This study demonstrates the indirect effects of non-thermal ambient air plasmas (NTP) on seed germination and plant growth. It investigates the effect of plasma-activated water (PAW) on 3-day-old seedlings of two important farm plants—barley and pea. Applying different types of PAW on pea seedlings exhibited stimulation of amylase activity and had no inhibition of seed germination, total protein concentration or protease activity. Moreover, PAW caused no or only moderate oxidative stress that was in most cases effectively alleviated by antioxidant enzymes and proved by in situ visualization of H₂O₂ and ˙O₂⁻. In pea seedlings, we observed a faster turn-over from anaerobic to aerobic metabolism proved by inhibition of alcohol dehydrogenase (ADH) activity. Additionally, reactive oxygen/nitrogen species contained in PAW did not affect the DNA integrity. On the other hand, the high level of DNA damage in barley together with the reduced root and shoot length and amylase activity was attributed to the oxidative stress caused by PAW, which was exhibited by the enhanced activity of guaiacol peroxidase or ADH. Our results show the glow discharge PAW at 1 min activation time as the most promising for pea. However, determining the beneficial type of PAW for barley requires further investigation.

Crops are often subjected to various abiotic stresses and interactions between them may occur, but how plants cope with them remains poorly understood. This study explored how combined nitrogen and drought stress impact tomato vascular stem anatomy, nutrient partitioning and amino acids profile. Tomato seedlings were exposed to control (CTR; 100N + 100%W), N stress (N; 50%N), drought stress (W; 50%W), or combined stress (N + W; 50%N+50%W) for 27 days. All treatments similarly reduced the phloem and xylem areas. Plants under N + W stress exhibited increased root synthesis of asparagine and arginine (up to 230% compared to W stress and 66% compared to N stress) and showed a higher reallocation and synthesis of osmolytes such as K⁺ and proline, respectively. This, along with the specific increase in other amino acids related to osmoregulation (alanine, tyrosine and phenylalanine), contributed to an enhanced stomatal closure and lower transpiration rate compared to W stressed plants. Conversely, N stressed plants responded mainly through N remobilization from the photosynthetic machinery, leading to decreased chlorophyll content (up to 32%) and photosynthetic rate (up to 57%). Under single W stress, plants invested more in the root system as a strategy to increase W and nutrients' uptake, compared to those grown under N + W stress, and maintained the photosynthetic rate at the level of CTR plants. It is concluded that tomato plants employed distinct mechanisms for reallocating nitrogen and regulating osmosis to withstand either single or combined stresses and that amino acids and nutrients' homeostasis have an important role in these processes.

As future crop production is threatened by the increasing incidence of insect pests caused by changing climate, it is crucial to focus on searching for alternative methods of insect pest management. This review summarizes the current knowledge on the effect of silicon (Si) on the incidence, growth, development, longevity, survival, feeding efficiency, and reproduction parameters of phloem sap-feeding and chewing insects of plants. While Si may negatively impact the biological parameters of both insect guilds, the effect is generally more pronounced in chewing insects and often varies under different cultivation conditions. In addition to the direct effect of Si on insect pest performance, the potential mechanisms of Si-mediated resistance of infested plants are discussed. These involve increasing plant mechanical properties (Si-based or other organic barriers), and boosting biochemical defence responses, such as increased antioxidant activity, stimulated activity of defence enzymes, attraction of parasitoids and predators of insect pests, and synthesis of toxic and taste-repelling compounds. These changes create a complex Si-induced defence system that enables infested plants to better withstand insect pest attack, ultimately reducing pest damage and improving agricultural crop yields.