RT Journal Article SR Electronic T1 Changes in Photosynthesis, Stomatal Resistance and Abscisic Acid of Vitis Labruscana Through Drought and Irrigation Cycles JF American Journal of Enology and Viticulture JO Am J Enol Vitic. FD American Society for Enology and Viticulture SP 239 OP 246 DO 10.5344/ajev.1978.29.4.239 VO 29 IS 4 A1 W. T. Liu A1 R. Pool A1 W. Wenkert A1 P. E. Kriedemann YR 1978 UL http://www.ajevonline.org/content/29/4/239.abstract AB Concord grapevines (Vitis labruscana) grown in pots under natural climate fluctuations were followed through drought and irrigation cycles to study the changes in abscisic and phaseic acid and the effect on stomatal and photosynthetic activity.When leaf water potential reached -16 bars, stomatal closure was essentially complete (15 to 25 sec•cm-1), and photosynthesis was minimal (1 to 5 mg CO2 dm-2 hr-l). Small pot grapevines had a prehistory of mild, repetitive, water stresses which, relative to the large pots, was associated with lower photosynthesis rate at light saturation (26 compared to 32 mg CO2 dm-2 hr-1), and higher abscisic acid (0.33 compared to 0.14 mg kg-1 fresh weight) and hydrolyzable abscisic acid (0.14 compared to 0.04 mg kg-1 fresh weight). A prolonged (more than two weeks) and/or severe stress (leaf water potential less than -16 bars) led to large increase of ABA content (2.5 mg kg-1) and incomplete recovery of photosynthetic potential despite reopening of stomata on restoring plant water status for rewatering.The plant water status of grape leaves affects stomatal opening and thus photosynthesis. With increasing water stress other biochemical processes become affected such as an increase in abscisic acid.