Effect of iron deficiency induced changes on photosynthetic pigments, ribulose-1,5-bisphosphate carboxylase, and photosystem activities in field grown grapevine (Vitis vinifera L. cv. Pinot noir) leaves

The effect of iron deficiency on photosynthetic pigments, ribulose-1,5-bisp hospliate carboxylase (RuBPC), and photosystem activities were investigated in field grown grapevine (Vitis vinifera L. cv. Pinot noir) leaves. The co ntents of chlorophyll (Chl) (a+b) and carotenoids per unit fresh mass showe d a progressive decrease upon increase in iron deficiency. Similar results were also observed in content of total soluble proteins and RuBPC activity. The marked loss of large (55 kDa) and small (15 kDa) subunits of RuBPC was also observed in severely chlorotic leaves. However, when various photosyn thetic electron transport activities were analysed in isolated thylakoids, a major decrease in the rate of whole chain (H2O --> methyl viologen) elect ron transport was observed in iron deficient leaves. Such reduction was mai nly due to the loss of photosystem 2 (PS2) activity. The same results were obtained when F-v/F-m was evaluated by Chi fluorescence measurements in lea ves. Smaller inhibition of photosystem I (PSI) activity was also observed i n both mild and severely chlorotic leaves. The artificial electron donors, diphenyl carbazide and NH2OH, markedly restored the loss of PS2 activity in severely chlorotic leaves. The marked loss of PS2 activity was evidently d ue to the loss of 33, 23, 28-25, and 17 kDa polypeptides in iron deficient leaves.