Chlorophyllase Activity Research Articles

Effects of aluminium on photosynthetic performance in Al-sensitive and Al-tolerant maize inbred lines

Maize plant inbred lines, one Al-sensitive (B-73) and two Al-tolerant (F-2 and L-2039), were grown hydroponically in the presence of 200 µM Al. After 13 d of growth, root and shoot lengths, photosystem 2 (PS2) activity, chlorophyll (Chl) content, 5-aminolevulinic acid (5-ALA) synthesis rate, chlorophyllase (Chlase) activity, and N, Mg, Fe, and Mn contents in leaves were determined. PS2 activity and Chl content were most severely affected by Al in B-73, but F-2 was almost unaffected. This was in accordance with Al-accumulation in the plants. The observed changes in B-73 coincided with 5-ALA synthesis inhibition, Chlase activation, and leaf deprivation of Fe and Mg. In Al-treated L-2039 plants, the leaf Mg and Mn contents were decreased. Also, an excessive Chlase activation was found in Al-treated L-2039, without a substantial Chl loss. This may indicate the activation of different enzyme pools in tolerant and sensitive genotypes under low-stress conditions.

Characterization of chlorophyll degradation in banana and plantain during ripening at high temperature

Bananas fail to fully degreen when ripening at tropical temperatures, but this abnormal symptom does not occur in plantain. To elucidate the temperature effect on banana degreening, comparison of the colour change and chlorophyll degradation pathway between banana and plantain during ripening at 20 or 30 °C was carried out. Compared to bananas ripening at 20 °C and plantains at 20 °C or 30 °C, bananas at 30 °C contained significantly higher levels of chlorophylls, chlorophyllide a and pheophorbide a at the end of the ripening process, linearly correlating to the colour scores of a ∗, b ∗ and Hue angle. Whilst higher chlorophyllase activity was recorded in both banana and plantain at 30 °C as to the fruits at 20 °C, 30 °C inhibited Mg-dechelatase activity in banana, but not in plantain. The reduction of Mg-dechelatase activity in banana peel at 30 °C may contribute to repressed chlorophyll degradation and lead to uneven degreening.

An evaluation of the basis and consequences of a stay-green mutation in the navel negra citrus mutant using transcriptomic and proteomic profiling and metabolite analysis.

A Citrus sinensis spontaneous mutant, navel negra (nan), produces fruit with an abnormal brown-colored flavedo during ripening. Analysis of pigment composition in the wild-type and nan flavedo suggested that typical ripening-related chlorophyll (Chl) degradation, but not carotenoid biosynthesis, was impaired in the mutant, identifying nan as a type C stay-green mutant. nan exhibited normal expression of Chl biosynthetic and catabolic genes and chlorophyllase activity but no accumulation of dephytylated Chl compounds during ripening, suggesting that the mutation is not related to a lesion in any of the principal enzymatic steps in Chl catabolism. Transcript profiling using a citrus microarray indicated that a citrus ortholog of a number of SGR (for STAY-GREEN) genes was expressed at substantially lower levels in nan, both prior to and during ripening. However, the pattern of catabolite accumulation and SGR sequence analysis suggested that the nan mutation is distinct from those in previously described stay-green mutants and is associated with an upstream regulatory step, rather than directly influencing a specific component of Chl catabolism. Transcriptomic and comparative proteomic profiling further indicated that the nan mutation resulted in the suppressed expression of numerous photosynthesis-related genes and in the induction of genes that are associated with oxidative stress. These data, along with metabolite analyses, suggest that nan fruit employ a number of molecular mechanisms to compensate for the elevated Chl levels and associated photooxidative stress.

