The Physiological Significance of Phenylacetic Acid in Abscising Cotton Cotyledons

Abstract

The physiological role of phenylacetic acid (PAA) as an endogenous regulator of cotyledon abscission was examined using cotton (Gossypium hirsutum L. cv LG 102) seedlings. Application of 100 micromolar or more PAA to leafless cotyledon abscission-zone explants resulted in the retardation of petiole abscission and a decrease in the rise of ethylene evolution that normally accompanies aging of these explants in vitro.The partial inhibition of ethylene evolution in these explants by PAA was indirect since application of this compound stimulated short-term (<24 hours) ethylene production. PAA treatment partially suppressed from little activity to activity equal to that of IAA itself (13; see Wightman et al. [16] for discussion). To our knowledge, the possible role ofPAA as an endogenous regulator in leafabscission has not been examined. This research was undertaken to explore this possibility. Portions of these studies have been presented in abstract form (12). MATERIALS AND METHODSPlant Material and Experimental Procedure. Cotton (Gossypium hirsutum L. cv LG 102) seeds were sown in plastic pots containing vermiculite and were grown as described previously (11). Seedlings were watered daily with one-third strength, modified Hoagland solution (3). Seedlings were used when the cotyledons reached full maturity as indicated by cessation of petiole elongation and cotyledon expansion (18-27 d after sowing).All experiments described in this paper were conducted a minimum of three times. Whenever possible, each treatment within an experiment was replicated (n = 2 or 3). Due to the nature of some of the experiments, replication within an experiment was not feasible. Data

Distinct Characteristics of Indole-3-Acetic Acid and Phenylacetic Acid, Two Common Auxins in Plants

“…Polar transport has been recognized as one of the fundamental characteristics of auxins, since IAA was first identified as a naturally occurring auxin that moves directionally, generates concentration gradients and promotes cell elongation in plant tissues. However, previous studies using exogenously applied PAA or 14 C-labeled PAA have suggested that PAA is another naturally occurring auxin but is not transported in a polar manner ( Haagen Smit and Went 1935 , Morris and Johnson 1987 , Procházka and Borkovec 1984 , Suttle and Mansager 1986 ). Here, we provide further evidence that endogenous IAA and PAA show distinct transport characteristics in maize coleoptiles.…”

“…Active and polar auxin transport profiles of IAA have been demonstrated in various plant tissues; 14 C-labeled IAA is directionally transported in the stem segments of light-grown peas ( Morris and Johnson 1987 ), etiolated epicotyl segments of peas ( Procházka and Borkovec 1984 ) and petiole segments of cotton ( Suttle and Mansager 1986 ). On the other hand, the movement of 14 C-labeled PAA is limited and exhibits little, if any, polarity in the same plant tissues ( Procházka and Borkovec 1984 , Suttle and Mansager 1986 , Morris and Johnson 1987 ). Interestingly, a previous study reported that PAA inhibits the polar transport of 14 C-labeled IAA in intact plants and stem segments of peas ( Morris and Johnson 1987 ).…”

Auxin transport and the regulation of petiole abscission in cotton (Gossypium hirsutum L.): A comparison of indol-3yl-acetic acid and phenylacetic acid

“…A previous study has demonstrated that polar transport of PAA does not occur in segments from cotton cotyledonary leaf petioles [19] . Nevertheless, direct application of PAA to the abscission zone at the base of a debladed cotyledonary petiole inhibits abscission, and to an extent that is comparable 0 40…”

“…Distance from apical end of internode (mm) to the response to IAA ( [19] and above) . Although PAA does not undergo polar transport, it is readily taken up by cells from an external solution by a pH-dependent, non-mediated accumulation of the undissociated species [10] .…”

“…Its combined properties of auxin-like regulatory activity and lack of polar transport make PAA a useful biochemical probe to explore the role of polar auxin transport in the regulation of developmental processes . An earlier study demonstrated that direct application of PAA to the abscission zones of cotyledonary node explants of cotton delays petiole abscission (albeit less effectively than IAA), but that distal applications of PAA to the petiole stumps were ineffective [19] . Our results confirm that these responses are the result of the failure of PAA to undergo polar transport .…”