In this project, we focused on molecular mechanisms, which are involved in regulation of plant cell life and death. Also, efforts were being made to find out fundamental mechanisms during plant growth and environmental adaptation. The results are summarized as follows. (1) Arabidopsis BI-1 gene is a widely conserved endoplasmic reticulum membrane protein known as a cell-death regulator. We demonstrated that over-expression of BI-1 protein suppressed cell death induced by various stimuli such as hydrogen peroxide, salicylic acid and elicitor. Furthermore, the functional relationship between AtBI-1 and calcium signaling was also demonstrated. (2) Cell division in plant is controlled by the CDKs. We found four CDK-activating kinases (CAKs) of Arabidopsis and proposed a CDK-phosphorylation cascade. (3) The tapetum degradation is an event of the programmed cell death (PCD). We employed Bax and BI-1 genes to regulate PCD in the tapetum. (4) Trienoic fatty acids (TAs) are the major polyunsaturated fatty acid species in the membrane lipids in plant cells. We showed that TAs in chloroplast membrane lipids are involved in defense responses of plants against avirulent bacterial pathogens. Namely, linolenic acid, the most abundant TA, activated the NADPH oxidase that is responsible for oxidative burst. (5) We demonstrated that plants have Na⁺/K⁺ transport proteins, which played important role in adaptation of cells to hyperosmotic conditions. (6) The plant hormone ethylene regulates a wide range of developmental processes and the response of plants to stress and pathogens. Cross-talk between ethylene and sugar signaling was found. This indicates that a pathway controlling degradation of transcription factors responsible for ethylene signaling is a key for controlling plant growth and stress response.