Abscisic acid (ABA) levels increase significantly in plants under stress conditions and ABA is thought to serve as a key stress-response regulator. However, the direct effect of ABA on photosynthesis and the effect of mesophyll ABA on yield under both well-watered and drought conditions are still the subject of debate. Here, we examined this issue using transgenic Arabidopsis thaliana plants carrying a dominant ABA-signaling inhibitor under the control of a mesophyll-specific promoter (FBPase::abi1-1, abbreviated to fa). Under normal conditions, fa plants displayed slightly higher stomatal conductance and carbon assimilation than wild-type (WT) plants; however, these parameters were comparable following ABA treatment. These observations suggest that ABA does not directly inhibit photosynthesis in the short term. fa plants also exhibited a variety of altered phenotypes under optimal conditions, including more vigorous initial growth, earlier flowering, smaller flowers and delayed chlorophyll degradation. Furthermore, under optimal conditions, fa plant seed production was less than a third of that observed for the WT. However, under drought conditions, WT and fa seed yields were similar due to a significant reduction in WT seed and no reduction in fa seed. These findings suggest that endogenous basal ABA inhibits a stress-escape response under non-stress conditions, allowing plants to accumulate biomass and maximize yield. The lack of a correlation between flowering time and plant biomass combined with delayed chlorophyll degradation suggests that this stress-escape behavior is regulated independently and upstream of other ABA-induced effects such as rapid growth and flowering.

Abscisic acid (ABA) is known to be involved in stomatal closure. However, its role in stomatal response to rapid increases in the vapor pressure deficit (VPD) is unclear. To study this issue, we generated guard cell-specific ABA-insensitive Arabidopsis plants (guard-cell specific abi1-1; GCabi). Under non-stressed conditions, the stomatal conductance (g) and apertures of GCabi plants were greater than those of control plants. This supports guard-cell ABA role as limiting steady-state stomatal aperture under non-stressful conditions. When there was a rapid increase in VPD (0.15 to 1 kPa), the g and stomatal apertures of GCabi decreased in a manner similar that observed in the WT control, but different from that observed in WT plants treated with fusicoccin. Low VPD increased the size of the stomatal apertures of the WT, but not of GCabi. We conclude that guard-cell ABA does not play a significant role in the initial, rapid stomatal closure that occurs in response to an increase in VPD, but is important for stomatal adaptation to ambient VPD. We propose a biphasic angiosperm VPD-sensing model that includes an initial ABA-independent phase and a subsequent ABA-dependent steady-state phase in which stomatal behavior is optimized for ambient VPD conditions.

This study is aimed to explore the properties of cellulose nanocrystals (CNC)/polyvinyl alcohol (PVA) composite films with and without 1,2,3,4-butane tetracarboxylic acid (BTCA), a nontoxic crosslinker. CNC and CNC-PVA nanocomposite films are prepared using solution-casting technique. Differential scanning calorimetry (DSC) analyses show that crosslinking increased the glass transition temperature but reduced the melting temperature and crystallinity. Furthermore, high CNC concentrations in the PVA matrix interfere with PVA crystallinity, whereas in specific ratio between CNC and PVA, two different crystalline structures are observed within the PVA matrix. Film surfaces and fracture topographies characterized using scanning electron microscope indicate that at certain CNC-PVA ratios, micron-sized needle-like crystals have formed. These crystalline structures correlate with the remarkable improvement in mechanical properties of the CNC-PVA nanocomposite films, that is, enhanced tensile strain and toughness to 570% and 202 MJ m , respectively, as compared to pristine PVA. BTCA enhances the tensile strain, ultimate tensile stress, toughness, and modulus of CNC films compared to pristine CNC films. Water absorption of crosslinked CNC and CNC-PVA nanocomposite films is significantly reduced, while film transparency is significantly improved as a function of PVA and crosslinker content. The presented results indicate that CNC-PVA nanocomposite films may find applications in packaging, and though materials applications.

Photosynthesis is limited by three main factors: stomatal conductance (gs), mesophyll conductance (gm) and maximum capacity for Rubisco carboxylation (Vcmax). It is unclear how limiting factors vary under stress, particularly during long-term stress acclimation. In this work, we compared for the first time photosynthesis limitation resulting from long-term acclimation to three major abiotic stresses: drought, salinity and temperature. We used saplings of Ziziphus spina-christi, a thermophilic and drought-tolerant tree, which recently became more abundant in the Mediterranean, presumably due to increased winter temperatures. Stress acclimation was investigated by measuring growth, gas exchange, chlorophyll fluorescence and leaf structure. For each stress, photosynthesis-limiting factors were compared. We developed an integrative stress index that allowed us to precisely define stress level, enabling a comparison between stress types. Photosynthesis under all stresses was limited mostly by gs and gm (80-90%); whereas biochemistry (Vcmax) made a minor contribution (10-20%). The relative contribution of gs and gm on photosynthetic limitation was influenced by stress type. During acclimation to drought or salinity, photosynthesis was limited by a decline in gs, while intolerance to low temperatures was driven by decline in gm. In all the stresses, gm decreased only under progressive reduction in leaf physiological functionality and was associated with low turgor under drought, an increase in leaf Na+ under salinity and low leaf hydraulic conductance (Kleaf) at low temperatures. Mesophyll structure (mesophyll surface area exposed to the intercellular air spaces, leaf thickness, % intercellular air spaces) did not explain gm acclimation to stress. Current work gives methodology for stress studies, and defines the main factors underlying the plant response to climate change. The ability to minimize mesophyll-imposed limitations on photosynthesis was found as a strong indicator of progressive stress tolerance. Moreover, the results demonstrate how warming climate benefits the photosynthetic function in thermophilic species, such as Ziziphus spina-christi.