Research of the Activity of Chlorophyllase in Plants Growing in the High Radiation Background Zone

The research objects have been Alhagi pseudalhagi, Zygophyllum L. and Argusia sibirica L. Choice of the plants is connected to the fact that they are the most widespread ones in the chosen site, ground of which is dirtied by 238U, 232Th, 226Ra and 40K. The work has been aimed on researching impact of the low-dosed ionizing radiation to photosynthesis of plants. The findings show that between concentrations of photosynthetic pigments in experimental and control plants growing in identical soil-climatic conditions there are certain distinctions being sometimes very considerable ones. Besides, in the concrete natural conditions photosynthetic reaction of different species to irradiation proves to be different and for a plant taken separately the reaction has seasonal character. Analysis of the dynamics of green pigments’ synthesis for Argusia sibirica L. at the first two phases of development has shown that the photosynthesis intensity was practically similar in experimental and control plants. At the same time final phase of the plant’s development was notable for decrease of the photosynthesis intensity, resulting in the inhibition of speed of the pigments’ synthesis. For Alhagi pseudalhagi both at the initial, and the final phase of vegetation period there was observed decrease of the chlorophylls’ synthesis. At the middle phase the ionizing radiation favored increase of pigments’ concentration in this plant at nearly 30%. The fact of increase of chlorophylls’ concentration in leaves of the researched plants under impact of radiation can be accepted as stimulation of pigment biosynthesis. Taking into account that biosynthesis of pigments is also specified by activity of chlorophyllase enzyme, we deemed expedient to research change of the enzyme’s activity. Activity of the enzyme was judged by us from increase of chlorophyllid’s number in the sample within a certain period of the pigment’s incubation with the enzyme preparation. It was revealed that for all the researched plants, where is found out biostimulation of the chlorophyll’s synthesis, activity of the chlorophyllase decreases. We can suppose that decrease of chlorophyllase’s activity under impact of the ionizing radiation is reason for intensification of chlorophylls’ synthesis. In other words, it can supposed that the chlorophyllase isn’t catalyst of the biosynthesis of the chlorophyll a, but on the contrary, performs at this time some hydrolytic function realizing decay of the chlorophyll’s molecules.

Controlling sol-gel properties enhancing entrapped membrane protein activity through doping additives

Chlorophyllase, a membrane protein, was entrapped in tetramethoxysilane (TMOS)—derived sol-gel and activity examined through a modification of sol-gel properties with doping additives. Polyvinyl alcohol or polyethyleneglycol as uncharged polymeric additives reduced the activity of entrapped chlorophyllase by 60 and 70% respectively, explained by restricted accessibility of chlorophyllase, as revealed by nitrogen desorption experiments. Entrapped chlorophyllase demonstrated 10% activity yield in polyethylenimine-doped gel relative to a polyethylenimine-free control, explained by electrostatic interaction between positively charged polyethylenimine and negatively charged chlorophyllase, considering that polyethylenimine led to a gel with a slightly reduced specific surface area and pore volume, but 20% larger pore size. When chlorophyllase was introduced into sol-gel together with various amounts of glycerol, it demonstrated only slightly lower activity in those gels, even though sol-gel demonstrated decreased specific surface area and pore volume with increasing amount of glycerol. Lipase, as additive, reduced activity of entrapped chlorophyllase, explained by its effect on gel formation, and thus gelation time and gel properties, whereas activity of sol-gel entrapped chlorophyllase associated with monogalactosyl diglyceride (MGDG), was increased by 40%. This study provides an in-depth understanding of the change in sol-gel properties as affected by a wide variety of additives, and the consequent affect on the activity of the membrane protein chlorophyllase.

