Gas exchange and carbon balance in peach leaves infected by Taphrina deformans

Abstract

Gas exchange was investigated in peach ( Prunus persica L.) leaves, naturally infected by Taphrina deformans (Berk.) Tul, in an attempt to clarify the mechanism(s) of carbon balance. Photosynthesis, respiration, glycolysis, intercellular CO 2, CO 2 release in the light in CO 2 -free air, CO 2 burst and CO 2 compensation point were measured in freshly detached leaves at 21%, 2% and 100% O 2, using a CO 2 infrared gas analyser. Photosynthesis was also determined in the field (non-detached leaves) by a portable open gas exchange system, which also measured transpiration and calculated intercellular CO 2. A striking decrease in net photosynthesis, in the light/dark CO 2 release ratio and lack of CO 2 burst were documented in curled leaves, compared to controls. An evident increase in respiration, CO 2 release in the light in CO 2-free air (particularly at 2% O 2), intercellular CO 2 concentrations and a steep rise in the CO 2 compensation point were also noted. Refixation of the CO 2 produced by stimulated respiration (apparently not inhibited in the light) may account for part of the net photosynthetic inhibition. High intercellular CO 2 concentration, lack of CO 2 burst, scarce O 2 sensitivity by photosynthesis and illuminated leaf CO 2 release in CO 2-free air have been considered indicators of weak photorespiration in curled leaves. Gas exchange unbalance (i.e. CO 2 release by illuminated leaves) seems to be responsible for the rise in the intercellular CO 2 concentration, the marked increase in the CO 2 compensation point and would imply great heterotrophy in curled leaves.