Dark-grown maize

Fig. 7. Time course of development of osmotic responsiveness by plastid membranes from dark-grown maize after continuous illumination. (From Forger and Bogorad )...

Fig. 8. Relationship of development of A/B phosphorylation and osmotic responsiveness during continuous illumination of dark-grown maize. (From Forger and Bogorad. ")...

The independence of the development of A/B phosphorylation capacity from the accumulation of chlorophyll can be shown more easily and dramatically. Figure 9 shows the courses of development of A/B phos-phorylating capacity and of chlorophyll accumulation in dark-grown maize exposed to light for 1 min and then returned to darkness. A/B activity rises for about 8-10 h after plants have been returned to darkness. On the other hand, chlorophyll accumulation continues for only about 2-4 h following brief exposure. Again, these two processes appear to be independent. Chlorophyll is not filling the holes. 

Table V. The Cumulative Effect of Short Exposures to Light on Pigment Content and A/B Phosphorylation Capacity of Dark-Grown Maize Leaves...

Fig. 7. Profiles of 254 m/i absorption and i-adioaclivity ( P) in a 10-34 sucrose gradient of ribosomes and pol)ribosoines from plastids (unwashed 1000 g pellets) of illuminated and unilluminated dark-grown maize. Twenty grams of leaves which had absorbed 0.04 mC P-phosphate in darkness were used for each preparation. Upper and center panels are from identically treated leaf material, but preparation 60 min Light-f RNase was incubated with 3 ng (3.7 /ig/ml) of RNase for 5 minutes at room temperature before centrifugation through the sucrose gradient.

Eleven-day-old dark-grown maize plants were used. Sixty-seven grams of leaf tissue was used for each preparation. Each set was permitted to absorb 0.4 mC T-phosphate. Preparation and sucrose density gradient centrifugation were as described for Twice washed 1000 g pellet, Fig. 6. 

Fig. 9. Titration of plastid RNA pol)merase from illuminated and unillumi-nated dark-grown maize leaves with calf thymus DNA.

The data presented here show that shortly after etiolated leaves have been illuminated, the rate of synthesis of plastid RNA and certain plastid enzymes increases. Mego and Jagendorf (1961) found that the protein content per plastid increases markedly as etiolated bean leaves become green. Williams and Novelli (1964) found ribosomes of illuminated leaves from dark-grown maize to be more active than ribosomes from unilluminated leaves in the in capacity to incorporate amino acids into trichloroacetic acid-insoluble materials, but the increased activity could be detected only after a few hours of illumination or after 1 hour in the light followed by 1 hour of darkness. Thus,... 

The regulation of the appearance of the 66 kDa polypeptides may take place at a post-transcriptional step. In maize, transcripts of the two genes, psaA and psaB, are present in dark-grown plants [90], and therefore, if maize does not accumulate 66 kDa polypeptides in the dark, there must be some mechanism to prevent translation of the mRNA or to degrade newly synthesized polypeptides. There is no information on the transcripts for other polypeptides of PS I in dark-grown plants. 

Figure 6. Increased extractable PAL in maize roots caused by root-feeding of glyphosate to intact plants (39). Dark-grown, 3-day-old maize seedlings were transferred to 1 mM glyphosate (%), or water (O) and enzyme activity was monitored over a 3-day time course during dark growth.

Experiments described from this laboratory were done using 3-day-old light-grown or dark-grown seedlings of the maize cultivar Merit. The seedlings were raised as described in [20]. 

Fig. 2. A proplastid in a dark-grown (etiolated) maize leaf. Fixation and staining as for section shown in Fig. 1. Many ribosomes are seen (e.g., R regions). PB, prolamellar body. Strands of DNA are seen in the clear areas below each D not all sites of DNA are marked.

Allosteric mutants have been found for C. reinhardtii and for maize endosperm. A significant finding was made by Ball et al. who isolated a starch-deficient mutant of C. reinhardtii having an ADP-Glc PPase, which could not be effectively activated by 3-PGA. The inhibition by P was similar to the wild type. The starch deficiency was observed in the mutant whether the organism was grown photoautotrophically with CO2 or in the dark with acetate as the carbon source. Thus, the allosteric mechanism seems to be operative for photosynthetic or nonphotosynthetic starch biosynthesis. 

Temperature treatment Maize seedlings were grown at 24 and a PPFD 350 umol photons m (16 h/day) for ten days. Plants were shifted ftom dark to 5 350 umol m s for six hours,... 

Maize (Zea mays L. CV. COl) s eds were grown in soil-filled plastic trays in dark for 2 days. The pots were then transferred to continuous illumination (55p mol m S " ) at 28 2°C. After 7 days of growth/ 15 segments/ each measuring 1 cm X 3 cm, were excised from the second leaf and incubated on 4 layers of moist filter papers at 28 2 C. Detached leaf segments were allowed to age for 3 days. The leaf segments in separate petridishes were irradiated with either philips... 

Zucchini hypocotyls (Cucurbitapepo, var. All Green Bush) were grown for 5 days in the dark at 25 C or 7 days in white light (14 h/day) maize coleoptiles Zea mays var. Caldera 535) were grown for 5 days in the dark pea plants (Pisum sativum var. Alderman, a kind gift of Dr D.A. Morris) were grown in the light for 21 days and second internodes harvested for use. 

Plant material. Maize (Zea mays L., INRA cv LG 11) seeds were germinated and grown in moist vermiculite in the dark at 25 C. The vermiculite was daily soaked with 0.5 litre with or without (R,S)-fenpropimorph (20 mg/1). Roots were excised after 7 days. 

Fig. 1. Electron micrograph of chloroplast in thin section. The chloroplast shown is of a maize plant grown in the dark and exposed to light for 16 h. The leaf tissue was fixed with glutaraldehyde and osmium and was post-stained with uranyl acetate. Many grana can be seen.

Fig. 1. A section through a chloroplast of a leaf of a maize plant grown in darkness and then exposed to light for 16 hours. Fixation glutaraldehyde-osmium. Post-stain uranyl acetate. Ribosomes (R) are seen in and outside of chloroplast s small densely stained particles. G, one of the many grana.

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