Analysis of Boron and B-pectin Complex Content in the Abscission Zone during Floral and Fruit Abscission in Tobacco (Nicotiana tabacum)

Abstract

After fruit development has been triggered by pollination, the abscission zone (AZ) in the pedicel strengthens its adhesion to retain the fruit. In tobacco, unpollinated flowers are shed from the AZ, while enlargement of the same tissue occurs in pollinated flowers. The abscission rate depends on effective pollination. In this study, we focused on pectin and boron (B) distribution and their functions in the AZ. B is an essential micronutrient that forms cross-links in pectin, which are important for organ differentiation and maturation. B content and the formation rate of the borate-ester cross-linked rhamnogalacturonan II dimer (dRG-II-B) were measured in tobacco. Expression of NtGUT1, which is important for the formation of dRG-II-B, and the B transporter NtNIP3;1 were analyzed in the peduncle and AZ. To determine B content and dRG-II-B formation rate, the following samples were collected: bud peduncle, bud AZ, fruit peduncle, fruit AZ, and flower AZs, which were treated to prevent pollination or were artificially pollinated. Samples treated in HNO 3 were assayed for total B content with ICP-MS. Endo-polygalacturonase (EPG)-treated alcohol-insoluble residues were assayed for formation rates of dRG-II-B with HPLC. Although there was more total B in fruit AZs than in branches, no differences in total B, watersoluble B, and B relevant to cross-linking with RG-II were found between buds and fruits. The formation rates of dRG-II-B were also the same in peduncles and AZs in both buds and fruits. These have the same characteristics of variation with or without pollination. Expression of both NtGUT1 and NtNIP3;1 was highest in AZs of flowers before opening, however, expression of NtGUT1 in flower AZs without pollination was not significantly different from after artificial pollination. These results suggest that the presence of relatively large amounts of B and pectin is important in structural enhancement of AZs after anthesis, but is not related to abscission with or without pollination.

Developing Yield and Fruit Quality of Date Palms Cv. Zaghloul by Drenching the Soil with Micronutrients Compound and Amino Acids

“…Palms drenched by 120 g micronutrients + 150 ml amino acids/palm/year gave the highest percentage of fruit set ( 89 This might be due to that micronutrients contain some elements that have the main role in increasing the percentage of a set and retained fruit such as boron and zinc (Etman et al, 2007;Hansch and Mendel, 2009). These increment in fruit set percentage due to boron may be attributed to its role in maintaining high pollen survival, germination, and pollen tube elongation (Zia et al, 2006;Harhash and Abdl-Nasser, 2010) and for fruit retention percentage, it has a role in cell wall metabolism in higher plants (Blevins and Lukaszewski, 1998), growth and development of fruit (Goldbach, 1997 andMarschner, 2012) formation of borate cross-links of pectin in presence of Ca ++ to produced more cemented cell wall (Blevins and Lukaszewski, 1998), especially in abscission zone during fruit development which results in improving fruiting rate (Tsukahara et al, 2013). Moreover, zinc increases fruit removal force due to its involvement in many enzymatic reactions that regulate protein and carbohydrate metabolism necessary for growth and development (Harhash and Abdl-Nasser, 2010;Sarrwy et al, 2012) and can be enumerated as promotion of the metabolism of auxin and pollen formation (Marschner, 2012).…”