Effects of Oxygen Concentration and Ethephon upon the Respiration and Ripening of Banana Fruits

A respiratory climacteric and accumulation of soluble solidsof pulp were induced in banana fruits by (2-chlorethyl) phosphonicacid (ethephon) at oxygen concentrations of 3–21% (v/v).However, induction of peel colour change by ethephon was retardedor prevented at oxygen concentrations of 10% (v/v) or less.Thus pulp tissue ripened whilst the peel remained green. Respirationrate, soluble solids content of pulp, and peel colour were notaffected by ethephon at oxygen concentrations of 1% (v/v) orless. The kinetics of respiratory response to ethephon are consistentwith a model in which ethylene (derived from ethephon) is acoupling-activator of respiration. In this model ethylene decreasesthe affinity of an enzyme system for its substrate, but acceleratesthe release of product.     

壳聚糖提高香蕉幼苗抗冷性的效应

壳聚糖(CS)预处理可降低低温胁迫下香蕉幼苗叶细胞膜脂过氧化水平和膜透性增加的程度以及超氧化物歧化酶(SOD)、过氧化物酶(POD)活性的下降幅度,提高过氧化氢酶(CAT)的活性;0.3%的壳聚糖的保护效果最好.     

Purification and characterization of Mn-peroxidase from Musa paradisiaca (banana) stem juice

Mn-peroxidase (MnP), a biotechnologically important enzyme was purified for the first time from a plant source Musa paradisiaca (banana) stem, which is an agro-waste easily available after harvest of banana fruits. MnP was earlier purified only from the fungal sources. The enzyme was purified from stem juice by ultrafiltration and anion-exchange column chromatography on diethylamino ethylcellulose with 8-fold purification and purification yield of 65%. The enzyme gave a single protein band in SDS-PAGE corresponding to molecular mass 43 kDa. The Native-PAGE of the enzyme also gave a single protein band, confirming the purity of the enzyme. The UV/VIS spectrum of the purified enzyme differed from the other heme peroxidases, as the Soret band was shifted towards lower wavelength and the enzyme had an intense absorption band around 250 nm. The K(m) values using MnSO4 and H2O2 as the substrates of the purified enzyme were 21.0 and 9.5 microM, respectively. The calculated k(cat) value of the purified enzyme using Mn(II) as the substrate in 50 mM lactate buffer (pH 4.5) at 25 degrees C was 6.7s(-1), giving a k(cat)/K(m) value of 0.32 microM(-1)s(-1). The k(cat) value for the MnP-catalyzed reaction was found to be dependent of the Mn(III) chelator molecules malonate, lactate and oxalate, indicating that the enzyme oxidized chelated Mn(II) to Mn(III). The pH and temperature optima of the enzyme were 4.5 and 25 degrees C, respectively. The enzyme in combination with H2O2 liberated bromine and iodine in presence of KBr and KI respectively. All these enzymatic characteristics were similar to those of fungal MnP. The enzyme has the potential as a green brominating and iodinating agent in combination with KBr/KI and H2O2.     

Some properties of white and yellow plantain (Musa paradisiaca,Normalis) starches

Starch obtained from yellow and white plantain varieties were subjected to proximate analysis, physicochemical and rheological characterization in order to evaluate their properties. Yellow plantain variety gave higher yield of starch than the white variety. The two varieties differed in the purity of starch extract; white plantain starch contained: ash (1.09%), protein (0.640%) and fat (0.276%) while yellow plantain starch contained: ash (0.95%), protein (0.325%) and fat (0.403%). The amylose content of yellow plantain starch (24.36% (apparent), 26.13% (total)) was similar to that of white plantain starch (24.24% (apparent), 26.01% (total)). Scanning electron microscopy revealed bimodal irregular shaped granules (3.74–7.00 and 10.00–33.00 μm) in white plantain starch and elliptical granules (11.22–41.00 μm) in yellow plantain starch. Both starches differed markedly in their physicochemical properties. Their differences in gelatinization temperature (yellow plantain, 64.99–73.90 °C; white plantain, 68.08–77.15 °C), swelling and solubility patterns, and pasting characteristics indicated that yellow plantain starch had weaker granule architecture compared with white plantain starch. Further evidence of differences in properties was obtained from flow and viscoelastic properties of the starch gels, paste clarity and freeze–thaw stability.     

