Mutants of barley heat-sensitive for chloroplast development

Abstract

Six nuclear gene mutants of barley, heat-sensitive for chloroplast development, are described. These conditional lethal mutants in six different genes can be grown as homozygous viable plants in the field, their mutant phenotype only being expressed with development at high temperature. Chlorophyll accumulation in the mutants but not in the wild type is inhibited by a growth temperature of 310C. The degree of temperature sensitivity varies amongst the mutants. For example, partial inhibition of chlorophyll production is evident in the mutant vir-zf is4 above 20 ~ while inhibition is complete at a growth temperature of 29 ~ The mutant vir-zi ts49 remains green at 29 ~ but is bleached at 31 ~ The reduction in chlorophyll content of the leaves at high growth temperatures is accompanied by the appearances of structural abnormalities in the chloroplasts and reduced photochemical activity per mg chlorophyll. The inhibitory effect of elevated temperatures is confined to some early stage of plastid development as the light-dependent conversion of ctioplasts into chloroplasts in the mutants is not inhibited at 32 ~ Leaf elongation in the mutants compared with the wild type is not affected by high growth temperatures. When the mutants are grown at temperatures permitting normal chlorophyll accumulation, the chloroplast thylakoid membranes appear to be no less heat stable than in the wild type.

A Temperature-Sensitive Chlorophyll b-Deficient Mutant of Sweetclover (Melilotus alba)

“…Smillie et al (29) described a number of temperaturesensitive, recessive nuclear gene viridis mutants. The mutant phenotype was expressed at high as well as low temperatures and resulted in pale yellow and pale green plants.…”

Plastid Replication and Development in the Life Cycle of Higher Plants

“…The formation of ribosomal RNA of plastids is known to be reduced to low levels at elevated (32 to 34°C) temperatures in a number of plants including rye, oat, wheat, barley, and bean (20). The activity of a number of chloroplast enzymes is known to be temperature dependent, with the absolute value varying with plant genotype (70).…”

A Cytoplasmically Inherited Barley Mutant Is Defective in Photosystem I Assembly Due to a Temperature-Sensitive Defect in ycf3 Splicing

“…One of these lines, termed CL3, exhibits a viridis (homogeneously lightgreen colored) phenotype, which is much more pronounced at elevated temperatures . Wild-type barley seedlings become chlorotic at growth temperatures in excess of 32°C (Smillie et al, 1978). Some temperature-sensitive mutants, which were previously described, showed heat sensitivity for chloroplast development at temperatures lower than those producing chlorosis in wild type and also, a decrease of PSI and PSII activities (Smillie et al, 1978).…”