Characterization and regulation of multiple forms of endo-1,4-β-glucanase genes during longan fruit growth and development

Endo-1,4-β-glucanase (EGase, EC 3.2.1.4) is proposed to be involved in the control of cell wall modification. However, the relationship between EGase and longan fruit growth remains obscure. In the present work, the expression profiles of three Dl-EGase genes in pericarp and aril tissues of longan fruit during growth and development were characterized; moreover, the effects of plant growth substances, naphthalene acetic acid (NAA) and thidiazuron (TDZ) on their expressions of fruits at two different developmental stages were also investigated. The results showed that high levels of EGase activities in aril were in accordance with rapid aril growth, and three Dl-EGase genes exhibited different expression patterns in pericarp and aril during fruit growth and development. Dl-EGase1 and Dl-EGase3 seemed to be associated with the growth of both pericarp and aril, while Dl-EGase2 was closely related to pericarp growth. In addition, treatment of NAA and TDZ at the stage of pericarp growth increased the EGase activities and induced the expressions of all the three Dl-EGases. However, when NAA or TDZ was applied at the rapid aril growth stage, the accumulations of Dl-EGase1 and Dl-EGase2 in the pericarp, and the accumulations of Dl-EGase1 and Dl-EGase3 in the aril were induced. Furthermore, the expression patterns of the three Dl-EGases showed different tissue specificity. It is thus speculated that Dl-EGase genes played a different role in longan fruit growth and were developmentally regulated, and more importantly, the responses of Dl-EGases to plant growth substances were different and dependent on fruit development stage and fruit tissue.     

Mode of action of nitric oxide in inhibiting ethylene biosynthesis and fruit softening during ripening and cool storage of ‘Kensington Pride’ mango

The mode of action of nitric oxide (NO) in inhibiting ethylene biosynthesis and fruit softening during ripening and cool storage of mango fruit was investigated. Hard mature green mango (Mangifera indica L. cv. ‘Kensington Pride’) fruit were fumigated with 20 μL L⁻¹ NO for 2 h at 21 °C and allowed to ripen at 21 ± 1 °C for 10 d, or stored at 13 ± 1 °C for 21 d. During ripening and cool storage, ethylene production and respiration rate from whole fruit were determined daily. The 1-aminocyclopropane-1-carboxylic acid (ACC) content, activities of ACC synthase (ACS), ACC oxidase (ACO), and fruit softening enzymes such as pectin esterase (PE), endo-1,4-β-d-glucanase (EGase), exo- and endo-polygalacturonase (exo-PG, endo-PG) as well as firmness and rheological properties of pulp were determined at two- and seven-day intervals during ripening and cool storage, respectively. NO fumigation inhibited ethylene biosynthesis and respiration rate, and maintained higher pulp firmness, springiness, cohesiveness, chewiness, adhesiveness, and stiffness. NO-fumigated fruit during cool storage and ripening had lower ACC contents through inhibiting the activities of both ACS and ACO in the fruit pulp. NO-fumigated fruit showed decreased activities of exo-PG, endo-PG, EGase, but maintained higher PE activity in pulp tissues during ripening and cool storage. In conclusion, NO fumigation inhibited ethylene biosynthesis through inhibition of ACS and ACO activities leading to reduced ACC content in the fruit pulp which consequently, reduced the activities of fruit softening enzymes during ripening and cool storage.