Genesis of ultra-specialized histology with stable traits in mesophyll of drought tolerant apple cultivars

Abstract

Even if some biological defense responses are activated instantaneously after stress occurrence, but other mechanisms of drought tolerance could be probed, detected and diagnosed as sable traits at mesophyll level. The present observations demonstrated multilateral modifications in different leaf parts, specialized parenchyma tissues and cribro-vascular bundles that facilitate vital activities in tolerant apple cultivars. In 2006, long deficit irrigation occurred in commercial apple collection containing 93 cultivars located in Karaj-Iran. Entire bearing 16-Year-old trees lost completely the crop except 16 CVs which were assessed for yield per tree since June drop to physiological maturity. Based on thehypothesis, stable traits were developed against drought stress through phenomenon of genesis. 19 different anatomical traits of mesophyll were accurately assessed in the selected resistant CVs compared with the susceptible "Golden Delicious" and native "Assali" as the controls. Microscopic studies computed on the transversal sections of mesophyll prepared by microtome ascertained ultra-specialized histological traits in the selected CVs. Morphologically, basal part of the main vein was completely spherical, outfitted, highly ordered and tidy tissues. Epidermis underlying layer was composed of well-organized tissues containing uniform cells by shape and size, inserted consistently next to one another in neat order with no intercellular space. Contrarily, controls showed opposite rhythm in all examined characters. Also, the mean number of epidermis layers at leaf margin resulted higher related to susceptible CVs. The mean number of vascular bundles and stomata decreased in tolerant CVs. These observations put in evidence some stable ultra-specialized histological traits of mesophyll, as a result of genesis route.