Murray E. Duysen

The effect of imposed watet stress on the development and ultrastructure of wheat chloroplasts

SummaryEtiolated 6-day old wheat (Triticum aestivum L. cv. ‘Chris’) seedlings were subjected to osmotic stress by the application of polyethylene glycol 12 hours prior to exposure to continuous illumination for a 48 hours period.Stress impaired seedling growth and altered plastid development. The number of grana per plastid and the number of thylakoids per grana were significantly different in plastids from stressed and non-stressed leaves after 48 hours of development in the light. Chlorophyll production was similarly decreased in stressed leaves. After 12 hours of greening a swelling or dilation of thylakoid membranes became common. The dilation continued during the remainder of the experimental period and frequently reduced the grana and stroma thylakoid systems to a series of vesicles. There was no significant increase in the number and size of plastoglobuli as a result of the thylakoid dilation. Extensions containing crystalline-like bodies commonly developed from stressed plastids after 24 hours of greening. A reduction in both chloroplast and cytoplasmic ribosomes was noted in stressed leaves.

Electron transport and chloroplast ultrastructure of a chlorophyll deficient mutant of wheat

A non-lethal chlorophyll deficient mutation was induced by use of the chemical mutagen ethyl methanesulfonate. Chloroplasts from the control and mutant plants were found to be very similar ultrastructurally. Thylakoid membrane volume was only slightly greater in plastids from the control as compared with plastids from the mutant. The chlorophyll content of the mutant was reduced by over 60%. This decrease in chlorophyll was not accompanied by a similar decrease in electron transport. Uncoupled electron transport rate based on a unit chlorophyll basis was nearly twice as great for mutant chloroplasts as for control plastids. However, electron transport rate based on a unit membrane volume was similar in mutant and control plants. At high irradiance the relative quantum requirement of the control and mutant was similar when expressed on membrane volume.

BLUE AND WHITE LIGHT EFFECTS ON CHLOROPLAST DEVELOPMENT IN A SOYBEAN MUTANT

Phenotypic difference for chloroplast development between the normal green (CL1) and the Cy9y9 soybean mutant was observed when the plants were grown under 18W m−2 white or blue light. Under these conditions the mutant soybean accumulated less Chi b, neoxanthin, carotene and less total pigment than the CL1 genotype. Chloroplasts of the Cy9y9 line were deficient in the LHP complex relative to that of chloroplasts from the normal soybean. Specific differences were noted between chloroplasts from plants grown under blue and white light. Accumulations of a 34 kD (PSII) and a 16–17 kD (PSI) membrane polypeptide were decreased by blue light in both soybean genotypes. Blue light induced a greater accumulation of a 32 kD (PSII) polypeptide than white light. Blue light reduced granal thylakoid stacking and increased the proportion of stroma thylakoids compared to those that developed under white light. PSI electron transport activity was stimulated by the blue light treatment more than that of PSII.

Micronutrient toxicity in buffalograss

Abstract The growth responses of buffalograss [Buchloe dactyloides (Nutt.) Engelm.] to elevated micronutrient levels in the fertilizer solution were investigated. Seedling plants established in peat‐lite mix in 11‐cm (0.6 L) pots in the greenhouse were irrigated with solutions containing 0.5, 1, 2, 4, 6, 8, or 12 mM of boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), or zinc (Zn). The control solution contained (in μM): 20 B, 0.5 Cu, 40 Fe, 10 Mn, 0.5 Mo, and 4 Zn. A standard macronutrient concentration was used for all treatment solutions. Boron and Mo induced visual toxicity symptoms more readily than other micronutrients. Boron toxicity was characterized by chlorosis often accompanied by bleached leaf tips, while Mo toxicity resulted in leaf necrosis. The lowest levels that induced visual foliar toxicity were 0.5 mM B, 2 mM Cu, 4 mM Fe, 6 mM Mn, 1 mM Mo, and 4 mM Zn. Chloride did not induce foliar abnormalities in the concentration range tested. Biomass yield was reduc...

Chloramphenicol effects on chlorophyll degradation and photosystem I assembly in the chlorina CD3 wheat mutant

We previously reported that applications of chloramphenicol to the chlorina wheat mutant, CD3, decreased the leaf Chl a/b ratio and enhanced accumulations of LHC proteins and LHC complexes during greening (Duysen et al. 1985). We have now examined Chl degradation and the change in Chl a/b ratios in wheat leaves kept in the dark as a measure of LHC destruction. Chl b was stable in chloroplasts of the CD3 wheat kept in darkness up to 5 days. Chloramphenicol significantly increased Chl b accumulations and impaired Chl a degradation in both CD3 mutant and normal wheat relative to untreated plants. Our Chl data suggest that the chloramphenicol induced accumulation of the LHC complex in the mutant wheat results from enhanced processing of LHC into the membrane rather than impairment of LHC degradation. The photosystem I (PSI) fraction of the CD3 wheat mutant was examined relative to that of normal wheat after 3 days greening. PSI was deficient in 25, 26, 26.5 kD LHCI protein in the mutant but both wheats accumulated low quantities of the 27–29 kD LHCII protein as detected by Western blot analysis. Chloramphenicol enhanced accumulations of several LHCI proteins primarily near 25 kD in the mutant and the 27–29 kD LHCII protein in normal wheat. The fluorescence emission and absorbance spectra suggest that chloramphenicol enhances accumulations of dissociated LHC in the PSI preparation of normal and CD3 mutant wheat.

The significance of protein synthesis early in the etioplast to chloroplast conversion of wheat leaves as demonstrated by cycloheximide treatment

SummaryCycloheximide (CH) at 5, 7, or 10 μg/ml altered plastid ultrastructure and pigment synthesis when applied to etiolated wheat tissue. CH at 5 μg/ml reduced the number of thylakoid membranes/granum but had little effect on the number of grana/plastid section or on plastid length. At 7 μg/ml, CH prevented normal conversion of etioplast to chloroplast during a 20 hour greening period but did not completely block the breakdown of the prolamellar body or membrane formation. A 4 hour light exposure prior to treatment was not adequate to stimulate normal chloroplast differentiation. A 10 hour greening period prior to treatment with 10 μg/ml CH permitted near normal chloroplast development. Chloroplast developed under these conditions possessed fewer grana/plastid section 3and fewer membranes/granum as compared with the controls. CH did not prevent the formation of crystalline prolamellar bodies during the 7.5 hour dark period following a 10 hour pre-light period nor did CH prevent the conversion of the prolamellar body to chloroplast membranes during a second greening period. Proteins synthesized on cytoplasmic ribosomes were required for chlorophyll and carotenoid synthesis, membrane formation and grana development associated with the conversion of etioplasts to chloroplasts in wheat. The CH block occurs early in greening (10 hours) and CH has minor effects on granal stacking and formation beyond the initial 10 hour light period.

A Chlorophyll B Deficient Mutant of Wheat with an Altered Photoadaptation Response

Chloroplasts of higher plants and algae are not static structures, but respond to varying environmental conditions with a high degree of plasticity. Variation is seen not only between sun and shade adapted plant species, but also within a single species grown under light regimes differing in quality and quantity (1,2). This process of photoadaptation, which results in maximal photosynthetic efficiency for a given light regime, involves both short term regulatory mechanisms, such as the state1-state2 transition, and long term alterations in thylakoid membrane structure, composition, and function. In general, high light-adapted plants show decreased thylakoid stacking, decreased photosynthetic unit sizes, increased chl a/b ratios, and higher maximal rates of photosynthetic electron transport than do low light-adapted plants.