Changes in Homogalacturonan Metabolism in Banana Peel during Fruit Development and Ripening.

Though numerous studies have focused on the cell wall disassembly of bananas during the ripening process, the modification of homogalacturonan (HG) during fruit development remains exclusive. To better understand the role of HGs in controlling banana fruit growth and ripening, RNA-Seq, qPCR, immunofluorescence labeling, and biochemical methods were employed to reveal their dynamic changes in banana peels during these processes. Most HG-modifying genes in banana peels showed a decline in expression during fruit development. Four polygalacturonase and three pectin acetylesterases showing higher expression levels at later developmental stages than earlier ones might be related to fruit expansion. Six out of the 10 top genes in the Core Enrichment Gene Set were HG degradation genes, and all were upregulated after softening, paralleled to the significant increase in HG degradation enzyme activities, decline in peel firmness, and the epitope levels of 2F4, CCRC-M38, JIM7, and LM18 antibodies. Most differentially expressed alpha-1,4-galacturonosyltransferases were upregulated by ethylene treatment, suggesting active HG biosynthesis during the fruit softening process. The epitope level of the CCRC-M38 antibody was positively correlated to the firmness of banana peel during fruit development and ripening. These results have provided new insights into the role of cell wall HGs in fruit development and ripening.

Identification and functional analysis of the CorA/MGT/MRS2-type magnesium transporter in banana.

Magnesium (Mg) plays an irreplaceable role in plant growth and development. Mg transporters, especially CorA/MGT/MRS2 family proteins, played a vital role in regulating Mg content in plant cells. Although extensive work has been conducted in model crops, such as Arabidopsis, rice, and maize, the relevant information is scarce in tropical crops. In this study, 10 MaMRS2 genes in banana (Musa acuminata) were isolated from its genome and classified into five distinct clades. The putative physiochemical properties, chromosome location, gene structure, cis-acting elements, and duplication relationships in between these members were analyzed. Complementary experiments revealed that three MaMRS2 gene members (MaMRS2-1, MaMRS2-4, MaMRS2-7), from three distinct phylogenetic branches, were capable of restoring the function of Mg transport in Salmonella typhimurium mutants. Semi-quantitative RT-PCR showed that MaMRS2 genes were differentially expressed in banana cultivar 'Baxijiao' (Musa spp. AAA Cavendish) seedlings. The result was confirmed by real-time PCR analysis, in addition to tissue specific expression, expression differences among MaMRS2 members were also observed under Mg deficiency conditions. These results showed that Mg transporters may play a versatile role in banana growth and development, and our work will shed light on the functional analysis of Mg transporters in banana.

Overexpression of MaTPD1A impairs fruit and pollen development by modulating some regulators in Musa itinerans.

BACKGROUND: Pollen formation and development is important for crop fertility and is a key factor for hybrid development. Previous reports have indicated that Arabidopsis thaliana TAPETUM DETERMINANT1 (AtTPD1) and its rice (Oryza sativa) homolog, OsTPD1-like (OsTDL1A), are required for cell specialization and greatly affect pollen formation and development. Little is known about the role of the TPD1 homolog in banana pollen development. RESULTS: Here, we report the identification and characterization of TPD1 homologs in diploid banana (Musa itinerans) and examine their role in pollen development by overexpressing the closest homolog, MaTPD1A. MaTPD1A exhibits high expression in stamen and localizes in the plasma membrane. MaTPD1A-overexpressing plants produce no pollen grains and smaller and seedless fruit compared to wild-type plants. Transcriptome analysis showed that in plant hormone, starch and sucrose metabolism, and linolenic acid metabolism-related pathways were affected by overexpression of MaTPD1A, and the expression of several key regulators, such as PTC1 and MYB80, which are known to affect anther development, is affected in MaTPD1A-overexpressing lines. CONCLUSIONS: Our results indicate that MaTPD1A plays an important role in pollen formation and fruit development in diploid banana, possibly by affecting the expression of some key regulators of pollen development.

Banana fruits with high content of resistant starch: Effect of genotypes and phosphorus fertilization.