Water-deficit Stress, Ethylene Production, and Ripening in Avocado Fruits

Differential rates of water loss were achieved in picked avocado (Persea americana Mill.) fruits, either by controlling the evaporation rate or by supplying water through the fruit stalk. A negative linear correlation was found between the daily rate of water loss from fruits and their ripening, as determined by the time from harvest to peak of ethylene production. Ripening rate was hastened by 40% in fruits which had lost water at rate of 2.9% fresh weight per day, compared with those which lost only 0.5% per day.     

Respiratory Contribution of the Alternate Path during Various Stages of Ripening in Avocado and Banana Fruits

The respiration of fresh slices of preclimacteric avocado (Persea americana Mill. var. Hass) and banana (Musa cavendishii var. Valery) fruits is stimulated by cyanide and antimycin. The respiration is sensitive to m-chlorobenzhydroxamic acid in the presence of cyanide but much less so in the presence of antimycin. In the absence of cyanide the contribution of the cyanide-resistant pathway to the coupled preclimacteric respiration is zero. In uncoupled slices, by contrast, the alternate path is engaged and utilized fully in avocado, and extensively in banana. Midclimacteric and peak climacteric slices are also cyanide-resistant and, in the presence of cyanide, sensitive to m-chlorobenzhydroxamic acid. In the absence of uncoupler there is no contribution by the alternate path in either tissue. In uncoupled midclimacteric avocado slices the alternate path is fully engaged. Midclimacteric banana slices, however, do not respond to uncouplers, and the alternate path is not engaged. Avocado and banana slices at the climacteric peak neither respond to uncouplers nor utilize the alternate path in the presence or absence of uncoupler.

The maximal capacities of the cytochrome and alternate paths, V_cyt and V_alt, respectively, have been estimated in slices from preclimacteric and climacteric avocado fruit and found to remain unchanged. The total respiratory capacity in preclimacteric and climacteric slices exceeds the respiratory rise which attends fruit ripening. In banana V_alt decreases slightly with ripening.

The aging of thin preclimacteric avocado slices in moist air results in ripening with an accompanying climacteric rise. In this case the alternate path is fully engaged at the climacteric peak, and the respiration represents the total potential respiratory capacity present in preclimacteric tissue. The respiratory climacteric in intact avocado and banana fruits is cytochrome path-mediated, whereas the respiratory climacteric of ripened thin avocado slices comprises the alternate as well as the cytochrome path. The ripening of intact fruits is seemingly independent of the nature of the electron transport path.

Uncouplers are thought to stimulate glycolysis to the point where the glycolytic flux exceeds the oxidative capacity of the cytochrome path, with the result that the alternate path is engaged.

     

Plant defense induced in in vitro propagated banana (Musa paradisiaca) plantlets by Fusarium derived elicitors

Perception of microbial signal molecules is part of the strategy evolved by plants to survive attacks by potential pathogens. To gain a more complete understanding of the early signaling events involved in these responses, we used fungal components of Fusarium under in vitro condition and checked the rise in signal molecule, salicylic acid (SA), and marker enzymes in defense reactions against the pathogen. SA level increased by 21 folds in elicitor treated plantlets as compared to that of control plantlets and there was marked increase in phenylalanine ammonia-lyase(PAL), peroxidase(POX), polyphenol oxidase(PPO) along with higher total phenolic content. Present results indicated that use of fungal components had successfully induced systemic resistance in in vitro cultured banana plantlets.     

