Two expansin cDNAs from Prunus armeniaca expressed during fruit ripening are differently regulated by ethylene

Little is known about gene expression during fruit ripening of apricot (Prunus armeniaca L. cv. Bergeron), especially for enzymes involved in cell wall modifications. A partial cDNA clone encoding a protein homologous to expansin was isolated from a ripe apricot fruit cDNA library. This clone was used to isolate two full-length expansin cDNAs, Pa-Exp1 (accession no. U93167) and Pa-Exp2 (accession no. AF038815) from the same cDNA library. The predicted polypeptides encoded by these two cDNAs are different and belong to the α-expansin family; Pa-Exp1 and Pa-Exp2 are two different members of a multigene family. These two clones are mostly expressed in fruit, during its ripening. Pa-Exp1 mRNA accumulated abundantly at the half-ripe stage of fruit development and decreased thereafter. Pa-Exp2 mRNA level increased from the immature-green stage to the half-ripe stage where it peaked before declining. During the ripening process, Pa-Exp1 and Pa-Exp2 gene expression appeared to be positively correlated with fruit size. Post-harvest treatments by air, ethylene, and 1-methyl cyclopropene led us to conclude that Pa-Exp1 appears to be developmentally down-regulated by ethylene while Pa-Exp2 is not affected. The relationship between Pa-Exp1, Pa-Exp2 and the softening process is also discussed.     

Soperoxide dismutase activity in ripening cucumber and pepper fruit

Superoxide dismutase (SOD, EC 1.15.1.1) was identified from ripening cucumber ( Cucumis sativus L.) and pepper( Capsicum annuum L.) fruits, Gel filtration revealed the presence of two major peaks of SOD with molecular masses of about 32 000 and 40 000. Peroxidase activity was observed mainly in material with a molecular mass above 70 000. SOD activity was inhibited by cyanide but not by chloroform-ethanol, indicating a cupro-zinc enzyme. SOD activity levels were high in immature-green fruits of both species, declining in cucumbers to a minimum during the mature-green stage and in peppers during the mature-green and breaker stages. SOD levels increased again until peppers became orange and cucumbers turned yellow, and finally decreased with ripening. The possible connection between SOD activity and tolerance to sunscald is discussed.     

Promotion of ethylene evolution and ripening of tomato fruit by galactose

Mature green tomato fruit (Lycopersicon esculentum Mill. cv `Rutgers') were infiltrated with 0.5 milliliters of sterilized, distilled water alone, or containing enough glucose or galactose to allow for a concentration of 400 micrograms per gram fresh weight after infiltration. All fruit showed a transient peak of ethylene production within 6 hours due to the slight wounding by vacuum infiltration. In addition, galactose-treated fruit underwent a temporal increase in ethylene production after 25 hours, whereas, the glucose and H₂O-control fruit did not. Furit infiltrated with galactose subsequently produced ethylene and ripened substantially earlier than glucose or H₂O-control fruit.     

Biochemical changes associated with the ripening of hot pepper fruit

Hot pepper ( Capsicum annuum L. cv. Chooraehong) fruit underwent a respiratory climacteric during ripening. However, the rate of ethylene production was low, reaching a maximum of approximately 0.7 μl kg⁻¹ h⁻¹ at the climacteric peak when the surface color was 30 to 40% red. Ripening was accompanied by a loss of galactose and arabinose residues from the cell wall. The content of uronic acid and cellulose in the wall changed only slightly during ripening. The average molecular weight of a cell wall hemicellulosic fraction shifted progressively toward a lower molecular weight during ripening. Total β-galactosidase (EC 3.2.1.23) activity increased 50-fold from the immature green to the red ripe stage. No polygalacturonase (EC 3.2.1.15) activity was detected at any stage of ripeness. Thus, the loss of galactose and arabinose residues from the cell wall, as well as the observed modification of hemicelluloses during ripening, seem to be unrelated to active polygalacturonase. Soluble polyuronide content remained relatively constant at approximately 60 μg (g fresh weight)⁻¹ as fruit ripended.     

Effects of ethylene and acetylene on mango fruit ripening

Mangoes (var. Tommy Atkins) were exposed to ethylene and acetylene over a range of concentrations at high humidity for 24 h at 25°C, then ripened in air alone. Ripeness was assessed after 4 and 8 days by analysis of texture, colour development, soluble solids and acid contents. Ethylene in air at concentrations of 0.01 ml litre^-1 and above or acetylene at 1.0 ml litre^-1 were found to initiate ripening. Treatment with 0.01 ml litre^-1 acetylene resulted in limited softening but had no effect on the other ripening changes analysed. Individual ripening processes responded differently to treatment: texture changes were most rapidly affected, while the rate of acidity losses was often reduced in ethylene treated fruits. Acetylene-treated fruits at concentrations of 0.01 and 0.1 ml litre^-1 showed delayed ripening when compared to those treated with either 1.0 ml litre^-1 acetylene or ethylene. Increased acetylene concentrations of 2.0 ml litre^-1 gave a similar response to 1.0 ml litre^-1, although in some instances there were indications of inhibitory effects.     

