STUDIES ON PH CHANGES IN MAIZE HAPLOID SU SPENSION-CULTURES .1. CHANGES IN THE PH OF THE NUTRIENT MEDIUM IN SHAKEN FLASKS

In recent years the significance of haploid cell suspensions has grown immensely in biotechnological research on maize. Finely aggregated ce ll suspensions form the most important objects used in genetic transfo rmation experiments. However, their use is limited in many cases eithe r by the fact that after a long period of culture they lose their rege neration ability or by the accumulation of genetic alterations during culturing. The loss of regeneration ability and the genetic alteration s can probably be attributed to stress factors arising in the course o f culture. In the present paper investigations were made into the pH c hanges occurring during the culture of three haploid maize cell line s uspensions grown on modified BM medium in shaken flasks. Ar inoculatio n the pH of the cultures was adjusted to 5.8, after which culturing wa s carried out at 110 rpm. The actual pH of the medium was measured in the first case after 1 week, and in a further experiment every day for two weeks. The results indicate that for all the cell lines the pH de creased drastically from 5.8 to around 4.3. The data of daily measurem ents show that this reduction took place within the first two days, fo llowed by a relatively uniform period. Around the 8th day the pH gradu ally began to rise again. When changes were made in the rotary rate of the shaker, and thus in the dissolved oxygen content of the medium, i t was found that although the pH reduction was a general phenomenon, t he. pH of the uniform period varied depending on the quantity of disso lved oxygen. The pH was lower at higher rotary rates than at lower rat es acid it would appear that at higher rates of dissolved oxygen the p eriod with uniform pH is longer. The present paper attempts to find an explanation for this phenomenon.