Respiration metabolism in mitochondria of pea seedlings of different age under water deficit and rewatering

Abstract

The effects of an osmoticum (mannitol) on growth, water content, respiration, and proline con tent in epicotyls of etiolated two day old (S 2 ) and three day old (S 3 ) pea (Pisum sativum L., cv. Flora 2) seedlings were studied. Water deficit was produced by placing plant roots in 0.6 M mannitol for 2-4 days. Control S 3 epicotyls contained more water than S 2 epicotyls; they were also characterized by more intense mitochondrial activity (in state 3, V 3 ) and by the higher value of the respiratory control (RC) due to a fourfold decrease of proportion of weakly phosphorylating cyanide resistant respiration (CRR). After 2 day long treatment with the osmoticum, S 2 epicotyls lost more water than S 3 ; water deficit in them attained 40% (28% in S 3 ). In S 3 treatment, epicotyls continued to grow at the almost unchanged rate, and the content of proline in them changed insignificantly, whereas in S 2 seedlings epicotyl growth stopped, and proline accumulated in them. In the presence of the osmoticum, V 3 and RC reduced, but in S 3 treatment they retained higher than in treatment S 2 . In mitochondria of S 3 subjected to dehydration, the proportion of the cytochromic pathway of oxidation (V cyt ) remained high, but the absolute values of the respiration rate reduced, whereas in S 2 both these indices reduced and the proportion of CRR increased. After rewatering, indices of mitochondrial activ ity (the rate of substrate oxidation, RC value) were restored, but in S 3 they were higher. The ratio of V cyt to CRR in S 3 shifted toward CRR, whereas in S 2 , in contrast, it was shifted toward V cyt . When temperature dur ing seedling growth and experiment performing was declined from 22°C (in control) to 18°C, growth of S 3 epicotyls was retarded to the rate characteristic of S 2 at 22°C. Under the effect of osmoticum, they, like S 2 , acquired a capacity to accumulate proline. Nevertheless, mitochondrial activity in such S 3 turned out to be higher than in S 2 grown at 22°C. The results obtained than, as distinct from traditional notes, 3 day old pea seedlings manifested the higher tolerance to water deficit than 2 day old seedlings.Abbreviations: AO-alternative oxidase; RC-respiratory con trol; S 2 and S 3 -2 and 3 day old seedlings, respectively, sub jected to osmoticum action and subsequent rewatering; SHAMsalicylhydroxamic acid; TMPD-N,N,N',N' tetramethylphe nylendiamine; V 3 -the respiration rate in mitochondria in state 3; V 4 -the respiration rate in mitochondria in state 4; V cytactivity of cytochromic pathway for oxidation.