In the cells irradiated with 2 and 5 min of UV B however, the pH of the medium returned to baseline by 300 min. Cell viability when checked after 24 h of irradiation showed that irradiation with UV B for 2 min and 5 min did not cause cell death, however, irradiation for longer than 5 min caused 80 100 % cell death. We have therefore used 5 min of UV B as the standard irradi ation time for all further experiments. Suramin is known to bind with cell surface components such as the systemin receptor and interfere with the signaling events and this system is affected by UV B irradi ation in L. peruvianum cells. Since UV B irradiation of C. roseus cells caused alkalinization of the medium, we investigated whether suramin could inhibit the UV B induced medium alkalinization.

The results show that the UV B induced alkalinization was inhibited by suramin. Suramin inhibited alkalinization of the growth medium for all exposure times of UV B irradia tion. Heparin, which is similar to suramin in possessing polysulfonated groups, had no effect on alkalinization of the medium induced by UV B irradiation. UV B induced H2O2 production and involvement of protein kinases in UV B induced H2O2 production The oxidative burst, a rapid consumption of oxygen and production of reactive oxygen species such as H2O2, is a typical early event in plant defense responses. With 5 min of UV B irradiation of C. roseus cells H2O2 production increased six fold compared to control cells.

We next examined effects of suramin, an inhibitor of G protein inhibitor, N acetyl cysteine, a puta tive ROS scavanger, verapamil, a calcium channel blocker and staurosporine, a serine threonine kinase inhibitor, SB 203580, a P38 MAPK inhibitor, PD 98059, an ERKK inhibitor and SB 600125 JNK inhibitor. The UV B induced H2O2 production was suppressed by all the inhibitors except the MAPK cascade inhibitors. This indicated that upon receiving the UV B signal by a putative receptor in C. roseus cells, calcium influx and acti vation of serine threoine kinases are required to induce H2O2 production. However, activation of the MAPK cas cade occurs downstream of H2O2 production. Activation of protein kinases in response to UV B irradiation in C. roseus suspension cell cultures Many protein kinases are known to respond to both biotic and abiotic stresses. Two kinases, MAPKs and CDPKs, have been implicated to play pivotal roles in response to diverse stimuli. Previous studies have Dacomitinib demon strated that C. roseus cells also respond to UV B irradiation by expressing biosynthetic genes and production of TIAs. To establish a functional link between these proc esses, we first examined the possible activation of MAPK and CDPK in cells irradiated with UV B.