Active injections of cytokinins by a free-living sap-feeding insect: a possible mechanism to delay herbivory induced senescence

Manipulations of plants by insects via growth hormones, such as cytokinins (CKs), have been suggested for decades. The focus has been on most obvious cases like “green-islands”. Evidence for an active transfer of CKs by the insect as well as manipulations of the plants perception of CKs has been elusive. We present the results on the interaction between the sap feeding mirid Tupiocoris notatus and the wild tobacco Nicotiana attenuata. We detected an increase of CK-levels and changes in CK related transcripts upon T. notatus attack. Two active CKs (isopentenyladenine and its riboside) have been detected in fifty-fold higher concentrations in the insects compared to leaves. Experiments with 15N-labeled plants showed that T. notatus transfers these CKs to the leaves on which it feeds. Plants with impaired CK perception showed a reduced attractiveness for mirids. While nutrient content was only marginally influenced by mirid feeding in wildtype plants, it was altered in plants with altered CK metabolism. Our results suggest that an active transfer of CKs by a free living insect maintains a homeostasis of nutrients even in highly damaged leaves to optimally exploit the food source.