Leaf age and photosynthesis in <i>Vitis vinifera</i> L.

Abstract

The photosynthetic activity of individual vine leaves was measured on potted plants grown out doors, using both infrared C0₂ analysis and ¹⁴C0₂ fixation techniques. Peak photosynthetic activity occurred at the time when the leaf became fully expanded, approximately 40 days after unfolding. Thereafter, photosynthesis declined gradually.
The increase in photosynthesis during leaf expansion was not attributable to increased chlorophyll concentration, altered spectral characteristics, or to any outstanding anatomical change. Nevertheless, a sensecent leaf was readily distinguished anatomically from an expanding or mature leaf.Irrespective of leaf age, sucrose was the major ¹⁴C0₂ fixation product. Oligo- saccharides also incorporated label, and accounted for a higher proportion of the ¹⁴C fixation products in older leaves. Regardless of leaf age, malic and citric acids became labelled, but the formation of ¹⁴C tartaric acid was restricted to the rapidly expanding foliage. The amino compounds serine and aspartic acid showed some incorporation of label in all leaves examined.