No abstract

Addition of 100 millimolar KCI, NaCI, or Na2SO4 strongly promoted acidification of the medium by cells of Nicotiana tabacum/gossii in suspension culture. Acidification was greater in the case of NaCl-adapted than in that of wild type cells, and strikingly so in KCI medium when fusicoccin (FC) was present. Back-titration indicated that net proton secretion in KCI medium was increased 4-fold by FC treatment in the case of adapted cells; but was not even doubled in wild type cells.

Radioactive dihydrofusicoccin (^H-FC), known to have the same biological activity as fusicoccin on plant tissues, has a specific affinity in vitro for sites locahzed on subcellular, postmitochondrial particles from maize coleoptiles. The analysis of the kinetics of dihydrofusicoccin binding suggests the presence of two classes of sites, one class with a high affinity and a second class with a lower affinity. The high affinity class of sites has a dissociation constant (K^) of 1.2 X 10"^ mol dm~^, and an apparent pH optimum at 5.5. Binding is antagonized by non-physiological pH, high temperatures and protein-reactive substances like HgCl2, p-chloromercuribenzensulphonate and glutaraldehyde. Treatment of aihydrofusicoccin-bound membrane preparations with Triton X-100 leads to the solubilization of a protein fraction associated v^th dihydrofusicoccin. These data suggest a protein nature for the receptor sites.

No abstract

Pesci, P. 1987. ABA-induced proiine accumulation in barley leaf segments: Dependence on protein synthesis. -Physiol. Plant. 71: 287-291.The kinetics of proiine accumulation in barley {Hordeum vulgare L. cv. Georgie) leaf segments showed a lag phase of ca 3 h when the increase was induced by abscisic acid (ABA), but not when the accumulation of the imino acid was promoted by isobutyric acid (IBA). Cycloheximide (CHI) supplied together with ABA, either from the beginning of the treatment or some time before the end of the lag ph^e, completely abolished ABA-induced proline accumulation, whereas no block was observed when the inhibitor was supplied after the lag phase. Cordycepin (COR) exibited a similar effect. The IBA-induced increase in proline was not influenced by CHI for at least 5h. When segments were pretreated with ABA for a period longer than the lag phase in the absence of salts in the external medium, there was no significant increase in proline. If KCl was added to the incubation medium after such a pretreatment, however, proline increased even after removal of the hormone from the external medium. This increase in proline occurred without any lag phase, and was only partiaUy inhibited by CHI and rapidly and totally blocked by fusicoccin (FC). These results suggest that some protein, characterized by a fast turnover and possibly conferring the sensitivity to KCl, is synthesized during the early hours (lag phase) of the ABA treatment. The synthesis of this protein(s) does not seem to be involved in the increase in proline induced by IBA and is thus a peculiar aspect of that mediated by ABA.