PROLINE AND ABA INDUCING CHILLING TOLERANCE VIA DIFFERENT MECHANISMS

Exogenous proline and ABA can induce chilling tolerance. Whether there is any relationship between the proline and ABA in inducing chilling tolerance is not known. We attempted to elucidate their interrelationship by comparing the time course of proline and ABA induced chilling tolerance and of the uptake of proline and ABA in the cultured cells of maize (Zea mays L. Black Mexican Sweet). The uptake of proline was increasing continually during a 24 h culture at 28°C. However, the proline induced chilling tolerance became significant after 6 h treatment and reached maximum after 12 h. When cells were transferred to a ABA-containing medium the uptake of ABA in the cells reached almost plateau in 2 h period. The ABA induced chilling tolerance was insignificant at 6 h, became significant at 12 h, and reached maximum at 24 h. Although the rate of ABA induced chilling tolerance was slower than the rate of proline induced chilling tolerance, there was no any increase in endogenous free proline in the ABA treated cells. Statistical analysis indicates that there is no interrelationship between proline and ABA in the induction of chilling tolerance in maize. ABA induces specific proteins which may play essential role(s) in the development of chilling tolerance. None of these proteins was observed in proline treated cells. We concluded that the induction mechanisms of chilling tolerance between proline and ABA are independent in maize.

Mitotic blocking agents for suspension cultures of maize 'Black Mexican Sweet' cell lines

Good metaphase arrest (25% mitotic index) in maize (Zea mays L.) 'Black Mexican Sweet' suspension cultures can be obtained with colchicine treatment alone, but only if very high concentrations (0.5%; 12.5 mM) are used. This colchicine concentration is 5- to 10-fold greater than that required for optimum mitotic arrest in cell cultures of other plant species. In contrast, we report that the herbicide amiprophos methyl (APM) is a much more efficient metaphase inhibitor for 'Black Mexican Sweet' suspension cultures than colchicine. Low concentrations (50 μm) of APM applied for 21–28 h produce a similar 25% mitotic index, and the growth-inhibiting effects of this treatment are undetectable 24 h after the removal of APM from the culture medium, APM, therefore, may be a useful agent for mitotic arrest in experiments which require survival of the treated cells. Another antitubulin herbicide, trifuralin, also was tested for ability to promote metaphase arrest in 'Black Mexican Sweet' cultures, but it proved to be ineffective.Key words: mitotic arrest, colchicine, phosphoric amide herbicide.