Effect of Temperature on Breaking of Morphophysiological Dormancy and Seed Germination Leading to Bulblet Production in Two Endemic Tulip Species from Greece

Due to botanical tulips' economic interest coupled with limited information regarding their seed germination, we investigated the effect of temperature on dormancy release and germination in two endangered local endemic tulip species of Greece (Tulipa hageri Heldr., T. orphanidea Heldr.). Their germination responses at five constant temperatures (5, 10, 15, 20, and 25 °C) were evaluated in growth chambers, while the type of seed dormancy and the temperature effect on its release were determined based on open-sourced, R-derived species-specific ecological profiles illustrating abiotic conditions of their wild habitats. The results indicated a range-specific temperature dependence in seed germination for both studied species with seed germination observed only in very low temperatures (5-10 °C). The seeds of both species after dispersal had an underdeveloped embryo. The existence of a complex morphophysiological seed dormancy was confirmed in both species by the significant embryo development only at 5 and 10 °C (almost doubled after 30 days) coupled with observed delay in germination only at low temperatures. Furthermore, to facilitate their cultivation and ex situ conservation, the germinated seeds were planted in pots to develop bulblets in greenhouse conditions resulting in bigger T. orphanidea bulblets compared to T. hageri.

Influence of Temperature on Seed Germination of Five Wild-Growing Tulipa Species of Greece Associated with Their Ecological Profiles: Implications for Conservation and Cultivation

Although tulips are famous worldwide as ornamental plants, the knowledge about the seed germination of wild-growing species remains limited. The aim of the present study was to investigate the effect of temperature on seed germination of the local, wild-growing Greek endemics Tulipa bakeri and T. goulimyi and the sub-Balkan endemic T. undulatifolia, which are threatened with extinction, as well as the Mediterranean T. australis and the Asiatic T. clusiana naturalized on Chios Island (Greece). The germination responses at five constant temperatures (5, 10, 15, 20, and 25 °C) were assessed for all studied species in growth chambers under a 12:12 light-dark photoperiod. The ecological profile for each species was developed in R using open-source bioclimatic data; this was built to illustrate the abiotic environmental conditions of their wild habitats, to facilitate the examination of temperature effects on seed germination, and to facilitate their cultivation in artificial environments. The results indicated that the seed germination requirements of the studied species had a range-specific temperature dependence, reflecting their natural adaptation to local ecological conditions. Seed germination of T. bakeri, T. australis, and T. clusiana was observed only in a narrow range of very low temperatures (5-10 °C), whereas germination of T. undulatifolia and T. goulimyi occurred at temperatures between 5 and 15 °C. A temperature increase to 20 or 25 °C resulted in the absence of seed germination for all five Greek tulip species. The germinated seeds were planted in pots and bulblets were developed under greenhouse conditions. Seeds and bulblets constitute valuable genetic materials for the cultivation and ex situ conservation of these five Greek tulip species, three of which are threatened with extinction.

Ecological Preferences and Diversity of Essential Oil Composition in Endangered Wild-Growing Populations of Sideritis sipylea Boiss. (Lamiaceae) of the East Aegean Islands (Greece): Evidencing Antioxidant Potential, Antimicrobial and Cytotoxic Activities

Plants from the genus Sideritis (Lamiaceae) have been widely used in folk medicine for a long time and consequently are a focus of the scientific community. Despite this interest, explicit data about the essential oils (EOs) of the Endangered Sideritis sipylea have not been readily available to date. In this study, we investigated the ecological preferences of Greek S. sipylea and the chemical composition of the essential oils of wild-growing S. sipylea populations from two Greek islands (S1: Samos, S2: Lesvos); we explored concomitant associations with environmental factors; and we assessed their (i) antioxidant potential (two tests), (ii) antimicrobial activity against six microbial and two fungal strains, and (iii) cytotoxic effect in two human and one murine cell lines. We compiled an ecological profile in R based on all known Greek localities of S. sipylea, outlining for the first time its preferences regarding temperature (3.48 ± 1.53 °C to 30.70 ± 1.11 °C) and the precipitation regimes (5.92 ± 2.33 mm to 136 ± 11.43 mm) shaping its natural occurrence in the wild. The chemical analysis (42 compounds in total) confirmed the domination of monoterpene hydrocarbons in both samples (with quantitative and qualitative differences) and identified 12 new constituents reported in S. sipylea for the first time (e.g., Bicyclogermacrene and Cumacrene). Dominant compounds in S1 (39 constituents) were β-Myrcene (20.4%) followed by β-caryophyllene (11.8%), bicyclogermacrene (7.1%), β-pinene (6.3%), carvacrol (6.2%) and α-terpinene (6.1%), whereas in S2 (26 constituents) the main ones were α-pinene (37.3%), β-pinene (15.1%) and sabinene (12.1%), followed by β-caryophyllene (5.6%) and bicyclogermacrene (5.5%). The strong antioxidant capacity and cytotoxic activity of S. sipylea EOs are reported herein for the first time, while new insight is provided regarding their effect on bacterial and fungal strains (four ones originally tested herein). The biological activity analysis demonstrated variation among samples, with S2 being more potent than S1. Altogether, the results of the present study demonstrate the high biological potential of S. sipylea EOs with an interesting antioxidant capacity and antimicrobial and cytotoxic effects and reveal associations of natural chemodiversity with climatic factors.

Exploring the Ecological Preferences and Essential Oil Variability in Wild-Growing Populations of the Endangered Local Greek Endemic Thymus holosericeus (Lamiaceae)

Thymus holosericeus Čelak. (Lamiaceae) is a taxonomically isolated and endangered local endemic thyme species which is geographically isolated in four Ionian Islands (West Greece). The present study investigated the essential oil (EO) composition, the ecological preferences, and their correlations in three T. holosericeus wild-growing populations from Zakynthos (ΤH-Z), Cephalonia (ΤH-C) and Lefkada (ΤH-L). The variations in essential oil yield and the composition of T. holosericeus populations were evaluated using hydrodistillation, GC/MS, TLC and NMR analysis. The climatic conditions of each sample were organized and analyzed in RStudio with the raster package and in SPSS with Pearson's Canonical Correlation Analysis (CCA), respectively. The aerial parts of the plants varied in EO yields from 1.92 to 2.28% w/v. The analysis of EO constituents revealed noteworthy qualitative and quantitative inter-population variation. The composition of EOs revealed the presence of linalool (82.77%) and borneol (5.95%) as major compounds in ΤH-Z, while carvacrol (35.34%), geraniol (23.98%), linalool (14.37%), borneol (5.66%), thymol (4.27%) and p-cymene (4.08%) were the main compounds in ΤH-C and linalool (40.37%), geraniol (39.42%) and borneol (5.20%) were dominant components in ΤH-L. The results of the gas chromatography procedure have also been confirmed by ¹H and ¹³C-NMR and TLC analysis. The ecological profile showed an average annual precipitation of 942 ± 18.33 mm and the temperature limits in which T. holosericeus seems to adapt to are 6.80± 1.08 °C 27.70 ± 0.70 °C. Regarding the examined samples, TH-C was adapted to the driest summer and coldest winter conditions, TH-Z was adapted to the lowest annual precipitation with the most complex climatic conditions, and TH-L was adapted to the highest summer temperatures with the lowest precipitation in the wettest period of the year. For each sampled population, the CCA identified the association of the samples' EOs composition with the prevailing local environmental conditions.