Different substances from the natural origin which have beneficial effects on plant growth and development, stress resistance, and crop yield and quality can be called biostimulants or biostimulators. Their physiological effects depend on their composition as they contain various organic and mineral compounds which plants can use as metabolites, growth regulators, and nutrients; however, biostimulants cannot be considered biofertilizers. Biostimulants applied in plant production have been widely considered as an environment‐friendly agricultural practice—and so are now among tools used in sustainable agriculture. Here, we discuss the results of the biostimulants’ effect investigations performed in Croatia, focused on horticultural crops, with edible plant species, such as tomato, garlic, bell pepper, lettuce, strawberry, garden cress, and basil, as well as ornamentals, such as wild rose, wax begonia, Mexican and French marigold, moss rose, everlasting flower, common zinnia, English primrose, and scarlet sage. The investigated biostimulants were applied at all plant growth stages, from germination to full plant and fruit or flower commercial maturity, using the seed treatment, foliar application, or irrigation. To evaluate biostimulant effectiveness, various morphological, physiological, and quality traits were analyzed. In this wide array of studies, the evaluated biostimulants mostly enhanced seed and transplant vigor, stimulated vegetative growth, improved nutrient acquisition and distribution within the plant, increased antioxidative capacity of plant tissues, contributing to higher stress tolerance, and improved plant yield and fruit/flower quality. In general, the research reviewed here implies possible benefits of biostimulant application in horticultural production, especially in stressful growth conditions, such as the transplant stage, reduced fertilization, or incidence of other abiotic stress. Considering possible interactions among the contained physiologically active compounds, the effects on plants may depend on dose, time of treatment, growth conditions, and plant species. Therefore, further research of biostimulant applications in horticultural production is suggested.

Plants must cope with different environmental stresses during their whole lifetime. Abiotic stresses like drought, salt, mineral nutrition disturbances and temperature stress are commonly interconnected through some physiological events in stressed plants, such as the synthesis of protective plant compounds as a response to stress. Many of these, produced within plant primary or secondary metabolism, act as functional compounds not exclusively in plants but in other organisms as well. Concurrently, many of the active compounds in biostimulants which can support plant stress tolerance and productivity in adverse growth conditions are the metabolites or intermediates that may influence the plant's edible parts nutritional quality. Such effects of biostimulants application are not elucidated enough, therefore, we aimed to give an overview of recent advances in the research related to the interplay among abiotic stress, plant response, biostimulants effects and plant‐derived functional food, focusing on plant metabolites as the link which connects the environment with the food chain.

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Sunflower seeds (hybrid Luka) were primed with water (hydropriming) or sodium hydrosulphide (NaHS) solutions (0.1, 0.5, 1.0 and 1.5 mM NaHS) and subsequently dried to initial moisture content. Unprimed (control) and primed seeds were germinated in a growth chamber on paper towels moistened with water or polyethylene glycol (PEG) 6000 solutions (2.5, 5.0 and 10%), mimicking different drought stress levels. To evaluate the response of the primed seeds to drought in the germination stage, the germination energy (GE), germination rate (SG), seedling fresh mass (SW), hydrogen peroxide and free proline content (PRO), as well as lipid peroxidation rate (malondialdehyde; MDA) were established. The results show strong effects of the imposed drought stress and the metabolic response to oxidative stress through lower germinability and proline accumulation in seedlings. NaHS priming showed some positive effects on seed germination depending on stress level and the concentration of NaHS. Sunflower seeds were also germinated in pots filled with soil, at optimal (70% of field water capacity [FWC 70%]) and drought conditions (FWC 30%), in natural outdoors conditions. When plantlets developed the first pair of leaves, the number of plants (emergence rate [ER]), shoot mass (SM) and leaves mass (LM) were determined, as well as the total activities of catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR) and dehydroascorbate reductase (DHAR). There was a significant influence of an interaction between drought stress and priming, whereas drought stress inhibited plant emergence and early growth (SW and LW), and strong antioxidative enzymatic response to drought stress was clearly established in the leaves. Although seed priming showed some influence on enzyme activities, it was mostly related to seed hydropriming effects, while NaHS seed priming was less effective, influencing only DHAR. Altogether, the results imply that sunflower seed priming with NaHS may not have a prolonged impact on the antioxidative defence mechanism based on CAT and ascorbate/glutathione cycle during sunflower early growth in drought conditions.