Acute diquat poisoning in children: a single-center retrospective observational study.

Drought stands out as a major bottleneck to agricultural productivity, quality, and global food security, disrupting morphological, physiological, and biochemical processes, adversely affecting growth and development, nutrient uptake, C-assimilation and partitioning (; ; ; ), and drastically reducing yields of major staple food crops by 40% to 50% (). Moderate-to-severe water deficit, even of short duration, can impair multiple components of the photosynthetic apparatus to variable extents. Stomata closure is an early response to an increasing water deficit, reducing water loss by transpiration, but also limiting latent heat loss (thereby increasing leaf temperature), and reducing C-assimilation by limiting CO diffusion into the leaf (; ). Under progressive drought severity, non-stomatal impairments become increasingly important at photochemical and biochemical levels (; ; ; ). In addition, harsher conditions will be imposed under the simultaneous occurrence of other limiting conditions, particularly heat and high irradiance, promoting to photoinhibition () and broadly constraining cellular processes. Under such conditions, a decline in energy use through photochemistry can secondarily boost the production of highly reactive oxygen species (ROS) and chlorophyll (Chl). This can exacerbate cellular oxidative stress in key structures, namely, the photosynthetic apparatus, by affecting photosystem (PS) proteins and promoting membrane lipoperoxidation (; ; ), resulting in chronic photoinhibition of photosynthesis and reduced plant productivity (). Metabolic reprogramming has a key role in plant acclimation to climatic extremes (; ; ). Under water deficit conditions, plants can activate the synthesis and accumulation of compatible solutes to preserve osmotic homeostasis and cell turgor, namely, of non-structural sugars [e.g., sucrose, glucose, fructose, and raffinose family oligosaccharides, (RFOs)], and sugar alcohols (e.g., sorbitol and mannitol). They act as osmoprotectants that stabilize membranes and protein conformation by promoting hydration around them (; ; ), as well as ROS scavengers, especially sugar alcohols (; ; ). The drought acclimation response also includes the synthesis of other protective molecules with energy dissipation and antioxidant roles (; ). Among these, photoprotective pigments (e.g., zeaxanthin, lutein, and β-carotene) control ROS formation and scavenging, and promote the thermal dissipation of excess radiant energy, acting at the level of antenna complexes and PS reaction centers (; ; ). Antioxidant defenses further include enzymes (e.g., of the Haliwell–Asada cycle and catalase), and other non-enzymatic molecules (e.g., ascorbate, glutathione, HSP70, aquaporins, and dehydrins) (; ; ; ). Complementarily, sugars are also associated with membrane stabilization and ROS scavenging, being part of stress perception mechanisms and crosstalk in abiotic stress pathways, acting in signaling, osmotic adjustment, and osmotic homeostasis to maintain cell turgor and protein conformation under water deficit (; ; ; ). Collectively, these mechanisms safeguard the structural integrity of chloroplast and cellular membranes and ensure the proper functioning of photosynthetic and metabolic proteins. Among the most important stress impacts are those imposed on cell membranes, often involving the lipoperoxidation of polyunsaturated fatty acids (PUFAs) due to direct ROS action (; ), and the action of phospholipases and galactolipases that are stimulated under stress conditions (). The lipid matrix of chloroplast membranes is mostly composed of polar lipids (phospholipids and galactolipids), with their functional performance strongly dependent on their fluidity, which in turn is closely related to the predominant PUFAs (). To keep fluidity, integrity, and function, membranes undergo dynamic lipid remodeling, particularly at the chloroplast level, through synthesis and/or modification of pre-existing FAs. This is a vital feature and indicator of stress acclimation, particularly in response to heat (; ), high irradiance (), and drought (; ; ).