Heat stress: Effects of abscisic acid and kinetin on response and recovery of tobacco leaves

The effects of kinetin and ABA application before or after heatshock were studied by determining the following parameters:CO₂, fixation, leucine incorporation into protein and leakageof ³⁶Cl or ¹⁴C-labeled metabolites. Kinetin pretreatment increasedthe heat damage while post-treatment enhanced recovery. ABApretreatment did not reduce heat damage while post-treatmentenhanced recovery, but to a lesser extent than kinetin. Thesefindings are not consistent with the assumption that ABA playsa role in increasing the resistance of plants to stresses. (Received October 27, 1977; )     

Decreased cytokinin production in the roots as a factor in shoot senescence

Summary The cytokinin content of root exudate of sunflowers increases during the exponential growth phase of the plants. The concentration of cytokinins drops, however, by a factor of ten when the plants have reached their final size. The reduced supply of cytokinins from the root to the shoot is regarded as one of the factors bringing about shoot senescence.     

Effects on toxicity of eliminating a cleavage site in a predicted interhelical loop in Bacillus thuringiensis CryIVB δ-endotoxin

Abstract When activated by treatment with mosquito ( Aedes aegypti ) gut extract, the Bacillus thuringiensis CryIVB δ-endotoxin lysed A. aegypti cells in vitro. SDS-PAGE and N-terminal sequence determination showed that in addition to removal of the C-terminal half of the molecule, the activated toxin had undergone proteolytic cleavage at two internal regions producing 47–48-kDa and 16–18-kDa polypeptides. Aligning the CryIVB protein sequence with the crystallographic structure of the CryIIIA toxin suggested that one set of cleavages occurred in a region before the start of the N-terminal helical bundle and the second cleavage site occurred in a predicted loop between helices 5 and 6 in the bundle at arginine-203. To investigate the suggestion by Li et al. [8] that interhelical proteolysis is important in the cytolytic mechanism of these toxins, arginine-203 was substituted by alanine. The mutated toxin now resisted proteolysis at this position and showed a marked decrease in cytolysis in vitro but an increase in larvicidal activity.     

Regulation of Mg,K-ATPase Activity in Guard Cells of Commelina communis by Phytochrome and ABA

The microsomal fraction obtained from guard cell protoplastswas assayed for ATPase activity at pH 6.5. Triton X-100 didnot affect this stimulation of activity of ATPase by K⁺ up to5 mM, but the detergent abolished the stimulatory effect ofK⁺ at higher concentrations. The ATPase activity was inhibitedby N,N-dicyclohexylcarbodiimide and ABA. Irradiation with redlight enhanced the ATPase activity more than did irradiationwith far-red light. ABA and irradiation with red or far-redlight were effective only in the presence of K⁺. These resultssuggest the possibility that the ATPase activity is modulatedonly indirectly by light and ABA. (Received January 9, 1989; Accepted July 10, 1989)     

Model flavoproteins : Interaction of ribofIavin-5'-mono-phosphate with poly-(α -L-lysine) and poly-(α -L-histidine)

The interactions of flavin mononucleotide (riboflavin-5'-monophosphate) with two polypeptides, poly-(α-L-lysine) and poly-(α-L-histidine) in water and 0.05 M phosphate buffer were studied by measuring circular dichroism in the pH range 3 to 11. The interation of flavin mononucleotide with the two polypeptides was due to hydrophobic as well as ionic associations and was further influenced by the involvement of the ribityl side chain. The results of the present study have shown that small changes in the environmental conditions of the interacting molecules could modify their mode of interaction considerably. CDRI Communication No. 2816.