Effects of root restriction on the ultrastructure of phloem in grape leaves

Abstract

In this study, the ultrastructure of phloem and its surrounding parenchyma cells in grape leaves from plants subjected to root restriction or without (control) was systematically investigated for the first time through transmission electron microscopy. The results show that the sieve element (SE) and companion cells (CC) in the main veins of leaves subjected to root restriction were smaller in size than those in the control leaves. The number of plasmodesmata between CC and SE in leaves subjected to root restriction was greater than in the control leaves, but the number of plasmodesmata between phloem parenchyma cells (PP) in leaves subjected to root restriction was less than in the control leaves. Also, the average diameters of SE and CC in the branch veins were smaller in leaves subjected to root restriction than in the control leaves, but their cell walls were thicker and the number of plasmodesmata between PP was less. In the minor veins, the SE and CC were smaller in leaves subjected to root restriction than in the control leaves, and the number of plasmodesmata between CC and SE, SE and PP, and CC and PP were greater. Moreover, less intercellular space among PP cells was observed in minor veins of leaves subjected to root restriction, which was in contrast to the main veins where more intercellular space among PP cells was observed in the leaves subjected to root restriction compared to control leaves. These results therefore demonstrated that changes in the ultrastructure of the phloem of grape leaves are a result of adaptation to the stress of root restriction.

Key words: Root restriction, leaf, phloem, ultrastructure.