Banana fertilization practices aim to increase agricultural yield and the effects of these practices on fruit components have not been well explored. This study aimed to evaluate the effects of phosphate fertilizer levels on production parameters and accumulation of dry matter, phosphorus, starch and resistant starch in green fruits. Four banana genotypes were cultivated under the same cultural practices, with varying levels of phosphate fertilizers during three production cycles. Bunches were harvested and evaluated for total fruit mass, average finger mass and yield. Fresh green fruit pulps were analyzed for dry matter, phosphorus, starch and resistant starch content. The results showed that the effects of phosphate fertilizer were genotype dependent and that the increase of P2O5 rates applied in banana fertilization promoted an increase in fruit production with higher levels of phosphorus, starch and resistant starch.

Banana and plantain production systems in Benin: ethnobotanical investigation, varietal diversity, pests, and implications for better production.

BACKGROUND: The cultivated banana and plantain (Musa spp.) are valuable for nutritional and socio-economic security for millions of people worldwide. In Benin, banana and plantain are among the most produced, consumed, and traded commodities. Its production is mainly for local consumption and remains insufficient to the demand. However, the varietal diversity of banana and plantain cultivated in Benin is not documented. This study aims at characterizing the banana and plantain cropping systems, genetic diversity, and production constraints as a baseline to the full utilization of this resource in crop improvement and to identify the potential production and agronomic qualities. METHODS: A baseline investigation of ethnobotanical attributes of banana cultivars was done in 51 randomly chosen villages in southern Benin. Interviews with randomly selected representative farmers were carried out. Key informant interviews and focus group discussions were used for global confirmatory investigation of survey data. Socio-demographic data and indigenous knowledge on the farmer uses of banana and plantain diversity, such as cultural practices, origin, and availability of banana and plantain planting materials, and the constraints and criteria of varietal preference cited by farmers were ranked. RESULTS: Eighty-seven locally recognized cultivars were found: 73 of banana and 14 of plantain groups. The most popular cultivars were Sotoumon (banana) (52.94%), Aloga (plantain) (41.17%), Planta (banana) (33.33%), and Adjangan (plantain) (27.45%). Of the eleven production constraints identified, the main biotic challenges were banana weevil Cosmopolites sordidus Germar and banana bunchy top virus (BBTV), while abiotic problems were drought and the wind. Some local varieties like Amandan, Assonwonnou, Coleti, and Ninkouin are extremely rare owing to agronomic and economic preference perceptions. CONCLUSION AND IMPLICATIONS: This study provides a baseline for banana diversity in Benin and the West African region and entry points for biological characterization and production improvement. This would enable the exploitation of this resource for plant breeding towards biotic and abiotic challenges facing banana production.

Effect of modifying concentrations of calcium and magnesium on in vitro development of banana CV. Prata-Anã (Genomic group AAB) / Efeito da modificação das concentrações de cálcio e magnésio no desenvolvimento in vitro de bananeira CV. Prata-Anã (Grupo genômico AAB)

Research suggests that the development of micropropagated banana plants can be improved by altering nutrient concentrations in the culture medium. The aim of this study was to evaluate the in vitro development of banana plants exposed to varying concentrations of calcium and magnesium sulfate. The shoot tips of banana cv. Prata- Anã were inoculated in flasks (volume, 250 cm3) containing 50 mL of MS culture medium. The culture medium contained varying concentrations of CaCl2 (0, 220, 440, 880 mg L-1) and MgSO4 (0, 185, 370, 740 mg L-1. A completely randomized experimental design was employed, based on a 4 × 4 factorial scheme (four levels of CaCl2 concentration, and four of MgSO4). The MS culture medium containing 880 mg L-1 of CaCl2 but no MgSO4 showed the highest increment in the number of leaves (6.0). The highest number of roots was observed in the absence of CaCl2 and MgSO4 in the medium. Additionally, the shoot length was longer (5.05 cm) when the MS medium was supplemented with 185 mg L-1 of MgSO4. The optimum in vitro development of banana cv. Prata-Anã was obtained when the MS medium was supplemented with 880 mg L-1 of CaCl2 and 370 mg L-1 of MgSO4.

