Planta
Planta 150, 269-274 (1980)
9 by Springer-Verlag 1980
Chloroplast Development and the Synthesis of Chlorophyll a and b and Chlorophyll Protein Complexes I and II in the Dark in Tradescantia albiflora (Kunth) Heather Y. Adamson 1, Roger G. Hiller 1, and Maret Vesk 2 i School of Biological Sciences, Macquarie University, North Ryde, N.S.W. 2113 and 2 Electron Microscope Unit, University of Sydney, N.S.W. 2006, Australia
Abstract. Continued synthesis of chlorophyll a and chlorophyll b occurs in Tradescantia albiflora Kunth on transfer to darkness. This synthesis continues for several days and may result in a doubling of chlorophyll content per leaf. It is accompanied by continued cell division and development of normal chloroplast ultrastructure, including stacked thylakoids. Key words: Chlorophyll synthesis o p m e n t - Tradescantia.
Chloroplast devel-
Introduction Some gymnosperms and many lower plants are able to synthesize clorophyll in complete darkness (Sachs 1859; Stahl 1909 ; Lubimenko 1928 ; Seybold and Egle 1938 ; Meyers 1940; Michel-Wolwertz and Bronchart 1974; Oku et al. 1974; Laudi and Manzini 1975). The possibility that some angiosperms may also be able to synthesize chlorophyll in the dark is acknowledged (Boardman 1966; Kirk and Tilney-Bassett 1978), but the phenomenon is poorly documented. The significance of the findings by Goodwin and Owens (1946) and R6bbelen (1956) of traces of chlorophyll a in etiolated seedlings of Arena sativa and Arabidopsis thaliana, respectively, is diminished by the failure of these authors to demonstrate that there was no carryover of chlorophyll in the seed (Kirk and TilneyBassett 1978). Although Godnev et al. (1959) have demonstrated that mature plants of CeratophylIum demersum, Potamogeton pelfoIiatus, Elodea canadensis, and Phaseolus multiflorus are capable of incorporating 14C from 14C02 into chlorophyll in total darkness, there is no direct quantitative evidence for chlorophyll biosynthesis in angiosperms in the dark. The experiments of Godnev et al. (1959) were not designed to
detect net accumulation of chlorophyll in the dark; nor were their techniques suitable for measuring the absolute or relati+e rate of chlorophyll synthesis. As they pointed out, " i t is not the quantitative assessment of chlorophyll biosynthesis in the dark which is of primary importance, but the adduction of evidence that it takes place at all". Twenty years later this is still the case. There is so little evidence that angiosperms can synthesize chlorophyll in the dark and so much evidence to the contrary that it is generally accepted that angiospermous plants do not make chlorophyll in the dark. While studying the effect of light intensity on the growth of Tradescantia albi.flora (Kunth), we observed that chlorophyll synthesis apparently continued when these plants were transferred to total darkness. This paper documents the accumulation of substantial amounts of chlorophyll a and b in the dark in both immature and mature leaves and provides some insight into the associated chloroplast and leaf development. A preliminary account of the work has been published elsewhere (Adamson 1978).
Materials and Methods Well watered 6 8-week old Tradescantia albiflora plants, 6 per 15-cm pot, grown from matched cuttings in high light in a glasshouse were either maintained in high light or were transferred to an inner darkroom (25~ C) from which all light was rigorously excluded. To ensure that leaves of the same developmental age were always compared, a small hole was punched in the third smallest leaf in every shoot apex in every pot (Fig. la) before any plants were transferred to darkness. An initial random sample of these shoots was harvested at the beginning of each experiment. At each harvest, leaves 1 to 5 were removed from each shoot in each sample and leaves of the same developmental age (number) were pooled. These were used to obtain estimates of initial leaf area, chlorophyll content per leaf, number of cells per leaf, and chlorophyll content per cell. Leaf areas were determined by photocopying leaves, cutting out the shapes, and weighing and calculating the areas. Cell numbers per leaf were estimated using a modification of the tech-
0032-0935/80/0150/0269/$01.20
H.Y. Adamson et al. : Chloroplast Development in Tradescantia
270
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Planta 150, 269-274 (1980)
9 by Springer-Verlag 1980
Chloroplast Development and the Synthesis of Chlorophyll a and b and Chlorophyll Protein Complexes I and II in the Dark in Tradescantia albiflora (Kunth) Heather Y. Adamson 1, Roger G. Hiller 1, and Maret Vesk 2 i School of Biological Sciences, Macquarie University, North Ryde, N.S.W. 2113 and 2 Electron Microscope Unit, University of Sydney, N.S.W. 2006, Australia
Abstract. Continued synthesis of chlorophyll a and chlorophyll b occurs in Tradescantia albiflora Kunth on transfer to darkness. This synthesis continues for several days and may result in a doubling of chlorophyll content per leaf. It is accompanied by continued cell division and development of normal chloroplast ultrastructure, including stacked thylakoids. Key words: Chlorophyll synthesis o p m e n t - Tradescantia.