AtCLH2, a Typical but Possibly Distinctive Chlorophyllase Gene in Arabidopsis

AbstractChlorophyllase (EC 3.1.1.14) is involved in the first step of chlorophyll degradation. Isolation of chlorophyllase genes greatly facilitates characterization of chlorophyllase properties and elucidation of molecular regulation of their in vivo activities. There are two chlorophyllase genes, AtCLH1 and AtCLH2, in Arabidopsis thaliana. The in vivo roles of AtCLH1 have been reported previously. However, few studies have been carried out on AtCLH2. Here, we show that purified recombinant Chlase2, encoded by AtCLH2, exhibits in vitro chlorophyllase activity. Interestingly, “activation” of in vitro activity of the recombinant Chlase2 required higher concentrations of a detergent or a polar solvent. To determine its activity in vivo, the expression of AtCLH2 was inhibited by RNA interference. RNAi plants showed decreased contents of chlorophyllide without a substantial change in the total amount of the extractable chlorophyll and consequently presented lower chlorophyllide to chlorophyll ratios in their leaves. In addition, the two AtCLHs exhibited differential expression patterns. Our results suggest that AtCLH2 might play a distinctive role in chlorophyll catabolism in vivo.

Varietal differences in catabolic intermediates of chlorophylls in Olea europaea (L.) fruit cvs. Arbequina and Blanqueta

A comparative study of the chlorophyll catabolism in fruit of Olea europaea, cvs. Arbequina and Blanqueta during the ripening, has demonstrated a temporal disparity in chlorophyll disappearance between varieties. In ‘Blanqueta’ fruit, the early cleavage of the macro-ring of the chlorophyll molecule implies a fast loss of chlorophylls before the synthesis of anthocyanins. The displacement in the time of this process agrees in each variety with the maximum levels of in vivo chlorophyllide and chlorophyllase activity (EC 3.1.1.14). The temporary difference in the activation of chlorophyllase and the rest of enzymes implied in the pheophorbide a oxygenase pathway is responsible for the step to colorless products. In addition, the different involvement of minor oxidized chlorophylls in the varieties implies a different participation of chlorophyll catabolic oxidatives enzymes. The greater oxidative activity in the fruit of the ‘Blanqueta’ variety can indirectly have an influence on the lower oxidative stability of corresponding oils.

Gender-specific responses of Piper betle L. to low temperature stress: changes in chlorophyllase activity

Gender based differences in response to low temperature stress in leaf chlorophyll (Chl), and carotenoids (Car) contents and chlorophyllase (Chlase) activity were monitored in male (Kapoori Vellaikodi and Madras Pan Kapoori) and female (Bangla Mahoba, Desi Bangla and Kaker) betel vine landraces. Although female plants contained nearly two fold more Chl than male counterparts, the low temperature induced Chl loss was comparable, however, male plants showed higher Chl a/b ratio than females. Chlase activity increased due to cold stress in all the landraces. Male plants always showed higher activities of Chlase, which may be one of the reasons for the rather low Chl contents in male plants.

Seedling Nutrient Status before Submergence Affects Survival after Submergence in Rice

Vast rainfed lowland areas in Asia periodically experience flash floods that adversely affect survival and productivity of rice (Oryza sativa L.). Progress has been made in developing more tolerant germplasm, but fewer efforts have been devoted to identifying proper management options. We evaluated the effects of nitrogen (N) and phosphorus (P) added before submergence on seedling survival after submergence. Two experiments were conducted using two cultivars, submergence‐tolerant FR13A and intolerant IR42. In the first experiment, N was applied at two different times and, in the second, N and P were used in a fertile and a P‐deficient soil. Seedlings (21‐d‐old) were submerged in concrete tanks for 12 d. Addition of P seems to enhance tolerance of plants grown on P‐deficient soils. Survival of both cultivars decreased substantially in seedlings with high N concentration, with higher survival in FR13A. Leaf N and chlorophyll concentration before submergence were higher in N‐treated seedlings, whereas chlorophyll a/b ratio was lower. In both cultivars, photosynthesis and root–shoot ratio decreased and chlorophyllase activity increased after submergence with increasing N and with higher activity of chlorophyllase in IR42. Survival was negatively correlated with leaf N concentration, but positively correlated with root–shoot ratio and stem starch concentration before submergence and with chlorophyll concentration and chlorophyll a/b ratio after submergence. Crop establishment could therefore be enhanced in areas where untimely flooding is anticipated by avoiding excessive N application.

