Barley mutants

Gramine Donaxine), CjjHjgN. This substance was first found in barley mutants by von Euler and Hellstrbm, and later in Arundo donax... 

Raskin, I. Ladyman, J.A.R. (1988). Isolation and characterization of a barley mutant with abscisic-acid-insensitive stomata. Planta 173, 73-8. 

FIGURE 6. Postulated excitation energy transfer sequence between the chlorophyll-proteins of photosystem I, with low temperature fluorescence emission peaks shown. This model has proven useful in predicting and interpreting the fluorescence emission spectra of barley mutants lacking one or more of the chlorophyll-proteins of photosystem I. Thus the viridisk23 mutant fluoresces at 720 nm and completely lacks LHCI, whereas the chlorophyll b-less mutant fluorescences at 730 nm, and LHCI can be detected by immunoblotting. 

Johnson PE, Patron NJ, Bottrill AR, Dinges JR, Eahy BP, Parker 100. ML, Waite DN, Denyer K. A low-starch barley mutant, Riso... 

GS2 deficient barley mutants isolated under conditions that suppress photorespiration grow without phenotypic aberrations under nonphotorespiratory conditions (2% O2, 0.7% GO2), but mutants with less than 40% of the wild-type GS2 activity show severe phytotoxic symptoms, mainly chlorophyll destruction, when... 

A final test of the model of biexponential PSII fluorescence decay was performed using the chlorina Chi b- barley mutant. This mutant does not display the PSII-alpha/beta antenna size heterogeneity but rather has a uniform population of unconnected antennae with 50 Chi a associated with each PSII (6). In agreement with the model, at Fo we observed lifetimes of about 60 and 300 ps due to PSII and a lifetime of about 95 ps associated with PSI (data not shown). As the PSII reaction centers are closed, the amplitude of the 60 ps component decreases while the amplitude of a component with a lifetime of about 1 ns increases in a complementary fashion. All aspects of this work will be discussed more fully elsewhere. 

Thylakoids from chlorina barley mutant and its wild type were prepared as previously described (10) and resuspended in Tricine 30mM (pH 8), NaCl lOmM, MgCl 5mM, sucrose 0.2M. 

Gaussian parameters for the decomposition of the room temperature absorption spectra of chlorina barley mutant and its wild type, Iml grown peas and continuous light grown peas. 

Although immunocytochemistry and biochemical methods have shown that photosystem I is restricted to the non-appressed thylakoids, and photosystem II is mostly found in appressed thylakoids, a more precise localisation can only be made by freeze-fracture electron microscopy. The differences in composition of appressed and non-appressed regions is reflected in the marked differences in their freeze-fracture appearance. The identiGcation of these particles has been made possible by comparing the freeze-fracture ultrastructure of wild type thylakoids with that of well-characterised photosynthetic mutants. Although these differences are sometimes subtle changes in the size of a population of particles on a particular freeze-fracture face, they are mostly revealed as differences in the freeze-fracture particle density, i.e., the number of particles per nvc . Some of these are summarised for different barley mutants in Table 1. From these, and other experiments, the location of the... 

TABLE 1. Freeze-fracture particle density of some barley mutants. 

The recently isolated chlorina- mutant (15), which is chlorophyll-deficient when grown at 15 C due to the loss of much of its LHCI (and LHCII), has been shown to recover when the temperature is increased to 22 C. This is the first barley mutant in which existing tissue recovers after transfer from the restrictive temperature. This is the result of de novo synthesis and insertion of the missing chlorophyll fl/h-proteins into the thylakoid, where they become functionally associated with their respective reaction centres, as shown by the loss of the 720 nm peak, and appearance of a 740 nm peak. 

A Chi b-less barley mutant, chlorina f2, has the capability of synthesizing precursors of LHC apoproteins and assembling them into thylakoid membrane. However the mutant thylakoids contain very low levels of LHC-I and LHC-II apoproteins and one or two of major apoproteins have been reported to be missing We also showed that Chi b-less rice chlorina mutants contained mRNA for apoprotein of LHC-II. All the five proteins related to LHC-I and LHC-II are present but in reduced amounts. These observation led to a suggestion that newly synthesized apoproteins are stabilized only when they are associated with Chi b. To examine this possibility, we have measured the synthesis and turnover of the apoproteins of LHC-I and LHC-II in Chi b-less mutants of rice and barley. 

Seedlings of rice (Oryza sativa L. cultivar Norin No.8) and a Chi b-less mutant chlorina 2 derived from this cultivar, and a barley mutant (Hordeum vulgare L. chlorina f2) and a wild type strain related to chlorina f2, were grown for about 30 days in greenhouse. 

