TY - JOUR T1 - Grapevine Anatomy as a Possible Determinant of Isohydric or Anisohydric Behavior JF - American Journal of Enology and Viticulture JO - Am. J. Enol. Vitic. DO - 10.5344/ajev.2015.14090 SP - ajev.2015.14090 AU - Einat Gerzon AU - Iris Biton AU - Yossi Yaniv AU - Hanita Zemach AU - Yishai Netzer AU - Amnon Schwartz AU - Aaron Fait AU - Giora Ben-Ari Y1 - 2015/06/19 UR - http://www.ajevonline.org/content/early/2015/06/12/ajev.2015.14090.abstract N2 - Plants vary in their stomatal sensitivity in response to water stress. Some plants, termed isohydric, keep their water potential constant by rapid stomatal closure. In contrast, anisohydric plants close their stomata only when the plant water potential decreases dramatically. The distinctions between isohydric and anisohydric strategies among different cultivars of the same species are often unclear. This raises the question, whether these modes of behavior can be considered two distinct strategies? In our study, we compared these strategies using two wine grape cultivars: Grenache, which known to be near-isohydric and the anisohydric cultivar Shiraz. The plants were exposed to a prolonged period of water deficit, and their physiological responses were recorded. When water potential was measured in the stem tissue of the two cultivars at mid-day, and in leaf tissue at pre-dawn, a consistently lower value of stomatal conductance was found in the ‘Grenache’ plants compared to the ‘Shiraz’. The ‘Shiraz’ plants exhibited a more vigorous response to water deficit, demonstrating vegetative growth and lower defoliation compared to the ‘Grenache’ plants. An analysis of the anatomical architecture of the two cultivars revealed that ‘Grenache’ plants have a larger xylem vessel diameter, higher hydraulic conductivity and a higher density of stomata than the ‘Shiraz’ plants. A summary of our results and those of other investigators suggests that isohydric and anisohydric strategies may not be a result of distinct mechanisms, but rather of a well defined time-regulated response. Plants defined as isohydric may be in greater danger of developing a possibly fatal xylem embolism, compared to anisohydric plants, and therefore their response to water deficit must be rapid. This accelerated response results in “avoiding” the drought stress, but lowers the plant’s ability to survive the moderate stress of prolonged drought. However, this is their only option to minimize the risk of xylem cavitation. ER -