Photocontrol of Anthocyanin Synthesis in Milo Seedlings

Abstract

Prolonged irradiation at moderately high intensities is a requirement for anthocyanin synthesis in many plants. Action spectra for anthocyanin formation, however, are different for nearly every species examined (1,5,6,7,9). In general, a maximum is present between 400 and 500 mg (blue) or one between 400 and 500 m, and another between 600 and 800 myi (blue & red). In some species a second controlling photoreaction which requires brief irradiances at relatively low intensities is present (1, 6). The latter exhibits all the characteristics of phytochrome (4) with a promotive action on anthocyanin production by the red region of the spectrum (600-700 me) that is reversed by far red (700-800 miL).A somewhat more responsive and experimentally convenient plant than the species previously used was desired to facilitate work on anthocyanin and examination of the photoreactions involved. Sorghum seedlings attracted attention because of marked reddening of the plants at an early stage of growth. Preliminary experiments showed that seedlings of many varieties of sorghum produced a great deal of anthocyanin. The availability of large lots of seeds of Wheatland milo (Sorghum vulgare Pers.) prompted its selection for further studies, some results of which are described herein. Materials & MethodsSeeds of Wheatland milo were germinated in darkness on 8-mesh stainless-steel screens immersed in aerated tap water. Temperatures of 25 to 26 C during germination and subsequent shoot growth produced seedlings of adequate size in 3Y2 to 4 days.The temperature during the treatments and during the post-treatment incubation period was maintained at 20 C. When intact seedlings were placed in petri dishes the root tended to lift the shoot away from the substrate. Excising the roots resulted in no measurable effect on the amount of anthocyanin produced in the internode so long as the seed remained attached to the shoot. Therefore, the standard procedure was to remove the roots prior to treatment. The intact shoots with seeds attached were placed on water-soaked filter paper in petri dishes or plastic boxes. These shoots were exposed to various light Received June 16, 1962. 25 regimes, then harvested immediately or after a period of incubation in complete darkness. When a darkincubation period was used, the seedlings were generally harvested 24 hours after the beginning of the light treatments. In this way the total time allowed for anthocyanin synthesis was kept constant irrespective of the duration of the light period. Experimental evidence indicated that with light periods up to 9 hours, dark-incubation periods of 24 hours produced only about 15 % more anthocyanin than was formed with dark-incubation periods of 15 hours. At the conclusion of the experiment the seed and the coleoptile were discarded and the first internode was cut into small segments. Usually, five first internodes were extracted in 5 milliliters of 1 % HCl methanol and held 24 hours at 5 C. Anthocyanin content was determined from absorbancy values (1 = 1 centimeter) at...

Regulatory Mechanisms in Anthocyanin Biosynthesis in First Internodes of Sorghum vulgare: Effect of Presumed Inhibitors of Protein Synthesis

“…The internal concentration at the site of action is n'ot known, but it is probably less than in the external solution. Factors of penetration and problems of degradation could also account for the higher concentrations required (26 (4,20) others implicate one of them in a role in gene activation (9). The inhibitor data reported here stuggest that nucleic acid (mRNA) as well as protein synthesis are necessary for cyanidin biosynthesis in Sorghum.…”

“…The inhibitor data reported here stuggest that nucleic acid (mRNA) as well as protein synthesis are necessary for cyanidin biosynthesis in Sorghum. If the photoreactions control specific enzyme syntheses (17), the varied limiting factors cited in anthocyanin biosynthesis (4,20,23,25) cotuld be explained on a common basis. But it is difficult as yet to differentiate between cause and effect, and more precise information awaits the demonstration of flavonoid biosynthesis from C, and C., prectursors in cell-free preparations.…”

“…apigeninidin, while light accelerated the production of luteolinidin and was an obligatory requirement for the third type, cyanidin (4,23).…”

Photocontrol of Anthocyanin Synthesis

“…There are some points that are seldom mentioned when the data of the action spectroscopy studies are used in discussions 1 Research partially supported by a National Science Foundation Grant, PCM76-80932, to A. L. M.…”

“…As an example, consider the differences in the spectral sensitivity of anthocyanin synthesis in young seedlings: BL2 is the only effective region in sorghum (2); BL and FR are about equally effective in mustard (17); FR is more effective than BL in turnip (13); and BL is more effective than FR in tomato (11). The causes of these differences are still poorly understood and are partly responsible for the state of uncertainty about the nature of the HIR photoreceptor (9, 15).There are some points that are seldom mentioned when the data of the action spectroscopy studies are used in discussions 1 Research partially supported by a National Science Foundation Grant, PCM76-80932, to A. L. M.2 Abbreviations: BCJ: incandescent lamps with an integral dark red filter, having a cut-off at about 650 nm; BL: blue; R: red; FR: far red; W: white; HIR: high irradiance response; P: total phytochrome = Pr + Pfr, TD: total duration of exposure.about the possible identity of the HIR photoreceptor. (a) The experimental conditions (length, irradiance and mode of application of the light treatments, temperature, age of the system) used in different studies vary quite widely, as shown by the short list given in Table I.…”