Plants respond to higher temperatures by the action of heat stress (HS) transcription factors (Hsfs), which control the onset, early response, and long-term acclimation to HS. Members of the HsfA1 subfamily, such as tomato HsfA1a, are the central regulators of HS response, and their activity is fine-tuned by other Hsfs. We identify tomato HsfA7 as capacitor of HsfA1a during the early HS response. Upon a mild temperature increase, HsfA7 is induced in an HsfA1a-dependent manner. The subsequent interaction of the two Hsfs prevents the stabilization of HsfA1a resulting in a negative feedback mechanism. Under prolonged or severe HS, HsfA1a and HsfA7 complexes stimulate the induction of genes required for thermotolerance. Therefore, HsfA7 exhibits a co-repressor mode at mild HS by regulating HsfA1a abundance to moderate the upregulation of HS-responsive genes. HsfA7 undergoes a temperature-dependent transition toward a co-activator of HsfA1a to enhance the acquired thermotolerance capacity of tomato plants.

Corals and lichens are iconic examples of photosynthetic holobionts, i.e., ecological and evolutionary units resulting from the tightly integrated association of algae and prokaryotic microbiota with animal or fungal hosts, respectively. While the role of the coral host in modulating photosynthesis has been clarified to a large extent in coral holobionts, the role of the fungal host in this regard is far less understood. Here, we address this question by taking advantage of the recent discovery of highly specific fungal–algal pairings corresponding to climatically adapted ecotypes of the lichen-forming genus Umbilicaria. Specifically, we compared chlorophyll a fluorescence kinetics among lichen thalli consisting of different fungal–algal combinations. We show that photosynthetic performance in these lichens is not only driven by algal genotype, but also by fungal host species identity and intra-host genotype. These findings shed new light on the closely intertwined physiological processes of fungal and algal partners in the lichen symbiosis. Indeed, the specific combinations of fungal and algal genotypes within a lichen individual—and the resulting combined functional phenotype—can be regarded as a response to the environment. Our findings suggest that characterizing the genetic composition of both eukaryotic partners is an important complimentary step to understand and predict the lichen holobiont’s responses to environmental change.

Rehabilitation of degraded forests can be a huge challenge as these areas usually face problems including weed invasion, nutrient-deficient soil, lack of seed source and inability of native tree species to colonise or regenerate naturally. Human intervention is thus needed to accelerate the process of rehabilitation. In this regard, using the right species is as important as providing the right environment to encourage the survival and establishment of seedlings. Therefore, the aim of this study was to compare the photosynthetic characteristics and leaf traits of Shorea leprosula trees grown under the sun and shaded environments in a degraded forest. Shade trees were found to have about 20% higher leaf dry weight and 5% higher leaf area as well as significantly (p < 0.05) more chlorophyll than leaves on sun trees. Leaves in shade trees attained maximum photosynthesis at lower photosynthetic photon flux density (PPFD) compared to sun trees. When comparing both sun and shade trees, fast chlorophyll induction curve showed no significant differences in maximum quantum yield of PSII photochemistry (Fv/Fm) and thus was almost unaffected by the leaf ambient light environment. This indicated that although shade trees received lower light intensity compared to sun trees, the physiological responses indicated that the former were capable of minimising light limitation through foliar morphological and physiological adaptations. Our results thus suggested that S. leprosula, being an economically valuable timber species, can be planted in areas with partial shade or in gaps for the purpose of rehabilitation.

Date palms are highly economically important species in hot arid regions, which may suffer ozone (O-3) pollution equivalently to heat and water stress. However, little is known about date palm sensitivity to O-3. Therefore, to identify their resistance mechanisms against elevated O-3, physiological parameters (leaf gas exchange, chlorophyll fluorescence and leaf pigments) and biomass growth responses to realistic O-3 exposure were tested in an isoprene-emitting date palm (Phoenix dactylifera L. cv. Nabut Saif) by a Free-Air Controlled Exposure (FACE) facility with three levels of O-3 (ambient [AA, 45 ppb as 24-h average], 1.5 x AA and 2 x AA). We found a reduction of photosynthesis only at 2 x AA although some foliar traits known as early indicators of O-3 stress responded already at 1.5 x AA, such as increased dark respiration, reduced leaf pigment content, reduced maximum quantum yield of PSII, inactivation of the oxygen evolving complex of PSII and reduced performance index PITOT. As a result, O-3 did not affect most of the growth parameters although significant declines of root biomass occurred only at 2 x AA. The major mechanism in date palm for reducing the severity of O-3 impacts was a restriction of stomatal O-3 uptake due to low stomatal conductance and O-3-induced stomatal closure. In addition, an increased respiration in elevated O-3 may indicate an enhanced capacity of catabolizing metabolites for detoxification and repair. Interestingly, date palm produced low amounts of monoterpenes, whose emission was stimulated in 2 x AA, although isoprene emission declined at both 1.5 and 2 x AA. Our results warrant more research on a biological significance of terpenoids in plant resistance against O-3 stress.

BACKGROUND AND AIMS:The processes connected with prey capture and the early consumption of prey by carnivorous Dionaea muscipula require high amounts of energy. The aim of the present study was to identify processes involved in flytrap energy provision and ATP homeostasis under these conditions.METHODS:We determined photosynthetic CO2 uptake and chlorophyll fluorescence as well as the dynamics of ATP contents in the snap traps upon closure with and without prey.KEY RESULTS:The results indicate that upon prey capture, a transient switch from linear to cyclic electron transport mediates a support of ATP homeostasis. Beyond 4 h after prey capture, prey resources contribute to the traps' ATP pool and, 24 h after prey capture, export of prey-derived resources to other plant organs may become preferential and causes a decline in ATP contents.CONCLUSIONS:Apparently, the energy demand of the flytrap for prey digestion and nutrient mining builds on both internal and prey-derived resources.

Two field exercises were carried out to compare chlorophyll a fluorescence measurements taken in the field by field teams working on the same project. In the first exercise (2007, Passo Pura, Ampezzo, Udine, Northern Italy) the operators took measurements on the same leaf areas (maintaining fixed leaf clips); in the second (2009, Monterotondo Marittimo, Grosseto, Central Italy) the teams worked independently, but addressing a common research question. The results of the first exercise showed that: (a) F-V/F-M was stable and had little variation among teams and instruments; (b) the results from the different teams correlated well; (c) the most suitable parameters of fast kinetics analysis are those measured on the normalized fluorescence transients. In the second exercise, when the teams worked independently, the results were much more variable and the correlations between measurements of different operators were weak. These results suggest that field chlorophyll a fluorescence measurements taken by different teams/operators can be comparable only if particular care is taken to the internal variability of the samples and a standardized sampling strategy is applied. A statistically sound representation of a population can be then reached. (C) 2010 Elsevier B.V. All rights reserved.