22
3. Increasing antioxidant scavenging power
4. Activating repair mechanisms after the post-desiccation rehydration process
These mechanisms act through various actions, including morphological and cell
wall changes, hormone accumulation, ROS scavenging, photosynthetic activity
diminishment, and osmolyte and protein synthesis. One recurrent finding of tolerance studies is that sensitive species have a point of no return when subjected to
desiccation stress, after which these species are unable to recover even after rehydration. However, some algal species behave like resurrection plants and are fully able
to recover after rehydration (i.e., fully desiccation tolerant). In fact, algal species
inhabiting the upper rocky intertidal zones display a greater tolerance to desiccation
stress than those in the mid- and lower intertidal zones, particularly in terms of development arrest and physiological and molecular alterations. The following sections
review desiccation stress in algae according to tolerance mechanisms, with emphasis
on how they help explain the vertical distribution of algae within the intertidal zone.
2.2.1 Decrease of Photosynthetic Activity
To our knowledge, Schonbeck and Norton (1978) were the first to address desiccation stress as a key factor controlling the vertical distribution of brown algae within
the rocky intertidal zone. This investigation demonstrated that algae subjected to
desiccation display diminished photosynthetic activity that is recovered after rehydration. Moreover, the recovery process was found to be faster in species inhabiting
the upper, rather than lower, intertidal zones, an effect since confirmed by other
researchers (Dring and Brown 1982; Leuschner et al. 1998; Contreras-Porcia et al.
2011; Flores-Molina et al. 2014; Guajardo et al. 2016; Fierro et al. 2016, 2017).
Dring and Brown (1982) studied intertidal brown algae photosynthesis during desiccation and recovery periods, and although all of the assessed species evidenced
decreased photosynthesis due to tissue water loss, the extent of recovery was greater
in upper shore species. In relation to water loss, Leuschner et al. (1998) determined
that for Zostera noltii (Alismatales) inhabiting the German Wadden Sea, carbon
dioxide assimilation is dependent on the water content in leaves, with higher water
content translating into higher CO 2 assimilation. Importantly, leaf water content is a
factor directly impacted by the duration of air exposure.
Algal photosynthetic activity declines during air exposure to reduce damages
associated with the photosynthetic by-products of desiccation stress and excessive
UV light exposure (Gómez et al. 2004; Chaves et al. 2009; Contreras-Porcia et al.
2011; Dinakar et al. 2011). Several studies have assessed the underlying mechanisms of decreased algal photosynthetic activity. For example, Wiltens et al. (1978)
analyzed the chlorophyll fluorescence of the desiccation-tolerant red algae
Porphyra sanjuanensis and established that rehydration resulted in rapid recovery
from severe desiccation. In particular, the fluorescence changes observed during
the desiccation/rehydration cycle suggested that (1) electron transport between
photosystems I and II and water splitting are partial desiccation-sensitive reactions; (2) intersystem electron transport becomes blocked at ~25% water content;
L. Contreras-Porcia et al.
3. Increasing antioxidant scavenging power
4. Activating repair mechanisms after the post-desiccation rehydration process
These mechanisms act through various actions, including morphological and cell
wall changes, hormone accumulation, ROS scavenging, photosynthetic activity
diminishment, and osmolyte and protein synthesis. One recurrent finding of tolerance studies is that sensitive species have a point of no return when subjected to
desiccation stress, after which these species are unable to recover even after rehydration. However, some algal species behave like resurrection plants and are fully able
to recover after rehydration (i.e., fully desiccation tolerant). In fact, algal species
inhabiting the upper rocky intertidal zones display a greater tolerance to desiccation
stress than those in the mid- and lower intertidal zones, particularly in terms of development arrest and physiological and molecular alterations. The following sections
review desiccation stress in algae according to tolerance mechanisms, with emphasis
on how they help explain the vertical distribution of algae within the intertidal zone.
2.2.1 Decrease of Photosynthetic Activity
To our knowledge, Schonbeck and Norton (1978) were the first to address desiccation stress as a key factor controlling the vertical distribution of brown algae within
the rocky intertidal zone. This investigation demonstrated that algae subjected to
desiccation display diminished photosynthetic activity that is recovered after rehydration. Moreover, the recovery process was found to be faster in species inhabiting
the upper, rather than lower, intertidal zones, an effect since confirmed by other
researchers (Dring and Brown 1982; Leuschner et al. 1998; Contreras-Porcia et al.
2011; Flores-Molina et al. 2014; Guajardo et al. 2016; Fierro et al. 2016, 2017).
Dring and Brown (1982) studied intertidal brown algae photosynthesis during desiccation and recovery periods, and although all of the assessed species evidenced
decreased photosynthesis due to tissue water loss, the extent of recovery was greater
in upper shore species. In relation to water loss, Leuschner et al. (1998) determined
that for Zostera noltii (Alismatales) inhabiting the German Wadden Sea, carbon
dioxide assimilation is dependent on the water content in leaves, with higher water
content translating into higher CO 2 assimilation. Importantly, leaf water content is a
factor directly impacted by the duration of air exposure.
Algal photosynthetic activity declines during air exposure to reduce damages
associated with the photosynthetic by-products of desiccation stress and excessive
UV light exposure (Gómez et al. 2004; Chaves et al. 2009; Contreras-Porcia et al.
2011; Dinakar et al. 2011). Several studies have assessed the underlying mechanisms of decreased algal photosynthetic activity. For example, Wiltens et al. (1978)
analyzed the chlorophyll fluorescence of the desiccation-tolerant red algae
Porphyra sanjuanensis and established that rehydration resulted in rapid recovery
from severe desiccation. In particular, the fluorescence changes observed during
the desiccation/rehydration cycle suggested that (1) electron transport between
photosystems I and II and water splitting are partial desiccation-sensitive reactions; (2) intersystem electron transport becomes blocked at ~25% water content;
L. Contreras-Porcia et al.