Contrasting patterns of hormonal and photoprotective isoprenoids in response to stress in Cistus albidus during a Mediterranean winter

Biological outliers: essential elements to understand the causes and consequences of reductions in maximum photochemical efficiency of PSII in plants

MAIN CONCLUSION

By studying Cistus albidus shrubs in their natural habitat, we show that biological outliers can help us to understand the causes and consequences of maximum photochemical efficiency decreases in plants, thus reinforcing the importance of integrating these often-neglected data into scientific practice. Outliers are individuals with exceptional traits that are often excluded of data analysis. However, this may result in very important mistakes not accurately capturing the true trajectory of the population, thereby limiting our understanding of a given biological process. Here, we studied the role of biological outliers in understanding the causes and consequences of maximum photochemical efficiency decreases in plants, using the semi-deciduous shrub C. albidus growing in a Mediterranean-type ecosystem. We assessed interindividual variability in winter, spring and summer maximum PSII photochemical efficiency in a population of C. albidus growing under Mediterranean conditions. A strong correlation was observed between maximum PSII photochemical efficiency (Fv/Fm ratio) and leaf water desiccation. While decreases in maximum PSII photochemical efficiency did not result in any damage at the organ level during winter, reductions in the Fv/Fm ratio were associated to leaf mortality during summer. However, all plants could recover after rainfalls, thus maximum PSII photochemical efficiency decreases did not result in an increased mortality at the organism level, despite extreme water deficit and temperatures exceeding 40ºC during the summer. We conclude that, once methodological outliers are excluded, not only biological outliers must not be excluded from data analysis, but focusing on them is crucial to understand the causes and consequences of maximum PSII photochemical efficiency decreases in plants.

Cistus albidus L.-Review of a Traditional Mediterranean Medicinal Plant with Pharmacological Potential

Cistus albidus L. (Cistaceae) is a medicinal plant that has been used therapeutically since ancient times in the Mediterranean basin for its important pharmacological properties. The ability of C. albidus to produce large quantities of a wide range of natural metabolites makes it an attractive source of raw material. The main constituents with bioactive functions that exert pharmacological effects are terpenes and polyphenols, with more than 200 identified compounds. The purpose of this review is to offer a detailed account of the botanical, ethnological, phytochemical, and pharmacological characteristics of C. albidus with the aim of encouraging additional pharmaceutical investigations into the potential therapeutic benefits of this medicinal plant. This review was carried out using organized searches of the available literature up to July 2023. A detailed analysis of C. albidus confirms its traditional use as a medicinal plant. The outcome of several studies suggests a deeper involvement of certain polyphenols and terpenes in multiple mechanisms such as inflammation and pain, with a potential application focus on neurodegenerative diseases and disorders. Other diseases such as prostate cancer and leukemia have already been researched with promising results for this plant, for which no intoxication has been reported in humans.

Ethylene and Jasmonates Signaling Network Mediating Secondary Metabolites under Abiotic Stress

Plants are sessile organisms that face environmental threats throughout their life cycle, but increasing global warming poses an even more existential threat. Despite these unfavorable circumstances, plants try to adapt by developing a variety of strategies coordinated by plant hormones, resulting in a stress-specific phenotype. In this context, ethylene and jasmonates (JAs) present a fascinating case of synergism and antagonism. Here, Ethylene Insensitive 3/Ethylene Insensitive-Like Protein1 (EIN3/EIL1) and Jasmonate-Zim Domain (JAZs)-MYC2 of the ethylene and JAs signaling pathways, respectively, appear to act as nodes connecting multiple networks to regulate stress responses, including secondary metabolites. Secondary metabolites are multifunctional organic compounds that play crucial roles in stress acclimation of plants. Plants that exhibit high plasticity in their secondary metabolism, which allows them to generate near-infinite chemical diversity through structural and chemical modifications, are likely to have a selective and adaptive advantage, especially in the face of climate change challenges. In contrast, domestication of crop plants has resulted in change or even loss in diversity of phytochemicals, making them significantly more vulnerable to environmental stresses over time. For this reason, there is a need to advance our understanding of the underlying mechanisms by which plant hormones and secondary metabolites respond to abiotic stress. This knowledge may help to improve the adaptability and resilience of plants to changing climatic conditions without compromising yield and productivity. Our aim in this review was to provide a detailed overview of abiotic stress responses mediated by ethylene and JAs and their impact on secondary metabolites.

The threshold between life and death in Cistus albidus L. seedlings: mechanisms underlying drought tolerance and resilience

Drought can lead to important shifts in population dynamics if it occurs during seedling establishment. With the aim of elucidating the underlying mechanisms of drought tolerance and resilience, here we monitored the survival of seedlings of the Mediterranean shrub Cistus albidus L. throughout a year growing in the natural Park of the Montserrat Mountains (Spain) and, additionally, we studied the response to severe drought and subsequent recovery after rewatering of seedlings grown in growth chambers. To find possible mechanisms explaining how seedlings respond to drought, growth and survival together with physiological-related parameters such as chlorophyll contents, vitamin E and stress-related phytohormones were measured. We found that survival decreased by 30% at the end of summer and that the main proxy of seedling survival was total chlorophyll. This proxy was further confirmed in the growth chambers, where we found that seedlings that recovered from drought had higher levels of total chlorophyll compared with the seedlings that did not recover. Furthermore, modulation of vitamin E and jasmonates contents appeared to be crucial in the drought response of C. albidus seedlings. We propose a prediction model of survival that includes total chlorophyll height, leaf mass area and maximum photosystem II efficiency with chlorophyll contents being a good long-term predictor of C. albidus seedling survival under severe stress, which, in turn, could help to better foresee population fluctuations in the field.

Transient photoinhibition and photo-oxidative stress as an integral part of stress acclimation and plant development in a dioecious tree adapted to Mediterranean ecosystems

Mastic trees (Pistacia lentiscus L.) are dioecious perennial plants that are highly adapted to Mediterranean climates but display a high sensitivity to winter periods. In order to understand how sex, leaf phenology and ecological context could condition sensitivity to winter and associated mechanisms to acclimate to these conditions, photoinhibition and photo-oxidative stress markers were examined in mastic trees (P. lentiscus) from a natural population growing in the Garraf Natural Park for a consecutive 12-month period (seasonal study), as well as in three populations naturally growing in the Montseny Natural Park, including the highest altitudes described for this species, during winter (altitudinal study). Results from these studies indicate that both the winter period and higher elevation influenced the degree of photoinhibition, but this was not conditioned by sex. In fact, winter photoinhibition occurred transiently even though it was accompanied by chlorophyll loss and malondialdehyde contents. Stress acclimation was achieved through biochemical adjustments in chloroplasts, characterized by anthocyanin shielding, increased de-epoxidation state of the xanthophyll cycle as well as tocopherol accumulation, and phenological adaptations, the latter allowing a complete resetting of the physiological performance of leaves. Moreover, although females showed higher lipid peroxidation than males during the coldest winter months, at the highest elevation and during flowering in spring, this oxidative stress was mild and transient with no negative consequences for the physiology of plants. It is concluded that evergreen mastic trees acclimate to winter conditions and higher elevations by activation of antioxidant defenses together with phenological adjustments, altogether playing a crucial role in plant survival. Sexual dimorphism in mastic trees appears as a relevant factor when considering sensitivity to photo-oxidative stress in winter and altitudinal conditions.