Histological Identification of Physiological Changes in Vascular Cell Morphology in the Lower Stem of Winter Barley (Hordeum vulgare L.) during Freezing

Abstract

The physiological changes caused by freezing stress in the vascular cells of the lower stem of winter barley (Hordeum vulgare L.) were identified using standard histology and microscopy. Zones 1 and 2 denoted the bottom and middle regions, respectively, and zones 3 and 4 the apical regions of the stem. The four zones of the lower stem where freezing injuries occurred were categorized as void formation, tissue separation due to ice formation, and partially or fully clogged vessels with darkly stained unknown substances. In zone 1, an uneven, semi-circular region was identified. Within the innermost leaves in the apical areas, there was evidence of partial and total tissue necrosis. In the apical parts of the mesophyll, ice formation and frost triggered cell plasmolysis. In every zone, three different kinds of vascular cell wall ruptures were noted. Zones 3 and 4 defined various forms of vessel cell wall bursts. In all zones, bordered pits manifested as narrower cell walls inside xylem vessels, perhaps impeding the spread of ice within the vessels. According to this study, freezing might have started at the basal region and moved upward to the lower stem’s apical region. The findings imply that physiological changes in cereal crops recovering from freezing can be studied using conventional microscopy.