Tissue-Specific Ultrastructural Remodeling of Chloroplasts and Root Cell Endoplasmic Reticulum in Halophyte Suaeda altissima in Response to Bacterial Elicitor FLG22

Abstract The paper analyzes dynamic changes in the ultrastructure of chloroplasts in various leaf tissues, as well as the endoplasmic reticulum membrane system of root cortex cells in the halophyte Suaeda altissima in response to the bacterial elicitor flg22. In the leaf tissues, a gradient of chloroplast sensitivity was revealed: the most vulnerable were the plastids of the water-storage parenchyma, where progressive destruction of thylakoids was observed. Chloroplasts of Kranz cells and vascular bundle parenchyma cells exhibited high resistance at the early stages of biotic stress. The detection of thylakoid “supergrana” in the chloroplasts of these cells formed under the action of flg22 indicates the presence of adaptive mechanisms aimed at protecting the photosynthetic apparatus in cells that are critically important for C4 metabolism. In the root cortex cells treated with flg22 activation of vesicular transport was observed, including the formation of paramural bodies and the release of exosomes into the periplasmic space three hours after treatment. This observation confirms the hypothesis that exocytosis, mediated by the formation of multivesicular bodies, is a universal mechanism for the delivery of protective molecules to the apoplast in response to the PAMP (pathogen-associated molecular pattern) signal. Activation of the endocytic pathway (formation of early endosomes) and reorganization of the trans-Golgi network were also observed in the root cortex cells, indicating a complex rearrangement of membrane traffic necessary both for signal transmission leading to receptor recycling and for immune effector functions. The data obtained demonstrate that the perception of the PAMP signal triggers differentiated cellular responses, the depth and nature of which are determined by the functional specialization of plant tissues.