Characterization of senescence-associated proteases in postharvest broccoli florets

Reduced Fertilization to Improve Sustainable Use of Resources and Preserve Postharvest Quality of Fresh-Cut Wild Rocket (Diplotaxis tenuifolia L.) in Soil-Bound and Soilless Cultivation

Reducing fertilizer input is a goal for helping greenhouse farming to achieve higher sustainability in the production process while preserving overall crop performance and quality. Wild rocket plants were cultivated in a plastic greenhouse divided into two independent sectors, one for soil-bound (SbS) cultivation and another equipped for soilless (ScS) cultivation systems. In both SbS and ScS, the crop was subjected to treatments consisting of a high- and a low-input fertilization program (HF and LF treatment, respectively). Water use efficiency (WUE) and partial factor productivity (PFP) for nutrients (N, P, K, Ca, and Mg for ScS, and N for SbS) were measured. Rocket leaves, separated for the cultivation system and fertilization program and collected at different cuts during the growing cycle, were cold stored at 10 °C until 16 d. On each sampling day (at harvest and during storage), the sensory parameters, respiration rate, dry matter, color, electrolyte leakage, antioxidant activity, total phenols, total chlorophyll and ammonia content were evaluated. In ScS, the PFP for all nutrients supplied as fertilizers showed a significant increase with the LF treatment, with values higher than 30% recorded for N, K, and Ca. As for the postharvest performance, rocket leaves cultivated in ScS showed better qualitative traits than those cultivated in SbS, as suggested by the lower values of ammonia content and electrolyte leakage recorded at the end of storage period in samples grown in ScS. Moreover, in ScS, the data showed lower membrane damage in LF than HF rocket leaves. Finally, regarding total chlorophyll content, even if no effect of each treatment was recorded in SbS, rocket cultivated in ScS showed a better retention of this parameter by applying LF rather than HF treatment. In addition to this, a PLS model (R2 = 0.7) able to predict the cultivation system, using as a variable non-destructively measured total chlorophyll content, was implemented. Low fertilization input, both in SbS and in ScS, allowed satisfying production levels and more sustainable management of nutrients. LF treatment applied to ScS also had in positive effects on the postharvest quality of fresh-cut rocket leaves.

Prediction of top round beef meat tenderness as a function of marinating time based on commonly evaluated parameters and regression equations

This study investigates the influence of 24-hr marination (with different plant extracts and vinegar) at refrigerated conditions on commonly evaluated physicochemical and textural attributes, including pH, water-holding capacity (WHC), collagen solubility, moisture, drip loss, and shear force values of beef meat. The results reflected the appropriate correlation between each pair and indicated the efficiency of the household marination procedure to acquire more palatability and tender beef meat. Therefore, to predict beef meat tenderness by applying the Warner-Bratzler shear force (WBSF), a strong positive correlation with the drip loss (p < .01) and a notable negative correlation with the moisture content (p < .01) emphasized the importance of moisture improvement and shear force reduction in affecting tenderness of baked beef meat. The regression equations and R-squared values were revealed the favorable correlation between collagen solubility and WHC (y = 0.1035x-0.8431, R 2 = .98) as well as moisture and WBSF (y = -0.3297x + 102.58, R 2 = .99) in marinated beef meat. Electrophoresis patterns of isolated myofibrillar proteins disclosed remarkable degradation of myosin heavy chain (MHC), desmin, actin, and tropomyosin during the first day of aging. The noticeable ultrastructural destruction and connective tissue solubilization were observed by microscopy images. These outcomes were a good tenderness predictor be utilized in retailing and industrial scale.

A novel phase change coolant promoted quality attributes and glutamate accumulation in postharvest shiitake mushrooms involved in energy metabolism

Cold chain transportation is an important link in postharvest logistics of agricultural products. In current study, we developed a novel water-based phase change coolant (PCC), which showed longer effectiveness in maintaining low temperature condition compared with ice, and applied in preserving the postharvest mushrooms. The results showed that the novel PCC effectively inhibited water loss, as well as maintained quality attributes including firmness, color, phenolics, flavonoids, and thus prolonged the shelf-life of mushrooms. Low temperature condition created by the novel PCC treatment maintained high level of energy charge by activating the activities of SDH, CCO, H⁺-ATPase and Ca²⁺-ATPase, resulting in the delay of postharvest senescence. In addition, sufficient energy supply decreased the consumption of glutamate as carbon skeleton by inhibiting GDH activity, improved glutamate accumulation, and therefore maintained sensory properties as a result. Thus, the novel PCC might be an excellent substitute for ice in cold chain transportation of mushrooms.

