EFFECT OF BASF-13.338 ON RESISTANCE OF PHOTOSYNTHETIC APPARATUS OF TRITICUM-AESTIVUM L. TO ULTRAVIOLET-B RADIATION

Photosynthetic electron transfer was studied in thylakoids isolated fr om control and BASF 13.338 (4-chloro-5-dimethylamino-2-phenyl-3-(2H) p yridazinone) grown wheat (Triticum aestivum L.) seedlings. When thylak oids were irradiated with ultraviolet-B for GO min, a drastic decrease in the rate of whole chain (H2O-->MV) electron transport took place i n control thylakoids. Such reduction was found to be mainly due to the loss of photosystem II (H2O-->DCBQ) activity The BASF 13.338 thylakoi ds (thylakoids isolated from seedlings grown in the presence of BASF 1 3.338) showed greater resistance to ultraviolet-B radiation. The photo system I (DCPIPH2-->MV) activity was insignificantly reduced in both c ontrol and BASF 13.338 thylakoids. The artificial electron donor manga nese chloride (MnCl2) failed to restore the ultraviolet-B radiation-in duced loss of photosystem II activity in both control and BASF 13.338 thylakoids, while addition of diphenyl carbazide (DPC) and hydroxylami ne (NH2OH) significantly restored the photosystem II activity in contr ol thylakoids. It is concluded that ultraviolet-B irradiation inactiva tes the donor side of photosystem II. This was also confirmed by data on inhibition of the variable part of chlorophyll fluorescence (F-v) w ithout appreciable change in the F-o level. The: marked loss of photos ystem II activity was evidently due to the loss of D1, 33, 23, and 17 kDa polypeptides. This conclusion was confirmed by immunological studi es showing that the content of the D1 protein of the photosystem II re action centre and of the 33, 23 and 16 kDa proteins of the water split ting complex was diminished significantly in ultraviolet-B treated con trol thylakoids whereas in BASF 13.338 thylakoids a less loss was evid ent. Thus the inhibitory effect of ultraviolet-B in BASF 13.338 grown thylakoids was less than that in control thylakoids.