Coaction of three factors controlling chlorophyll and anthocyanin synthesis

Abstract

In a three-factor analysis the rate of chlorophyll a (Chl) accumulation in excised mustard cotyledons was studied as a function of kinetin, light (operating through phytochrome, P fr) and an excision factor. It was found that the three factors operate additively provided that the P fr level is high enough. When the P fr level is below approximately 1 per cent (ϕλ<0.01) the effectiveness of the excision factor decreases while the effect of kinetin remains additive. The observed additivity is explained by a model where the three factors operate independently through a common intermediate (presumably 5-aminolevulinate) in the biosynthetic chain leading to Chl. With regard to the coaction of the excision factor and phytochrome it is concluded that the production of the excision factor requires the operation of phytochrome (even though saturated at a low P fr level) while the action of the excision factor is independent of phytochrome. This conclusion was confirmed by experiments in which the rate of light-mediated anthocyanin synthesis was measured in excised mustard cotyledons. The effect of excision in the case of anthocyanin formation differs kinetically from the effect of excision on Chl formation.

The Effects of Cytokinin and Light on Hypocotyl Elongation in Arabidopsis Seedlings Are Independent and Additive

“…whether the signaling pathways are independent and whether the responses are additive or multiplicative (Kasemir and Mohr, 1982;Tong et al, 1983). The relationship between light and cytokinin may differ for other developmental responses, including other de-etiolation responses.…”

“…In a multiplicative (or interactive) relationship, the surface of the curve in the threedimensional plot would form a valley or trough following a minimum along which the product of light and cytokinin is the greatest. Thus, cytokinin and light, at subsaturating levels, contribute additively to the inhibition of hypocotyl elongation, as they do to some other responses (Ford et al, 1981;Kochhar et al, 1981;Kasemir and Mohr, 1982). If light and cytokinin act independently and additively to inhibit hypocotyl elongation, and if the inhibition of hypocotyl elongation is a saturable response, then at saturating light levels, light should mask cytokinin responses.…”

“…The interaction between cytokinin and light responses was first reported by Miller (1956), who found that cytokinin (kinetin) in the dark could elicit several responses that were induced by red Iight, such as leaf disc expansion in bean and seed germination in lettuce. Other investigators have described the interaction between light and cytokinin responses in the context of processes such as betacyanin synthesis (Koehler, 1972), anthocyanin accumulation (Kasemir and Mohr, 1982), hypocotyl elongation (Cohen et al, 1991), chloroplast development, and gene expression (Feierabend and de Boer, 1978;Tobin, 1986, 1988;Longo et al, 1990;Abdelghani et al, 1991;Reski et al, 1991;Smart et al, 1991;Smigocki, 1991;Kusnetov et al, 1994). However, it is not known at what leve1 cytokinin and light responses interact.…”

Cytokinin, Acting through Ethylene, Restores Gravitropism to Arabidopsis Seedlings Grown under Red Light

“…In the dark cytokinin can induce expression of genes that are normally induced by light (Flores and Tobin, 1986;Chory et al, 1991). Chloroplast development, which normally depends both on the inductive actions of light and on chlorophyll synthesis, proceeds at least partially in the dark when cytokinins are applied (Kasemir and Mohr, 1982;Chory et al, 1991). Cytokinin also inhibits hypocotyl elongation and acts inde-pendently and additively with light, in the sense that neither factor can cause further inhibition under conditions in which the other factor is saturating (in cucumber, Cohen et al, 1991;in Arabidopsis, Cary et al, 1995;Su and Howell, 1995).…”

Developmental Stages of Cucumber Seedlings

“…When older etiolated seedlings were allowed to green, the pattern of Chl accumulation varied with age of seedling in barley (1), cucumber (7,20), mustard (12), and bean (21). Developing cucumber seedlings from 2 to 7 d after wetting have been exposed to light for greening studies (3, 5-9, 13, 17).…”