Pesquisas sugerem que o desenvolvimento de plantas de bananeira podem ser melhoradas pela alteração das concentrações no meio de cultura. O objetivo deste estudo foi avaliar o desenvolvimento in vitro de bananeira submetida a diferentes concentrações de cloreto de cálcio e sulfato de magnésio. Ápices caulinares de bananeira cv. Prata-Anã foram inoculados em frascos (volume, 250 cm3) contendo 50 mL de meio de cultura MS. O meio de cultura contendo diferentes concentrações de CaCl2 (0, 220, 440 e 880 mg L-1) e MgSO4 (0, 185, 370, 740 mg L-1). O delineamento experimental foi inteiramente casualizado, em esquema fatorial 4 × 4 (quatro concentrações de CaCl2 e quatro de MgSO4). O meio MS contendo 880 mg L-1 de CaCl2 na ausência de MgSO4 proporcionou maior incremento no número de folhas (6,0). Maior número de raiz foi observado na ausência de CaCl2 e MgSO4 no meio. Além disso, maior comprimento de parte aérea (5,05 cm) foi obtido em meio MS suplementado com 185 mg L-1 de MgSO4. O melhor desenvolvimento in vitro de bananeira cv. Prata-Anã foi obtido em meio MS suplementado com 880 mg L-1 de CaCl2 e 370 mg L-1 de MgSO4.

The effect of a plant extract enriched in stigmasterol and ß-sitosterol on glycaemic status and glucose metabolism in alloxan-induced diabetic rats.

Banana is an extensively cultivated plant worldwide, mainly for its fruit, while its ancillary product, the banana pseudostem, is consumed as a vegetable and is highly recommended for diabetics in the traditional Indian medicine system. The present study was aimed at elucidating the mechanism of antihyperglycaemia exerted by the ethanol extract of banana pseudostem (EE) and its isolated compounds viz., stigmasterol (C1) and ß-sitosterol (C2), in an alloxan-induced diabetic rat model. Diabetic rats which were administered with C1, C2 and EE (100 and 200 mg per kg b. wt.) for 4 weeks showed reduced levels of fasting blood glucose and reversal of abnormalities in serum/urine protein, urea and creatinine in diabetic rats compared to the diabetic control group of rats. Diabetic symptoms such as polyphagia, polydipsia, polyuria, urine glucose and reduced body weight were ameliorated in the diabetic group of rats fed with EE, C1 and C2 (100 mg per kg b. wt., once daily) for 28 days. The levels of insulin and Hb were also increased, while the HbA1c level was reduced. The altered activities of hepatic marker enzymes viz., aspartate transaminase (AST), alanine transaminase (ALT) and alkaline phosphatase (ALP); glycolytic enzyme (hexokinase); shunt enzyme (glucose-6-phosphate dehydrogenase); gluconeogenic enzymes (glucose-6-phosphatase, fructose-1,6-bisphosphatase and lactate dehydrogenase) and pyruvate kinase were significantly reverted to normal levels by the administration of EE, C1 and C2. In addition, increased levels of hepatic glycogen and glycogen synthase and the corresponding decrease of glycogen phosphorylase activity in diabetic rats illustrated the antihyperglycaemic potential of EE and its components. The histological observations revealed a marked regeneration of the ß-cells in the drug treated diabetic rats. These findings suggest that EE might exert its antidiabetic potential in the presence of C1 and C2, attributable to the enhanced glycolytic activity, besides increasing the hepatic glucose utilization in diabetic rats by stimulating insulin secretion from the remnant ß-cells.

Optimization of extraction parameters on the antioxidant properties of banana waste.

