Grana Formation Research Articles

Greening of Etiolated Bean Leaves in Far Red Light

Eight-day-old dark-grown bean leaves were greened by prolonged irradiation with far red light. Growth, chlorophyll content, oxygen-evolving capacity, photophosphorylation capacity, chloroplast structure (by electron microscopy), and in vivo forms of chlorophyll (by low temperature absorption and derivative spectroscopy on intact leaves) were followed during the greening process. Chlorophyll a accumulated slowly but continuously during the 7 days of the experiment (each day consisted of 12 hours of far red light and 12 hours of darkness). Chlorophyll b was not detected until the 5th day. The capacity for oxygen evolution and photophosphorylation began at about the 2nd day. Electron microscopy showed little formation of grana during the 7 days but rather unfused stacks of primary thylakoids. The thylakoids would fuse to give grana if the leaves were placed subsequently in white light. The low temperature spectroscopy of intact leaves showed that the chlorophyll a was differentiated into three forms with absorption maxima near 670, 677, and 683 nanometers at -196 C during the first few hours and that these forms accumulated throughout the greening process. Small amounts of two longer wavelength forms with maxima near 690 and 698 nanometers appeared at about the same time as photosynthetic activity.

Formation of Chlorophyll b, and the Fluorescence Properties and Photochemical Activities of Isolated Plastids from Greening Pea Seedlings

Chlorophyll b was first detectable after 10 minutes of illumination of etiolated pea seedlings (Pisum sativum L. var Greenfeast) with continuous white light. The chlorophyll a/b ratio decreased from 300 at 10 minutes to 15 after 1 hour. There was little change in the chlorophyll a/b ratio between 1 and 2 hours, and it declined to 3 between 2 and 5 hours of illumination. In red light, the time courses of total chlorophyll synthesis and chlorophyll a/b ratio were similar to those in white light for the first 5 hours of illumination. But with increasing time of illumination with red light, there was an increase in the chlorophyll a/b ratio to 7 after 30 hours. Illumination with white light of very low intensity also gave high chlorophyll a/b ratios. Seedlings which had been illuminated for varying periods and then returned to darkness always showed an increase in chlorophyll a/b ratio during the dark period. It is concluded that the synthesis of chlorophyll b is controlled by light.The onset of the transfer of excitation energy from carotenoids to chlorophyll a correlated with the appearance of chlorophyll b. The detection of chlorophyll b and the onset of energy transfer from carotenoids to chlorophyll a preceded by several hours the appearance of Hill activity in the isolated pea plastids. The detection of the large fluorescence emission band at 735 nm at 77 K also preceded the observation of Hill activity, but it correlated with the phase of rapid chlorophyll synthesis. There was a good correlation between Hill activity and the formation of grana. The fluorescence kinetics which are characteristic of mature chloroplasts appeared considerably later than grana or the observation of Hill activity.It is concluded that the formation of photosynthetic membranes and the assembly of the photosystems is not a single step process, at least in the initial stages of chloroplast development from the etioplast.

Effects of Pyrazon on Bean Chloroplast Ultrastructure

The fine structure of the chloroplasts of bean(Phaseolus vulgarisL., var. Tendercrop) was grossly altered by treatment with 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) when plants were grown in a treated medium. Alterations occurred first at the leaf margins and preceded visual symptoms. Chloroplasts became spherical and swollen rather than discoid, clumped rather than peripherally arranged, and were totally devoid of starch. Grana formation was inhibited; the thylakoids became swollen and perforated, and they ultimately disintegrated. Concomitant with grana inhibition was the increase in size and number of lipid globules. Occasional breakage of the outer chloroplast membrane was observed. It is proposed that these changes result because pyrazon inhibits thylakoid structural protein formation.

