The Effects of Propagation Techniques on Leaf Vascular Anatomy, Modulus of Elasticity, and Photosynthetic Traits in Micropropagated and Grafted Plants of the Dutch Elm Hybrid ‘Dodoens’

Abstract

Understanding how plants are able to change their structural, physiological, and mechanical properties in response to various propagation methods can help to improve both their performance and their survival when transferred to field conditions. To identify changes between the routinely applied vegetative propagation techniques of in vitro micropropagation and splice grafting we assessed leaf performance for any differences in midrib vascular traits, nanomechanical properties of tracheary element cell walls, and photosynthetic traits in the dutch elm hybrid cultivar Dodoens (i.e., open-pollinated Ulmus glabra ‘Exoniensis’ × Ulmus wallichiana P39). The propagation techniques appear to have had a direct effect on a large portion of the vascular traits. In the micropropagated plants, the water-conducting area within the primary xylem tissue contained a significantly greater number of tracheary elements which suggests hydraulic safety. In the grafts, the water-conducting area contained a significantly smaller number of tracheary elements, in which the lumen areas were slightly larger than those of the micropropagated plants, resulting in a significantly higher size to number ratio which may indicate a fast and more effective water transport system. Quantitative nanomechanical mapping measurements from atomic force microscopy (AFM) revealed that the tracheary elements of the micropropagated plants formed stiffer cell walls quantified by the reduced Young’s modulus of elasticity (MOE) than those of the grafts. The effect of the rootstock might contribute to the differences in vascular traits, as well as to the differences in cell wall stiffness and cell wall deformation observed between the stock types. The micropropagated plants were subjected to a more sensitive stomatal regulation of gas exchange resulting in the lower rates of net photosynthesis and transpiration. But the higher values of both instantaneous water-use efficiency (WUEinst) and chlorophyll a fluorescence yields found in the micropropagated plants indicate a higher acclimation capacity to stressful environmental conditions specifically for this stock type. Both stock types formed compact homogeneous clusters clearly separated from each other in the multivariate leaf trait analysis.