BACKGROUND: Banana is grown worldwide and consumed as ripe fruit or used for culinary purposes. Peels form about 18-33% of the whole fruit and are discarded as a waste product. With a view to exploiting banana peel as a source of valuable compounds, this study was undertaken to evaluate the effect of different extraction parameters on the antioxidant activities of the industrial by-product of banana waste (peel). METHODS: Influence of different extraction parameters such as types of solvent, percentages of solvent, and extraction times on total phenolic content (TPC) and antioxidant activity of mature and green peels of Pisang Abu (PA), Pisang Berangan (PB), and Pisang Mas (PM) were investigated. The best extraction parameters were initially selected based on different percentages of ethanol (0-100% v/v), extraction time (1-5 hr), and extraction temperature (25-60°C) for extraction of antioxidants in the banana peels. Total phenolic content (TPC) was evaluated using Folin-Ciocalteu reagent assay while antioxidant activities (AA) of banana peel were accessed by DPPH, ABTS, and ß-carotene bleaching (BCB) assays at optimum extraction conditions. RESULTS: Based on different extraction solvents and percentages of solvents used, 70% and 90% of acetone had yielded the highest TPC for the mature and green PA peels, respectively; 90% of ethanol and methanol has yielded the highest TPC for the mature and green PB peels, respectively; while 90% ethanol for the mature and green PM peels. Similar extraction conditions were found for the antioxidant activities for the banana peel assessed using DPPH assay except for green PB peel, which 70% methanol had contributed to the highest AA. Highest TPC and AA were obtained by applying 4, 1, and 2 hrs extraction for the peels of PA, PB and PM, respectively. The best extraction conditions were also used for determination of AAs using ABTS and ß-carotene bleaching assays. Therefore, the best extraction conditions used have given the highest TPC and AAs. CONCLUSIONS: By-products of banana (peel) can be considered as a potential source of antioxidants in food and pharmaceutical industry.

Antioxidant effcacy of unripe banana (Musa acuminata Colla) peel extracts in sunflower oil during accelerated storage.

BACKGROUND: Sunflower oil is prone to oxidation during storage time, leading to production of toxic compounds that might affect human health. Synthetic antioxidants are used to prevent lipid oxidation. Spreading interest in the replacement of synthetic food antioxidants by natural ones has fostered research on fruit and vegetables for new antioxidants. METHODS: In this study, the efficacy of unripe banana peel extracts (100, 200 and 300 ppm)  in stabilizing sunflower oil was tested under accelerated storage (65°C) for a period of 24 days. BHA and α-tocopherol served as comparative standards besides the control. Established parameters such as peroxide value (PV), iodine value (IV), p-anisidine value (p-AnV), total oxidation value (TOTOX), thiobarbituric acid reactive substances (TBARS) and free fatty acid (FFA) content were used to assess the extent of oil deterioration. RESULTS: After 24 days storage at 65°C, sunflower oil containing 200 and 300 ppm extract of unripe banana peel showed significantly lower PV and TOTOX compared to BHA and α-tocopherol. TBARS, p-AnV and FFA values of sunflower oil containing 200 and 300 ppm of unripe banana peel extract exhibited comparable inhibitory effects with BHA. Unripe banana peel extract at 200 and 300 ppm demonstrated inhibitory effect against both primary and secondary oxidation up to 24 days under accelerated storage conditions. CONCLUSIONS: Unripe banana peel extract may be used as a potential source of natural antioxidants in the application of food industry to suppress lipid oxidation.

Characterization of Musa sp. fruits and plantain banana ripening stages according to their physicochemical attributes.

This study aimed at understanding the contribution of the fruit physicochemical parameters to Musa sp. diversity and plantain ripening stages. A discriminant analysis was first performed on a collection of 35 Musa sp. cultivars, organized in six groups based on the consumption mode (dessert or cooking banana) and the genomic constitution. A principal component analysis reinforced by a logistic regression on plantain cultivars was proposed as an analytical approach to describe the plantain ripening stages. The results of the discriminant analysis showed that edible fraction, peel pH, pulp water content, and pulp total phenolics were among the most contributing attributes for the discrimination of the cultivar groups. With mean values ranging from 65.4 to 247.3 mg of gallic acid equivalents/100 g of fresh weight, the pulp total phenolics strongly differed between interspecific and monospecific cultivars within dessert and nonplantain cooking bananas. The results of the logistic regression revealed that the best models according to fitting parameters involved more than one physicochemical attribute. Interestingly, pulp and peel total phenolic contents contributed in the building up of these models.

Analysis of the abilities of endophytic bacteria associated with banana tree roots to promote plant growth.