Hot Water Treatment of Postharvest Mei Fruit to Delay Ripening

Mei (Prunus mume `Daqinghe') fruit were immersed in 20 °C (control), 47 °C (HWT47), 50 °C (HWT50), or 53°C (HWT53) water for 3 min after harvest, then stored at 20 °C. Firmness, peel color, chlorophyll, chlorophyllase activity, soluble solids content (SSC), titratable acidity (TA), respiration, ethylene production, and pectinmethylesterase (PME) and polygalacturonase (PG) activity were monitored to determine the effects of hot water treatment in delaying fruit ripening. Control fruit displayed a typical climacteric pattern of respiration and ethylene production. Peak CO2 production and ethylene production were observed 6 days after harvest. Fruit softening was accompanied by decreases in hue angle, chlorophyll content, SSC, and TA and increases in chlorophyllase and PME and PG activity. Hot water treatment delayed the onset of the climacteric peaks of CO2 and ethylene production. The delays were associated with delays in fruit softening, consistent with lags in the rise of PME and PG activity; delays in yellowing and chlorophyll breakdown, consistent with lags in the rise of chlorophyllase activity; and delays in loss of SSC and TA. The shelf life of fruit increased by 6 days, or 60%, with HWT47, and by 8 days, or 80%, with HWT50 or HWT53.

Optimization of tetramethoxysilane-derived sol gel entrapment protocol stabilizes highly active chlorophyllase

Entrapment of membrane proteins is a challenging task compared to that involving soluble proteins. Chlorophyllase, a membrane protein, was successfully entrapped in tetramethoxysilane-derived sol-gel. Pre-gel sol typically consists of an aqueous suspension of chlorophyllase, precursors including tetramethoxysilane and/or methytrimethoxysilane, and sodium fluoride as catalyst. To obtain a highly active entrapped enzyme preparation, the effects of various immobilization parameters, including the chemical compositions of pre-gel sol (water/silane ratio, precursor type and proportions, enzyme loading, sodium fluoride concentration), and sol-gel process parameters (aging and drying time and approach) have been investigated. Chlorophyllase demonstrated the highest activity in gel derived from a pre-gel sol with water/silane ratio of 30 and enzyme loading of 0.257 mgprotein/ggel, and showed moderately lower activity in organically modified sol-gel than that in hydrophilic sol-gel. The effects of water/silane ratio and precursor combinations on the activity of entrapped chlorophyllase were also studied by examining the pore morphology of gel via nitrogen adsorption-desorption. Longer aging time leads to an entrapped chlorophyllase preparation with higher activity. Chlorophyllase preparation demonstrated negligible activity after air-drying for 12 h while lyophilized chlorophyllase preparation demonstrated 8, 4 and 4 times higher activity than air-dried, vacuum-dried and solvent-dried preparations. Chlorophyllase demonstrated 30% higher activity in the improved sol-gel protocol than that from a non-optimized sol-gel protocol developed in a previous study.

Development of a high-throughput purification method and a continuous assay system for chlorophyllase

In the degradation of chlorophyll, chlorophyllase catalyzes the initial hydrolysis of the phytol moiety from the pigment. Since chlorophyll degradation is a defining feature of plant senescence, compounds inhibiting chlorophyllase activity may delay senescence, thereby improving shelf life and appearance of plant products. Here we describe the development of a 96-well plate-based purification and assay system for measuring chlorophyllase activity. Integrated lysis and immobilized metal affinity chromatography plates were used for purifying recombinant hexahistidine-tagged Triticum aestivum (wheat) chlorophyllase from Escherichia coli. Chlorophyllase assays using chlorophyll as a substrate showed that the immobilized fusion protein displayed kinetic parameters similar to those of recombinant enzyme purified by affinity chromatography; however, the need to extract reaction products from a multiwell plate limits the value of this assay for high-throughput screening applications. Replacing chlorophyll with p-nitrophenyl-ester substrates eliminates the extraction step and allows for continuous measurement of chlorophyllase activity in a multiwell plate format. Determination of steady state kinetic constants, pH rate profile, the inhibitory effects of metal ions and esterase inhibitors, and the effect of functional group-modifying reagents validated the utility of the plate-based system. The combined purification and assay system provides a convenient and rapid method for the assessment of chlorophyllase activity.

