Gradients in stomatal conductance, xylem sap ABA and bulk leaf ABA along canes of Vitis vinifera cv. Shiraz: molecular and physiological studies investigating their source

Abstract

Gradients were observed in xylem sap ABA and in stomatal conductance along canes of Vitis vinifera L. cv. Shiraz. To investigate the source of the ABA responsible for these gradients a series of girdling and decapitation experiments were carried out. Leaf stomatal conductance and bulk ABA of leaves and apices were measured in control plants and in response to apex removal or girdling. Gradients in leaf ABA were observed over the first eight expanded leaves of field-grown Shiraz, with higher concentrations of ABA observed towards the apex. Gradients in stomatal conductance that correlated negatively with the concentration of ABA in the leaf ([ABA]leaf) were also observed over the first eight leaves. No significant effect of decapitation was observed on either leaf ABA or stomatal conductance except for the leaf immediately below the apex where a transient increase in [ABA]leaf was observed after 24 h with no corresponding decrease in conductance. Girdling resulted in an increase in [ABA]leaf in leaves distal to the girdle without the corresponding effect on conductance. These effects were further studied at the level of gene activity. To facilitate this, gene sequences encoding two key enzymes involved in the biosynthetic pathway of ABA in grape, zeaxanthin epoxidase (Zep) and 9-cis-epoxycarotenoid dioxygenase (NCED), were isolated and characterised. The cDNA sequences were used as probes to measure the abundances of their respective mRNAs in the leaf and apical material. Levels of expression of one of the two genes encoding NCED, VvNCED1, reflected the gradients in [ABA]leaf in control vines, however treatment-induced changes in ABA were not always associated with corresponding changes in VvNCED1 expression. The abundances of both the VvNCED2 mRNA and Zep mRNA increased with increasing leaf age and did not appear to be associated with either the [ABA]leaf or the expression of VvNCED1. Our results indicate that observed gradients in g s are correlated with [ABA] gradients in mature leaves and xylem sap and that these [ABA] gradients are not derived directly from the apical tissues but, at least partially, from local synthesis.

Involvement of Abscisic Acid in the Coordinated Regulation of a Stress-Inducible Hexose Transporter (VvHT5) and a Cell Wall Invertase in Grapevine in Response to Biotrophic Fungal Infection

“…In order to determine whether these stress treatments were activating ABA biosynthesis in the plant tissues, we examined the key rate-limiting steps in the plant ABA biosynthetic pathway catalyzed by ZEP and NCED (Liotenberg et al, 1999). Previous studies on grapevine leaves have showed that water stress specifically induced VvNCED1 but not VvZEP, and this is associated with an increase in bulk leaf ABA concentrations (Soar et al, 2004(Soar et al, , 2006. Our analysis shows that powdery and downy mildew infection and wounding also led to rapid and significant increases in VvNCED1 expression, but no consistent pattern in VvZEP expression was observed (Fig.…”

“…In grapevine, a single VvZEP gene and two VvNCED genes (VvNCED1 and -2) have been identified, but only VvNCED1 transcription appears to be linked to ABA biosynthesis in leaves under stress conditions; VvNCED2 appears to be developmentally regulated (Soar et al, 2004). Leaves infected Figure 3.…”

Improving water use efficiency of vineyards in semi-arid regions. A review

“…As it is well known, abscisic acid is one of the main hormonal regulators described for stomatal conductance (Lovisolo et al 2010;Pou et al 2008;Rodrigues et al 2008;Soar et al 2004;Speirs et al 2013). Also, it is the fundamental molecule behind the basis of the partial root zone drying strategy since roots under water stress produce abscisic acid and this signal is transported to leaves via xylem inhibiting stomatal conductance and growth rate.…”

Comparative Study of the Tissue-Specific Distribution of ABA fromArachis HypogaeaL. and Expression of the 9-CIS Epoxycarotenoid Dioxygenase 1 (AhNCED1) During Plant Development

“…Some of the leaf ABA increase could therefore be root derived (1). The first sensing of drought typically occurs underground: roots sense a decrease in water availability, and rapidly send an ABA signal to the leaf, using the xylem as a conduit (17). However, during the fruiting stage, it is probable that the mature peanut leaves, which have more mesophyll cells and guard cells containing a lot of chloroplasts, are more sensitive to induced AhNCED1 expression and ABA biosynthesis.…”