Morphological, anatomical, physiological and biochemical adaptations of Pittosporum tobira (Thunb.) W.T.Aiton and P. heterophyllum Franch. to the illumination level

Abstract

Anatomical, morphological, physiological and biochemical adaptations of leaf as the most ecologically sensitive organ in the species P. tobira and P. heterophyllum, grown in the zones of greenhouse complex with different degree of illumination (1 zone – the level of illumination is 100–300 lx, zone 2 – 3000–7000 lx, and zone 3 – more than 10 thousand lx).) were studied. We revealed the structural morphological and anatomical adaptations, which manifested in the increase of leaf structure xeromorphy (thickening of the leaf, adaxial epidermis and columnar parenchyma, increasing pubescence density) under conditions of high insolation. With a low level of illumination in plants of both species, the thickness of the lamina decreased, mainly due to the mesophyll – the number of layers of the columnar parenchyma and the size of the cells reduced. Interspecific differences in the content of photosynthetic pigments in both species studied were found. A common trend in plants under low light conditions was decrease of chlorophyll a compared with the control, whereas the concentration of chlorophyll b in the leaves of plants increased with shading and high insolation. The result of the adaptation of the photosynthetic apparatus of Pittosporum plants, which normalizes its functioning, is a decreasing chlorophyll index both during shading and intense solar radiation. The maximum is determined in the range of 3–7 thousand lx. Such light regime is optimal for plants of the species studied. The observed decreasing pigment index in P. heterophyllum leaves is considered as an adaptive response of more light-loving species of the genus to their cultivation in the shade. The dependence of the peroxidase activity in Pittosporum leaves on the illumination level was studied. Adaptive reactions manifested in changes of peroxidase fractional composition in the leaves of the plants grown in different conditions. The obtained results on the activation and inactivation of the enzymatic activity of free and cell wall-associated peroxidase are interesting for using as an additional diagnostic indicator of stress degree for the plants of the interiors. It was established that adaptive changes in experimental plants were determined by the origin of species and their ecological and biological features.