Daily time course of whole-shoot gas exchange rates in two drought-exposed Mediterranean shrubs

An evidence-based systematic review of rosemary (Rosmarinus officinalis) by the Natural Standard Research Collaboration

An evidence-based systematic review of rosemary (Rosmarinus officinalis), including written and statistical analysis of scientific literature, expert opinion, folkloric precedent, history, pharmacology, kinetics/dynamics, interactions, adverse effects, toxicology, and dosing.

The crucial role of plant mitochondria in orchestrating drought tolerance

BACKGROUND

Around the world, the frequency and intensity of droughts is increasing as a result of global climate change, with important consequences for the growth and survival of agricultural and native plant species. Understanding how plants respond to water stress is thus crucial for predicting the impacts of climate change on the crop productivity and ecosystem functioning. In contrast to the large number of studies assessing drought impacts on photosynthesis, relatively little attention has been devoted to understanding how mitochondrial respiratory metabolism is altered under water stress conditions.

SCOPE

This review provides an overview of the impacts of water stress on mitochondrial respiration (R), combining studies at the whole-plant, individual organ, cellular and organelle levels. To establish whether there are clear patterns in the response of in vivo R to water stress, a wide range of root, leaf and whole-plant studies are reviewed. It is shown that water stress almost always inhibits R in actively growing roots and whole plants. However, in fully expanded, mature leaves the response is more variable, with water stress reducing R in near two-thirds of reported studies, with most of the remainder showing no change. Only a few studies reported increases in leaf R under severe water stress conditions. The mechanisms responsible for these variable responses are discussed. Importantly, the fact is highlighted that irrespective of whether drought increases or decreases respiration, overall the changes in R are minor compared with the large decreases in photosynthetic carbon gain in response to drought. Based on recent work highlighting the link between chloroplast and mitochondrial functions in leaves, we propose a model by which mitochondrial R enables survival and rapid recovery of productivity under water stress conditions. Finally, the effects of water stress on mitochondrial function, protein abundance and overall metabolism are reviewed.

Effects of long-term exposure to elevated CO(2) conditions in slow-growing plants using a (12)C-enriched CO(2)-labelling technique

Despite their relevancy, long-term studies analyzing elevated CO(2) effect in plant production and carbon (C) management on slow-growing plants are scarce. A special chamber was designed to perform whole-plant above-ground gas-exchange measurements in two slow-growing plants (Chamaerops humilis and Cycas revoluta) exposed to ambient (ca. 400 micromol mol(-1)) and elevated (ca. 800 micromol mol(-1)) CO(2) conditions over a long-term period (20 months). The ambient isotopic (13)C/(12)C composition (delta(13)C) of plants exposed to elevated CO(2) conditions was modified (from ca. -12.8 per thousand to ca. -19.2 per thousand) in order to study carbon allocation in leaf, shoot and root tissues. Elevated CO(2) increased plant growth by ca. 45% and 60% in Chamaerops and Cycas, respectively. The whole-plant above-ground gas-exchange determinations revealed that, in the case of Chamaerops, elevated CO(2) decreased the photosynthetic activity (determined on leaf area basis) as a consequence of the limited ability to increase C sink strength. On the other hand, the larger C sink strength (reflected by their larger CO(2) stimulatory effect on dry mass) in Cycas plants exposed to elevated CO(2) enabled the enhancement of their photosynthetic capacity. The delta(13)C values determined in the different plant tissues (leaf, shoot and root) suggest that Cycas plants grown under elevated CO(2) had a larger ability to export the excess leaf C, probably to the main root. The results obtained highlighted the different C management strategies of both plants and offered relevant information about the potential response of two slow-growing plants under global climate change conditions.

Leaf morphology, photochemistry and water status changes in resprouting Quercus ilex during drought

Functional and morphological (structural) characteristics of Quercus ilex L. leaves under drought stress were studied in the forest and in a nursery. We compared undisturbed individuals (controls) with resprouts emerging after clear-cut or excision. When soil water availability was high, gas-exchange was similar in resprouts and controls, despite higher midday leaf water potential, midday leaf hydration and relative water content (RWC). In moderate drought, stomatal closure was found to limit photosynthesis in controls, and in severe drought non-stomatal limitations of photosynthesis were also greater than in resprouts. Leaf structure and chemical composition changed under drought stress. Leaves tended to be smaller in controls with increasing drought, and resprouts had larger leaves and lower leaf mass area (LMA). The relationship between nitrogen (N) content and LMA implied lower N investment in photosynthetic components in controls, which could be responsible for their increased non-stomatal limitation of photosynthesis. Changes were more apparent in leaf density (D) and thickness (T), components of LMA. Decreases in D were related to reductions in cell wall components: hemicellulose, cellulose and lignin. In resprouts, reduced D and leaf T accounted for the higher mesophyll conductance (g_mes) to CO₂ measured.

Effect of drought and high solar radiation on 1-aminocyclopropane-1-carboxylic acid and abscisic acid concentrations in Rosmarinus officinalis plants

The endogenous concentrations of ACC and ABA were measured, at predawn and at maximum solar radiation, during a summer drought, and recovery after autumn rainfalls, in rosemary (Rosmarinus officinalis L.), a drought-tolerant species, growing under Mediterranean field conditions. During the summer, plants were subjected to both water deficit and high solar radiation. Plants showed severe reductions in shoot water potential to -3 MPa, which were associated with drastic stomatal closure (73%), a decrease in net photosynthesis, reaching almost zero, and a severe chlorophyll loss (74%). Despite the severity of the stress, plants recovered after the autumn rainfalls. The concentration of ACC was not enhanced by drought, and at predawn these concentrations remained constant at approximately 600 pmol ACC-1 DW throughout the experiment. Thus, ethylene did not regulate the response of rosemary to drought. However, a sharp increase in ACC levels between predawn and midday was observed. This increase was positively correlated to the intensity of the incident solar radiation. ACC levels recorded in June at midday reached 16 000 pmol g DW and in October values of 1000 pmol g-1 DW were observed. In contrast, in drought-stressed plants predawn concentrations of ABA were up to 130-fold those of recovered plants, and the levels of ABA scored at midday were double of those scored at predawn. In conclusion, although drought-stressed rosemary plants showed a relatively moderate ABA accumulation (approximately 500 pmol g-1 DW#, at predawn), it seems to be an essential factor for the regulation of the plant response to stress, thereby enabling a rapid recovery after stress release, although other mechanisms can not be excluded. As drought stress did not induce ACC accumulation, it was concluded that ethylene production was not a major factor in the drought stress resistance of rosemary plants. The increased ACC and ABA concentrations at midday were correlated with day length and light intensity and not with the water status of the plant.