Histological evaluation of pineapple transgenic plants following 8 years of field growth

Pineapple is among the most important fruits worldwide. However, the narrow genetic base of current commercial cultivars renders the industry at risk from environmental and other biological threats. Hence, there is a need to develop improved cultivars with tolerance to biotic and abiotic stresses. Our prior research resulted in the establishment of a method for genetic transformation of pineapple. The genetically modified pineapple plants generated were characterized following acclimatization and during the subsequent 8 years under field conditions. The current work highlights the results obtained for histological characterization of roots and leaves of transgenic pineapple plants. The four treatments investigated were macropropagated control plants (untransformed), micropropagated control plants (untransformed), and micropropagated genetically transformed plants (clones 90 and 98). Twenty indicators were measured in plants: two of them did not show statistically significant differences among the four groups of plants (2/20 = 10.0%); six showed “Low” overall coefficients of variation (OCV) (6/20 = 30.0%); 12 showed “Medium” OCVs (12/20 = 60.0%); and only two indicators showed “High” OCVs (2/20 = 10.0%). Consideration of medium OCVs showed that the biomass of transgenic plants was slightly greater than those of the non-transgenic controls. Statistically significant differences between the lines were recorded except in the central cylinder diameter of roots and the D leaf adaxial cuticle thickness. “High” OCVs were observed for root exo- and endodermis thickness where transgenic clones showed statistically significantly higher values. In terms of the roots, five out of nine histological indicators showed “Medium” OCVs: cortex, rhyzodermis, and parenchyma thicknesses, pith diameter, and thickness of the transversal root ratio. Again, genetically transformed materials showed statistically significantly higher averages. Only three out of seven histological indicators showed “Medium” OCVs in the leaves: D leaf abaxial cuticle thickness, chlorophyll parenchyma thickness, and D leaf aquifer parenchyma thickness. As noted above, statistically significantly higher values were recorded in the transgenic pineapple plants. Since the differences observed did not ultimately affect fruit yield (as shown in our previous work), they do not appear to be consequences of genetic transformation that impact on reproductive yield.