Leaf age effects on chlorophyll, Rubisco, photosynthetic electron transport activities and thylakoid membrane protein in field grown grapevine leaves

Changes in chlorophyll, fluorescence, Rubisco, soluble proteins, photosynthetic activities and thylakoid membrane protein patterns were investigated in field grown grapevine (Vitis vinifera L. cv. Pinot noir) leaves at different leaf positions along the shoot: basal leaves (BL; aged leaf, 90-100 days old), middle leaves (ML; mature leaf 50-60 days old) and apical leaves (AL; young 20-30 days old). The level of total chlorophyll and soluble proteins on a fresh leaf mass basis was higher in ML and AL and lower in BL. When various photosynthetic activities were followed in isolated thylakoids, BL showed significant inhibition of whole chain and photosystem 2 (PS2) activity. A smaller inhibition of PS1 activity was also observed. The same results were obtained when Fv/Fm was measured on dark-adapted leaves using a PAM fluorometer. The artificial exogenous electron donor Mn2+ failed to restore the loss of PS2 activity, while DPC and NH2OH significantly restored the loss of PS2 activity in BL. The marked loss of PS2 activity in BL was primarily due to the loss of 33, 28-25, 23 and 17 kDa polypeptides. A marked reduction of Rubisco activity in BL is mainly due to the significant loss of SSU (nuclear encoded protein - 15 kDa) and marginal loss of LSU (chloroplast encoded protein - 55 kDa) polypeptides.