Expression of ABA synthesis and metabolism genes under different irrigation strategies and atmospheric VPDs is associated with stomatal conductance in grapevine (Vitis vinifera L. cv Cabernet Sauvignon)

Abstract

The influence of different levels of irrigation and of variation in atmospheric vapour pressure deficit (VPD) on the synthesis, metabolism, and transport of abscisic acid (ABA) and the effects on stomatal conductance were examined in field-grown Cabernet Sauvignon grapevines. Xylem sap, leaf tissue, and root tissue were collected at regular intervals during two seasons in conjunction with measurements of leaf water potential (Ψleaf) and stomatal conductance (gs). The different irrigation levels significantly altered the Ψleaf and gs of the vines across both seasons. ABA abundance in the xylem sap was correlated with gs. The expression of genes associated with ABA synthesis, NCED1 and NCED2, was higher in the roots than in the leaves throughout and highest in the roots in mid January, a time when soil moisture declined and VPD was at its highest. Their expression in roots was also inversely related to the levels of irrigation and correlated with ABA abundance in the roots, xylem sap, and leaves. Three genes encoding ABA 8’-hydroxylases were isolated and their identities confirmed by expression in yeast cells. The expression of one of these, Hyd1, was elevated in leaves when VPD was below 2.0–2.5 kPa and minimal at higher VPD levels. The results provide evidence that ABA plays an important role in linking stomatal response to soil moisture status and that changes in ABA catabolism at or near its site of action allows optimization of gas exchange to current environmental conditions.

Abscisic Acid Down-Regulates Hydraulic Conductance of Grapevine Leaves in Isohydric Genotypes Only

“…On the one hand, ABA accumulation in the xylem sap of intact grapevine plants was highly dependent on the genotype, suggesting that ABA biosynthesis capacity or catabolism varied across genotypes. These variations may be due to differential expression of genes associated with ABA synthesis, such as NCED1 and NCED2, or genes coding for enzymes involved in ABA degradation to inactive compounds, including the ABA 8'-hydroxylases (Riahi et al, 2013;Speirs et al, 2013). On the other hand, exogenous ABA application to detached leaves using a high concentration (32 mmol m 23 (+)-ABA) reduced K leaf by up to 50% for the most sensitive grapevine genotype (Fig.…”

“…Compounds were identified by retention times and multiple reaction monitoring. Parent and product ions were the same as previously described (Speirs et al, 2013).…”

Promises and challenges of eco-physiological genomics in the field: tests of drought responses in switchgrass

“…For example, ABA-sensitive genes in guard cells both cause variation in leaf water potential through stomatal regulation and respond directly to water potential (e.g. Tardieu and Davies, 1992;Speirs et al, 2013). Therefore, inference regarding leaf water potential as a predictor should be interpreted carefully, possibly corroborated with comparisons among treatments.…”

Grapevine adaptations to water stress: new perspectives about soil/plant interactions

“…In grapevine, the importance of ABA synthesis in roots in response to decreasing Ψsoil was recently shown by Speirs et al (2013). They reported that the expression of ABA biosynthetic genes NCED1 and NCED2 was higher in the roots than in the leaves upon drought and highest in the roots in months when soil moisture declined, vapor pressure deficit (VPD) was at its highest and stomatal conductance was impaired.…”