Responses of carboxylating enzymes, sucrose metabolizing enzymes and plant hormones in a tropical epiphytic CAM orchid to CO₂ enrichment

Abstract

After exposure to a doubled CO 2 concentration of 750 µ µ µ µ L L − − − − 1 for 2 months, average relative growth rate (RGR) of Mokara Yellow increased 25%. The two carboxylating enzymes, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPCase), responded differently to CO 2 enrichment. There was a significant daytime down-regulation in Rubisco activity in the leaves of CO 2 -enriched plants. However, PEPCase activity in CO 2 -enriched plants was much higher in the dark period, although it was slightly lower during the daytime than that at ambient CO 2 . Leaf sucrose-phosphate synthase (SPS) and sucrose synthase (SS) activities in CO 2 -enriched plants increased markedly, along with a night-time increase in total titratable acidity and malate accumulation. There was a remarkable increase in the levels of indole-3-acetic acid (IAA), gibberellins A 1 and A 3 (GA 1+3 ), isopentenyladenosine (iPA) and zeatin riboside (ZR) in the expanding leaves of plants grown at elevated CO 2 . It is suggested that (1) the down-regulation of Rubisco and upregulation of SPS and SS are two important acclimation processes that are beneficial because it enhanced both photosynthetic capacity at high CO 2 and reduced resource investment in excessive Rubisco capacity; (2) the increased levels of plant hormones in CO 2 -enriched M . Yellow might play an important role in controlling its growth and development.

Elevated Carbon Dioxide Improves Plant Iron Nutrition through Enhancing the Iron-Deficiency-Induced Responses under Iron-Limited Conditions in Tomato

“…CO 2 could enhance the activity of nitrate reductase in plants (Buchanan et al, 2000), which is a major enzyme in NO synthesis through the nitrite reduction (Yamasaki et al, 1999;Meyer et al, 2005). Alternatively, elevated CO 2 could increase auxin levels (Li et al, 2002;Teng et al, 2006), which then induces NO accumulation . These issues require further investigation, but we propose that elevated CO 2 first increases NO levels in roots by enhancing the nitrate reductase activity and then enhances FER expression.…”

CAM Photosynthesis in Bromeliads and Agaves: What Can We Learn from These Plants?

“…However, divergent results about the influence of elevated CO 2 in CAM plants have been reported during the last decades [147][148][149][150][151][152][153], demonstrating that the enrichment of CO 2 into the atmosphere can trigger complex responses in CAM plants. For example, elevated CO 2 had no effect on diel CO 2 uptake by Kalanchoë daigremontiana [147] nor on nighttime CO 2 uptake in Clusia uvitana and Portulacaria afra [154,155], whereas in several other CAM species more significant impacts of elevated CO 2 on the daytime, nighttime and/or diel carbon acquisition have been reported [148,150,151,153]. Changes in morphology, anatomy and biochemistry driven by modifications in atmospheric CO 2 concentration have also been observed in some CAM plants, commonly associated with concomitant alterations in their growth rates and biomass accumulation.…”

Cross–talk between nitric oxide and Ca2+in elevated CO2-induced lateral root formation

“…16,19,20 Recent studies showed that elevated CO 2 increased auxin level and response, 2,3,21 and that production of NO was promoted in tomato roots under co-treatment with elevated CO 2 and iron deficiency. 11 Consequently, in this paper, we proposed that cross-talks between NO and Ca 2+ involving in elevated CO 2 induced LR formation.…”