Transcriptome profiling of postharvest shoots identifies PheNAP2- and PheNAP3-promoted shoot senescence

The juvenile shoots of Phyllostachys edulis have been used as a food source for thousands of years, and it is recognized as a potential source of nutraceuticals. However, its rapid senescence restricts bamboo production and consumption, and the underlying molecular mechanisms of rapid shoot senescence remain largely unclear. In the present study, transcriptome profiling was employed to investigate the molecular regulation of postharvest senescence in shoots, along with physiological assays and anatomical dissections. Results revealed a distinct shift in expression postharvest, specifically transitions from cellular division and differentiation to the relocation of nutrients and programmed cell death. A number of regulatory and signaling factors were induced during postharvest senescence. Moreover, transcription factors, including NAM, ATAF and CUC (NAC) transcription factors, basic helix-loop-helix transcription factors, basic region/leucine zipper transcription factors, MYB transcription factors and WRKY transcription factors, were critical for shoot postharvest senescence, of which NACs were the most abundant. PheNAP2 and PheNAP3 were induced in postharvest shoots and found to promote leaf senescence in Arabidopsis by inducing the expression of AtSAG12 and AtSAG113. PheNAP2 and PheNAP3 could both restore the stay-green Arabidopsis nap to the wild-type phenotype either under normal growth condition or under abscisic acid treatment. Collectively, these results suggest that PheNAPs may promote shoot senescence. These findings provide a systematic view of shoot senescence and will inform future studies on the underlying molecular mechanisms responsible for shoot degradation during storage.

The time of the day to harvest affects the degreening, antioxidant compounds, and protein content during postharvest storage of broccoli

Harvesting of broccoli at several moments of the day affects the rate of senescence during storage. In this work, broccoli heads were harvested at several moments and then kept at 20°C in order to analyze protein metabolism and antioxidant compounds. Almost no differences were detected in the contents of total and soluble proteins, and free amino acids. Only an increment in free amino acids was detected by day 3 in samples obtained at 8:00 hr. With reference to antioxidants, the contents of ascorbic acid, carotenoids and xanthophylls, phenols, and flavonoids were similar in samples harvested at different moments. However, an increment was detected in carotenoids, phenols, and flavonoids during storage of samples collected at 18:00 hr on day 3 and samples collected at 13:00 hr on day 5. The combination of delay of senescence and increment in antioxidants suggest harvesting at 12:00 or 18:00 hr. PRACTICAL APPLICATION: Broccoli is a vegetable with an important level of nutrients. However, it is also highly perishable and suffers a high rate of senescence and loss of quality during postharvest. In this work, it is demonstrated that the simple practice of harvests in different moments of the day can affect the postharvest behavior of broccoli, and it is suggested to carry out the harvest toward the end of the day.

O3-Induced Leaf Senescence in Tomato Plants Is Ethylene Signaling-Dependent and Enhances the Population Abundance of Bemisia tabaci

Elevated ozone (O3) can alter the phenotypes of host plants particularly in induction of leaf senescence, but few reports examine the involvement of phytohormone in O3-induced changes in host phenotypes that influence the foraging quality for insects. Here, we used an ethylene (ET) receptor mutant Nr and its wild-type to determine the function of the ET signaling pathway in O3-induced leaf senescence, and bottom-up effects on the performance of Bemisia tabaci in field open-top chambers (OTCs). Our results showed that elevated O3 reduced photosynthetic efficiency and chlorophyll content and induced leaf senescence of plant regardless of plant genotype. Leaf senescence in Nr plants was alleviated relative to wild-type under elevated O3. Further analyses of foliar quality showed that elevated O3 had little effect on phytohormone-mediated defenses, but significantly increased the concentration of amino acids in two plant genotypes. Furthermore, Nr plants had lower amino acid content relative to wild-type under elevated O3. These results provided an explanation of O3-induced increase in abundance of B. tabaci. We concluded that O3-induced senescence of plant was ET signal-dependent, and positive effects of O3-induced leaf senescence on the performance of B. tabaci largely resulted from changes of nutritional quality of host plants.

