Roh. Horticulture, Environment and Biotechnology.53:233-239

The promoter of the sunflower HD-Zip protein gene Hahb4 directs tissue-specific expression and is inducible by water stress, high salt concentrations and ABA.

Basis of several bioassays and the discovery of auxin.

Hisamatsu.Journal of Horticultural Science & Biotechnology.84:447-453.

4.2 Physiological and biochemical symptoms:

Analysis using brassinazole 2001, a specific inhibitor for BR biosynthesis, and the measurement of BRs in TMV-infected tobacco leaves indicate that steroid hormone-mediated disease resistance (BDR) plays part in defense response in tobacco.

Plant biotechnology, Biochemical engineering, Web alert.

The HrsACO in petals from ACC-treated flowers was down-regulated after 3h and 9h, in 1-MCP-treated flowers after 3h, and in ABA-treated flowers after 9h. In style–stigma plus stamen tissues the HrsACO mRNAs were enhanced by ACC treatment after 1h and 9h, and by ABA after 3h. In contrast, HrsACO gene expression was down-regulated after 6h in all treatments. In the ovaries, HrsACO up-regulation was initially only observed following 1h of 1-MCP treatment. The same treatment showed the opposite effect after 9h. The ACC treatment did not affect this gene, while ABA repressed the transcript accumulation after 6h and 9h.

Complex regulation of ABA biosynthesis in plants will be available on

Plant biology: abscisic acid in bloom.

A variety of ABA synthesis or response loci have been implicated in controlling meristem function or flowering time (reviewed in ). The aba1 and abi1 mutants exhibit early flowering under short days () and abi3-4 mutants flower early regardless of daylength (), while the ABA hypersensitive mutant hyl1 exhibits delayed flowering (), consistent with an inhibitory role of ABA in the floral transition. Studies of the flowering promoting gene LEAFY showed that LFY expression is strongly induced by a combination of sucrose and GA, but that ABA fully blocks the GA-induced increase regardless of the GA3 concentration (). Although ABA did not completely eliminate LFY promoter activity, the ABA effect appeared “epistatic” to the GA effect. Genetic interactions with DET1 () and CONSTANS (), and physical interactions with TIMING OF CAB EXPRESSION (TOC1) and a CONSTANS-related factor () suggest that ABI3 affects flowering through cross-talk with light and circadian rhythm controls. However, these interactions are complex in that the epistatic relationships vary depending on photoperiodic conditions. Flowering and fruit production is also enhanced in abi3 mutants, apparently reflecting the delayed senescence and continued photosynthesis of cauline leaves ().

Cress root inhibition This bioassay is based on theability of auxin to stop root growth.

Martinez M, Rubio-Somoza I, Carbonero P, Diaz I.

Although the number of available mutants is still far from saturating the biosynthesis pathway, any mutants deficient in bioactive hormones are useful for studying the roles of those hormones in physiological and developmental processes. Such studies have confirmed the role of endogenous ABA in dormancy induction and stomatal regulation. However, they have also shown that many responses induced by either environmental stresses (e.g. drought, cold or salinity) or exogenous ABA probably do not require endogenous ABA to mediate response to the environmental cues.

Abscisic acid biosynthesis and catabolism.

Studies of the ABA biosynthesis and response mutants of Arabidopsis have complemented similar studies in other species. The hormone deficient mutants have been valuable in providing confirmations of proposed biosynthetic pathways, such as the “indirect” carotenoid pathway of ABA synthesis and the plastidic MEP pathway of synthesis for ABA precursors. Detailed biochemical studies have identified enzymes responsible for the many steps of ABA biosynthesis and candidate genes or gene families have been identified for nearly all of these. The roles of specific family members are being tested by expression analyses and reverse genetics. Expression of several of these enzymes increases in response to drought and ABA, resulting in positive feedback regulation of ABA biosynthesis. ABA also promotes synthesis of enzymes required for its degradation, providing a mechanism for homeostasis of ABA accumulation.

BMC Bioinformatics 6: 114 (2005).

Effects of postharvest storage and dormancy status on ABA content, metabolism, and expression of genes involved in ABA biosynthesis and metabolism in potato tuber tissues.