Patterns of Ehtylene Production in Senescing Leaves

Abstract

Changes in the patterns of ethylene production, chlorophyll content, and respiration were studied in relation to the senescence of intact leaves and leaf discs. The primary leaves of pinto bean, which abscise readily during natural senescence, and tobacco and sugar beet leaves, which do not abscise, were used. A decrease in the rate of ethylene production and respiration, during the slow phase of chlorophyl degradation, was observed in leaf-blade discs cut from mature leaves and aged in the dark. During rapid chlorophyl loss both ethylene production and respiration increased and then decreased. These climacteric-like patterns were shown by leaf discs of all three species. Discs taken from leaves that had been senescing on the plant also showed a climacteric-like rise in ethylene production but not in respiration, which decreased continuously with leaf age. Climactericlike patterns in the rise of ethylene and respiration for leaf discs were also shown by the petioles of both bean and tobacco leaves. This indicates that the rise of ethylene and respiration is characteristic of the general process of senescence in leaves and is not restricted to the abscission process. In contrast to the ethylene-forming systems in climacteric fruits and many flowers, the one in leaves declines sharply in the early stages of senescence. The subsequent rise of ethylene production appears to be associated with the rapid phase of chlorophyl breakdown, and may indicate the final stage of the senescence process during which ethylene could be actively involved in inducing leaf abscission.Ethylene is known to be involved with both Chl degradation in leaf blades and with the abscission process (9,24, 25). Beyer (6) demonstrated that the leaf blade is the primary receptor site for exogenous ethylene in leaf abscission. Aharoni (1) found that the principal site of ethylene production in response to a short period of water stress was also the blades rather than the petioles of leaves. McAfee and Morgan (21) found that ethylene levels in cotton leaf petioles were two to six times as high as those in leaf blades. Less attention was paid to the changing pattern of ethylene production by leaf blades during their senescence. Some studies in which ethylene production by the whole leaf was measured revealed a decrease in ethylene production with leaf age (12,13,20,23) climacteric in fruits. This study did not distinguish between the contribution of the tomato petiole and leaf blade to the ethylene production pattern observed. Since abscission is directly concerned with the petiole it seemed important to determine patterns of ethylene production in leaf blades and petioles in abscising and nonabscising leaves during senescence. In this study we examined patterns of ethylene production by senescing leaf blades and by leaf petioles with and without abscission zones. The capacity of leaves at various ages to produce ethylene in response to IAA and kinetin was also studied. MATERIALS AND METHODSTobacco (Nicotiana tabacum L. cv. Xanthi), pinto be...

Auxin-Induced Ethylene Production as Related to Auxin Metabolism in Leaf Discs of Tobacco and Sugar Beet

“…4) and water stress (2). This surge of ethylene production declines sharply, and later on, in an advanced stage of senescence, there is a rise of ethylene production in a climacteric-like pattern (4). Exogenous IAA stimulated ethylene production that lasted for several days in tobacco leafdiscs.…”

Ethylene Production by Attached Leaves or Intact Shoots of Tobacco Cultivars Differing in Their Speed of Yellowing during Curing

“…The role of ethylene as an initiator of senescence is well documented for flowers and fruits (1,4,18,20), but evidence for a similar role in foliar senescence is lacking (14,20,21). Although some workers propose that a rise in ethylene production triggers senescence in leaves (4,13,17,18) Plant Material and Culture.…”

“…Although some workers propose that a rise in ethylene production triggers senescence in leaves (4,13,17,18) taut by clamping it between two bars of Plexiglas, and tightened with wing nuts. The space provided between the basal end of the leaf and center edge of the bag was carefully sealed with waterbased cellulose filler, Polyfilla (5), thus avoiding wounding of the leaf.…”

“…Although some workers propose that a rise in ethylene production triggers senescence in leaves (4,13,17,18) Plant Material and Culture. Four cultivars of tobacco (Nicotiana tabacum L.) were used in this study, Coker 86, WR-5, Coker 258, and NCBY, certified seeds of which were obtained from the Philippine Tobacco Research and Training Center, Ilocos Norte, Philippines.…”

“…The time required for yellowing during flue-curing differs among Philippine tobacco cultivars, ranging from 35 to 60 h (15). This study assesses the possible relationship between rates of ethylene production in tobacco leaves and the known speeds of yellowing of the leaves during flue-curing.The role of ethylene as an initiator of senescence is well documented for flowers and fruits (1,4,18,20), but evidence for a similar role in foliar senescence is lacking (14,20,21). Although some workers propose that a rise in ethylene production triggers senescence in leaves (4,13,17,18) Plant Material and Culture.…”