Expression Fluctuations of Genes Involved in Carbohydrate Metabolism Affected by Alterations of Ethylene Biosynthesis Associated with Ripening in Banana Fruit

The banana is a typical climacteric fruit that undergoes ethylene dependent ripening. During fruit ripening, ethylene production triggers a developmental cascade that results in a series of physiological and biochemical changes. The fruit transcriptomes of untransformated wild-type (WT) and RNAi transgenic banana plants for Mh-ACO1 and Mh-ACO2 have been previously sequenced and analyzed, and most of the differentially expressed genes were enriched in ‘carbon fixation in photosynthetic organism’, ‘cysteine and methionine metabolism’, ‘citrate cycle (tricarboxylic acid cycle, TCA cycle)’, and ‘starch and sucrose metabolism’ based on Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation. In this research, we investigated the expression fluctuations of genes involved in carbohydrate metabolism affected by alterations of ethylene biosynthesis associated with ripening in banana fruits. Expression profiles of sucrose synthase, sucrose phosphate synthase, neutral invertase, and acidic invertase/β-fructofuranosidase, as analyzed by Avadis and Trinity, showed that both analyses were complementary and consistent. The overall gene expression tendency was confirmed by the implementation of quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR) with mRNAs of banana fruits in Mh-ACO1 and Mh-ACO2 RNAi transgenic plants. These results indicated that altered expression of genes associated with ethylene biosynthesis strongly influenced the expression levels of genes related to starch and sucrose metabolism, as well as the glycolysis pathway in ripening banana fruits.

Ethylene enhances water transport in hypoxic aspen

Water transport was examined in solution culture grown seedlings of aspen (Populus tremuloides) after short-term exposures of roots to exogenous ethylene. Ethylene significantly increased stomatal conductance, root hydraulic conductivity (L(p)), and root oxygen uptake in hypoxic seedlings. Aerated roots that were exposed to ethylene also showed enhanced L(p). An ethylene action inhibitor, silver thiosulphate, significantly reversed the enhancement of L(p) by ethylene. A short-term exposure of excised roots to ethylene significantly enhanced the root water flow (Q(v)), measured by pressurizing the roots at 0.3 MPa. The Q(v) values in ethylene-treated roots declined significantly when 50 microM HgCl(2) was added to the root medium and this decline was reversed by the addition of 20 mM 2-mercaptoethanol. The results suggest that the response of Q(v) to ethylene involves mercury-sensitive water channels and that root-absorbed ethylene enhanced water permeation through roots, resulting in an increase in root water transport and stomatal opening in hypoxic seedlings.

Bananas--physiology and biochemistry of storage and ripening for optimum quality

Bananas (Musa spp.) are a major food crop of the humid tropics, and although edible cultivars are diverse and numerous, most of our knowledge of the physiology and biochemistry of these fruits relates to a few dessert cultivars of the AAA type, mainly of the Cavendish subgroup, which dominate the export trade between tropical and temperate zones. The preclimacteric period of banana fruits after harvest determines their transportability, and its duration is very sensitive to changes in fruit maturity, storage temperature, ethylene concentration, and other factors; progress in measurement and resolution of each of these effects is described. Changes in composition of the ripening fruits, especially in the development of flavor volatiles, are reviewed. Progress in understanding the integration of the biochemical changes controlling ripening in banana fruits is discussed. Recent work on storage, ripening, and factors relating to sensory assessment of fruit quality is discussed for cultivars of Musa types not used in major export trades.