Plant growth and productivity are affected by multiple abiotic stresses. Abiotic stresses such as drought and extreme temperatures are serious threats to agriculture and result in deterioration of the environment. Understanding how plant adapt to freezing temperatures and survive the formation of ice within their tissues has received a wide attention. However, several critical questions still need to be addresses in order actually to improve cold hardiness in economically important crops under field conditions. Moreover, the use of model systems based on cell and tissue cultures of Arabidopsis while providing a wealth of information, has perhaps led to an over extrapolation of the data, thus ignoring the context of the whole plant and its interaction with the environment. It has been suggested that plants have common mechanisms in their physiological responses and tolerance to drought and low temperature. Both stresses lead to loss of cellular water, hence specific as well as common metabolic responses are expected. Haberlea rhodopensis Friv. belongs to the group of desiccation tolerant or resurrection plants having the unique ability to survive desiccation to an air-dry state. This is an endemic species descending from tropic-subtropic family of Gesneriaceae survived as a tertiary relict on the Balkan Peninsula. In contrast to the most of the resurrection plants, H. rhodopensis additionally evolved cold tolerance as in its native habitats it is exposed to the harsh winter conditions and freezing temperatures. Thus, it is an excellent model system to study the cold acclimation strategies allowing high freezing tolerance in its natural habitat.
Our project will investigate the biochemical and physiological response of Haberlea rhodpensis to freezing temperatures. The study of Haberlea rhodopensis responses can contribute to reveal hidden mechanisms allowing this resurrection species to survive multiple stressful conditions. Very little information is available on the physiological and biochemical response of resurrection species to freezing temperatures, which could be concomitant to desiccation. Understanding these protective mechanisms in angiosperm resurrection plants offers the opportunity to dissect and identify those traits that might be important for the ultimate development of drought tolerant crops under multiple environmental stresses.
The most relevant physiological processes that reflect the interaction of the plant with the environment will be investigated. Chlorophyll fluorescence and gas exchange techniques provide important information on the functionality of photosynthetic apparatus that combines with other physiological and biochemical studies. Key regulatory photosynthetic enzymes will provide an integrated understanding of the functionality of the photosynthetic apparatus. The integration of classical analysis of chlorophyll fluorescence with a detailed analysis of energy partitioning will reveal the function and extent of the different components of energy management in photosystem II (PSII). Unlike the majority of previous studies on DT plants, we will specifically investigate the potential importance of other forms of thermal dissipation supplementing the primary xanthophyll cycle- and DpH-dependent non-photochemical (NPQ). In order to better interpret the dynamics of energy utilization in the various quenching pathways and to understand the direct relationship between desiccation and the operation of the xanthophyll cycle when plants experienced growth at low temperature, we will perform the biochemical analysis of leaf carotenoid levels, including xanthophylls and carotenes, as well as of the activities of enzymes involved in the xanthophyll cycle.
Haberlea rhodopensis is a homoiochlorophyllous resurrection plant (i.e. keeping most of its chlorophyll content upon desiccation), a features that allows to resume photosynthesis upon rehydration, while also making it susceptible to reactive oxygen species formation. The antioxidant status of plants after different stress treatments will be assessed by measuring the activity of catalase, superoxide dismutase, ascorbate peroxidase glutathione reductase, glutathione-S-transferase and of their individual isoforms. The content of ascorbate and glutathione will also be measured.
The biochemical profile of some potential relevant and common compatible solutes associated with low temperature and drought will be monitored: soluble sugars. Sugars act not only as a source of energy, but also as a cryoprotectant, and as signaling molecules leading to the induction of specific genes, proteins and metabolites, all of which contribute to increased freezing tolerance. Enzyme activity related to the production of those metabolites will be assessed.
We will assess the content of other specific stress responsive proteins, mainly of chaperone and dehydrin type, that increases in response to low temperature exposure. These proteins are assumed to play a role as cryoprotective component and to prevent the denaturation of various cellular components – macromolecules and membranes, both under drought and cold conditions.
Leaf abscisic acid (ABA) and indole-3 acetic acid (IAA) will be analyzed to better understand if changes in endogenous levels of these phytohormones are associated with the tolerance of Haberlea rhodopensis to cold t stress. Considering that there is strong evidence for the important roles of polyamines in plant defense against cold stress, we will investigate endogenous changes in putrescine, spermidine and spermine, the most abundant polyamines in plants, in order to understand if this hormonal pathway is part of a metabolic reconfiguration of this species. Hormonal cross-talk via signaling pathways will be also investigated.
Deadline 2018/2020
Programme ACCORDI BILATERALI CNR-BAS 2016-2018
Institute IBE – Institute of Bioeconomy
Contact Francesca Rapparini francesca.rapparini@ibe.cnr.it
Link https://www.cnr.it/en/bilateral-agreements/project/2116/biochemical-and-physiological-mechanisms-of-cold-hardiness-in-resurrection-plant-species-haberlea-rhodopensis-friv
Role COORDINATOR