Abscisic acid (ABA) has been implicated as a regulatory factor in plant cold acclimation. In the present work, the cold-acclimation properties of an ABA-deficient mutant (aba) of Arabidopsis thaliana (L.) Heynh. were analyzed. The mutant had apparently lost its capability to cold acclimate: the freezing tolerance of the mutant was not increased by low temperature treatment but stayed at the level of the nonacclimated wild type. The mutational defect could be complemented by the addition of exogenous ABA to the growth medium, restoring freezing tolerance close to the wild-type level. This suggests that ABA might have a central regulatory function in the development of freezing tolerance in plants. Cold acclimation has been previously correlated to the induction of a specific set of proteins that have been suggested to have a role in freezing tolerance. However, these proteins were also induced in the aba mutant by low temperature treatment.
A method for displaying mitochondria and proplastids in root tip sections of Tradescantia paludosa and cereals was modified from Altmann and Volkonsky. Root tips were fixed in 3% glutaraldehyde in phosphate buffer, pH 7.1, or acetate buffer, pH 4.8, for 3 hr, rinsed and postchromed overnight in 3% potassium dichromate, all at room temperature (20 C), dehydrated through a tertiary butanol series and embedded in ester wax. Four-micrometer sections were stained in hot acid fuchsin in aniline water, rinsed, treated with 1% sodium phosphomolybdate for 30 sec, rinsed and stained progressively with azure B for 3-10 min before being made permanent. Mitochondria and proplastids were stained brilliant crimson against a light blue cytoplasm with deep blue chromosomes. Previously reported difficulties with Altmann staining techniques are attributed to the erratic action of the classical fixatives used.
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