How short-term temperature stresses affect leaf micromorphology and ultrastructure of mesophyll cells in winter rye Secale cereale L.

The effect of short-term high (+ 40 °C, 2 h) (HT) and positive low-temperature (+ 4 C, 2 h) (LT) stresses on leaf micromorphology and ultrastructure of mesophyll cells in winter rye was investigated. After HT, leaf blade relief became reticulate, while under control conditions and after low-temperature stress, leaf blade relief was folded. The ultrastructure of the leaf mesophyll cells of control plants was nominal: in the chloroplasts of regular lenticular shape, a well-developed thylakoid system immersed in a fine-grained stroma was clearly visible. Short-term HT caused the destruction of thylakoid membranes. A wave-like packing of granal thylakoids, a significant expansion of the lumenal spaces, and a disruption of the structural connection between the granal and stroma thylakoids were noted. There was an accumulation of lipid drops in the cytoplasm. LT stress caused intensive formation of plastoglobules, a decrease in the number and size of starch grains in the chloroplasts. Destruction of thylakoid membranes was not seen. After HT stress, the mitochondria noticeably "swelled", and the membranes of the cristae became less contrasting. After LT stress, significant changes occurred in the morphology of organelles: some of the mitochondria kept a round shape, but some acquired a lenticular or "dumbbell" shape. It was found that, depending on the type of temperature exposure, various adaptive programs are implemented in plant cells, which are accompanied by a complex of ultrastructural changes, thanks to which plants are able to successfully tolerate short-term exposure to stressful temperatures during active vegetation.