ABA biosynthesis and degradation contributing to ABA homeostasis during barley seed development under control and terminal drought-stress conditions

Abstract

Drought is one of the most severe environmental stress factors limiting crop yield especially when occurring during anthesis and seed filling. This terminal drought is characterized by an excess production of the phytohormone abscisic acid (ABA) which plays an important role during seed development and dormancy. All the genes putatively involved in ABA biosynthesis and inactivation in barley were identified and their expression studied during plant ontogeny under standard and drought-stress conditions to learn more about ABA homeostasis and the possible mode of cross-talk between source and sink tissues. Out of 41 genes related to ABA biosynthesis and inactivation 19 were found to be differentially regulated under drought stress in both flag leaves and developing seed during seed filling. Transcripts of plastid-located enzymes are regulated similarly in flag leaf and seed under terminal drought whereas transcripts of cytosolic enzymes are differentially regulated in the two tissues. Detailed information on the expression of defined gene family members is supplemented by measurements of ABA and its degradation and conjugation products, respectively. Under drought stress, flag leaves in particular contain high concentrations of both ABA and the ABA degradation products phaseic acid (PA) and diphaseic acid (DPA); whereas, in seeds, besides ABA, DPA was mainly found. The measurements also revealed a positive correlation between ABA level and starch content in developing seeds for the following reasons: (i) genes of the ABA controlled SnRK2.6 and RCAR/PP2C-mediated signal transduction pathway to the ABF transcription factor HvABI5 are activated in the developing grain under drought, (ii) novel ABA- and dehydration-responsive cis-elements have been found in the promoters of key genes of starch biosynthesis (HvSUS1, HvAGP-L1) and degradation (HvBAM1) and these transcripts/activity are prominently induced in developing seeds during 12 and 16 DAF, (iii) spraying of fluridone (an ABA biosynthesis inhibitor) to drought-stressed plants results in severely impaired starch content and thousand grain weight of mature seeds.

ABA mediates PEG-mediated premature differentiation of root apical meristem in plants

“…[5][6][7] It has shown that high levels of ABA at micromolar inhibit root growth, whereas lower levels of ABA stimulate root growth. A recent study showed that root growth stimulation by low concentration of ABA is .…”

Vacuolar Transport of Abscisic Acid Glucosyl Ester Is Mediated by ATP-Binding Cassette and Proton-Antiport Mechanisms in Arabidopsis

“…S5 and S6). Since ABA-GE levels were reported to increase during seed maturation and germination (Chiwocha et al, 2003;Seiler et al, 2011), we hypothesized that AtABCC14 may be involved in ABA-GE transport. In a targeted approach, we tested the Arabidopsis ABCC transporters AtABCC1, AtABCC2, and AtABCC14 for their ability to transport ABA-GE using membrane vesicles isolated from yeast heterologously expressing these proteins.…”

Yield stability for cereals in a changing climate

“…Cell wall invertase is also an important component in controlling sugar transport during grain filling in rice and maize (Miller and Chourey 1992;Hirose et al 2002). Under drought conditions, ABA levels increased in developing barley seeds, resulting in induction of b-amylase genes and a reduction in starch accumulation and quality (Seiler et al 2011). However, the fact that wheat germplasm that maintains grain number under young-microspore-stage drought conditions but does not maintain grain size when stressed at anthesis indicates that the genetic control may be different .…”