Effects of Red, Far Red, and Blue Light on Enhancement of Nitrate Reductase Activity and on Nitrate Uptake in Etiolated Rice Seedlings

Abstract

The effects of red (R), far red (FR), or blue light (B) on the enhancement of nitrate reductase (NR) activity and on nitrate uptake in etiolated rice seedlings were examined. On 5-minute ilumination foUowed by 12-hour dark, R caused marked increase of NR activity, but FR and B caused only slight increase. Illumination with 560 ergs per square centimeter per second of R for 5 minutes caused maximal increase. The effect of R was almost completely counteracted by subsequent illumination with 2,000 ergs per square centimeter per second of FR for 10 minutes, indicating that NR induction was mediated by phytochrome. Exogenous supply of inducer nitrate was not required during the 5-minute illumination and the R-FR cycles, if the seedlings were transferred to nitrate solution at the beginning of the dark incubation. NR activity in the shoots was found high when shoots were illuminated but was low when only roots were illuminated. On continuous illumination for 12 hours, B had more effect on NR increase than R.Nitrate uptake during 6-hour dark was not increased by exposure to R, FR, or B for 5 minutes at the beginning. On continuous illumination for 6 hours, R slightly increased nitrate uptake, whereas FR and B had no effect.NR' activity in green leaves is known to be increased by light (3,6,18,21); the light energy transformed to chemical energy by photosynthesis is used in induction of NR (1,5,15,16 MATERIALS AND METHODSRice seeds (Oryza saliva var. Nihonbare) were sterilized by treatment with 70o alcohol for 5 min and then with saturated bleaching powder solution for 30 min. The seeds were rinsed with running tap water and allowed to germinate for 48 h in the dark at 30 C. Seedlings of nearly uniform size were selected and transplanted onto a Saran net floating on tap water in a pot. The pot was placed in a zinc box with a lid. The box was covered with light-proof cloth and placed in a dark room at 28 C for 6 days.Six-day-old seedlings were collected in a beaker and washed thoroughly with several changes of distilled H20 under dim green light. Root portions of groups of 20 seedlings were then soaked in distilled H20 in 125-ml Erlenmeyer flasks. The flasks were covered with aluminum foil and only the shoots were exposed to R, FR, B, or R-FR cycles. For exposing only the roots to light (Table II), the shoots were covered with aluminum foil. After illumination as indicated, seedlings were transferred to other Erlenmeyer flasks containing 120 ml of 10 mm KNO3. The flasks were placed in a zinc box covered with light-proof cloth and incubated for 12 h at 28 C. When the seedlings were exposed to light continuously or intermittently, they were soaked in 120 ml of KNO3 before illumination and left in the irradiation box for 12 h at 28 C.A dim green safelight was obtained from one 10-w fluorescent

Growth of rice plants under red light with or without supplemental blue light

“…Promotion of the uptake and/or reduction of N by supplemental blue light might have occurred, and may be related to the enhancement of the photosynthetic rate per leaf area. For example, general responses, such as promotion of stomatal opening (Sharkey and Raschke 1981) and the activity of nitrate reductase (Jones and Sheard 1977, Sasakawa and Yamamoto 1979), observed under blue‐light conditions may be related to the promotion of the uptake and/or reduction of N in rice plants grown under RB conditions.…”

Effects of NO (+ NO2) pollution on growth, nitrate reductase activities and associated protein contents in glasshouse lettuce grown hydroponically in winter with CO2 enrichment

“…!owed a pattern w!iic!i has been observed in other plant species (Me!zer et al, 1989;Bowsher et al, 1991: Becker et al, 1992. Tliese enhanced NaR activities are induced by red !ight and repressed by far-red !ight (Sasakawa & Yamamoto, 1979;Rajasekhar, Gowri & Campbe! !, 1988) which imp!ies the involvement of phytoc!irome.…”

Light Regulation of Nitrate uptake, Assimilation and Metabolism

“…Spirodela polyrhiza (Lemnaceae), a moncot water-plant, has been much used for studying nitrogen metabolism in relation to phytochrome; however, no influence on nitrate uptake by the phytochrome system was found (Appenroth et al 1992). The literature gives very little information on phytochrome effects on nitrate uptake in higher plants, and when examined generally no or very small effects on nitrate uptake as influenced by the phytochrome system have been found (Sasakawa and Yamamoto 1979). Interestingly, oligonucleotide arrays revealed a nitrate transporter gene regulated by PHYA in Arabidopsis.…”

“…In higher plants, i.e. rice seedling, different light qualities, including blue light, were tested, but neither 5 min nor 6 h illumination with blue light stimulated nitrate uptake (Sasakawa and Yamamoto 1979).…”