Superando a crise de fertilidade em bananeiras Cavendish: morfoanatomia, histoquímica e bioquímica do nectário

Abstract

Banana parthenocarpy is one of the main barriers to genetic improvement of the crop. This phenomenon confers a high degree of sterility, which can be observed among the main commercial cultivars, especially those belonging to the Cavendish subgroup, which leads to low or total absence of seeds after hybridization. This work aimed to broaden the knowledge about the morphoanatomical and histochemical structures that compose the pistillate flower nectary, as well as to investigate the presence of phenolic compounds and enzymatic activities, involved in the female fertility of banana plants of the Cavendish subgroup. For the study, the diploid Calcutta 4 and the subgroup Cavendish Grande Naine cultivar were used. Five stages of floral development were considered: S1 (partial-vertical emission); S2 (total-vertical emission); S3 (total-horizontal emission); S4 (pre-anthesis); and S5 (anthesis). It was found that at stages S1 and S2 the Grande Naine nectaries showed significant differences for length and diameter, when compared to the diploid Calcutta 4. The morphoanatomical analysis showed a predominance of narrow nectariferous ducts and pluristratified papillae in Calcutta 4. In Grande Naine, disintegration of cells in the nectariferous ducts, absence of transmitting tissue and greater amounts of vascular bundles in stage S5 were observed. Histochemical tests revealed the association of phenolic compounds and lipids in the vacuoles adjacent to the vascular bundles, with greater presence in Grande Naine. The histochemical test for total proteins revealed to be expressive in pluristratified papillae of both genotypes. Pistillate flowers (female) were lyophilized for 72 hours for subsequent removal of the nectary and determination of phenolic compounds (PC), antioxidant activity (DPPH•• and ABTS•+), enzymatic (peroxidase - POD and polyphenoloxidase - PPO) and total proteins (TP). Fresh flowers were used to remove the nectary, followed by morphological characterization (length and diameter); morphoanatomica; and histochemical tests for phenolic compounds, proteins and lipids. The results obtained showed that stage S3 had higher significant values, with a decrease occurring as it reaches stage S5. Comparing Calcutta 4 and Grande Naine, respectively, the following results were obtained in S3: PC (32.43 and 36.18 mg GAE.g-1); DPPH•• (735.2 and 454.4 μM Trolox/g); ABTS•+ (647.8 and 555.5 μM Trolox/g); POD (0.89 and 0.78 μMoles.min-1.g-1); PPO (3.75 and 2.76 μMoles.min-1.g-1); TP (3.20 and 2.42 μMoles.min-1.g-1). This study showed that phenolic compounds and enzymatic activities can be indicators of female fertility. This is the first work that presents a more detailed approach to possible events at an anatomical, histochemical and biochemical level, the result of which allows exploring the S3 stage for further advances in seed formation and fertility in Cavendish banana trees.