Dissertation committee:
Χρήστος Κατσαρός, Ομότιμος Καθηγητής ΕΚΠΑ (επιβλέπων)
Παναγιώτης Αποστολάκος, Ομότιμος Καθηγητής ΕΚΠΑ (μέλος τριμελούς επιτροπής)
Σωτήρης Ορφανίδης, Διευθυντής ερευνών ΙΝΑΛΕ (μέλος τριμελούς επιτροπής
Νικόλαος Χριστοδουλάκης, Καθηγητής ΕΚΠΑ (μέλος εξεταστικής επιτροπής)
Αθανάσιος Εξαδάκτυλος, Καθηγητής Πανεπιστήμιο Θεσσαλίας (μέλος εξεταστικής
επιτροπής)
Παρασκευή Μαλέα, Καθηγήτρια ΑΠΘ (μέλος εξεταστικής επιτροπής)
Ιωάννης Αδαμάκης, Επίκουρος Καθηγητής ΕΚΠΑ (μέλος εξεταστικής επιτροπής)
Summary:
Seagrasses are aquatic plant organisms that grow in coastal and transitional waters. Among the angiosperms that occur in the Mediterranean, the species occupy a dominant position are Cymodocea nodosa, Ruppia cirrhosa and Posidonia oceanica. They form meadows of vital importance, for coastal and marine ecosystems. Unfortunately, over the past eighty years, these ecologically and economically important habitats have declined in several areas due to extreme fluctuations in key water parameters such as transmitted radiation, salinity levels, high temperatures and acidification conditions (Waycott et al., 2009). In this PhD thesis, the effect of different abiotic conditions was studied (acidification, temperature, salinity) in three dominant species of (Cymodocea nodosa, Posidonia oceanica and Ruppia cirrhosa), with main purpose to determine the scope, limits and the way and the effects of climate change at the cell structure.
Shoots of the seagrasses were transferred from the control area to the two venting areas at different times. Epidermal cells of young leaves were examined using transmission electron microscopy (TEM) and tubulin immunofluorescence. After one
week at pH 7.8, the cell structure of Posidonia oceanica was normal, while in Cymodocea nodosa, microtubule (MT) network and cell structure were affected. In addition, in C. nodosa, ultrastructural analysis revealed a gradual degradation of the nuclei, a disorganization of the chloroplasts, and an increase in the number of mitochondria and dictyosomes. The exposure of both plants for 3 weeks at pH 6.8 resulted in the aggregation and finally in the dilation of the endoplasmic reticulum (ER) membranes. Tubulin immunofluorescence revealed that after three weeks, the MT cytoskeleton of both plants was severely affected. All these alterations can be considered as indications of an apoptotic-like programmed cell death (AL-PCD), which may be executed in order to regulate stress response.
High temperature affects the microtubule (MT) organization and the cell structure of young epidermal leaf cells of the seagrass The interphase MT network was affected by the increased temperature, the effect being time dependent and expressed
in both the form and the orientation of the MT bundles. There was also a severe disturbance in dividing cells with thick and short MTs in the mitotic spindle and atypically organized phragmoplasts. TEM observation revealed cells with uncompleted cell plates consisting of swollen vesicles and branched cisternae, with no phragmoplast MTs. These cells bear a nucleolus with segregated fibrillar and granular zones, an increased number of swollen mitochondria, and numerous parallel arrays of endoplasmic reticulum cisternae in the cortical cytoplasm. The possible relationship of these changes with a response mechanism in order to face elevated temperature effects of climate change is analyzed.
High salinity and high temperature, alone and in combination, affected ion equilibrium in the plant cells. Cell structure, especially the nucleus, chloroplasts, mitochondria and organization of the MT cytoskeleton, was also altered. Both temperature and salinity stress negatively affected photosynthetic activity as evidenced by ΔF/Fm’, following an antagonistic interaction type. All biological levels were strongly affected by temperature and salinity stress, however, with the latter having more severe effects.
Keywords:
C.nodosa, P. oceanica, seagrasses, abiotic stress, acidification, temperature, salinity, programmed cell death
