Acclimation of chlorophyll biosynthetic reactions to temperature stress in cucumber ( Cucumis sativus L.)

Abstract

The adaptive responses of the greening process of plants to temperature stress were studied in cucumber (Cucumis sativus L. cv. Poinsette) seedlings grown at ambient (25°C), low (7°C) and high (42°C) temperatures. Plastids isolated from these seedlings were incubated at dierent temperatures and the net syntheses of various tetrapyrroles were monitored. In plastids isolated from control seedlings grown at 25°C, the optimum temperature for synthesis of Mg-protoporphyrin IX monoester or protochlorophyllide was 35°C. Temperature maxima for Mg-protoporphyrin IX monoester and protochlorophyllide syntheses were shifted to 30°C in chill-stressed seedlings. The net synthesis of total tetrapyrroles was severely reduced in heat-stressed seedlings and the optimum temperature for Mg-protoporphyrin IX monoester or protochlorophyllide synthesis shifted slightly towards higher temperatures, i.e. a broader peak was observed. To further study the temperature acclimation of seedlings with respect to the greening process, tetrapyrrole biosynthesis was monitored at 25°C after pre-heating the plastids (28± 70°C) isolated from control, chill-and heat-stressed seedlings. In comparison to 28°C-pre-heated plastids the percent inhibition of protochlorophyllide synthesis in 40°C-pre-heated plastids was higher than for the control (25°C-grown) in chill-stressed seedlings and lower than for the control in heat-stressed seedlings. Maximum synthesis of total tetrapyrroles and protoporphyrin IX was observed when chloroplasts were heated at 50°C, which was probably due to heatinduced activation of the enzymes involved in protoporphyrin IX synthesis. Prominent shoulders towards lower or higher temperatures were seen in chill-stressed or heat-stressed seedlings, respectively. The shift in optimum temperature for tetrapyrrole biosynthesis in chill-and heat-stressed seedlings was probably due to acclimation of membranes possibly undergoing desaturation or saturation of membrane lipids. Proteins synthesized in response to temperature-stress may also play an important role in conferring stress-tolerance in plants.Abbreviations: ALA = 5-aminolevulinic acid; Chl = chlorophyll; Chlide = chlorophyllide; MP(E) = Mg-protoporphyrin IX and its monoester; Pchlide = protochlorophyllide; Proto IX = protoporphyrin IX

Light and dark modulation of chlorophyll biosynthetic genes in response to temperature

“…Inhibition of Chl biosynthesis in chill-and heat-stress conditions occurs owing to the impairment of several Chl biosynthetic enzymes (Tewari and Tripathy 1998;1999). Chlorophylls and carotenoids are required for the assembly and stabilization of Light-harvesting chlorophyll a/b complex (Reinsberg et al 2001).…”

Role of Temperature Stress on Chloroplast Biogenesis and Protein Import in Pea

“…Intact plastids were isolated as described before (Tewari and Tripathy, 1999). Briefly, pea leaves were homogenized using a kitchen blender in 7 volumes of cold 13 grinding buffer consisting of 0.05 M HEPES, 0.33 M sorbitol, 1 mM MgCl 2 , 1 mM MnCl 2 , 2 mM Na 2 EDTA, 0.1% BSA, and 0.025% isoascorbate, pH 7.5.…”

“…Intact plastids were isolated from control, chill-, and heat-stressed seedlings as described earlier (Tewari and Tripathy, 1999). Aliquots of the samples were denatured in the presence of SDS-PAGE sample buffer (15.5 mM TrisHCl, pH 6.8, 720 mM 2-mercaptoethanol, 10% glycerol, and 3% SDS).…”

Regulation of protoporphyrin IX biosynthesis by intraplastidic compartmentalization and adenosine triphosphate

“…Intact chloroplasts were centrifuged at 2,000 g for 3 min, and the pellet was then re-suspended in the minimal amount of lysis buer consisting of 10 mM Tris-HCl (pH 7.5) and 1 mM EDTA (TE buer), and incubated for 10 min in ice (Tewari and Tripathy 1999).…”