Light and Temperature effect on diurnal photosynthetic metabolites of Phalaenopsis - A study on anions, carbohydrates, and carboxylase enzyme PEPC

MSc-thesis abstract (submitted 8 June 2017): Phalaenopsis is a popular commercial potted plant species that utilizes Crassulacean Acid Metabolism (CAM). Its cultivation is time consuming and conducted at high temperatures.
The aim of this study is to get phenotyping parameters for different cultivars.
Insight in the underlying processes might allow for a more optimized climate control for cultivation of different genotypes.

The main metabolites of the biochemical pathway for CAM photosynthesis have been studied under two light intensities (60 - 140 μmol m-2 s-1) and two temperature settings (27 - 31°C). Leaf discs were collected over a 24-hour period and analysed for anions and carbohydrates using HPLC. Furthermore, PEPC activity was measured with a spectrophotometer.

Results show that citrate does not play a role in nocturnal carbon accumulation. Malate is the main carbon storage compound and diurnal concentrations show a great fluctuation and further decrease under high light at 27°C whilst at 31°C clear light effects are absent.

The same results are obtained for starch in an inverted manner. Indications are found for genotypic specific partitioning of carbohydrates in starch or soluble sugars. A high temperature seems to decrease maximum carbon storage capacity which suggests lighting at high temperatures could be kept to a minimum. Higher PEPC activity is noted when higher rates of malate and starch conversion are found at 27°C in high light intensities.

Keywords: Phalaenopsis , Crassulacean acid metabolism , CAM , diurnal , temperature , light , malate , citrate , starch , PEPC