Expression of ethylene biosynthetic and signaling genes in relation to ripening of banana fruit after cold storage

Banana fruit are highly sensitive to chilling injury (CI), while the effect of different degrees of CI on the subsequent fruit ripening is largely unknown. In the present work, ripening characteristic of banana fruit after storage at 7 °C for 3 days or for 8 days, and expression levels of eight genes associated with ethylene biosynthetic and signaling, including MaACS1, MaACO1, MaERS1, MaERS3, and MaEIL1–4, were investigated. The results showed that banana fruit stored at 7 °C for 8 days exhibited more severe chilling symptoms than those at 7 °C for 3 days. Compared with banana fruit stored at 7 °C for 8 days, which showed abnormal ripening, more decrease in fruit firmness, while higher increase in ethylene production and hue angle were observed in banana fruit stored at 7 °C for 3 days, which could ripening normally. Moreover, gene expression profiles during ripening revealed that ethylene biosynthetic and signaling genes were differentially expressed in peel and pulp of banana fruit after storage at 7 °C for 3 days and 7 °C for 8 days. In the peel of fruit storage at 7 °C for 3 days, expression levels of MaACS1, MaACO1, MaEIL1, and MaEIL2 increased remarkably while MaERS3, MaEIL1, and MaEIL4 were enhanced in the fruit after storage at 7 °C for 8 days. In the pulp, with the exception of MaACO1 and MaERS3, expression levels of other genes did not exhibit a significant difference, between the banana fruit storage at 7 °C for 3 days and 7 °C for 8 days. Taken together, our results suggest that differential expression of ethylene biosynthetic and signaling genes such as MaERS3, MaACO1, and MaEIL2, may be related to ripening behavior of banana fruit with different degrees of CI after cold storage.     

Low-temperature-modulated fruit ripening is independent of ethylene in 'Sanuki Gold' kiwifruit

Fruit ripening in response to treatments with propylene, 1-methycyclopropene (1-MCP), and low temperature was characterized in 'Sanuki Gold' kiwifruit, Actinidia chinensis Planch. Propylene treatment immediately induced rapid fruit softening, increased AC-PG (polygalacturonase) and AC-EXP (expansin) mRNA accumulation, and stimulated an increase in the soluble solid concentration (SSC) and a decrease in titratable acidity (TA). After 3?d exposure to propylene, ethylene production and AC-PL (pectate lyase) mRNA accumulation were observed. 1-MCP treatment after 24?h exposure to propylene eliminated AC-PG mRNA accumulation and suppressed continued changes in SSC and TA. Application of 1-MCP at the start of the treatment, followed by continuous propylene exposure, markedly delayed fruit softening, and the expression of the cell wall-modifying genes, and changes in the SSC and TA, indicating that kiwifruit become insensitive to ethylene at least for 3?d following 1-MCP exposure. Surprisingly, significant fruit softening, mRNA accumulation of AC-PG, AC-PL, and AC-EXP, and decreased TA were observed without ethylene production in intact fruit stored at low temperature for 1 month, but not in fruit stored at room temperature. Repeated 1-MCP treatments (twice a week) failed to inhibit the changes that occurred in low temperature storage. These observations indicate that low temperature modulates the ripening of kiwifruit in an ethylene-independent manner, suggesting that kiwifruit ripening is inducible by either ethylene or low temperature signals.     

Wound ethylene and 1-aminocyclopropane-1-carboxylate synthase in ripening tomato fruit

Ethylene production, 1-aminocyclopropane-1-carboxylic acid (ACC) levels and ACC-synthase activity were compared in intact and wounded tomato fruits (Lycopersicon esculentum Mill.) at different ripening stages. Freshly cut and wounded pericarp discs produced relatively little ethylene and had low levels of ACC and of ACC-synthase activity. The rate of ethylene synthesis, the level of ACC and the activity of ACC synthase all increased manyfold within 2 h after wounding. The rate of wound-ethylene formation and the activity of wound-induced ACC synthase were positively correlated with the rate of ethylene production in the intact fruit. When pericarp discs were incubated overnight, wound ethylene synthesis subsided, but the activity of ACC synthase remained high, and ACC accumulated, especially in discs from ripe fruits. In freshly harvested tomato fruits, the level of ACC and the activity of ACC synthase were higher in the inside parts of the fruit than in the pericarp. When wounded pericarp tissue of green tomato fruits was treated with cycloheximide, the activity of ACC synthase declined with an apparent half life of 30–40 in. The activity of ACC synthase in cycloheximide-treated, wounded pericarp of ripening tomatoes declined more slowly.Abbreviation ACC 1-aminocyclopropane-1-carboxylic acid