Mutagenicity of the Musa paradisiaca (Musaceae) fruit peel extract in mouse peripheral blood cells in vivo

Plants are a source of many biologically active products and nowadays they are of great interest to the pharmaceutical industry. In the present study, the mutagenic potential of the Musa paradisiaca fruit peel extract was assessed by the single-cell gel electrophoresis (SCGE) and micronucleus assays. Animals were treated orally with three different concentrations of the extract (1000, 1500, and 2000 mg/kg body weight). Peripheral blood cells of Swiss mice were collected 24 h after treatment for the SCGE assay and 48 and 72 h for the micronucleus test. The results showed that the two higher doses of the extract of M. paradisiaca induced statistically significant increases in the average numbers of DNA damage in peripheral blood leukocytes for the two higher doses and a significant increase in the mean of micronucleated polychromatic erythrocytes in the three doses tested. The polychromatic/normochromatic erythrocyte ratio scored in the treated groups was not statistically different from the negative control. The data obtained indicate that fruit peel extract from M. paradisiaca showed mutagenic effect in the peripheral blood cells of Swiss albino mice.     

香蕉凝集素基因的克隆及在成熟果实中的特异性表达

采用RT-PCR的方法克隆香蕉凝集素(Bankc)基因,对其全序列进行了测定并与已发表的BanLec基因序列进行了比较。采用定量PCR的方法对该基因在果实成熟过程中和香蕉不同组织中的表达进行了研究,结果表明：BanLec基因的表达同时具有发育特异性和组织特异性,即仅在果实中表达,而且其表达量随果实成熟度的变化而变化。     

An Improved Protocol for Microcallus Production and Whole Plant Regeneration from Recalcitrant Banana Protoplasts (Musa spp.)

One important limitation for routine production of somatic hybrids in banana (Musa spp.) is the difficulty in protoplast regeneration. To facilitate protoplast regeneration in banana, the crucial step of microcallus production was optimised for the following parameters: nurse culture medium, duration of microcalli on nurse culture, differing nurse cells, and filter composition. A comparative study between two nurse cell media, Ma₂ and PCM, significantly affected the number of microcalli produced, which was 90 × 10³ per Petri dish on Ma₂ with 0.5 μM zeatin and 9.0 μM 2,4 D, and 30 × 10³ per Petri dish on PCM. Moreover, continuous production of microcalli was achieved on Ma₂ and the frequency of embryogenic cell aggregates was higher among microcalli on Ma₂-medium. However, no cell division was observed in protoplasts cultured on Ma₂ in which nurse cells were maintained for 2 weeks suggesting a requirement of effective presence of nurse cells for cell division of banana protoplasts. Use of a filter in conjugation with nurse cells resulted in greater than 7-fold increase in the number of microcalli. Flow cytometry analysis of 124 protoplast-derived plants showed the presence of hexaploid plants (mother plant is triploid) at the frequency of 4%. Together, these data are indicative of the complex factors involved in the regulation of plant cell division and growth. Each individual aspect must be optimised for efficient protocol development.     

影响体胚发生途径香蕉(Musa spp.,AAB Group)植株再生的因素

香蕉品种‘Agbagaba'和‘Orishele'的胚性细胞悬浮系(ECS)在液体培养基中分别预培养1和2周后,将其接种在RD1和M3培养基上,于光照或黑暗条件下进行体胚的再生.从沉积细胞体积(SCV)为1 mL(1 mL SCV)的ECS获得的再生体胚数量因预培养时间、再生培养基的种类及培养条件的不同而异.植株的再生率及从1 mL SCV的ECS获得的再生植株数量也受上述体胚再生条件的间接影响.     

Partial Characterization of C(x) Cellulase and Cellobiase from Ripening Tomato Fruits

Cellulolytic enzymes were studied in extracts from the locular contents of ripening fruits of Lycopersicon esculentum var. KC-146. When acting on carboxymethyl cellulose, the enzyme preparations were capable of decreasing the viscosity of the reaction mixture and generating reducing groups, oligosaccharides, and glucose. Cellobiose cellotriose, cellotetrose, and cellopentose also served as substrates for glucose production.