Dissertation committee:
1.Σοφία Ριζοπούλου, Ομότιμη Καθηγήτρια Τμήμα Βιολογίας ΕΚΠΑ (Επιβλέπουσα),
2.Κυριάκος Γεωργίου, Ομότιμος Καθηγητής Τμήμα Βιολογίας ΕΚΠΑ,
3.Μαρία Σόνια Μελετίου Χρήστου, τ. Επίκουρη Καθηγήτρια Τμήμα Βιολογίας ΕΚΠΑ ,
4.Κοσμάς Χαραλαμπίδης, Αναπληρωτής Καθηγητής Τμήμα Βιολογίας ΕΚΠΑ,
5. Δημήτριος Χατζηνικολάου, Αναπληρωτής Καθηγητής Τμήμα Βιολογίας ΕΚΠΑ ,
6.Ιωάννης-Δημοσθένης Αδαμάκης, Επίκουρος Καθηγητής Τμήμα Βιολογίας ΕΚΠΑ,
7.Δημήτριος Στραβοπόδης, Αναπληρωτής Καθηγητής Τμήμα Βιολογίας ΕΚΠΑ
Summary:
In this PhD thesis the water relations and ecophysiological characteristics of four native, perennial geophytes of the Mediterranean ecosystem were investigated. The plant material collected from the field and used in the PhD thesis consisted of underground organs (bulbs, tubers, rhizomes), flowering stalks, pedicels and flower petals of the native Mediterranean species (in alphabetical order), Cyclamen graecum, Iris germanica, Pancratium maritimum and Sternbergia lutea.
The geophytes are one of the bioforms of the Mediterranean ecosystems, which show a characteristic seasonality, alternating the vegetative period with dormancy. Geophytes are either monocots or dicots; their annual growth buds are protected below the soil surface on a perennial organ (bulb, tuber, corm or rhizome) and their growing season alternates with a period of dormancy.
The geophyte Cyclamen graecum Link is native to the eastern Mediterranean, widespread in the southern part of Greece, mainly in the Peloponnese, the islands of the Saronic Gulf, the eastern Aegean islands, Crete, Rhodes, the southern coast of Turkey and Northern Cyprus.
The geophyte Pancratium maritimum L. is widespread in the Mediterranean Basin, the Canary Islands and areas of the Black Sea. It is a perennial, bulbous plant that completes its biological cycle during the summer drought.
The geophyte Iris germanica L. is a plant known by the common names blue lily, lily or wild lily and has a distribution throughout Europe and southwest Asia. It can be found throughout Greece. Nowadays, populations on the islands and southern Greece are mainly cultivated, while natural populations are found in central and northern Greece.
The geophyte Sternbergia lutea (L.) Ker Gawl. ex Schult.f., commonly known as yellow lily, grows almost all over Greece, in stony and dry sites, usually at low altitudes.
In each of the considered geophytes, the plant tissues were divided into: underground organs, tuber for Cyclamen graecum, bulb for Pancratium maritimum and Sternbergia lutea and rhizome for Iris germanica; leaves, petals, pedicel and stem for Cyclamen graecum, and leaves, floral axis and petals for Pancratium maritimum, Iris germanica and petals for Sternbergia lutea.
In the PhD thesis, emphasis has been given to the water status of their leaves and the identification of substances (i.e. osmolytes) that may contribute to the understanding of the ecophysiological behaviour of these geophytes and could be related to thei water status.
Measurements were made on the dry plant material in order to determine seasonally the water status using a psychrometer and compounds that contribute to its maintenance and/or balance, such as free proline accumulation, soluble sugar and starch content.
Concerning the geophyte Cyclamen graecum Link the highest values of total sugars were recorded in tubers in September, in leaves in December and in petals in October, while the lowest values occurred during December in tubers, and November in leaves and petals. The highest proline accumulation was measured in tubers and leaves during February, in petals in November, while the minimum values were recorded in tubers in September, in leaves in November and in petals in September. The highest starch content was measured in tubers in April and in leaves in March, while the lowest values were determined in tubers in June and in leaves in November.
Concerning Pancratium maritimum L., variations in the amounts of total sugars, proline and starch were measured throughout the year. The highest values of total sugars were determined in February in bulbs, in April in leaves and July in petals, while the lowest values in July in bulbs, in October in leaves and June in petals. The highest proline values were measured in bulbs in December, in leaves in September and in petals in July. Regarding starch, the highest levels were found in bulbs during May, in petals and flowering axis during July, while the lowest levels were found in bulbs in January, in flowering axis and petals during August, and in leaves during September.
Regarding the geophyte Iris germanica L., the highest values of total sugars were measured in the rhizomes in May, in the leaves in April, while the lowest values were measured in the rhizomes during October and in the leaves in June. The maximum proline values were measured in rhizomes and leaves during January, while the minimum values were measured in rhizomes and leaves in March. Finally, as regards starch, the maximum values were measured in rhizomes in April and in leaves during October, while the minimum values were measured in rhizomes in January and in leaves during February.
Concerning the four geophytes, the emergence of new leaves has been accompanied by high osmotic potential values, which decrease progressively in the period from January to July.
In the geophyte Sternbergia lutea (L.) Ker Gawl. ex Schult.f., there is an increase in the accumulation of specific substances such as proline, soluble sugars and starch in different months during the year. In detail, the highest values of total sugars were measured in bulbs during May and in leaves during January, while the lowest values were obtained in bulbs during in August and in leaves during March. The highest proline values were investigated in bulbs during August, in leaves during December, while the lowest values were measured in bulbs in February and in leaves during April. The highest starch values were determined in bulbs during May and in leaves in November. The lowest values were determined in bulbs during December and in leaves during January. The data show that the leaves of Sternbergia lutea maintain a relatively stable water status during the three-month period (February to April).
In a controlled experiment at the Department of Botany of the Department of Biology of the University of Athens (Greece), with Pancratium maritimum, bulbs were collected in September (i.e., when they had completed their biological cycle). The bulbs were planted in pots, they were watered with tap water for 3 months, and were grown under conditions simulating the Mediterranean summer season (16 h photoperiod, 26 °C). Then, they have been divided into 4 groups and watered with sodium chloride solutions (concentrations: 0%, 1.5%, 3%, 6%, respectively) for 68 days. Proline, soluble sugars and starch in bulbs and leaves were also measured in plant parts. Non-statistically significant differences in proline content were measured in bulbs, but significant differences were estimated in leaves, where the highest content was measured in plants receiving 6% solution, while the lowest was measured in those receiving 1.5% solution. Higher sugar content was determined in bulbs irrigated with 0% NaCl, while the lowest value was recorded in bulbs irrigated with 6% NaCl solution. Then, stomatal frequency, area and frequency of stomata in close contact in three leaf areas (i.e., base, middle, tip) were measured in laves from plants exposed to different treatment groups. The results showed a positive correlation between stomatal frequency and salinity in the base and middle leaf section, and between salinity and the frequency of close contact stomata in the middle leaf section.
The results indicate significant differences in the levels of total soluble sugars, free proline and starch between the different plant tissues. In addition, correlations were detected between the above mentioned compounds and abiotic stress parameters, such as elevated temperature and water deficit. These findings contribute to our understanding of the resistance of native Mediterranean geophytes to the abiotic environmental conditions in the Mediterranean region.