Hot air treatment decreases chlorophyll catabolism during postharvest senescence of broccoli (Brassica oleracea L. var. italica) heads

AbstractA hot air treatment was applied to broccoli (Brassica oleracea L. var. italica) florets and its effect on chlorophyll catabolism during postharvest senescence was analyzed. Florets were treated at 48 °C for 3 h and then placed in darkness at 20 °C. During storage, the yellowing of florets occurred simultaneously with a decrease in chlorophylls and an increase in pheophytins. Heat treatment delayed the appearance of yellowing by 2–3 days and a similar extension of shelf‐life could be inferred. Also, the treatment delayed the onset of chlorophyll catabolism and slowed both the rate of chlorophyll a degradation and pheophytin accumulation. No effect on chlorophyll b degradation was found. Chlorophyllase and Mg‐dechelatase activities increased from the first day of storage in untreated florets, whereas peroxidase‐linked chlorophyll bleaching activity increased from day 3. In heat‐treated florets, chlorophyllase activity did not increase until day 2 and then increased at lower rate than in controls. Mg‐dechelatase and peroxidase‐linked chlorophyll bleaching activities were similar in treated and control florets during the first 2 days of storage, but thereafter the activity of both enzymes was lower in heat‐treated samples. In conclusion, a treatment at 48 °C for 3 h delayed chlorophyll a catabolism in broccoli during postharvest senescence and decreased the activities of chlorophyllase, Mg‐dechelatase and peroxidase, three of the enzymes probably involved in chlorophyll degradation in plants. Copyright © 2006 Society of Chemical Industry

The relationship between chlorophyllase activity and chlorophyll degradation during the course of leaf senescence in various plant species

In the present study we compared the changes in chlorophyllase (Chlase) activity and chlorophyll content during leaf senescence in eleven plant species, using an improved Chlase activity assay. Parsley (Petroselinum sativum L.), vinca (Vinca rosea L.), squash (Cucurbita pepo L.), tomato (Lycopersicon esculentum L.), canola (Brassica napus L.), tobacco (Nicotiana glutinosa L.), wheat (Triticum aestivum vulgare L.), and sunflower (Helianthus annuus L.) revealed a decline in Chlase activity corresponding to the descent in chlorophyll concentration. Melia (Melia azedarach L.) and nasturtium (Tropaeolum majus L.), on the other hand, retained high Chlase activity throughout senescence, even when most of the chlorophyll had disappeared. Barley (Hordeum vulgare L.) showed an increase in Chlase activity upon senescence of young seedling leaves, but when leaves of older plants were senesced, Chlase activity declined in correlation with the disappearance of chlorophyll. High levels of chlorophyll were retained in de...

Mechanistic Analysis of Wheat Chlorophyllase

Chlorophyllase catalyzes the initial step in the degradation of chlorophyll and plays a key role in leaf senescence and fruit ripening. Here we report the cloning of chlorophyllase from Triticum aestivum (wheat) and provide the first detailed mechanistic analysis of the enzyme from any source. Purification of recombinant chlorophyllase from an E. coli expression system indicates that the enzyme functions as a dimeric protein. Wheat chlorophyllase hydrolyzed the phytol moiety from chlorophyll (kcat=566 min-1; Km=63 ?M) and was active over a broad temperature range (10–75 °C). For the first time, we demonstrate that the enzyme displays carboxylesterase activity toward p-nitrophenyl (PNP)-butyrate, PNP-decanoate, and PNP-palmitate. The pH-dependence of the reaction showed the involvement of an active site residue with a pKa of ~6.5 for both kcat and kcat/Km with chlorophyll, PNP-butyrate, and PNP-decanoate. Using these substrates, solvent kinetic isotope effects ranging from 1.5–1.9 and 1.4–1.9 on kcat and kcat/Km, respectively, were observed. Proton inventory experiments suggest that a single proton is transferred in the rate-limiting step. Our analysis of wheat chlorophyllase indicates that the enzyme uses a charge-relay mechanism similar to other carboxylesterases for catalysis. Understanding the activity and mechanism of chlorophyllase provides insight on the biological and chemical control of senescence in plants and lays the groundwork for biotechnological improvement of this enzyme.

