Xylem embolism and drought-induced stomatal closure in maize

Abstract

Water relations during drought and xylem vulnerability to embolism were studied on four maize ( Zea mays L.) genotypes having contrasting grain yields under drought conditions. Drought provoked a drop in xylem pressure, leaf water potential and whole-plant transpiration. Transpiration was reduced to a minimum value when xylem pressures reached ca. -1.6 MPa. This value corresponded to the threshold xylem pressure below which xylem embolism developed to a substantial degree in leaf midribs. Therefore, xylem embolism always remained low in leaf veins, even when plants exhibited clear water-stress symptoms. This suggests that stomatal closure during drought contains xylem embolism to a minimum value. Cavitation resistance was not related to grain yield under drought conditions for the four genotypes evaluated. However, it can be speculated that an increase in cavitation resistance by cultural practices or genetic selection may increase drought survival in maize.

Declining hydraulic efficiency as transpiring leaves desiccate: two types of response*

“…A large body of evidence indicates that xylem cavitation in the stem is common under water stress, and the role of desiccation-induced cavitation in leaves is supported by observation of embolism in major veins of plants (Canny 2001;Cochard 2002;Bucci et al 2003). Certainly, xylem cavitation is inevitable at some point as leaves desiccate, and studies of water potential relaxation data (including those shown here), indicate a dramatic loss of K leaf at water potentials less than −2 MPa.…”

“…Extensive work on stems has shown that the conductivity of the xylem is critically dependent on water potential ( Ψ ), usually declining rapidly as Ψ inside the xylem apoplast falls below a threshold value (Sperry & Tyree 1988). Leaves are clearly sensitive to water stress-induced depression of hydraulic conductance (Linton & Nobel 2001;Cochard 2002;Brodribb & Holbrook 2003b;Lo Gullo et al . 2003;Brodribb & Holbrook 2004a), and due to the disproportionately large contribution leaves make to whole-plant hydraulic resistance, leaf vulnerability has the potential to dictate how plants respond to shortterm water stress.…”

Diurnal and seasonal variation in root xylem embolism in neotropical savanna woody species: impact on stomatal control of plant water status

“…Stomatal conductance has been shown to decline even in the absence of reduction in bulk leaf water potential (Davies, Mansfield & Hetherington 1990), suggesting that stomata are able to sense loss of root conductivity (Fuchs & Livingston 1996) through chemical signals transported from roots to leaves in the xylem sap (Zhang & Davies 1987). Although common negative relationships between stomatal behaviour and the degree of embolism have been found within species (Sperry, Alder & Eastlack 1993;Cochard 2002) and across different ages of the same species (Domec et al . 2004), no trends have yet been established across species.…”

Relating Xylem Cavitation to Gas Exchange in Cotton

“…An alternate view is that plants, especially crop plants, tend to maximize, rather than optimize, performance and "operate at the edge of dysfunction" [43]. In this view, an adaptive advantage conferred by stomata in angiosperms is to prevent catastrophic xylem embolism rather than respond to reduced hydraulic conductivities resulting from xylem cavitation [42] [44]- [46]. It should be borne in mind that while the present work is consistent with both the ideas of a feedback and feed-forward mechanism of stomatal control, the temporal resolution of the experiments did not allow disproof of either.…”