zmsbt1 and zmsbt2, two new subtilisin-like serine proteases genes expressed in early maize kernel development

Two subtilisin-like proteases show highly specific and complementary expression patterns in developing grains. These genes label the complete surface of the filial-maternal interface, suggesting a role in filial epithelial differentiation. The cereal endosperm is the most important source of nutrition and raw materials for mankind, as well as the storage compartment enabling initial growth of the germinating plantlets. The development of the different cell types in this tissue is regulated environmentally, genetically and epigenetically, resulting in the formation of top-bottom, adaxial-abaxial and surface-central axes. However, the mechanisms governing the interactions among the different inputs are mostly unknown. We have screened a kernel cDNA library for tissue-specific transcripts as initial step to identify genes relevant in cell differentiation. We report here on the isolation of two maize subtilisin-related genes that show grain-specific, surficial expression. zmsbt1 (Zea mays Subtilisin1) is expressed at the developing aleurone in a time-regulated manner, while zmsbt2 concentrates at the pedicel in front of the endosperm basal transfer layer. We have shown that their presence, early in the maize caryopsis development, is dependent on proper initial tissue determination, and have isolated their promoters to produce transgenic reporter lines that assist in the study of their regulation.

A role for an endosperm-localized subtilase in the control of seed size in legumes

Here, we report a subtilase gene (SBT1.1) specifically expressed in the endosperm of Medicago truncatula and Pisum sativum seeds during development, which is located at a chromosomal position coinciding with a seed weight quantitative trait locus (QTL). Association studies between SBT1.1 polymorphisms and seed weights in ecotype collections provided further evidence for linkage disequilibrium between the SBT1.1 locus and a seed weight locus. To investigate the possible contribution of SBT1.1 to the control of seed weight, a search for TILLING (Targeting Induced Local Lesions in Genomes) mutants was performed. An inspection of seed phenotype revealed a decreased weight and area of the sbt1.1 mutant seeds, thus inferring a role of SBT1.1 in the control of seed size in the forage and grain legume species. Microscopic analyses of the embryo, representing the major part of the seed, revealed a reduced number of cells in the MtP330S mutant, but no significant variation in cell size. SBT1.1 is therefore most likely to be involved in the control of cotyledon cell number, rather than cell expansion, during seed development. This raises the hypothesis of a role of SBT1.1 in the regulation of seed size by providing molecules that can act as signals to control cell division within the embryo.

2-D zymographic analysis of Broccoli (Brassica oleracea L. var. Italica) florets proteases: follow up of cysteine protease isotypes in the course of post-harvest senescence

Zymographic analysis of Broccoli florets (Brassica oleracea L. var. Italica) revealed the presence of acidic metallo-proteases, serine proteases and cysteine proteases. Under conditions which were denaturing for the other proteases, the study was restricted to cysteine proteases. 2-D zymography, a technique that combines IEF and zymography was used to show the presence of 11 different cysteine protease spots with molecular mass of 44 and 47-48kDa and pIs ranging between 4.1 and 4.7. pI differences could be ascribed to different degrees of phosphorylation that partly disappeared in the presence of alkaline phosphatase. Post-harvest senescence of Broccoli florets was characterized by decrease in protein and chlorophyll contents and increase of protease activity. In particular, as determined by 2-D zymography, the presence of cysteine protease clearly increased during senescence, a finding that may represent a useful tool for the control of the aging process.