UV-C treatment delays postharvest senescence in broccoli florets

Central broccoli heads (cv. de Cicco) were harvested and treated with UV-C light (4, 7, 10, or 14 kJ m −2). All treatments delayed yellowing and chlorophyll degradation at 20 °C but the irradiation dose of 10 kJ m −2 allowed retaining the highest chlorophyll content yet had lower amounts of pheophytins than every treatment other than 7 kJ m −2. This dose was selected to analyze the effect of UV-C on postharvest broccoli senescence at 20 °C. The UV-C treatment delayed yellowing, chlorophyll a and b degradation , and also the increase in pheophytins during storage. The activity of chlorophyll peroxidase and chlorophyllase was lower in UV-C treated broccoli. Instead, Mg-dechelatase activity increased immediately after the treatment, but after 4 and 6 d this activity was lower in UV-C treated florets than in controls. Treated broccoli also displayed lower respiration rate, total phenols and flavonoids, along with higher antioxidant capacity. The results suggest that UV-C treatments could be a useful non-chemical method to delay chlorophyll degradation, reduce tissue damage and disruption, and maintain antioxidant capacity in broccoli.

Involvement of 1-methylcyclopropene in ripening of harvested mei (Prunus mume) fruit

SummaryHarvested mei (Prunus mume) fruit were stored at 20°C after exposure to 500 nl l–1 1-methylcyclopropene (1-MCP) for 8 h. Firmness, peel colour, chlorophyll content, chlorophyllase activity, soluble solids content (SSC), titratable acidity (TA), respiration and ethylene production, and cell wall hydrolysis enzyme activities were monitored to determine the efficacy of 1-MCP treatment in delaying mei fruit ripening compared to untreated control fruit. Results showed that control ‘daqinghe’ mei fruit displayed typical climacteric patterns of respiration and ethylene production. Peak CO2 production and ethylene production were observed after 6 d. Fruit softening was accompanied by a progressive decrease in colour parameters expressed as hue angle (h°), chlorophyll content, SSC, TA and increases in chlorophyllase, pectin methylesterase (PME) and polygalacturonase (PG) activities. 1-MCP treatment prior to the climacteric increase significantly delayed the onset of the climacteric peaks of CO2 and ethylene production. These delays were associated with reductions in fruit softening, consistent with delaying the activities of PME and PG. Fruit treated with 1-MCP exhibited less peel colour change from green-to-yellow because of their lower levels of chlorophyllase activity and less chlorophyll breakdown. Moreover, 1-MCP treatment also significantly retarded reductions in SSC and TA compared with control fruit. The shelf-life of mei fruit ripening was increased by 4 d following 1-MCP treatment. Thus, 1-MCP treatment can markedly extend the post-harvest life of ‘daqinghe’ mei fruit.

