Activities of Ribulose Bisphosphate Carboxylase and Phosphoenolpyruvate Carboxylase and ¹⁴C-Bicarbonate Fixation during in Vitro Culture of Pinus radiata Cotyledons

Abstract

The activities of ribulose bisphosphate carboxylase (RuBPC) and phosphoenolpyruvate carboxylase (PEPC), as indicators of autotrophic and nonautotrophic CO2 fixation, were measured in excised cotyledons of Pinus radiata D. Don cultured for 21 days under shoot-forming (SF) and nonshoot-forming (NSF) conditions. The activity of RuBPC was found to increase in both SF and NSF cultures during the initial 5 days of culture. However, it leveled off from day 5 to day 10 and subsequently began to decrease until the end of the culture period under the SF conditions. In contrast, in the NSF cultures, RuBPC activity increased until day 15, when it was twofold higher than the maximum activity found in the SF cultures. An increase in PEPC activity of about 2.5 times the level of activity in freshly excised cotyledons was observed during the initial 5 days of culture under the SF conditions. PEPC activity began to decline after day 5 until it reached the level of activity seen in NSF cotyledons by day 15. In contrast, the activity of PEPC did not show any significant increase during the initial 10 days of culture under the NSF conditions. The Km (phosphoenolpyruvate) of PEPC from SF cotyledons was about 35% higher than that of NSF cotyledons. Cotyledons from two culture periods (days 5 and 15) were incubated for 15 seconds with NaH'4CO3. The label in the malate and aspartate fractions as a percentage of total 14C incorporation was 3 times higher in the SF cotyledons than in the NSF cotyledons. A higher incorporation of 14C into products of photosynthesis under the NSF conditions was also observed.

Effects of sucrose on photosynthesis and phosphoenolpyruvate carboxylase activity of in vitro cultured strawberry plantlets

“…CRH-102, Centre de Recherche en Horticulture, F.S.A.A., Universit6 Laval, Qu6bec strawberry plantlets. Similar observations have also been made during in vitro culture of Pinus radiata D. Don cotyledons (Kumar et al 1988), in exponentially growing cell cultures (Bender et al 1985) and in developing wheat (Triticum aestivum L., var Cheyenne or Anza) leaves (Aoyagi & Bassham 1986). Increased PEPC activity might be a response of tissue-cultured plantlets to the presence of sugar in the culture medium as was suggested for cell cultures upon high demand in carbon skeleton for cell anabolism (Bender et al 1985).…”

“…In fact, high PEPC activity was measured in in vitro strawberry plantlets, especially at the early stages of their transfer to rooting medium. Kumar et al (1988) also observed an important PEPC activity, particularly in the initial 5 days of culture, in P. radiata cotyledons cultured in vitro under shoot-forming conditions. These authors suggested that increased PEP carboxylation may be attributed to its role in the anaplerotic supply of carbon skeletons to the tricarboxylic acid cycle as well as to amino acid and protein synthesis.…”

Alternative and cytochrome pathway respiration during shoot bud formation in cultured Pinus radiata cotyledons

“…Biondi and Thorpe (1982) pears to have a special relationship with the alternative reported that respiration rates in shoot-forming tissue pathway (AP). Kumar et al (1988) determined that phoswere initially high between days 0 and 3, then decreased phoenolpyruvate carboxylase activity increased in shootto a minimum aroond day 9 and remained relatively forming tissue during the initial 5 days of culture, then steady up to day 20. Bender et al (1987) found increased declined to the level of non-shoot-forming tissue by day '''C-labeiing iti malate aod citrate in shoot-formiog tissue 15.…”

Les β-carboxylations dans les systèmes cellulaires de type C3

“…'inverse de ceux de Ia RuhisCO. Cependant, rien n'est encore connu sur les mecanismes de regulation inverse de ces deux enzymes pendant le cycle cellulaire (Nato et Mathieu, 1978;Rogers et al, 1987 (Kumar et al, 1988).…”

“…'augmentation de l'activite PEPC (Kumar et al, 1988). Par ailleurs, lorsque des cellules ont des difficultes d'approvisionnement en eau, les echanges H•/K• sont inhibes et le pH stat est inactif (Venekamp, 1989) ; une diminution de l'activite PEPC est alors ohservee (Becker et Fock, 1986).…”