Biochemical and spectroscopic characterization of a novel metalloprotease, cotinifolin from an antiviral plant shrub: Euphorbia cotinifolia

A high molecular mass novel metalloprotease, cotinifolin is purified from the latex of Euphorbia cotinifolia by a combination of anion exchange and hydrophobic interaction chromatography. The nonglycosylated enzyme has a molecular mass of 79.76 kDa (ESI-MS) and the isoelectric point of the enzyme is pH 7.7. Cotinifolin hydrolyzes denatured natural substrates such as casein, azoalbumin, and hemoglobin with high specific activity. The K(m) value of the enzyme was found to be 20 μM with azocasein. The enzyme is not prone to autolysis even at very low concentrations. Polyclonal antibodies specific to enzyme was raised and immunodiffusion reveals that the enzyme has unique antigenic determinants. Maximum caseinolytic activity of cotinifolin is observed in the range of pH 7.0-8.0 and temperature of 50 °C. Using 0.2 mL of 1 mM solution of each metal ion, the purified protease was inhibited slightly by Ba²⁺ and Mn²⁺, moderately by Mg²⁺, Ca²⁺ and Cs²⁺ and significantly by Zn²⁺, Cu²⁺ and Co²⁺. On the other hand, substantial activation in caseinolytic activity was achieved by Ni²⁺. The enzyme activity was also inhibited by EDTA and o-phenanthroline but not by any other protease inhibitors. Perturbation studies by temperature, pH, and chaotrophs of the enzyme also reveal its high stability as seen by CD, fluorescence and proteolytic activity. Spectroscopic studies reveal that cotinifolin has secondary structural features with α/β type with approximately 9% of α-helicity. Easy availability and simple purification procedure makes the enzyme a good system for biophysical study, biotechnological and industrial applications.

Chlorophyllase versus pheophytinase as candidates for chlorophyll dephytilation during senescence of broccoli

Degradation of chlorophylls during senescence is a highly regulated process which requires the concerted action of several enzymes. Traditionally, it has been stated that the dismantling process of the chlorophyll molecule begins with a dephytilation step, followed by Mg(2+) removal and other breakdown reactions. Recently, new evidence suggests the possibility of a rearrangement in the first two steps of this process, occurring Mg(2+) removal prior to the loss of the phytol side chain. With the purpose of approximating to the real sequential order of these reactions and to assess if dephytilation occurs on intact (catalyzed by chlorophyllase) or Mg-free (catalyzed by pheophytinase) chlorophyll, expression of both genes was analyzed in broccoli tissue during senescence. Samples of broccoli florets treated with plant hormones, such as cytokinin and ethylene were utilized, as to assess the effect of such compounds on the expression of these genes. Results showed that chlorophyllase expression did not correlate to typical expression patterns for genes related to senescence, since a decrease in expression during senescence was found for one of the two chlorophyllase genes analyzed, and the hormonal-treatment effects on gene expression did not match those observed on chlorophyll content for both chlorophyllase genes. Pheophytinase expression patterns, on the other hand, displayed an increase in the first 3 days of induced senescence, followed by lower expression values towards the end of the experiment. Samples subjected to postharvest treatments mostly showed an inhibition of pheophytinase expression, especially in samples in which degradation of chlorophylls had been delayed. These results suggest that pheophytinase expression correlates to the visual manifestation of postharvest treatments, supporting the possibility that this enzyme is responsible for the dephytilation step in chlorophyll breakdown.

Apoplast proteome reveals that extracellular matrix contributes to multistress response in poplar

BACKGROUND

Riverine ecosystems, highly sensitive to climate change and human activities, are characterized by rapid environmental change to fluctuating water levels and siltation, causing stress on their biological components. We have little understanding of mechanisms by which riverine plant species have developed adaptive strategies to cope with stress in dynamic environments while maintaining growth and development.

RESULTS

We report that poplar (Populus spp.) has evolved a systems level "stress proteome" in the leaf-stem-root apoplast continuum to counter biotic and abiotic factors. To obtain apoplast proteins from P. deltoides, we developed pressure-chamber and water-displacement methods for leaves and stems, respectively. Analyses of 303 proteins and corresponding transcripts coupled with controlled experiments and bioinformatics demonstrate that poplar depends on constitutive and inducible factors to deal with water, pathogen, and oxidative stress. However, each apoplast possessed a unique set of proteins, indicating that response to stress is partly compartmentalized. Apoplast proteins that are involved in glycolysis, fermentation, and catabolism of sucrose and starch appear to enable poplar to grow normally under water stress. Pathogenesis-related proteins mediating water and pathogen stress in apoplast were particularly abundant and effective in suppressing growth of the most prevalent poplar pathogen Melampsora. Unexpectedly, we found diverse peroxidases that appear to be involved in stress-induced cell wall modification in apoplast, particularly during the growing season. Poplar developed a robust antioxidative system to buffer oxidation in stem apoplast.

