biologia plantarum

Biologia plantarum 58:139-146, 2014 | DOI: 10.1007/s10535-013-0371-8

Seasonal dimorphism and winter chilling stress in Thymus sibthorpii

V. Lianopoulou¹, A. Patakas², A. M. Bosabalidis^1,*

¹ Department of Botany, School of Biology, Aristotle University, Thessaloniki, Greece

² Department of Natural Resources and Enterprise Management, University of Ioannina, Agrinio, Greece

Seasonal dimorphism (summer/winter) has been so far studied only in a few plants and has been focused on summer drought stress. However, Thymus sibthorpii in the study area appears to be affected by winter chilling stress and not by summer drought stress. Thus, the winter leaves were thicker and more compact compared to the summer leaves and they had more stomata and peltate hairs, more sclerenchymatous fibers, vacuoles with phenolics, and chloroplasts than the summer leaves. In addition, their chloroplasts possessed large grana and starch grains. In the summer leaves, cell vacuoles in mesophyll did not contain phenolics, and chloroplasts were devoid of starch grains and had large plastoglobuli. Physiological measurements revealed higher net photosynthetic rate and chlorophyll content in the winter leaves than in the summer leaves. Proline and soluble sugar content along with antioxidative enzyme (superoxide dismutase, peroxidase, ascorbate peroxidase, glutathione reductase) activities were increased in the winter leaves.

Keywords: antioxidative enzymes; chlorophyll; chloroplast; net photosynthetic rate; proline; sugars

Subjects: dimorphism; temperature - low; stomata density; trichomes; chloropast; starch; plastoglobuli; chloroplast ultrastructure; net photosynthetic rate; transpiration rate; stomatal conductance; proline; soluble sugars; chlorophyll content; superoxide dismutase; peroxidase; ascorbate peroxidase; glutathione reductase

Received: February 7, 2013; Revised: May 13, 2013; Accepted: May 14, 2013; Published: March 1, 2014Show citation