An increase in environmental temperature is one of the most common stress factors for plant organisms. The study of the plants’ adaptation to stress factors remains extremely important and relevant. This article presents the results of a acute short-term influence of hyperthermia on species of two subgenera of the genus Haworthia Duval. We investigated the different levels of antioxidant protection and damage degree of the members of two subgenera of the genus Haworthia at the biochemical level, measuring the lipid peroxidation, superoxide dismutase and peroxidase activities, total flavonoid content and content of photosynthetic pigments with a spectrophotometer. To determine the drought tolerance of plants, the water supply of tissues, water shortage and loss of water after an hour of wilting were measured. The values for different groups were compared by ANOVA followed by the Tukey multiple comparison test. The studied plants were warmed in a thermostat at temperatures of 40 °C and 50 °C for three hours under the conditions of natural light. The control group of plants was kept at 25 °C. The research has shown that H. attenuata, H. limifolia and H. cymbiformis are characterized with the increase of concentration of malonic dialdehyde at 40 °C and 50 °C, but a significant difference of values wasn’t received,which indicates the relative resistance of these plants to the influence of high temperatures. The sharp increase of temperature causes the highest level of lipid peroxidation in H. parksiana plants, along with which, warming to 50 °C launches a mechanism of activation and synthesis of superoxide dismutase and flavonoids for the plants. The studied species of the subgenus Haworthia have a photosynthetic system relatively resistant to thermal stress in comparison to the subgenus Hexangulares. H. limifolia plants have a slight inhibition of photosynthesis. The adaptation of H. cymbiformis to thermal stress is due to the strategy of accumulation of a pool of active enzymes, superoxide dismutase, peroxidase, flavonoids under normal conditions and the activation of new peroxidase enzymes as a result of stress. H. attenuata is characterized by activation of new enzymes of superoxide dismutase and peroxidase under stress. It was found that H. cymbiformis and H. attenuata are more heat resistant in comparison with the other two species. Acute short-term hyperthermia has a different influence on the antioxidant system of different species of Haworthia. H. limifolia has the highest drought tolerance, H. cymbiformis has the lowest, the other two species from different subgenera have similar drought tolerance indicators. We did not find any dependence of the mechanisms of action of the antioxidant system under hyperthermia on the type of adaptation to arid conditions at the anatomical level in plants of different subgenera of the genus Haworthia.

The anatomical and morphological structure of vegetative organs Adenium obesum of different ages of the preregenerative period were investigated. It is known that plants of this type are included in the list of CITEC, as their numbers in nature is constantly decreasing. The representatives of Adenium obesum is a popular ornamental plant, and characterized by broad medical and biological characteristics (antibacterial, anti-cancer, antiviral, antioxidant, etc.). The plants of this type belong to the succulents by thickening of the basal part of the stem. However, scientific information regarding the anatomical and morphological researches, characteristics and formation of thickened basal part of the stem is not enough known. As a result of investigations it was found, that after germination the hypocotyl part of plants constantly increase and thickens to form a thickened basal part of the stem. The thickening occurs of the cortical-medullary type. The upper part of the stem and general root significantly thickening only in border areas of the basal part. The periderm formation in the early stages of ontogenesis of A. obesum probably caused by adaptation to life in the arid climate conditionsIt also became known that the representatives of this type are well developed the excretory tissue as non-articulate lactiferous vessels, which, our opinion, are, synthesized most biologically active substances. Confirmed that succulent, woody plant Adenium obesum is caudiciform plant and in the growth process forming «caudex». Досліджено анатомо-морфологічну будову вегетативних органів Adenium obesum різних вікових станів прегенеративного періоду. Відомо, що рослини цього виду занесені до списку CITEC, так як їх чисельність в природі

In the course of evolution, the formation of succulent variations in the underground and surface parts of plants in different taxa could occur simultaneously under the influence of similar abiotic factors, in particular as an adaptation to arid conditions, and similar structural features even in distant families are a manifestation of convergent evolution. Along with this, the development of such adaptive structures in ontogeny can occur in different ways in different taxa. Studying the anatomical and morphological features of the vegetative organs of Fockea edulis (Asclepiadoideae, Apocynaceae) at the early stages of ontogenesis and comparing them with those of other plants will improve the understanding of the features of growth and development of caudex-like plants. The research was conducted on seedlings, juvenile and immature plants of F. edulis. When comparing the features of the development of vegetative parts of three representatives of the Apocynaceae family, we found that the strategy of succulent traits development in F. edulis at the organ level is characterized by the active development of the hypocotyl already at the seedling stage, similar to Adenium obesum, and the subsequent formation of an expanded basal part of the stem due to the combined cortex-pith thickening and radish-like root due to the growth of xylem parenchyma. However, Petopentia natalensis is characterized by a mesophytic seedling. It was established that secondary thickening in the basal part of the stem occurs in two individual ways: in Adenium obesum, the cambium generates solid rings of phloem and parenchymatized xylem; in P. natalensis and F. edulis, the bundle type of conducting elements is preserved. The thickening of the tap root in F. edulis is similar to that in A. obesum.

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