Physiology of development, germination and ubiquitination in pea seeds

The development of entire seeds and axes of Pisum sativum L. cv. Spring was followed between 18 and 47 days after flowering, in terms of changes in fresh weight, dry weight, water content, protein level and chlorophyll content. The seed developed normally, but somewhat slower than suggested in other reports. Fresh immature seeds and axes placed in culture were able to germinate after a lag phase which varied depending upon the time of detachment of the seed from the legume pod and the axis from the seed. The seeds from all stages tested produced a viable seedling. Except for the least mature, the axes germinated fully, but grew only slightly. Root growth was particularly impaired. Ubiquitin conjugates were identified by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), Western blotting and labelling with rabbit anti-ubiquitin followed by 125 I goat antiRabbit-IgG. Ubiquitinated proteins were detected in seeds during development and germination, but not in dry mature seeds. Only free ubiquitin was observed in extract from dry seed. A correlation between higher concentration of ATP in the seed, and presence of ubiquitin conjugates was observed. These results demonstrate that pea seed can contain both unconjugated and conjugated ubiquitin