Chloroplast Reactions of Photosynthetic Mutants in Zea mays

Abstract

Three seedling lethal mutants of Zea mays with impaired photosynthesis are described. These recessive mutants were selected on the basis of high chlorophyll fluorescence. They have normal chlorophyll pigmentation but are unable to fiX C02 fully. Evidence is presented from fluorescence characteristics of isolated chloroplasts that both photosystem I and II mutants were isolated. Using conventional measures of photosynthetic electron transport, we suggest that the photosystem I mutant has limited ability to reduce NADP. The other two mutants are clearly blocked in photosystem II, one possibly lacking the primary electron acceptor.The use of genetic mutants is an indispensable tool in the study of complex biochemical reactions. This approach for gaining insight into the mechanism of the photosynthetic process has been successfully employed, most notably by Levine (13) with Chlamydomonas and by Bishop (6) with Scenedesmus. However, very little work has been done using genetic mutants of higher plants (14). Most of the work with higher plants has involved mutants selected on the basis of pigment abnormality. A mutant of Vicia faba which appears to be inhibited in the ferredoxin-NADP oxidoreductase has been described (11). Homann and Schmid (12) have reported a mutant of Nicotiana which lacks Hill activity and a series of mutant Oenothera were reported (8) which resulted in blocks of either photosystem I or II. These-were the major photosynthetic mutants reported in higher plants and all showed some degree of pigment and structure abnormalities.Following the development of an acceptable screening technique for selection of mutants in higher plants (20), we have isolated a number of full green photosynthetic mutants of maize and here report on the characterization of three such mutants. MATERIALS AND METHODSPlant Material. Maize seedlings were grown to the three leaf stage (about 10 days) in a controlled environment chamber. They were subject to 14 hr of light at 30 C and 10 hr of darkness at 25 C. Light was provided by fluorescent (coolwhite type) and incandescent lamps at an intensity of 5 X 104 ergs cm-2 sec'1. Kernels were germinated and grown in vermiculite contained in 7-X 38-cm plastic trays. Plants were provided with a nutrient solution (Ortho 12-6-6) weekly. The maize stocks used were from lines treated with the mutagen EMS2, and most were previously selected as necrotic or seedling lethal. The method of mutant induction and the genetic handlings of the material have been described by Neuffer (22). Briefly, it consists of treating pollen with mutagen, pollinating, selfing all the progeny of treated plants to make any mutation homozygous, and examining the resulting plants.Mutant Selection. Suspected mutant plants from the above maize stocks were screened for inactivation of photosynthesis by a technique described elsewhere (20). The procedure is a modification of that used for green algae (4, 9), and selects for plants with abnormally high Chl fluorescence.Chloroplast Isolation. Twice-washed leaves o...

tie-dyed1Functions Non-Cell Autonomously to Control Carbohydrate Accumulation in Maize Leaves

“…4I) yet increased chlorophyll autofluorescence (Fig. 4J) similar to some high-chlorophyll fluorescence mutants (Miles and Daniel, 1974). Yg-str* pale-green mutant tissues do not accumulate starch (Fig.…”

Characterization of Three Photosystem II Mutants in Zea mays L. Lacking a 32,000 Dalton Lamellar Polypeptide

“…Recently, a large collection of photosynthesis mutants was obtained in Zea mays (28) using elevated levels of Chl fluorescence to screen specifically for mutants blocked in photosynthesis (29). By employing this technique, both fully green and yellow-green nuclear mutants with blocks in electron transport, photophosphorylation, and dark reactions have been identified (26,28).The present study describes the characteristics of three nuclear photosynthesis mutants in maize. Two of these mutants, hcf*-33 and hcf*-19G, are fully blocked in PSII, whereas a third mutant, hcf*-19YG, is partially blocked in PSII.…”

“…To date, most higher plant photosynthesis mutants are characterized by gross pigment losses which are often accompanied by major alterations in thylakoid membrane morphology and the loss of many lamellar polypeptides (9,15,36,37). Recently, a large collection of photosynthesis mutants was obtained in Zea mays (28) using elevated levels of Chl fluorescence to screen specifically for mutants blocked in photosynthesis (29). By employing this technique, both fully green and yellow-green nuclear mutants with blocks in electron transport, photophosphorylation, and dark reactions have been identified (26,28).…”

“…Recently, a large collection of photosynthesis mutants was obtained in Zea mays (28) using elevated levels of Chl fluorescence to screen specifically for mutants blocked in photosynthesis (29). By employing this technique, both fully green and yellow-green nuclear mutants with blocks in electron transport, photophosphorylation, and dark reactions have been identified (26,28).…”

Characterization of Two Photosynthetic Mutants of Maize1

“…Any limitations in photosynthetic electron transport result in the increased loss of absorbed light through fluorescence. The first hcf mutants were isolated in 1972 (Miles and Daniel, 1974), and over 100 mutants have been isolated since then (Miles, 1994).…”