Strigolactones promote the localization of the ABA exporter ABCG25 at the plasma membrane in root epidermal cells of Arabidopsis thaliana.

The phytohormones strigolactones crosstalk with abscisic acid (ABA) in acclimation to osmotic stress, as ascertained in leaves. However, our knowledge about underground tissues is limited, and lacking in Arabidopsis: whether strigolactones affect ABA transport across plasma membranes has never been addressed. We evaluated the effect of strigolactones on the localization of ATP BINDING CASSETTE G25 (ABCG25), an ABA exporter in Arabidopsis thaliana. Wild-type, strigolactone-insensitive, and strigolactone-depleted seedlings expressing a green fluorescent protein:ABCG25 construct were treated with ABA or strigolactones, and green fluorescent protein was quantified by confocal microscopy in different subcellular compartments of epidermal root cells. We show that strigolactones promote the localization of an ABA transporter at the plasma membrane by enhancing its endosomal recycling. Genotypes altered in strigolactone synthesis or perception are not impaired in ABCG25 recycling promotion by ABA, which acts downstream or independent of strigolactones in this respect. Additionally, we confirm that osmotic stress decreases strigolactone synthesis in A. thaliana root cells, and that this decrease may support local ABA retention under low water availability by allowing ABCG25 internalization. Thus, we propose a new mechanism for ABA homeostasis regulation in the context of osmotic stress acclimation: the fine-tuning by strigolactones of ABCG25 localization in root cells.

Alkaline soil primes the recovery from drought in Populus nigra plants through physiological and chemical adjustments.

Perennial plants are frequently exposed to severe and prolonged drought, and when the balance between water transport and transpirational demand is compromised trees are in danger of embolism formation. To maintain the physiological balance, plants can rely on mechanisms to quickly recover the lost xylem hydraulic capacity and reduce the prolonged impact on photosynthetic activity upon rehydration. Among factors helpful for plants to sustain acclimation and adaptation responses to drought and promote recovery, maintaining an optimal nutritional status is crucial for plant survival. This study aimed to investigate the physiological and biochemical responses under drought and recovery of Populus nigra plants grown in soil with impaired nutrient bioavailability obtained by adding calcium oxide (CaO) to the substrate. Although the CaO treatment did not affect plant growth, in well-watered conditions, treated poplars displayed an impaired inorganic ions profile in tissues. Under drought, although CaO-treated and untreated plants showed similar physiological responses, the former closed the stomata earlier. During water stress relief, the CaO-treated poplars exhibited a faster stomatal opening and a higher capacity to restore xylem hydraulic conductivity compared to not-treated plants, probably due to the higher osmolyte accumulation during drought. The content of some inorganic ions (e.g, Ca2+ and Cl-) was also higher in the xylem sap collected from stressed CaO-treated plants, thus contributing to increase the osmotic gradient necessary for the recovery. Taken together, our results suggest that CaO treatment promotes a faster and more efficient plant recovery after drought due to a modulation of ions homeostasis.

Do the ends justify the means? Impact of drought progression rate on stress response and recovery in Vitis vinifera.

Plants are frequently exposed to prolonged and intense drought events. To survive, species must implement strategies to overcome progressive drought while maintaining sufficient resources to sustain the recovery of functions. Our objective was to understand how stress rate development modulates energy reserves and affects the recovery process. Grenache Vitis vinifera cultivar was exposed to either fast-developing drought (within few days; FDD), typical of pot experiments, or slow-developing drought (few weeks, SDD), more typical for natural conditions. FDD was characterized by fast (2-3 days) stomatal closure in response to increased stress level, high abscisic acid (ABA) accumulation in xylem sap (>400 µg L-1 ) without the substantial changes associated with stem priming for recovery (no accumulation of sugar or drop in xylem sap pH). In contrast, SDD was characterized by gradual stomatal closure, low ABA accumulation (<100 µg L-1 ) and changes that primed the stem for recovery (xylem sap acidification from 6 to 5.5 pH and sugar accumulation from 1 to 3 g L-1 ). Despite FDD and SDD demonstrating similar trends over time in the recovery of stomatal conductance, they differed in their sensitivity to xylem ABA. Grenache showed near-isohydric and near-anisohydric behavior depending on the rate of drought progression, gauging the risk between hydraulic integrity and photosynthetic gain. The isohydry observed during FDD could potentially provide protection from large sudden swings in tension, while transitioning to anisohydry during SDD could prioritize the maintenance of photosynthetic activity over hydraulic security.

Grapevine TPS (trehalose-6-phosphate synthase) family genes are differentially regulated during development, upon sugar treatment and drought stress.

Trehalose-6-phosphate synthase (TPS) performs the first step in the biosynthetic pathway of trehalose-6-phosphate and trehalose. These two molecules play key roles in the control of carbon allocation and of stress responses in plants. We investigated the organization of the TPS gene family and its developmental and environmental expression regulation in grapevine, a major horticultural crop. We identified three novel genes in the family, and assessed the expression of the 11 family members in tissues and developmental phases. Two potentially biosynthetic TPS isoforms belonging to Class I were preferentially expressed in leaf (VvTPS1_A) and in fruit (VvTPS1_B) respectively. Sucrose treatment induced expression of VvTPS1_B, but not of VvTPS1_A, and a progressive decrease of sucrose concentration. Expression of a few Class II genes was affected by sucrose treatment. Application of osmotic stress by withdrawing irrigation also induced a decrease in sucrose and an increase of glucose content, and down-regulation of the VvTPS1_A gene. We discuss the possible role of these potential biosynthetic TPS genes. Subgroups of TPS genes, including both Class I and ClassII isoforms, followed a co-expression pattern in different conditions, suggesting that Class II TPS proteins may directly or indirectly interact with TPS biosynthetic genes. Our results pave the way for clarification of the role of TPS isoforms in grapevine responses to environmental stress.