A total of 40 endophytic bacterial isolates obtained from banana tree roots were characterized for their biotechnological potential for promoting banana tree growth. All isolates had at least one positive feature. Twenty isolates were likely diazotrophs and formed pellicles in nitrogen-free culture medium, and 67% of these isolates belonged to the genus Bacillus sp. The isolates EB-04, EB-169, EB-64, and EB-144 had N fixation abilities as measured by the Kjeldahl method and by an acetylene reduction activity assay. Among the 40 isolates, 37.5% were capable of solubilizing inorganic phosphate and the isolates EB-47 and EB-64 showed the highest solubilization capacity. The isolate EB-53 (Lysinibacillus sp.) had a high solubilization index, whereas 73% of the isolates had low solubilization indices. The synthesis of indole-3-acetic acid (IAA) in the presence of L-tryptophan was detected in 40% of the isolates. The isolate EB-40 (Bacillus sp.) produced the highest amount of IAA (47.88 µg/ml) in medium supplemented with L-tryptophan and was able to synthesize IAA in the absence of L-tryptophan. The isolates EB-126 (Bacillus subtilis) and EB-47 (Bacillus sp.) were able to simultaneously fix nitrogen, solubilize phosphate and produce IAA in vitro. The results of this study demonstrated that the isolates analyzed here had diverse abilities and all have the potential to be used as growth-promoting microbial inoculants for banana trees.

In vitro propagation and assessment of the genetic fidelity of Musa acuminata (AAA) cv. Vaibalhla derived from immature male flowers.

An efficient in vitro propagation method has been developed for the first time for Musa acuminata (AAA) cv. Vaibalhla, an economically important banana cultivar of Mizoram, India. Immature male flowers were used as explants. Murashige and Skoog's (MS) medium supplemented with plant growth regulators (PGRs) were used for the regeneration process. Out of different PGR combinations, MS medium supplemented with 2 mg L(-1) 6-benzylaminopurine (BAP) + 0.5 mg L(-1) α-naphthalene acetic acid (NAA) was optimal for production of white bud-like structures (WBLS). On this medium, explants produced the highest number of buds per explant (4.30). The highest percentage (77.77) and number (3.51) of shoot formation from each explants was observed in MS medium supplemented with 2 mg L(-1) kinetin + 0.5 mg L(-1) NAA. While MS medium supplemented with a combination of 2 mg L(-1) BAP + 0.5 mg L(-1) NAA showed the maximum shoot length (14.44 cm). Rooting efficiency of the shoots was highest in the MS basal medium without any PGRs. The plantlets were hardened successfully in the greenhouse with 96% survival rate. Random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) markers were employed to assess the genetic stability of in vitro regenerated plantlets of M. acuminata (AAA) cv. Vaibalhla. Eight RAPD and 8 ISSR primers were successfully used for the analysis from the 40 RAPD and 30 ISSR primers screened initially. The amplified products were monomorphic across all the regenerated plants and were similar to the mother plant. The present standardised protocol will find application in mass production, conservation and genetic transformation studies of this commercially important banana.

Thermotherapy, chemotherapy, and meristem culture in banana.

Bananas that provide a staple food to the millions of people are adversely affected by several viruses such as Banana bunchy Top Virus (BBTV), Banana Streak Virus (BSV), and Cucumber Mosaic Virus (CMV). These viruses are known to have a devastating effect on crop production and constraint to the international exchange and conservation of banana germplasm-a cornerstone for breeding new cultivars. The viruses are particularly problematic in vegetative propagated crops, like bananas, because of their transmission in the planting material. Different virus eradication techniques have been developed, such as thermotherapy, chemotherapy, and meristem culture for providing virus-free planting material. Meristem culture proved to be the most effective procedure to eradicate phloem-associated viruses. This method requires isolation of meristematic dome of plant under the aseptic conditions and culture in an appropriate nutrient medium to develop new virus-free plants. Thermotherapy is another widely used virus eradication technique, which is initially carried out on in vivo or in vitro plants and eventually combined with meristem culture technique. The plantlets are initially grown at 28°C day temperature and increase it by 2°C per day until reaches 40°C and the night temperature at 28°C; maintain plants at 40°C for 4 weeks; excise meristem and culture onto the regeneration medium. In chemotherapy technique, antiviral chemical compound Virazole(®) is applied on meristem culture. Combination of these techniques is also applied to improve the eradication rate.

