Probing a Membrane Matrix Regulating Hormone Action

Abstract

Lipids which are active oleanimins, i.e., those which stimulate respiration and auxin-induced cell elongation of pea stem sections, also initiate a period of Trace quantities of various lipids and their derivatives can enhance respiration and the growth-promoting effect of auxin on pea stem sections. Stowe and Dotts (45) proposed the term "oleanimin" for these physiologically active oily substances and have demonstrated that the only consistent, common properties of oleanimins are that they possess molecular lengths longer than 20 A and have a low polarity.Preliminary experiments showed us that marked ethylene production is associated with the oleanimin effect, whereas no significant ethylene is produced by auxin application alone at the optimal concentration for growth of pea stem sections. The relationship of ethylene production to growth has been investigated by many workers with various organs of plants as noted in the review by Pratt and Goeschl (38), but some inconsistencies remain. Burg and Burg (5, 7) and Chadwick and Burg (9) showed that the inhibitory effect of supraoptimal concentration of IAA on the growth of pea stem and root was attributable to the auxin-induced ethylene, while Andreae et al.(2) postulated that it was unlikely that ethylene can play more than a minor role in mediating inhibition of pea root growth by IAA. According to Holm and Abeles (15) ethylene was partially responsible for the inhibition of elongation that occurred at supraoptimal concentrations of 2,4-D applied to excised soybean stems.Penny and Stowe (37), having demonstrated the stimulating effect of oleanimins on respiration, noted that the similar concentrations and chemistry of effective molecules, along with other facts, suggested that there is only one site at which oleanimins act to increase both growth and respiration. Since a high rate of ethylene production is often accompanied by raised respiration in various phenomena such as fruit ripening (4), wounding (31, 32), physiological disorder (20), etc., it could be that the effect of oleanimins on growth is a result of respiratorily enhanced ethylene synthesis followed by ethyleneregulated growth.In this study, the kinetics of growth and ethylene production of pea stem sections were examined, concurrently with the requirements of oleanimin-induced ethylene production, and the effects of ethylene on growth, in order to establish if oleanimin action can be attributed to the effects of ethylene.MATERIALS AND METHODS Bioassay. Progress No. 9 dwarf peas (Pisum sativum L.) were soaked in a thin layer of water for about 6 hr and grown on vermiculite under weak continuous red light at 25 C. On the 7th day after soaking, 10-mm sections were cut from the third internode 2.5 mm below apical hooks which had just reached a 900 angle. Ten randomized sections were placed in 20 ml of solution in a 10-cm Petri dish for each test. The basal medium used contained 1.5% sucrose, 5 mm KH,PO, (pH 5.5

Effects of Some Organic Solvents on Ethylene Evolution from Young Cotton Bolls

“…One or more enzymes involved in ethylene biosynthesis, rather than a promoter, could be isolated or imbedded in a membrane. This possibility could explain the lack of stimulation of ethylene production by injected methionine, but would not explain stimulation by boll extract; or, the synthesis of ethylene-producing enzymes may be induced by organic solvents, as suggested for long chain lipids by Iwata and Stowe (6). Unlike the results I obtained with organic solvents, however, they found that vitamins E and K1 stimulated ethylene production only when they also added auxin.…”

Sterol Molecular Modifications Influencing Membrane Permeability

“…At this point the experiments by Stowe and his co-workers must be cited (17,25). These workers postulated that certain oily substances, oleanimins, are active in the pea bioassay by forcing apart the lecithin molecules and thereby changing membrane properties (25).…”

“…These workers postulated that certain oily substances, oleanimins, are active in the pea bioassay by forcing apart the lecithin molecules and thereby changing membrane properties (25). According to their rules for lipid activity, sterols should be active, but sitosterol (25) and stigmasterol (17) were not when tested by themselves. In fact, stigmasterol, when added with the active oily substance heptadecylbenzene, partially inhibited the full response produced by the oleanimin (17).…”

“…6B). The latter two sterols are the major higher plant sterols (14), and their inability to influence membrane permeability was at first disturbing, especially because both sterols were active in a red beet system (9) and in the pea bioassay oleanimin test (17 (16,21) depends upon the fatty acid composition and pairing in the lecithin molecule (5). As previously pointed out (9), if sterols in higher plants actually play a role in the structure and function of membranes then the particular sterol, or combination of sterols, that are involved in any specific case will be determined by all the functions of the membranes and not by only one function.…”

“…According to their rules for lipid activity, sterols should be active, but sitosterol (25) and stigmasterol (17) were not when tested by themselves. In fact, stigmasterol, when added with the active oily substance heptadecylbenzene, partially inhibited the full response produced by the oleanimin (17). In light of what is known about the stabilizing effect of sterols on plant membranes (9,11), it appears that stigmasterol prevented the phospholipids from being forced apart by heptadecylbenzene.…”