Biochemical Studies on Development of Mitochondria in Pea Cotyledons during the Early Stage of Germination

Abstract

L-Leucine-U-'4C was incorporated into mitochondrial protein in pea (Pisum sativum var. Alaska) cotyledons during the imbibing stages. Incorporation was almost completely inhibited by cycloheximide but not by chloramphenicol. Both antibiotics did not affect increases in mitochondrial activities and components of the cotyledons during imbibition. Therefore, mitochondrial development seems to be achieved by a transfer of protein pre-existing in the cytoplasm into the mitochondria rather than by de novo synthesis of mitochondrial protein. Cycloheximide stimulated an increase in bile saltsoluble protein of mitochondria in imbibing pea cotyledons. The recovery of cytochrome oxidase activity after sucrose density gradient centrifugation was enhanced, and the morphological properties of mitochondria were altered by cycloheximide.When water is supplied to dry seeds, a marked increase occurs in their respiratory activity. A number of studies have demonstrated that mitochondrial development takes place in the cotyledons or endosperms during the later stages of germination (1, 3-5, 8. 9, 13, 22). A rapid increase in mitochondrial activity was also observed during the early stages of germination of pea seeds (34). In a previous paper (20), we reported a rapid development of mitochondria including increases in their components and activities in the cotyledons of pea seeds during the imbibing stages. The structure of mitochondria seems to be stabilized as hydration proceeds. Recently, similar results were reported by Solomos et al. (31).Our studies have been expanded in an attempt to elucidate the mechanism of development of pea cotyledon mitochondria during the imbibing stages. The purpose of the study described in this paper was to determine if the development involves the de novo synthesis of mitochondrial protein. The synthesis of mitochondrial protein is the result of two systems controlled by different genes; one is the cytoplasmic protein-synthesizing system controlled by nuclear genes, and the other is a mitochondrial protein-synthesizing system. The former is inhibited by CHI' and the latter by CAP (2,25,30,32,33). This paper deals 'Abbreviations: CHI: cycloheximide; CAP: D-threochloramphenicol; SDGC: sucrose density gradient centrifugation; RCR: respiratory control ratios.with the effects of the antibiotics on the development of mitochondria in pea cotyledons during the imbibing stages. Our study would suggest that development does not require a de novo synthesis of mitochondrial protein but seems to be achieved by a transfer of pre-existing cytoplasmic protein to immature mitochondria. MATERIALS AND METHODSPlant Material. Surface-sterilized pea seeds (Pisum sativum var. Alaska) were germinated in the dark at 28 C in Petri dishes containing deionized water or antibiotic solution (1 or 0.5 mM CHI, 5 or 1 mm CAP) 2.5 times that of the dry seed weight.The cotyledons were taken at the appropriate age, washed with water, and used as the experimental material. L-Leucine-U-14C was supplied to the seeds by germinati...

Cyanide-insensitive Respiration in Pea Cotyledons

“…These developmental changes extend to the mitochondria. The mitochondria present in the dry seed are relatively disorganized, but develop rapidly to supply the energy needs of the cotyledons (2,(12)(13)(14)(15)(16)(17)(18)23).…”

Biochemical Properties of Mitochondrial Membrane from Dry Pea Seeds and Changes in the Properties during Imbibition

“…The transformation must be brought about by assembly of polypeptides with relatively high mol wt into the phospholipid-rich membrane. Nawa and Asahi (5) showed that mitochondrial development in pea cotyledons during the early stage of germination did not require de novo synthesis of mitochondrial protein. We propose that the polypeptides assembled pre-exist in a soluble form in the fragile mitochondria or in the cytoplasm.…”

“…In peas, a rapid development of cotyledon mitochondria, i.e., the formation of their membrane and an increase in their biological function, takes place in the imbibition stage (4,7). The development does not require de novo synthesis of mitochondrial protein, and seems to result from transport of pre-existing cytoplasmic protein into immature mitochondria (5).…”

Isolation-Inflicted Injury to Mitochondria from Fresh Pollen Gradually Overcome by an Active Strengthening during Germination

“…However, protein synthesis was not required, and Cyts were present at a constant level throughout the germination process. As in Typha pollen, the evolvement of mitochondrial properties during germination of seeds of several species is similarly independent of de novo protein synthesis (10,11,16). In other seeds such as the peanut, however, de novo protein synthesis associated with the formation of new mitochondria has been demonstrated (3,13,14).…”