Species-specific response to acute hyperthermal stress of Haworthia (Asphodelaceae) plants

Abstract

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.

Crassula genus plants response to temperature stress depends on anatomical structure and antioxidant system

“…Absence an additional epidermal protection may be accompanied by the stress influence of high temperature on internal leaf structures. Similar results were observed on haworthias and representatives of the Cactaceae family [15,16,37] and rhododendrons, where the least heat-resistant species were those which had the thinnest leaves, thinner outside cell walls and larger epidermal cell surface areas [38]. In C. muscosa, hyperthermia caused stress already at 40 °C, and at 50 °C the MDA content was tripled.…”

“…Increase of peroxidase activity in response to high temperature treatment was also confirmed by other researchers [33,34]. At the same time, other species displayed somewhat different results as for the role of peroxidase in the antioxidant response to high temperature: peroxidase activity increased or stayed the same for rhododendrons and haworthias [15]; activity increased, decreased or stayed the same [16,34]. Anatomical structure studies has shown that representatives of С. perfoliata var.…”

“…According to litera- ture sources, negative effect of high temperature on the photosynthesis-involved pigments is more common, especially in case of long-term exposure [29,35,36]. At the same time, our results from studying the Crassula genus representatives as well as other species [15][16][17] show varied influence of short-term hyperthermia, even among representatives the same genus: one species might have an increase of chlorophyll and carotenoid amounts as a stress response (for example C. muscosa), while in another the said amounts stay stable (for example in C. brеvifolia) or decrease of pigments numbers (С. perfoliata var. minor at 50 °C).…”

“…Compensatory interactions of different antioxidants are also described in studies by other researchers, namely -when some antioxidant enzymes are suppressed, others activate [39]; decrease of peroxidase activity is accompanied by extra carotinoid synthesis [40]. According to literature data, the increase of hyper-or hypothermia causes a uniform decrease of SOD activity in many plant species [15,16,41]. Some researchers studied multidirectional reaction SOD on heat stress in plants of different species, indicating different ways to adapt [34,42,43].…”

“…In addition, some other representatives of this family don't show any change in content of such osmoprotectors as prolin and sugars under hyperthermia [12,13]. The assumption of high specificity of plant reaction to temperature stress is partially confirmed, because, according to latest literature data and the results of our previous studies , conducted on representatives of such families as asphodelaceae, Cactaceae, rosaceae, hyperthermia may cause multi-directional reactions on biochemical level in plants with different anatomical features [14][15][16][17]. Thus, the purpose of our work was to establish the connection between anatomical and morphological features of certain Crassula species with peculiarities of biochemical reactions to abrupt temperature increase which are a complex characteristic of resistance to hyperthermia.…”