Effects of ABA, antitranspirants, heat and drought stress on plant growth, physiology and water status of artichoke transplants

Abstract

In semiarid regions of the U.S., artichoke [Cynara cardunculus L. var. scolymus (L.) Fiori] seedlings planted in the field during late summer or early fall generally experience simultaneous high air temperatures and short drought episodes causing transplant shock and delay in root and shoot development. This experiment was conducted to determine the effects of heat (35/20°C, day/night temperature regimes vs. 25/10°C) and drought (30% water holding capacity vs. 60%) stresses on plant growth, physiology and water status of artichoke cv. ‘Green Globe Improved’ transplants during 14 days after transplanting (DAT). Heat stress significantly inhibited shoot but not root growth 14 DAT. In contrast, drought stress significantly inhibited root growth between 7 and 14 DAT. Transpiration (E), stomatal conductance (gs) and photosynthetic rate (ACO2) decreased by transplanting (within 24h) regardless of treatments. Thereafter, E and ACO2 significantly increased by heat compared to 25/10°C temperature regime 3 DAT. However as heat stress progressed E, gsACO2 and leaf water potential were reduced. Drought stress sharply reduced E, gs and ACO2 within 1 DAT and leaf water status as early as 3 DAT. The combination of heat and drought stress significantly reduced shoot and root growth 7 and 3 DAT, respectively. This suggests that to prevent transplant shock by heat and drought it is desirable to prevent leaf dehydration. Thus, consecutive greenhouse experiments were also conducted to evaluate the effects of three film-forming antitranspirants (Antistress, Transfilm and Vapor Gard) and abscisic acid (ABA: 0, 500, 1000, and 2000mgL−1) foliar application on physiological responses and shoot water status of artichoke transplants exposed to drought stress (water withholding). ABA at 1000mgL−1 enhanced drought tolerance of transplants, a response that was associated with the maintenance of shoot water status via stomatal closure. Film-forming antitranspirants were not effective to mitigate drought stress. These results suggest that exogenous ABA could be a useful plant growth regulator to condition artichoke transplants to withstand temporal drought stress conditions and reduce transplant shock.