Abstract
Aleppo pine (Pinus halepensis Mill.), a native species of the Mediterranean region, has been suggested as a species that when introduced in degraded areas could facilitate the long-term colonization and expansion of late-successional species. Due to climate changes, plants need to withstand extreme environmental conditions through adaptation and changings in developmental pathways. Among other paths, plants undergo changes in developmental pathways controlled by phytohormones. At the same time, somatic embryogenesis has been widely used as a model to understand the mechanisms involved in plant response to different stresses. In this study, in order to induce a strong effect of temperature stress on plants regenerated from somatic embryos, higher temperatures (40 °C for 4 h, 50 °C for 30 min, and 60 °C for 5 min) than the control (23 °C) were applied during the induction stage of somatic embryogenesis in Pinus halepensis. A morphological characterization of the embryogenic cultures showed small differences in the number of starch grains, lipid bodies, and phenolic compounds between treatments. Results showed that high temperatures (60 °C) led to higher rates at the maturation stage of somatic embryogenesis when compared to the control (23 °C), strengthening the productivity through the increase in the number of somatic embryos obtained. Finally, analysis of endogenous concentration of cytokinins showed that different conditions applied during the initiation phase of somatic embryogenesis led to different hormonal profiles; isoprenoid cytokinins showed a clear defined pattern with the higher total hormone concentration being found in embryonal masses induced at 50 °C for 30 min, while different aromatic cytokinins presented different individual responses to the treatments applied. These differences corroborate the idea that cytokinins could be potential regulators of stress–response processes during initial steps of somatic embryogenesis.
Highlights
Aleppo pine (Pinus halepensis Mill.) is native of the Mediterranean basin and the most important and broadly distributed pine tree in the area, covering ca. 3.5 million hectares of forest area both as natural stands and in reforestation programs [1,2]
Despite the fact that there were no significant differences between treatments at initiation and proliferation rates (Tables 1 and 2), a decreasing pattern could be seen as the temperature rose along the high induction temperatures applied during initiation
As far as we know, this is the first study developed in Aleppo pine that focus in the initiation of embryonal masses under high temperatures analyzing both the phytohormones involved in the success of the Somatic embryogenesis (SE) process as well as the cytological characterization of embryogenic cultures
Summary
Aleppo pine (Pinus halepensis Mill.) is native of the Mediterranean basin and the most important and broadly distributed pine tree in the area, covering ca. 3.5 million hectares of forest area both as natural stands and in reforestation programs [1,2]. 3.5 million hectares of forest area both as natural stands and in reforestation programs [1,2]. It prevails in the driest and warmest sites, especially in the western Mediterranean, due to its tolerance to high temperatures and drought stress [3,4,5]. Despite the fact that recent increase in the minimum temperature seems to improve the growth of P. halepensis [10,11] its capacity to withstand drought displays strong variations across the species distribution area [12] and the impacts, frequency and magnitude of extreme events are uncertain. The capacity of forest ecosystems to cope with this problem will rely on the relationship between how fast these changes occur and how fast forest trees can adapt to them [4]
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