Perfis de compostos voláteis de banana submetidos a diferentes tratamentos pós-colheita e suas correlações com a expressão diferencial dos receptores de etileno / Volatile compounds profile of bananas submitted to different post-harvest treatments and its correlations to differential expression of ethylene receptors

O aroma de frutos é um atributo fortemente associado à qualidade, e quaisquer alterações ambientais ou tratamentos pós-colheita podem alterar a sua composição. Acredita-se que a biossíntese de voláteis seja um dos processos regulados pelo etileno. Estudos indicam que a expressão diferencial dos elementos que compõem os receptores de etileno desempenha importante papel na sinalização dos processos ligados ao amadurecimento, entre eles a formação do aroma. Os objetivos deste trabalho são: caracterizar as alterações decorrentes de tratamentos pós-colheita no aroma de banana durante o amadurecimento, e correlacionar com as variações nos padrões de expressão gênica diferencial dos receptores de etileno. Bananas pré-climatéricas variedade Nanicão foram divididas em quatro grupos: controle (não tratado), etileno (100ppm/12h), 1-MCP (100ppb/12h), armazenados a 20°C, e grupo frio (armazenado por 15 dias a 13°C). Foram analisados diariamente a produção de etileno e de CO2 por CG. Foram analisadas a cor da casca, açúcares solúveis e amido. Os compostos voláteis foram isolados por microextração em fase sólida (SPME) em frutos inteiros e polpas e analisados em CG-MS. Para confirmar os resultados e verificar se as alterações encontradas se repetem em outras variedades de bananas, o estudo foi repetido no Horticultural Sciences Department, na Universidade da Florida (EUA), em bananas var. 'Grand Naine'. Em paralelo, realizou-se a quantificação relativa da expressão dos receptores de etileno (ETR1, ERS1, ERS2 e ERS3) por PCR em tempo real. Com relação ao perfil de voláteis, os resultados indicam que os frutos não se diferenciam no período pré-climatérico. Porém, o perfil de voláteis do grupo controle foi significativamente diferente do grupo frio, tanto na polpa quanto no fruto inteiro no período climatérico. Esse efeito foi mais pronunciado na Nanicão do que na 'Grand Naine'. Compostos típicos como o acetato de isoamila foram drasticamente reduzidos nos frutos submetidos ao frio, e não foram encontrados na Nanicão. Não houve diferenças significativas com relação ao perfil de aromas entre o grupo controle e o grupo etileno. Com relação aos frutos tratados com 1-MCP observou-se o atraso na formação de alguns compostos sem alterar, contudo, o perfil final de voláteis. Com relação ao padrão de transcrição dos receptores de etileno, o frio reduziu o acúmulo dos transcritos do ETR1, ERS2 e ERS3 em todos os pontos. ERS1 parece estar correlacionado com a síntese de esteres. Os resultados sugerem que o mecanismo pelo qual o etileno regula o metabolismo de biossíntese de aromas parece contar com a participação relevante de determinados tipos de receptores. A correlação temporal encontrada entre as alterações no perfil de transcritos de três destes e os efeitos sobre a produção de compostos voláteis reforçam esta hipótese

Fruit aroma is an attribute strongly associated to quality, and any change in the environment or post-harvest treatment could affect its composition. Volatile biosynthesis is a process that is believed to be regulated by ethylene. Studies demonstrate that differential expression of ethylene receptors have an important role in fruit ripening processes, including aroma synthesis. The aims of this study are: evaluate modifications due to post-harvest treatment on the aroma of banana fruit during ripening, and correlate to variations on differential expression of ethylene receptors. Pre climacteric bananas of 'Nanicão' variety were divides in four groups: control (without treatment), ethylene (100ppm/12h), 1-MCP (100ppb/12h), stored at 20°C, and cold storage group (stored for 15 days at 13°C). Daily measurements were conducted of ethylene production and respiration using GC. Peel color, soluble sugars and starch were analyzed. Volatile compounds were isolated by solid phase microextraction (SPME) in whole fruits and pulp and analyzed by GCMS. To confirm the results ant to verify if the findings repeat in another banana variety, this study was repeated at Horticultural Sciences Department, at University of Florida (EUA), under supervision of Dr. Jeffrey K. Brecht, in bananas Cavendish cv. 'Grand Naine'. Also, relative quantification of the expression of ethylene receptors (ETR1, ERS1, ERS2 and ERS3) was analyzed using real time PCR. Regarding the volatile profile, groups did not differentiated in pre-climacteric period. But the volatile profile of control group significantly differentiates from cold storage group, in both pulp and whole fruit, in post climacteric period. This effect was more pronounced in bananas 'Nanicão' than 'Grand Naine'. Typical banana aroma compounds like isoamyl acetate were drastically reduced in fruits under cold storage, and were not found in 'Nanicão'. There were not any significant differences between control group and ethylene treated. Regarding 1-MCP treated fruits, there was a delay on the synthesis of some compounds without affecting the final volatile profile. Regarding the transcription pattern of ethylene receptors, cold storage reduced mRNA of ETR1, ERS2 and ERS3 in all samples. ERS1 receptor seems to be correlated to ester synthesis. These results suggest that the mechanism whereby the ethylene regulates the biosynthesis of aroma, seems to count with relevant participation of some receptors. The temporal correlation found in the differential expression of three receptors and the effect on volatile compounds synthesis reinforces this hypothesis