Formation of the Prolamellar Body in 8-Day, Dark-Grown Seedlings

The development of the prolamellar body in etioplasts of dark-grown seedlings of Phaseolus vulgaris is followed through the 8th day. From 2 to 6 days there is an increase in plastid size and starch content and synthesis of a system of porous lamellae which appear to arise, as such, from the inner component of the plastid envelope. From 6 to 8 days much of the starch disappears accompanied by rapid membrane synthesis resulting in an extensive prolamellar body. A model of the prolamellar body is discussed in which the basic structural unit is a six-pointed star with four tubules joining at each node. Observation of face views of the porous peripheral lamellae at their juncture with the prolamellar body suggests the origin of the prolamellar body by the continued contraction of the porous lamellae and the formation of interconnecting tubules between adjacent lamellae. The pores of the peripheral lamellae appear to correspond to the areas of stroma within each star module. Short lengths of membranes of individual peripheral lamellae fuse, forming short overlaps which resemble small, two-compartmented grana. It is postulated that this is the initial step in grana formation.

The effects of inhibitors of protein synthesis on the differentiation of plastids in etiolated bean seedlings

It has been shown that inhibitors of protein synthesis do not influence the breakdown of the crystal-lattice-like structure of the prolamellar bodies in the plastids when etiolated plants are exposed to light. The formation of grana and the greening of leaves are however considerably inhibited, depending on the concentration of the inhibitor used.

Submicroscopic Structure and Development of the Chloroplasts of <i>Funaria hygrometrica</i> and <i>Bryum</i> sp

Freshly collected specimens of Bryum sp. (gametophyte) and Funaria hygrometrica (gametophtye and sporophyte) were used for the study of the fine structure and development of chloroplasts. The fully-developed chloro-plasts of both species are ellipsoidal. The chloroplasts are bounded by a well-defined dense membrane. The laminar systems within the chloroplasts have their double closed lamellae or discs arranged into stacks or grana. The stroma lamellae are merely extensions of grana discs which form some sort of a continuity between the grana. In general, the stacks of Funaria chloroplasts are more compact than those of Bryum. Osmiophilic globules occur in the chloroplasts of both species.The development of chloroplasts of both species may be summarized as follows:1. In the proplastids, vesicles and osmiophilic globules cccur.2. The lamellae are formed locally by fusion of the vesicles.3. The number of lamellae increased with size of the chloroplasts, and the lamellae form closed double membranes or discs.4. The discs become arranged into stacks which indicate grana formation.5. Osmiophilic globules are present at all stages and show an increase in size with the advance of development.

Submicroscopic structure and development of the chloroplasts of Cibotium chamissoi

Embryonic and mature leaves of Cibotium chamissoi were used for the study of the fine structure and the development of chloroplasts. The chloroplasts of Cibotium are spherical in cross-section, about from 0.5 to 0.8 μ in diameter, and more or less elliptical in outline, when cut obliquely. They are bounded by a well-defined outer membrane. The grana are distributed more or less uniformly throughout the chloroplast, except in those instances in which an irregular peripheral zone is devoid of grana. The grana are randomly oriented between the stroma lamellae. The thickness of the lamellae within the grana was measured about 95 å. At the boundary of the grana, an osmiophilic substance is present. In addition to this substance, relatively large osmiophilic globules also occur in the stroma. From various stages of developing leaves, the following stages of developing chloroplasts were found: 1. (a) The first ultrastructure to be seen within the proplastids are vesicles. In most cases they also contain osmiophilic globules. A dense margin indicates a membrane. 2. (b) The lamellae layers are formed locally by the fusion of the vesicles. 3. (c) The number of lamellae layers increased with size of the chloroplasts. 4. (d) Within the plastids, lamellae appear in bundles, which indicate the grana formation. Lamellated grana are connected by the stroma lamellae, which are less numerous.

Grana formation and synthesis of chloroplastic proteins induced by light in portions of etiolated leaves

A comparison between plastids from etiolated and green leaves with the electron microscope shows a radically different structure in these two types of particles. The leucoplasts do not contain grana; they show a finely granular structure. They are smaller than chloroplasts. By simply exposing to light fragments of etiolated leaves, the transformation of leucoplasts into normal characteristic chloroplasts is induced within a few hours. This transformation is accompanied by a significant net synthesis of chloroplastic proteins that occur at the expense of free amino compounds of which etiolated leaves contain a considerable reserve.