Induction of Leaf Abscission in Cotton Is a Common Effect of Urea- and Adenine-Type Cytokinins

Abstract

Cytokinins of the urea and adenine type induced leaf abscission in young cotton (Gossypium hirsutum) plants in the following order of activity: N-phenyl-N'-1,2,3-thiadiazol-5-ylurea (thidiazuron) >> N-phenyl-N'-(2-chloro-4-pyridyl)urea > isopentenyladenine > 6-benzyladenine > zeatin = dihydrozeatin > kinetin. It is suggested that ethylene production is implicated in this response because it was stimulated by the compounds in cotton leaf discs with nearly the same effectiveness. Moreover, similar to thidiazuron (JC Suttle [1985] Plant Physiol 78: 272-276), isopentenyladenine-induced defoliation was inhibited by aminoethoxyvinylglycine, and the effect was restored by 1-aminocyclopropane-1-carboxylic acid.The phytohormonal cytokinins are N6-substituted adenine compounds that have been implicated in the regulation of many physiological processes including cell division and expansion, seed germination, flowering, and senescence (e.g. ref. 7). In addition to these natural cytokinins, synthetic compounds of different chemical classes demonstrated cytokinin-like activities (5, 9). Among them the N6-substituted adenine derivatives, e.g. Kn' and BA, and the heterocyclic ureas, e.g. TDZ and 4 PU-30, are the most effective substances known (9,10,19). In particular, TDZ and its derivatives displayed qualitatively similar biological properties to purine cytokinins in a range of bioassays including cytokinin-dependent ethylene production systems (19,23). The question is still open as to whether the biosynthesis and/or metabolism of cytokinins are influenced or a common site of action with endogenous cytokinins exists (1 1).As an additional physiological effect, TDZ induced abscission of young, nonsenescing, and mature cotton leaves (2). In this function, the compound is used in agriculture as a cotton defoliant to facilitate mechanical and manual harvesting (13). Results indicated that the effect was mediated by an increase in endogenous ethylene (16). This phytohormone is currently regarded as an important regulator of leaf abscission (6,13,15). However, TDZ-induced defoliation seems to be restricted to plants of the Malvaceae (1 1).Abbreviations: Kn, 6-furfurylaminopurine (kinetin); ACC, l-aminocyclopropane-l-carboxylic acid; MACC, N-malonyl-l-aminocyclopropane-l-carboxylic acid; AVG, aminoethoxyvinylglycine; DZ, DL-dihydrozeatin; IP, N6-(A2-isopentenyl)adenine; 4 PU-30, Nphenyl-N'-(2-chloro-4-pyridyl)urea; TDZ, N-phenyl-N'-1,2,3-thiadiazole-5-ylurea (thidiazuron); Z, zeatin. 234In contrast, purine-type cytokinins usually delay leaf senescence and abscission (e.g. Ref. 21). However, in exceptional cases such as in explants of Phaseolus (14) and leaves of Streptocarpus (20), promotion of the abscission process probably caused by stimulated ethylene (1) has been observed also.In cotton, ethylene production was increased by thidiazuron as well as by natural and synthetic cytokinins of adenine type (17). However, little information has been given in the literature on the potency of adenine-type cytokinins in defoliatin...

Enhancement of ethylene biosynthesis and germination by cytokinins and 1‐aminocyclopropane‐l‐carboxylic acid in Striga asiatica seeds

“…The inability of ACC and the cytokinins, each applied alone, to stimulate ethylene biosynthesis together with the notable enhanced ethylene production following treatment of seeds with cytokinin-ACC combinations (Tabs 1 and 2) indicate that treatment with cytokinins increases the capacity of the seeds to convert ACC into ethylene. This is consistent with several reports on stimulation of ACC oxidation in plant seeds and vegetative parts following enhancement of ACC oxidase activity by cytokinins (Suttle 1986, Yip and Yang 1986, Khan and Huang 1988, Grossman 1991. The relative activity of the cytokinins on ACC oxidation, as revealed by the ethylene released, was TDZ > TZ > BA > KIN.…”

“…The relative activity of the cytokinins on ACC oxidation, as revealed by the ethylene released, was TDZ > TZ > BA > KIN. This order of activity is similar to that reported by Suttle (1986) and Grossman (1991) for elicitation of ethylene from cotton leaf discs.…”

“…In the present communication we demonstrate that the cytokinins trans zeatin (TZ), benzyladenine (BA), kinetin (KIN) and thidiazuron (TDZ) induce Striga asiatica germination by increasing the capacity of the seed to convert the ethylene precursor 1-aminocyclopropane-l-carboxylic acid (ACC) into ethylene. The elicitation of the phytohormone from the seeds corresponds closely to the cytokinin activities of the compounds in stimulation of ethylene biosynthesis in several plants, as reported by several workers (Suttle 1986, Grossman 1991.…”

Thidiazuron: A multi-dimensional plant growth regulator

“…It was firstly used as a defoliant for cotton. Premature activation of the abscission zone affects water potential or chlorophyll content in some members of Malvaceae family (Grossmann, 1991). Although, TDZ protected chlorophyll degradation in detached leaves of geranium (Murthy et al, 1998;Visser et al, 1995).…”

Chemical Defoliant Promotes Leaf Abscission by Altering ROS Metabolism and Photosynthetic Efficiency in Gossypium hirsutum

“…In addition, there are still some problems in the practical use of defoliant, for example, the leaves dehydrated but not shed, and the effect of defoliants being tightly associated with the application schedule, dosage, and air temperature. Early studies showed that adenine cytokinins could induce cotton leaves abscission by increasing the content of ethylene [29,30]. Botton et al also reported that cytokinin (ben-zyladenine, BA), could cause fruits abscission by crosstalk signaling pathways, mainly involving sugars, ROS, ABA, and ethylene [31].…”