as compared with fresh tubers. In extreme cases no periderm developed, even though the lesion has stopped developing.

DIVISION OF STARCH‐CONTAINING CELLS

DIVISION OF CERTAIN CELLS whose contents indicate a state of physiological specialization has been reported recently by several investigators. Bloch (1947) noted the retention of the power of multiplication for a considerable time after differentiation by some idioblasts such as oil cells, tannin cells, and cells containing crystals of calcium oxalate. In Ricinus the secretory cells whose contents give the reactions of tannin and fatty acids divide along with the rest of the ground parenchyma cells in the intercalary rib meristem of the internodal regions (Bloch, 1948). Ball (1950) observed that tannincontaining cells as well as clear cells could function as initials of files of cells at the margins of callus cultures of Sequoia sempervirens. The present paper reports observations on division of the starch-containing cortical parenchyma cells of young potato tubers (var. Irish Cobbler). Multiplication of these cells occurs during the normal development of the young tuber. Their division is of interest not only because they are physiologically differentiated cells but also because of the prevalent idea that division of starch-containing cells is preceded or accompanied by digestion of the starch grains. This idea is supported by the observations of some investigators on the development of wound periderm in the potato. Priestley and Woffenden (1923) observed that within a few days of the formation of a suberin or fatty deposit on the cut surface of a potato tuber, the cells just below the surface rapidly lose their starch content and the cork meristem then arises within this region. Steward et al. (1932) found that potato discs respiring in air showed extensive starch disappearance to a depth of 0.8 mm. below the cut surface and the development of a cork cambium in this surface region of starch depletion. Their figure 8A shows that the starch depletion in the surface region was partial rather than complete. One brief reference to the division of potato tuber cells that contain starch grains has been found in the literature. Nemec (1899) noted that the spindle fibers in the vicinity of vacuoles or starch grains adjacent to the nucleus were shorter t-han the other fibers and he figured two large starch grains near a dividing nucleus. Division of cells containing starch would be expected to take place in any developing homogeneous tissue in which starch storage begins before enlargement of that tissue by cell division has ceased. It seems probable, therefore, that division of starch-containing cells is not