Histogenesis and Genetics of a Plastid‐controlled Chlorophyll Variegation in Tobacco

Abstract

A mosaic pattern of leaf variegation in a sector on a normal green tobacco seedling resulted from maturation of both green and white cells within the tissue derived from the second histogenic layer (L–II) of the shoot apex. While mature cells of L–II origin contained either green plastids or colorless plastids, single cells in young leaves contained both normal green plastids and colorless, defective mutant plastids. The genetic determiner of the defective plastid type, designated DP1, was located in the plastid itself. Only a small number of mutant plastids were found in anyone cell. A threshold number of DP1 above which green plastids were inhibited and below which they developed normally is suggested. Random segregation of DP1 and dP1 in cytokinesis, close to the threshold value and without loss of either determiner, could account for the small, intermingled patches of green and white cells derived from the mosaic histogenic layer. The mosaic histogen usually remained mosaic; however, complete segregation during mitosis to DP1 or dP1 occasionally occurred in sectors within which lateral buds developed in a stabilized condition, either normal or mutant (green or white). Occasional replacement of L–III by L–II apparently introduced the mosaic condition into L–III of the original variegated plant and resulted in an additional pattern of variegation. Patterns of variegation in which the sporogenous tissue was derived from a stable L–II with homoplastidic cells produced only green or only white offspring. Variegated seedlings were obtained only when L–II was mosaic. Contrasting statements on the inheritance of variegations appearing in the literature result from failure to describe accurately the pattern of variegation. Description in terms of plastid types in mature histogens is essential, and plastid segregation in somatic tissue of mosaic L–II must be determined. Variegation should only be used as a general term and further described as stable when the histogens are homoplastidic or mosaic when the histogens are heteroplastidic. Complete description of the inheritance of a plastid mutant must record inclusion or loss in successive cell generations of sexual seedlings. DP1 is inherited only maternally and is found in fewer of the offspring than expected on the basis of its segregation in mitosis. When present in the egg cell and, therefore, the zygote, DP1 can be included in all 3 histogenic layers of the seedling, thereby producing many more variegated patterns than were possible from the original mosaic plant.

Efficient induction and selection of chloroplast-encoded antibiotic-resistant mutants in Nicotiana

“…N. tabacum line 92 is a cytoplasmic malesterile, alloplasmic substitution line containing N. undulatatype cytoplasm (10). Clonal line VBW, containing albino plastids (10), is from a variegated N. tabacum mutant, Dpl, containing defective plastids in the pale sectors of its leaves (11).…”

Leaf-variegated mutations and their responsible genes in Arabidopsis thaliana.

“…What is characteristic to leaf variegation is formation of white and green sectors in the same leaf. It means that a green tissue contains normal chloroplasts (originated from plas-tids as they develop thylakoids internally), whereas a white tissue lacks developed chloroplasts and only contains abnormal plastids (Burk et al, 1964;Shumway and Weier, 1967). The fact that a single recessive mutation can result in such a sector formation suggests that a loss of the gene function may affect the leaf cells unequally.…”

Correlation between Chlorophyll and Chlorogenic Acid Content in Tobacco Leaves

“…A cytoplasmic chlorophyll-variegated mutant of tobacco, whose inheritance and morphological characteristics are identical to that described by Burk et al (4), was used to study the relation between chlorophyll quantity and polyphenol accumulation. Eighteen plants in 25-cm pots were randomly arranged on greenhouse benches into three replications.…”