CONCLUSION

These findings suggest that multistress response in the apoplast constitutes an important adaptive trait for poplar to inhabit dynamic environments and is also a potential mechanism in other riverine plant species.

Differential effect of equal copper, cadmium and nickel concentration on biochemical reactions in wheat seedlings

Influence of 75 microM copper (Cu), cadmium (Cd) and nickel (Ni) on growth, tissue metal accumulation, non-protein thiols (NPT) and glutathione (GSH) contents, membrane damage, lipid peroxidation and protein oxidation as well as protease, glutathione S-transferase (GST) and peroxidase (POD) activities were studied in the shoots and roots of wheat seedlings after 7 days of metal exposure. The greatest growth reduction was found in response to Cu treatment; however accumulation of this metal in the wheat tissues was the lowest compared to the other metals used. All metals caused enhancement of electrolyte leakage from cells as well as increased lipid peroxidation and protein carbonylation. Proteolytic activity was enhanced only in Cu-exposed seedlings and in the roots it coincided with elevated protein carbonylation. The most pronounced increase in POD activity in the shoots was found after Ni treatment while in the roots in response to Cu. In contrast to Cu, application of Cd and Ni resulted in accumulation of NPT and induction of GST activity, which suggested involvement of these mechanisms in metal tolerance in wheat.

Transcriptional activation of a 37 kDa ethylene responsive cysteine protease gene, RbCP1, is associated with protein degradation during petal abscission in rose

Cysteine proteases play an important role in several developmental processes in plants, particularly those related to senescence and cell death. A cysteine protease gene, RbCP1, has been identified that encodes a putative protein of 357 amino acids and is expressed in the abscission zone (AZ) of petals in rose. The gene was responsive to ethylene in petals, petal abscission zones, leaves, and thalamus. The expression of RbCP1 increased during both ethylene-induced as well as natural abscission and was inhibited by 1-MCP. Transcript accumulation of RbCP1 was accompanied by the appearance of a 37 kDa cysteine protease, a concomitant increase in protease activity and a substantial decrease in total protein content in the AZ of petals. Agro-injection of rose petals with a 2.0 kb region upstream of the RbCP1 gene could drive GUS expression in an abscission zone-specific manner and was blocked by 1-MCP. It is concluded that petal abscission is associated with a decrease in total protein content resulting from rapid transcription of RbCP1 and the expression of a 37 kDa protease.

Protein extraction for proteome analysis from cacao leaves and meristems, organs infected by Moniliophthora perniciosa, the causal agent of the witches' broom disease

Preparation of high-quality proteins from cacao vegetative organs is difficult due to very high endogenous levels of polysaccharides and polyphenols. In order to establish a routine procedure for the application of proteomic and biochemical analysis to cacao tissues, three new protocols were developed; one for apoplastic washing fluid (AWF) extraction, and two for protein extraction--under denaturing and nondenaturing conditions. The first described method allows a quick and easy collection of AWF--using infiltration-centrifugation procedure--that is representative of its composition in intact leaves according to the smaller symplastic contamination detected by the use of the hexose phosphate isomerase marker. Protein extraction under denaturing conditions for 2-DE was remarkably improved by the combination of chemically and physically modified processes including phenol, SDS dense buffer and sonication steps. With this protocol, high-quality proteins from cacao leaves and meristems were isolated, and for the first time well-resolved 1-DE and 2-DE protein patterns of cacao vegetative organs are shown. It also appears that sonication associated with polysaccharide precipitation using tert-butanol was a crucial step for the nondenaturing protein extraction and subsequent enzymatic activity detection. It is expected that the protocols described here could help to develop high-level proteomic and biochemical studies in cacao also being applicable to other recalcitrant plant tissues.