Deg proteases are involved in protein quality control in prokaryotes. Of the three Arabidopsis () homologs, Deg1, Deg5, and Deg8, located in the thylakoid lumen, Deg1 forms a homohexamer, whereas Deg5 and Deg8 form a heterocomplex. Both Deg1 and Deg5-Deg8 were shown separately to degrade photosynthetic proteins during photoinhibition. To investigate whether Deg1 and Deg5-Deg8 are redundant, a full set of Arabidopsis knockout mutants were generated and their phenotypes were compared. Under all conditions tested, mutants were affected more than the wild type and and mutants. Moreover, overexpression of Deg5-Deg8 could only partially compensate for the loss of Deg1. Comparative proteomics of mutants revealed moderate up-regulation of thylakoid proteins involved in photoprotection, assembly, repair, and housekeeping and down-regulation of those that form photosynthetic complexes. Quantification of protein levels in the wild type revealed that Deg1 was 2-fold more abundant than Deg5-Deg8. Moreover, recombinant Deg1 displayed higher in vitro proteolytic activity. Affinity enrichment assays revealed that Deg1 was precipitated with very few interacting proteins, whereas Deg5-Deg8 was associated with a number of thylakoid proteins, including D1, OECs, LHCBs, Cyt , and NDH subunits, thus implying that Deg5-Deg8 is capable of binding substrates but is unable to degrade them efficiently. This work suggests that differences in protein abundance and proteolytic activity underlie the differential importance of Deg1 and Deg5-Deg8 protease complexes observed in vivo.

Regulation of the rate of transpiration is an important part of plants' adaptation to uncertain environments. Stomatal closure is the most common response to severe drought. By closing their stomata, plants reduce transpiration to better their odds of survival under dry conditions. Under mild to moderate drought conditions, there are several possible transpiration patterns that balance the risk of lost productivity with the risk of water loss. Here, we hypothesize that plant ecotypes that have evolved in environments characterized by unstable patterns of precipitation will display a wider range of patterns of transpiration regulation along with other quantitative physiological traits (QPTs), compared to ecotypes from less variable environments. We examined five accessions of wild barley (Hordeum vulgare ssp. spontaneum) from different locations in Israel (the B1K collection) with annual rainfall levels ranging from 100 to 900 mm, along with one domesticated line (cv. Morex). We measured several QPTs and morphological traits of these accessions under well-irrigated conditions, under drought stress and during recovery from drought. Our results revealed a correlation between precipitation-certainty conditions and QPT plasticity. Specifically, accessions from stable environments (very wet or very dry locations) were found to take greater risks in their water-balance regulation than accessions from areas in which rainfall is less predictable. Notably, less risk-taking genotypes recovered more quickly than more risk-taking ones once irrigation was resumed. We discuss the relationships between environment, polymorphism, physiological plasticity and fitness, and suggest a general risk-taking model in which transpiration-rate plasticity is negatively correlated with population polymorphism.

Cellulose, a major constituent of our natural environment and a structured biodegradable biopolymer, has been shown to exhibit shear piezoelectricity with potential applications in energy harvesters, biomedical sensors, electro-active displays and actuators. In this regard, a high-aspect ratio nanofiber geometry is particularly attractive as flexing or bending will likely produce a larger piezoelectric response as compared to axial deformation in this material. Here we report self-assembled cellulose nanofibers (SA-CNFs) fabricated using a template-wetting process, whereby parent cellulose nanocrystals (CNCs) introduced into a nanoporous template assemble to form rod-like cellulose clusters, which then assemble into SA-CNFs. Annealed SA-CNFs were found to exhibit an anisotropic shear piezoelectric response as directly measured using non-destructive piezo-response force microscopy (ND-PFM). We interpret these results in light of the distinct hierarchical structure in our template-grown SA-CNFs as revealed by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (TEM).

Begomoviruses are vectored in a circulative persistent manner by the whitefly The insect ingests viral particles with its stylets. Virions pass along the food canal and reach the esophagus and the midgut. They cross the filter chamber and the midgut into the haemolymph, translocate into the primary salivary glands and are egested with the saliva into the plant phloem. Begomoviruses have to cross several barriers and checkpoints successfully, while interacting with would-be receptors and other whitefly proteins. The bulk of the virus remains associated with the midgut and the filter chamber. In these tissues, viral genomes, mainly from the tomato yellow leaf curl virus (TYLCV) family, may be transcribed and may replicate. However, at the same time, virus amounts peak, and the insect autophagic response is activated, which in turn inhibits replication and induces the destruction of the virus. Some begomoviruses invade tissues outside the circulative pathway, such as ovaries and fat cells. Autophagy limits the amounts of virus associated with these organs. In this review, we discuss the different sites begomoviruses need to cross to complete a successful circular infection, the role of the coat protein in this process and the sites that balance between virus accumulation and virus destruction.