Annals of Botany

Good graft for cool cucumbers

The cucumber plants in my unheated greenhouse are  currently fruiting prolifically. However, even at this stage, an unseasonably cold night can affect plant performance: Cucumis sativus is  a cold-sensitive species. Its near relative, Cucurbita ficifolia,  the figleaf gourd, is by contrast much less cold-sensitive. Zhou et al. of Hangzhou, China and Barcelona, Spain (pp. 839–848) have used the difference between the two species to  study the role of root-to-shoot signalling in the response to chilling.  A major part of their experimental protocol involved the use of C.  cucumis shoots grafted onto C. ficifolia rootstocks. Chilling  of C. cucumis affected significantly the rate of photosynthesis  at saturating light; this effect being more marked when the root zone  was chilled than when the shoot was chilled. Grafting onto the C.  ficifolia rootstock did not affect the response to shoot chilling  but ameliorated significantly the response to root chilling. In all other  experiments, whole plants were subjected to the chilling conditions and,  as expected, ungrafted plants showed, amongst other things, a reduction  in carboxylation activity and in Rubisco content, while the concentration  of reactive oxygen species in the leaves increased. Effects on the activities of ROS-scavenging enzymes were more variable. In all these respects,  shoots that had been grafted performed better than self-rooted shoots:  carboxylation activity and Rubisco content were less reduced, ROS accumulated to lower concentrations and activities of ROS-scavenging enzymes were  higher. Further, in ungrafted plants chilling caused a very marked increase  (nearly 50-fold) in the ABA concentration in root xylem exudate and a  marked decrease in cytokinin concentration also. In grafted plants, there  was a much smaller increase (approx. 10-fold) in ABA content and an increase  in cytokinin content. These experiments throw more light onto the role  of root–shoot communication in the response to chilling and suggest  a way of increasing the tolerance to chilling in cold-sensitive plants.