Abscisic acid expansion

Thompson, A. J., J. Andrews et al. (2007). Overproduction of abscisic acid in tomato increases transpiration efficiency and root hydraulic conductivity and influences leaf expansion. Plant Physiol. 143(4) ... 

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]. 

Growth inhibitors like abscisic acid (dormin) and abscisin II retard growth, promote abscission, and induce dormancy. They were discovered in the 1960s [18]. They directly affect cell division and expansion and induce stomatal closure [8]. 

Abscisic Acid. ABA is a potent inhibitor of cell division in the developing roots of Lemna minor (Newton 1977). This effect, plus an apparent direct inhibitory effect on cell expansion in Lemna roots, contributes to the overall inhibitory action of ABA on root elongation in this aquatic plant. 

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). 

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