Chloroplast Development in 4-Chloro-5-(dimethylamino)-2-(α,α,α-trifluoro-m-tolyl)-3 (2H)-pyridazinone (Sandoz 6706)-treated Wheat Seedlings

Abstract

The first visible effect following the application of sublethal doses of 4-chloro-5-(dimethylamino)-2-(a ,a,a-trifluoro-mtolyl)-3(2H)-pyridazinone (hereafter referred to as 6706, manufacturer's code number) to germinating wheat grains was the formation of albinistic seedlings. These seedlings grew and developed as well as untreated seedlings for 9 days. Hilton et al. (12) studied the effect of 6706 on established green leaves and meristematic tissues of several different species. They found that Hill reaction and CO2 fixation were inhibited in green leaves and that chloroplast development was blocked in embryonic cells.The action of 6706 on wheat seedlings grown under high light intensities appears to be similar to that of 3-amino-s-triazole (4) and of 3,4-dichlorobenzylmethylcarbamate (5). These herbicides cause the loss of grana-fret membranes and chloroplast ribosomes. Burns et al. (9) suggested that the mode of action of these herbicides was the inhibition of carotenoid synthesis. We investigated the effect of 6706 on the ultrastructure, ribosome, and pigment composition of the aberrant plastids of wheat seedlings which were grown in dark only, light only, or dark followed by light.MATERILIS AND METHODS Wheat seedlings (Triticum vulgare L. var. Maricopa) were germinated and grown in Petri dishes (15 grains per dish) containing either 10 ml of 0.1 mi 6706 or distilled water, under one of the following conditions: (a) 6 days in light at 1 ft-c, or 1500 ft-c, 16-hr photoperiod, 21 C; (b) 6 days in darkness except for exposure to dim green light during watering, 23 C; or (c) 6 days in darkness followed by 1, 4, or 12 hr of light. The light intensity used during greening was either 1 ft-c, 75 ft-c, or 1500 ft-c, 23 C. Following germination, plants were watered with distilled water. On the 6th day shoots were harvested, weighed, and prepared for either ultrastructural, sedimentation, or pigment studies.Sedimentation and ultrastructural studies were performed as discribed in an earlier publication (5) except that (a) grinding media used to isolate ribosomes contained 4% Triton X-100 (Rohm and Haas, Philadelphia) and (b) fixing solutions used in electron microscope preparations contained 0.01 M cacodylate-HCI buffer (pH 7.2) instead of phosphate buffer.

Photooxidative Destruction of Chloroplasts and Its Effect on Nuclear Gene Expression and Extraplastidic Enzyme Levels *

“…of unprotected Chl is high enough, the entire plastidic compartment can be destroyed under appropriate light conditions and only small chlorophyll-free rudiments without detectable internal structure remain (Bachmann et al, 1967;Troxler et al, 1969;Bartels and Hyde, 1970;Reiss ef al., 1983: Oelmiiller et al, 1986bSimpson et al, 1986a;Schuster et al, 1988b).…”

Light Effects on Several Chloroplast Components in Norflurazon-Treated Pea Seedlings

“…' In plants lacking carotenoids, as a result of nuclear mutation or herbicide treatment, under high light growth conditions plastids are arrested at a rudimentary stage in development (4). By contrast, in low fluence-rate light, carotenoid-deficient chloroplasts develop normally and are similar to plastids from normal plants grown under low light (5,6,42). mRNAs coding for Cab failed to accumulate in high light-grown, carotenoid-deficient plants.…”

The Fate of Chloroplast Proteins during Photooxidation in Carotenoid-Deficient Maize Leaves

“…The most dramatic effect is that Chl fails to accumulate due to rapid photooxidation, resulting in albino seedlings which are incapable of photoautotrophic growth (1,6). Herbicides which block the accumulation of colored carotenoids exhibit phenotypes very similar to those of the nuclear albino mutants (23).…”

“…Although the structural and functional roles of plastid carotenoids are not well understood, their importance in protecting Chl in which photooxidation is minimized, can accumulate low levels of Chl (6,15). Under either low-fluence or far-red growth conditions, chloroplast development appears normal, with carotenoid-deficient chloroplasts showing the ultrastructure typical of normal chloroplasts grown in low light (5,18,30).…”