Photosynthetic functioning of individual grapevine leaves (<i>Vitis vinifera</i> L. cv. Pinot noir) during ontogeny in the field

Abstract

Field studies were conducted to investigate ontogenic changes in photosynthesis of a single grapevine leaf (Vitis vinifera L. cv. Pinot noir) subtending the fruit. A 40-day-old leaf was physiologically most active with regard to net photosynthetic (Pn) and electron transport rates. Variable to maximum fluorescence ratios of dark-adapted leaves (F_v/F_m = 0.77) were higher in mature leaves than in expanding (0.66) or senescent ones (0.65). Lower F_v/F_m values in these stages seemed to be caused not by photoinhibition but by a low photochemical capacity as suggested from the chlorophyll a/b ratios. In isolated thylakoids, lower rates of whole chain and PSII activity were observed in expanding and senescent leaves, while higher rates were observed in mature leaves. A similar trend was noticed for Rubisco and total soluble proteins. The artificial exogenous electron donors Mn²⁺ failed to restore the loss of PSII activity in senescent leaves, while DPC and NH₂OH significantly restored the loss of PSII activity. The m arked loss of PSII activity in senescent leaves was primarily due to the loss of 33, 28-25, 23 and 17 kDa polypepides. A marked loss of Rubisco activity in senescent leaves is mainly due to the loss of 15 (SSU) and 55 (LSU) kDa polypeptides.