4’-Reduced- abscisic acid

Morgan, J.M. (1980). Possible role of abscisic acid in reducing seed set in water stressed wheat plants. Nature, 285, 655-7. 

Finally, there are some examples for reduction of various compounds, which are of biochemical interest. Racemic abscisic acid was reduced with Aspergillus niger affording (—)-(l/5 ,2// )-2/,3/-dihydroabscisic acid with >95% ee (equation 43)117. 

When subjected to drought stress, excised wheat Triticum aestivum L.) leaves increase ethylene production as a result of an increased synthesis of ACC 71 and an increased activity of the ethylene-forming enzyme (EFE) which catalyzes the conversion of ACC 71 to ethylene. Rehydratation to relieve water stress reduces EFE activity to levels similar to those in non-stressed tissue. Pretreatment of the leaves with N-benzyladenine (BA) 75 or indole-3-acetic acid lAA 76 prior to drought stress caused further increase in ethylene production. Conversely, pretreatment of wheat leaves with abscisic acid ABA 77 reduced ethylene production to levels of non-stressed leaves, accompanied by a decrease in ACC 71 content, Eq. (29). 

Figure 5. Accumulation of abscisic acid in detached mature leaves of Xanthium strumarium after the fresh weight had been reduced by 10%...

Figure 6. Decrease in abscisic acid content of wilted leaves of Xanthium after stress was relieved. Detached leaves were wilted by reducing the fresh weight by 10%. Stress was relieved after 5 hr by submerging leaves into distilled water for 5 min.

The phenolic acids of interest here [caffeic acid (3,4-dihydroxycinnamic acid), ferulic acid (4-hydroxy-3-methoxycinnamic acid), p-coumaric acid (p-hydroxycinnamic acid), protocatechuic acid (3,4-dihydroxybenzoic acid), sinapic acid (3,5-dimethoxy-4-hydroxyxinnamic acid), p-hydroxybenzoic acid, syringic acid (4-hydroxy-3,5-methoxybenzoic acid), and vanillic acid (4-hydroxy-3-methoxybenzoic acid)] (Fig. 3.1) all have been identified as potential allelopathic agents.8,32,34 The primary allelopathic effects of these phenolic acids on plant processes are phytotoxic (i.e., inhibitory) they reduce hydraulic conductivity and net nutrient uptake by roots.1 Reduced rates of photosynthesis and carbon allocation to roots, increased abscisic acid levels, and reduced rates of transpiration and leaf expansion appear to be secondary effects. Most of these effects, however, are readily reversible once phenolic acids have been depleted from the rhizosphere and rhizoplane.4,6 Finally, soil solution concentrations of... 

The photosynthetic efficiency mainly depends on the openness of stomata, particularly in C3 crops, while their closure tends to avoid excessive water loss. Abscisic acid (ABA) mediates water loss from the guardian cells of the stomata, which is triggered by a decrease in the water content of the leaf and inhibits leaf expansion. In muskmelon seedlings, ABA could improve the maintenance of the leaf water potential and relative water content, and reduce electrolyte leakage [55]. 

The subject has been reviewed on a number of occasions over the past ten years and the reader is referred to these articles for general overviews [3-8], as well as more specialist discussions of antibody techniques for specific plant hormones, viz, cytokinins [9,10], abscisic acid [11], gibberellins [12,13] and auxins [14]. The basis of all immunological techniques is, of course, the availability of antibodies of high specificity for the substance of interest. High specificity is necessary to reduce, or ideally eliminate, the possibility of false results due to cross-reacting substances present in the analyte competing for the... 

Plant hormone analysis tends to be a very difficult task due in part to the low levels that occur naturally. Over the past several years Weiler and his coworkers and a number of other groups have developed extremely sensitive immunoassays for many of the natural plant hormones ( ). These assays have greatly reduced the time and effort required to analyze indoleacetic acid, cytokinins, gibberellins, and abscisic acid. 

Transpiration is a process that involves loss of water vapour through the stomata of plants. The loss of water vapour from the plant cools the plant down when the weather is very hot, and water from the stem and roots moves upwards or is pulled into the leaves. When less water is available for the plants, dehydrated mesophyll cells release the plant hormone abscisic acid, which causes the stomatal pores to close and reduce the loss of water during release of oxygen and intake of carbon dioxide. Fig. 2.7 (a) shows the transpiration effect in plants with open and closed stomata. 

Abscisic acid inhibits frond cell expansion in duckweed (Newton 1977), reducing both the increase in width and length of the developing frond. ABA has similar though somewhat weaker effects on Spirodela (Van Staden and Born-man 1970), and in both cases the inhibitory effects of ABA can be partially overcome by cytokinin (Van Overbeek et al. 1968, Van Staden and Bornman 1970). 

---