Chloroplast devel-
Introduction Some gymnosperms and many lower plants are able to synthesize clorophyll in complete darkness (Sachs 1859; Stahl 1909 ; Lubimenko 1928 ; Seybold and Egle 1938 ; Meyers 1940; Michel-Wolwertz and Bronchart 1974; Oku et al. 1974; Laudi and Manzini 1975). The possibility that some angiosperms may also be able to synthesize chlorophyll in the dark is acknowledged (Boardman 1966; Kirk and Tilney-Bassett 1978), but the phenomenon is poorly documented. The significance of the findings by Goodwin and Owens (1946) and R6bbelen (1956) of traces of chlorophyll a in etiolated seedlings of Arena sativa and Arabidopsis thaliana, respectively, is diminished by the failure of these authors to demonstrate that there was no carryover of chlorophyll in the seed (Kirk and TilneyBassett 1978). Although Godnev et al. (1959) have demonstrated that mature plants of CeratophylIum demersum, Potamogeton pelfoIiatus, Elodea canadensis, and Phaseolus multiflorus are capable of incorporating 14C from 14C02 into chlorophyll in total darkness, there is no direct quantitative evidence for chlorophyll biosynthesis in angiosperms in the dark. The experiments of Godnev et al. (1959) were not designed to
detect net accumulation of chlorophyll in the dark; nor were their techniques suitable for measuring the absolute or relati+e rate of chlorophyll synthesis. As they pointed out, " i t is not the quantitative assessment of chlorophyll biosynthesis in the dark which is of primary importance, but the adduction of evidence that it takes place at all". Twenty years later this is still the case. There is so little evidence that angiosperms can synthesize chlorophyll in the dark and so much evidence to the contrary that it is generally accepted that angiospermous plants do not make chlorophyll in the dark. While studying the effect of light intensity on the growth of Tradescantia albi.flora (Kunth), we observed that chlorophyll synthesis apparently continued when these plants were transferred to total darkness. This paper documents the accumulation of substantial amounts of chlorophyll a and b in the dark in both immature and mature leaves and provides some insight into the associated chloroplast and leaf development. A preliminary account of the work has been published elsewhere (Adamson 1978).
Materials and Methods Well watered 6 8-week old Tradescantia albiflora plants, 6 per 15-cm pot, grown from matched cuttings in high light in a glasshouse were either maintained in high light or were transferred to an inner darkroom (25~ C) from which all light was rigorously excluded. To ensure that leaves of the same developmental age were always compared, a small hole was punched in the third smallest leaf in every shoot apex in every pot (Fig. la) before any plants were transferred to darkness. An initial random sample of these shoots was harvested at the beginning of each experiment. At each harvest, leaves 1 to 5 were removed from each shoot in each sample and leaves of the same developmental age (number) were pooled. These were used to obtain estimates of initial leaf area, chlorophyll content per leaf, number of cells per leaf, and chlorophyll content per cell. Leaf areas were determined by photocopying leaves, cutting out the shapes, and weighing and calculating the areas. Cell numbers per leaf were estimated using a modification of the tech-
0032-0935/80/0150/0269/$01.20
H.Y. Adamson et al. : Chloroplast Development in Tradescantia
270
a.
120 100
~. 8O Leaf2
Leaf4
Leaf3
-10 40 20 0 L~I ~D
L ~ I ~ D
L~I~D
b.
. Leaf2
Leaf3 l~__~Leaf 4 1
<