Five major apoproteins were detected in the normal strains of rice and barley. Three bands in the molecular mass region of 26 kDa, 25 kDa and 24 kDa are the apoproteins of LHC-II and two or three bands of 20-21 kDa correspond to the apoproteins of LHC-I. All the five apoproteins were detected but in reduced amounts in the rice and barley mutants (Table 1). The barley mutant was particularly deficient in the 25 kDa apoprotein . ... 

Table 1 Relative abundances of LHC apoproteins in rice and barley mutants determined on the basis of thylakoid membrane proteins.

The two Chi b-less mutants synthesized the five apoproteins as rapidly as the correspond ng wild type plants (Fig. 2). However, the accumulations of the 25 kDa apoprotein were significantly slowed down at the late stage of labelling time in rice and barley mutants. 

Of the first 31 chlorina mutants characterised in the Copenhagen mutant collection, 9 were found to be characterised by unusually high F680/F740 and Fm/Fo ratios, when examined by low temperature fluorescence emission spectroscopy and room temperature fluorescence induction kinetics (1). Of these nine, four showed these properties when grown in the glasshouse at 17°C, but not at 22°C. This paper describes one of these temperature-sensitive mutants, chlorina- y which is the first barley mutant in which mutant leaf tissue returns to normal as the result of being shifted from the restrictive temperature. 

EXPERIMENTS TO INCORPORATE IN - VITRO SYNTHESIZED PHOTOSYSTEM I COMPONENTS INTO THYLAKOIDS OF THE BARLEY MUTANT viridis - zb 3... 

We therefore choose the barley mutant viridis zb to elucidate the mechanisms governing the synthesis and/or the assembly of PSI-subunits during the greening of etiolated seedlings. 

FIGURE 1 Responses of oxygen yield r and fluorescence yield f of leaves adapted to a light intensity of lo Wm"2 (i3Hz) to an additional light of 20 Wra 2. A,B barley - vrild type C, D c hi oro phyl 1-b-1 ess barley mutant... 

Experiments with wild type and a chlorophyll b-less barley mutant are used to demonstrate that the amplitude of qNP depends upon the size and composition of the antenna. Analyses of light dosage response curves of the fluorescence yield increase induced by a single turnover flash In background continuous light of variable Intensity are used to quantitate the decrease of the relative effective absorption cross section of PS2 units associated with qNP. 

Experiments to Incorporate in-vitro Synthesized Photosystem I Components into Thylakoids of the Barley Mutant viridis - zb63 783... 

Unlike monocarbonyl compounds, j3-diketones and their hydroxylated derivatives often do not correspond to the hydrocarbons in their chain length distribution (Tulloch, 1976). This difference apparently reflects the different pathways involved in the biosynthesis of these two classes of compounds. Genetic evidence obtained with barley mutants indicates that hydrocarbons and /3-diketones are generated by two genetically distinct enzyme systems... 

The structure and composition of )3-diketones and hydroxy-/8-diketones of plant waxes strongly suggest that the latter are derived from the former. In support of this conclusion it was shown that wax of barley mutants lacking hydroxy-j8-diketones had a compensatory increase in /3-diketones (von Wettstein-Knowles, 1972). Presumably /8-diketones are hydroxylated in a manner similar to that discussed above for the synthesis of secondary alcohols from hydrocarbons. 

Alkan-2-ols (mainly C13 and C,s), thus far found frequently in plants which contain /3-diketones, are probably derived by decarboxylation of /8-keto acids followed by reduction (Fig. 15). On the basis of the composition of wax in barley mutants it has been suggested that the same /8-keto intermediate serves as a precursor of /8-diketones and alkan-2-ols (von Wettstein-Knowles, 1976). However, direct evidence for this hypothesis is not yet available. 

Ho THD, Shih S, Kleinhofs A (1980) Screening for barley mutants with altered hormone sensitivity in their aleurone layers. Plant Physiol 66 153-157 Ho THD, Nolan RC, Shute DE (1981) Characterization of a gibberellin-insensitive dwarf wheat, D 6899 Evidence for a regulatory step common to many diverse responses to gibberellins. Plant Physiol 67 1026-1031... 

Krol M, Spangfort MD, Huner NPA, Oquist G, Gustafsson P, Jansson S. Chlorophyll alb-hmdm.% proteins, pigment conversions and early light-induced proteins in a chlb-less barley mutant. Plant Physiol. 1995 107 873-883. 

P. von Wettstein-Knowles, Biosynthetic relationships between B-diketones and esterified alkan-2-ols deduced from epicuticular wax of barley mutants, Holec. gen. Genet. 144 43 (1976). 

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