Effect of Benzyladenine Treatment Duration on δ-Aminolevulinic Acid Accumulation in the Dark, Chlorophyll Lag Phase Abolition, and Long-Term Chlorophyll Production in Excised Cotyledons of Dark-Grown Cucumber Seedlings

Abstract

Cotyledons excised from dark-grown cucumber (Cucumis sativus L. cv. Aonagajibai) seedlings were incubated in the dark with the cytokinin benzyladenine for different time periods. Then, various greening parameters were examined, including protochlorophyli(ide) to chlorophyli(ide) photoconversion and 8-aminolevulinic acid accumulations in the dark, both triggered by a 5-minute red-Ught pulse.Benzyladenine rapidly stimulates 8-aminolevulinic acid accumulation, protochlorophyli(ide) regeneration, and lag-phase abolition. The red-Ughtpulse-induced protochlorophyll(ide) to chlorophyll(ide) photoconversion does not appear to be affected by benzyladenine treatment. Long-term chlorophyll production in the light is stimulated after longer incubations with the cytokinin.Rates of 8-aminolevulinic acid accumulation in the dark were similar to chlorophyll production rates in the Ught (maximum rates of 20 and 19 to 23 nanomoles per gram fresh weight per hour, respectively, in mole equivalents). The data strongly suggest that benzyladenine aboUlshes the lag phase by triggering 8-aminolevulinic acid synthesis potentiation and that the cytokinin has other stimulatory effects on chlorophyll production after longer incubations.Cytokinins have been reported to stimulate (or inhibit aging processes of) a number of parameters related to greening, such as Chl synthesis (10, 11, 23), ALA2 synthesis (12), ALA dehydratase activity and rate of Pchl(ide) regeneration (22), and the Shibata shift and amount of bound Pchl(ide) (6). Except for the reports on Chl and ALA synthesis, which used excised tissues, all of the above reports used aged seedlings in the dark. With excised tissues, which are often used in studies of greening, several workers (9,11,13,25) reported that the cytokinin effect on Chl synthesis in the light depends on the duration of dark preincubation with cytokinins. Ford et al. (13) reported that ALA synthesis in the light, in a manner similar to Chl synthesis activity, also varies in response to duration of dark preincubation with 6-benzylaminopurine. Naito et al. (20) observed the changes in BA effect on ALA production during dark incubation but did not correlate them with the elimination of lag in Chl accumulation in light. In fact, very little is known about how changes in greening parameters ' Present address:

External calcium requirements for light induction of chlorophyll accumulation and its enhancement by red light and cytokinin pretreatments in excised etiolated cucumber cotyledons

“…Phytochrome phototransformation induces the synthesis of the chlorophyll precursor, 6-aminolevulinic acid (Masoner and Kasemir 1975;Huang et al 1989) and is also involved in induction of the synthesis of mRNA for Chl-binding proteins (Bennett et al 1984;M6singer et al 1988;Wehmeyer et al 1990). Applied cytokinins shorten or eliminate the lag phases for Chl accumulation (Beevers et al 1970;Fletcher and McCullagh 1971;Fletcher et al 1973;Dei 1982;Lew and Tsuji 1982) and synthesis of 6-aminolevulinic acid (Lew and Tsuji 1982;Dei 1985).…”

Effect of Jasmonic Acid on Photosynthetic Pigments and Stress Markers in <i>Cajanus cajan</i> (L.) Millsp. Seedlings under Copper Stress

“…Cytokinin treatment enhanced the amount of δ-ALA accumulation in Cucurbita pepo [4]. Cytokinin is the phytohormones promoting light harvesting potential capacity of the plant, thus exerting a co-operative effect on the process of greening [17][18][19]. It is reasonable to assume that the JA treatment may increase cytokinin concentration which enhanced δ-ALA either at synthesis level or at its activity level but further investigation is needed to prove that.…”

Regulation of Root Greening by Light and Auxin/Cytokinin Signaling in Arabidopsis

“…In addition, there are no notable differences in chlorophyll contents in leaves between wild-type and auxin signaling mutants that have greenish roots (see Supplemental Figure 1 online). However, cytokinins promote photomorphogenesis at the early stage of greening in cotyledons (Chory et al, 1994) and induce chlorophyll biosynthesis (Lew and Tsuji, 1982) via transcriptional activation of regulatory genes (Masuda et al, 1995). In addition, some auxin signals have been proposed to be involved in the repression of photomorphogenesis (Kim et al, 1996(Kim et al, , 1998Nagpal et al, 2000).…”