The role of meta-topolins on the photosynthetic pigment profiles and foliar structures of micropropagated 'Williams' bananas.

The effect of five topolins (meta-Topolin=mT; meta-Topolin riboside=mTR; meta-Methoxy topolin=MemT; meta-Methoxy topolin riboside=MemTR and 6-(meta-methoxy)-9-(tetrahydropyran-2-yl)-topolin=MemTTHP) on the photosynthetic pigments and leaf structures of micropropagated 'Williams' bananas was compared with the commonly used benzyladenine (BA). Surface-decontaminated explants were cultured for 70 d on modified Murashige and Skoog (MS) basal medium and supplemented with 10, 20 or 30µM cytokinins (CKs). At 10 d intervals, the photosynthetic pigments were quantified via spectrophotometric methods for 7 cycles. Generally, the maximum pigment content was attained between 40 and 50 d. The control plantlets had the highest pigment content (1150µg/g FW). Among the CKs, 10µM MemTTHP generally had the best pigment stimulatory effect at the same period. After 40 d, scanning electron microscopy (SEM) of the foliar surface showed that the stomata density was highest in 10µM MemTTHP-treated and lowest in 10µM MemTR-treated plantlets. The stomatal structure and pore area also varied with the type and concentration of CK added. Generally, prolonging culture duration as well as increasing CK concentrations reduced the pigment content. However, the drastic breakdown in chlorophyll pigments beyond 50 d was slightly inhibited by the presence of mT, mTR, MemTTHP and BA compared to the control. The CK-treated plantlets at equimolar concentration had comparable chlorophyll a/b and total chlorophyll/carotenoid ratios after 10 d; probably as an adaptive measure. At the end of the current study, 10µM mT and mTR plantlets remained green as reflected by the higher total chlorophyll/carotenoid ratio as well as by the visual observations. A well-developed photosynthetic apparatus enhances the survival of in vitro plantlets during the acclimatization stage. Current findings provide some insight into the role of meta-topolins on photosynthetic parameters in vitro, which inevitably partly contributed to the better acclimatization capability of meta-topolin-regenerants.

Physiological responses and endogenous cytokinin profiles of tissue-cultured 'Williams' bananas in relation to roscovitine and an inhibitor of cytokinin oxidase/dehydrogenase (INCYDE) treatments.

The effect of supplementing either meta-topolin (mT) or N(6)-benzyladenine (BA) requiring cultures with roscovitine (6-benzylamino-2-[1(R)-(hydroxymethyl)propyl]amino-9-isopropylpurine), a cyclin-dependent kinase (CDK) and N-glucosylation inhibitor, and INCYDE (2-chloro-6-(3-methoxyphenyl)aminopurine), an inhibitor of cytokinin (CK) degradation, on the endogenous CK profiles and physiology of banana in vitro was investigated. Growth parameters including multiplication rate and biomass were recorded after 42 days. Endogenous CK levels were quantified using UPLC-MS/MS while the photosynthetic pigment and phenolic contents were evaluated spectrophotometrically. The highest regeneration rate (93 %) was observed in BA + roscovitine while mT + INCYDE plantlets produced most shoots. Treatment with BA + roscovitine had the highest shoot length and biomass. Although not significant, there was a higher proanthocyanidin level in BA + roscovitine treatments compared to the control (BA). The levels of total phenolics and flavonoids were significantly higher in mT + roscovitine treatment than in the mT-treated regenerants. The presence of roscovitine and/or INCYDE had no significant effect on the photosynthetic pigments of the banana plantlets. Forty-seven aromatic and isoprenoid CKs categorized into nine CK-types were detected at varying concentrations. The presence of mT + roscovitine and/or INCYDE increased the levels of O-glucosides while 9-glucosides were higher in the presence of BA. Generally, the underground parts had higher CK levels than the aerial parts; however, the presence of INCYDE increased the level of CK quantified in the aerial parts. From a practical perspective, the use of roscovitine and INCYDE in micropropagation could be crucial in the alleviation of commonly observed in vitro-induced physiological abnormalities.