Biochemical and physiological changes during chlorophyll degradation in lime (Citrus aurantifolia Swingle cv. ‘Paan’)

SummaryLime (Citrus aurantifolia Swingle cv. ‘Paan’) native to South East Asia, has a distinct flavour and quality characteristics. Maintenance of the green colour in the peel of lime is a desirable quality attribute during storage. Post-harvest chlorophyll degradation in lime was studied in fruit stored at room temperature (30°C) at a relative humidity (RH) of 70 – 85%. Within 7 d of storage, the total chlorophyll content decreased to 53.9% of its initial level. The highest chlorophyllase activity (1.68 units mg–1 protein) was observed after 4 d of storage and declined thereafter. Peroxidase activity differed from chlorophyllase activity and increased significantly to 6.25 units mg–1 protein after 9 d of storage, (i.e., at the late maturity stage). Respiration rate and 1-aminocyclopropene-1-carboxylic acid (ACC) oxidase activity did not significantly affect the chlorophyll degradation process in lime.The total nitrogen content of lime peel was inversely correlated with its chlorophyll content. A higher soluble protein content was observed in yellow peel than in mature green peel. A colour index chart was developed for maturity stages 1–4 in lime based on peel colour changes from mature green to full-yellow, and its correlation with chlorophyll content and fruit quality attributes.

Physiological changes in boysenberry fruit during growth and ripening

SummaryBoysenberries (Rubus hybrid) were harvested at five developmental stages (green, “turning”, pink, red and purple) to study changes associated with flavour, colour and firmness, with a particular focus on the different enzymes involved in chlorophyll degradation or cell wall degradation. The level of reducing and non-reducing sugars increased 109- and 52-fold, respectively, between the “turning” and the purple stage. Titratable acidity increased by 84% between the green and the pink stage, but dropped by 41% between the red stage and full ripening. Total phenols displayed their highest values in green and “turning” fruit. Chlorophyll a and b degradation occurred mainly during the early stages of development, and was paralleled by a 2.3-fold increase in chlorophyllase activity and a 5-fold increase in Mg-dechelatase activity between the green and the red stages. Chlorophyll peroxidase activity was high at the green stage, but did not change significantly after the “turning” stage. This is the first report on the activity of chlorophyll-degrading enzymes in Rubus spp. fruits. Anthocyanins increased 11-fold between the “turning” and the pink stages, and an additional eight-fold between the pink and the purple stages. Fruit firmness decreased noticeably during ripening, with a concomitant 10.75-fold increase in polygalacturonase activity, beginning at the “turning” stage. Endo- -1,4-glucanase and -galactosidase activities rose 9.2- and 6.7-fold, respectively, after the pink stage and paralleled the major softening process taking place between the pink and purple stages, when fruit firmness decreased from 3.83 N to 0.29 N. Pectin methylesterase activity was high in pink and red fruit, but decreased by 21% as the fruit turned from red to purple. This is the first report on cell wall enzyme activities whose combined action might be required for the breakdown of natural cell wall substrates during ripening in boysenberry, as happens in other soft fruits.

Postharvest application of 1-MCP to improve the quality of various avocado cultivars

1-Methylcyclopropene (1-MCP), an ethylene action inhibitor, significantly delayed the ripening of the avocado cultivars ‘Ettinger’, ‘Hass’ and ‘Pinkerton’. Application of 1-MCP at low concentration (300 nl l −1), prior to the climacteric increase, was effective and delayed the onset of the climacteric peaks of CO 2 and ethylene production. The delay was associated with reductions in fruit softening and in electrical conductivity (EC), the latter being an indicator of membrane permeability. The 1-MCP-treated ‘Ettinger’ and ‘Pinkerton’ avocado fruit maintained a greener peel color because of their lower levels of chlorophyllase activity and less chlorophyll breakdown. Treatment with 1-MCP at 300 nl l −1 prior to cold storage reduced chilling injury (CI) symptoms that are expressed as mesocarp discoloration and reduced polyphenol oxidase (PPO) and peroxidase (POD) activities in avocadoes stored at 5 °C for 3.5 weeks. PPO and POD activities were low in harvested fruit and increased significantly during cold storage and shelf life at 20 °C. 1-MCP was effective in reducing pulp browning in all the tested avocado cultivars. Mesocarp discoloration in avocado was found to be correlated with increases in EC values and PPO and POD activities.