| Abstract: | Cotyledon mitochondrium respiration and oxidative phosphorylation activity of PEG primed and unprimed (control) soybean seeds which have been exposed to low temperature imbibition before germination are studied. The ADP stimulated respiration rates of control mitochondria are evidently higher than state Ⅲ respiration rates of mitochondria from primed seed when L-Mal, α-Kg and Succ are used as substrates respectively. The mitochondria from the unprimed do not possess respiratory control (RC.) On the contrary, mitochondria from the primed, even after seeds being exposed to 2–3 ℃ imbibition for 24 h, phosphorylate normally. The ADP/O and RC values are consistent with those of theoretical expectation. When NADH is used as substrate, unprimed seed mitochondria still possess oxidative phosphorylation activity, while ADP/O and RC values are obviously lower than those of mitochondria from the primed. The emerging sequence of the activity of the diverse phosphorylation sites during germination is also studied. When a different substrate is used, the emerging sequence of the primed is as follows: 1. NADH (12 h), 2.α-Kg (24 h), 3. L-Mal and Succ (48 h). This corresponds to occurrence sequence of ADP stimulated respiration in control mitochondria. The above results show that low temperature imbibition has an irreversible destructive effect on oxidative phosphorylation activity of control mitochondria, and PEG priming has a protective effect on structure and function of the mitochondria under low temperature imbibition stress. The mechanism of soybean imbibitional chilling injury and protective effect of PEG priming are discussed. |