Enhanced expression of serine proteases during floral senescence in Gladiolus

Programmed cell death during senescence in plants is associated with proteolysis that helps in remobilization of nitrogen to other growing tissues. In this paper, we provide one of the few reports for the expression of specific serine proteases during senescence associated proteolysis in Gladiolus grandiflorus flowers. Senescence in tepals, stamens and carpels results in an increase in total protease activity and a decrease in total protein content. Of the total protease activity, serine proteases account for about 67-70% while cysteine proteases account for only 23-25%. In-gel assays using gelatin as a substrate and specific protease inhibitors reveal the enhanced activity of two trypsin-type serine proteases of sizes 75 kDa and 125 kDa during the course of senescence. The activity of the 125 kDa protease increases not only during tepal senescence but also during stamen and carpel senescence indicating that it is responsive to general senescence signals.

Water deficit induces variation in expression of stress-responsive genes in two peanut (Arachis hypogaea L.) cultivars with different tolerance to drought

Peanut (Arachis hypogaea L.) is an important subsistence and cash crop in the semi-arid tropics where it often suffers from drought stress. Although its ecophysiological responses are studied, little is known about the molecular events involved in its adaptive responses to drought. The aim of this study was to investigate the involvement of membrane phospholipid and protein degrading enzymes as well as protective proteins such as "late embryogenesis-abundant" (LEA) protein in peanut adaptive responses to drought. Partial cDNAs encoding putative phospholipase D alpha, cysteine protease, serine protease and a full-length cDNA encoding a LEA protein were cloned. Their expression in response to progressive water deficit and rehydration was compared between cultivars differing in their tolerance to drought. Differential gene expression pattern according to either water deficit intensity and cultivar's tolerance to drought were observed. A good correspondence between the molecular responses of the studied cultivars and their physiological responses previously defined in greenhouse and field experiments was found. Molecular characters, as they were detectable at an early stage, could therefore be efficiently integrated in groundnut breeding programmes for drought adaptation. Thus, the relevance of the target genes as drought tolerance indicators is discussed.

The two main endoproteases present in dark-induced senescent wheat leaves are distinct subtilisin-like proteases

We have previously reported the occurrence of two serine endoproteases (referred to as P1 and P2) in dark-induced senescent wheat (Triticum aestivum L.) leaves. P1 enzyme was already purified and identified as a subtilisin-like serine endoprotease (Roberts et al. in Physiol Plant 118:483-490, 2003). In this paper, we demonstrate by Western blot analysis of extracts obtained from dark-induced senescent leaves that an antiserum raised against P1 was able to recognise a second protein band of 78 kDa which corresponded to P2 activity. This result suggested that both enzymes must be structurally related. Therefore, we purified and characterised P2 activity. According to its biochemical and physical properties (inhibition by chymostatin and PMSF, broad pH range of activity, thermostability and ability to hydrolyse Suc-AAPF-pNA) P2 was classified as a serine protease with chymotrypsin-like activity. In addition, P2 was identified by mass spectrometry as a subtilisin-like protease distinct from P1. Western blot analysis demonstrated that P1 appeared in extracts from non-detached dark-induced senescent leaves but was undetectable in leaves senescing after nitrogen (N) deprivation. In contrast, P2 was already present in non-senescent leaves and showed increased levels in leaves senescing after N starvation or incubation in darkness. P1 signal was detected at late stages of ethephon or methyl jasmonate-induced senescence but was undetectable in senescent leaves from plants treated with abscisic acid. None of the three hormones have any effect on P2 protein levels. These results indicate that despite their biochemical and structural similarities, both enzymes are probably involved in different physiological roles.

Plant serine proteases: biochemical, physiological and molecular features

In the latest two decades, the interest received by plant proteases has been on the rise. Serine proteases (EC 3.4.21)-in particular those from cucurbits, cereals and trees-share indeed a number of biochemical and physiological features, that may prove useful toward understanding of several mechanisms at the subcellular level. This critical review focuses on the characterization of most plant serine proteases, and comprehensively lists information produced by more and more sophisticated research tools that have led to the current state of the art in knowledge of these unique enzymes.