[Main bacterial groups in banana soil under rotated and continuous cropping].

Banana wilt is the main disease in banana production, while banana-leek rotation can effectively control the occurrence of the disease. In order to understand the variations of soil bacterial groups under banana-leek rotation and banana continuous cropping, soil samples under these two cropping systems were collected to extract crude DNA, and the bacterial 16S rDNA in V3 region was amplified by PCR. The PCR products were then separated by DGGE, and the main different bands were sequenced and compared with the records of NCBI to identify the germs. Under banana-leek rotation, soil bacterial diversity was richer, and the main bacterial groups were Bacteroidetes, Proteobacteria, Actinobacteria, Chloroflexi, and Acidobacteria; while under banana continuous cropping, the soil bacterial diversity was somewhat decreased, and the main bacterial groups were Firmicutes, Proteobacteria, Actinobacteria, and Chloroflexi.

Spermine-induced morphogenesis and effect of partial immersion system on the shoot cultures of banana.

Contribution of exogenous polyamines (PAs) and polyamine-inhibitors on plantlet regeneration patterns of banana (cv. Nanjanagudu Rasabale-AAB) was studied and the performance of regenerated shoots in temporary immersion system was evaluated. The rhizome explants (without shoot bud) of in vitro shoots produced a mixture of embryogenic and nonembryogenic calli on modified MS medium. The analyses of endogenous pools of polyamines showed higher levels of PAs in embryogenic than in nonembryogenic calli. Supplementation of various levels of (10-50 microM) spermine (Spm), spermidine (Spd), and putrescine (Put) to cultures with secondary embryogenesis showed that about 50% of embryogenic calli rapidly produced secondary embryos only in the presence 40 microM Spm but not in other treatments. The crucial role of Spm was further confirmed by the use of 0.1 mM each of alpha-DL-Difluromethylornithine and alpha-DL-Difluromethylarginine along with Spm where the presence of inhibitors concomitantly inhibited the secondary embryogenesis. The shoots obtained from the embryogenic cultures were checked for their performance on solid medium (SM) and partial immersion system (PIS). The rate of shoot multiplication was higher in PIS than in SM throughout 6 weeks culture period. Uniformity in elongation of all the shoot buds was observed in PIS but not in SM. Evaluation for the acclimatization, survival under greenhouse conditions revealed the better performance of PIS-derived plants than those from SM.

Pectate lyase gene expression and enzyme activity in ripening banana fruit.

Two distinct cDNA clones showing sequence homology to higher-plant pectate lyase (Pel) genes were isolated from ripening banana fruits. The transcripts were detected only in fruit tissue and both were strongly ripening-related. Yeast transformation with the most highly expressed Pel clone produced a recombinant protein with pectate lyase activity, demonstrating that this sequence was likely to encode a pectate lyase protein in planta. An assay developed for measuring the action of the endogenous enzyme from banana pulp tissue revealed a significant increase in calcium-dependent pectate lyase activity during ripening. The enhanced levels of enzyme activity corresponded with an increase in soluble polyuronides from banana pulp.

Pectate lyase activity during ripening of banana fruit.

Pectate lyase (PEL) activity was demonstrated in ripe banana fruits on supplementing the homogenizing medium with cysteine and Triton X-100. The enzyme was characterized on the basis of alkaline pH optimum, elimination of the activity by EDTA and activation by Ca(2+). PEL activity was not detected in preclimacteric banana fruits. PEL activity increased progressively from early climacteric and reached maximum level at climacteric peak and declined in post climacteric and over ripened fruits. Replacing pectate with pectin in PEL assay manifested enzyme activity even in preclimacteric fruits. In contrast to PEL, polygalacturonase activity progressively increased during fruit ripening even in postclimacteric fruits.